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  1. #41
    Member handlewanker's Avatar
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    Default Re: fretting on 30 taper tooling

    I'm quite stunned by your revelations mainly because it's something I realised a few years ago when I started into CNC and the mill I have also has Bellville washers for the drawbar retention system.

    To my mind a system that relies on a spring in the relaxed state is not a system I would admire for a holding design, but that is the name of the game and unless a different method is devised you're (we're) stuck with it.

    I designed or rather doodled, a few drawbar retention designs, using a toggle design without Bellville washers, but actually getting down to doing something that is as far as it got......so I hope and pray that the Bellville washer system I got on my Chinese mill will outlive me and function for a time yet.

    If I ever get some serious "events" with the retention system I have then I would remove the Bellville washers completely and go to a simple nut on the end of the drawbar the same as my Bridgeport and all other manual mills have......OK, so it's not the same as a power drawbar but it will do the same job of holding the tool in the spindle and it's fail safe.

    At least the spindle is fixed in position in the head, not like a quill system spindle end that goes up and down for the Z axis feed, so if the need arises fitting a simple nut to the drawbar would do the trick......I hope id doesn't get to that stage as I quite like the power aspect for gripping and releasing.

    I think the real need is to ascertain the actual retention power that holds the tool up in the spindle.....trying to pull the tool down when retained will indicate the holding force you have or have not …..whatever.

    I think a simple indication would be to attach an eyebolt to the mill table and then fix a hook in the tool holder and see if you can pull the tool down ….you will be able to it just depends on how much force it takes.

    To make a more sophisticated test apparatus you could use a lever 300mm long with a fulcrum 20mm from one end fixed to the mill table....this will give you a 15:1 ratio...…. you could then pull up on the short end with the spindle mounted tool and use a scale under the far end that pushes down to show the kilograms it takes to pull the tool down...…..nothing like knowing what you are dealing with.

    What you will be doing is seeing how much it takes to compress the Bellville washers and slacken the tool in the spindle...…...it only takes a mm which is the cause of the fretting due to the tool end waggling loosely in the spindle bore under down pull from the cutting forces......the bigger the cutter diam or depth of cut the worse it gets.
    Ian.



  2. #42
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    Default Re: fretting on 30 taper tooling

    Hi Ian,

    I guess the proper way to do this test is using a drawbar force gauge. As long as the drawbar force is within spec, I wouldn’t concern about holding the tool in the “relaxed” state of the spring washers. For a 30 taper spindle, it is normal to have about 1000lb of drawbar force. So if you can flex anything with you hand it means something is way off.

    Jason


    Sent from my iPhone using Tapatalk



  3. #43
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    Default Re: fretting on 30 taper tooling

    Discussing the viability of Belleville washers for use as a holding force is probably off topic for this thread. I'm trying to keep it focused. It isn't that I'm not interested, it is that I'm hoping to help some other poor wayward soul in the future when they have a similar problem and stumble on the thread. This way they'll be able to get the data as quickly as possible without going through a ton of pages. This is partially why I've tried to summarize all of my steps in a few co-located postings.

    However, I will say that although I agree with you that hydraulics might be a superior solution, I think the important thing to realize is that designers are trying to economize as much as possible. Belleville washers are used extensively, I believe, in this application. My guess is that in the grand scheme of function versus dollars, the low cost of Belleville washes wins out. As for how best to test the 'strength' of the pull... I hear what you are saying, but I have some additional thoughts. The pull force measured by something like the Clamprite is a pretty standard paradigm. But, the issue here is that the force is not linear. My guess is that the problem with my system is that the washers are likely a tad thinner. Add that up over 80 washers and you end up with insufficient deflection of the washers when in retention mode. But this, ultimately, is what is going to address fretting. Although it might take 5000 lbs to actually pull the tool out, I'll end up with all sorts of chatter (and then fretting) if I only have 100PSI at the tools static (retained) state. Well, that is my thought. I'm sure someone can poke holes in this as I specifically do not claim to be an all knowing machine tool designed. And, frankly, I think you and I are addressing the same concern.

