Testing handle attachment methods - mini corby fasteners & epoxy only...

aarongough

aarongough

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Mar 12, 2013
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Hey all!
I had a thread the other day where I was asking for advice about avoiding crazing or whitening around the pin holes during the peening process. Several people recommended that I switch to Corby bolts. I had some miniature corby bolts that I had ordered previously but never used, so I thought I should have a look at them again and see if I could get them to work for my knives.

Given that the fasteners were so small I was a little worried about their strength, so to satisfy myself I did some destruction testing yesterday, and also took a video of it!

The question of just using epoxy by itself has also come up several times. I've tested this in the past and didn't have good results, but I wanted to test it again on video... Surprisingly the results were different this time, you'll have to see for yourself!

Warning! Knife abuse ahead :)

[video=youtube;PGmydrLT2Fo]https://www.youtube.com/watch?v=PGmydrLT2Fo[/video]

I'm pretty sure that pop that you hear at 1:57 in the video is actually the fastener nearest to the ricasso breaking in half. The other fasteners held though. The fasteners were at a serious disadvantage during this test as the tang on that scrap blade was tapered which means that the bolts were slightly bent during installation. I bet that proper installation in a tapered tang, or on a flat tang would be even stronger.

Thanks to Elementfe for the tip about sanding the epoxy into the tang and scales, seems to work well!

EDIT: The corby bolts I used were these ones from Jantz - http://www.knifemaking.com/product-p/cp627.htm
 
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Since I use non-stainless for my kitchen knives, the scale failures I've had using only epoxy (with various means of bridging and locking it in) seem related to corrosion working its way under the scale.
Perhaps the wet sanding technique would help with that, time for some torture testing!
 
elementfe said:
Since I use non-stainless for my kitchen knives, the scale failures I've had using only epoxy (with various means of bridging and locking it in) seem related to corrosion working its way under the scale.
Perhaps the wet sanding technique would help with that, time for some torture testing!
Click to expand...

That makes sense, I will admit that was a failure mechanism I hadn't thought about much though as I haven't seen it first-hand. I shall make sure I keep it in mind!
 
Ive never liked corby bolts due to the massive weak point at their neck. They really need an 82 degree taper on the head. I use flared tubing now most of the time and I think its a really strong fastening mechanism.

I gave up on corbys after I snapped one while tightening it during installation. That was not fun :(
 
Corby bolts are only tightened hand snug, never torqued down hard. They are mechanical fasteners, not clamps, relying on the shoulder to provide a secure tension.. The scales should already be sanded to fit flush with the tang.

I have used thousands of Corby bolts ( I buy then by the 100 count) and have NEVER had a bolt fail in use. I have had handles destroyed by all sorts of damage, including one run over by a truck, but the bolts are still in place.

I use the mini-Corby bolts only on small kitchen blades, and occasionally on a handle that appears to have two rows of pins. My go-to fastener is a 1/4" Corby bolt.

One big plus is that they can be used in assembly of multiple knives in production easily. Using slow cure epoxy and rubber gloved hands, I slip all the males through one half of all the scales (with a little epoxy on the shaft), and all the females in the other scales. Once all are ready, I pick up a blade, apply epoxy to both sides of the tang, set one scale on it, turn over and set the other scale in place, and snug the bolts down with a stubby screw driver. I only run them down to just snug at first. Once all knives have the handles on, I wipe off all squeeze out, and give the bolts a little more snugging down. Afterv all are snug, I wipe off any new squeeze out and then wipe down with an acetone dampened cloth. Obviously, I change the gloves several times. The slow cure epoxy allows going back up to an hour later and checking for epoxy drips or bolts that need a tad more tightening.
 
KalEl said:
Ive never liked corby bolts due to the massive weak point at their neck. They really need an 82 degree taper on the head. I use flared tubing now most of the time and I think its a really strong fastening mechanism.

I gave up on corbys after I snapped one while tightening it during installation. That was not fun :(
Click to expand...

I have sheared the head off a corby as well, however that isn't necessarily indicative of the strength overall of the fastener. The threads of the fastener give you a lot of mechanical advantage when tightening it up, and with any small fastener it's easy to break things....

Once they're fastened up it looks like the tensile strength is pretty good.

bladsmth said:
Corby bolts are only tightened hand snug, never torqued down hard. They are mechanical fasteners, not clamps, relying on the shoulder to provide a secure tension.. The scales should already be sanded to fit flush with the tang.

I have used thousands of Corby bolts ( I buy then by the 100 count) and have NEVER had a bolt fail in use. I have had handles destroyed by all sorts of damage, including one run over by a truck, but the bolts are still in place.

