Re: Flush Cup Swivels
I got mine from McMillan but wherever you get them from follow these directions and you'll be good to go.
McMillan Flush Cup Installation
Good thread. Some interesting solutions. Here's the way I would suggest you do it, at least with our cups. The flush cups measure (O.D.) about .557" to .558". Use a 9/16" end mill or drill (.562") and drill a hole about 1/4" deep. This will let the flush cup slide in about 1/2 deep so that it will not chip the gelcoat if you try to screw it in. Then use a 17/32 drill bit and go another 3/8" deeper. This will let the threads "bite" about .015" on both sides. Then swab the inside of the hole with glue of choice, degrease the outside of the flush cup, and start the flush cup into the hole. Use a 1/4" hex wrench to screw in down into the hole until it is flush with the stock. Making the 17/42 hole about 1/8" extra deep leaves room for the glue to puddle up without oozing up into the cup. Using the threads to control the depth lets you put it right where it has to be for the swivel loop to function, and this is the reason we designed the external threaded cup that the old U.M.'s plant makes for us. Too much hassle trying to control the depth with the old smooth or grooved sided cups. Also, our cups are stainless steel to meet mil-spec rusting standards, and then blackened. The standard U.M. cups are carbon steel.
We do so many of these that I have some solid carbide stepped cutters ground on old dull 5/8" cutters that do all this on one pass. You just run it down until the lip of the full 5/8" diameter starts to kiss the stock and you are good to go. If any of you gunsmiths does a lot of these and wants one of the carbide step cutters let me know and I will get a current cost on having one ground for you.
Dick D.
A colleague and I did a couple of stocks and the whole thing took about an hour using a drill press and the required bits, in the end it looked like they were done at the factory.