    My guess is that I need to add some shim washers to decrease the total length of the cylinder holding the Belleville washers. This is all assuming that the original washers were a tad thicker. Decreasing the length of the cylinder would increase the compression of the washers, thereby increasing the pull force on the stud. The balance here, of course, is that if I compress too much, then the bottom clamping collet will not drop far enough to allow the ball bearing to retract; the result would be an inability for the retention knob to clear the retention bearings (aka a stuck tool).

    Adding the following to the archive... Earlier in this thread, someone mentioned that they had some washers from Dyna. They provided the measurements from those washers. I took the P/N listed (which matched something that I got from the ex Dyna guy), AM-201010, and did some searching on the internet. I got a hit that provided all the specs, so I thought that would be something to keep in this thread:

    fretting on 30 taper tooling-oem-dyna-belleville-washer-part-number-match

    Finally, here are the part numbers for the whole retention assembly (note the ball bearing sizes in there too, in case you lose one!):

    Draw bar DM4400M ( 19-0042 )

    1.- T00201011-6 Draw bar = 1
    2.- T0112-04004 hex-screw= 1
    3.- T0899-03016 steel ball 3/16"= 6
    4.- T0201013 Washer = 1
    5.- T0268-201010 Disk Spring = 80 pcs.
    6.- T00201014-1 Guide top chuck =1
    7.- T0639-01800-P O-ring P18 = 1
    8.- T0639-01200P O-ring P12 = 1
    9.- T00201017-5 Stud Chuck = 1
    10.-T00201018 Set Screw M4 = 1

    Last edited by MrMetric; 02-18-2020 at 08:31 PM. Reason: adding specs for original belleville washers


  4. #44
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    Default Re: fretting on 30 taper tooling

    If as you say, the compressive length of the stack is reduced you will get more holding force in the retained position but also a coil bond situation on the down push with the Bellvilles and the tool will be stuck up the hole.

    I think you are more on the button with 100 psi holding in force than 5000...….I have to wonder how many others have this problem without realising it.

    For the system to work at it's best the washers need to be completely compressed or flat to one another when the drawbar is at it's down position and the tool released...…...that would momentarily put the washers under maximum stress and coil bound, but it would only be for a short duration while the tool is out.....the drawbar needs to have a rapid down/up movement to take the strain off of the washers or they will eventually lose their springiness.

    I expect you could measure the height of the compressed washers to ascertain when they were completely compressed as that would be the minimum height in the spindle when the drawbar is down and the tool is just released......that would then give the washers their maximum available force when in the up position.

    The total force available is determined by the configuration of the washers to one another......ie, in pairs back to back and in sets etc.

    The total movement should not exceed about 6mm of travel as this is all the drawbar needs to move to go from retained to release.

    At a guess I would think a single washer can deflect about 2mm from relaxed to completely compressed flat......with 40 pairs of washers that is 80mm of movement, so the stack needs to be paired together probably in sets of 4 or more....whatever...…. to maximise the compressive force and give you only 6mm +/- of travel.

    You could then get more pressure in the holding position where you need it most but the release mechanism will need to be in the tons range to compress the washers for release.

    I wonder if a solid rubber block in place of the washers would give more force with a shorter travel.
    Ian.



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    Default Re: fretting on 30 taper tooling

    I think that we are pretty much on the same path of thought here.... I sent my Clamprite out for validation so that I can eliminate that as being a potential source of error. I'm guessing it will be fine, and I'll have to take the retention system apart again. When I do that, I plan on taking accurate measurements of the cylinder in which the Belleville washers reside so that we can do some real calculations. That will be the only definitive way to settle some of this. The one thing I don't really know is how the stacking affects the measurements. Take a single Belleville washer that is spec'd to take 500N to compress to 50%. If we then take two washers and stack them as (), I'm assuming that it still takes 500N to compress to 50% (but now at twice the distance). Now let's consider a stacking order that is (()). I am thinking that it takes 1000N to compress that arrangement to 50%, at a compression distance equivalent to 50% of the () ordering. Do you agree?