I use the mini-Corby bolts only on small kitchen blades, and occasionally on a handle that appears to have two rows of pins. My go-to fastener is a 1/4" Corby bolt.

One big plus is that they can be used in assembly of multiple knives in production easily. Using slow cure epoxy and rubber gloved hands, I slip all the males through one half of all the scales (with a little epoxy on the shaft), and all the females in the other scales. Once all are ready, I pick up a blade, apply epoxy to both sides of the tang, set one scale on it, turn over and set the other scale in place, and snug the bolts down with a stubby screw driver. I only run them down to just snug at first. Once all knives have the handles on, I wipe off all squeeze out, and give the bolts a little more snugging down. Afterv all are snug, I wipe off any new squeeze out and then wipe down with an acetone dampened cloth. Obviously, I change the gloves several times. The slow cure epoxy allows going back up to an hour later and checking for epoxy drips or bolts that need a tad more tightening.
Click to expand...

I did my first batch glue-up last night using the Corby bolts and it was quite a pleasant process. I'm not at all worried about the fasteners failing in use, I think they'll be strong enough for sure.

I found last night that squeeze out kept showing up for well over an hour after I'd tightened up the bolts, but I think once I get used to the process it will be very painless.

I'll probably switch to the 3/16" rivets from JephCo as opposed to the 5/32" ones from Jantz as the JephCo ones look a little beefier, and are also less expensive so that way I can buy them in bulk.
 
One thing I forgot to mention is matching the bolt, scales, and knife tang. The shaft length chosen should allow the bolt to be nearly fully seated when the scale is on. This requires a few measurements and drilling the seat to a pre-determined shoulder depth. Don't try to drill it a certain depth, instead drill it until it has a certain amount of un-shouldered hole left on the tang side of the scale. If the tang is .100" and the bolt shaft is .375" then the seat left undrilled should be about .165 on each scale. That will allow the bolt to go snug, with the male stud nearly fully seated in the female receptor. This gives a strong bolt

If the shaft is not long enough, either drill the seat deeper, or select a longer shaft bolt. If the shaft is too long, you can select a shorter shaft bolt, or just grind it down as needed on both the male and female parts.

Also, NEVER put epoxy in the female bolt hole. It will prevent the male stud from screwing in (just like a cylinder full of water will not allow the piston to move downward), as there is too tight a clearance for the epoxy to be squeezed out along the threads. This could easily make someone break a bolt trying to get it screwed down. I suspect it is also the cause of people saying that the threads got "stuck" and would not go all the way down.
If epoxy gets in the hole when inserting the bolt in the scale, clean it out with a toothpick and/or a pipe cleaner.
 
bladsmth said:
One thing I forgot to mention is matching the bolt, scales, and knife tang. The shaft length chosen should allow the bolt to be nearly fully seated when the scale is on. This requires a few measurements and drilling the seat to a pre-determined shoulder depth. Don't try to drill it a certain depth, instead drill it until it has a certain amount of un-shouldered hole left on the tang side of the scale. If the tang is .100" and the bolt shaft is .375" then the seat left undrilled should be about .165 on each scale. That will allow the bolt to go snug, with the male stud nearly fully seated in the female receptor. This gives a strong bolt

If the shaft is not long enough, either drill the seat deeper, or select a longer shaft bolt. If the shaft is too long, you can select a shorter shaft bolt, or just grind it down as needed on both the male and female parts.

Also, NEVER put epoxy in the female bolt hole. It will prevent the male stud from screwing in (just like a cylinder full of water will not allow the piston to move downward), as there is too tight a clearance for the epoxy to be squeezed out along the threads. This could easily make someone break a bolt trying to get it screwed down. I suspect it is also the cause of people saying that the threads got "stuck" and would not go all the way down.
If epoxy gets in the hole when inserting the bolt in the scale, clean it out with a toothpick and/or a pipe cleaner.
Click to expand...

Yeah the sizing thing is kind of a pain, and I need to sort that out a bit better. Given that I tested with the smallest fasteners they make at least I know it only gets better from here in terms of strength!

Interesting that you've had that experience with the epoxy stopping the bolts from going together... The epoxy that I'm using (West Systems 105/205) is pretty thin, and I didn't have any issues with it when it was in the fasteners, screwing the male side in simply squirted the excess out through the threads. Maybe the fasteners I have are made to a looser tolerance than yours? Maybe the epoxy is just less viscous than what you're using?
 
