Homemade Power Drawbar

[zmotorsports]

I had originally built a power drawbar for my PM935TV mill when I set it up last year.  However, after seeing one on youtube that a guy made and liking his design much better than my own, I decided to copy it.  Thanks to Colin @ Comp Edge X.

My original design used a 1" stroke pneumatic cylinder to push from the to down and force the socket onto the drawbar as well as pop it loose from the taper.  This one mounts the pneumatic cylinder next to the pneumatic butterfly and "pulls" the butterfly down along with the socket mating with the drawbar and popping it loose from the taper.

This is not recent as I actually fabricated this power drawbar about 7 or 8 months ago and have been using it ever since.  I am new here so I thought I would throw it in the projects section.

Here are my preliminary drawings for the base plate and top plate along with all of the ports and screw holes for the butterfly air gun.




Top plate roughly layed out.  I will get exact once I put it on my mill table and indicate off measurements exactly using the DRO.


Top plate machined to size and drilled/tapped for the butterfly air ratchet.


Bottom plate machined to size and drilled for the mounting location as well as the holes drilled and countersunk for the vertical guide rods.  Also pictured are the guide rods.


Guide rods mocked into position.  Bronze and brass in the background to be used for the bushings and the "tees" for the fittings.


Completed unit and bolted on the mill.


Looks much better than my first attempt and it works just as well.

I also have a youtube video of Part 1 and Part 2 if you search under my username "zmotorsports".

Mike.

[EdK]

That sure turned out nice Mike. I'll need to pick your brain about it if I end up getting the PM mill. How much CFM does it take to operate? I have just a small compressor.

Ed

[zmotorsports]

Ed, I believe that butterfly impact requires about 4 CFM @ 90 psi.

Mike.

[PixMan]

I love that idea, and the execution!

How does one determine the difference in torque normally applied when tightening a collet by hand versus the torque that system applies? That's my only concern, as the 7/16-20UNF thread isn't all that strong. Still I find myself using more or less force depending upon the tool. A milling cutter that could pull down and mill my new hard jaws gets cranked pretty good, while a drill chuck for a small hole doesn't need that. Do you get one setting with that, or do you vary air pressure for more or less clamp pressure?

Also, when I release a collet by hand the drawbar unscrews up and I tap the end of it to release the tool & collet from the taper "lock." Does that system automatically eject the tool & collet by virtue of being fixed and preventing the drawbar from riding up as it unscrews? I assume so, and that the "hammer" part of the tool works well to break the taper lock.

One of those would be even more appropriate on my mill that's so tall. When some vertically challenged friends have used the machine, it's a long reach!

[zmotorsports]

(06-12-2015, 07:30 AM)PixMan Wrote: I love that idea, and the execution!

How does one determine the difference in torque normally applied when tightening a collet by hand versus the torque that system applies? That's my only concern, as the 7/16-20UNF thread isn't all that strong. Still I find myself using more or less force depending upon the tool. A milling cutter that could pull down and mill my new hard jaws gets cranked pretty good, while a drill chuck for a small hole doesn't need that. Do you get one setting with that, or do you vary air pressure for more or less clamp pressure?

Also, when I release a collet by hand the drawbar unscrews up and I tap the end of it to release the tool & collet from the taper "lock." Does that system automatically eject the tool & collet by virtue of being fixed and preventing the drawbar from riding up as it unscrews? I assume so, and that the "hammer" part of the tool works well to break the taper lock.

One of those would be even more appropriate on my mill that's so tall. When some vertically challenged friends have used the machine, it's a long reach!

The torque is obviously determined by the pneumatic butterfly of your choice, however, I have found for some things a quick "zap" with the control will draw up the drill chuck just fine for example.  Yet for a larger collet that can have forces trying to pull down like you mentioned, I simply hit the control button a little longer than a mere "zap" and I am positive it draws it into the spindle taper with a bit more force.  I know that isn't very precise but it works.

The standard drawbar is actually stronger than you would think.  There are companies that manufacture these power drawbars and use the very same technique and many shops have been using them for decades.  A Kurt power drawbar for example is very similar if you were to remove the cover, but the Kurt power drawbar can run anywhere from $1000.00-$1400.00 depending upon mill make/model and mounting.

