Relief in Tapers

darkzero

darkzero

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Some machine spindles & tooling have reliefs on the taper. A couple off the top of my head, backplates for American long nose taper (L type) or Morse Taper arbors made by Jacobs.

I've always wondered but never found out why. Doesn't seem to be a standard. For instance, Jacobs puts the reliefs on their Morse Taper & straight shank arbors but no one else does. What are they for?
 
On a Jacobs taper (for drill chucks) I believe the relief is for wedges to be driven in to remove the arbor from the chuck if needed.
images
 
The MT5 taper in the nose of my lathe spindle has a relief in the middle, a rather wide one at that. Is that the kind of relief you are asking about?
Since alignment of the tool is best assured by contact at the extremities of the taper, relief in the mid section of one or both of the tapers could be a hedge against poor fitting tapers that would not otherwise seat well. Just guessing here.
 
Jacobs does mark their in that location but it doesn't make sense to me for them to spend the extra time & money to put that relief there for that reason only. L spindle adapters have them internally.


Here's a couple of examples:

BISON_BackPlates_Series8250.jpg


spin_prod_224402001
 
The few Brown & Sharpe taper shanks I've made over the years, I always relieved the middle of the taper. In fact, some of them I under cut the lower end of the taper so only the upper 1/3 was only touching the taper in the spindle. Ken
 
I agree with Tozguy and Darkzero. R8 tooling also has relief in the center. It has been my understanding that this was done to ensure that the reference datum's were at either end of the collet/adapter.
 
That makes sense, I like those answers. Thanks Tozguy, Ken, & RJ
 
4gsr said:
The few Brown & Sharpe taper shanks I've made over the years, I always relieved the middle of the taper. In fact, some of them I under cut the lower end of the taper so only the upper 1/3 was only touching the taper in the spindle. Ken
Click to expand...

Along the same lines, my R8 taper only seems to contact the upper part while the cylindrical lower section seems to be an easy fit and just along for the ride. If this is not normal would someone please hit the buzzer.
 
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