Corby Bolts question

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lel

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I bought some Corby style bolts from Tracy and want to use them on my next knife. They are medium and have .183" Shaft and .250" Shoulder. What I have tried so far:

1. I drilled the hole in a scale for the shaft with a drill bit a little thicker than .183". Then without moving the scale I changed the drill bit to 1/4" and partially drilled it for a shoulder. There were 2 problems with this approach: a. the hole for the shaft was a little off center. b. The shoulder part was to tight and I could not insert the bolt in without applying a lot of pressure, and by "a lot" I mean I could barely rotate the bolt with a screwdriver.
2. I went to Home Depot and bought a set of step drills. One of them has 3/16" on the tip and 1/4" is a next step. I tried it on several pieces of scrap wood and did not like the result either. In this case the shoulder hole is too loose. I can see a small gap between the bolt and the material which I can fill with an epoxy but I do not like it. What I am looking for is a solution that will give me a nice tight (but to too tight) fit.

What do you guys use and what works the best for you? Any ideas what am I doing wrong?

I see that Texas knife supply has a step drill that might do the job, but they are currently sold out. I watched a Subhilt making video by S.R. Johnson and he uses something similar to this drill, probably just made from a regular drill bit. It looks pretty easy to make for someone who has a lathe and some basic skills to operate it...

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Sergiy
 
I made my own step drill using an F size drill which is .257

Just an FYI so you're not upset. I have one of the single flute step drills that you speak of from TKS. Mine is from Jantz though and it's supposed to be made for the Corby screws. It's made from 1/4" stock though, making the Corby (which is also 1/4") a tight fit. For that reason I never use it and decided to make my own using the F drill.

FWIW, if you have a lathe and a Dremel or Foredom it's a simple matter to make a Step Drill of any size by using your rotary tool as a simple tool post grinder.

I made a holder from G10 for my grinder that fits onto my Lathe Tool Post for just this purpose. It works great and allows me to make a bunch of handy tooling for my knifemaking.


:cool:
 
All the suppliers sell the drills for Corby bolts. Try K&G,Jantz, Sheffield, Pop's, etc.


With some skill ,you can make one by carefully grinding down a drill bit that is the right size for the bolt body, but buying one will assure the alignment is good.

Corby Bolt installation:
NOTE - this procedure requires parallel tang surfaces, and scales with well mated flat inner surfaces.

When you drill the tang pre-HT, drill the tang holes about 1/8"oversize of the bolt shank size. You want a little room for error when inserting the bolts. This is normally a good policy for all tang holes, regardless of handle construction.

Once the tang is shaped and drilled (pre-HT), slightly relieve the inner areas on the tang ( the places that will be under the scales) by at least .010" to allow for a shallow epoxy reservoir in the final glue up. Leave a 1/8" circle around each bolt hole un-relieved to assure a firm seat in final assembly, and leave a 1/8" lip around the perimeter. A ball burr in a Dremel tool does this well. If you just bolt the flat scales on a flat tang with no reservoir, the glue may all squeeze out and create a glue starved joint.The slight relief also assures that the edges are seated flush, and thus cuts down on the small gaps that often show up after the glue is dry.

When the scales and tang are ready, clamp one scale in place on the tang and drill 1/8" pilot holes through it from the tang side, centering these holes in the tang holes. Drill pilot holes for all holes you will be needing, including thong holes and decorative pins/rivets. Remove the scale from the tang and set the blade aside. Completely finish the blade before final assembly.

Take the pair of scales, and tape or clamp them together. Drill the 1/8" pilot hole on the front bolt hole through both scales ( only this one hole for now). Re-drill with a bit the size of the bolt shaft. Separate the scales. Change the drill bit to the shoulder drill for the bolts you are using, and re-drill that hole with the shoulder drill until the shaft hole has about 1/8" left. Check the fit with a Corby bolt, and ream the hole a bit by carefully wiggling the scale against the bit if needed. A properly drilled shoulder hole will just allow the bolt to be inserted straight in with just a bit of snugness.The proper depth of the hole can be calculated by subtracting the tang thickness from the female bolt shaft length. Each shaft hole in the scales should be one half of this number plus .050" to allow the bolts to seat with just a little thread to go. This can be easily done by eye,too. Just remember that you can always drill the hole a little deeper, but adding wood back is a lot harder.

If all is good, screw in a Corby bolt and tighten just snug ( never torque down on a Corby).The bolt won't be tight on the scales, because the tang is not there, so tape or clamp the scales together to assure things don't move, and drill the remaining 1/8" bolt pilot hole through both scales. Re-drill for the Corby bolt shaft hole, then drill the shoulder holes, and insert the second bolt to check the fit and alignment.
When both Corby bolts are seated, drill pilot holes for any other holes needed ( pins, thong holes, etc.).

At this point, I sand and polish the front edges of the bolted together scales. You won't be able to do this area once assembled.

