Adhesion of Different Handle Materials

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gregfisk

gregfisk

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I’ve recently started making a new knife handle design that has brought with it several challenges. The most difficult challenge has been getting the different materials to stick together while shaping the handle. Here are a few of the blocks. They’re made of several materials glued together. This is before sanding them into shape.
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Some of the materials included are micarta, g10, aluminum, copper, plastic, corian, bamboo and several types of wood. I started out using a 2 part epoxy. Nothing special, just the 5 minute type you get at the big box store. As soon as I started to grind the handle into shape it would come apart at one of the joints. Usually this would happen when one of the steel pieces would heat up. I then tried a good CA glue hoping that would handle the heat and pressure of grinding better.
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This did deal the heat a bit better but the joints still wouldn’t hold for very long before something would let go. So, I bought some better slow curing epoxy after reading that the longer the cure time the stronger the bond the epoxy makes.
D274AFB5-03AA-447A-9497-34B34880EBBF.jpeg

This 30 minute epoxy from Bob Smith Industries worked much better than the other adhesives that I had tried so far but I was still having failures where the metal spacers were. The spacers would get hot and the glue would fail. The funny thing was that if I held the failed joint together until it cooled back down it would stick again. At least until I installed the tang and filled up the handle with glue and it didn’t matter anymore. Still not happy, I did more research and came up with something else to try.
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This epoxy resin is very different than any other product I’ve ever tried. It’s a slow cure epoxy and has a very different smell to it. The biggest difference is that it stays flexible after it dries. And it does a much better job dealing with the heat. I still have to be careful when using thicker pieces of steel for my spacers but it’s much better than anything else I’ve tried so far. I also tried to glue a favorite pair of shoes back together and it worked perfectly. After a friend past away his wife gave me a bunch of 2x72 course and medium scotch bright belts. The course belts were all failing at the seam and I couldn’t use them. I tried several different glues to try and fix them with no luck at all. After fixing my shoes I thought about the belts and gave it a go. The belts were all new except that they had failed at the taped seems. After gluing the seams together the belts are like new again and work great. Anyway, I thought I would share my experience. And maybe help someone else out with a project, that might benefit from this unique epoxy resin.
 
I definitely encounter this. Here are a couple things that help me.
1) cut items as close to size as you can, this reduces overall grinding.
2) work in batches, once spacers are too hot to touch, move onto the next peices while it cools.
3) jb weld works too.
 
Greg, did you see the tech sheet on that C-tough? - "Note: Shear strength will increase significantly if bonding parts are allowed to cure 24 hours at 25°C(77°F) followed by 30 minutes cure at 120°C(250°F) after the initial 24 hour cure at room temperature (if possible)."

the shear strength is 3600-4600 psi

 
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plus you need surface area to provide the epoxy something to hold on to, you may want to look into prepping the contact area's (degreasing and sanding or increasing surface area)
 
I would be concerned about the long term durability of these handles. Various woods and materials react differently as time, temperatures and humidity change. I expect it to have multiple highs and lows that may make the handle uncomfortable as time goes by.

some suggestions :
- ensure all materials are dry
- group the non-organic material
- let sit for at least 6-8 weeks after the handle is shaped. store in low humidity
- Readjust the handle after each week or 2
- ensure you can go 4-5 weeks with no movement before attaching to a knife.
 
Something I do to help materials adhere to each other. After sanding flat, I score in a cross hatch pattern with a sharp point. I want deep gouges. Then I sand again, though the cross hatch pattern should still be visible. This allows the epoxy to get into the cracks, and secures the pieces together better. I also keep a bucket of water next to me, and try not to let the pieces get past warm. Fresh belts or sanding pads work well, and short contact time, followed by a dunk in the water help keep temps low. Hidden pins can be a life saver on more complex pieces as well.
 
JoBone said:
I expect it to have multiple highs and lows that may make the handle uncomfortable as time goes by.
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This is a great point and something that caught me out. I found two decent solutions. One was to stabilize it, the other was to put a tiny groove between each layer so any dimensional change would go un noticed.

If stabilizing isn't possible, I wonder if drying by baking and then applying a few coats of thin CA would do the trick.

As to the original post of how to keep it stuck together while shaping etc, slow cure epoxy like GFlex works pretty well. Another option is to drill it and use internal bracing dowels.
 
I didn’t expect to get so much advise when I posted this, I appreciate that. I do clean all parts and rough sand them. I’ve done the crisscross scratching and that does help. I think waiting for the epoxy to fully cure like Harbeer mentions is important. One thing I should mention regarding long term durability. I drill the tang hole all the way through the handles. And when I install the blade I pour the hole full of epoxy so it is very strong after that. I’ve also been drilling two 1/8” holes the length of the handle and installing pins before doing my grinding. Something I started doing because they kept falling apart. The mention of the kitchen sink is pretty funny. I actually just cut up an old utility sink made out of thick bright white plastic of some sort but haven’t tried it yet. Do people really dunk their wood handles in water to cool them while grinding?
 
