Machinists Guide To The Thompson - A Technical Review

[reconbob]

This won't take long. Consider the background of this book:

 

A "mechanical engineer" has "access" to two used M1928A1 Thompson submachine guns.

He has no prior experience with Thompson submachine guns. He has no experience machining

or manufacturing Thompson submachine guns or parts. He disassembles the guns, measures

the parts to the best of his ability, and makes CAD drawings. No parts have been made using

these drawings. No guns have been made using these drawings. He finds a publisher who is

willing to publish this body of work without checking any of it and it is sold as a manual and

guidebook for manufacturing a working M1928A1 Thompson submachine gun.

 

Does this sound like a recipe for success? Of course not. And its not. I guess we can't

blame the author - he's just an enthusiast who thinks he knows everything and was given

a forum for his pet project. But the author knows so little, he does not even know that he

doesn't know.

 

Obviously the author (in New Zealand) and publisher are not aware

that here in the USA original ordnance drawings for Thompson parts are readliy available to

check the drawings in the book. Most of the dimensions in the book are wrong. Even worse,

the author has applied absurd tolerances to his work. Every three place decimal such as

0.125" has a tolerance of +/-0.01". (0.02" total) Try this and virtually none of

the parts would fit. As just one example the tolerances for the rails on the receiver and trigger

frame are very specific so that they properly interlock and slide together freely. On the

original ordnance drawings not one of these tolerances is +/- 0.01".

 

Another example - his drawing of the barrel does not even have the barrel thread, does not

have the chamber dimensions and instead has a drawing of a fired .45 ACP cartridge casing.

To use as a guide. Starting to get the idea?

 

The book is filled with other nonsense:

 

- it appears that the author thinks there is a slot machined into the left side

of the receiver 0.03" deep for the ejector to fit into?

 

- make the round bolt head and the rectangular bolt body separately, then just

weld them together. Same with the actuator - make the cocking knob separately

and weld together. Sure, no problem.

 

- harden the receiver to between Rc 34 and Rc 54.

 

- harden the bolt to Rc 34 to Rc 54....(on ordnance drawings the minimum hardness

for the bolt is Rc 62.

 

- "barrel must be fitted with heat.Heat upper receiver to 200 degrees Celsius and

chill barrel in freezer before fitting"

 

I could go on and on with this, but I don't want to appear to be piling on. Again, I

don't blame the author - he just doesn't know any better. From a technical standpoint

this book is useless.

 

 

Bob Bower/Phila Ordnance

 

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Edited August 27, 2012 by reconbob

[Gio]

Bob,

 

I am by no means a machinist but I thought the same as you. I don't think that he took the barrel off the reciever the short time I had my book I don't recall seeing a pic or scan of just the barrel.

 

I am like you I blame the publisher for not seeing through for what the book is.

 

It would have been a great book if the author had used a prestine example of a 21 Colt and just took pics of the part and made CAD drawings of each and told hardness and metal used.

 

Oh well live and learn.

 

Frank

[woodsy]

As a New Zealand gunsmith for the past 43 years, and a specialist MG collector for the past 30 years, I can assure you that the author is not a part of the knowledgable NZ firearms community. He is an aspiring politician for the Green Party (need I say more?) and has 18 years experience as an 'engineer'. I suspect this experience is in an office rather than a workshop! Whilst the author clearly has inflated views on his own ability, clearly the publisher is not any better!

 

I have owned 2x 21A's, 5x M1928A1's, and an M1A1 over the years. I still have my ex IRA 21A (#750) and a 'Tommy Gun' marked Savage M1928A1, plus some accessories.

[Piep]

Bob

Any of us that bought the book knew after we received it that this would be the final analyses and I agree

with you, IT'S worthless....

I for one will be putting mine on my table at the next gun show.

Thank you for all the tech info that you share with us on a regular bases.

 

Bob

[RoscoeTurner]

I've learned from experience not to rush out and buy the latest gun book that might interest me without seeing it at a show first. There are a lot of good books out there but a lot of junk too.

[easycompany104]

Great topic with very useful information and glad it was shared among the members. I am a machinist and have understood every detail mentioned. Basically someone would turn useful parts into paper weights by machining incorrect tolerances. Also a safety factor here which could result in injury.

[reconbob]

The more I read the worse it gets -

 

- The author drew the ejector as an unthreaded rod that slides straight

into the ejector hole and is retained in place by being seated in an oval shaped

slot in the left side of the receiver. I really think he does not know that this part

unscrews from the receiver. If he does know, and he is just dodging having to deal

with the thread, I can't see any thing to prevent this "new" ejector from simply falling

out of the receiver since it is not retained by anything.

 

- in this book the buffer pilot hole in the back of the receiver is dimensioned as

being on the centerline of the bore. This is wrong. The centerline of the buffer pilot

hole is 0.1" BELOW the centerline of the bore. If you drill the hole where he tells you

to the buffer pilot will not fit.

 

- the author draws a 3/8 radius at the rear corner of the 45 degree angle cuts for the

bronze lock. This is what the bad West Hurley receivers have and such a radius is

not present on original drawings or guns. Perhaps the guns he examined were damaged

and he thinks they are supposed to be this way?

 

- the breech entry - where the square face of the front of the bolt pocket meets the

round hole for the bolt head - is 90 degrees in the drawings in this book. On REAL

guns that work this surface must be counterbored/relieved to accept the radius on the

front of the bolt body or the bolt will not close.

 

I think its time for the publisher to weigh in on this.