    And, to further this discussion a bit.... I'm assuming that a (())(()) arrangement would be 4x the travel at 1000N using the same example as above. And, finally ((())) would be representative of 2x travel, 1500N. Right? (the real mind tease is when you start doing (())(())(())(), but that is just evil)

    I think there is something else I should point out here. We have bandied about several units and not all of them are actually convertible. I've been stating PSI (pounds per square inch) but I don't think this is correct. My Clamprite is actually measuring lbs-f, which is pure lbs. My mistake.... What we do have is a few different bits of information:

    1. From Robert: "The pull force pressure for the Draw bar on the 4400M should be 300kg or 4267 PSI" [my addition: units are different. 300kg == 661 lbs]
    2. From post #27 PDF: ""Steep Taper 30 5340 N / 1200 lb-f" [my addition: 5340N == 544kg-f] <-- ASME B5.50 (CAT/ANSI)

    The problem is that these two aren't really correlating well. If I'm reading this correctly, Robert's information (Dyna mfg specs) place the draw force at 661 pounds, which is half that of the PDF document's "international standards" of 1200 pounds (lb-f is the equivalent of lb). All of this is very... confusing! Maybe my 400lb-f as shown in the photo after my reassembly isn't that bad after all? I haven't been able to find any further 'standards' on clamping force, unfortunately. But, now that we have some information on the *original* Belleville washers as a function of deflection (see previous post), we hopefully can get some answer. Unfortunately the McMaster Carr parts don't have that data provided. Sigh. Although this might not matter to you Australian folks because I think McMaster Carr is a USA only supplier.

    My inclination here is that maybe I'm trying to understand this too much. That is the engineer in me, LOL. The other approach is to handle this empirically by adding another friggin washer at the top of the stack (same orientation as the top one, which will be cup down), reassemble, and measure with my handy force gauge. Adjust until I get to some agreed upon number. Hmm, this is sounding appealing!



  6. #46
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    Default Re: fretting on 30 taper tooling

    In all counts you are right and on the right track.

    The arrangement of the Bellville washers will affect the poundage of the stack and the travel rate.

    If they were all placed in the () configuration you would get a weak stack but lots of travel which you don't need.

    Pairing them together in a (()) configuration will increase the poundage but you will need more pairs for the travel length.

    As you say, you can arrive at a force that is feasible to hold the tool in the spindle by arranging the stack with trial and error...….very time consuming and also without a suitable means to ascertain the down pull it's throwing stones in the dark etc, but it would get there eventually...….pioneers are a very hardy breed.

    You also need to have the same arrangement with the same number of washers in all groups of washers or the group with less pairs will compress completely first and you will end up with bum results.

    Interpreted that means (((()))) one group....((())) second group and so on......all groups must have the same amount of washers until the spindle cavity is full to the top and you can get the nut on....whatever.

    I personally would do the down pull test, as I stated previously, by attempting to pull the tool out of the spindle.....how much force is needed to not pull it down is a question......that is also a question as when you pull the tool down you also increase the retention force but by that time the tool is chewing the spindle bore...….it only takes a mm to do that.

    Overkill is an expensive business all round...…..if you only ever use small diam cutters the problem will not arise but drills etc with a weak retaining force will show up when they pull the chuck down on the up stroke.

    The holding force needs to be measured at the very moment when the tool unseats and starts to move down...….any further movement increases the force as the washers compress.

    You can then experiment with the washer stacking configuration to see how practical any arrangement is.....you only want about 6 mm of travel to completely remove the tool but that force increases as the tool moves down to the point of release......it's the top end of the travel that is critical.

    If you are working with an ATC the problem is a real critical one.

    I have to wonder if the makers of CNC mills and spindles actually realise the forces that are present (or not) when the tool is at it's least retained state.....when you need it most.

