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dmgauntt

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Posts: 27
Reply with quote  #1 
For several years my team had trouble with set screws in motor mounts.  After having been tightened down onto the motor shaft several times, we discovered that removing the set screw could become impossible.

I discovered that this is caused by splaying.  The pressure on the end of the screw slowly causes it to splay (widen or spread out).  Once the diameter of the end of the screw is larger than the hole, it cannot be removed.

The way to prevent this is to grind the thread from the last couple of millimeters of the screw.  When the screw splays out, it is still smaller than the hole and can be removed.
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jgraber

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Posts: 149
Reply with quote  #2 
What kind of screws are you using for setscrews?  
I have seen the splay problem with plain steel screws in #8-32 or #10-32, because plain steel is softer than the hardened steel motor shaft.

I have never seen this splay problem with the new (past couple years) black alloy socket cap screws as setscrew.  They are 170kpsi, and some rockwell hardness number greater than the motor shaft.   They are strong enough to use as "thread forming tap" in BEST Aluminum block with a 11/64" pilot hole.  That size hole is tighter than slip-fit, but a little looser than usual "thread cutting tap" spec hole for a #10-32 screw.
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jgraber

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Posts: 149
Reply with quote  #3 
What kind of screws are you using for setscrews?  
I have seen the splay problem with plain steel screws in #8-32 or #10-32, because plain steel is softer than the hardened steel motor shaft.

I have never seen this splay problem with the new (past couple years) black alloy socket cap screws as setscrew.  They are 170kpsi, and some rockwell hardness number greater than the motor shaft.   They are strong enough to use as "thread forming tap" in BEST Aluminum block with a 11/64" pilot hole.  That size hole is tighter than slip-fit, but a little looser than usual "thread cutting tap" spec hole for a #10-32 screw.
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dmgauntt

Junior Member
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Posts: 27
Reply with quote  #4 
We had been using the plain steel screws before.  This year my team will be experimenting with the 1/4" couplers, but failing that I will recommend the black alloy socket cap screws.
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