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  1. #1
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    New Power Drawbar.

    After wrestling with the lever drawbar and suffering some rubbing and occasional drawbar backing out due to the rubbing I decided to reinvent the wheel and make a new power drawbar.

    Here is the CAD file if anyone is interested. A360

    One thing to note is that my cylinder is an MP4 2 stage, which only has about 2400lb of force at 100psi. I would recommend anyone doing this use the Fabco MP4 3 stage to get about 3600lb of force at 100psi.
    It's the same footprint in the cad file btw.

    My belleville stack is set up for 2100lbs right now. Once I upgrade my cylinder I will change the stack to a 3200lb stack. This should be fine for most operations.

    Here is a mcmaster parts list for the small parts I used. I had a bunch of 1018 3/8" steel laying around for the bases and 1/4" for the uprights, just TIG welded together.

    https://www.mcmaster.com/#91292A143
    https://www.mcmaster.com/#9657K305
    https://www.mcmaster.com/#9712K435

    Steve303 - if you see this post - your private messenger box is full.



    Video:

  2. #2
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    Re: New Power Drawbar.

    I like your PDB Brian. Clean and simple design. Thanks for posting your cad file.

    Steve

  3. #3
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    Re: New Power Drawbar.

    I am looking for a 3 stage pneumatic cylinder for my draw bar build. I am thinking of ordering a Fabco MP4X1X3X1FF. Anyone know what cylinders Tormach uses on their PDB's?

    Steve

  4. #4
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    Re: New Power Drawbar.

    Steve - I found this gem on eBay $100 shipped. It's an MP4x2x4 stage (I would have preferred 3 stage but beggars can't be choosers).

    Then I rearranged my 12 Bellevilles to be in groups of 3 ((()))((())) so the drawbar force should be about 3200lbs.

    The new cylinder can eject a tool easily down to about 70psi. So all is good.
    Attached Thumbnails Attached Thumbnails IMG_6004.jpg   IMG_6003.jpg  

  5. #5
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    Re: New Power Drawbar.

    Quote Originally Posted by brianbonedoc View Post
    Steve - I found this gem on eBay $100 shipped. It's an MP4x2x4 stage (I would have preferred 3 stage but beggars can't be choosers)..
    Why couldn't you remove a stage and turn it into a 3 stage?

  6. #6
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    Re: New Power Drawbar.

    Yeah I thought of that but the connecting rods would need to be rethreaded and it really doesn't matter at this point other than being tall. The added weight from one chamber is negligible.

  7. #7
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    Re: New Power Drawbar.

    I assume these cylinders must spin the drawbar, but how does it engage while spinning?

  8. #8
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    Re: New Power Drawbar.

    The cylinder pushes down on the drawbar to release the tool in the same manner as the Lever Draw Bar does on the Pulsar. Tormach's Power Draw Bar works the same way. There is a spindle nut which prevents loading the spindle bearings. If you take a look at Brian's video you can see the spindle nut is threaded on the top of the draw bar above the lower plate.

    Ray's PDB for the Torus spins the drawbar.

    Steve

  9. #9
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    Re: New Power Drawbar.

    Isn't the drawbar screwed into the collet? How can it release without being unscrewed. I must be missing something/

  10. #10
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    Re: New Power Drawbar.

    kvom - yes it's confusing at first but actually quite simple. The washers at the top of the drawbar are Belleville spring washers, they act like strong springs pushing up on the drawbar and thus the collet with a force of about 3200lbs.

    The plunger of the air cylinder pushes down with more than that 3200lbs, which forces the drawbar and collet down, out of the spindle slightly and therefore releases the tool.

    What is confusing is the spindle nut. You don't want to force 3200lbs straight down across the spindle bearings, so the spindle nut is there so that the bellevilles gets pinched between the spindle nut and the top of the drawbar. That is why you see the base of the PDB rise a bit when activated as the whole assembly is essentially free floating and servers to pinch the bellevilles rather then force them straight down.

  11. #11
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    Re: New Power Drawbar.

    That cylinder was a great find Brian, I went ahead and ordered new as I could not find anything used that would work.
    Steve

  12. #12
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    Re: New Power Drawbar.

