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Touch Off Gauge

Dabbler said:
Sorry tom, but an MT3 has a similar problem to R8 - please let me explain.

You put a 1/2" end mill in either R8 or MT3, and it slips until it has been full collapsed in the spindle, making height setting nullified - but - neither r8 or mt3 will register at the precisely the same spot.

If you have an r8 or mt3 - to - er32 collet adapter, and then clamp that 1/2" end mill int the ER collet, you still cannot guarantee its Z height. that 's because while clamping in an r8 spindel it can be out .001 or .0015 by clamping it harder or softer. In mt3, the problem is even worse: you can easily overtighten an mt3 and shorten your tool by as much as .004. I have had this demonstrated to me, because I didn't believe it.

-- the problem is draw bar pressure. the CATxx and similar tool holders always register to exactly the same place and that is why CNC machines use that style or the Sandvik trilobe tool holders. there are now even more sophisticated tool holding systems for CNC but now I digress.
Click to expand...
Is it the same if the tool change occurs only in the ER collet and the R8/MT arbor isn't moved?
 
Dabbler said:
...you still cannot guarantee its Z height. that 's because while clamping in an r8 spindel it can be out .001 or .0015 by clamping it harder or softer. In mt3, the problem is even worse: you can easily overtighten an mt3 and shorten your tool by as much as .004. I have had this demonstrated to me, because I didn't believe it.
Click to expand...

Interesting. Like you. I assumed it might be some amount but not that much. Is the MT3 deviation more that R8 because its a slightly more slender taper?

I've been using my Milwaukee cordless ratchet wrench on my drawbar mostly because its just convenient to reach the nut on my tippy toes. Once the socket is on, easy to spin on/off nice & quick. It does have a clutch but I never tighten the drawbar that much. I guess a guy could use a set point torque wrench for some consistency but on a manual machine with frequent tool changes & always measuring what you cut... its probably not as critical as CNC.
 
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