i had an idea to make a main construction for cnc router out of square steel tubing, and for "silencing" vibrations i thought to put sand into frame. would this make any significant improvement or is this waste of time ?

pozdravi,Turpija,
I am one of the guys{caknut}from the Epoxy granite machine bases thread where we a attempting vibration reduction.Hollow steel tubes will resonate like a pipe organ because of the hollow nature.Sand is a good choice to dampen resonances as it is cheap and if not suitable can be removed.The next step is epoxy and sand and not changeable.Read the posts on the epoxy granite and decide if you want to try it.Raw sand is a good starting point.
Hvala
Larry

Great info Mr Larryard!

And speaking of pipe organ.. Where are you guys buying your steel tubing?
I need some for my project. Not really loud but some good sounding steel.
_

Good sounding steel is for Steel drum bands,not for CNC machines.Steel drums go ding,ding boom,boom,sand damping is not suitable as you will get dud,dud.The various sizes and lengths of steel tubeing in a CNC machine will resonate at different frequencys hopefully in key and in concert,making a new hit single.If not you could possibly us it to cut aluinium,I understand servos are smooth,while steppers resonate possibly adding to the musical experience.Nesretan Turpiga,I kazano we are the ludovati decki.
Αποτελέσματα αναζήτησης για 'apollonius de perga': Δεν βρέθηκαν λέξεις.

AdamAnt:good sounding steel is no sounding steel

i was thinking if the steel tubing will echo any noise on my system i will try spray foam (insulation) , it would be light and should dampen any vibrations

Pozdrav lgalla !

So sand would make a difference (improvement) considering dampening vibrations, that's nice to hear ;)
And i've saw some of those epoxy with sand solutions, but i did't research where could i get all the supplies, and for first hand sand seems like a logical solution ;) epoxy sand can allways be added later ...


2 derstap: that (poliurethane) foam, yellow right, would probably make it better than just tubes alone but sand is way havier, and that's also what good machine makes better ;)

I over engineer everything. Lead shot in 90w gear lube with a drain hole large enough for media changes if it doesn't work. Doesn't work for the pipe organ thing however.

I have an 80/20 router and was thinking of trying the urethane foam in the extrusion.
Dertsap,I was wondering if you tried the foam in yours or just thinking of trying it?
I agree it should help.
Cutmore

I have an 80/20 router and was thinking of trying the urethane foam in the extrusion.
Dertsap,I was wondering if you tried the foam in yours or just thinking of trying it?
I agree it should help.
Cutmore

i do plan to use it but i haven't tryed it yet , i want to make sure i'm all done with my wiring and such before i do so

If one was to fill a frame with anything,depending on the size of the machine,The verticals are easy.How would you fill the horizontal tubes? Larry

IGALLA,
If you use something like expanding foam it would be easy to fill in any direction.
Dertsap,
Thanks for the reply.
Cutmore

Or try this www.mkprofiles.com/profile_systems/foamed_profiles.asp

I thought the pipes of a pipe organ were traditionally made out of lead?

Quick Google search:
http://www.madehow.com/Volume-5/Pipe-Organ.html

Most pipes are made from metal. Metal pipes are most often made from alloys containing various amounts of tin and lead. Pipes may also be made from other metals, such as zinc and copper. The vibrating reeds inside reed pipes are usually made of brass.

I saw someone restoring a pipe organ once, and there was enough lead in the pipe it was soft enough to bend by hand.

I over engineer everything. Lead shot in 90w gear lube with a drain hole large enough for media changes if it doesn't work. Doesn't work for the pipe organ thing however.

Richard, have you actually done something like this?? I'm working on a harmonics problem in my Z axis [it's a 6 x 6 .250Hss post over 4ft long] and am wondering if this would do what I need. It's fairly straight forward, well except that a person can't buy lead shot anymore.. Would steel shot work as well in the same situation??

Can a person even buy lead anymore??

Jerry

..... Would steel shot work as well in the same situation??

Can a person even buy lead anymore??

Jerry

Look up a company called Metallex. I think that is the name, they refine lead from old batteries and may be able to put you onto a source for lead shot. Steel shot will work it is just not as heavy.

You should also read a bit about constrained layer damping and elastomeric damping with weights. This is based on finding the location of maximum deflection along the beam and gluing on weights via a rubber interface. The weight and rubber have a different resonant frequency so they interfere with the harmonic vibration of the structure. You are quite likely familiar with this idea in the form of crankshaft dampers which have a ring of metal bonded to a hub via soft rubber. Also I think it is applied in propeller design but this could date back a few years.

Can a person even buy lead anymore??

Jerry

Dear Jerry,

Over here you can get lead shot at scuba stores, but buying weight belts on ebay is usually the cheapest source. I'm not sure if the same applies in Canada.

Best wishes,

Martin

Can a person even buy lead anymore??

Jerry

Yes!

http://www.marsmetal.com/newpages/aaleadshot.html


Martin

Hi Jerr.How are you?
Ever heard the expression"Get the lead out"A 6"X6"X48" tube is one cu/ft or 500 lbs of shot.You got big motors?Why not try the sand idea first.
Is the resonance from the steppers or the spindle?
Appears we have a parallel universe or thread happening here.
Trumpet or trumbone?Really doesn't matter.If you filled it[the musical instrument] with foam or what ever nothing is going to resonate or make any music..The main irritation of the resonance is the air in the tube.Foam filling will eliminate the irritation but I don't know if it will eliminate the vibration.
Sorbothane to the rescue?Pads between joints absorb 94% shock and provides shock absorbing.Used as gaskets in speakers,provides reduction in vibration transfer from the motor or speaker.Useful in a machine.I donut know.
Edmond scientific has sorbothane sheets 12"X12"X1/8" for $20.
Apparently you can cover your hand with a sheet of sorbohane and hit it with a hammer and not feel a thing due to the high damping visco-elastic nature.
Maybe for a million bucks I would try it,other wise I will accept the claim.
Larry

Jerry, Yes the shot thing works but I was being "ironical". There is a high density rubber compound available for sound and vibration dampening. I think it is rubber and lead in a heavy paste like slurry that dries on like paint or plaster. We used it to quiet down the old steel tube type bar feeders on lathes. I would think you could apply it internally to your tube and not have much of a weight problem. I'll look around and see if I can find it again. It used to be sold as a sound proofing solution to OSHA's rules.

Sorry to reply so late. Been awful busy for a retiree.

Trumpet or trumbone?Really doesn't matter.If you filled it[the musical instrument] with foam or what ever nothing is going to resonate or make any music..The main irritation of the resonance is the air in the tube.Foam filling will eliminate the irritation but I don't know if it will eliminate the vibration.

Larry

Dear Larry,

My limited understanding is that hollow tubes have a tendency to form standing waves acoustically if there is a length of tube in which they can form. That's how organ pipes work (I think). If you deny the airspace, the waves do not form, so stuffing tubes with anything should work on that front. Sand, lead shot or foam ought to work.

I am unsure about how to ensure that the "stuff-filled" tube performs best however.

If you go for a two part polyurethane foam (boat bouyancy type), you could fill the sections from any angle. That is not easy with sand or lead shot unless you can pour into vertical sections.

