Recommendation? The Corby Bolt Dance

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Cushing H.

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I both like and dislike corbys. they give a nice secure hold to the scales. BUT, they can be kind of a pain to get in place. Specifically, if you drill the hole with the internal shoulder too high, the internal screw does not engage. On the other hand, if you drill with the shoulder too low (especially with thin blade stock), you can easily get a situation where the bolt thread bottoms out, and does not put any/enough holding tension on the scale. that is what I mean by the "dance" .... gotta get the depth of the hole just right, and sometimes it is kind of a dance.

The only way out of this I can think of is to adopt a "standard" depth, based on a standard thickness of scale material under the shoulder on the bolt (say ... 0.1" or so), and then, after fitting the bolt, grind down slightly the length of the internal female and male screws until you get a snug fit. Has anyone taken this approach, and is it a reliable one?
 
Are these kinds of bolts necessary?
I have only used normal pins out of brass, stainless, micarta, carbon fibre etc for my knives and not one of them has shown any signs of scales coming of.
 
Cushing H. said:
grind down slightly the length of the internal female and male screws until you get a snug fit. Has anyone taken this approach, and is it a reliable one?
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While I don't use Corbys or do full tangs very often, this is what I do if necessary.
I'm sure there's some info out there, but for some reason my criteria is 2 revolutions so 2 threads are engaged. As I'm sure you're aware, there shouldn't be a lot of tension forces that need to be restrained here, and the epoxy should prevent any backing out of the screw.
 
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Scaniaman said:
Are these kinds of bolts necessary?
I have only used normal pins out of brass, stainless, micarta, carbon fibre etc for my knives and not one of them has shown any signs of scales coming of.
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Necessary? No. But they do have some advantages, and there are a number of makers here that use them a lot.
 
People are to much of a rush to get their corby's in.

You must size the barrel and thread shaft for the hole in the material so it fits perfectly when assembled. If you do not, it will become apparent at the worse time.
 
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I use a lot of Corby bolts and I have figured a measurement with the drill press that works from a little over 0.115 inches down to 0.065 inch thick blanks.
 
I use them on every full tang knife I make nowdays.

I like to have at least 1/16'' of an inch of material under the shoulder.

Here is an example with 1/8'' steel and 1/4'' scales going 3/16'' into each scale. You'd have to modify the corby fastener so that the head to head distance is ~0.25''.



This gives you ~ 0.1275'' to avoid the "VOID" depending on the corbies you're using.

Edit #1: (Application)

I drill my holes initially with a #13 bit. This makes the counter bore pilot nice and snug to keep my counter bore from pop's knife supply straight. I then set the stop on my mini-mill so that I drill the counter bores to the same depth. I modify the corby fasteners to the desired length chucked up in my hand drill on the belt grinder.

Edit#2 (Example @ 08:10):
 
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I run mine as deep as possible, also leaving about 1/16 of handle material not including the liners. Nothing worse than setting them too shallow and grinding through the head.
If needed I take them down to the appropriate length on the disc grinder.
 
I keep a little over an 1/8 inch of handle material under the shoulder. I have used the same depth and it had worked for 0.250 inch blanks.

I like to adjust depth so when I bolt the two scales together for finishing the front faces the Corbys just tighten complelty.
 
I try not to overthink it. I clamp my handle scales on either side of the knife tang and then put my corby on top to see how long I want them. Then I pencil mark on the scale where I want the shoulder to be and set the depth on my drill press. Every scale will now be the same depth. Throw the corby female end in a drill and grind down on flat platen if necessary.

Oh also, get a purpose specific bit for them. I grabbed mine from usaknifemaker and I would gladly spend the money again if I wore it out.
 
I also leave a minimum of .060 under the shoulder. I also do a dry fit to make sure I'm not gonna bottom out. ;) From time to time I've had to modify the length a little bit, but it's usually not a big deal.
 
Ok , thanks. Seems like several of you grind the female part of the Corby to make sure it does not bottom out. Glued up a handle today... and shortening the corby actually went very easily.

Definitely agree on the special purpose bit. Still using the one I ground myself (for which I got yelled at), but it is still going strong...
 
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I use them on every full tang knife I make. Male corby is never a problem, my females lose 1mm to the screwdriver notch, and then 2mm to the bore that goes into the head, so I need to plan carefully.

my routine for 2mm blades is like this:

1) drill both sides with the pass thru drill bit (3/16")
2) female goes always on the left side
3) Using a the larger diameter drill bit (1/4") I fix the drill table so its only 1mm below the drill in its maximum extension, this prevents over drilling. All the drills have an angle at the head, but I measure 1mm to the tip, this leaves a marginal extra amount of wood in the hole shoulder
4) right side I extend to 3mm to the tip

This leaves me with both parts fully inserted and a turn or two of play avoiding the corby sides to be fully engaged, and deep enough so you don't suddendly see "an eye" hole on the female side.

Pablo
 
PEU said:
I use them on every full tang knife I make. Male corby is never a problem, my females lose 1mm to the screwdriver notch, and then 2mm to the bore that goes into the head, so I need to plan carefully.

my routine for 2mm blades is like this:

1) drill both sides with the pass thru drill bit (3/16")
2) female goes always on the left side
3) Using a the larger diameter drill bit (1/4") I fix the drill table so its only 1mm below the drill in its maximum extension, this prevents over drilling. All the drills have an angle at the head, but I measure 1mm to the tip, this leaves a marginal extra amount of wood in the hole shoulder
4) right side I extend to 3mm to the tip

This leaves me with both parts fully inserted and a turn or two of play avoiding the corby sides to be fully engaged, and deep enough so you don't suddendly see "an eye" hole on the female side.

Pablo
Click to expand...
Mostly though I am asking about the situation where you have a thin tang .... and if you do as you describe, the male screw "bottoms out" on the inside of the female side .... so that the scales are loose and not pulled tight against the tang. (or did I miss something in your description??)
 
Cushing H. said:
Mostly though I am asking about the situation where you have a thin tang .... and if you do as you describe, the male screw "bottoms out" on the inside of the female side .... so that the scales are loose and not pulled tight against the tang. (or did I miss something in your description??)
Click to expand...

The part where I say "a turn or two of play avoiding the corby sides to be fully engaged" I meant to say that it's not "bottoming" and still has a turn or two left but can't move anymore. Hope the clarification helps

Pablo
 
If you use a piloted counterbore, and drill over a solid surface, you can *never* over cut the relief because the pilot will bottom out.

So if your pilot is .156" or so tall, you'll leave a shoulder on each scale that's exactly the same, for about .312". Add .062" for a thin knife and a .330" barreled Corby is just about spot on. Add .125" for a thicker knife, and your .330" still gets about .050" barrel engagement on the opposite, which seems to work, too.
 
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