View Full Version : Spot Annealing

August 30, 2005, 10:09 AM
I’ve read in Brownell’s Gunsmith Kinks about spot annealing using a 12 volt battery. The application was for tapping scope mounts on a hard receiver. I want to use this application for unbonding screws that have been permanently loctited. It seems you could control exact heat location using this method better than a torch.

Loctite’s web calls for some 250 to 400 degree F to unbond its permanent products. Does anyone know the temperatures involved with such a technique? Can anyone offer experiences using this technique?

August 30, 2005, 11:25 AM
It's much easier to use a soldering iron. Just hold the tip of the iron against the screw for a short time. The heat goes exactly where you want it.

Harry Bonar
August 31, 2005, 07:31 PM
Dear Shooter:
Some of the methods are good; I like the soldering arm with a spot of solder. However, you have changed the chemical state of the steel in the area of peak pressure.
On such guns I prefer aperature sights on the reciever, they are virtually as accurate as a scope at "normal" gun hunting distances.
I frown on some of the "professional" advice I get from Brownells; such as the 11 1/2 thread pitch on Turkish Mausers - I called the error to their attention and I never saw an alteration of that site!
Harry B.

September 2, 2005, 08:31 AM

All sorts of odd techniques abound, and some work better than others. I would suggest the battery approach is too hard to control predictably since the current will have different magnetude and heating effect with any variation in contact intimacy. I designed a contact resistance measuring instrument for spot welding machines, and I know how easily one can alter the heat peak temperatures and distribution just with variations in contact pressure. Morever, the Loctite is not a conductor, so wherever it is between the screw and the receiver current will flow poorly and not heat well.

200°F-400°F is not hot enough to anneal a receiver. A receiver that was quenched and hardened and drawn in that temperature range would be too brittle to be safe. Non-deforming hammer-head hard is about RC-50. It takes around 800°F to draw most oil-hardening alloys to that. Tempered barrels are typically drawn at 1100°F (around RC-30) to remain elastic enough to withstand chamber pressures. At the very least, any reciever you have would have been drawn back higher than 575°F to get above the upper end of the 500° embrittlement range. As long as you aren't getting tempered steel above its original draw temperature, you aren't going to anneal it appreciably.

Just put the screw driver in place and apply torque and a hot air gun until it gives.