I think the C-tough is similar to G-flex only at a much lower cost. Regarding uneven surfaces I guess I’ll see what happens in the future. I use a wiping varnish and then a paste wax which I apply with a heat gun. I put about 15 coats of wiping varnish with sanding every few coats. Any imperfections are smoothed out by the time I’m done.
 
I was asking since the edge mentioned dunking into water to keep the handle cool. It seems like that would be hard on the wood and the joints.
 
IF the black palm and other soft woods are stabilized, you should be able to dunk them in water to cool. The hardwoods, G10 and metals will be OK wet. Black Palm splinters easily.

I have done this stacking with my scraps and used them for bottle opener handles. The early ones broke during prying. I drilled .125 inch holes lengthwise near the center (next to your tang shaft), and added rod (hidden pins). None broke after that.

stacked handles1.jpg


stacked handles2.jpg
 
I tend to only dunk the handles when there is metal spacers in the handle. It's hard on the joints, but keeps the epoxy from melting or burning with the heat build up. If just wood, I don't dunk.
 
How much benefit do people get from stabilizing wood? Is it done to negate shrinkage or aid in adhesion? Or is it done so that the wood takes a finish better? It seems like if the wood is already dry the benefit would be minimal?

Bensbites, can you see jb-weld at the seams when you glue layers together with it? I know it’s really good product but I’ve been reluctant to try it for fear of seeing it in the seam.
 
gregfisk said:
How much benefit do people get from stabilizing wood? Is it done to negate shrinkage or aid in adhesion? Or is it done so that the wood takes a finish better? It seems like if the wood is already dry the benefit would be minimal?

Bensbites, can you see jb-weld at the seams when you glue layers together with it? I know it’s really good product but I’ve been reluctant to try it for fear of seeing it in the seam.
Click to expand...

Stabilizing helps reduce movement, and allows for a higher grit finish, it also reduces maintenance since the wood will have less effect due to humidity.
As far as jb weld, when I use it, I dye it black with system 3 epoxy dye and tend to use it next to black micarta spacers.

I still think you will see the biggest improvement by not letting your metal get hot. When I run batches of 5 handles, that’s enough time for the handle to cool while I work on the other 4.
 
This is a very good post, and advice from various people, TY!

It's something I run into a lot, and I definitely use a some of the stuff mentioned by others; particularly scoring things or getting the surface super rough. Occasionally I dunk if I'm working with woods I know can take it, but rarely. But really for me the best solution if you can is @Bensbites working in batches. I always do handles with metal in them while working on something else.
 
I spent some time reading through this thread again and there is some really good information here. Something I didn’t mention is that I grind my handles down to the shape I want and then I install the end caps which are made out of aluminum. I drill partial holes in the ends of the handle and on the inside of the caps to give the glue something to grab onto and up the shear strength. The aluminum caps get hot fast when grinding and it helps to do them at the end. I dip just the end cap in water to cool them down. Something I did recently was switch the machine that I do my heavy grinding on. I have three 6x48 belt grinders each with its own grit sandpaper. I was running the 60 grit on my 1960s Delta which is my favorite sander but it runs pretty slow compared to my other two sanders. So I put the 60 grit ceramic belt on the fastest machine and that made a big difference at keeping the temperature down. I may eventually change the pulleys on the Delta to speed it up but this works fine for now. Something that was mentioned here is using fresh belts, and doing that with the faster speed really helped keep the heat down. This is the first time I’ve made several handles at once and I did what Bensbites suggested and kept swapping between them as I was grinding away. That’s a great way to keep working and not have to stop and wait for your project to cool down. I can’t say enough good about the C-tough epoxy I’m using now. It does a great job holding everything together and it has a very long working time. Longer than anything else I’ve tried. And I’ve never used an epoxy resin that stays so flexible once its fully cured.
 
