I recently came upon a complete-enough set of drawings for the M1928 variant of the Thompson SMG online.
My intention is to use these drawings ( with the least number of modifications ) to make conversion parts for an airsoft M1A1.
Definite parts are:
Cutts Compensator (see below)
Finned barrel (On hold until I get an M1A1 to copy the mounting from)
Other parts may be added as my skill and/or machinery improves.
Those possibilities include:
Lyman adjustable rear sight (likely - I have a set of drawings)
M1928 upper receiver (I'd need a proper milling machine for this - Not a realistic prospect just on my lathe)
The photo shows the Cutts compensator I machined from aluminium.
The changes from original spec are the material, the dovetail angle and the slot cutter diameter used.
Still have the blade sight to finish.
More to follow as parts are done.
Nice work. If you do manage to make M1928 receivers, there's definitely a market for them.
When I want your opinion - I'll tell you what it is!
The hardest part about the receiver is the ejection port. The drawing does give some cutter info, but not really enough to get my head around - should be easier to grasp when I get one in my hands. The other issue is my lathe is OK for the limited milling involved in the compensator and the smaller parts, but the receiver is way too big.
It's entirely possible my first may not have a properly cut port, if at all. 
Surely you could get around that minor detail though, the rest of your work is very impressive
I'd definitely say it would be worthwhile trying to do the reciever. With the CYMA M1/28 on the way there may be a few people looking to convert them into a proper 1928. I look forward to seeing more of your work though, the compensator certainly looks good. 
I'm impressed, certainly would be interested in a compensator
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Thanks.
This one took a couple of days to do. BUT, this is really the first thing I've made on a lathe in 20 years! A lot of the time was "re-learning" techniques. There was time spent working out how to make it with the tools I have. I made a threaded arbor to hold the thing while it was being machined, and I had to make a new slitting saw arbor long enough to do the slots. I also wasted a lot of time trying to workout why the thread didn't match the arbor before I realised it just needed deburring. 
The blade forsight is my next headache. The double-curve on the 1928 blade is not easy to do without a profile cutter. I'm going to look through my router bits to see if I have something suitable. Failing that, something like the angular profile of the M1A1 sight will be done to begin with.
WRT making more:
Having done one, and worked out the foibles, making the second will be much easier. I made notes with that in mind, including where I could do things differently to make them quicker. Plus I have the threaded arbor I made out of steel to hold it without marking the surface.
This compensator has been made with a 0.75"-28 NS thread for the barrel (per the drawing). My barrel will be made with a threaded muzzle to match. I'm not sure yet how the Airsoft foresight is fitted, but real-steel M1A1 barrel muzzles were tapered for the blade/ring foresight. An M1A1 barrel could be threaded for a compensator (and late-production 1928s had unfinned barrels), but a threaded barrel can't be tapered for the blade/ring. Both types were drilled an pinned after assembly for added security.
Final finish is another aspect I'm dreading.
I'm in discussion with a local plating company to see if they can anodize this to look like blued steel (hence my question in another thread).
If that doesn't pan out, home anodising is an option I'm considering, though painting seems more likely ATM.
WRT receivers:
Another "problem" I've realised today is that they're very long for "home shop" equipment. 13 inches travel is needed to be able to mill the sides without relocating the blank. That's too much for most machines that would be in my price range. Yes, a lot have tables big enough, but few can actually traverse far enough to be useful for that.
Arc Euro Trade sell an X1 with a long table that could just handle it, though, but I'm trying hard not to spend that kind of money right now. The metric ones are out of stock ATM so I'm relatively safe. 
OK. I now have my Thompson, (geez it's heavy!) and have had a cursory look it its construction. I've taken the front grip off, but that's it so far.
Now I see why they talk about barrel snapping.
The outer barrel and grip mount are cast (I assume) as a single piece. On the real steel, they're separate, and the load on the sling is taken by the grip mount and front end of the receiver, not the barrel (which holds the grip mount into a slot on the receiver). I'm not sure if the screwed-on grip mount, or actually the receiver's threads, could take the load if it's separated from the barrel.
Putting a compensator on a standard barrel is a no-go as the front sight is again cast as part of the barrel, and so is not removable.
It's looking more and more like a new receiver is needed to do the job properly. 
I dismantled my gun today. 
Only the upper part. Made some measurements, compared them to the real drawings. Externally, it's within the tolerances on the drawings.
Internally, it's similar, but there are obviously differences.
Having seen the ejection port on my gun, I now understand what the drawing shows. I have a couple of ideas WRT barrel fitting and hop, etc. mounting.
So, the only impediment now is having the appropriate machinery to make the receiver.
