Investment Cast Receivers

[Paladin601]

Just curious for some of you Tech guys.

 

What do you think the feasibility of a Thompson Receiver that is made with new technology:

 

1. 3D scan of an existing receiver.

 

2. Making of the Mold of receiver using 3D printing.

 

3. Investment cast of the Receiver

 

4. Clean up surfaces and true them using a Milling center.

[dalbert]

I'm sure Reconbob will weigh in here, but I think your tolerances might not be correct if you did this. There are 2 books out that pretty much looked at this from a reverse engineering standpoint, and both volumes were berated on the board for their assumptions made using measurements of existing Thompson parts. I think making a cast of a receiver is pretty much the same thing.

 

That being said, the Chinese were certainly successful in reverse engineering the TSMG, probably in the 1920's.

 

David Albert

dalbert@sturmgewehr.com

[Paladin601]

I am just so fascinated by 3d scan and the 3d printing and what we can do with it. Probably so, on the tolerances being to great.

[buzz]

Don't forget that cast steel is not very strong.

 

The material properties of steel like the strength and toughness depend a lot on how the steel is cooled and worked because it has a crystal structure.

 

The Thompson receiver is pretty beefy for such a low powered cartridge but I'm guessing there are spots where a casting would be trouble.

 

Setting all that aside, my choice would be to just buy a receiver from reconbob.

 

It's very hard to beat the efficiency of just paying an expert to use his expensive equipment to do the work.

 

if I was going to start some kind of hobby production of an item, I would pick something that's not being made by anyone else, where I could make a batch and sell the extras on gunbroker.

 

I think somebody turned out a batch of reproduction reising compensators once, apparently they are always blowing the fins off. I would do something like that.

Edited August 28, 2014 by buzz

[GUNGUY45]

For low production, 3-D printed injection tooling works, but the foundrys I deal with hate them.

The cost to build a proper mold for investment casting a Thompson receiver wouldn't be cheap.

Demand just won't support it.

I think Bob, & Doug are doing it the right way, machining from bar.

I quote Investment cast tooling for a living.

 

Pete

[Paladin601]

Thanks everyone.

[james m]

I'm wondering if some of the new aluminum alloys such as used in AR15/M16 production would make more sense today? These receives are certainly tough and wear resistant.

Jim

[reconbob]

I have some knowledge of what they are now calling 3D printing, but I would certainly not admit to

being an expert. I get emails all the time asking if I want to attend free seminars on the process But I have

yet to attend one.

I do know the basics - instead of a 2D flat sheet drawing, computer technology of today enables what

they call a 3D model. This is a three dimensional file that can be viewed, rotated, sliced to "look" at 2D

views etc. This 3D model can be imported into a system which will create an actual solid model by "printing"

the piece by slicing it into very thin layers, printing or rendering them into a solid, and stacking them together

one upon the next resulting in a finished piece.

As I said I am a little behind the times but the way I saw this done was to have a liquid pool of a resin that

would be hardened by ultraviolet light. The machine would shine the UV light on the pool hardening the surface

into the first layer, then one after another succeeding layers were hardened as the earlier layers sank down into

to pool. I believe the machine I saw could do layers 0.01" thick so a 1/2 inch thick piece would be made from

a "stack" of 50 layers. Now - this was almost 20 years ago and I know they have come a long way.

One note - it is hard to believe but back when the Thompson was made - including WW2 - engineering drawings

were drawn by hand, and also copied by hand by putting a sheet over the original and tracing it. If you look

at the title block of any WW2 or earlier drawing you will see blocks for "Drawn by", "Checker", "Tracer", etc.

It was commonplace for factories to have large well lit rooms with hundreds or draftsmen where this work

was done.

Investment castings usually do not have the same tensile strength as forgings or parts made from bars which

are rolled because rolled/forged pieces have strengthened grain structure that Buzz alludes to. However, investment

castings can be plenty strong for gun parts. M1903A3 Springfield, M-1 Garand, M-14. and BAR receivers have all

been investment cast (by aftermarket manufacturers) and Ruger has led the way in making the major firearm

components from investment castings.

I am sure an investment cast Thompson receiver would be strong enough but I do not know if you could get

a piece that long and thin to come out straight. Its an interesting idea....

 

Bob

Edited August 28, 2014 by reconbob

[cocoabill]

Sounds like the 3D printed version would make a fine and dandy display receiver right out of the printer.

[Paladin601]

I have talked to people in the defense industry who say they are working on 3d printing in metal, but will not say what type of metal or how strong it will be.

 

The real problem is that if one can be made, the government would take it away.

[buzz]

A cast steel receiver would be less strong, less hard, more porous, more prone to fatigue cracking, and less ductile than a receiver made from bar or a forging. By a wide margin.

But the question is this - was the original design of the receiver conservative enough that a receiver made from weaker metal would still work OK?

The only way to find that out would be to actually cast some receivers and then torture test them to failure and see how they hold up compared to a forged receiver.

