Hardening drawbar threads

[daved20319]

Note that these drawbars have a tool extraction feature, which is why the have the collar at the bottom and the cone nut on top. No need to hit the drawbar to release tools. This one is for the vertical spindle.

Hey, Bill, would you mind expanding on this a bit? And would it work on a smaller mill like the Sieg XS-3? I'm really enjoying my mill, and get more comfortable with it every time I use it, but whacking that drawbar with a hammer to released the collet still feels wrong. Besides, my drawbar is kind of a sloppy fit, so I've been considering making a replacement. I'm glad this post came up, based on what I've been reading here, I'd have picked the wrong material for sure. Thanks.

Dave

[corbin]

Many people over tighten the drawbar. I worked with a fellow that could twist them off and strip them easily. One time he had an endmill suck out and ruin the work so he decided the collet was not tight enough and always over tightened them to the point of damaging them and the collets.

If you understand what causes an endmill to suck out of a collet and learn how to prevent it you won't have to over tighten the drawbar.

I've had endmills suck out of a collet. What causes this to happen? I've since switched to using an endmill holder with a lock screw on the side, but sometimes I still have to use collets with certain bits.

corbin

[Alistair Hosie]

I too would not harden something that is clearly designed not to be hardened.Leave it well alone before you strip something . In fact why not fit a brass end piece and thread that to to the thread in your new drawbar to save your new threads from being stripped.In effect a sacrificial end piece in brass if your concerned with damage.Alistair

[Bob Fisher]

I have had an end mill suck out of the collet, 3/4 in shank too, switched collets and all ok after. Probably a cheap Chinese collet. Don't know what torque I apply when I tighten the drawbar, I think I will try a clicker torque wrench to get an idea of what I have been doing. Bob F.

[willmac]

Hey, Bill, would you mind expanding on this a bit? And would it work on a smaller mill like the Sieg XS-3? I'm really enjoying my mill, and get more comfortable with it every time I use it, but whacking that drawbar with a hammer to released the collet still feels wrong.
Dave

Dave - I doubt if this feature would work on most R8 machines. It requires the mill spindle to have a register at the top of the spindle taper, above the toolholder that the collar at the left of my photo can engage. When you loosen the drawbar, it will turn for maybe a couple of turns until that collar engages, and then further rotation forces the tool holder out of the spindle. This places zero load on the spindle bearings and requires no hammering.

The vertical spindle drawbars go into the spindle from the bottom and are secured by the cone nut at the top. They are quite quick to swap.

[dian]

overtightening drawbar:

the specified torque for a 16 x 2 mm thread (8.8) is 200 nm. my wrench is 30 cm. how can you overtighten that? applying 670 nm over your head? nobody can do that.

its hard enough to tighten the collet nut properly and that is at breast height. er32: 100 foot-pounds, er40: 130.

willmac, how does this bar eject the toolholder?

edit: o.k., i see above post. what taper does the thiel have. or, on what mills can you use that feature?

[willmac]

Dian -

Thiel 159 has 40 taper in both horizontal and vertical spindles. The toolholder ejection feature is found in other German mills, but I can't say how widespread beyond that. I seem to remember that some Cincinnati mills had a similar arrangement, but I may be remembering wrong.

[goose]

Inspiration. It's funny, turns a cloudy day sunny.


Inspiration:

The old is just a dog poop 7/16 threaded rod and loose nut.
The new is below, a knurled top piece with an 11/16 hex integrated into the design. I used O1 tool steel (unhardened) for the rod, I think the better steel is less likely to stretch under tension or cross thread in a collet.





Here it is assembled with Loctite and fresh out of the black oxide solution.



And now installed on the mill, ready for action.

[Shuswap Pat]

I have used Gr8 or B7 redirod. Just D&T the end of your broken drawbar, and locktite a piece of redi rod - it is tough material, rolled threads, cost effective, hard to beat.

Patrick

[willmac]

Goose -

That looks very good. You will appreciate it every time you swap tools, which if you are like me is frequently.