WRT compensators:
I gather someone, at some time, made compensators cut to go over the M1A1 blade ring sight. That's certainly something I can look at.
Update:
Fore sight blade "done".
The side profiles were shaped using wood router bits.
It's there. It "works". I'm not completely happy with the shape and finish, but it's the best I can do right now.
I have an interim idea WRT a "front end kit" where a finned barrel is fitted to an existing receiver, but I'm not 100% sure how to fix it.
In my "Front end thread", I've realised that I've given no idea of the size of this part.
So here goes. That's the muzzle of my M1A1:
the way AZR did the cutts compensator, was to cut a slot in the top, and have it fit over the M1a1's existing front blade sight, and use a grub screw to attach it to the barrel.
Looks great though
I've looked into that, and the part that's milled flat for the blade sight would need to be milled through.
Would an M1A1-fittable Cutts be something people would be interested in?
BTW, those photos are all larger than the attachment window shows if you want to see more detail.
Would an M1A1-fittable Cutts be something people would be interested in?
yup 
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Would an M1A1-fittable Cutts be something people would be interested in?
OK. I'll have a go at making one.
the way AZR did the cutts compensator, was to cut a slot in the top, and have it fit over the M1a1's existing front blade sight, and use a grub screw to attach it to the barrel.
Any photos of this? I can't find any, and am having trouble visualising how the grub screw stops it from coming off.
IMO, a single grub screw in from underneath wouldn't be all that secure.
IMO, a single grub screw in from underneath wouldn't be all that secure.
It'd be fine it it was a tight fit. You could also drill a recess, or even drill tap the grub screw into the bottom of the barrel, if needs be?
I've got a compensator off a blank firer knocking around here, i was considering just grinding the old M1A1 sight off, then turning it to the right diameter to slot into the steel one, but it'd still be wrong, as it'd had the wrong barrel and receiver, so i've not really done aything with mine other than fit the foregrip handle.
Late production M1928A1s had unfinned barrels the same as M1s and M1A1s, but with threaded muzzles for the compensator. Both are shown on the drawing I have (the unfinned shown as "Optional Design"), so it's not entirely inaccurate.
WRT fitting a real-steel compensator on the airsoft, the thread is 0.75"-28NS-3 on the drawing. This is roughly equivalent to 3/4-28 UNEF, I understand.
Info for the barrel's thread off the drawing (tolerance in brackets):
Major dia. = 0.7500 (-0.0062)
Pitch dia. = 0.7268 (-0.0030)
Minor dia. = 0.7062 max
I've used a standard 28TPI 60 degree thread form on mine. Getting close will do you, though, the steel compensator will rethread the soft barrel for you. 
WRT fitting by cutting bits off the M1A1:
Taking off the "pin ends", but leaving the rest would greatly help WRT milling the compensator, but I've just had the idea that they might be useful to help hold the thing on. Though if you're going to cut things off, you might as well drill through and use a pin like the real ones. This could be an option for those wishing to do it "destructively", but without the facilities to make a 3/4" thread. It'd also be "reversable" to some extent as the only difference would be the missing pin.
Another idea just came to me - Grub screws in the holes where the pin would normally go. Hmmm.
I've got the turning done in the M1A1-fittable. It's the same as above, but with a larger, smooth bore where the original is threaded.
I just need to work out how to do the milling without the threaded arbor.
I've got a compensator off a blank firer knocking around here, i was considering just grinding the old M1A1 sight off, then turning it to the right diameter to slot into the steel one, but it'd still be wrong, as it'd had the wrong barrel and receiver, so i've not really done aything with mine other than fit the foregrip handle.
Late production M1928A1s had unfinned barrels the same as M1s and M1A1s, but with threaded muzzles for the compensator.
Just what I was going to say
A Proud Member Of 'Team Spleen!' who play mainly at Gunman Airsoft, Tuddenham, Suffolk.
I've recently started resurrecting this project. I decided to resurrect the thread as well in case anyone has it on e-mail subscription.
Now I have a milling machine, I am planning to make a receiver. That means I need to put the barrel on hold so I can make it fit the hole in the front.
So, while waiting for a new alignment device for the milling machine, I decided to carry on with another part of the project which doesn't need the wide-scale accuracy the receiver does - the Lyman adjustable sight.
I've given up on the prospect of getting a reasonably-priced original, so I put my machinery to work.
Here's what I have so far:
And assembled:
This is the slide and eyepiece assembly that rides up and down on the leaf. All the parts, including the screw, are made from mild steel bar stock, based on original drawings. I'll probably oil blue them later. The only significant modifications being metric holes and metric threads. That means no compatibility with original parts.
