Epoxy and fiberglass

Brock Cutlery

Brock Cutlery

Joined
Jan 10, 2015
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Got a question for those with some years here.
I used to build R/C planes, wood, epoxy, and fiberglass.

I am wondering is a thin sheet of glass between joints, thinking wa handle joints specifically, would increase the bond strength?
One of the big issues, especially with inexperienced, is squeezing out all the epoxy from the joint.
But not just this. Seems like it might strengthen the joint, and secondarily would keep more epoxy between the layers.

Thoughts appreciated.
 
how thick is this thin sheet?
are you trying to solve a problem that doesn't really exist? :)
sounds like the glass complicates a simple bonding method IMO

Aren't thousands of wa handles made simply and proven in use?
 
Generally, wood to wood contact makes a joint as strong as the wood. Wood to metal is somewhat weaker. It seems you are addressing a problem that is nonexistent.
 
Brock Cutlery said:
Got a question for those with some years here.
I used to build R/C planes, wood, epoxy, and fiberglass.

I am wondering is a thin sheet of glass between joints, thinking wa handle joints specifically, would increase the bond strength?
One of the big issues, especially with inexperienced, is squeezing out all the epoxy from the joint.
But not just this. Seems like it might strengthen the joint, and secondarily would keep more epoxy between the layers.

Thoughts appreciated.
Click to expand...
Thinner layer of epoxy between the bonding material is much . . . .. much stronger then thick one .
 
also you could increase the surface area of the mating bond by spot drilling holes into the side of each mating piece, like dimples.
 
I don't have experience but just brainstorming: Why not wood glue for non-oily wood to wood joints? Lots of times the wood glue joint is stronger than the wood and movement cracks the wood rather than a glue joint failure.

You could also use some hidden pins parallel to the tang through all the pieces. If you have the hidden tang running through all the pieces, if you cut some notches and epoxy the tang in, it seems like that and pins would be plenty of insurance?

I have a bunch of Japanese kitchen knives with various standard Japanese wa handles (the common ones made by a Japanese handle shop), and they're all just wood to wood/horn and I've never had an issue. And they all look just burned in for install.

The only time I had an issue with a hidden tang handle on a knife, I believe it was due to different natural woods that probably weren't dry enough and a wide swing in relative humidity from where it was made and where I live (not one I made but one I bought from Europe).

Unless the glass were a glass membrane that is permeable, more glue joints = more potential failure points.
 
I'm sure we all recognize that a dish washer would certainly create all sorts of problems on these types of handles.
 
Thanks for all the thoughts. The way I make my wa handle joints, I cut a cross hatch pattern on each piece, including spacers, to increase surface area for bonding.
I don't know if a thin glass sheet would increase the bonding between the cross hatch patterned pieces. I guess testing would have to be done.
I have never had a joint fail, but my oldest knife is less than three years old. I do have confidence in my work. Just wondering if it could be stronger yet.
 
Best method to increase bond strength (which is overkill, and a waste of time, but I like the feeling I get) with epoxy (assuming you rough the surface a little) is to heat the wood a bit prior to application, then allow soak-in time of about five minutes or so. This is called pre-wetting, and is not a waste of time when end grain (from curly or figured wood) is involved. No joint starvation at all because the heat simultaneously does three things:
  • expands the air out of the wood, then sucks the epoxy in as it cools,
  • Lowers the viscosity of the epoxy to below water viscosity, which increase capillary wicking into the wood pores.
  • then the heat starts to kick off the epoxy into higher viscosity sooner, which is what truly eliminates joint starvation, and sets up the epoxy sooner.
 
John Blazy said:
Best method to increase bond strength (which is overkill, and a waste of time, but I like the feeling I get) with epoxy (assuming you rough the surface a little) is to heat the wood a bit prior to application, then allow soak-in time of about five minutes or so. This is called pre-wetting, and is not a waste of time when end grain (from curly or figured wood) is involved. No joint starvation at all because the heat simultaneously does three things:
  • expands the air out of the wood, then sucks the epoxy in as it cools,
  • Lowers the viscosity of the epoxy to below water viscosity, which increase capillary wicking into the wood pores.
  • then the heat starts to kick off the epoxy into higher viscosity sooner, which is what truly eliminates joint starvation, and sets up the epoxy sooner.
Click to expand...

That sounds like great advice! How would it affect oily wood reaction, like ironwood?
I slice up the surfaces a bit with xacto, then remove oil via denatured alcohol. Would the heat also wick the oil back into the cleaned grain?
I have to try this heating! Very cool.
 
I was assuming dry wood, but forgot that you guys use a lot oily woods, so the heat can have a counter effect. I used this method when I built my boat (mahogany) for lots of end grain areas. So actually heat would be great trick prior to degreasing the wood. Heat the oily wood with a heat gun til it sweats out a lot of oil. Then while hot, wipe with mineral spirits followed by lacquer thinner. Then score surface, heat again, (a little less heat) prior to applying the epoxy.
 
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