Lead shot and sand add mass to the tube which should mean that more energy is required to set up vibrations and resonance. Obviously, lead does that a lot better than sand. However, a foam fill probably does a better job of making the steel section stiffer for the simple reason that the foam links opposing faces of the tube together and therefore increases the I value, and hence reduces bending. Any thoughts on this?

This is something that loudspeaker stand designers know about.....(and I do not)

Best wishes,

Martin

.....Lead shot and sand add mass to the tube which should mean that more energy is required to set up vibrations and resonance. Obviously, lead does that a lot better than sand. However, a foam fill probably does a better job of making the steel section stiffer for the simple reason that the foam links opposing faces of the tube together and therefore increases the I value, and hence reduces bending. Any thoughts on this?...Martin

It is not just a matter of increasing mass and it is certainly not a matter of making the tube stiffer.

The tube is behaving like a tuning fork not an organ pipe. Adding mass or making it stiffer merely changes the resonant frequency; extra mass lowers it increased stiffness raises it. Sometimes just adding mass will bring it down so low that it is of little consequence because the machine does not excite at low frequencies very well.

What the lead shot does very well and sand to a lesser extent is add mass that is not connected to the tube and which does not really have a resonant frequency. Lead shot is far more effective: When the tube vibrates it bounces against the shot which bounces away and into other shot. Because lead is soft the energy is not transferred very well and so it tends to get dissipated mostly by deforming the shot.

The most effective damping is constrained layer where there are two masses that are bonded together via an elastomeric material. Vibrational energy does not pass between the two masses very well because it has to cross two interfaces that have radically different elastic moduli and density. This is how the rubber paint-on compound Richard mentions works; it is lead particles in an elastomeric binder.

Do a Google using the following:

Principles of Rapid Machine Design
by
Eberhard Bamberg
M.Sc., Advanced Manufacturing Systems
Brunel University, 1993

This comes from a link someone put in a thread some time back. The author did his doctorate project designing and building a toolgrinder and he went into damping extensively. The most effective solution for hollow tubes was to line them with a rubber membrane and then pour concrete which contained an agent to creat expansion into the membrane lined cavity. This meant that there was a solid concrete core in intimate contact with the tube via the rubber. In some cases he put a hollow cardboard tube inside the concrete as a core and the effect was more or less the same; it is not the mass that is added it is the manner in which it is incorporated. This is the kind of thing I was referring to in my earlier post.

It is not just a matter of increasing mass and it is certainly not a matter of making the tube stiffer.

The most effective solution for hollow tubes was to line them with a rubber membrane and then pour concrete which contained an agent to creat expansion into the membrane lined cavity. This meant that there was a solid concrete core in intimate contact with the tube via the rubber. In some cases he put a hollow cardboard tube inside the concrete as a core and the effect was more or less the same; it is not the mass that is added it is the manner in which it is incorporated. This is the kind of thing I was referring to in my earlier post.

Dear Geof,

Many thanks.

This is interesting stuff...

Best wishes

Martin

...interesting stuff...Martin

More interesting stuff for you see below.

Hi Martin,I will try to prove I really don't know what I am talking about as far as machinery goes but what works for damping related to speakers.
Sand in stands works.Some guys build double walled cabinets and fill the space with sand.Lead lining as you suggested works great.
Adding mass works up to a point.Steel looks good on paper but is the worst material for a speaker cabinet.Damping materials are high loss materials,not nessesarialy high mass but elastic in nature.Lead is a good dampener due to elastic nature,although mass in this case helps.
Combining three or four different material layers results in good damping as the mulitple resonances tend to cancel each other.
I like the polyurethane foam idea,If high density ,as connecting the walls of the tube should reduce vibration and the foam has no resonance.
It appears viscos elastic materials are the cats meow,not mass.
From Geof's PDF,steppers have many different resonances depending on speed.Would the sorbothane gaskets used on the stepper mounts be a good idea?Sorry having a hard time posting as a real arcade keeps on popping up.
Larry

From Geof's PDF,steppers have many different resonances depending on speed.Would the sorbothane gaskets used on the stepper mounts be a good idea?

For problems with stepper motors I would suggest looking at a damper as described in this thread.
http://www.cnczone.com/forums/showthread.php?t=32284

John

I'm liking the idea of potting a something into the center of the post using silicone. I'm wondering if I'd need to embed the inner post completely w/ silicone or if it could be just potted w/ strategically located 'blobs' to hold it into the needed position? I'm thinking I'd need 9, four around the top four faces, and same for the bottom, plus one on the bottom face to support it up off the bottom.

The only reason I ask is because I'm wondering if the silicone would even harden inside a sealed box like this? Maybe over time.. like years it may.. but doesn't it need direct exposure to humidity to cure?

Because I have a 6 x 6 -0.250 HSS post I could easily fit a 5 x 5 tube up inside.. this would mean I'd need ~250-275 cubic inches of silicone [if I potted the entire post] This is 15-17 tubes of silicone.. thats gotta stink :)

Two questions. A: Is the general censur that this going to work.. ?

B: Should I have a back-up plan in that I could fill the 5 x 5 tube w/ something if this didn't work? [after it's been installed.. like pouring in high psi grout??]

Thanks guys
Jerry

Oh, one other question.. could I do this same thing but use expanding foam instead of silicone? Say using a 2-4pound expanding urethane foam??

Oh, one other question.. could I do this same thing but use expanding foam instead of silicone? Say using a 2-4pound expanding urethane foam??

I think probably not; the foam cures quite rigid and you need something flexible. Also it is the mass of the flexible interface that absorbs the vibrational energy and foam has less mass.

You are correct about the silicon not curing in a confined space, if it did it would cure in the tube. You need the two part RTV silicone or you could use polyurethane. It is possible to get polyurethane to cure at different flexibility and I think you need something fairly squishy; much squishier than a typical O-ring I think.

Geof, do you have any particular brands in mind [for the Polyurethane]? I looked at LePage's website but I can learn more from reading the small print on the tubes in the pictures [which isn't readable] than what they put on their website.. I'm not sure where to find some reasonably priced stuff..

suggestions..? Remember..I need 15-17 of these things.. so $20/tube is out..

Jerry

I think probably not; the foam cures quite rigid and you need something flexible. Also it is the mass of the flexible interface that absorbs the vibrational energy and foam has less mass.

You are correct about the silicon not curing in a confined space, if it did it would cure in the tube. You need the two part RTV silicone or you could use polyurethane. It is possible to get polyurethane to cure at different flexibility and I think you need something fairly squishy; much squishier than a typical O-ring I think.

Dear Geof,

I'm chasing my tail on this one.

As my limited understanding goes (I'm recent to this concept)....

1) the "rubbery" interface needs to be of high mass.

2) the "rubbery" interface should not be rigid.

3) the "rubbery" interface needs to be in intimate contact with both components. That means it has to be "thin", I think.

IMVVHO, these three requirements pretty much practically exclude any material (known to me) that might be applied to the internal surfaces of a steel box section.

Jerry suggested silicone. I tried using "pourable silicone" once, and it takes an age to cure even in a 4" cube.

A permanently squidgy alternative might be bitumen, but you still have to get rid of the water or spirit solvent.

BTW, all may be revealed on page 90 of the article you first suggested I might care to read. My pdf reader is a bit slow, and never made it past page 8 of it. I do seem to be having a general "IT" crisis...

