couplers

Working on my hobby gear. I was having to get couplers from wobbling. When you get a new motor that has shaft flattened the whole way, that presents a problem. Unless you have a real tight fit, your ok. Now I find that most have .12/- or + leeway which don't cut the mustard! I got a tap and die 3mm set and screws to match and drill 4 or 5 mm from the original screw. This way the coupler will not wobble but you have to check it out. The second screw will help take care of the .12 leeway on flat spot. Correct me if you think i'm wrong, ok! I found that having a round shaft with 1 screw can be had by just notching a big enough slot for the set screw is enough. This way the coupler will be spot on and not wobble, keep fingers crossed! Forgot, I did have to use a pop can and cut real small pieces and lay them flat on motor shaft but that takes some doing and came real close. Got ideas, express them, all ears! I got my coupler from Steve and it is spot on and is a class act, thank you Steve.

Which couplers are you using? and what kind of shaft? Flex or solid. Can you post a photo or a link?

Solid couplers. Shaft is 1/8". Now once the coupler is smooth and shaft in place, noise level drop a bunch. Shaft going into coupler goes in without touching anything . This is on a Thailand longtail. I haven't tested as ice is still on the pond. Motors are outrunners. Now one has a 2836-2700 kv another has a 2212/6-2200 turnigy with round shafts but I flattened and I think that might be the problem. That is why I posted. The more I think about it , I will only notch where set screw touches the rod. BTW, thanks for response! Have good day!

If , as you say, the shaft goes into the coupler without touching anything, you must have the wrong size coupler or poorly manufactured ones.
The shaft should be a neat push fit into the coupler with no wobble or looseness. Even with a flat area on one side.
Perhaps you have one item metric & the other imperial. They are usually a loose combination.

That was my guess too, 3mm motor shaft and 1/8" (3.175mm) coupling.
3mm is a fairly common small motor size and there are couplers available.