Originally Posted by
SCzEngrgGroup
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.