4 Attachment(s)
Balance of the CarveTight Spindle
As many of you know, the CarveTight spindle was not balanced as well as it could have been when it first came out. A while after its release, LHR reported that it operated more smoothly if the 16mm bolt was replaced by a 20mm bolt and two washers. I have recently got my hands on a CarveTight spindle and thought I would test it for balance. Although its balance was certainly improved by the new bolt and washers, it can still be better. There are two variables which have to be simultaneously adjusted to balance the CarveTight (without drilling new holes). The mass of the paw and bolt as well as the position of their center of mass. The original paw and bolt had too little mass and their CM was too far toward the end of the bolt. The new bolt with washers had too much mass and the CM was also too far toward the end of the bolt. I found that if you cut the 20mm bolt down to 17mm (middle bolt in the picture), the balance was better. The mass is about right but the CM is still too far down the bolt. At this point I abandoned the washers and started to make my own weight. I made weights from 1/2 inch diameter stainless discs with an offset hole matching the paw. I slowly filed down longer bolts and thicker discs until I reached the best balance I could. The resulting bolt length turned out to be very close to the original 16mm bolt and the thickness of the disc about 1/16".
This was the best I could do since slight changes in other variables easily sway the balance. For example, the balance is sensitive even to how tight the bolt is tightened. With slightly different diameter shanks, the balance would change considerably. The bore diameter of this CT, as mentioned in another post, is 0.5025-0.5030. Chucking a 0.5025" shank (turned ER11 adapter) verses the 0.04995" (CW carving bit) or a 0.5000 stainless shank all changed the balance. I suppose that the Rock chuck must suffer from the same variations. This is a consequence, after all, of the side paw clamping design.
I am not so sure that perfect balance is really that important with the CW. After all there are large cutting forces and torques during the normal operation of carving. Why not, however, do the best we can. My recommendation to LHR after my day of balancing would be to have the paw made thicker by about 1/16" and use the 16mm bolt. The balance is considerably better than with the 20mm bolt and washers. A new paw would be an easy upgrade. For those of you with the 20mm bolt and washers, try knocking a few mm off of the end of that 20mm bolt.
