I'm working on a product, that, if all goes well, i will need to be turning out multiple units as quickly as i can. I have a couple questions about fixturing, and how i can make my production process the easiest.

What i will be making will start out as a cookie, or slug, cut off of t-6061 alum, 2.5 inches in diameter, and about .750" thick.

My thinking was to take a couple of the larger "tooling plates" that i have that are all alum, and bore some countersinks into it, drill a hole through the center, and put a rubber "O" ring down inside, and through the hole in the middle of the depression, i would attach a suction, or vacuum pump of some kind, to hold the slug in place during machining.

I will need full access to the top and the upper .250 of the slug, so side clamps are out.

My thinking is that i would have multiple depressions, and thus could machine multiple parts in one pass, then, have a second set of depressions, that i could then flip the cookies over in, to machine the backsides.

My questions are as follows.

What should i use as a gasket material in the depressions, to make a seal between the cookies, and the fixture?

What can i use to make the vacuum? obviously a shop vac isnt really gonna work in this case, just not enough surface area to work on, so i'm thinking its going to have to me a fairly decent vac source.

and since i'm running full flood coolant, what do i do about any coolant that may get sucked into the vac ports, do i just have an accumulator of sorts, so that the fluid gets collected before the pump?

I was wondering if i could use something like the harbor freight vacuum pumps, but i didnt know if anyone had one, every tried what i'm doing, or had any idea if it would work...

i tried searching for some of this stuff, but everything i searched for came back, "no matches found"

I'm looking for any input, ideas, thoughts, and so forth, if anyone has done anything similar to what i'm talking aobut, and you have pictures, i sure would love to see them...

I doubt you will get enough holding power.

2.5" diameter is 4.91 square inches.

Full vacuum, which is not possible, is 14.7 pounds per square inch.

You will have less than 72 pounds holding your part down, it will certainly spin and very likely will lift out under the force of the cutter.

Side clamps are not out, you have 0.5" of space to clamp on the side; top clamps are out.

Do you have a decent sized vise? Make yourself some custom jaws with a 2.5" diameter hole about 0.45" deep and you will have plenty of holding power.

EDIT:

When you want to scale up for high volume start another thread and I will suggest how you can make a multiple holder using air clamping.

You'll spin your wheels trying to get a vacuum to work and it wont!
Geof has the solution"

I'm working on a product, that, if all goes well, i will need to be turning out multiple units as quickly as i can. I have a couple questions about fixturing, and how i can make my production process the easiest.

What i will be making will start out as a cookie, or slug, cut off of t-6061 alum, 2.5 inches in diameter, and about .750" thick.

My thinking was to take a couple of the larger "tooling plates" that i have that are all alum, and bore some countersinks into it, drill a hole through the center, and put a rubber "O" ring down inside, and through the hole in the middle of the depression, i would attach a suction, or vacuum pump of some kind, to hold the slug in place during machining.

I will need full access to the top and the upper .250 of the slug, so side clamps are out.

My thinking is that i would have multiple depressions, and thus could machine multiple parts in one pass, then, have a second set of depressions, that i could then flip the cookies over in, to machine the backsides.

My questions are as follows.

What should i use as a gasket material in the depressions, to make a seal between the cookies, and the fixture?

What can i use to make the vacuum? obviously a shop vac isnt really gonna work in this case, just not enough surface area to work on, so i'm thinking its going to have to me a fairly decent vac source.

and since i'm running full flood coolant, what do i do about any coolant that may get sucked into the vac ports, do i just have an accumulator of sorts, so that the fluid gets collected before the pump?

I was wondering if i could use something like the harbor freight vacuum pumps, but i didnt know if anyone had one, every tried what i'm doing, or had any idea if it would work...

i tried searching for some of this stuff, but everything i searched for came back, "no matches found"

I'm looking for any input, ideas, thoughts, and so forth, if anyone has done anything similar to what i'm talking aobut, and you have pictures, i sure would love to see them...

