Fixing a disk to a shaft with set screws (disk is too large for them), or?

If you have room for collars, you could sandwich your disc between two lock collars. If you don't want to make the collars they are readily available from industrial suppliers like McMaster-Carr.

Ted
 
Chewy said:
Plus, you could drill and tap an angled hole for a set screw. Also you could make a small collar, say 3/8" wide and drill it for a set screw. Then attach the collar to the face of the brass with small screws. I would use 3 myself. That would make the hub.
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Angled set-screws would run pretty hard into the "no mill" problem. I'm going to have to get one soon.

The collar idea could work with some setup effort, as the next post noted. I'm reluctant to go in that direction (or pre-made collars), though, since it would compromise the application, if only in principle.

The goal is to have the disk be a weight whose mass is as close to a pivot as possible (hence a wide but short disk rather than a longer but thinner rod). The more mass that's farther from the pivot, the farther from an ideal weight it would be. So I'd prefer a clean disk with no other appendages, and certainly none between it and the pivot. Indeed, I intend the weight itself to be the mount for the pivot.

Now I'm thinking that CA glue for a mostly-permanent attachment might be the cleanest and easiest solution. I just have to get the hole to be a tight sliding fit, which I should be able to do (I now have reamers in 0.249, 0.25 and 0.251 in.). A fully-movable mount is obviously best, but I probably won't have to move or remove it, I just need an out in case I do, and CA at least offers a hope for that.
 
Loc-tite retaining juice is a good choice here also . No need for a slip fit . :encourage:
 
mmcmdl said:
Not thread loc . Retaining fluid for bearings etc.
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Interesting. I'll research that. It's removable with heat, then?

But I still need that tight sliding fit. I need a very precise right angle between the disk and the shaft. One of my big worries is that I'll ruin the disk if the fit comes out even a bit too loose (I'll practice first) or tilted.
 
How about a two-piece attachment system? A smaller piece that would be the collar, small enough in diameter to drill and thread for a set screw with what you've got. But in addition to the set screw hole, through-drill (say) 3 holes and countersink them for flat head screws (they would be parallel to the collar's center hole). Your larger piece would be turned with a pocket to accommodate the collar, and deep enough so the collar is coplanar with the larger piece. The larger piece is drilled/tapped to match the 3 holes in the collar. I think you can figure out how to attach the large piece to the collar :)

This approach doesn't have anything sticking out to mess up your center of gravity, and all the pieces can be made of brass so you don't have any odd thermal effects to confound your "g" calculations. Well, the set screw might be something different.....and maybe you want TWO set screws so the center of gravity isn't slightly offset from the rod's center. I'd use something nonmagnetic. But that reminds me to ask: is Invar nonmagnetic?

For even more "fun" you could ditch the 3 screws and thread the two pieces. That might facilitate fine adjustments of the weight, but at the expense of changing the center of gravity as you do so.
 
I would take the thinner disk, center it in the lathe chuck, then drill and tap it to 1/2" NF. I would then take a piece of 3/4" diameter brass, drill and ream it for the 1/4" shaft, turn it to 1/2" diameter to a shoulder, and thread it 1/2" NF, using the disk to check the fit of the threads. After threading, part off the piece leaving a full-diameter "hub" wide enough to hold a #10 or 1/4" set screw. Now you have a hub to screw into the disk which you can secure with Loctite.

Install it on the shaft with the hub away from the critical area. If brass is too heavy, make the hub from aluminum.
 
Your weight-attaching scheme needs to hold it in place while it's swinging back and forth, right? So a friction fit with something like an O-ring or spring clip might not work too well.
 
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