# Stacked Set Screws



## MikeMc (Jul 10, 2015)

I've seen mention of stacked set screws, one atop another in the same hole several times.
  Since the set screws adjusting the gibbs in my old lathe kept loosening I turned some hexhead set screws down to stub ends like came on my machine and ran another setscrew in on top to hopefully keep the gibb tension firm.
  Is this where those that have seen stacked set screws usually show up?
Thanks,
MikeMc


----------



## Tony Wells (Jul 10, 2015)

Lots of places. But they also make a screw just for that purpose, called a socket jam screw. It's got a hex all the way thru, and is relatively short. Works like a charm.


----------



## RJSakowski (Jul 10, 2015)

Use stacked set screw wherever you want to reduce the possibility of a setscrew loosening.  For jib adjustments and the like the adjustment screw is rarely tightened down so some means of locking the adjustment is required.  Alternatively , a cap screw with a lock nut is used.   If double set screws are used, bear in mind that tightening the top screw will set the bottom screw slightly deeper.  For critical adjustments, you may want to compensate for that offset.  For cap screws with lock nuts, the effect is just the opposite:  tightening the lock nut will slightly withdraw the adjustment screw.

Re: the screws theat Tony refers to, some of the locking set screws of that type have a larger hex socket than the standard set screw which permits an Allen wrench to be inserted through the locking set screw to make the adjustment which is then locked in place by the second set screw.


----------



## MikeMc (Jul 11, 2015)

Never seen a socket jam screw.
Have to look into that.
Thanks for the feedback.
MikeMc


----------



## wa5cab (Jul 11, 2015)

The gib screws on Atlas built machines do not need locking set screws as they all have lock nuts.  To properly adjust and lock this style, you must use both a box end wrench and a screw driver that properly fits the screw.  And it always requires two hands to do the adjustment.


----------



## Silverbullet (Jul 11, 2015)

I've even had them on pulleys  on machines . When doing repairs you come accross lots of things that you wouldn't think  of having to deal with. Lots of time they're used where vibration is a problem .


----------



## wa5cab (Jul 11, 2015)

But they are not used on any Atlas gib screws.  The normal places where you use set screws to lock set screws, the locking screw must be below flush.  That is not a requirement on a gib screw.  If your gib screws don't stay properly adjusted, you are not properly locking the lock nuts.  In about 35 years of service, I have never had any gib screw come loose and move.


----------



## MikeMc (Jul 11, 2015)

My lathe came without lock nuts on the gib screws and when I put nuts on there was an interference.
It's been weeks ago so I forget where.
I'll try looking for smaller nuts.
Thanks for the info.
MikeMc


----------



## wa5cab (Jul 12, 2015)

The correct nuts are thin pattern, commonly called jam nuts.  Readily available from many sources.


----------