gregfisk said:
I spent some time reading through this thread again and there is some really good information here. Something I didn’t mention is that I grind my handles down to the shape I want and then I install the end caps which are made out of aluminum. I drill partial holes in the ends of the handle and on the inside of the caps to give the glue something to grab onto and up the shear strength. The aluminum caps get hot fast when grinding and it helps to do them at the end. I dip just the end cap in water to cool them down. Something I did recently was switch the machine that I do my heavy grinding on. I have three 6x48 belt grinders each with its own grit sandpaper. I was running the 60 grit on my 1960s Delta which is my favorite sander but it runs pretty slow compared to my other two sanders. So I put the 60 grit ceramic belt on the fastest machine and that made a big difference at keeping the temperature down. I may eventually change the pulleys on the Delta to speed it up but this works fine for now. Something that was mentioned here is using fresh belts, and doing that with the faster speed really helped keep the heat down. This is the first time I’ve made several handles at once and I did what Bensbites suggested and kept swapping between them as I was grinding away. That’s a great way to keep working and not have to stop and wait for your project to cool down. I can’t say enough good about the C-tough epoxy I’m using now. It does a great job holding everything together and it has a very long working time. Longer than anything else I’ve tried. And I’ve never used an epoxy resin that stays so flexible once its fully cured.
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let’s get into the nitty gritty details. I can work with this.
1) I have a series of jigs I use on my tablesaw to get to shape they are faster and more consistent than shaping on a sander. You can shape the bulk of the handle, then cut the endcap close, glue it on and shape it. If it’s just a ferrule cap, I work them, the dip just the tip in water to keep it cool.
2) start with 24 or 36 grit belts.

edit: now that I look back I see thinner metal spacers that may not work on a table saw. I have had mixed luck cutting laminated non ferrous metals on my saw.
 
Bensbites said:
let’s get into the nitty gritty details. I can work with this.
1) I have a series of jigs I use on my tablesaw to get to shape they are faster and more consistent than shaping on a sander. You can shape the bulk of the handle, then cut the endcap close, glue it on and shape it. If it’s just a ferrule cap, I work them, the dip just the tip in water to keep it cool.
2) start with 24 or 36 grit belts.

edit: now that I look back I see thinner metal spacers that may not work on a table saw. I have had mixed luck cutting laminated non ferrous metals on my saw.
Click to expand...

Great, love digging deeper into this stuff. Jigs are a great way to go for all the right reasons. There are thin aluminum and copper spacers in the handles and even some thicker copper ones. So in this case I don’t think it would be safe to run them through the table saw. That’s an excellent idea though for another time. I did make a jig for drilling the two pin holes and the tang hole that run the length of the handle. It is basically a clamp that holds the material together from two sides and then has the holes properly spaced on the top for drilling on the drill press. I put that clamp in my drill press vice and that holds the handle together while I drill the holes. I built it because at the beginning using the old epoxy the handles would fail while drilling the hole. I think using heavier grit sandpaper is another great idea Bensbites and something I’m planning on ordering next time. I’ve been using 60 grit ceramic belts on my 6x48 sander and 40 grit ceramic on my 2x72. 40 grit on the 6x48 should really help, with not only the speed of grinding but the heat issue as well.
 
gregfisk said:
Great, love digging deeper into this stuff. Jigs are a great way to go for all the right reasons. There are thin aluminum and copper spacers in the handles and even some thicker copper ones. So in this case I don’t think it would be safe to run them through the table saw. That’s an excellent idea though for another time. I did make a jig for drilling the two pin holes and the tang hole that run the length of the handle. It is basically a clamp that holds the material together from two sides and then has the holes properly spaced on the top for drilling on the drill press. I put that clamp in my drill press vice and that holds the handle together while I drill the holes. I built it because at the beginning using the old epoxy the handles would fail while drilling the hole. I think using heavier grit sandpaper is another great idea Bensbites and something I’m planning on ordering next time. I’ve been using 60 grit ceramic belts on my 6x48 sander and 40 grit ceramic on my 2x72. 40 grit on the 6x48 should really help, with not only the speed of grinding but the heat issue as well.
Click to expand...
I have cut copper, brass, and nickel silver up to 1/8th in thick on a standard tablesaw with a all purpose wood blade. There are many smaller steps for additional safety around this, mostly around fire prevention. Please research this yourself. I start with 24 grit.
 
24 grit! I wonder how that would have felt that time I jammed my knuckle into a brand new ceramic 60 grit belt for the second time in 4 days. A scab was just starting to form when I did it the second time. Man did that hurt.

I have cut aluminum on my chop saw many times with a carbide blade but never on a table saw. I can see it working if you’re careful, especially if you have a jig to hold it in place.
 
gregfisk said:
24 grit! I wonder how that would have felt that time I jammed my knuckle into a brand new ceramic 60 grit belt for the second time in 4 days. A scab was just starting to form when I did it the second time. Man did that hurt.

I have cut aluminum on my chop saw many times with a carbide blade but never on a table saw. I can see it working if you’re careful, especially if you have a jig to hold it in place.
Click to expand...
My knuckles have healed. Give me time. I have 5 knife orderes to fill.
 
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