SMLE bolthead manufacturing process

I have been around machining and manufacturing for most of my life. Sometimes in my work, sometimes as a source of recreation. With my recent bolt opening on being fired problem with my No.1 Mk.3* and having read many of Peter Laidler's excellent articles on these rifle, my curiousity is killing me.

Can anyone fill me in on the machining process in the manufacture the boltheads? With the required indexing on the bolt body, the volume of boltheads that did not meet the index specification first time had to be enormous. With variations in the manufacturing process and associated parts there must have been a large fall-out of spec. parts? Any insight on the process and percentage of non-compliance parts would be appreciated.

I would have thought numbers of rejected parts were minimal.

None of the drawings carry any manufacturing process information. The great mystery is : what happened to the "process" books?

If you don't mind making a lot of swarf, you could try:

Start with a bar of steel of about 2" diameter.

Lathe turn the step for the threaded "tail".

Cut the thread, bore a basic striker hole and part off the workpiece at the approximate final length. .

Now, wind that threaded lump into a master jig and mill a couple of datum surfaces; the top and front faces of the lug would be a good start.

Once you gave a couple of these datum surfaces, the part can be transferred from jig to jig in a succession of carefully set-up machines until you arrive at a component ready to be polished and heat treated.

I’m not saying that this is how it was actually done; it’s just a quick thought.

The "Go-No Go" metrology after each separate machining process is potential nightmare, requiring a sizeable tray of precision gauges.

These precision gauges, in turn, had to be regularly inspected and re-certified by the metrology staff.

In one of Ian Skennerton's books there is a picture of the production gauging for a SMLE. It shows a substantial pile of intricate gizmos.

There was a small herd of "tool setters" whose job it was to "set" each machine and its jigs and cutting / drilling etc. tools. If a drill, reamer, etc broke, got tired or was due for scheduled replacement, these characters would bring their specialised gauges and jigs around and do the job. The machine operator had different gauges to assess the task that they, in turn, were doing. And then there were the inspectors.

These days, many CNC machining centres have integral CMM (Co-ordinate Measuring Machine) systems. After a LOT of precise set-up and tool setting, these wonderful devices not only automatically feed in the raw metal and go to work with multiple cutting tools, the CMM probes also MEASURE all critical cuts on the fly, between stages. It's not that the machines are inaccurate, but that a CNC machine so equipped, can either ADJUST for tool wear (up to a point), or trigger an alarm to tell the "operator" that a tool needs replacing / resetting. "Operators" need good programming skills.

For half a million dollars and six months training, you too could be making your own bolt heads!

Oh, and then there is heat-treating and surface finishing..........

The threads appear to be 20 tpi, given that, there is one thread every 0.050". If my memory serves me from one of Peter's articles the No.1s indexed + or - 16 degrees and the No.4s were + or - 3 degrees. So assuming the length of the area to be threaded is exactly the same length on each part, in the case of the No.4 the threads must start cutting the thread + or - 0.000414" from the correct starting point, so they end in the correct place. In the case of the No.1 that dimension is 0.002208". This is quite difficult to do on a recurring basis, making me think the percentage of failed parts on the first try were quite high. This starting point for the threads to index correctly assumes the bolt body threads start in the same correct location everytime. Even if the bolthead were made in two pieces and not one, the problem would still exist. And perhaps the bolthead is made in two pieces, I do not know.

It would seem to me that there was a trmendous amount of hand fitting to these rifles and with the volume that were made the fitting crew must have been quite large.

Beware! The thread form on a No1 bolthead is another "Enfield special" and very odd, even for them. It is, indeed, 20TPI. BUT, it conforms to "Gauge No. 675". It certainly isn't Whitworth or any "normal" thread.

You also need a dinky slotting machine to cut the "window" for the extractor; and it isn't just a simple rectangular slot, either.

And then there's the extractor screw thread; "42 TPI "Enfield Standard"".

Quote:

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Originally Posted by Bruce_in_Oz

You also need a dinky slotting machine to cut the "window" for the extractor; and it isn't just a simple rectangular slot, either.

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Bruce, I must confess, that little slot has had me perplexed as to how it was done. My first thought was perhaps a double broaching operation? I would have loved to see the entire step by step machining of these rifles. If made in the same way, I wonder what one would cost to build in today's monetary values?

As I have stated earlier, I am quite new to Enfield rifles, but, the more I look at them and try to guess what the manufacturing process might have been, the more I marvel at them. There was a lot of work put into each one. I would think that very few, if any, were actually assembled and not fitted.

Having watched the price of size 3 no4 bolt heads get to silly money I have to wonder why no one has started making them. What would they cost t make say a few thousand on a cnc machine? $150USD doesnt seem an outragious sale price. Even making a size 4 (and yes Peter I know it means the reciever is worn out).

