3 replies to this topic

[Phil Hackett]

I have never been a fan of hollow set screws for holding gears and wheels onto axles. They were never designed for fastening: they are LOCKING screws. My main objection is that the screws I have seen and inspected do not have good screw thread and can ream and strip threads very easily. I know there are a newer generation of hollow set screws but I have not seen them yet and I am discussing what many racers already have in their cars and boxes. Hollow set screws should be a use once item.

These are close-up pictures of some hollow set screws and the full-length cup-point screws Sonic uses in their own products.

Below: the Sonic screw. Notice the full depth of threads, the small radius at the crest and root of the threads, the 60 degree angle, and the smoothness of the flanks of the threads.
This is a proper set screw.



Below: note the flat crests and the flat roots of the threads and the surface finish of the threads. The threads are shallow. Of the three examples shown, this is the best one which isn't saying much.



Below: This screw has high and low spots on the crests and burrs. This screw has also been used. Note the deformed end. If the material deforms further it will push a burr up into the starting thread. You could strip the wheel or gears threads just be installing the screw.



Below: The deformation of the end of this hollow screw is obvious. The surface finish is rough.

[Zippity]

The bottom three look, dare I say it, screwed.

Thanks for the presentation.

[Duffy]

Awesome and pretty starkly persuasive, Phil.

As a Geeky Toolmaker, I'll add that the "Use Once" statement will also apply to the rim, because you've already begun to deform that thread. The market-fresh integrity of the tapped hole in that rim will be a problem all its own, but let's focus on what we can control.

You'll never torque a hollow setscrew to the extent you can a proper hi-grade one; it'll either expand or crack at some unpredictable point, and then you've lost not just the rim but the wrench as well, as the hex gets rounded and will degrade any socket you use it with thereafter--and don't bother trying to grind to a new hex: you'll burn out the temper!

Duffy

[Matt Sheldon]

While I only use them in select applications, I have found the Koford Gold Billet Set Screw to be as nice as any quality wise and regarding thread interference. One very nice bonus however to the Sonic set screw pictured is the compression cone (mating portion of the screw that comes in contact with the axle). Most hollow set screws have what is called a "cup" end which is designed to not dig into its mating surface.

All that being said set screws in general are by design a compression fastener hollow or not.