SMLE bolthead manufacturing process

[Peter Laidler]

The indexing of the threads to the bolt was that when the load is imparted onto the bolthead, it is taken down the bolt head down onto the shoulder and then onto the bolt body and NOT the thread. That's why we only permit a small degree of bolthead overturn.

Boltheads....... If they can build-up or successfully re-metal MGC king-pins to oversize and then grind to spec size, with all the load and safety factors that that entails, then remetalling a simple bolt head is simplicity itself. And therefore talk about remaking them is quite beyond me! It seems to me that there's a world shortage because people simply a), collect them because there's a world shortage. b) collect them just in case there might be a world shortage. c) collect them in case they ever need one in the event of a world shortage. d) collect them because they've got a set of (probably incorrect) gauges and insist on over CHS'ing their rifles.

Why stop at a No4 bolt head? Why not lets really cater for the truly worn out stuff and go for a No10 bolt head and all imbetween?

[Son]

Here's a couple of pictures taken of a display board showing some of the steps SMLE components go through from (in most cases) casting or forging to finished article and assembly.
First, the whole board, (photographed at an angle to eliminate glare) and then a close up of the bolt and bolt head.

Attachment 46739

Attachment 46740

[Bruce_in_Oz]

Good point, Peter.

Yes, it is perfectly feasible to "build up" a bolt head using hard chrome or vapour deposition.

However, the fact that a "longer than normal" range bolt head is required would definitely indicate that something else is amiss.

1. The bolt body is worn beyond tolerance at the locking shoulders.

2. The body (receiver) is worn beyond tolerance at its locking shoulders.

3. The receiver is STRETCHED or distorted. Possible but rare.

4. The barrel is defective. With the SMLE breeching up on the internal breech ring, this is unlikely. It is "possible" on a No4 which breeches on the receiver (body) front face.

Just a note on "wild" machining: think about what sort of "creative" tooling was used to cut the RADIUSED cartridge lifter guide rails inside the receiver of the M1 Garand. Then think about how all of the incredibly precise machining was preserved when that odd-shaped chunk of 8620 steel went through heat-treatment.

Then, if you ever get your sticky paws on a Mauser C-96 "Broomhandle" pistol, check out a 19th century design that is like a jigsaw puzzle made by machinists with a sense of humour.

[spentprimer]

The indexing of the threads to the bolt was that when the load is imparted onto the bolthead, it is taken down the bolt head down onto the shoulder and then onto the bolt body and NOT the thread. That's why we only permit a small degree of bolthead overturn.

Since the load needs to be on the shoulder of the bolt head and not on the threads, the amount of backlash in the threads is what would provide the + or - degrees of over or under turn of the bolt head to index correctly. If memory serves me one of your articles indicate the No.1 had a + or - of 16 degrees and the No.4 had 3 degrees. Granted, the two rifles are of different designs, given the difference of 13 degrees in indexing tolerance, was there a problem in the field that warranted this change? was the manufacturing technique improved to be able to hold this tighter tolerance of the threads? did the thread design change? One would think that tighening the indexing specification would cause more failed parts for this reason.

[breakeyp]

I would think that the thread would have to start at the same place in the bolt body as well.

[browningautorifle]

Here's a couple of pictures taken of a display board

I just love to see that ultra rare stuff now. You can stand there and follow the machining in your head for hours it seems.

[Peter Laidler]

You're right Paul. The bolt is also indexed too! You can just see where this thread is going can't you......... Along the road to mechanical perdition!

[breakeyp]

Peter my education came with some sample parts that Springfield Sporters had on hand. They had bought and quickly sold the Mauser manufacturing plant in Santo Domingo. Mr. Rogers kept a partially manufactured bolt extractor for the Mauser bolt rifle. A round bar of steel about four inches in diameter was chucked and six or eight (I can't remember) extractors were cut from the same billet. They were attached to each other and in the last steps the little webs holding them in place were cut off.

If you want to see the full steps to produce the US M1903 Springfield, there is a book with beautiful sketches of each machining operation to make the rifle. Title was US Model 1903 Springfield as was republished by Wolf printing Co. In WWI, the US contracted with Machinery's Handbook publisher to make the book that was to be used by companies to determine their quotes to build the rifle. The detail is staggering. I think the title is right===If anyone needs more detail I can go look the books up.

[jmoore]

Here's a couple of pictures taken of a display board showing some of the steps SMLE components go through from (in most cases) casting or forging to finished article and assembly.
First, the whole board, (photographed at an angle to eliminate glare) and then a close up of the bolt and bolt head.

Attachment 46739

Attachment 46740

Very useful! Doesn't divulge nearly all the secrets of production, but would provide lots of clues.

Approaching near net shape forgings. Very expensive.

[Bruce_in_Oz]

Forging is an "oldie but a goody".

The process of belting a hot piece of steel into a general shape imparts some interesting "alignments" in the internal crystal structure. This is a good thing. Sometimes it takes several re-heats and a couple of sets of dies to achieve the final shape that is then finish-machined where needed. Think about all of the "drop-forged" wrenches etc in your trusty toolbox.

Apparently the constant, regular pounding of the big forging plant at the old Lithgow factory could be heard and felt for quite a distance around when it was running.

The receiver body of the Bren started life as a forging. It takes a very big hammer to bash out a shape that big.

Lee Enfield receiver bodies started out as a vaguely recognizable forged blob. Then the machinists cut away everything that didn't look like the desired end product.

Out of necessity, a lot of "high-tech" found its way into the gun-making business during WW2.

There is a famous, possibly apocryphal story about all of this:

During WW2 GM engineers went to Colt to look at the works before taking up a contract to make Browning-pattern machine-guns.

At the end of the tour, when asked for some thoughts, the GM engineer said something like: "You guys don't make guns, you make swarf; guns are your by-product!"