Best wishes,

Martin

I put a call into my local lumber supply store and they have a product that doesn't still tooo well to metal but will remain flexible and will cure in a closed environment [inside a tube] I'm going to pick up a tube of it tonight and see how well it does or does not stick to bare [unprepared] metal. If it's even half decent that's what I'll use. All in all, it'll cost me $125 to do it.. but if it works it's well worth it... if it doesn't.. I'm going to fill the inside tube up w/ grout.. and hope that does it..

I've also got to do some more tests on my mill tonight because I've changed a couple things on it [potted in the last of the gib's on the Z axis post] so this may have elliminated a large portion of my problem already..

I'll post what I find out..

Jerry

i think the spray foam would work to dampen vibration, i use styrofoam sm quite often on parts with a long stick out , hollow , etc , i'll shove it where ever i can if vibration is an issue , generally ive done it on larger sized steel parts where jacks and extra clamps cannot be used

.....1) the "rubbery" interface needs to be of high mass.

2) the "rubbery" interface should not be rigid.

3) the "rubbery" interface needs to be in intimate contact with both components. That means it has to be "thin", I think......


I think it does not matter too much about the mass of the rubbery interface, of course if it is rubbery it is not rigid and I think the intimate contact thing means well bonded over the whole area but not too thin. The damping occurs in the rubber but it is because it is bonded on both sides to something with a radically different stiffness. Just rubber does not work; again look at the crankshaft damper example it is a metal hub a rubber annulus and a metal outer ring. Remove the rubber annulus and just have solid metal all the way out doesn't work and just putting a rubber ring on the hub doesn't work.

US composites to the rescue again.
Jer,they have 2part polyurethanes around $60.00/gal and silicone RTV at $120.00/gal
Different shore hardness is available from rubbery to hard.
A gallon is 231 cu/in.
Larry

Thanks Guy's. Tonight I picked up some "DAP- Dynaflex 230" It's a "Premium Elastomeric Latex Sealant" not rated for metal but I've got a test coupon of 10ga m.s. pc's bonding as we speak. It won't tell me if it will harden in an enclosed environment or not but the tube says it will.

some interesting facts.. it's supposed to be able to allow 50% of joint opening movement [so in my case w/ a 1/4" gap.. i can move 1/8"]

Actually as I'm reading this it does say it's for metal.. well.. we'll see what happens.. I'm using prime 10ga which has not be treated in any way [still has the oily varnish type coating on it..] for my test.

If it does all it says it'll do.. then i'll be a happy fella..

Oh.. and it's only ~$5 for a 300ml tube.. thats a plus also..

I'll let you guy's know tomorrow what the bond was like.

Btw Larry, have you bought from US composites?? How is it bringing stuff across the line?? HazMat charges etc??

Jerry

Hi,
I have a completely different situation than most spoken of here. I made my 4'x8' CNC wood router out of 15 pound 6" x 6" I Beams (1/4" thick). The horizontal X axis spans about 10 feet. The whole thing works pretty well until I try to plow through hard wood at any depth more than about 1/4", at which point I get some pronounced vibrations. The whole I beam appears to vibrate (probably in twist) slightly.

Next week I intend to weld 1/4" plates to both ends of the I Beam. I think that will help somewhat. I suppose I could weld a flat piece of 6" by 1/4" flat stock along the entire back of the beam (the beam is oriented with the center web running up and down like an I) so I would have something more like a tube, which could then be filled with sand.

I've run out of money on this project for the time being, so expensive fill materials are out.

Any ideas would be appreciated.

Henry

Jer the stuff in tubes will cure in thick sections but who knows how long,Years?
If you must use calking type stuff,Lepage PL 9000 at Home Depot sticks madly to anything and seems to cure in a few days to a very stiff flexible joint.The problem I see with any cartridge type material is changes in flexibility over time as the solvents may take months or years to stabilize.The US Composites stuff is catalyst type materials ensuring complete cure.
Epoxy,urethane foam and urethane rubbers are shipped non Hazmat.RTV silicone is Hazmat.
Ever thought of an E/G fill?
Unscientific testing:Take a scrap of steel tubing and hit with hammer:Resonate ding results.Fill with sand,dud results.Try some Great Stuff foam from Home Depot and do the hammer test.The tone will tell a lot of the effectiveness of the damping of the core material without costly analyzers .
Larry

All good points Larry. I may have to do some "un-scientific" testing to see the effects of foam. It'd sure be easier than putting this second tube inside. I really had high hopes for this Latex stuff but so far it's just starting to "skin up" 24hr's after I pushed it outta the tube.. I'm losing faith in a hurry.

One thing that's nice is that the harmonic's of the system seem to have been dampened a bit by the final grout/pot in of the Z axis post rail carriages. It's still not 100% but it's better. The other thing I didn't mention is that most of the vibration problems occur when I have my collet extension in place. It's ~5.5" long and then I had a 6" 1/2" EM in it.. :rolleyes:" I know.. some of you machinist types are shaking your head.... It does appear that when using the same EM w/out the extension that the vibration is GREATLY reduced.. yet it's still there.. so I'm going to have to do something.. I only get the harmonic vibrations at certain speeds [it comes and goes w/ different RPM's] so it's not an out of balance problem..

Sigh.. long weekend is here and I'll be working on offical work stuff so I probably won't get too far w/ the problem.. it still works for me.. I've just got to keep the feeds under 450ipm.. when i feed over 0.030" w/ 50% on a 1/2"EM.. and I'm limited to only 9k on the spindle..

Sigh..

Jerry

.....The other thing I didn't mention is that most of the vibration problems occur when I have my collet extension in place. It's ~5.5" long and then I had a 6" 1/2" EM in it.. :rolleyes:" I know.. some of you machinist types are shaking your head.... It does appear that when using the same EM w/out the extension that the vibration is GREATLY reduced.. yet it's still there.. so I'm going to have to do something.. I only get the harmonic vibrations at certain speeds [it comes and goes w/ different RPM's] so it's not an out of balance problem....

This is a bit of a wild setup :) .

Just because it comes and goes with rpm does not prove there is not an unbalance component so you should consider checking that because 9000 is approaching the borderline for balance being important.

The number of flutes on the cutter can have an influence and there is an interplay between this and rpm. The excitation for the vibration comes from the cutting edge hitting the part and if this occurs at a frequency which is a multiple of a harmonic frequency anywhere in the structure things can get very agitated. High frequencies are probably coming from the tool and holder and low frequencies from the machine frame but it all rolls in together.

Haha.. I figured you'd use stronger language than 'Wild setup' haha.. :rolleyes: you should see it this am.. I'm running a 2.313" facing cutter in it how.. It's actually a bit better over the 1/2"EM for vibration. I think it's the "fly wheel" effect [running at that 8-9K]

The vibration I get is w/ the tool just in the air. The machine isn't moving [a possible cause for excitation] I can understand the tool chattering when in the mat'l and it could be a balance thing.. I just noticed that my extension has a center hole down the middle of it. I'm tempted to fill it w/ lead shot [I've got that much in just old shells] and see if it impacts the vibration problem or not.