Someone mentioned to me he was looking at getting old ones "welded up" to do the job, that worries me. Im no metalurgist but welding an 80 year old hardened high carbon? steel bolthead...oh boy.......

http://www.esabna.com/EUWeb/SA_handbook/585sa3_1.htm

"In welding high carbon or alloy steels, however, there is a danger that the weld deposit and heat-affected zone will contain a high percentage of martensite, a hard, brittle form of steel. Such welds have extreme hardness and low ductility, and may even crack while cooling. "

bottom cheeks flutter....

regards

---------- Post added at 01:12 PM ---------- Previous post was at 01:10 PM ----------

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Originally Posted by spentprimer

8><--- the more I marvel at them. There was a lot of work put into each one. I would think that very few, if any, were actually assembled and not fitted.

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Yes indeed....looking at a no4 receiver v a modern bolt action and the mind just boggles at the number of machining processes on the old stuff....

There was method to old time production madness. A major feature was the creation of dedicated machinery that did one job. That's it. Cutting threads in one pass with consistant radial positioning Cutting a slot. Maybe even just cutting a portion of a slot. Then the piece part was moved to the next station which completed the next task. Things a CNC still can't do well, if at all, in some cases.

Another example of a product not easily milled from scratch is the M1/M14 receiver, even with multi-axis CNC machines. Special tooling sometimes is the only way to go.

Consider also that many barrels also have timed threads.

yeah they had "castle" turrets on the lathes....each side of 6? or 8? held a one tool job...

Quote:

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Originally Posted by ssj

yeah they had "castle" turrets on the lathes....each side of 6? or 8? held a one tool job...

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That sort of thing is the father of CNC machinery. A general purpose piece of equipment which can be relatively easily retooled for different jobs.

I'm thinking of machinery that is built expressly to do one operation on a specific part, or maybe a few operations at once. But not good for much of anything else except for the one part that it was built to process. When production is done, then the machine is usually scrapped or rendered down for components. The dedicated tooling/machinery could be fairly small and ganged with other tools in a small area. So what would now be normally done on one machine with multiple operations and "flexible tooling" (i.e. quick change), was done at a series of stations, each performing only a single task or two.

Of course, there would be the usual lathes, turret lathes, various sorts of milling machines, drill presses, etc. which weren't special built, but did have assigned tooling for the production line.

Somewhat in between the two types of equipment would be such things as rifling machines. Good for only one task, but capable of being converted to different bores and twists fairly easily and without permanent modification.

Not quite on topic, but during the bulk of L-E production the machinery was usually remotely powered via overhead belting. So less cost there when changing out machines. Way higher maintenance requirements, though!

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?

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

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.

Quote:

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Originally Posted by 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.

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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.

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

Quote:

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Originally Posted by Son

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

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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.

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!

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.

Quote:

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Originally Posted by 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

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

Approaching near net shape forgings. Very expensive.

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!"

Quote:

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Originally Posted by Bruce_in_Oz

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!"

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Bruce, that is a little bit like a hairy cut ... the important part is what is left when done removing the swarf!

Just a thought regarding the bolt head threading operation: If the step was prone to rejects, one would think that it would be incorporated as early as possible during mfg. From the photo, quite the opposite seems to be the case. Threading the shank is one of the last operations.

If you are making one sample, you would probably do the thread first.

If you are doing 5,000 a week. doing the front bit first makes more sense.

Clamp it in a special jig, line up the appropriate datum surfaces and check the tool setting.

The trick MAY have been, especially with the "fully-treaded" SMLE types, to invert the thread cutter and run the lathe IN REVERSE. That way you are cutting AWAY from the critical bearing face on the rear of the body. Some folks also set up a tool post at the BACK of the saddle/cross-slide and run the tool the "right way' up but the gearbox in reverse, still cutting AWAY from the shoulder. Diff'rent strokes, etc.

Quote:

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Originally Posted by Bruce_in_Oz

The trick MAY have been, especially with the "fully-treaded" SMLE types, to invert the thread cutter and run the lathe IN REVERSE

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I would not be surprised that they were cut with the head fixed in place. Moving threading tool with spring retracting jaws/forming cutters that do the operation in one fell swoop. I think there's one in storage somewhere, but haven't seen it in years.

Is the thread cut and not rolled?
I have cut a few threads up to shoulders with a reversed lathe and the tool in the post upside down. I haven't had any time on modern lathes, so make do with what I have available and a few Jedi mind tricks when it comes to "creative" processes. :madsmile:

Quote:

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Originally Posted by spentprimer

Bruce, I must confess, that little slot has had me perplexed as to how it was done. My first thought was perhaps a double broaching operation? I would have loved to see the entire step by step machining of these rifles. If made in the same way, I wonder what one would cost to build in today's monetary values?

As I have stated earlier, I am quite new to Enfield rifles, but, the more I look at them and try to guess what the manufacturing process might have been, the more I marvel at them. There was a lot of work put into each one. I would think that very few, if any, were actually assembled and not fitted.

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And with all that, Lithgow managed to make the SMLE in about half the man hours if I remember correctly(?) Didn't the chaps from Pratt & Whitney make some suggestions as well?

After Canada adopted the Ross, HMG suddenly became much more cooperative with dominions wanting to set up arms factories...