Will a Setscrew work?? 4

[TJK1]

I am bolting a 1/4" thick bracket to a 1/16" thick chassis wall. The fastener will go thru a clearance hole in the chassis and there will be a nut on the inside of the chassis. I do not have room for any type of head on the fastener, so I was planning on using a set screw. The set screw would first be threaded into the 1/4 bracket. I would then stick the set screw thru the clearance hole in the chassis. I would then hold the end of the set screw with an allen wrench while I thighten a nut on the other side of the set screw, inside the chassis. Would this work?? Wouldn't the bearing of the threads of the setscrew against the internal threads of the bracket be sufficient to create a strong joint?? I could also use some permanent threadlocker perhaps on the threads inside the bracket. Would a setscrew work in this application??

 

[MintJulep]

Why not a flat-head screw in a countersunk hole in your plate?

Or a PEM stud.

Or simply a screw from the inside, short enough to not come through.

 

[TJK1]

Thanks MintJulep. The 1/4" thick bracket is only .300 inches tall and since I need to use at least a #10 screw, even the head of a countersunk screw is too big, since it measures about .380 dia. A PEM stud sounds good but we don't have time to get them. Your idea of just putting a screw in from the inside sounds the best. However I was planning on using 6061-T6 for the bracket. .300 minus the screw (.19)only leaves about .05 wall thickness. Do you think a stn stl screw or a steel zinc plated screw would work O.K. being threaded into a through tapped hole in the 6061-T6 aluminum? I know it is recommended to use a helicoil in aluminum, but this is a permanent assy. what are your thoughts??

 

[MikeHalloran]

Of the choices given, the least awful IMHO is a stud or setscrew, permanently embedded in the bracket, and a nut inside the chassis with a little loctite.

The larger pitch radius of the helicoil gives you more shear area in the aluminum. We don't know whether it would be necessary for your assembly, but you should be able to figure it out.







Mike Halloran
Pembroke Pines, FL, USA

 

[MintJulep]

6061-T6 for the bracket. .300 minus the screw (.19)only leaves about .05 wall thickness. Do you think a stn stl screw or a steel zinc plated screw would work O.K.

No, I don't.

 

[KENAT]

.05 isn't much wall thickness and if you put in a helicoil it will eat into this assuming you keep the #10 screw. I'd have concern not just from strengh but from manufacturing, sometimes I've seen holes near the edge of something cause the sides to bulge, don't know if this would be a problem for you.

You could probably do a simple stress analysis to see if the .05 is likely to fail. What kind of load is your bracket under?

Is there any way you can re-design to use more smaller fasteners? This might give you more wall thickness although you still may not be able to go small enough to use flat heads.

We use SS fasteners into aluminium threads at my place quite a lot without too much trouble but the environment is typically pretty benign so corrosion isn't too much of a concern and most items aren't heavily loaded. At previous employers this would have been a no no.


KENAT, probably the least qualified checker you'll ever meet...

 

[MikeHalloran]

A less awful choice than those given is to reduce the bracket thickness to something approaching that of the chassis, and retain them mechanically, e.g. with self- piercing rivets.



Mike Halloran
Pembroke Pines, FL, USA

 

[strokersix]

Be aware that setscrews are generally harder than bolts so they dig into the shaft or whatever they are holding. They are intended for compression instead of tension and may not be able to take the tensile loading as well as a bolt.