Remove the bolts, and reassemble on the blade to test fit everything. If the holes need to be a tad deeper to allow the bolts to mate more, carefully deepen the shoulder holes. You need at least 1/16" of wood to allow the bolts enough wood to hold the scales firmly. Once the bolts are snug and all is good, you can sand the edges down to the tang. This will help with alignment and glue-up in final assembly.

Using a slow set epoxy ( I use T-88 ,and dye mine to match the wood color), put a little epoxy in the bolt holes in the scales and slide in the bolts, rotating them to assure the epoxy coats the entire inner hole surface. Using a tooth pick, clean out any epoxy that got in the threaded holes. Now, put epoxy on both sides of the tang,. Set the female bolt scale in place, then set the male bolt scale in place on the other side. Mate the bolts and give each a gentle turn to make sure the bolts are not cross threaded. Once the blots are both started, tighten alternately until the epoxy starts squeezing out. Don't tighten more than snug. The bolts will be very strong, and only need to hold the scales in place securely, not clamp them down with force. Check that the scales are aligned to the tang as desired ( loosen and adjust if needed). Wipe off excess epoxy, making sure to get it all off the front of the scales and ricasso, and set aside to cure for at least 24 hours. After the epoxy is set ( four to six hours for T-88) wipe the ricasso area with acetone to remove any squeeze-out or excess epoxy. You will tank yourself for this when doing the final polishing of the handle.

After the epoxy has fully cured, cut/grind off any excess bolts sticking out, re-drill any remaining holes to the size needed, and epoxy in any decorative pins, mosaic rivets, or thong tubes. Shape, sand , and finish the handle as desired.

Stacy
 
If you would like the step drill I have from Jantz, which, after looking, is not the same drill that TKS sells, I would be happy to send it to you if you PM me your address.

Jantz offers a single fluted stub drill with a single fluted pilot. The step drills I'm making are almost identical to the TKS drill except made from an F drill rather than a 1/4" drill


:thumbup:
 
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Thank you for your input, guys. Stacy, great tutorial, a lot of little details and tricks I still have to learn.

David, I have sent you an e-mail, can not do the PM, due to my "Registered User" status.

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Sergiy
 
I think Tracy use to sell a reamer for this purpose. I drill the pilot hole to fit the shaft, and then chuck up the reamer to make the shoulder hole. The reamer is ground down to fit the shaft/pilot hole, and then abrubtly transitions to a 1/4" reamer. I actually use the reamer to "drill" the 1/4" hole needed for the shoulder in handle materials. It works well and makes a perfect fit and flat bottom hole.

I haven't seen this tool on there lately, but you might see if a local machine shop could lathe the tip of a 1/4" reamer down for you to fit in the .183" shaft/ pilot hole.

--nathan
 
I don't like the step drills. When I use 1/4" corby's, I drill to 11/64" and ream the tang with a chucking reamer to 3/16". I then glue the scale to the tang, let it set up, and drill a 3/16" hole with a brad point bit through the scale using the hole in the tang as a guide. I then glue the other scale on, flip the knife over and use the 3/16" brad point to drill right through.

After that, I use a 1/4" piloted counterbore (3/16" pilot). I set the depth stop on my drill press to leave about 1/8" of scale above the tang and counterbore the holes.

I do things this way because it leaves a perfectly square shoulder for the step in the corby to seat against and it has made things a lot more consistent for me (nothing is more aggravating than cracking a scale or having to punch out a damaged bolt). I use brad point bits for drilling the scale because I was having a lot of issues with tearout on hardwood scales (chunks breaking out where the drill point would punch through the bottom side of the scale).

Hope it helps,

Nathan
 
There is an easy way to do this. Its called a counter bore. It has a guide that is the same size as your first guide hole that should have been drilled through. Then all you do is slowly drill to the depth you need. This way there is a tight fit both inner and outer. A little epoxy or CA and tighten it up and file off the excess
 
sometimes you can change the hole size a little by speeding up or slowing your rpm on your drill
 
Thank you, Rusty. It looks like Tracy will soon be selling them in sizes I need - for medium and small corbys.

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Sergiy
 
I purchased some Fluted Reamers from Pop's. They are outstanding!!
 
Mike Quesenberry said:
You tell em' Rusty, a counterbore is the proper tool for corby rivets.
Click to expand...


Ive tried all of those other ways and all I did was mess up some good handle material, you may get lucky and get one right but why risk it. Counter bores aren't cheap but neither is a set of really good Ironwood scales or Mammoth ivory. When you only have one shot at it why risk screwing it up.
 
Rusty has it right. Corby bolts where made to be used in conjunction with counterbores. The knife supply houses carry them.
 
I usually get better results if I drill the larger hole first. I find that the smaller drill bit will tend to drift to the center of the larger hole because of the point on the larger bit.

I used this technique when I put bamboo scales on my Tenacious.

Ric
 
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