As the other poster said, soft jaws. Make a copy of your vise jaws in aluminum. Cut them so you get a piece of the radius in each one. You don't need a complete circle in the jaws, just make sure they are closed on something when you cut the jaws. Even .25" of depth in the jaws will do a whole lot. At work I use soft jaws almost exclusively. It also makes setting your offset easy, as unless you unbolt them from the vise they will always be in the same place.
There are other kinds of fixtures you could make. There are low profile side clamps that use cam action. You'd want a pair of fixed blocks to center the blank against though.

ok, i had wondered if the vac would be strong enough, guess that confirms my fears that it wouldnt be...

So, if i'm gonna go the route of making half moon clamps, (vice jaws) then i could use compressed air and some short throw, medium to large diameter(I'm thinking 1 inch) air cyls and just do it that way.. i have 185psi compressed air on tap at all times...

another plus of going that route is i dont have to worrie about coolant inside of vacuum pumps and all that jaz.

..So, if i'm gonna go the route of making half moon clamps, (vice jaws) then i could use compressed air and some short throw, medium to large diameter(I'm thinking 1 inch) air cyls and just do it that way.. i have 185psi compressed air on tap at all times...

185psi air, that is high!!! But not high enough.

A 1" diameter cylinder will give you about 145 pounds of force closing your air vise, not enough I am afraid. You would need something like a 3" or 4" diameter cylinder.

If you do not have a vise make yourself some halfmoon clamps that are closed using a couple of bolts, just like a split clamp except one half is machined into your plate.

hmm thats an interesting thought.. so tell me, do you really think i need over 2000 lbs of clamping force? a 4" cyl * 185 psi = 2323.6 lbs of force.. wow, sounds like i'm really gonna be crushing these things..

or is my math wrong? area of a circle is pi*r^2
3.14 * 2^2 = 12.56in^2
12.56 * Air pressure, 185 = 2323.6

now i know that there are some losses, and i know that my compressor comes on at 180 and turns off at 195 (according to multiple unrelated gauges)

but for your example on the 1" cyl, i get 3.14*1^2*185=580.9lbs of force.

where am i going wrong on the math?

hmm thats an interesting thought.. so tell me, do you really think i need over 2000 lbs of clamping force? a 4" cyl * 185 psi = 2323.6 lbs of force.. wow, sounds like i'm really gonna be crushing these things..

or is my math wrong? area of a circle is pi*r^2
3.14 * 2^2 = 12.56in^2
12.56 * Air pressure, 185 = 2323.6

now i know that there are some losses, and i know that my compressor comes on at 180 and turns off at 195 (according to multiple unrelated gauges)

but for your example on the 1" cyl, i get 3.14*1^2*185=580.9lbs of force.

where am i going wrong on the math?

R not D. .5x.5xpi

please explain further. a 4" diameter cyl would have a radius of 2", 2^2 or 2 squared is 4. 3.14 times 4 = 12.56

the formula is pi times r squared, right? thats the area of the circle, or piston, then multiply that times the air pressure to get the output force?

please explain further. a 4" diameter cyl would have a radius of 2", 2^2 or 2 squared is 4. 3.14 times 4 = 12.56

the formula is pi times r squared, right? thats the area of the circle, or piston, then multiply that times the air pressure to get the output force?

You can use a smaller cylinder if you provide a lever or cam to give mechanical advantage. A 1" cylinder with a 16:1 lever will give the same clamping force as a 4" cylinder with 1:1 lever, and you shouldn't need much travel on the workpiece end, so even a 1" travel cylinder should work. You could also use a hydraulic cylinder instead of a pneumetic one, and run MUCH higher pressures (like > 1000 PSI).

Regards,
Ray L.

I always like to err on the side of holding things too tight rather than too loose but notice I did give you a range; 3" for about 1300 lbs and 4" for about 2300 lbs.

The lever suggestion is also very viable and you can also get force multiplication by using a toggle clamp or a sliding wedge. These are more complicated to build but when your volumes increase it becomes worthwhile putting in the extra effort on the fixturing to reduce the reloading time.

An advantage with both the toggle clamp and wedge is that they can be self locking so if you lose air pressure you do not get parts flying around. In this case you need a double acting cylinder because force is necessary to unlock.

please explain further. a 4" diameter cyl would have a radius of 2", 2^2 or 2 squared is 4. 3.14 times 4 = 12.56

the formula is pi times r squared, right? thats the area of the circle, or piston, then multiply that times the air pressure to get the output force?

yes, but where you calced the area of a 1" cylinder you used 1" for the radius, and it's .5"
.5"*.5" = .25"
.25"*3.14*air PSI = 145

Check out Mitee Bite clamps to clamp by the edge. There are some cheap clones of those floating around that are available from places like Shars.

