Power draw bar idea - Feasible?


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    Default Power draw bar idea - Feasible?

    I've been mulling over how to pull off a power draw bar. Looking at Hoss's very cool air-cylinder + lever design, and Tormach's triple pancake cylinder stack, I couldn't help but feel both options put extra weight on the head, and/or required expensive pneumatics.

    Then I thought, what if I took a small disc brake calliper from a car or motorcycle, put a thrust bearing in the pot and used that to push the drawbar down.

    It would require having a master cyl. that was driven by either pneumatics or possibly a motor with lead screw, as well as some plumbing. The advantage is that the master + power source can be located anywhere, so size and weight aren't a real concern.

    I was assuming series stacked Belleville washers (7000N force to flat)

    Feasible? What are the kind of forces can a brake calliper exert?




    Cut off the one side, insert thrust bearing, bolt to mill (might need extra support bolts)

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    Power drawbars on commercial machines often use an "air over hydraulic" system similar to what you describe. You can generate as much force as you want, with proper design. The idea is to use a small air cylinder to move a small hydraulic piston which pressurizes the hydraulic fluid, to move a larger hydraulic cylinder. The small cylinders, of course, must have much longer travels than the large cylinders, as both must displace the same volume of fluid.

    A brake caliper can easily tolerate in excess of 1000 PSI.

    Regards,
    Ray L.



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    Sounds very feasible to me. A clutches slave cylinder would work too. I investigated using one and blew it off. Not because it didnt or wouldnt work just lazy. You really wouldnt need the thrust bearing. The spindle wont be turning during a change. Try it, I will watch. You might try a simple 17-19mm motorcycle master cylinder with lever as a test.



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    sscnc did something similar to what you are proposing.

    http://www.youtube.com/watch?v=0HmdWtJOkPU]X2 Electric-Hydraulic drawbar - YouTube

    He ultimately decided
    Even though this works, I've decided not to use it and instead go with a single small air cylinder mounted on top similar to Hoss's setup.
    Hoss

    http://www.hossmachine.info - Gosh, you've... really got some nice toys here. - Roy Batty -- http://www.g0704.com - http://www.bf20.com - http://www.g0602.com


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    There is also this approach:

    http://www.cnczone.com/forums/tormac...d_drawbar.html

    Replace the lever and cam arrangement with either an air cylinder or electric linear actuator , and you have a nice, compact, light-weight solution. The cylinder on the spindle shaft is a dual-hydraulic cylinder with the belleville springs inside it, so the only force the spindle sees during release is the small force applied to the small piston at the top of the cylinder.

    Regards,
    Ray L.



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    PsyKotyk,
    I prefer this approach that I did on my G0704 than what I believe you were referring to from the X2.
    The scissor like action puts no strain on the spindle and acts fast.
    g0704.com/Projects.html#pdb
    You could make your own multi-stage air cylinder like I did if you want a custom, smaller, lighter setup.
    A more compact setup here.
    g0704.com/Projects2.html#pdb2
    Hoss

    http://www.hossmachine.info - Gosh, you've... really got some nice toys here. - Roy Batty -- http://www.g0704.com - http://www.bf20.com - http://www.g0602.com


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    Quote Originally Posted by PsyKotyk View Post
    I've been mulling over how to pull off a power draw bar. Looking at Hoss's very cool air-cylinder + lever design, and Tormach's triple pancake cylinder stack, I couldn't help but feel both options put extra weight on the head, and/or required expensive pneumatics.

    Whats wrong with extra weight on the head? The Z motor can handle it. I don't think the acceleration in wear is significant. One could argue the extra weight helps with dampening. Rapids would be slightly decreased but its not going to make a measurable difference to your cycle times.

    You can buy a cheap new air compressor for $100. The "expensive" pneumatics can also be used for a misting system and cleaning.

    I do think your idea is very innovative. I think its true value would be shown in lighter weight mills where added headstock weight can be detrimental to performance.



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    If you are using it with a manual tool change, you can use a foot powered master cylinder.

    I used a foot master cylinder on a motorcycle dyno to vary the load.

    Don



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    Default I just built one..

    I just made one for my Novakon mill. It is a 2" air cylinder acting against a hydraulic booster. Go to the latest posting where I have pictures and a youtube link.
    http://www.cnczone.com/forums/novako...ld_thread.html



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    After exchanging a couple of PM's with Air_GuNNeR (love his power drawbar setup!) I had some ideas as well..

    I'm thinking of a pneumatic cylinder, about 2" bore and maybe 1" travel.. This would be mounted on the side of the head, and would push on an head mounted hydraulic cylinder, something with a small diameter but fairly long travel (well, about 1" to match the pneumatic cylinder), let's say a 0.25" piston. I'd connect a stainless braided brake line (I have a few lines I removed from the race car as preventive maintenance that would be perfect for this) to this master cylinder and connect it to a large diameter, small stroke cylinder on top of the drawbar, with a scissor type setup similar to what most people do with the pneumatic drawbar actuators.

    2" bore pneumatic cylinder at 50psi = 157lbs. For 3000lbs at the belleville stack, that's a 19:1 ratio. The 0.25" piston has 0.049sqin of surface area, so I'd need a big piston with 0.9359 sqin. Let's make it 0.940, which gives me a diameter of 1.094"! And for 0.050" of movement to collapse the bellevilles and push the drawbar down, I'd need.. 0.955" of travel at the small piston! How about that.. I swear I was making it up as I went.

    Hmm..



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    Of course it just occurred to me that with my dimensions above, there would be over 3000psi in the system, which may not be a great idea. Still, I think scaling up the system to reduce the pressure to 1000psi or so would be feasible.. And one other thing - the only reason I'd go through the trouble of doing something like what I just described, is if I didn't have enough headroom to mount a more conventional setup.. Which I don't :\ My basement has a really low ceiling and I can't really mount a multi stack cylinder on top of the head without losing a fair bit of Z travel. Same reason I want to mount my motor upside down on the side of the head..



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    Quote Originally Posted by TiagoSantos View Post
    After exchanging a couple of PM's with Air_GuNNeR (love his power drawbar setup!) I had some ideas as well..

    I'm thinking of a pneumatic cylinder, about 2" bore and maybe 1" travel.. This would be mounted on the side of the head, and would push on an head mounted hydraulic cylinder, something with a small diameter but fairly long travel (well, about 1" to match the pneumatic cylinder), let's say a 0.25" piston. I'd connect a stainless braided brake line (I have a few lines I removed from the race car as preventive maintenance that would be perfect for this) to this master cylinder and connect it to a large diameter, small stroke cylinder on top of the drawbar, with a scissor type setup similar to what most people do with the pneumatic drawbar actuators.

    2" bore pneumatic cylinder at 50psi = 157lbs. For 3000lbs at the belleville stack, that's a 19:1 ratio. The 0.25" piston has 0.049sqin of surface area, so I'd need a big piston with 0.9359 sqin. Let's make it 0.940, which gives me a diameter of 1.094"! And for 0.050" of movement to collapse the bellevilles and push the drawbar down, I'd need.. 0.955" of travel at the small piston! How about that.. I swear I was making it up as I went.

    Hmm..
    Tiago,

    That is precisely the "air over hydraulic" system I described earlier that is used on large VMCs. There are a few people on here who've done that, but it gets complicated and expensive for the hydraulic parts, and you have to make sure the hydraulic system stays topped up. 3000 PSI in a hydraulic system is not a problem at all - many/most cylinders can run more than that.

    Regards,
    Ray L.



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Power draw bar idea - Feasible?

Power draw bar idea - Feasible?