Anyway she's cutting like a hot darn this morning.. 350ipm 1.64"step over at 0.60" DOC @ ~8K... just humming along.. I can see I've got to do a bit more work to get the spindle sqr to the table.. I'll have to sweep it w a DI at some point but for roughing off my table right now.. it's working pretty well!

Jerry

Anyway she's cutting like a hot darn this morning..

Jerry, any chance for a video?

I'll see what I can round up for a vid. I'll have to find a better place to post it.. maybe U-tube.. I'll post a link in a bit here..

Go easy on me guy's, it's STILL not painted.. and the shop is a mess right now.. :)

Jerry [Playing when I should be working!!<-- even if it IS the weekend :D]

Haha.. I figured you'd use stronger language than 'Wild setup' haha.. :rolleyes: .........

Considering I made an 18" extension out of 1" cold rolled with a 1/2" mill in the end yours is tame. I didn't run at 9k though :) .



..... I just noticed that my extension has a center hole down the middle of it. I'm tempted to fill it w/ lead shot [I've got that much in just old shells] and see if it impacts the vibration problem or not...........

The problem with this is that for the shot to have much effect it cannot be packed tight. But if it is loose in a rotating tool it is going to create an out of balance situation.

Geof, your alot more adventurous than I. I'm just glad I didn't end up w/ a 8" ext. as I'd probably have an end mill sticking through the Xd-90 on my garage by now.

I found a couple of my vibration problems. Seem's the idiot who build this thing forgot to properly tighten a couple major bolts on one end of the gantry. Once I solved the problem for him and tightened them up.. the next 90% of the vibration problems disappeared.. interesting... at this rate I'll get most of them... but still be left w/ 0.001% [of the original value] of vibration. Which I can live w/.

Got a vid I'll post up.. just gotta get to my downstair comp and d/l it and edit it so it's a teeny bit smaller..

Jerry [note to self.. empty dust collector BEFORE the bottom AND TOP sections are full.... 3 garbage bag's later.. and a second shower for the day so far... :rolleyes:]

Unscientific testing:Take a scrap of steel tubing and hit with hammer:Resonate ding results.Fill with sand,dud results.Try some Great Stuff foam from Home Depot and do the hammer test.The tone will tell a lot of the effectiveness of the damping of the core material without costly analyzers .
Larry


Dear Larry,

Thanks for that suggestion. I was thinking along the same lines as regard whacking the trial section and listening to what it sounded like with different fills.

Lead shot is expensive, but if you live by the sea, there are companies that will roll up to your dock and fill the bilges of boats with lead shot ballast.

As an alternative, sand is very cheap.

Two part boat foam might work, but I'm not sure how well it might pour into long narrow spaces without some parts not curing simultaneously. My supplier issues all sorts of warnings about not pouring too deep sections. They cite exotherm, but I can see circumstances where one part of the foam cures slower than the next, and blows the cured part "up the pipe" while it is still expanding. The people who fill boat masts with the stuff must know a trick or two.


My (late) two cents, even though the thread has moved on..

Best wishes,

Martin

....Two part boat foam might work, but I'm not sure how well it might pour into long narrow spaces without some parts not curing simultaneously. My supplier issues all sorts of warnings about not pouring too deep sections. They cite exotherm,...

Deep sections + large cross section + good insulating properties + exothermic reaction = hot enough to ignite; maybe even hot enough to explode.

Masts are lacking the large cross section.

Deep sections + large cross section + good insulating properties + exothermic reaction = hot enough to ignite; maybe even hot enough to explode.

Masts are lacking the large cross section.

Dear Geof,

Err.. maybe,

Masts are usually aluminium (or something entirely more exotic these days if you have a billionaire sponsor).

The exotherm should not, IMVVO , be a great problem given that the surface area from which the heat has to dissipate is pretty large compared to the volume of foam for a given length of spar.

I am still curious about how to pour two part foam into long lengths of narrow tubes without encoutering problems. Obviously, it can be done, but I can anticipate problems with differential rates of curing , and expansion of the foam along the length of the hollow tube. I may well be wrong.

Best wishes,

Martin

Well for those of you who's been w/ me for the last couple years. Answering my crazy questions and helping me along.. here is a first look at my nearly completed machine.. This isn't the thread to go into all the details on what else needs to be done and what I have done here but.. here is a short vid instead.

Enjoy.. :D

http://www.youtube.com/watch?v=nQytmfvUc7M

Jerry

Great stuff Jerry! The size and the color ---> really intimidating. I love it!

I'm not sure I follow the 'color' bit but.. the size.. well.. I've never been one to do things in half measures. :D

J

I'm not sure I follow the 'color' bit..

http://www.youtube.com/watch?v=5blbv4WFriM

http://www.youtube.com/watch?v=6A0rwG39Jzk
_

Great stuff Jerry! The size and the color ---> really intimidating. I love it!

Dear Walter,

Ah.. the darkness, ah... the "sportiness".

BTW Jerry, fabulous machine.

Best wishes,

Martin

Thanks Sir.. :)

Here is an article on chatter and vibration Dealing with aluminum so maybe not totally pertinent but it is an interesting read.

http://www.mmsonline.com/articles/010101.html

And your machine does look and sound impressive...but then I said that months ago when you were building.

Well... I've played some more with my vibration issue's. In the mean time I spun the front bearing nut outta the nose on my Ekstrom spindle. I talked to them and have since tightened it back in, but it's gonna have to go down for service in the next while.. just to make sure it's all ok..

Anyway, I'm using a SM-C73 spindle from them, and have it mounted using the back body screw mounting holes. I got to thinking the other day.. I wonder if mounting it this way is the reason it's vibrating. I'm wondering if maybe switching to a nose mount would help in this regard..

Also, I've come to the conclusion that the latex stuff I tested for the potting in a center mass in my Z axis just isn't going to work.. so back to the drawing board.. I've found a Devcon urethane compound which is like water when mixed but then harden's into an solid form. It will return to shape after a 650% elongation. It's supposed to be pretty soft.. and flexable.. [maybe too soft] and I could try this but first.. figured I'd ask what others thought.. being as it's gonna cost me ~$500 for what I need.. btw.. it's called "Flexane 80 Liquid". It has less than a Shore hardness of A94 [because the 94 series is that hard.. and its 'more rigid than the 80" in the book.. I have no idea how rigid that is.. in comparison the durometer..

Getting sick of running this spindle down at 8-9k.. and ~200ipm w/ a 1/2" EM 0.06" x 50% in wood.. it should run way harder than that.. and not cause problems..

I've actually got to wondering if the spindle doesn't have something wrong w/ it.. I bought it 'new-used' so it shouldn't .. but then who know's..

Anyway, something isn't right.. but I can't for the life of me figure out what it is..

Jerry

This is a question - not in any way meant to be informational.

- Medium grade oil - 50 - 80 wt range filling the columns
- Small styrofoam beads

Certainly not optimized, just wondering.

Harryn, I think the intent of vibration reduction is to put a solid mass in suspenion, yet connected to the vibrating mass via a non-rigid connection. The connecting member then 'eats up' vibration by being heated from the continous movement and reduces the energy which is finally disipated in moving the inner mass.

I think the comment earlier about oil and lead shot was based on the idea that the lead would absorb the vibration, while the oil would dampen the movement [rattling] of the lead.

I'm not sure how the oil and styrofoam beads would accomplish either of these two things? Feel free to expound on the idea..

