I had several 64-66 (and 69-70) exterior door handles re-chromed. They are made from pot metal. The rear tapped holes on two (the driver's side naturally) were damaged, either by disassembly, the plating process or both. The hole in question has a 10-24 thread and is about 0.60 inch deep so if 1/8 to 3/16 inches of the threads are damaged, it increases the chance that a strong pull will strip the entire thread, leave the screw in the door and make the handle useless. There is not enough material on the handle to tap deeper, tap a larger hole or to use a heli-coil for repairs, so an alternative method was sought.
Enter JB Weld - will it work. Sure, one time. I can put some JB Weld in the screw hole, attach the handle to the door and will never be able to remove the screw again, JB Weld is that good. A method to use an appropriate screw to reform the damaged threads and remove the screw without damaging the threads is required. In my situation, there was enough existing damaged thread to provide a base for the JB Weld to adhere to.
What is needed is called a "release agent". It is used in the molds to make, for example, consoles, or even die cast pot metal door handles, to facilitate removal of the item from the mold. The problem is what to use as a release. Some release agents can affect the material, JB Weld in this case, so that eliminates most petroleum based materials, acetone, thinner, etc. Other considerations: availability - needs to be handy; price - cheap; non-toxicity - can't pour the left-overs down the drain; ease of application - spray would be nice, brush-on would be acceptable.
My test set-up consisted of a leftover piece of 3/4 inch thick hardwood from a wine rack project. I drilled several appropriate sized thru holes and tapped them 10-24. Then I destroyed about 1/4 inch of the threads at the top with a 0.190 inch drill bit thereby creating a similar situation to the door handle problem. My intent was to thread about 1/8 inch of the screw into the tapped hole, apply JB Weld (with a toothpick) to the next 1/4 inch section of thread, screw it in for the 1/4 inch and let the JB Weld set overnight. By screwing in the screw first, I hoped to match the new threads with the existing. I applied the release agent and waited a day, then applied the JB Weld.
That was yesterday, today was a good day. I tried two different release agents as I only had two 10-24 screws available for the test. To release the screw, I did NOT immediately back it out, but screwed it in a full turn or so, then I backed it out.
The first test did not work. The JB weld came apart, some was on the wood and some on the threads. The release agent was a special Teflon based lubricant called Tri-Flow (made by Sherman-Williams, it may no longer produced but it was handy).
The second test used - (wait for it) - Pam. Yup, Pam vegetable spray, and it's cholesterol free.
I will repeat the tests today.
Jim
