06-12-2015, 08:28 AM
(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.