Jerry

Harryn, I think the intent of vibration reduction is to put a solid mass in suspenion, yet connected to the vibrating mass via a non-rigid connection. The connecting member then 'eats up' vibration by being heated from the continous movement and reduces the energy which is finally disipated in moving the inner mass....Jerry

Golly gee he does read the documents you refer him too!!!!!! Give the man a gold star or two :D

Well.. if the truth be told.. I didn't READ.. like.. word for word the doc's.. but from the little I know this is the 'gist' of what happens.. Chad over in the Mach3support forum made an interesting observation today. He said, if it comes and goes.. [starts at 10k and then goes away] its a harmonic's problem.. if it's continous it's a balance problem.. and I agree.. I guess I have to sit down and figure out if it's a harmonic's or if it's a balance thing..

Since I've spun that bearing nut out I'm worried that it's got worse.. oh well.. I'll have to play w/ it tonight..

So Geof, any suggestions as to how hard or how soft is tooo soft [or hard]? What is A94 Shore in comparison to say 60du? Are we talking rubber bands or rubber tires here..??

Thanks sir..

Jerry

The vibration coming in and out at different rpm does not necessarily indicate it is balance over harmonic. Actually if you get vibration when it it not cutting it is balance but you might only notice it when the rpm hits a harmonic frequency for the structure. I had a problem with a barfeed on a lathe vibrating like crazy at certain spindle speeds; which just happened to be the rpm I wanted to run at. This one I solved by bolting heavy weights on a driving the harmonic below the running speed. You cannot take the same approach because you are wanting to move the mass that is vibrating so you need to go the energy absorbing route.

I don't have any definite knowledge on how hard the rubber should be but I expect it would depend on what is the typical frequency you want to damp. I think soft for low frequencies and hard for high. Hard would be tire soft would be rubber band??????

It is actually an interesting challenge.

EDIT: P.S. when somebody compliments you, you are supposed to say "aw shucks, thanks" not tell them it was not really warranted.:)

Ya it is an interesting problem.. I'm tempted to just get a new Z axis made.. use 1" pl and dam the torpedo's.. I'm getting the vibration somewhere in the range of 120+Hz which I would think is pretty low.. [8000rpm's/60sec=133.33Hz] so I'll take the soft approach.. hey whats a guy got to lose right.. if it doesn't work.. I'm only out ~$500 for the gunk + the co$t of a new Z axi$.. :D ya should come out to $a$k.. the money grow$ on tree'$ out here :rolleyes:

Before I go spend any more money on the problem.. I'll run the thing again tonight a get a better feel for the spectrum in which it goes 'off' and post that for your perusal.

Jerry

Just did some searching and found out that shore and durometer and like Petrol and gas.. never knew! They also state that 20A is like a rubber band while 80A would be a car tire or a runner sole.. while 95 would be a skate board wheel.. so.. I'm thinking that 80 may be even up there on the hardness scale.. I'm not sure where that leaves me..

Btw, Geof.. any thoughts on the nose mount vs back mounting of my spindle motor??

Thnks

Jerry

Martin P/U foam is highly re-active.Typically you have 30 seconds to mix and pour,which would dictate small pours.High density foams are less troublesome as they expand less.
My two fartlings worth
Larry

.....Btw, Geof.. any thoughts on the nose mount vs back mounting of my spindle motor??

Thnks

Jerry

Not quite sure what you mean by this but if you have the option of mounting something at either end that means it would be possible to attach it at both ends; which is what I would do for increased rigidity.

Larry, the P/U stuff I'm speaking of is a liquid which harden's into a rubber compound when hardened.. it doesn't expand like the p/u foam does.. they recommend it for casting etc..

Geof, well it's a typical industrial router body. Rect. block body w/ a round nose sticking out the bottom and a air vent at the top. The back of the body [it's plastic and metal] has four 6mm screw holes and is noted 'ok' for mounting in the manual, but I've also seen them mounted by the round/barrel type nose w/ a clamp [think muffler clamp] type mount..

There's a GIF of it.. it's small but gives you the idea.. [off Ekstrom's site]

Jerry [nope.. didn't get a chance to do any testing tonight.. worked till 9pm.. had supper.. helped the wife w/ son... helped clean the basement.. now it's time for sleep.. sigh.. there's always tomorrow.. which never come's.. and the "honey do's" never end..]

there's always tomorrow.. which never come's.. and the "honey do's" never end..]

Oh boy oh boy! Do I recognize that part?! :D

..... worked till 9pm.......blah blah blah...... now it's time for sleep.. sigh....]

Whatta Wimp! :D why when I was forty years younger I would work around the clock and start fresh the next day.

I wondered if you router had some sort of flimsy flange. The clamp around the barrel is probably all that is needed provided it makes good contact and is itself nice and stiff.

ya.. I know... I'm not gonna deny it.. I've only worked ~65hrs of overtime in the last 12 days.. sigh..[not including the time I've spent on my own business projects] some day I'll grow up and be all tuff.. oh.. and I'm a first time 3 month old dad.. that's the icing on the cake :D

Anyway.. I got to thinking that maybe the harmonic's could set up in the body of the router and then that excites the tube and away it goes.. If there is any flexability in the router body mnt [to the spindle bearings/housings] then that could be a major contributing factor.. But I don't know for sure.. I've finally been released from Honey-doo duties now so I can go do some real testing.. I'll post up in an hour or so..

Jerry

Hay Jarret,the foam was into responce to Martin on mast filling.The P/U molding rubbers from US Comp is 30 min cure and different shores,which I also don't understand.The soft one is like silicone,the medium like pencil eraser,the hard like car tiers.The big problem with resonances is say your resonance is 120 Hz.A filling or compound may kill the 120Hz but harmonics of 120 Hz may still exist such as 240 or 480 etc.The good news is the higher the resonance the easier it is to suppress.A structure of 3 different materials or more with different resonances tends to cancel one another.
Try the un scientific approach.Hold 2 boards on each end of the tube and see if the resonance is lower.If so the air column is part of the problem.Get you father in law to hot glue plywood to the bottom of the tube and fill with sand.If that does not work you only spent $10.Sorry for no answers but you must locate the source and deal with it rather than blowing another 500bucks.
Larry
Gotta agree with Geof,35years ago I could work around the clock,but now 12 hrs a day/7days a week is all I can do,you know 12/7.

Well gang.. news from the front.. I did some testing today.. started out w/ no tools no nut just the spindle [after re-tightening the nut w/ some permatex blue on the threads] I could run it up to 18k and I extended and retracted the z axis to the stops.. no real detectable vibration. There was two points when spooling up that I could tell it wasn't far from going into harmonic's but it didn't [I tried to make it by hunting for those rpm's and trying to make it but naddaa..]..

next I put a 2"lng 1/4B-EM in in and spun it up.. again it went through a couple points [more noticable this time] where it was ready or would just start to go harmonic..

Lastly I tried a 5/8" F-EM in it and spun it up.. while it did get into a vibration of fairly low amplitude [I wasn't worried that the EM was going to come otta the collet] it wasn't really that bad..it was vibrating.. I could feel it in the post when I put my hands on it..

