Best router bit for Kydex?

Self Made Knives

Well-Known Member
#1
I actually don't like Kydex sheaths, but I do make them when time and cost is a factor. I was just finishing up a little caper's kydex sheath by adding a couple pack strap slots on the sides. BAM! Router bit grabbed and ruined one side. Well, actually ruined the whole sheath, there's no fixing it now.

I'm using a 3/16" wood cutting router bit, but it is very grabby when going through multiple layers of kydex. Not too bad through one layer, but through two it's a very risky slot! I've done it before, but tonight, well let's just say good thing no young ears were around!

Is there a better bit for slotting kydex? There's got to be!


photo 1.JPG photo 2.JPG
 

C Craft

Well-Known Member
#2
Anthony, never tried one on kydex. However when using any router on wood you have to take the depth slow. I have cut practically every kind of material you can imagine. The best solution is to have a jig/straight edge, for the router base to run against. That way you basically eliminate side movement! I have a plunge router and I can sit it up for about 1/8" deep passes. I make a pass, shut down bring it back to the starting position and bring the router up to speed and drop it too the next sitting and make another pass. Continue this till you get to the depth you want or in this case a thru cut.

Another thing looking down on top of the router the router is turning clockwise, so when making a pass on a cut the router always want to pull to the right. If you have a guide for the base on the right side the bit turning will make it pull tight to that guide! A guide on both sides of the base makes it virtually impossible to screw up the cut.

Backing up is pretty much forbidden as now your router is still trying to pull to the right and the back up motion is trying to pull it away from the guide. Like I said complete the pass, shut down, go back to the start, crank the router and reset to next depth start and drop into the cut. Routers do not like to start in the material so a plunge router comes in handy for repeated cuts.

A router table is another route. but with a router table cut you have to be sure you are right, as you make your pass. Basically you are cutting blind and upside down. So stops would be imperative in a drop in type cut!!!

They make bits that have their own bearing attached to it but that bearing has to run against the surface to make such a cut! On soft wood or something like kydex the bearing spinning would make too much heat and the bearing will cut into the surface it is supposed to be running against and then the cut is screwed up!!! I hope all this makes sense its been a long day and I just thought maybe I could offer some advice. A guide is your friend and a plunge router is the cats pajamas!!
 

Self Made Knives

Well-Known Member
#3
Yeah C, I use a router table with a fence for this and it is a blind plunge. The bit is more grabby in one direction that the other, but since you're plunging blind I can't start the cut exactly at the beginning of a slot. I have to plunge in close to the end, and go and back and forth a little to complete the slot. I know the cnc router guys mill plastic a lot so I'm guessing there are plastic specific bits. Hoping somebody on here has kydex specific experience to save me some time.
 

C Craft

Well-Known Member
#4
Anthony, your words put me into thought check out these sites, most are for CNC machines, some have cobalt flutes. I wasn't sure how familiar you were with routers.

You can even use stops on a router table. All you have to do is set the stop so that your material can only move from start point of your cut to stopping point. The material slide on the router table acts as your third guide. Even with CNC machines the router makes a pass and then lifts straight up, goes back to starting point and plunges in and makes the next pass, and then repeat to desired depth!!

Guides and stops are truly your best friend when it comes to handling a router by hand and precision. Make practice cuts on a scrap and get all the bugs worked out before you make a pass on the good stuff!!

Just reread your post again:
Yeah C, I use a router table with a fence for this and it is a blind plunge. The bit is more grabby in one direction that the other, but since you're plunging blind I can't start the cut exactly at the beginning of a slot. I have to plunge in close to the end, and go and back and forth a little to complete the slot. I know the cnc router guys mill plastic a lot so I'm guessing there are plastic specific bits. Hoping somebody on here has kydex specific experience to save me some time.

Are you plunging the router or are you trying to plunge the material onto the router bit? Plunging the material onto the bit is a recipe for mistakes.

A good router table set up where you can actually plunge the router up into the material is not cheap. That takes a plunge router and a top of the line router table. Years ago I bought a cheap one and well................. I soon figured out I had a table with a straight edge and it did not work well for anything I wanted to do!! I went thru about 3 routers till I realized if I wanted one that worked well I had to buy a plunge router and learn how to use it!

