Found a good thread over on CNCZone that’s all about what to do when your vise clamping force is deforming your part. Precision bores can be particularly finicky if clamping force deforms them during the boring process. You want to use the lightest force that will still properly clamp the part.
One of the best suggestions was to mount a finished or semi-finished part that has the features that deform, but your dial indicator on it, and crank the vise handle until you start to measure deformation. If you’re using a torque wrench to tighten the vise, you can make the tightness that is just a little less than the deformation point repeatable. If not, you can at least see what the required force feels like.
There are also more specialized tools being made for this purpose, if you’re a gadget hound like me. In another thread (that has some great guidelines for precision boring on a mill), Geof talks about a tool he found called THE REPEATER:
The Repeater consists of a force gage (nice hydraulic force cell to have for other purposes too) and a vise handle with a torque limiting slip clutch. Set it to your desired clamping force and then when you reach that point the vise handle wilil just spin. That’s idiot-proof enough even for me!
The Repeater (as well as some other nifty tooling) is available from Proclamp Products.