Best,

BW

PS The clamping force issue is an interesting one. Very hard to find recommendations on that if you go searching. Carr Lane is one source. I was surprised by how little force they show as optimal for a step block clamping setup. Their issue was not to approach the failure point of the studs too closely. Their recommended torque on the bolts was WAY less than anyone I've ever seen tighten down anything on a mill table. LOL!

or use a lathe chuck clamped to the milling table, machine up some soft jaws, self centering, pleanty of holding power. I do it all the time. Last job was starting off as 2" diameter 52100, didn't budge a bit.

Multiple lathe chucks is your multiple fixtures. Use your G54-59 offsets for each chuck.

And a 3 jaw scroll chuck eliminates the problems with round soft jaws on a milling vice, including centering. For instance, if your OD is +-.005, but your milling opps require .002" concentric, your part center is going to move around.

ok, .5 vs 1 on the radius, got it, i see my mistake on that one.. and true you did give a range..

i was thinking about the cam/lever mechanical advantage idea, i have a couple cyl's that i could use, thier 1.125 piston diameter, and i do like the idea of having it setup so that if i were to loose air, i dont loose my part, break a cutter, and have to duck really fast.. hehehe, been there done that... not fun.

I dont see the need for hydro strength, first of all i dont have a source(pump) and secondly, if i were to spring a leak, i'd have to deal with hydro fluid in my coolant, i dont like the sounds of that.. I've been using the same coolant for over a year now(just adding water to make up for evap)

where i'm working with t6061 alum, i was wondering if i should consider using some hard plastic on the jaws of the clamp to keep from marring the surface of my part, perhaps something like cutting board material..

I like the simplicity of the lathe chucks, but i only have the ones that are on the lathes now, and that seems far more expensive than using materials i already have to make a more vice like mount... If i use some half circles or even "V" knotches for the parts to go in, i would think that i would get pretty consistant mountings.. fortunately these parts dont have to be ballanced, or rotate in thier end use, so if i'm off my mark by 5 thou then i'm still in good shape...

I've never used offsets that i'm aware of. My plan was to just have enough clamping locations, and then have the one program run all of them in one whack.. my thinking was something like a mini assembly line, the first station or clamp would do the top of the top, then station 2 would do the bottom of the top(the part gets flipped over) Then station 3 would do the top of the bottom part, and then the 4th clamp would do the bottom of the bottom.. I would have 4 parts on the table at any one time, each in different stages of compleetion, then as the parts move from one station to the next, you take the finished parts out, and put in new blanks, and just run the same program over and over, that one program would cut all 4 stations...

In my mind, its easy to draw, easy to program, and since there are no tool changes necessary, it should go pretty smoothly all the way through all 4 stations..

The other thought that i had was to lay out the stations so that each end of an air cyl is working on a clamp, so with 4 stations, i would only need 2 cyl's... the drawing is not to scale or anything, but it'll give you a good idea what i'm thinking... ofcourse this dosent include any kind of a failsafe.. better ideas on how to do that?

course, i guess, considering that i'm probably gonna have about a 1 hour cycle time to do all 4 parts, i guess, sliding hand operated clamps would be the easiest.. and simplest, and simple allways wins over complicated in the long run...

You have it pretty much worked out. Just a few comments:

Vee clamps do not hold as securely as a halfmoon, they can allow twisting because of the small area of contact.

An easy way to get high pressure for hydraulic clamping is to use a multiplier; have a large size air cylinder operating a much smaller hydraulic cylinder. Set it up with a reservoir much like a brake master cylinder so that when the air cylinder retracts it draws fluid into the hydraulic cylinder and allows any air bubbles to escape. Instead of hydraulic fluid or oil use coolant as the workinf fluid and you don't have any problems with leakage.

You multi-station approach is the way to go but see if you can figure out some sort of locating pin system so you cannot put partially finished parts in the wrong station.

I don't think any kind of plasitc in the clamps is a good idea - it won't hold securely enough. Aluminum clamps should not mar your parts if they're a matching contour and smooth on the contact faces.