 

Bob

Edited August 28, 2012 by reconbob

[kilroyjones]

 

- "barrel must be fitted with heat.Heat upper receiver to 200 degrees Celsius and

chill barrel in freezer before fitting"

 

Bob Bower/Phila Ordnance

 

 

 

WOW. That one line alone tells me everything I need to know about the man's lack of knowledge on TSMGs.

[mnshooter]

Hasn't even arrived yet, and I'm done reading it.

I'm hoping that like a really bad movie, there can be some traces of entertainment.

 

This will be the "Plan 9 From Outer Space" of gun books.

[Edo]

Here I go again!

 

I just got the book right before I posted my questions as to the credentials of the author. When I worded my post I was being diplomatic as I after reading the book cover to cover (as I do with all Thompson material I get my hands on.) I decided this guy didn't know S..T from Shinola and the book was certainly not worth anywheres close to what I paid for it. To you who said you would put it on your next gunshow table I hope you meant to warn the public about it. To sell it to the unknowing would be akin to the the sins of the publisher and writer. I have the original prints of the forward grip mount on the TSMG and the one on page 95 of the book in question shows the mounting bolt hole to be straight not angled and you can go on and on about how much BS is in this book...P.S. how about the crappy example of a Thompson he used in the photos? It has a cracked stock and two common screws on the side holding it together.

 

Edo

[mnshooter]

The last page is the best.

He suggests testing in a secluded area, (-a convenient mountain range?) and staying under cover to avoid the "eye in the sky".

No convenient mountain range; well, make a silencer from a pop bottle and test in your basement!

And remember, "don't tell anyone".

 

Beyond unbelievable.

 

And yet, my copy remains unclaimed at half price. Just can't understand it.

Edited September 3, 2012 by mnshooter

[RoscoeTurner]

Looks like the author has disappeared from the forum as well.

[mnshooter]

The last page is the best.

He suggests testing in a secluded area, (-a convenient mountain range?) and staying under cover to avoid the "eye in the sky".

No convenient mountain range; well, make a silencer from a pop bottle and test in your basement!

And remember, "don't tell anyone".

 

Beyond unbelievable.

 

And yet, my copy remains unclaimed at half price. Just can't understand it.

 

SPF

[prebans]

Hello:

 

First, I apologize for dredging up a very old topic. This thread came up in a Google search.

 

I am looking at writing a similar book for a different firearm. My goal is to include drawings for every part of the firearm to allow both owners and SOTs to fabricate replacement parts. (Spares are next to impossible to locate.)

 

Avoiding publishing useless garbage is vital to me. What suggestions would you offer to help me avoid this author's mistakes?

 

PS. If anybody has a used copy they want to be rid of, I'd like to see what this author wrote so I can avoid repeating the same mistakes.

Edited November 30, 2020 by prebans

[reconbob]

If you are writing a book for a different firearm, unless that firearm

is a Thompson i think you are in the wrong place, as this is the

Thompson Submachine Gun Forum.

 

Bob

[prebans]

If you are writing a book for a different firearm, unless that firearm

is a Thompson i think you are in the wrong place, as this is the

Thompson Submachine Gun Forum.

 

Bob

 

I am aware of that, Bob. But given that this book could be similar to the book you cited above, I want to avoid making the same sort of mistakes.

[TD.]

https://www.gunshowbooks.com/cgi-bin/webc.exe/st_prod.html?p_prodid=GS430024&sid=VR7NmIAp

[Waffen Und Bier]

Maybe it was written for those wanting to make non firing dummies like what some of the guards had on Hogan's Heroes.

[MG08]

Hello:

 

First, I apologize for dredging up a very old topic. This thread came up in a Google search.

 

I am looking at writing a similar book for a different firearm. My goal is to include drawings for every part of the firearm to allow both owners and SOTs to fabricate replacement parts. (Spares are next to impossible to locate.)

 

Avoiding publishing useless garbage is vital to me. What suggestions would you offer to help me avoid this author's mistakes?

 

PS. If anybody has a used copy they want to be rid of, I'd like to see what this author wrote so I can avoid repeating the same mistakes.

I have remanufactured small parts for obsolete MGs, ( Maxim, hotchkiss, Lewis) when the only source of data is reverse engineering from original parts. As an Engineer, I hire people who are experts in machine tool and part manufacture to assist . I engaged companies with the technology to determine exactly what the old materials used were. In some cases, those materials are no longer available.

 

Well, here are some suggestions .

Do you have any (ANY) manufacturing and engineering background in machine tools or machining ? if no, stop right now.

Have you looked around and asked around to see if original drawings are available? If no, go do so.

Do you have several of the guns as examples (Live complete guns not parts kits) to measure, evaluate and see how the parts were originally made ? If no, stop now.

 

Most of the military arms were manufactured with engineered tolerances for clearance, manufacturing capability, function, under most conditions and to allow for interchangeability of parts. Parts and tolerances were changed over the run of the gun and spares - early parts may or may not interchange with late production parts. the material used for a part can be critical, not only for ease of manufacture but for reliability and safety - so the gun does not disintegrate in your hands while firing it. ( I have seen a 1919 browning come apart due to using a mild A36 type steel for the side plate instead of the specified oil quenched 4140. The plate stretched and fractured )

 

Not trying to be a Debbie downer, but so as to not waste your time and other's, the book described in the OP was a waste of time and POS attempt to generate $$. Machining parts for guns is not just a cut, grind, weld to fit proposition. the original book as described above gives a good indication that the author had absolutely no knowledge of engineering drawing, designing or manufacturing processes. There are all kinds of good original copies of gun drawings on the interweb as examples of what a technical drawing should look like. You could start there -