Hard Rubber / Gutta Percha grip repair

BC38 · #1 02-15-2020, 08:29 PM

Anybody have any experience repairing hard rubber / Gutta Percha grips?

I bought this old 32 HE and the left grip is badly cracked from having had the screw severely over tightened.

Unfortunately, it appears to have been left this way for a LONG time, and the grip material is too hard to simply squeeze the crack closed.

How would I go about heating the material enough to make it more pliable / flexible so that I can squeeze the crack closed to repair it with some glue or epoxy - without the surface getting so soft that it is easily marred?

The things I've considered are immersion in hot water, hair dryer / heat gun, remove the escutcheon and heat it in a microwave.

Anybody experienced this kind of repair who can make some suggestions and share some techniques?

6string · #2 02-15-2020, 09:04 PM

I've worked with gutta percha in other contexts.
It is known to become pliable when submersed in hot (but below boiling temperature) water. It is this unique property that makes gutta percha still today a viable polymer.
However, the hardening process is a form if crystallization. Your crack may be just as possibly caused by shrinkage. In any case be careful of chips that can easily occur while handling. Brown spots in the black gutta percha tend to be quite brittle.

Your safest bet is to heat it in hot water, slowly raising the temperature and periodically removing the grip until it becomes pliant.
Once you get the split closed to a crack, you can use cyanoacrylate glue to fill the crack. Go slow, build up the filler with repeated applications if there are any gaps. Oh yeah, it is possible to dye CA glue black, or buy it tinted black.

Jim

PS: Here's an interesting bit of trivia that I encountered while reading about the Krakatoa volcano eruption in Sumatra, that occurred back in 1883.
Sumatra was a primary supplier of raw gutta percha, with it's principle use being for telegraph cable insulation.
The irony is that Krakatoa was the first natural disaster to be known throughout the world within hours thanks to the spread of the news via....underwater telegraph wires.

oldbrownhat · #3 02-15-2020, 09:42 PM

There was an article by Gil Sengel in Issue 251 of Rifle Mag. (2010) on repairing bone horn etc. materials. He rcommended cleaning the surface with acetone, warming it slightly with a hair dryer, then brushing thinned Acraglas into the area to be repaired. Apparently Brownells has a thinner for Acraglas. Regular epoxies can usually be thinned by warming, but it reduces working time! (Ask me how I know...). He also advised reinforcing the back, which you could probably do with some thin sheet metal across the crack area. I would think that on of the thin (water-consistency) CA glues would also work and wick into the crack just fine.

BC38 · #4 03-06-2020, 03:58 PM

Just thought I'd post info on what I ended up doing to repair these old grips.

I wrapped a couple of rubber bands around the cracked section to put tension in it.

Then I dropped them in a cup of very hot water for a few minutes to soften up the rubber.

When they softened up the rubber bands squeezed the crack closed,

I took them out and let them cool down.

When they were cooled down I took the rubber bands off, pried the crack open a little and let some superglue "wick" into the crack and then put some clamps on them to hold the crack closed while the glue set.

I noticed at that point the they had warped a bit and wouldn't lay flat anymore.

So after letting the glue set up a couple of days I dropped them in a cup of hot water again to soften them back up and clamped them down on a flat surface until they were cooled.

VOILA' nice and flat and no more crack.

I then used the edge of a sharp knife to scrape away the excess glue and shave down the slight uneveness at the crack.

I'll probably end up filling in the remaining surface crack, sanding a little and then recutting the checkering lines to improve the appearance even further.

They're never going to look perfect, but good enough for the condition of the rest of the gun.