R8 spindle advice required

[Michael GilliganParticipant @michaelgilligan61133]

Posted by not done it yet on 29/07/2019 09:24:10:

I think MG’s comment re tightening is wrong. Correct me if it is me that is wrong but slippage would surely loosen the threads, not tighten further?

.

Assuming right-hand threads and 'forward' rotation of the spindle:

1. Cutter jams in the work
2. Spindle continues to rotate until something breaks or stalls
3. During that brief time, the collet is being screwed harder onto the drawbar

Similar to the situation when unkeyed slitting saws slip on an arbor and over-tighten the clamp .. it's a result of friction, rotation, and momentum.

MichaelG.

[old martParticipant @oldmart]

The angle of an R8 spindle is much too steep to use without a drawbar. I believe that the main reason for the pin is to make sure the tool does not slip round when the drawbar is tightened. It has no other function except, as mentioned, it will ensure that every tool is fitted exactly in the same position each time. This aspect should not matter as the spindle is expected to run true.

Larger spindle tooling such as BT40 are of improved design, having drive lugs, but they can still be installed in two positions.

I am leaning towards omitting the pin for the following reasons:

A. The arguments against are compelling.

B. I save having to drill and tap and make a pin.

C. I think that holding the tooling still during the initial tightening of the drawbar should not be difficult. 

D. I have no plans to run the spindle in reverse.

Edited By old mart on 29/07/2019 14:03:48

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