Flexible blades breaking epoxy bond.

S

skillgannon

Joined
Apr 27, 2009
Messages
991
I made a fillet knife and a couple other very thin bladed flexible knives the past few days. I noticed when I flexed the blades i heard a crackling sound and final noticed the blades have cracked rhe epoxy at the top of the handle. With the Corby bolts the handles are tight and the gap isn't really visible. My epoxy is getting old and I'm wondering if it's bad epoxy or a issue with flexible blades. If so how do you keep thin blades from breaking the epoxy?
G2QFMBF.jpg
 
I cant really speak about filet knives, but this is a thing that can happen with folders between the thin flexible liners and scales. The only solution i know is to put the pins as close to the end without cracking anything or looking dumb. Also it probably wouldnt hurt to put one in the middle.

EDIT
I did an image search on filet knives and there are 3 types. One has a bolster/guard/ferrule thing, another is hidden tang, and the last has the last pin much further up the handle than yours (about midway between your pin and front end of the handle). I suspect this is not by accident. Again, i have never made a filet knife. But i have seen thin flexible metal epoxied to scales break free fairly quickly with little effort, and after moving pins towards the end of the scales the problem disappeared.
 
Last edited:
skillgannon said:
I made a fillet knife and a couple other very thin bladed flexible knives the past few days. I noticed when I flexed the blades i heard a crackling sound and final noticed the blades have cracked rhe epoxy at the top of the handle. With the Corby bolts the handles are tight and the gap isn't really visible. My epoxy is getting old and I'm wondering if it's bad epoxy or a issue with flexible blades. If so how do you keep thin blades from breaking the epoxy?
Click to expand...
I made two fillet knives (yet), first is like You but with three pins with first pin very close to "guard". I didn't noticed any cracks or weak connection between tang and handle. Second I made with steel guard because first was not very comfortable to hold especially with blade bent. I didn't noticed any cracks again.
 
I've had something like that happen. The knife is still laying around somewere, unsharpened.
I wouldn't fight it, I'd go around it and change the design to a hidden tang
 
The critical part is the front of the handle, where the scales meet the ricasso.
The bolsters/ferrules were developed for addressing that issue
 
I worried about this when l first made some leather skivving knives. Similar to a filet knife but a different profile. Wasn't the problem I thought it was gonna be. I've since made quite a few of these as well as filet knives. Not a problem but I do use G-flex.
 
It happens. Use a thicker blade stock and grind whatever flex you want into the blade. This way the handle wont flex.
 
G flex has minimized the issue for me...also hidden tang construction.
 
Thanks guys. I have been using Pops epoxy. At this point I will just make a new blade and this one goes into the beater bin. I can see where 3 bolts and flexible epoxy might work.
I just started using 15n20 and have been liking it for kitchen use. I will have to be careful with thin stock like AEB-L.
 
You can fix it. Remove the handle then use dremel with diamond bit (round shape) to make two little holes near ricasso like I used here. Then use two pins about 2 mm in diameter. Roughen pins on surface (I use cylinder diamond bit). Do I understand good that handle is from micarta or G10? Drill two holes through handle using holes in tang as guide. It is solid material so You can use another diamond bit (with tapered shape) to make holes a little bit larger from the outside. Put together tang, handle, pins and glue. Use clamps or rubber band. These two little pins need to be extended by hammer. Be careful when doing it. Clean handle from excess of glue. If You'll do all that right it will hold (imho).
Sorry for My limited language skills I hope You understand Me.
 
Last edited:
Peened on metal bolsters will prevent it too, I almost always put bolsters on fillet knives, partly because of this
 
I'm learning a lot from this. Things I never thought about. I'm also thinking that my epoxy is getting old. It's about 1 year open. I'm chucking that since I have new stuff anyway.

Thanks to jesenius for the 2 pin idea. I think I might try that.now to drill out the Corby bolts.
 
In the future put a ricasso on the blade, then distal taper from there to the tip .... and the problem will cease to exist.
 
skillgannon said:
I'm learning a lot from this. Things I never thought about. I'm also thinking that my epoxy is getting old. It's about 1 year open. I'm chucking that since I have new stuff anyway.

Thanks to jesenius for the 2 pin idea. I think I might try that.now to drill out the Corby bolts.
Click to expand...

I love Pop and deal with him as much as possible, but the 5 min 2 part epoxy he sells is the same as all the other on the market, and just isn't suitable for critical glue up like this, no 5 minute epoxy is. The only 5 min set time glues I would/will use are Loctite Speedbonder, which offer similar performance in 1 or 5 min fixture times, to the slower long-cure epoxies, but have their own caveats.

When it comes to Epoxy, West System G-Flex, or Acraglas, are the only two that are really suitable IMO.

However, regardless of the glue you use, finish and cleanliness of the mating surface are critical. A courser finish will adhere better, and or areas that the glue can get into, like lightening holes, etc. You can grind a rough hollow in the back of the scale with a course belt, or even blast the scale and tang with semi-course media (making sure the mask off the visible surfaces that need a fine finish, i.e. in the ricasso area of the blade/tang), to get much better adhesion.

I've had scales I couldn't beat off with a hammer, where I did this correctly, and some that popped off on their own as the humidity changed from summer (humid) to winter (ultra-dry) in my area, where I left too fine a finish on the scales or tang/liners/whatever.

You'll have to experiment, but you want as course a finish as you can get, without it causing any visible "defects" in the mating area between the handle material and the tang.
 
javand said:
I love Pop and deal with him as much as possible, but the 5 min 2 part epoxy he sells is the same as all the other on the market, and just isn't suitable for critical glue up like this, no 5 minute epoxy is. The only 5 min set time glues I would/will use are Loctite Speedbonder, which offer similar performance in 1 or 5 min fixture times, to the slower long-cure epoxies, but have their own caveats.

When it comes to Epoxy, West System G-Flex, or Acraglas, are the only two that are really suitable IMO.

However, regardless of the glue you use, finish and cleanliness of the mating surface are critical. A courser finish will adhere better, and or areas that the glue can get into, like lightening holes, etc. You can grind a rough hollow in the back of the scale with a course belt, or even blast the scale and tang with semi-course media (making sure the mask off the visible surfaces that need a fine finish, i.e. in the ricasso area of the blade/tang), to get much better adhesion.

I've had scales I couldn't beat off with a hammer, where I did this correctly, and some that popped off on their own as the humidity changed from summer (humid) to winter (ultra-dry) in my area, where I left too fine a finish on the scales or tang/liners/whatever.

You'll have to experiment, but you want as course a finish as you can get, without it causing any visible "defects" in the mating area between the handle material and the tang.
Click to expand...
Thanks. I ordered some. It's pricey. If it works it's worth it though.
I was using the 15 minute stuff and never had problems until last week.
 
I had this problem a while back and one thing I noticed was this. I always leave the tang rough(50-60 grit) but as I sand the flats the part under the front of the scales gets finished too fine. If I finish it to 600 then the ricasso under the front of the scales are too fine. I’ve started marking the front of the scales and then roughing up that part with a dremel and a carbide deburring bit.
 
You must log in or register to reply here.
Back
Top