Official Luthiers Forum!

After getting drawn into a FB discussion on gluing fingerboards with epoxy, I decided to set up a test.

Everyone was freaking out about how much heat it takes to release epoxy. Several respected folks here have said how cleanly & easily it releases when it reaches "the temperature" but nobody said how hot that was.

I glued a scrap of Amazon Rosewood to a piece of Sapele using West Systems 105/205. In the spirit of full disclosure my resin and hardener are very old, close to 20 years but I've never had a problem.

The test setup was allowed about 2 weeks to fully cure. I drilled holes on both sides of the joint for a thermistor that works with my multimeter.

I set the heating pad to about 250°F and clamped it against the test rig with a piece of 2X4.

I decided to go to 200°F (inside the wood at the joint) and try to take it apart. I moved the heating pad a couple of times trying to heat the joint evenly. The probe measured up to about 210°F on one side and 200°F on the other. I shut off the heat, released the clamp and tried my pallet knife thing. At first it still seemed solid then the knife started to get in and the whole thing released very quickly.

Sorry about these pics. Those maple pieces were butted against the rosewood so the heating blanket wouldn't be out there dangling in the breeze & burning up.


A view of the temp probe holes.

The only negative thing I experienced was the fumes of the opened joint. I'm not sensitive to epoxy and didn't react but I thought it was pretty nasty.

Although I measured around 200°F at the joint before taking it apart, I think it was actually hotter because heat was still migrating from the outer surface where the heat blanket was.

Kevin Looker

_________________
I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

I'll bet 5 minute epoxy will come loose at an even lower temperature. (perhaps too low)
Thanks for doing the test and publishing the data.

Thank you! Nothing like good old science to take the mystery out of things. That does indeed look easier than removing a hide glued board.

In my experience most glues soften around 180, but higher heat should be okay within reason. I've used heat guns, and also cheap travel irons set on low. I think you did well.

_________________
"Act your age, not your shoe size" - Prince

Thanks for taking the trouble Kevin, good to know.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Yeah very well done Kevin, good going, thanks for doing this.

Only thing is, how would you go about cleaning up the residue afterwards?
Removing is one thing, cleaning up is another.
Does it re-harden after heating and can it be sanded for re-gluing?
Chemical removal (solvents?)
Just wondering.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

The only solvent I tried was acetone and it did nothing.

I'd say chisel, scrape, sand. I scraped a little in this pic.

_________________
I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

As someone who has dealt with taking apart a lot of epoxy nightmares I can tell you that all epoxies are not equal in these regards.Temp ratings on epoxies vary wildly..... Some release as low as 160 like a conventional glue and I have used some that easily would resist with 500 degrees F. I used to epoxy broken cooling fins back on motorcycle heads and they never came off. And I have seen epoxies with ratings of 2000 degrees used in industrial applications.....

West 105 is a multi purpose epoxy that can be used as a filler, a finish coating or an adhesive. I use only structural bonding epoxies for any type of glue up. I also use System3 epoxy because even the T-88 structural will only hold up to 160 degrees making it release at temps similar to HHG.

Residue cleanup is best done while still very warm with a scraper with a fresh burr. As far as solvents go it's just MEC, nothing else will touch a good epoxy, another one of it's benefits.

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Gotta love that Methylene Chloride!
My inclination would be to run the neck or fingerboard over the jointer or use a close set hand plane. Here are some other suggestions:

https://www.tedpella.com/technote_html/ ... _Epoxy.pdf

Propane torch anyone?