You definitely should have the clamps match the contour of the parts, don't just use Vees - they won't hold securely, and the small contact area is far more likely to put flat spots on your parts, or score them (and the clamps) if the parts turn while cutting.

You could actually do four parts with only a single air cylinder, by putting a bar across each part of parts on the left and right of your fixture, and having the cylinder act in the center of that bar. That will ensure equal force on all four clamps, as the extra bars will balance the force applied to each, regardless of any minor dimensional differences.

Regards,
Ray L.

larger cyl operating a smaller one, got it, that makes sence,

on the v shaped clamps, i can see your point, i will machine the half moons....

i never thought about using the coolant as the operating fluid.. thats freakn brilliant.

I follow your idea about the bar and just using one cyl. the only drawback is that i have to have something in each station, or build in some stop pins...

I'm not too worried about getting things in the wrong locations, about the only think i could mess up would be to put a half done top, in the bottom machining stations, but as far as doing each half, dosent matter which side gets done first...

ok, i updated the drawing, i know what you mean, its just really hard for me to draw in paint... if i were at home and had my software, i could definately draw it better..

larger cyl operating a smaller one, got it, that makes sence,

on the v shaped clamps, i can see your point, i will machine the half moons....

i never thought about using the coolant as the operating fluid.. thats freakn brilliant.

I follow your idea about the bar and just using one cyl. the only drawback is that i have to have something in each station, or build in some stop pins...

I'm not too worried about getting things in the wrong locations, about the only think i could mess up would be to put a half done top, in the bottom machining stations, but as far as doing each half, dosent matter which side gets done first...

ok, i updated the drawing, i know what you mean, its just really hard for me to draw in paint... if i were at home and had my software, i could definately draw it better..

That's still more complicated than it needs to be. The new bars should be solid bars running all the way across each pair of clamps. These bars are completely free-floating. The lever connected to the air cylinder connects to a single pivot in the center of each bar. You can eliminate the extra parts connecting the two in your drawing. The clamps, of course, are also pivoted on the ends of the bars, so they will self-align.

Regards,
Ray L.

Here's the idea, on the left side of the drawing. (Paint SUCKS!)..

Regards,
Ray L.

yea, i just see one major drawback.. the cyl body has to be able to move... lemme draw up another thought that i had.. hehehe and i think its a good one.

i was looking around and i found a 2" bore, 6" stroke cyl.. why not use some aircraft grade cable, i just happen to have laying round, and use a few pullies....

so the cyl mounts in the middle, and then there is a bar across the piston rod, that attaches to 2 cables, these cables come down parallel to the cyl body, then hit a pullie, turn 90 deg out, and then go through a block and tackle kinda setup. so if there were 3 strands like drawn, then you'd have tripple the force, right? and 4 strands is 4 times? so, if i could do 6 strands, 6 inches of cyl travel is 1 inch of clamp movement, more than enough, and not accounting for losses, a 2" cyl @ 150psi air times 6x b&t multiplier, i get 2826lbs of force, now devide that by 4, and you get 706 lbs on each of the 4 positions..

is my math right on that?

yea, i just see one major drawback.. the cyl body has to be able to move... lemme draw up another thought that i had.. hehehe and i think its a good one.

i was looking around and i found a 2" bore, 6" stroke cyl.. why not use some aircraft grade cable, i just happen to have laying round, and use a few pullies....

so the cyl mounts in the middle, and then there is a bar across the piston rod, that attaches to 2 cables, these cables come down parallel to the cyl body, then hit a pullie, turn 90 deg out, and then go through a block and tackle kinda setup. so if there were 3 strands like drawn, then you'd have tripple the force, right? and 4 strands is 4 times? so, if i could do 6 strands, 6 inches of cyl travel is 1 inch of clamp movement, more than enough, and not accounting for losses, a 2" cyl @ 150psi air times 6x b&t multiplier, i get 2826lbs of force, now devide that by 4, and you get 706 lbs on each of the 4 positions..

is my math right on that?

