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IndustryArena Forum > MetalWorking Machines > Uncategorised MetalWorking Machines > hmm..drawbar force seems to be 245 lbs?
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  1. #37
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    Looking good... you wanna just make me one too since your having so much fun? I always questioned the $700 + price tag on these. This is why I designed one that was this easy to build. I think its a tool everyone that owns a CNC mill should have. Maybe I should get off my butt and make mine since you proved the design works.

  2. #38
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    Quote Originally Posted by DaOne View Post
    Looking good... you wanna just make me one too since your having so much fun? I always questioned the $700 + price tag on these. This is why I designed one that was this easy to build. I think its a tool everyone that owns a CNC mill should have. Maybe I should get off my butt and make mine since you proved the design works.
    thanks!

    i wish i could build more, but it just used scrap i had around and i dont have any more stainless. plus im about 3 unnecessary projects deep from working on what im supposed to be working on lol...

    i wouldnt count our chickens just yet..once i finish fabbing it and actually try it out, and maybe find some way to double check its readings at multi-hundred pound forces, then we can call this example of your design a success..but until then im still suspicious that either there really is a reason the clamp rites cost at least a few hundred, or that maybe something i thought would work wouldnt (like my homemade ram)

    if it all works out great then i may think about making another refined one (this ones sorta clunky and id probably change a few things about it on a second round

  3. #39
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    The ram is the only part that I question. The rest is sound. I would have used a lip seal instead of orings but the orings should work if they are tight. The ram will be pushed equally so I wouldn't worry that it can wiggle. It will be held straight when clamped. Also the plunger in the ram really only need to stick out a small amount over the ram body as it should not move but a tiny amount when force is applied.

  4. #40
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    This should help ya on your cylinder size to corrected psi. A little calculator I whipped up.
    Attached Files Attached Files

  5. #41
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    Any updates?

  6. #42
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    Quote Originally Posted by DaOne View Post
    Any updates?

    thanks for the calculator!

    nope no updates..i decided to move the mill from one side of the house to the other in 100F heat so its non-op at the moment..but as soon as its up and running again the first thing i will need to do is measure the drawbar force

    i did get a strain gage off ebay for $7.50 and mounted it what i think is successfully..but im not going to try and use it for the drawbar force gauge..at least not in the immediate future




  7. #43
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    This should help ya on your cylinder size to corrected psi. A little calculator I whipped up.

  8. #44
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    okay i did a bunch of work on it today and tried it out!

    the bad news:

    it doesnt work!

    the good news:

    i think its something simple!

    things to think about:

    -i am not able to bleed the air out of the gauge. i believe i can fill it in a way where there isnt any air inside the main block, but the gauge has a very small hole with lots of nooks and crannies. any ideas? i may be able to use a pressure sensor instead, which has a very short passage way that i may be able to fill up with a straw or something.

    -when i install it in the spindle, the needle increase by about one increment..about 40 lbs..hmm..thats with it already preloaded about 40 lbs

    -tightening the stud can easily cause the gauge to go up to about 800 psi

    -the stud tigthens pretty easily until you get to about 800psi..i dont think thats good. if there was no air in the system and it was all very strong, i think it would be very difficult to tighten it because everything would be incompressible, except the gauge.

    -the way i threw it together is pretty flimsy. i made the "bridge" out of aluminum..it should be taller and made out of steel. i think it will work for my drawbar, which at most will put out 600lbs..but for anything bigger, it needs to be more stout. easy to do though.

    -if we pretend that the whole thing was made of cheese, not including the toolholder or pullstud with welded threaded rod, then when its installed in the spindle, the drawbar grabs the pullstud and pulls up, against the tool holder. but since the contraption is made of cheese, it can _displace_ the stud relative to the tool holder, to the point where there is no force on the toolholder beyond gravity (i.e. a couple pounds). it wont fall out, but its just hanging there. i dont think thats whats happening here, but ill check. i dont think there is that much displacement going on, and its certainly tight in the spindle.

    this was very easy to make! if we can get this ironed out i bet alot of other people will make one and find it useful




