Stacked set screws ?

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: GlennW, Harold_V

gangel99
Posts: 174
Joined: Thu Jan 26, 2006 11:48 pm
Location: Fairfax, CA

Stacked set screws ?

Post by gangel99 »

I have a fancy brass door handle that keeps coming off its (square) steel shaft. It is held by a set screw that loosens over time. Threadlocker only extends the period a bit before it loosens again. I know that my Logan lathe has a few places where two set screws were used - and they were stacked one on top of the other. Would this be more effective?

My other ideas are to drill and tap an additional set screw hole or drill and tap into the shaft.
SteveM
Posts: 7763
Joined: Mon Jun 27, 2005 6:18 pm
Location: Wisconsin

Re: Stacked set screws ?

Post by SteveM »

Try a different grade of threadlocker.

Check with your distributor (e.g Fastenal) as to what's available.

The stacked set screws may help too. There are also set screws that have a piece of plastic material embedded in the side to prevent them from working loose, sort of like elastic stop nuts.

Steve
User avatar
mechanicalmagic
Posts: 1431
Joined: Sun Nov 04, 2007 12:11 am
Location: Pleasanton, CA Land of perfect weather

Re: Stacked set screws ?

Post by mechanicalmagic »

My guess as to the problem. You have a modern cup point setscrew, this narrow point bears down on the square steel shaft. Then the knob is used, the narrow point deforms the steel, and it all loosens up.

Possible solution: Make the set screw flat across the face that bears on the square shaft. More area in contact with the shaft, and in a place with less force. Better Loctite has been mentioned. If you have room, a second set screw might be used, but I think I'd wait for it to fail again.

Dave J
Every day I ask myself, "What's the most fun thing to do today."
9x48 BP clone, 12x36 lathe, TIG, MIG, Gas, 3 in 1 sheetmetal.
stevec
Posts: 1949
Joined: Thu Oct 21, 2010 12:40 pm
Location: N.S. Canada

Re: Stacked set screws ?

Post by stevec »

I Gotta try this! My guess is there's a mark on the square shaft, give it a good dimple with a drill, make sure the set screw seats in the dimple and re-install with a little locktite on the setscrew threads.
Good luck!
Steve
SteveM
Posts: 7763
Joined: Mon Jun 27, 2005 6:18 pm
Location: Wisconsin

Re: Stacked set screws ?

Post by SteveM »

mechanicalmagic wrote:My guess as to the problem. You have a modern cup point setscrew, this narrow point bears down on the square steel shaft. Then the knob is used, the narrow point deforms the steel, and it all loosens up.
There are other types of points available too:
Image

You could make an aluminum split collar to hold them on the lathe and machine the end down flat. The collar would keep you from messing up the threads with the hard chuck jaws.

Here are the self-locking ones to which I referred:
http://www.mcmaster.com/#set-screws/=irjttq

They are desctibed as:
"Upgraded with a nylon locking element, our self-locking hex-socket set screws are perfect for tough jobs. The locking element increases holding power and remains effective up to 250° F. All screws have a locking patch, except those noted as having a locking pellet. Screws are reusable and have a Class 3A thread fit. Dimensions meet ASME B18.3. Length listed is the overall length."

Steve
User avatar
ctwo
Posts: 2996
Joined: Tue Mar 27, 2012 12:37 pm
Location: Silly Cone Valley

Re: Stacked set screws ?

Post by ctwo »

I really like this topic because I have the same issue...my shaft cross section is more like an X than it is square, and the shaft and knob have a coarse, loose thread (the knob will pull off).

Plus, my mill has aluminum hand wheels for the lead screws which are set with a screw, and they loosen up quite often, until the threads in the aluminum are worn off...

I'd like to find a permanent fix for both! (well, they'd still have to come off eventually...) :arrow:
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...
gangel99
Posts: 174
Joined: Thu Jan 26, 2006 11:48 pm
Location: Fairfax, CA

Re: Stacked set screws ?

Post by gangel99 »

Thanks to all. It is indeed a cup point set screw so the first thing I will try is grinding it to a flat and better loctite. I am using the medium strength - did not want permanent strength but I guess if it fails the permanence will not be a concern. :D

Good guess about the dimples so that might be the next thing. As for buying a better fastener, that is last because all the others are right at hand.
spro
Posts: 8016
Joined: Mon Feb 20, 2006 11:04 pm
Location: mid atlantic

Re: Stacked set screws ?

Post by spro »

. Just something to think about ; early, not really early, had those square threaded shafts. They also had holes at some point which were spaced at a regular interval in relation to another at the outside. It was a matter of placing the two knobs or handles to where there was a hole.. A pointed setscrew would set inside for any number of years. Then it could be a problem with other types of trying to lock a loose square shaft with no hole by other means.
spro
Posts: 8016
Joined: Mon Feb 20, 2006 11:04 pm
Location: mid atlantic

Re: Stacked set screws ?

Post by spro »

I said placing bu t thayt, i'll do this left handed as my right wrist is locking up. The square threaded shaft doesn't make sense going into a knob or handle which is also threaded, yet square inside. The setscrew changed the register to where inside the handle, a "flat" side was presented and also those threads at two corners. So the torque wasn't against either one of four points of contact. They all locked locked together.
WJH
Posts: 1417
Joined: Sat Jan 16, 2010 9:29 pm
Location: Florida

Re: Stacked set screws ?

Post by WJH »

In the very old house in San Francisco that I am currently living in, I had the same exact problem.
I solved the issue by not changing the setscrew, but by milling a very slight angle on the square shaft in such a way that the handle could only move towards the door and not off the shaft, only about a 2 degree angle...
handle.jpg
dly31
Posts: 1052
Joined: Sun Jun 27, 2004 11:29 pm
Location: Northeast Alabama

Re: Stacked set screws ?

Post by dly31 »

I don't think a normal setscrew can be expected to stay tight in an assembly that is not close fitting to start with, even if the setscrew threads are permanently locked. Some sort of shim to snug up the fit would likely help a lot.
Don Young
Howard Gorin
Posts: 348
Joined: Tue Jan 07, 2003 2:56 am
Location: Waltham, MA

Re: Stacked set screws ?

Post by Howard Gorin »

My experience is that two setscrews or as it is called here stacked setscrews work very well.
Especially when the attached handle is subject to reversing motion.
One setscrew locks the handle to the shaft, the second setscrew locks the second setscrew to the first one.
Post Reply