So.. what does this tell me.. well.. I think my problem is either one of two things or both.. EXPENSIVE [not] EBAY tools.. and even more cheaply made EBAY [chinese] collets.. That and the extra long length's of tools that I'm running and voila.. problems..

So the solution is two things, first of all.. find the nearest garbage for these collets and replace them w/ something from a reputable tool company [most likely KARR in my case]

The second plan of attack is to add a mass in the center of the post. I'm wondering if I need to absolutely fill the z post or not..? I have 24" [high] of available room inside there, but does that mean it needs to be filled?

Being as I'm going to have a fairly high durometer urethane rubber in there [84A] I'm wondering if a smaller more concentrated mass isn't the ticket..? Say if I put a 12" long tube and potted it in the rubber. I could get a hundred pounds in a pretty small area.. depending what I put in there..I would think that is in excess of what I'd need but.. I'm open to suggestions...

The interesting thing is when I'm running that 2.05" facing mill in my extension [using two crappy collets] that it run's suprisingly smoothly.. I think it's the flywheel effect of the larger dia cutter.. but I'm not sure..

Anyway.. there's where I'm at.. I'd like to hear what ya'll think of my conclusions..

Jerry

Sorry larry I was in the mid's of typing that when you posted.. There is only one open end on tube but that doesn't mean it's not the air that's causing it. Your right I could just put some sand in there and see what it does to it.. It's a cheap experiment at least.. Worth a try anyway..

For the time being I'm using this large facing mill.. it works as I'm only notch's large sheets and what have ya.. but the time is coming when I'm going to have to go back down to my 1/2 and smaller stuff so a solution is going to be needed.

It's good to at least have a focus of where to go. . and things to try.. I feel like I'm at least doing something about it..

Jerry

Jer,the air in the tube will not be the cause the resonance only the amplifier of the problem.Try to zero in on the source first,which you have done,narrowing it down to collets or tooling or the spindle.Sympathetic resonance is also capable of turning the mounting nuts.
Half filling the tube will half the resonance.Possibily inserting an ABS tube in the tube and filling the space with 80A urethane will help.This would give the three different material resonances resulting in reduction of vibration.If it is not enough,another material can be used to fill the ABS tube.
BTW off subject,sorry my memory is bad.Is you gantry over 1000 lbs?How big are your motors?Your rack must be 12dp OR LARGER.Any info is useful.
Larry

Makes sense Larry.. I like the pricing of the P/u rubber from US-comp.. 1/5 of what I was going to pay locally... about 1/2 price once it gets to my door..
If I do buy from down there I think I'll shoot for 60dur instead of 80.. they say 60 is like a pencil eraser... sounds good to me..

The gantry is over 1800lb's.. I don't have an exact weight per say but thats an pretty educated guess [supported by CAD] I'm running two 640 oz-in Nema 34 steppers into 10:1 precision planetary's and then into a 2" x 12DP pinion.. it has a fair amount of power.. but I'm planning to replace it w/ some high torque [1100oz peak/~250cont] servo's and 25:1 reducers and a 1.5" pinion.. I can hit 1000ipm rapids on it right now so speed isn't a problem, but acceleration isn't what I want it to be so.. I need more juice.. a little extra force at the tool isn't going to hurt either..

HTH

Jerry

Harryn, I think the intent of vibration reduction is to put a solid mass in suspenion, yet connected to the vibrating mass via a non-rigid connection. The connecting member then 'eats up' vibration by being heated from the continous movement and reduces the energy which is finally disipated in moving the inner mass.



Jerry

Dear Jerry,

My very humble opinion is that you are trying to get rid of unwanted mechanical energy . IMVO, the only way you can do that is to to turn the vibes into heat, as you so rightly state. Grinding balls of lead, or fine sand might accomplish this, because there is real friction involved.

My suggestion of a foam fill will almost certainly be less effective.

Any structure, be it hollow metal, or whatever, will to a certain extent dissipate heat if it is stressed. Try bending a piece of metal backwards and forwards, I'm sure you know that.

Surely, you want loads of friction? How does some rubber compound between two pretty rigid components help? My guess is that it will act like a spring and conserve the energy you are trying to dissipate? OK.. a rubbery thing may get the energy to an acceptable level elsewhere in the vibration spectrum, but loads of grinding balls might be a better, simpler, and more practical solution.

I have put on my hard hat, awaiting the entire possibility that I will be comprehensively shot out of the sky......

Best wishes,

Martin

Martin, your for sure on the right track.. and thinking in the same vein as I.

I don't have any claim be being a vibration specialist of any sort. The sum of my experiance in this area is very limited. I built some concrete form's a couple years ago and they had some high HP vibrators on them.. [for those w/ dirty minds.. your wife wouldn't get w/in 50ft of these things.. if you were w/in the 50ft they gave you an instant headache (when turned on..) ... they made a jack hammer look like a tonka toy]

We had some problems getting rid of transmitted vibrations and ended up putting them on vibration isolation feet.. just a high tech hockey puck really.. anyway they worked.. kill'd alot of the transmitted noise..

Anyway to the problem at hand.. I think the reason rubber would work is the same principle as bending metal.. If you look at vibration you can break it down to be a form of "work".. we know that to do 'work' it takes power.. The vibration is 'in effect' reducing the efficency of the spindle to do 'work' just like a parasite.. it's "robbing" power that would normally be put into the tool to do a more profitable type of 'work' [we're hoping anyway :)].

We also know that to bend anything, it takes power.. bending metal takes way more "power" than bending rubber. The power available is alot less than 2kW [the ~ power of the spindle] it's safe to assume that the vibration has a power level well under 1kW.

The other problem w/ just trying to bend steel is that it won't bend on it's own, it needs to be 'controled' alot more than rubber. Rubber, on the other hand will bend or deflect easily when a load is applied. Because we only are dissipating a small amount of power [even if it IS really loud :)] we would never get to the point where we'd effect steel, instead the steel since it wasn't effected/bent would simply transmit the vibration. It may use up a tiny bit in the transfer of it, but not enough to absorb it all.

Having the rubber in between the outter section of steel and the inner section create's a situation where things get out of phase with each other while vibrating [an educated guess]. We are creating a stiff, solid type spring. There are several possible area's of work being done in this situation. First, the vibration is transmitted through the rubber, because the rubber is going to deflect it will begin to heat [not noticably.. but because it's being 'worked' it has to] some of the vibration will be transmitted into the inner section of steel [a tube]. The inner steel section has mass, so it takes power to move it.. it will also transmit some of that energy into what ever is inside the tube [steel shot or whatever] that also uses up energy. Lastly, the inner tube will transmit energy back into the rubber. This is where the out of phase part comes [or could come] into play. [The outter tube is pushing against the rubber, while the inner tube is pushing the opposite direction also against the rubber and they cancel each other out-- this may not happen w/out taking time to 'tune' the system.. taking into account spring rates (and all that jazz) of the rubber]

At the end of the day, the rubber act's just like the shock absorber in your car, it reduces the amount of vibration transmitted and what ever is left, is absorbed in the rest of the structure..

Also, as Larry pointed out, if the air colum is removed it can also help to reduce the effects of harmonic's.. all of this together should work to reduce the vibrations and improve the system.

Will it work... who know's.. but I'm gonna find out :D

sorry.. I got windy again.. I haven't been windy for a long time.. Geof will be :rolleyes: again..