    I'm amazed when I hear stories of tooling that has pulled out of a collet in a chuck under cutting loads.....they must have humungous draw bar retaining forces for their tooling.
    Ian.

    Last edited by handlewanker; 02-19-2020 at 10:58 PM.


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    Default Re: fretting on 30 taper tooling

    I have a LONG write-up on calculations... But, in the end, I realized that only a die hard would be willing to follow it to the end. From a simplistic point of view, however, I created a polynomial curve fit equation for the Belleville washers. I also did a detailed measurement plan of my spindle arrangement, with the goal being to find the height of the actual cylinder in which the washers reside, and the preload compression distance (at rest), compression with a tool in the holder, and compression at UNCLAMPED. The idea is that you want to target 900 - 1200 lbs with the tool clamped, but must also have travel sufficient to UNCLAMP. What I learned was interesting. Frankly, I could easily prove that the McMaster Carr washers wouldn't cut it. The problem is, any small change to the stacking arrangement requires new calculations because the deflections will all change, along with the total compressibility of the stack. You can adjust by adding shim washers, but that also changes everything. What a mess.

    The solution was to develop a program! At first, I thought I'd write something up in Java. But then I decided that Excel does an excellent job of showing everything in a spreadsheet and allows you to tweak numbers dynamically. Want to add a half millimeter to that shim washer to see what happens? No problem. So I finally did that. And, boy, is it interesting!!!! The polynomial equation isn't perfect, but it is better than nothing at calculating force at a specific deflection. And it seems to bear out pretty well. Sadly, however, I don't know if I can attach an Excel spreadsheet here. . And, even if I could, I chose to use VBA so that I could easily plop in new force formulas.

    To cut to the chase, however, I found that the McMaster Carr washers could really only be arranged to develop a maximum force of about 660 pounds while still maintaining the required travel. That was disappointing. So, I'm on the hunt for other washers that will work better.

    Man, I'm really glad I got that force gauge and started to think about this. Interesting stuff....



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    Default Re: fretting on 30 taper tooling

    Well, aren't you just the professional engineer with all the figures at your disposal or the capability to drag figures out of the air to display a situation that occurs.....my hat off to you for being so precise.

    Personally, not being an engineering wizz kid.....I'm a fitter and turner per se, long retired now...... and as such I work(ed) with what you see is what is happening so fix it etc.

    So.….a long story short I addressed the issue of drawbar pressure and retention issues as a problem and after spending some hours on my graphics pad designed a system that on one hand uses Bellville washers in a compression mode to clamp a tool with the ability that increases the clamping and retaining forces as the tool is clamped which is a lot different to the conventional system that relies on the Bellville washers relaxing as they expand to do the retaining.

    There are two ways....that I can think of...….for holding an object firmly...….one is the resilient method and the other is between a rock and a hard face method.

    If you consider the first method it's like a paper clip where you have a springy folded metal casing that is sprung open to hold the paper...…..you cannot increase the holding force as that is governed by the thickness of the metal and the designed bending ability.....when the paper clip is opened the springiness increases and as it closes it relaxes to the to grip the paper...…..the conventional drawbar retention method works on this principle too.

    The second method is a direct force application like the nut on the drawbar of a manual mill spindle......that is termed ….between a rock and a hard face, totally inflexible and totally rigid...….G clamps, bench vices, work holding clamps, vice grips and toggle clamps all work on this principle and they apply a huge holding force with little effort., that is, there is no springiness in their design.

    No one wants to have a drawbar for CNC work that has to be like a nut on a bolt to be manually tightened every time.....pushing a button and out it pops is the way of CNC.

    I would not hesitate to state that the method you will find on any CNC spindle is the Bellville washer type wit an air cylinder or other etc to apply the downward release force.

    So, a mechanism that removes the Bellville washers and applies a direct clamping force to the drawbar is 100% more reliable than a springy stack of washers that applies less force as it expands.

