Quill R8 Key

[sdelivery]

I see 2 causes.
First is the R8 adapter put in place without the key way lined up, as evidenced my grooves in R8 adapters
This happens more frequently with power draw bars but I see it on manual draw bars too
Second is R8 adapter not seated in taper.
Generally from a damaged or dirty drawbar threads, R8 adapter was not pulled tight into taper.

 

[B2]

Curious what forces are damaging the screw if the R8 taper is providing as robust of a seating as stated?

In my PM940-vs-cnc (geared) case the set screw sheered off due to excessive forces, sufficient to stall the 1.5kw motor. I tighten the draw bar by hand with wrench and so have a pretty good idea about reasonable torque.

I was cutting a slot with a two inch fly cutter into A-1 steel. The CNC program backed the cutter off the material, dropped it down a few thousands, and then moved into the steel to make the slot cut and return to continue the cycle. Somehow something went wrong and instead of dropping down only a few thousandths the head (and tool) was lowered over 1/8 inch. (this was NOT a CNC programing error, but a machine failure) Hence, upon entry to the steel the tool rammed into the work... actually stopping the motor after a handful of cuts. The set screw was not completely sheered off yet as I made corrections and continue the work taking off a lot more material. A couple of days days later and during some more less stressful work I noted that the tool begain to freewheeled in the spindle/quill when I went to take the tool out. I could not get the tool out until after I replaced the set screw.