Martin; My understanding about how the rubber between two pieces of metal acts to absorb the vibrational energy is that it is sort of like an impedance mismatch. All the materials have an intrinsic natural frequency that is dependent both on density and Young's Modulus but they are all different. The metal that is the source of the vibration does not pass the energy efficiently to the rubber because the rubber does not want to move at the same rate as the metal is pushing. Similarly the rubber does not pass the energy efficiently to the second metal. The net result is the energy is largely lost due to hysteresis in the rubber which gets warm.

Jer,I may need to put on my hardhat as Martin has done.I donut know,but perhaps shot filling is best if you can take the extra 500lbs of moving mass.
Jerry you may have another career as a loudspeaker box designer.Damping vibrations in a loudspeaker increases the output and clarity of the sound.The motor or speaker frame is not wasting energy moving cabinet walls,same as the spindle using power to vibrate the frame and cause chatter.Someone may say a loudspeaker cabinet does not have the same problematic vibrations.Actually it may be worse although steel tubing is harder to deal with.
Generally mass is a good thing,but not in the case of a steel structure or aluminum.Lead is good at suppressing vibrations not due to the weight mainly,but its flexability and absorption converting energy to heat.
My power supply is over heating gotta cool down back laterLarry

Dear Jerry and Geof,

Thank you both for not shooting me down out of hand. I shall however keep my helmet on....

I know next to nothing about vibration control, and I do apologise for posting on a thread where others know considerably more.

I guess that what I'm suggesting is that un-wanted vibration energy has to go somewhere. Heat is obviously the way out.

There are two approaches, but they are on the same spectrum. Kill those vibes (which you never will), or "manage" them to another frequency.

IMVVHO, if you have large sections to fill, the "kill" approach, with sand or lead seems more practical. It will never kill everything , put it does,at least,have the virtue of simplicity, as a "first stab".

Best wishes,

Martin

Back for the moment.
Geof should be a cabinet designer also.Jer &Geof are using audio terminology such as impedance mis match and out of phase.
Martin you know of vibration control as you want to glue lead sheet to mdf for a speaker as per our PM's.Rather than pre laminating the lead,Glueing the lead sheet with silicone to the inside of the completed cabinet would work wonderfully.Lead sheet is available from roofing supply houses.Tar would be a good damping material but probably not good in a speaker as solvents may soften the adhesives in the loudspeaker motor.
Computer PSU too hot gotta shutdown fastLarry

I haven't been paying too close attention here, but why not fill it with Walters magical EG stuff. Vibration damping is it's strong suit, correct?

[QUOTE=lgalla;35471
Martin you know of vibration control as you want to glue lead sheet to mdf for a speaker as per our PM's.[/QUOTE]

Dear Larry,

Just as the design was finalised, you come up with something else?????

Oh, B##ger...

Best wishes

Martin

Wow, I leave for an hour and a book gets posted up :)

Geof, thanks.. you have a knack for writing in only a few lines what I struggle to spew forth in many paragraphs..


Larry, currently the Z axis won't take too much more weight.. once in a while it loose's steps [always downward] soo It's time for an upgrade there. I'm going to put in a 10:1 planetary reducer [I've got a couple spare's kicking around] and see if that doesn't solve the problem. Then it should handle ~10x the weight at 1/10 the speed :D

Martin, there is no question that 100% removal of all the vib's probably isn't going to happen, however I think the rubber approach has a little more finess in that it burns the vibrations up [into heat] rather than lowers them solely due to increased mass. It's kind of like a car w/ bad shocks.. more weight will smooth the ride to a certain degree but new shock's will greatly improve the same ride.. In reality, it's no harder to fill w/ the rubber than it is to use the lead or foam or sand etc.. The whole experiance should only cost a couple hundred bucks. Btw, no need for the hard hat.. we're all learning something new here.. no condisention [sp] on my part :)

Larry.. sounds like ya need another fan.. or a 1kW power supply.. that otta do it :D

Ger I think the beauty of the E/G stuff is the mass of it...just the shear weight of a proper mix has to have some profound effects. It's also true that it will eat vibration from the elastic effects of the epoxy itself..

I think I'll order some 60A tomorrow and get this ball rolling.. I'm working on getting my hands on some good collets as well.. I can't wait to be able to bury my end mills and hog away :D

Sorry Martin,the original idea is still valid and good but from following the thread,new simpler solutions evolve.The ideas on the thread fine tune processes
and result in new ideas which may simplify the process.Your original idea of pre laminating is valid and better than post laminating which which may be easier to implement.Either way.
My 2 fartlings worth

....The whole experiance should only cost a couple hundred bucks....

Careful now! Coupla hundred here, coupla hundred there...pretty soon you are into real money :) .

Being a cheapskate at heart,I use to spray polyurethane bedliner with 5 sec gel.I added rubber crumb into the spray with a sandblast gun which did not alter the properties and greatly reduced the costs.Rubber crumb is ground up tires and dirt cheap.Help the enviroment?I dough-nut know filling a 6X6 tube with urethane and tires will help the enviroment but it is sure cheap.
Jer the best advice you gave me in the past was to keep obsolete computers and throw them off the mezzanine when frustrated with un corporative computers.I have to move by the end of the month and looking at units with 24ft ceilings.Is this high enough to acheive satisifaction?For now WD40 is keeping the fan spinning.
Oh!OH! burnt my hand on the chassis detect odor of WD-40 and smell of burnt circuit board.Perhapstime to rapidlyendthis sessionbeformeltdown!!!!(flame2)
LARRRRY

Geof, don't worry.. when you come out.. i'll show you how much I have into this farce.. I know all about a couple hundred here or there.. TRUST me..:D

The wife and I were talking about that this weekend.. she said something about ya but it's only $20.. and I reminded her how much I'd spent in the last year and 1/2, 'just $20 at a time'.. so.. we know the value of money.. I could have my morgage paid off right now.. but I'd have a VW bug in the garage instead.. so.. it's been worth it soo far.. :)

Geof, don't worry.. when you come out.. i'll show you how much I have into this farce.. I know all about a couple hundred here or there.. TRUST me..:D

The wife and I were talking about that this weekend.. she said something about ya but it's only $20.. and I reminded her how much I'd spent in the last year and 1/2, 'just $20 at a time'.. so.. we know the value of money.. I could have my morgage paid off right now.. but I'd have a VW bug in the garage instead.. so.. it's been worth it soo far.. :)

My philosophy is do not borrow; that way if things go sideways you stop spending money and there is no continuing effect.

And I don't think it is a farce. You may take longer than you thought and spend more money than you planned but your video showed something with real substance.

I hear ya! I'm working towards that goal myself [do not borrow] hopefully I'll be there in the next while..

I use the term Farce very loosely.. There are those (whom shall remain nameless [not that they frequent this site]) who would laugh me to scorn for even thinking of building something such as this.. to them, it's a farce.. however the proof is in the pudding... and I'm confident that the pudding is gonna taste GREAT :D

In reality it already does.. I'm milling some wood right now.. 3" facing cutter at 200ipm and 0.050"DOC.. it smells great.. nothing like the smell of fresh routed wood.. from a machine you've built w/ your own two hands..