Quick story, I recently had my son help me move everything out of my shop when we had a plumbing pipe bust and the plumber needed access to attic and floor, recently! Anyway my son helps me with a jig I made for cutting adjustable pegs for a book case. He was a little rough with it and I got on his case.
"Son you may not realize it but that is about $2800 of jig you are slinging around" What he says! I told him when I was building all those book cases a few years back I priced a jig to do this. I found one that was 4' in length and had to be set-up and moved, even if you wanted to do an 8' tall case. They wanted almost $1200 for it.
So I made that one and if you set this one up for it you can cut up to a 12' height on a bookcase. Once you get the jig set and the router set up I can do like a 12' piece in a matter of 3-5 minutes with no mistakes. So now you know to take care of it!!! As I stated earlier jigs are your best friend for router work!!

https://www.amanatool.com/products/cnc-router-bits/plastic-cutting-cnc-router-bits.html

Here is some from Amazon.
https://www.amazon.com/router-bits-plastic/s?page=1&rh=i:aps,k:router bits for plastic

https://www.toolstoday.com/cnc-router-bits-and-insert-bits/plastic-cutting-cnc-router-bits.html

Call some of these companies that supply plastic cutting bits, and ask to speak to the techs, most of them can tell you what you need for what you are trying to accomplish with the bits!!
 

Self Made Knives

Well-Known Member
#5
Man, I may have just had a light bulb moment. I had a long drive to my work location today which gave me a lot of time to think. Here's a quick sketch of how I was making the slot. I was plunging the sheath down on to the bit and holding it with my hands up against the fence.

photo 1.JPG

I got to thinking, it cuts slots just fine with single layer flat on the table. Ding Ding, light bulb! I bet it's grabbing due to the sheath being able to rock back and forth a little. You can't hold it perfectly stable with only your hands.

photo 2.JPG

I'll bet if I added a couple of wood runners underneath both sides with some double sided tape, it will work just fine. Maybe it's more of a stability problem and less of a bit problem.
 

GeneK

KNIFE MAKER
#6
Try attaching the wood block to the fence or table. This would have less pieces for the bit to move through. Or put larger slots in the wood blocks before attaching to the kydex so the bit doesn't have to cut the wood also. A spiral fluted bit may help also, not sure if they make one in the size you need or not.
 

C Craft

Well-Known Member
#7
I got to thinking, it cuts slots just fine with single layer flat on the table. Ding Ding, light bulb! I bet it's grabbing due to the sheath being able to rock back and forth a little. You can't hold it perfectly stable with only your hands.
Winner winner, chicken dinner. Not only are stops and guides your friend, any wobble in the equation is your enemy as well! Take and cut your slot in the shims larger than you need that way the bit doesn't contact them. Be careful as you make your pass if the shim gets away and contacts the bit at very high RPM, it becomes a projectile and it can also jerk your hand into the bit. I went back up and looked at the pics again. You could put a screw that fills the grommet hole at the top and bottom so the piece is solidly fastened to that shim. Then you don't have to worry about the shim getting away and Armageddon stepping in. I am not a fan of loose material when it comes to a router! I have had the router get snatched away when I thought there was no way it could do that and I have also had the work piece slung across the room. Err on the side of caution, that extra second or two to fasten the shim to the kydex might keep you from loosing your good looks. LOL

I am assuming that the router is set for thru depth! So if you are going to use shim under material make two sets. One that only allows the bit to contact the first layer. Make your first pass, shut down and go to a thinner shim and let the bit cut thru both layers!!

See Gene was thinking the same thing!! Loose pieces can do a lot of damage!!
 

Self Made Knives

Well-Known Member
#8
I'm going to try a test tonight with the wood runners. I do sort of have to do it all in one pass though, since it's a blind plunge I don't think I could be accurate enough with stop blocks. Blocks are great for square, symmetrical things, but a knife sheath ain't either of those! :)
 
#10
What about a 4 flute endmill mounted in your router?
I need to look and see if I have one. As long as the shank was the right size it would probably work great. Heck, now I'm even thinkin about using the eyelet holes for mounting screws and cutting them on the mill instead. That was the main issue, I couldn't see a good way to fixture a sheath for the mill. If it was screwed onto a wooden rail, held in the vice, then maybe you could just mill it. Except, my mill doesn't have a very high top speed like a router does. Would be a good experiment.
 
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