    Steve - no kidding. I actually scored it for $66 but the shipping on that monster was $33. It's in great condition too, and that weird thing at the top is an "adjust-a-stroke" which allow me to control the length of the stroke of the piston.
    In any case it works perfectly, I think you'll be more than happy with your setup.

  13. #13
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    Re: New Power Drawbar.

    Brian,

    Thanks for posting your Fusion360 file for the power drawbar. Now you have me scouring the internet for Fabco and Bimba multi-stage air cylinders!

    I have the last Torus mill (not the Torus Pro) sold by Novokon, and it looks like the electronics are identical to those shown in the Pulsar online manual. Much of my Torus mechanicals appear very similar, if not identical, to those of the Pulsar. Unfortunately my mill came with the standard drawbar and no Belleville washers or lever drawbar.

    I am trying to figure out how to retrofit my mill with a power drawbar similar to yours. I think I understand the air cylinder and supports shown in your cad model, but am struggling to see how to modify my mill to work with your model. I don't see yet how to add Belleville washers and the "spindle nut" to my mill. Did you make the spindle nut or did it come with your Pulsar?

    Thanks for any help or insights.

  14. #14
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    Re: New Power Drawbar.

    Download the Pulsar Spindle Assembly and the Lever Draw Bar Assembly from Novakon's web site. You can see how the LDB works. Rather simple, it pushes down on the draw bar nut compressing the spring washers, expanding the collet and releasing the TTS. The spindle nut is threaded on the top of the spindle.

    Pulsar Downloads

    Steve

  15. #15
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    Re: New Power Drawbar.

    Post a pic of the top of your mill head for us to get some ideas. It really wont be hard I am sure, but you may have to modify the cad design a bit.

  16. #16
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    Re: New Power Drawbar.

    Steve,

    Thanks for the link. Somehow I had missed the Spindle Assembly drawing as I was only looking at the drawings at the end of the Pulsar Manual. The spindle nut is missing from this drawing, right? And the LDB squeezes the Belleville washers between the spindle nut and the top of the drawbar?

    My Torus spindle is definitely different than the Pulsar spindle shown in the drawing.

    Brian, here are some pictures.

    Attachment 359524

    Attachment 359526

    Attachment 359528

    Attachment 359530

  17. #17
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    Re: New Power Drawbar.

    I would say to make a spindle collar that attaches to the flats on the spindle maybe with some grub screws - then the rest would work like the one I made.

  18. #18
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    Re: New Power Drawbar.

    Brian,

    Thanks for the idea of a spindle collar so that my spindle could be retrofitted for a power drawbar. It sounds like an easy enough little lathe project.

    It appears that some of your Belleville washers overflow the spindle cavity? The Spindle Asembly drawing that Steve referred to earlier implies that all of the washers fit into the spindle cavity.

    Also I finally found the spindle nut that you guys were referring to. It looks like it comes as part of the Lever Drawbar Kit from Novokon.

    I'll keep looking multi-stage air cylinders on ebay. If I could figure out how to build this hydraulic multiplier by AiR_GuNNeR then I could get by with a very modestly sized single stage air cylinder.

    http://www.cnczone.com/forums/novako...-thread-5.html

    https://youtu.be/hwVSKd0HHvM

  19. #19
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    Re: New Power Drawbar.

    I think the part i was missing is that it works with the TTS collet that remains screwed to the drawbar. Standard R8 collets wouldn't work.

  20. #20
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    Re: New Power Drawbar.

    Titanium boy- yeah some stick up out of the spindle. It was that way stock. It really doesnt matter. If u look at the tormach pics all of theirs are above the spindle. It's prob easier to find bellevilles if they are not confined to a specific outer radius. Just remember when u add up the force it should be a bit over 3000lbs but also have a combined stroke of >.060 preferably about .1. My setup has only about 0.064 of travel and works fine.

    Kvom- the Tts Collet is a std R8 but with the nose ground flat - otherwise it no different. In fact many here use the high quality hardinge Collet and grind it flat themselves

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