I've just gotta work on the small things.. like 133Hz oscilations :D

Sorry Martin,the original idea is still valid and good but from following the thread,new simpler solutions evolve.The ideas on the thread fine tune processes
and result in new ideas which may simplify the process.Your original idea of pre laminating is valid and better than post laminating which which may be easier to implement.Either way.
My 2 fartlings worth

Dear Larry,

Just for the hell of it, I've decided now to try a sandwich construction:

18 mm MDF
2 mm bitumen sheet
2 mm lead.

Over here, the bitumen sheet is called "Dedshete". It was original designed to damp down vibrations and "drumming" in car body panels, although loudspeaker builders use it for the same purpose. I'm pretty sure that bitumen/lead sheet is available commercially, (almost certainly at vast expense) so I'm not claiming that this is an original idea.

Anyway, thank-you everybody for pointing me in what I hope is the right direction.

Best wishes,

Martin

Martin sandwiches are good.ask Earl.
MDF is actually a sandwich by nature of the process.Pressing the mat of fibers results in a top and bottom skin of high density and a lower density core having an I beam effect resulting in an extremely stiff panel.Adding bitumen then lead results in a sandwich of 5 different material frequency's,out of phase,producing a "DEAD"structure to vibrations.How do we apply this to machine damping???Any thoughts?
MY 2 Pence worth.
Larry

Dear Larry,

Obviously there are going to be problems trying to make a sandwich inside a long hollow metal section, but I stumbled on some stuff called Green Glue last night.

http://www.greenglue.org/index.php

Suppose you have a solid core material that is sized so that it leaves an air-gap that is say 1/8" wide between the core and the inner surface of the metal box surface. I suppose ideally one might like to fill this up completely with some viscoelastic material. You might be able to do this by locatiing the core with temporary spacers, and then somehow injecting the gloop.

Another approach might be to drill a series of holes in the box section, and then just squirt in "dabs" of Green Glue or whatever.

Would it work??? Err, I simply do not know..

Best wishes

Martin

Deleted - somehow posted in wrong area.

Well I ordered some 50A P/U rubber today.. I should have it for the weekend.. so I'll post up how it goes.. I sure hope this works.. :D

Martin the green goo type material is very effective at it's job,but takes up to a month to cure.Probably longer on or in between steel tubes.Since Jerry's tube is sealed at the bottom he will pour a small amount of catalyzed urethane first and let it cure for a bit so the innertube does not contact steel at the tube bottom.Next he will again pour a small amount of urethane and place the inner tube equally spaced from the outer tube and let cure.Now the tubes are aligned without spacers.
Basically he has a Peanut butter sandwich.The heavy steel tubes with the urethane should have great losses.Hopefully only air column resonance is left and can be cured with lightweight fillers.Multi layer sandwiches can be done by using descending tube sizes.
The two heavy "skins" with the rubber core will vibrate out of phase or impedance mis match effectively ,effectively making Jerry "One happy camper"::D :D :D
Larry

Here's hoping Larry.. However, the plan isn't going to go exactly like that.. my problem is that the tube is an open column on the bottom only.. the top is already cap'd w/ drive mount plates etc.. so.. Prior to starting all this I'll first machine an mdf plug for [or possibly UHMW ] plugging the bottom of the tube.. then remove the spindle and insert the tube. The tube is going to be a 5 x 5 .250hss w/ a capped bottom end. The tube will be placed and pinched into position w/ 4 to 6 D&T'd holes thru the sides of the column. Then the plug is hot glued into place w/ a gap between it and the btm of the tube. Then P/u is introduced into the column from the top & flows down to fill the column. I'll probably only put in a small amount to start with and then leave that to gel.. once it's kicked off [ ~1hr] then I can start filling more and backing out the pinch screws as I go.. until it's filled.. and in a few ours after that.. it'll be the best dam vibration eating monster ya'll ever seen.. :D

If it needs to be tuned a bit, I can always add mass to the inside of the inner tube.. I'm using some pretty soft [50A] P/U so I'm hoping that's not going to be a requirment.. While that's all going on.. I need to remove the garage door opener so I can put my 10:1 reducer onto the top of the unit [need more clearance] so it will run the higher weight w/out losing steps.. Then.. I start working out how I'm going to mount my new servo to the Z axis.. while not taking up more height.. sigh.. there's always something to do :)

I came across that green glue stuff the other day as well. It says it needs at least one porous surface to cure, so I don't know if it would ever cure being sandwiched between two pieces of steel.

I came across that green glue stuff the other day as well. It says it needs at least one porous surface to cure, so I don't know if it would ever cure being sandwiched between two pieces of steel.

Dear mxpro32,

Thanks for the information. I missed that bit about porous surfaces. In other respects, it looks like a fairly interesting product. The resonance tests show a pretty impressive "dead cat bounce".

Best wishes,

Martin

Hi, Igalla mentioned earlier in the thread about rubber crumb from recycled / shredded tires. I contacted a local supplier (Hollister, CA - near San Jose)

Cameron Wright
West Coast Rubber Recycling
1501 Lana Way Hollister, Ca 95023
(phone number removed to keep him from the auto dialers)

www.groundrubber.com

He sells crumb from 30 mesh (sand like) up to 3/4 inch roundish balls - approx. US $ 12 - 15 / 50 lb bags, as well as bulk delivery for less. The also have a shredded material which is intended to look like shredded bark for landscaping use. It is more random in size / shape, which (might) mean it would absorb over a wider frequency range.

I played a little with recycled tire crumb in the past ( poured some liquid nitrogen on an old tire and smashed it with a hammer). Pretty interesting stuff, and it seems to be widely available near most major cities.

Did some un scientific research to day.I ramed a piece of plywood into a steel tube.Drop an untreated piece on the floor and you get a loud ring.The treated piece had a low dud.
Conclusions?Probably almost anything in the tube will help reduce resonances.The plywood did not fill the tube only half.Having a tight fit on only two sides worked well.Perhaps any polymer fill will work joining the four surfaces to gether.Larry

Interestingly enough.. Today I was at a SolidWorks 2008 roll out and while eating lunch I had the presenter model up a 6 x 6 .250 HSS tube and then check it to see what the natural freq of it was.. it was 253Hz... so after some more discussion about holes and other things added to it it was concluded that it should resonate at ~150Hz.. I didn't get a chance to get him to model it w/ the 50A P/U and center mass but he seemed to think that it would REALLY dampen the vibration of the tube.. I may get a buddy of mine to check this for me as he has the full FEA software that comes w/ Solidworks... I only have the cheapo FEA stuff.. so can't check it myself..

This software sure is amazing.. it just blow's me away w/ what they can check and predict now aday's..

Haven't done the P/u thing yet.. been too busy w/ work .. but I'll get there..

Jerry

Jerr,I am amazed also at the solidworks modeling.My gut feelings is the P/U and inner tube will work well.Does solidworks actually take gut feelings and tern them into reality?Unfortunately I don't have 20 grand for solidworks,only some scrap tubing and a hammer.
Larry

Yup it's pretty amazing.. No gut feelings however.. just COLD hard facts.. and it don't care if it show's ya what you want to see or not.. just the facts..

Your in luck.. you can buy a basic seat of SW for about $6k usd.. only the super duper extra extra fancy version cost's $20k.. and even I don't have that.. but I'm about 1/2 way there :D