    Basically it consists of a cam operated pull up mechanism attached to the top of the drawbar powered by a geared down 100 rpm motor that at the top of it's travel holds the draw bar rigidly up......it does not have Bellville washers to do the pulling and it can be retrofitted to any mill spindles that use Bellville washers etc.

    To release the tool the cam rotates 180 degrees to it's down position and the drawbar is pushed down.....6mm of travel is all that is required in most cases......very little force is required, but a huge rigid holding force can be applied at the top of it's stroke to retain the tool holder shank and it will work with any tool shank taper.

    It would be impossible for the cutting forces of any tool to pull the tool holder down or loosen it in the taper.

    Therefore the Bellville washers can be done away with as a holding force.

    I don't think a sketch is required as the design concept is logical if you think of it, maybe even patentable for someone who gets in first.
    Ian.



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    Default Re: fretting on 30 taper tooling

    Ian,
    It is an interesting project and one that I may eventually take on. But my immediate need is to get my machine up and running again with a safe solution (100 pounds force is *NOT* safe). What I can tell you, however, is that the throws on the DM4400m are a bit more than you are talking about, although that is a technicality.

    Here are a few measurements, if you are curious... The pressing piston drops about 14.1mm between at rest and unclamped. Someone put a shim in my system that prevents about 2.5mm of travel, so it was originally possible to drop about 16.5mm or so. My system consistently drops tools (when desired), however, so I'm leaving the shim. It might have been installed so that the hall effect reliably detected the UNCLAMPED state.

    Anyhow, I calculated about at 4.8mm gap between the bottom of the pressing piston and the top of the drawbar nut. That needs to be subtracted from any travel (can't measure UNCLAMPED directly). The long and the short of it is this:
    CLAMPED compression: 4.1mm
    UNCLAMPLED compression: 9.3mm

    Cylinder height: 123mm
    Air washer at bottom of stack: 5mm
    Encroachment of drawbar nut into the cylinder: 23.45mm . (just go with the precision... I understand the ability to measure this accurately is suspect)
    Resulting cylinder size, at rest: 94.55mm

    So, in the existing system, any washer setup needs to produce the desired force at (4.1 + X)mm of deflection, where X is any preload on the stack. That comes in the form of: (Cyl_height - Free_Stack_Height). At the same time, you still need (9.3 + X) deflection possible in the stack or you won't hit the UNCLAMPED Hall Effect sensor.



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    Default Re: fretting on 30 taper tooling

    I know what you mean....I measured the drawbar travel on my Skyfire mill to be about 6mm from clamped to unclamped + 2mm for thruster clearance. as I have a temporary manual release mechanism on top of the spindle due to the 12 volt electric thruster one being over voltaged at 36 volts and burnt out.

    I expect you will succeed in your endeavour by just applying more and more force until it does the trick.....measuring the force is another matter.

    It is possible that in the very fullness of time I may do the retrofit mechanism that I have designed and remove the Bellville washers completely even though they are doing the job as designed...….it takes a large amount of increasing force with a spanner to unclamp the tool, so that is one area I spit the dummy on.
    Ian.



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    Default Re: fretting on 30 taper tooling

    Just as a matter of interest attached is a sketch of the proposed drawbar clamp and unclamp mechanism....sans Bellville washers...…. I raved about.

    I was never very happy with the conventional Bellville washer type drawbar design but that is how it was conventionally and how the mill I bought was designed to work with so that is what I got, except the power drawbar part was actuated by an electrical linear thruster that soon failed after a few ups and downs.....long story.

    When this thread was posted and the prospect of the loose tool in the spindle fretting the spindle bore due to possible slack Bellville washer force, I decided to re-investigate my previous thoughts on a drawbar mechanism that worked better than the spring type.

    I'm a self professed inventor and have had a few successes in that field one way or another, both commercially and as a DIY need to do it.
    Ian.