Hi Aaron! Another great video! Very helpful and educational. You have to be pleased with the results of your heat treat process! Those blades really had good spring back and toughness beyond what I think anyone would expect out of a knife! Thanks for posting your test results and info. It really is helpful to us home hobbyists who are striving to improve what they make! Keep up the good work! DonO
 
PaMtnBkr said:
Hi Aaron! Another great video! Very helpful and educational. You have to be pleased with the results of your heat treat process! Those blades really had good spring back and toughness beyond what I think anyone would expect out of a knife! Thanks for posting your test results and info. It really is helpful to us home hobbyists who are striving to improve what they make! Keep up the good work! DonO
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Thanks Don!
Funnily enough those blades are actually not made of the same steel that I'm using now. They were O1, and I primarily use A2 now. My current A2 blades would spring back as well as those ones, but probably not flex as far before breaking... Mainly because I'm keeping them a bit harder these days to improve edge retention.

I agree that flexing of that kind is definitely far beyond what is needed in a knife, but I wanted to be hard on those handles! :)

-Aaron
 
Great video Aaron. The wet-sanding tip is really cool. I'm going to try this on my next blade.

TedP
 
While I use all of the hardware available depending on the type of knife I changed my major use to the Acorn/Luke/Dogbone style. After a conversation with Jeff @ Jephco, He showed me I can have just about every look I want with the one fastener type I can leave the slot for the tactical look and removability, sand it off for the pin look and yes even sand it a little more for the loveless look without the lopsidedness of the target look. AND if I feel I need epoxy there the threads for more surface area to hold the glue. Costs are about the same and they are available in 1/8", 3/16" ( my personal favorite), 1/4" and the 5/16" so they cover all the other bolts sizes.
 
Doubletrouble said:
While I use all of the hardware available depending on the type of knife I changed my major use to the Acorn/Luke/Dogbone style. After a conversation with Jeff @ Jephco, He showed me I can have just about every look I want with the one fastener type I can leave the slot for the tactical look and removability, sand it off for the pin look and yes even sand it a little more for the loveless look without the lopsidedness of the target look. AND if I feel I need epoxy there the threads for more surface area to hold the glue. Costs are about the same and they are available in 1/8", 3/16" ( my personal favorite), 1/4" and the 5/16" so they cover all the other bolts sizes.
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I agree that the luke rivets look very interesting as an alternative to Corbys. I have to work out if their standard sizes will work for my application, if they do I'll like use them instead of the Corbys simply because the threaded stud seems much sturdier than what you find on a similar sized corby.

Thanks for the input!
 
Good video Aaron. I had picked up the wet sanding tip too... I don't recall if I read it in an elementfe post or somewhere else.

But, you have certainly made me take a second look at corbys. Cheers.

Eric
 
Aaron,

When you are wet sanding and epoxying are you wet sanding, cleaning/ drying the surface and then gluing, or wet sanding and then gluing with the tang and scales still wet?

Thanks for taking the time to do so much testing and passing on the results to us!
 
KalEl said:
Aaron,

When you are wet sanding and epoxying are you wet sanding, cleaning/ drying the surface and then gluing, or wet sanding and then gluing with the tang and scales still wet?

Thanks for taking the time to do so much testing and passing on the results to us!
Click to expand...

It is literally using a bit of the epoxy to 'wet sand' the scales and tang then sticking them together. It seems to help adhesion due to thoroughly assuring the materials surface is in full contact with epoxy and not separated by air/film/dust...
 
LucyCustomKnives said:
Good video Aaron. I had picked up the wet sanding tip too... I don't recall if I read it in an elementfe post or somewhere else.

But, you have certainly made me take a second look at corbys. Cheers.

Eric
Click to expand...

It's funny how we look at a small fastener and will generally 'know' that it's weak, but when that fastener is mainly experiencing tensile strain even a tiny fastener can e very strong! That was what I came away with from the testing, my assumptions were turned on their head a bit which is always a fun experience!

You should have a look at the 'luke rivets' from JephCo as well. They look like they'd be an even stronger fastener if they work for your application!

KalEl said:
Aaron,

When you are wet sanding and epoxying are you wet sanding, cleaning/ drying the surface and then gluing, or wet sanding and then gluing with the tang and scales still wet?

Thanks for taking the time to do so much testing and passing on the results to us!
Click to expand...

Hey KalEl!
Sorry, I've probably confused people when I say 'wet sanding', what I meant was that you apply the epoxy and then use some sandpaper to sand the wet epoxy into the glue surfaces before clamping the joint together.

It's not terribly hard to do, and isn't even all that messy provided you're not excessive with the epoxy! If you have a sand-blaster then I believe that sand-blasting the glue surfaces will make for the strongest joint, but failing that sanding the epoxy into the glue surfaces should be a decent improvement!

You're more than welcome! Hope it's all useful.
-Aaron
 
Sorry to bring up this older threat but I still have a question about the wet sanding.
What gritt size do you use for that?
(good vid btw!)
 
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