Marlin locking block

[DeanoBeanCounter]

OK! :???: Somebody tell me if it's to dangerous or is it's safe to do. My Marlin model 93 has a worn out lock block. Can't find a replacement anywhere. I want to build it up by torch. I can't electric weld but I can torch weld and braze. I guess the lock block is hard steel and as far as I know only mild steel can be tempered. But if tempering needs to be done then I have what everybody else has accesses to, being water of all temperatures, fresh and salt water, used engine oil. OR, is this something only a gun smith can do? All comments are welcome. :confused:
Deano

[crazy mark]

Personally I wouldn't attempt this as you can make it brittle which is worse than to soft. Many years ago in metal shop I made a punch and hardened it. When dropped on the floor it actually broke into about 4 pieces. I was making pin punches for specialized chains in a mill for my Dad. Next time I did a lot better. Different people will have different opinions but remember it is you face close to that part. Mark

[leftiye]

Deano, You might consider leaving it soft, and case hardening it with Kasenite. That would avoid any brittleness issues. If the block simply fits between the bolt and the frame then hardness isn't an issue in its strength. If it has to bear against bending (as opposed to compression) forces, then I think you may be SOL. Your torch weld will definitely destroy any temper, and then the problems with retempering will begin. The gas welding will mess up your part by causing warpage, and lots of scale too. Have you tried seeing if Gunparts Corp. (Numrich Arms) has a replacement for your part?

One other method you might employ if you only want to build up a surface a few thou is to find a machine shop that has "metallizing" equipment. It is a torch that powdered metal is added to the flame, and this applies it to your surface. Probably a plasma torch.

Most standard welders be they torch, stick, or MIG will bugger up a part big time, and unless it is a simple thing to file them back to size and shape are therefore more trouble than they are worth (not to mention that they apply mild steel). I have when it's just a "pop" in a spot used a mig to build up metal on some parts. And as mentioned, it was a non critical part as per strength and easy to form to shape.

[BABore]

Coating it with powdered metal may not work well either. I've done it a few times on machine tool parts. You typically have to preheat the part to 400-800F before applying the torch/powder. Likely to anneal the bolt. How much is it undersized? you may be able to send it out for titanium nitride or iron nitride coating. A typical cutting tool usually only get a few ten thousandths of coating. You may be able to specify a heavier coat. Worth a look cause it won't change the parent material hardness and the coating will be very hard and abrasion resistant.

[Frank46]

Don't know if this would work in your case, but have you given hard chrome plating as a solution to your problem?. Don't know if it would cause problems with hydrogen embrittlement but maybe some of the other members here would have more to say on that subject. Frank

[Bret4207]

Depending on how much it needs to be built up, you could try electroplating. I think you can add up to .005 or maybe a bit more. Otherwise, make a new one or do a web search on parts houses and call or email them. Someone probably has one kicking aorund someplace.

[BABore]

I just checked, this morning, with a tooling shop that specializes in custom cutting tools. Flash chroming can add up to 0.005". Hard chroming can add 0.010" with a 10 hour steeping. You can go another 0.010" on top of that with another 16-20 hr soak. Both can be ground in to size as long as you leave a few thou. of chrome. I guess excessive pressure can cause flaking of the chrome. I made an educated guess and told them that the locking bolt was likely SAE 4140, heat treated, then drawn back to 35-40 Rc. The guy said the chrome should be able to handle that ok. Probably best to get all the pertinent facts and figures and contact a tool coating shop. Most have a Rockwell test machine, so they can check your bolt, and you'll have to tell them how thick a coating to apply or grind back to.

[Bret4207]

Used to be fairly common to see locking lugs on Win43, Savage 23, Savage 99 bolt built up by electroplating. I should think it would still work.

[Buckshot]

..............I would think (but I don't know) that the locking bolt very well would have been surface hardened so it would have a softer core to stand the shock. This is exactly what Mauser did as their actions were made of low carbon steel and then wear and pressure areas were selectively surface (case) hardened.

It sounds to me like the hard chroming would be the hot ticket. See below:

http://www.fototime.com/FEB48295FDD2804/standard.jpg

These dies I made for my Comblain were made from the front McPherson struts from an '87 Chevy Celebrity. The car had 178,000 miles on it when I changed them and as I was the 2nd owner, I'll bet they were factory originals. Thats a lot of up and down!

I thought they were just highly polished, but when trying to thread them the high speed steel just turned blue and squeeled. I had to use carbide to cut the threads. Then I found out they were hard chromed. All other work turning on the inside was done with common HSS. That hard chrome was HARD stuff I kid you not!

................Buckshot

[DeanoBeanCounter]

Thanks everyone. It does look like that hard chroming is the best bet. I'll let you know what I end up doing.
Deano