Letting the cylinder float is no problem at all. It doesn't need to be anchored to anything other than the two lever arms, so your total parts count is one cylinder, two lever arms, two clamp blocks. You have a pivot point on the lever arm, and one for each clamp. It doesn't get any simpler than that. Using cables, you have at least three pulleys, the cable, some means of constraining the motion of the balance arm - a lot more complex. And, a significant percentage of your total force will be lost as friction in the pulleys and cables. It's more complex mechanically, but where's the functional advantage?

Regards,
Ray L.

good point, i didnt think about it like that. if the cyl is mounted via clevis or other pivot methods on both ends, then it would be free to "float" and move both arms in opposing directions..

not to mention that after i posted that, i thought about all the filings and swarf that could get into all thoes moving parts and cause issues...

ok, i think i'm sold on the single cyl idea.. if i use a cyl at all, i'm just wondering how complex that is in comparison to just mounting 4 cantilever clamps.. my machine dosent move fast enough to need super fast changeouts...

Damn, I guess it's time I stop using washers and drywall screws to hold my aluminum parts down to my MDF table... LOL 2300lbs? 700lbs? I'm lucky if I get 30lbs with screws and wood.. Haven't lost a part yet, and I've done some 1.5" thick aluminum blocks. I'm working on some parts that would be nice to have automated clamping though, some good ideas here. I did see a Youtube video of something being machined (or was it "How it's Made" on the Discover channel....?) where they had pivoting top clamps that moved out of the way as the cutter came along, then moved back when it had passed. Now THAT was some clamp engineering!

wow, now thats the left hand knowing what the right hand knowing what the 14 other hands are doing.. automated move outta tha way clamping? pretty cool...

No kidding! Not quite sure how something like Mach would handle that... :)

ACK, HACK, COFF, CHOKE!!!!!

no really, if you programmed the clamps as on/off, theres plenty ways to do it.... i bet you'd be hand coding that part tho, cause i dont think mastercam or babcad could handle it...

I've actually been very impressed with what all i've seen a single instance of mach 3 handle all at once, even on an older and slower computer... so i cant say anything negative, cause personally, i love it. simple, easy to understand, but loads of features are in there so when you grow, it can too, and it just works, and thats really all we care about, right?

Years ago I designed and built a little mill fixture for the same size part! The parts were 6061 T3 and I had to buy the bar stock slightly over size so I could turn to 2.5000. Now you can get the material to size.
This was a part that had over 22,000 parts in the order. I went with the Vise jaws first and got the customer to buy off Q/A.

I make most fixtures like this out of 2" aluminum plate that can usually be found surplus. I have extensive hydraulics usage in such applications but I learned a long time ago to keep it SIMPLE!

These little parts had an elliptical funnel and 4 10-32 cap screw holes with an O-ring grove. I programmed them for 3D and ran these on a Bridgeport Series II boss 6 mill. Guys in the shop averaged around 200 parts a shift and we knocked the order out in about 6 months with a second fixture.

The sliding clamp was made out of some cold rolled 1" X 4" bar and worked great. The operator had to be careful to torque the bolts just right and before we but the torque wrench on them the threads had to be inserted! We taped them down with a small ball peen hammer!

I never finished the engineering because Bill my foreman had the job done and running before I could finish. Any way here is a old drawing!

Good luck!

i'm not sure if its in the drawing, or if i just missed it or what, i'm not real sure how you generated the clamping force, looks like there is a plate that grabs the parts to hold them in place and then you have slots to tighten down and hold the plate in place..

is that what the hammer tapping was about?
tension the hold down bolts a little, and then tap it with a hammer?

That's right, just as you would do using vise jaws. Not shown are the heavy / hardened 1.5 washers and 1/2-13 Allen head bolts! Also to apply pressure there were two evenly spaced 3" long 1/2-13 allen bolts that swung up from the edge of the 2" plate. The same thing could be accomplished with Edge/plate clamps!

I was taught to use a 4 - 8 oz ball peen for such applications. machinist touch and tap and feel the part nest/ seat into location. The material gets milled away so you cant harm the part. When that side was done you then have a machined service to locate with / no tap required.

Everyone needs to develop the "Touch", practice with a piece of round stock in standard vise jaws. Start a little angled and tap into position down on two matching parallels!


Keep in mind this tool was easily amortized because of the quantity.

Send me a part drawing and I can provide you planning and anything else you need!

Jim