In my work in the printing and binding industry as a maintenance tech, I had LOTS of opportunities to tackle small grub screws. My biggest enemy was operators not paying attention to little details like the condition of the tools that they use, among other things, and rounding out the cup of the screw. I would have to rebuild ink fountain key units on British Baker-Perkins web presses (about a dozen per fountain on an 8 unit double web press) and they had the worlds most bad ass loctite I have ever come across!! On really bad ones I would have to strip the unit completely down so I could get the smallest oxy-acetylene tip that I had inside to heat the gear that the grub screw was in. I eventually made a pointed tip for an 80 watt soldering iron, and put the point in the cup of the grub screw and held it there until the loctite softened. It took longer to heat, but at least I didn't have to take everything apart. The main object here is to burn off the locking material. If the cup of the grub screw was in good shape, I could remove them hot with no problem. It was just damn hard to hold onto the little boogers when they are cold much less when they are damn hot! So I just let them cool for a few minutes first.
When it comes to these little grub screws, the fit of the wrench is important, obviously. I have found in both hobby stuff and in industrial stuff, the quality of the tool and the grub screw varies. I have the habit at work and at home to have several different wrenches or driver bits to make sure I have one that fits. If you are replacing grubs screws, pay attention to the end as to what kind it is. They can be knurled, dog eared or just smooth. And the cupped end of the grub screw should not protrude above the surface of what it screwed into. The top of the hole support the screw and keeps it from splitting, which happens pretty easy even on larger set screws. If the screw is screwed into a thin shoulder of surface, you can file or grind a flat spot or drill a recess for the end of the screw to seat in so the end of the cup is below the surface. A substitute for loctite, if the hole is deep enough, is to torque down the grub screw, then torque down another one right on top. This works pretty well and I saw it a lot in industry.
Type at you later,
Dan McEntee