Corby Questions

[unky_gumbi]

So I picked up a handling job on 3 bayonets and the customer wants corby pins. I have never used them before so I have a couple of questions about them.
First I know its a stepped hole, but how much material do you leave behind? I am doing them in black linen micarta and to place the pins where he wants I have to use the weight reduction holes. The holes are .53" on average, the small holes are .116", X marks the holes he wants used.

Next, do I need to buy a specific drill bit for this or can I just use two bits to drill the holes? Drill the small through hole first for the threaded part, and the larger, 1/4" in this case, for the heads of the pins.

The bayonets are unfinished with no edge, but hardened already.

 

[Remyrw]

I highly suggest using the appropriate stepped bit. It's tough to get things perfectly lined up otherwise. You wind up with gaps around the bolt or a very difficult time getting it through.

For depth it really depends on how thick a handle you're doing. You want them to get tight, so if doing a thin handle you can't go too deep on the larger hole or you can't snug it down. In this case you have nothing behind the handle material there, so you need to make sure you don't get too thin either, it might just break through when tightening.

 

[jll346]

I purchased "Fluted Reamers" to make my holes for corby bolts. They work excellent.

 

[SBuzek]

On micarta you can leave about .050 is plenty.get the proper step bit it helps with alignment.I actually set my heads pretty deep,you can shorten the screw and female end as long as you have about 3 full threads catching.when you put it together have plenty of epoxy to fill the big holes in the handle and just snug them down and let it cure.you don't need clamps the bolts will do it.Don't over tighten or you will have a glue starved joint.
Stan

 

[unky_gumbi]

Thanks for all the answers looks like I will be buying a stepped bit.

I am using 3/8" but the lip for the guard and the part that extends back from the guard on the top are about 5/16" deep so there won't be much material taken away

 

[A. Brett Schaller]

I leave about .080 underneath. If you leave too much, you risk grinding through the solid part of the bolt when shaping your handle.

 

[james terrio]

I leave about .080 underneath. If you leave too much, you risk grinding through the solid part of the bolt when shaping your handle.

True. Trim off a bit of the threaded parts so there's just enough to hold it together snugly. 3 threads like Stan said is good. (The other advice about not over-tightening etc is all true as well.)

If you don't do this and grind the handle thin, you'll see a divot or even a hole on the outside of the bolt, where you got into the threaded part. This will make you say bad words and frighten the shop cat.

Stepped drills are nice but somewhat pricy. I just use two bits carefully and haven't had any problems. Practice on scrap first. It turns out the 3/16x1/4 bolts I get from Tracy fit perfectly with nominal drill bits. (same size, I don't need to use a slightly larger drill or turn the bolts down any) Other "brands" or sizes may vary in this regard, I don't know.

When used with a little forethought, Corby bolts with a good epoxy are the best way to fasten scales in my opinion. They're easy to use and make a super-strong joint. :thumbup:
They're also available in more sizes than they used to be, so you can get micro ones that will look like pins when finished.

I once rehandled a Becker Brute for a fellow that wanted to be able to put the original scales back on if he felt like it. I used Corbies and simply sawed the screwdriver slot deeper. No epoxy or even Loc-tite. The client reported testing the finished project clearing brush and doing some chopping in his yard; he said the new scales didn't even loosen, but if they had he was confident he could have snugged them up. That's what really sold me on Corbies.