We can already partially answer the question because the West Hurley guns were made from a lower grade steel than the originals and it can be seen that they do not hold up to normal use as well as the originals.

So you could say from that test that the Thompson receiver design is not conservative enough to tolerate a lower grade of metal.

Of course when a west hurley receiver cracks, you don't know if it's because the gun was subjected to abuse or the out-of-spec dimensions of the receiver made it eat itself.

Edited October 27, 2014 by buzz

[buzz]

Aside from all that, go for it. Might be a fun project.

[mnshooter]

Although I really do enjoy this interesting technical discussion,

after someone gets all this figured out, and makes 3D or IC receivers, who are they going to sell them to?

Anyone who wants a proven first quality Dealer Sample receiver can order one today from Bob,

or buy a display receiver from Doug, and do some relatively simple milling.

 

Now, printing your own dummy display gun -that would be fun. I want the program for C drums too.

Edited August 29, 2014 by mnshooter

[Paladin601]

I was looking at Pine Tree Investment cast (Ruger) you can just about have any metal, hardness a person could want, and I am sure they have all the probs list solved. Ruger seems to have a limit of 12" in length on their IC . but there are many more casters out there

 

But like it has been mentioned, who would be the market, I would be extremely small. Pricing would have to be less then what Bob and Doug ask. The only benefits I can see is less metal and reduced time at the mill. The bolt area could remain un touched.

 

Receivers could be done in a 10XX, 4140 and Aluminum. Trigger frame could be done as well

 

And start up money, impossible to get, since most of the banking industry is against the firearm industry.

[reconbob]

On what do you base your claim that investment castings are so far inferior to forged or rolled steel?

Maybe if you were conducting some type of ultimate tensile strength test there would be a big difference.

But if the tensile strength of a forging is, say 60,000 PSI and the tensile strength of a casting is 40,000 PSI

and the load you are applying to the part does not exceed 20,000 PSI it doesn't matter.

Most M1A receivers from a variety of manufacturers are investment cast. There was and is no concern

of all of the failures you describe.

 

Bob

[Paladin601]

Who me, Bob?, IC in steel or aluminum is just as stronger, has good grain structure as well.

[reconbob]

I just remembered that a few years back when I was setting up the 100% machined M1928A1

receivers I machined one from wax. They sell blue wax blocks for testing programs. The reason for the

wax is if you make a mistake the wax is so soft you don't break an expensive cutter. So when all

was ready I ran a piece of wax thru all of the fixtures and set-ups and ended up with a 100% machined

M1928A1 receiver made from wax. I put it up on Gunbroker figuring that it would attract a lot of interest

and that I might even machine more of them ,but it was a total dud. Very little interest and it sold for so

little there was no point in making any more of them.

 

Bob

[buzz]

You'd really have to test the cast receiver to be sure there was enough meat in it to make up for the lower strength.

 

It's worth considering the difference, because there is a significant reduction in the strength of a part if it's cast vs forged, like on the order of 25% lower tensile strength and 35% lower fatigue strength.

 

Also castings have inclusions and porosity you don't get with forgings. I had a cast trigger snap right in half on a competition AR setup, there was a big imperfection inside the cross section of the trigger.

 

 

I wonder if there would be any buyers for a machined plastic receiver for people to stick their parts kits onto for display.

Edited August 29, 2014 by buzz

[Paladin601]

Buzz, you are talking regular casting as opposed to investment casting.

 

IC is very advanced now, used in a lot of aerospace fittings and components, most of the Aluminum suspension parts on automobiles are made by IC, and those take a lot of pounding.

 

with the right tooling I would think on could make a receiver out of Carbon fiber for the Thompson, like they do for the AR's.

 

 

But like it was said, who would buy them, unless they were $150 cheaper then Philly and Richardson

 

And the Best/easiest to do this with I feel would be an M1/M1A1

Edited August 30, 2014 by Paladin601

[buzz]

I'm sure you're right.

 

It would be interesting to see the various receivers tested to failure.

Edited August 30, 2014 by buzz

[wwiifirearms]

Marty Pearl made investment cast M1A1's in the 1980's. They were cast and then finish machines. I have one and I don't see any issues with the quality of the casting. Some of the machining isn't 100% to spec(which is why I'm on PK's list). I think the tolerances are more related to the fact it was a $400 gun at the time, than the process. They just were making them fast and cheap.

[anjong-ni]

Bob, have you tried to run a block of "Clear Lexan" through your CNC machinery, and produce a 100%, see-through engraved receiver?

I'll take one...Phil

[Paladin601]

Bet that would be hard to machine and keep transparent

[Paladin601]

Just watched a Youtube Video from Jay Leno's Garage and he is making parts for his cars as I said scan-print- investment cast. Even intricate parts.

 

Now I just need the money.

[Jrickard81]

No one told Ruger that cast isnt strong enough