    Attached Thumbnails Attached Thumbnails fretting on 30 taper tooling-power-drawbar-24-c-jpg  


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    Default Re: fretting on 30 taper tooling

    Unfortunately that attached image is microscopic. On my computer, when I open up the attachment, the image is *maybe* 1.5 inches tall on the screen. I zoomed my browser in and the image is completely unreadable but I got the idea of what you are trying to accomplish. It is an interesting idea, although it strikes me as not being very forgiving on minor differences in height that may exist in the holder and/or stud.... I have to give this some thought.



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    Default Re: fretting on 30 taper tooling

    Yes, I saw that too.....I think when the Jpeg is saved on the Zone it's automatically downsized and if you blow it up again you get fuzzy lines......this is something new as before a sketch would be quite big and clear when you posted it.

    I quite agree with the possibility of the difference from tool holder to tool holder via the pull stud with a non flexible system as a couple of thou would mean the difference between tight or slack...……. a previous design I have has a set of Bellville washers in a housing that pulls the draw bar up in almost the same way using the force of the compressed washers to apply the up force and increasing as required instead of decreasing.

    This is more resilient and will overcome any difference no matter how large.....I wanted to get away from the spring washers, but I think as you say maybe that is a better route to pursue.
    Ian.



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    Default Re: fretting on 30 taper tooling

    Another option may be a high density, elastomeric washer or puck backed by a threaded nut. That way, using a force gauge, you could adjust the pull force exerted on the stud.

    There is an area that you are forgetting about though which could complicate things a bit. The pressing piston has a port for air. When it presses down on the drawbar nut, an o-ring on top of the nut effectively seals the connection. A solenoid then switches on, forcing air through the drawbar (effectively pressurizing the Belleville cylinder) and then the spindle. This helps prevent coolant and chips from entering the spindle. Getting air into the top of the spindle is an area that hasn't been addressed with the approach you are considering. This doesn't mean that it can't be done, it just means that a little more thought has to be put into the equation. And, unfortunately, pressure vessels are a bit of a pain in a member that can rotate at 6000RPM.



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    Default Re: fretting on 30 taper tooling

    Well I considered the practicality of the Bellville washers doing the forcing and discounted that as a bad deal.

    I went away completely from the Bellville washer method as it is a declining force whereas you need an increasing force to clamp and hold the tool shank in the spindle.

    A toggle clamp....or a cam mechanism.... is a solid force when it is actuated to hold the part etc, that is the principal I advocated.....between a rock and a hard face etc......springy washers are anything but that, and it requires more force to unseat the tool than you get to hold the tool.

    In the design I posted the force is applied by a cam mechanism driven by a 60 rpm geared motor.....it takes 1/2 second to actuate the drawbar either up or down.

    At the top of it's stroke the cam holds the tool rigidly......even a nut on a bolt is rigid with just finger tightening.

    The cam mechanism is connected to the drawbar by a housing with an angular contact bearing which separates the rotating lower part from the stationary upper part......10,000 rpm is practical the same as spindle bearings.

    You cannot have an air piston mechanism as that is springy and would mean you need to have it on constantly at very high pressure with nil leakage......without the Bellville washers you need to have it rigid...….like a nut on a bolt.
    Ian.



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    Default Re: fretting on 30 taper tooling

    I think you may have misunderstood my comment.... I wasn't talking about using an air cylinder for the force. What I was attempting to say is that the current design introduces air to clean out the chips/coolant by injecting it through a hole in the middle of the pressing piston. A cam system is fine, but it doesn't address how to get the air through the spindle so that you can clean out that refuse.



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    Default Re: fretting on 30 taper tooling

    Hmmmm..…..as I don't have anything like that on my mill or even thought it was needed...... I wasn't really aware that it was used by other people.

    I suppose that is belt and braces to ensure no foreign matter gets in the taper...….keeping the tool shanks clean is another matter either in the tool changer cabinet or a rack you store the tooling in.

    Actually as you have mentioned the process of blowing down the spindle bore and out of the bottom, that is also possible with that design I mentioned as the top of the spindle bore would be open......the Bellville washers would not be present, only the drawbar, so the inside of the spindle would be a hollow cavity for about half it's length, but I can't see how sufficient undirected air would get past the drawbar pull stud gripper as it's relies on the diam it sits in to do the closing...…..mine is a petal type design.

