Ejecting Drawbar?

[miker]

In the thread about R8 and MT3 tapers, JTiers wrote..

"If you can make an "ejecting" drawbar, you will put away the hammer and never whack it again.

My MT3 now pop out with a slight squeeze of two opposed wrenches. Sweet."

Could you please describe how this is achieved?

My new Mill has MT3 taper and I would prefer not to have to whack the drawbar.

Rgds

[dp]

That one got my attention, too.

[motorcyclemac]

I don't know about you guys....but I never have to hit my drawbar too much. Generally a light single tap with an end wrench will dislodge the taper. I suspect that if you are having to mushroom the end of the drawbar..you are seating it too tight.

I used to get pretty annoyed with one fellow I worked with.. He would routinely cinch that darned thing down like he was torquing commercial truck lug nuts. It would literally pull the threads off the drawbar.

I used to ask him sarcastically if he wanted some red loctite and a sluggin wrench... Damn man...go easy.

Cheers
Mac.

[J Tiers]

OK....





There are a few threads exposed on the back of the spindle of the mill. The outside collar/cap screws on, and the nut bears on it to pull in.

You can see an inside sleeve as well, which, when I UNscrew the bar hits the inside of the collar/cap, so the threads shove the MT3 tool shank out.

I put a wrench on each, one on cap (and thus spindle) and one on nut. Then if they are set with handles close, a squeeze "pops" the taper loose and I can unscrew easily and pull out.

Made them for the arbors and for the other taper tools, drill shank, shell mill shank, end mill holder etc. Most are 3/8-16, the arbors are 1/2-24.

notice the shank of the bar is thick down to where teh threads are. That's to NOT bend as otehrwise you might be "pushing a rope".

[dp]

It would literally pull the threads off the drawbar.

When my mill was fairly new and I didn't have a clue how to use it I over-tightened the draw bar. I also whacked it too hard on release. The result is the second picture down on this page:

http://metalworkingathome.com/?p=42

[DFMiller]

That sorta looks like is on my KX3 except that its a R8. I think Sir John says that is on the Seig MT3. Looks slick on MT3. Sure does seems not work on the R8 :-(

[dp]

OK....
There are a few threads exposed on the back of the spindle of the mill. The outside collar/cap screws on, and the nut bears on it to pull in.

Very cool - I don't have any leftover threads to use but that's clever.

[Benta]

On the Wabeco mills, the drawbar has two threads, one that goes into the tool holder (MT2, M10x1.25) and one at the top that goes into the spindle (M14x1.0).
This means that when you loosen the drawbar, the tool holder is pressed out of the MT2 taper due to the difference in thread pitches.
Works extremely well.

Benta.

[J Tiers]

Very cool - I don't have any leftover threads to use but that's clever.

You can see if there is a nut which could be any thinner on the back, you could trap a thinnish section under the nut, with a wider threaded exterior surface.

You could even see about threading the inside of the spindle for a differential thread setup as Benta mentioned.

I tried the differential thread, and it works. I found that it was important to have them in the correct relative position along the threads, you want to have enough threads of each engaged. Maybe I didn't give it enough time, but I didn't like it.

[Benta]

I found that it was important to have them in the correct relative position along the threads, you want to have enough threads of each engaged.

The way you mount a tool in the Wabeco is like this:
1: screw the drawbar in until it bottoms.
2: back out 2...3 turns
3: screw the toolholder into the spindle while holding the drawbar
4: when it is in, thighten the drawbar

This way the threads are always correctly engaged.

Regards,

Benta.