Usual preface, I’m with PreciseBits so while I try to only post general information take everything I say with the understanding that I have a bias.
Part of the issue with “too tight” is that most people go by the spec of the MAX torque on the LARGEST bore size for their collet. As an example I believe the HDM uses an ER20 collet. So that would be:
- 1.0-1.4mm 16Nm/12ft-lb
- 1.5-6.9mm 32Nm/24ft-lb
- 7.0-13.0mm 80Nm/59ft-lb
But most people will do a quick search and see a torque number for 80Nm/59ft-lb and go with that. Probably won’t check the nut type either which changes it.
On top of that almost all those numbers come from industrial machines and spindles with high quality collets and nuts. I don’t really expect a sub $2k spindle to have the same spec for hardness.
And again these are MAX torque before you risk hurting something. If that much is needed is a whole giant rabbit hole. See here for SOME of it:
Last thing i would say even if following all of the above correctly is that without some kind of lubrication on these they are WAY more likely to do this clean or not.
Story time: In the steel rule market the reseller of the very expensive Italian spindle that most of these machines used recommended using alcohol to clean everything. These are precision ground surfaces that doing so removes all the lubricant and puts water on the bare steel (100% alcohol barely exist… plus water in the air). It did not lead to good results… ISO tool holders would get stuck in the spindles and they were having to have the spindles rebuilt every couple years. That’s on top of VERY short life on the toolholders, collets, and nuts. Once we got them to stop doing that, things improved greatly.
So while you don’t want to get and kind of lube or the like inside the BORE of the collet. The rest of the spindle, collet, and nuts need it for reliable use.
As for if the damaged thread will screw up your setup… It would have to be MASSIVELY screwed up. Basically it would have to be able to overcome the forces from the two tapers (spindle and nut) to pull it off and add runout. Those tapers accuracy and condition along with the collet are the vast majority of where you end up with runout and slip resistance. That said, it may cause your clamping force to be slightly less. As you may have guessed though, that’s probably fine or even preferable.
Hope that’s useful. Let me know if there’s something I can help with.