  9. #45
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    i tried it with the electric pressure sensor, which allowed me to fill the sensor up completely with water, and the aluminum block by submerging it underwater and pumping all the air out. so this method had as little air in it as possible, only the teeny gap between the sensor and block before its screwed together.

    same thing! it measured about 150psi!

    i think my drawbar may actually have only about 150 lbs of force! im not sure how this happened..dyna says it should be 600+ lbs. ive noticed that there are 50 springs in mine but dyna says there should be 48. maybe someone replaced the springs sometime in the last 15 years and used very VERY crappy springs..but if my calculations are correct, even quality carbon steel springs from mcmaster would only get about 245 lbs of drawbar force. hmm. perhaps i should upgrade to chrome vanadium springs with a higher constant? ..this is all very suspicious..im starting to trust my "drawbar force gauge" though..

  10. #46
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    Hi, when you fit spark plugs the force is indicated by the compression of the washer........have you tried making a compression washer calibrated to give some force or other?

    Going to the press tool industry, when tremendous spring pressure is required we/they use a type of very incompressible rubber, red in colour that is almost plastic in consistency.....it gives tremendous spring force over a very short distance.

    I would suggest that you made a 3mm thick steel cupped washer and made a rubber washer with this material.....if the washer was made in the form of a cup and the rubber insert was inside it with another steel washer on top, provided you had clearance around the washer to allow for expansion laterally when compression is applied vertically, then if the rubber is for example 6mm above the edge of the cup it will give an indication of how much force is being applied when the rubber "spring" is compressed down to the edge of the cup.......thicker rubber= more spring pressure.

    You can calibrate the washer set-up by measuring the force to compress a series of progressively thicker washers until you get to where you want to go.
    Ian.

  11. #47
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    Quote Originally Posted by handlewanker View Post
    Hi, when you fit spark plugs the force is indicated by the compression of the washer........have you tried making a compression washer calibrated to give some force or other?

    Going to the press tool industry, when tremendous spring pressure is required we/they use a type of very incompressible rubber, red in colour that is almost plastic in consistency.....it gives tremendous spring force over a very short distance.

    I would suggest that you made a 3mm thick steel cupped washer and made a rubber washer with this material.....if the washer was made in the form of a cup and the rubber insert was inside it with another steel washer on top, provided you had clearance around the washer to allow for expansion laterally when compression is applied vertically, then if the rubber is for example 6mm above the edge of the cup it will give an indication of how much force is being applied when the rubber "spring" is compressed down to the edge of the cup.......thicker rubber= more spring pressure.

    You can calibrate the washer set-up by measuring the force to compress a series of progressively thicker washers until you get to where you want to go.
    Ian.
    i think you should delete the post you just made and file a patent for an inexpensive drawbar tool force verification wafer

  12. #48
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    LOL, I just saw a begger riding past on a horse.

    You won't know how much axial force is being applied unless it actually compresses a solid object like a crush washer, maybe even an annealed copper washer that crushes to a known thickness by a known force.

    BTW, the Bellville washers apply a force (to close the R8 collet in a TTS system) or pull up the drawbar to enable the tool gripper to retain the tool in an ISO 30 etc system......the cutting forces apply a reciprocal force to overcome the Bellville washers and release the tool/toolholder in both systems, that is the problem.

    If a mechanism is devised, whereby once the Bellville washers draw the drawbar up to retain the tool, the drawbar is held immovable to any downwards pull, then this is what is required, otherwise you just keep increasing the Bellville washer force until the problem goes away and that places an increased strain on the release mechanism.

    A ratchet mechanism is something like this.......it gets pulled up but locks at any predetermined position and only releases when the ratchet lock it triggered, allowing the release mechanism to depress the Bellville washers to lower the drawbar and release the tool.

    There is a certain amount of pressure required to purely seat and locate a tool in the taper, but if you exceed this pressure to retain a tool you place strain on the spindle taper for no gain in retention capability.

    In this "design" proposal the Bellville washers are there simply to seat the tool in the taper, that and nothing more.....the ratchet locking mechanism is there to make sure it stays there and can not move down an iota.

    It would be a simple matter to make the release mechanism firstly to trip the ratchet before it pushed the drawbar down to release the tool........if you think this is patentable, go for it.
    Ian.

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