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Broken hammer spring, or "Maybe it worked better on paper"

Posted: Mon Oct 01, 2018 10:42 pm
by WOLF257
I built a CETME from a parts kit a couple of years ago and it worked just like the book said it was supposed to... till the hammer spring broke.

Amazing how quick a rifle converted to fire semi-auto going burst fire will get your attention...

I made several interesting discoveries about the CETME, that hammer spring does a whole lot more than just make the rifle go BANG!

For those unfamiliar with the CETME, the hammer spring is also the sear and trigger spring so when one leg breaks off the spring the rifle starts doing wierd things.

The other discovery was that absolutely NOBODY makes a replacement spring and I was unable to find anything that could be effectively used as a replacement, AR-15 spring is too small and an AK spring won't fit into the trigger box.

I'm a machinist by trade so one of the guys at work said "Why don't you just make a spring?" so I did, and that turned into a real adventure.

I have a small hobby lathe and milling machine so I built a spring winding jig, it took quite a few tries before I found the right mandrel size and then I made 10 or 12 springs that either wouldn't work or failed before I got one that did work.

So here's the question, anybody got any idea how many rounds I need to fire before I can figure that spring will stay together?

I took the rifle to the range this past weekend and fired 50 rounds without a malfunction but it was only 50 rounds, which was all I had, but it seems to me that 50 isn't really enough to call it a success yet.

I know I can replace the trigger group with a an HK unit but I don't have the money right now and .25 cents for a piece of wire is a lot more economical.

For those that have read this far, thanks for letting me rant.

Jim

Re: Broken hammer spring, or "Maybe it worked better on paper"

Posted: Mon Mar 18, 2019 6:24 pm
by FamilyFirearms
Brownells sells spring wire in several different diameters that should do the trick and last.

Re: Broken hammer spring, or "Maybe it worked better on paper"

Posted: Mon Mar 18, 2019 7:19 pm
by Hammerdown
RTG parts has new hammer springs for the CETME under "more rifle parts". Just checked and still in stock.

Re: Broken hammer spring, or "Maybe it worked better on paper"

Posted: Wed May 22, 2019 11:15 pm
by OLDGUNNER1
Spring Making – It doesn't have to be too mysterious and like anything it is easy once one knows how. One can watch the videos and see where there must go, but I can offer a way where one won’t have to go to the trouble of buying the particular size of music wire. A while back I needed to make a spring out of # 9 wire and I had to buy a 60 foot roll of music wire and made a heavy duty winding tool....But for other small little springs I would do it this way.

For coil springs find an old spring, or new one, with the size of wire that I would need and enough wire to make my spring. I will take a chance that the original maker used an appropriate type of steel. I will take my torch and anneal the wire of the spring to dead soft. I will unroll the spring and this should give me a piece of just plain steel wire. I wouldn’t bother using a lathe but just wind the wire around anything the size of the spring that I would like. I would grind the ends of the spring to whatever design I would like. Now I would proceed in returning this to a ‘spring’. This can be done in a variety of ways...anything to heat the item up to about 700 degrees Fahrenheit...quench it and this will usually give me a usable spring. But actually this ideal temperature varies with the alloy but that would usually be unknown. I would wrap it in aluminum foil just to get a uniform heating. I find that my LEE Bottom Pour lead melting pot can easily bring things up to temperature, within limits of the unit. I bought that pot when they first came out. It sure has surprised me that it has lasted as long as it has.

I would use a thermometer to adjust the temperature. Actually mild steel or high carbon steel can be used but I would think that the original spring was actually made of okay wire...I will get a spring. And flat or leaf springs can be made the same way. That is make a spring the shape desired and heat-treat to around the 700 degrees.
And my melting pot makes excellent charcoal for my Black Powder. I think, I think that most make their Black Powder with too much burnt wood. I think that ever bit of wood ash in one’s BP degrades the quality. My BP does not smoke like the commercial BP.

Oh, and the fellow wondered how long the spring will last. I don’t think that any home-made spring will have a well defined life time. And typically ‘any’ metal spring will start to work-harden the first time it is sprung and it will break whenever it’s time has come.