Kydex sheath forming; 'taco bump'- stupid question?

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Northern_Wookiee

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Feb 7, 2022
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So as the title states, I feel like this might be a very rookie/n00b problem, but I keep running into it and don't know what to do to fix it. When doing a 'taco' style fold over sheath for knives with fairly thick handles, I get a "bump" or ugly transition on the spine where the scales stop and the blade begins. I understand *why* this happens, with the abrupt transition from thin blade to thick handle, but I can't quite figure out how to fix it. I'm using a metal press and what I think is good foam from knifekits.com. I've tried the straight press method, and I've tried folding a thin piece of harbor freight floor mat foam over with the kydex to try and force the 'bump' down against the blade spine, but to no avail. Do I need better/different foam, or do I need to disregard my instincts and let there be a 'ridge' on the back of the sheath, more akin to a "pancake" style sheath? Any help or advice would be greatly appreciated!
 
I *think* I know what you’re talking about, but before I type out a long, potentially irrelevant response 😁, would you be able to post a pic?
 
That’s very helpful! It’s possible to eliminate some of that bump, but not all of it. Additionally, each knife will have its own unique shape and may have more or less of that bump. Because the handle area is much thicker than the blade, you won’t get as nice a fold as with the thinner part of the knife, which causes that transition bump.

For your specific example, you can see that as you pressed the knife, the handle rotated down away from the fold in the kydex. This will exacerbate the bump you see. When you go to press the knife, make sure the spine of the blade and top of the handle are flush to the fold in the kydex. This should limit some, but not all of that bump.

Personally, I’ve had better luck sticking to pancake sheathes. I’ve found that I can get better retention, more clip customization, and I can guarantee the insides are clean before sliding my knife in and potentially marring the blade. If you measure carefully and don’t overdue the rivet-from-blade spacing, the footprint isn’t much bigger if at all than a taco sheath.

Again, that’s just my personal preference!
 
I’ve had good results eliminating the bump by using a tad more heat when forming. This allows me to slightly stretch the Kydex into the taco before I close the press. Basically forming the Kydex to the spine and the sides of the knife.
 
Cliff Carter Knives said:
That’s very helpful! It’s possible to eliminate some of that bump, but not all of it. Additionally, each knife will have its own unique shape and may have more or less of that bump. Because the handle area is much thicker than the blade, you won’t get as nice a fold as with the thinner part of the knife, which causes that transition bump.

For your specific example, you can see that as you pressed the knife, the handle rotated down away from the fold in the kydex. This will exacerbate the bump you see. When you go to press the knife, make sure the spine of the blade and top of the handle are flush to the fold in the kydex. This should limit some, but not all of that bump.

Personally, I’ve had better luck sticking to pancake sheathes. I’ve found that I can get better retention, more clip customization, and I can guarantee the insides are clean before sliding my knife in and potentially marring the blade. If you measure carefully and don’t overdue the rivet-from-blade spacing, the footprint isn’t much bigger if at all than a taco sheath.

Again, that’s just my personal preference!
Click to expand...
Luckily this is a very exaggerated example, I have to sand those particular scales WAY down (my second time making micarta, and my first time actually turning it into scales, it's more round than anything. Terrible shape! 😅) I had already reheated and relaxed the Kydex for the knife I'm currently working on, so couldn't get a picture of it with it's lump. I agree that I could eliminate the problem with a pancake, but the client specifically requested the taco style, so c'est la vie. I appreciate your advice!
 
Bill Siegle said:
I’ve had good results eliminating the bump by using a tad more heat when forming. This allows me to slightly stretch the Kydex into the taco before I close the press. Basically forming the Kydex to the spine and the sides of the knife.
Click to expand...
I'll give that a shot. I usually chicken out and form at around 300-315, what temps do you prefer? The kydex for the sheath I'm working on has a Hexcam pattern, so I'm a little worried about distortion if I pull/stretch too much.
 
I usually use 300 degrees and give the Kydex 3 minutes to thoroughly warm up. I have only used mono colors so I don’t know if you’d distort any patterns.
 
I haven't tried to make a Kydex taco sheath before. But I would get some good gloves that can take the heat and try to quickly preform it by hand, and then put them into the press.
 
I mark my spine centerline on the inside of the kydex, lay it flat on the foam and press the spine of the knife straight down on that mark and then fold the foam and kydex into a taco and then press. Stretches the kydex to the shape of the spine and eliminates most of the hump.
 
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