What protects a steel shaft from the marks left behind from set screws?

2Tite said:

A lead pellet inserted ahead of the set screw works well also. It will conform to the surface of the shaft and provide a larger bearing surface than harder materials.

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This is the choice for low-load situations by everyone who reloads shotgun shells !!

Although set screws have been used for nearly a century, it is actually a very poor way to connect a gear or other item to a shaft. (As evidenced by the number of mangled shafts removed from older machines.) Newer designs are using split collars which have the advantages of 360 degree shaft contact, perfect concentricity, zero shaft marring, and a huge increase in transmitted torque. Typically this technology is implemented 2 ways: angular wedge or crimped finger.

http://www.staffordmfg.com/Product-Categories/PowerRing(TM)-Shaft-Hub-Locks is a good example of a wedge type. Of course it requires a larger ID in the item being clamped to the shaft, but typically no extra width.

http://www.peerbearing.com/pdf/grip_it20brochure.pdf is a good example of the crimped finger type. Shown off to the side is the standard collar clamp that sits atop the fingers and squeezes them onto the shaft. Of course it requires extra width on the item being clamped to the shaft, but typically no extra diameter.

The advantage of this system for rehab is that it can sit atop butchered set screw flats or busted out keyway slots, and be stronger than the original design.... if you have the space to implement one of the designs.

Hope this helps.

Use 316 stainless set screws, grind the cup point off before use, 316 stainless fasteners are so soft that they will only lightly mar plain steel shafting with repeated use, while it is entirely possible that the OEM realized that said machine will not hold position this way simply grin and bear it.