    The design I posted was in first principles, just basic concept etc, and a working design per se would need to be generated for the machine spindle as needed.

    One question.....how would coolant or chips get up into the spindle bore if a tool is locked in......I imagine that it COULD occur if the tool was removed or the spindle bore was vacant between work pieces and chips blown off of the workpiece got blown up into the bore...…...but I think that is a long shot to happen.

    But then again, some machines work with a totally enclosed cabinet and ATC's with lots of coolant being blown about....it just wasn't on my radar for that scenario, the design was more in mind for the smaller hobby mills and manual mounted tooling where more placid conditions are present.....but anyone with a Bellville washer problem could use it...….how many mills are using an air blast down the spindle bore?
    Ian..



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    Default Re: fretting on 30 taper tooling

    Just as a matter of interest, I've just designed a simple gauge to set the pull pins for each tool shank so that they can be all pulled up to the same tension.

    It was apparent in what you said that the pull pins would have a huge impact on the holding strength of the method I proposed, so as I might adopt the system one day for myself I designed the setting gauge to get the pull pins all in the same position.....it only needs setting once for each tool shank no matter what the shank taper.
    Ian.



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    Default Re: fretting on 30 taper tooling

    I'm always interested in seeing what you are up to! Besides, with covid19 keeping everyone inside now, I have more time to think about this stuff. :-(

    I'm looking to build a tester that I can use to actually measure the deflection forces. The reason is that I've had my pull force gauge calibrated (wasn't far off) and, yet, my spreadsheet calculations aren't really bearing out all that well in reality. I need to do more research. I wish I had different types of washers that I could use in experiments. I also wish I had a jig I could use to measure the actual deflection force to validate against some of the specs because I'm getting a little suspicious of some of those. Finally, I need to figure out how the pressing piston works on my machine so that I can calculate the pressing force at different PSI of air pressure (or measure it empirically). I have a sneaky suspicion that I can't get more than about 800 pounds.

    Anyhow, bit frustrated with some oft this stuff. Right now I have about 325 pounds of force, which is the best I've been able to obtain. That is nowhere near the 900 that Dyna apparently sought, or the 1100 that ASME says you should have for a CAT30. But with only one type of washer, I'm sort of stuck right now.



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    Default Re: fretting on 30 taper tooling

    Well that is one reason I veered away from the Bellville washer concept thinking and went to the solid hard force design that is my pet theory......I always suspected that having the Bellville washers was a bad design.

    With the drawbar pushed down to release you might have or need 900 lbs, but in the up mode for gripping it might only be 300 or so when the washers relax.

    I expect that you could arrange the pack of washers in various configurations but measuring the variation is a challenge.

    In the end a lot will depend on the ability of the air cylinder to compress the stack if it is increased in holding force.

    I would hypothesise for a test that if you stacked the washer pack on a steel plate with a hole in it and put a bolt through the hole and hung a weight(s) underneath it you could add known weights to see how the stack compresses......at least you would know how much it takes to compress them......the crunch is that you need to have the force you need when the washers are being uncompressed as they grip the pull pin.

    It would be tricky to measure the length of the stack as they are arranged in the spindle........but not impossible.......just tricky.

    I suppose you could measure the depth of the spindle bore as this is the max the washers height can be beneath the drawbar nut and still screw it on........no way to compress the washers and then screw the nut on I suppose?

    I can only guesstimate the design of your spindle as I only have my spindle arrangement in a cut away picture from the original build offering when I was ordering my mill back in 2013.

    The model I ordered was not intended to have a drawbar arrangement as that basic model was designed for sale with an ER32 chuck on the spindle end, but I managed to have a bespoke order with an ISO 20 spindle taper which opened up the possibility of a power drawbar for tool changing etc.......and Bellville washers, but it works.....how well I don't know until a tool pulls down.
    Ian.



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fretting on 30 taper tooling

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