I am not sure how Kurt does theirs, but I made mine so that the pneumatic cylinder presses down all the way onto the drawbar BEFORE it reaches the end of its 1" stroke.  This uses the downward force from the air pressure to "pop" the taper loose between the tool and spindle and drops it out into your hand.  

I don't have a link to it right now but in my youtube video of the drawbar at the end of Part 2 I think I demonstrate how quick and simple it is.  

I was going to wait for a while to build mine as it was down a bit on my "to do" list but after only a few days of reaching up, holding the brake and wrenching then tapping on the drawbar I thought to myself the power drawbar project just made the top of the list.

After having one for nearly a year now I don't think I could go back to using a mill without one.

Thank you for the compliment and if I can answer any more questions, please don't hessitate to ask.

Mike.

[PixMan]

Mike,

I'm old school and have been changing tools with the manual drawbar and box wrench since about 1974. It's second nature to me, and doesn't take me much longer than a power drawbar. I get the exact feel I want with every tool, instantly. Of course I've a long work history of using CNC machining centers with automatic toolchangers too, so I know how nice a power drawbar is to the "Nth degree." I even own a complete set of cam-lock quick change holders for my mill, never have bothered to try it.

It was just curiosity on my part to want to know how the system gives the tool a "knock" to break the taper grip.

Thanks for explaining.

[zmotorsports]

No problem.

Mike.

[Kennyv]

Im With You Pixx but still curious myself need to see in action to understand  else I need to ask 100 Q's  . Ohh Btw ordered up a few mills Fri that I thought may be Ok for the work I intend to do on My New mill . I will get some tooling latter as needed  but Bc of the size of  the Mill  and considering  the Z travel limitations and HP it provides im not gona Go overboard with tooling . Thanks for your help And PM.   Sorry to be PIA  but needed to make quick decision  and order up  3-4 Indexable  tools to start with...

Mike hey I found ya   How ya doin Im Kenny V  the newbie PIA fella  I have a bone to pic with you.   Just  kidden    (Saw your video last night)  HEY GREAT JOB Nice work...  good presentation Too . still like to pick your brain tho

Stayed up till  2:30am   and watched allot of tool changer Auto drawbar stuff   Mods .. Than  got me thinking   hey I need me one of those  > . Than I said Naaa  if I start on that Project ill be consumed . I have lots more import things to  get straight in Garage. But than I said  hey wait  saw some folks use power drill motor  . Went out in garage  and realized dang not too long ago  threw away  and old electric screw gun...Good one too  O well.  see what you started ?
Than I found a nice Air Screw driver with F/ R Trigger it even has the feature when u press down it activates the arbor so what I was thinking can this work with a mill without a break ?
 would that even  have enough torque ??

  Thinking out loud here Correct me if im wrong even if it had enough torque   with a simple design F/R  w/  no eject  will  something like that work  without a break  Is that possible ?
If not   anyways  Im not in a hurry  with my little toy Mill (PM25 MV) you would have to hold tool and collet at same time while activation PDB  with a simple design F/R push down  ..  if so not sure would even  be worth it for the convenience. U would have to have arbor loaded Tools else hold a spindle wrench at same time  that's the way it would  hafta work no?
TIA any info .. thanks all u guys putting up with My dum  Q's im  visual learner so please don't beat me up
Kenny V

[EdK]

(06-13-2015, 04:18 PM)Kennyv Wrote: .... thanks all u guys putting up with My dum  Q's im  visual learner so please don't beat me up
Kenny V

Kenny,

You don't have to worry about anyone beating you up on this forum. It's not allowed and will be quickly dealt with if it were to happen. There's a reason I gave this forum the name I gave it, despite some people thinking it's silly (even if it kinda is)   .

Ed

[zmotorsports]

KennyV, thanks for the compliments. I hope you enjoyed the videos. I am new to making them so I promise I will get better.

I don't know if a powered screwdriver will have enough torque to tighten or loosen the drawbar, usually those power screwdrivers are in the 4-10 ft/lbs (30-120 in/lbs.) range so I would doubt it would be enough.

My power drawbar was on the "to do" list but down on it a bit. I re-prioritized my list the first week I had my mill and decided the power drawbar just went to the top of the list. Took me most of the first weekend to fabricate the first one. My second power drawbar took me about a week but a couple hours a night was all I had to spend on it.

Mike.