Power draw bar idea - Feasible?

[PsyKotyk]

- Inverted mount
- Not too sure about hinge forces. Using 8mm pin might not be enough. 1/4" aluminium plate might also be too weak.
- Trying to leave room around the pulley for the Stirling belt drive, in order to change the belt without removing the plates.
- Cyl. size and mounts unknown for now. Probably about 9" long with 2" stroke.

Huge thanks to all the guys who have "been there and done that". Saves me lots of experimental aggravation.

[SCzEngrgGroup]

No reason it wouldn't work. You'll want to make sure the curve on the end of the lever is such that the contact point remains very close to the center of the spindle, so avoid any unnecessary side-loading. I suspect though you'll find a lot of friction at that point, and a rolling contact (ball bearing) would be better. I did one years ago with a straight plunger riding in a sleeve bearing that pushed on the spindle, and a ball bearing riding on the lever arm. That eliminates the friction and wear that comes from having a high-force sliding contact, and keeps the force on the spindle purely axial, and always acting on-center.

Regards,
Ray L.

[Uguessedit]

Ray,

Did you use a servo or stepper to change your tooling over? Do you have a link to your build? I am setting up another new mill and would like to try something other than pneumatic if possible and if I recall from other posts your system sounded promising.

Actually, the Bellevilles on a VMC are considered a "wear item". The spring stacks, often 100-150 Bellevilles, DO need to be replaced regularly.

But, everything you've said is absolutely true. The Belleville force increases almost exponentially once you go beyond the rated compression, which can easily make the required release force 2X the working tension. And, when working with such large forces, mechanical multiplier, like levers, can get VERY inefficient, due to high frictional losses.

The many headaches associated with Belleville drawbars are the reason I went a completely different way on mine - I built a motor-driven drawbar. This has the added benefit that I can swap out an R8 tool just as easily as a TTS one. You can't do that with Bellevilles! Since I have several tools that I use all the time that are just not suitable for TTS (like a 4" face mill), this is an important feature. Drawbar tension can be set almost arbitrarily high - My PDB is capable of up to 75 ft-lbs, but I run the equivalent of 25 ft-lbs of drawbolt torque, and it is absolutely consistent. Never had a single issue with TTS pull-out, even on the most aggressive cuts, and the tool has never once failed to release.

Regards,
Ray L.

[JoanTheSpark]

This thread maybe?

https://www.cnczone.com/forums/mecha...-software.html