How much taper engagement should there be? R8 Collet/Tool Holder/ETC

[Robert LaLonde]

How much taper engagement should there be between an R8 tool/holder/collet and the surface of the R8 taper inside the spindle?

I would think must of the length of the taper, but I recently tested a machine where there is just a tiny contact ring near the large end of the taper on the tool. I tested a solid tool holder by marking it with a sharpie marker, but on other tools used in the same machine I could see the scuff mark in the same place. No other part of the taper showed signs of contact.

 

[mmcmdl]

Back when I ground tapers for larger shafts for pumps etc they required a 90% engagement using Prussian Blue . This was military work and I'm not positive what an R8 would require being it is drawn in with a bolt and is not a locking taper .

 

[RJSakowski]

My thought is that the mating surfaces should be engage along the entire length of the taper. Not doing so with a collet would result in a ring of contact with the tool shank. Also, as a number of people have pointed out, the locating key in the R8 socket is not intended to be a driving key. The drive force comes about solely due to friction between the two tapered surfaces.

 

[chips&more]

With the typical collet that has the three saw slits/cuts it depends. It depends on how close or far from its nominal size the collet is holding. I would think that if holding a nominal diameter the angle would be correct. But, if you are holding something other than nominal then the collet angle will change. And could have a slight difference in angle marriage with the spindle angle…Dave

I have a BP and BP collets and accessories. I see even wear all up and down the angle on all my stuff.