I have the print. tried to upload it, but the file size exceeds the forum limit

PM me your email address

 

I also would like to have them,

Hello Karl_T, could you please send me the files too?

 

Still looking for the original print; willing to trade or purchase if necessary.

-WRM

 

Just a suggestion here...

There seems to be no such thing as a print that's not missing a dimension someplace. Why don't you you take a screen shot of the print like the one I sent, then go into paint and red line where you need measurements? My son has a trunnion, many others here do as well.

Karl

 

I actually found the dimension I was looking for. I'll continue to model it and see how it goes. I'll still be on the lookout for the original print though, as I'd like to have the tolerances as well. Maybe once I'm finished with the project, I'll recreate all the drawings so that they're easier to read and use.

-WRM

 

Found a missing dimension (or at least, I can't seem to find it). In the picture below, I'm looking for the dimension that currently says, "1.148" at the top of the trunnion. I can't seem to find it on the print.

ETA: Nevermind, found it (1.1 to the front of the trunnion)

-WRM

 

Well, I've got the trunnion modeled as best I can with the drawings available to me (probably the same one that's floating around the 'net). I've found a handful of dimensions that weren't how I like them (like using a nominal dimension with a bilateral tolerance band instead of the mean dimension). I always like to model items with their dimensions in the middle of their tolerance band when permissible. I also found a couple dimensions that were WAY off. Maybe (hopefully) it's just me and I'm missing something. With any luck, the link below will take you to the new drawing I've created (in PDF format).

https://www.dropbox.com/s/8pve83urztfyyvz/Trunnion.PDF?dl=0

And here's the one I used to create my model:

https://www.dropbox.com/s/uj83n264sxjk7n0/Trunnion - as used to model.pdf?dl=0

Dimensions in red are either different from those in the drawing I used to model the trunnion, or they're entirely new dimensions that were missing. Here's a list of the differences I've found and a couple of questions.

1. I just guessed on this one
2. Drawing used showed "R0.135" but side plate drawings I have show R.135-.020 (so, .125 is the actual nominal)
3. Drawing used showed ".8310," but side plate drawing shows .8305+/-.0015 (making the nominal dim .8305)
4. Drawing used showed "3.001," but side plate drawing shows 3.001-.002 (making the nominal dim 3.000)
5. Drawing showed "1.873", but side plate drawings indicate this dimension is 1.857 (side plate drawing uses pintle hole for baseline measurements, and when going by the dimensions on the side plate drawings, this dim should be 1.857...a .018 difference)
6. Drawing used shows "3.770," but going by the dimensions on the side plate print (5.1225 (height of front of plate) - 4.9225 (height of rear of plate) + .0895 from top of rear plate section to center of hole) makes my dimension 3.712 (.058 difference)
7. Drawing used showed "2.880," but side plate drawing shows 2.879-.002 (making the nominal dim 2.878)
8. Dim pulled from side plate drawing
9. Drawing used showed ".573," but side plate drawing shows .573+.005 (making the nominal dim .5755)
10. (I'll talk about this one below; this one really has me scratching my head)
11. I just guessed on this one as well; can't find anything on the drawing about the depth of this hole...only the diameter
12. I just guess on this one too; thread depth is 1.000 minimum

About dimension #10... I know that the drawing I used to create mine shows this diameter as 1.680, but if I make this the diameter, it breaks through the top of the part slightly...right where that slot is going across the back of the trunnion. According to the barrel "drawing" I have (it looks to be made by the same guy who made the trunnion drawing), the portion of the barrel that goes through here has a diameter of 1.676. So, I would say that the diameter in the trunnion should be 1.680, but does that mean my "slot" is somehow incorrect?

I'm certainly not infallible, so maybe someone with an original print who might be unwilling/unable to share the print could at least point me in the right direction?

Also, here's a snip from the drawing I used to make my model; what is this dimension referring to? I can't figure this one out either:



Here's a few JPG's of my model at this point:





Note: The radii in the top/rear of the trunnion pocket is my doing; the drawing I used showed what looked like squared pockets, but I try to avoid that whenever possible...I have no idea if that would work on the real gun.

-WRM

 

Also, here's a snip from the drawing I used to make my model; what is this dimension referring to? I can't figure this one out either:

If you're still working on this, I believe this is actually referencing the offset from the centre of the pintle hole. The easiest way to confirm is to check it against the side plates - you'll find that it neatly aligns with the holes there.

As for #10, you're not alone with that problem. I believe that the cut is not a uniform depth. If you look at the last picture (the clean & bright trunnion) you'll notice that the cut is noticeably more shallow in the centre, but deeper towards the sides. I have found one image of a trunnion with the cut breaching through into the void below, but I'm wondering if someone just followed these prints without questioning it too closely!

 

#10, I know that diameter does not beak through.

If you'd like to send your phone and a good time to call, my son could take measurements off his trunnion. Its an original WW2 AC weapon that has seen action in war, so it would have wear on the #10 diameter. Also these trunnions aren't the same from manufacturer to manufacturer - that's one reason KMP calls out match drilling on the RSP.

From memory, the slots on the very top, ahead of the top cover, don't look right to me. But, I'm not near the weapon right now. If you can wait a bit, I'd be glad to check your numbers against mine. I have a M3 aircraft trunnion, again won't be exactly the same.

One thing I've learned from making a lot of missing parts. "Its only a gun, tolerances aren't tight"

Karl

 

Here's some pics of trunnions I've found online; that diameter doesn't break through on any of them, but they all show that "slot" that runs along the top/back:









-WRM

 

Ok, so I have a dimension question clarification for the 'flange' at the base of the barrel support thread. Based on the original trunnion drawings, the thickness works out to be .1505" (going to middle of all tolerances), but on a lot of drawings I see the dimension listed as .187". Did it change over time? Is it not that critical of a dimension?

Also, some people seem to have dimensioned the threaded 'spud' as being much longer than I calculate on the drawings. I calculate it to be 1.5945" (going to the middle of all tolerances) and some have it dimensioned as long as 1.812".

Or are the sketches I'm seeing with the different dimensions the M3 version and are slightly different than the M2 version?

 

Yes the slot is crested in the center of the trunnion and deeper on the outside edges like the BMG Parts picture ,so it is a bi angle cut , one from each side towards the center of the trunnion to keep it from breaking into the barrel channel .

 

If you're still working on this, I believe this is actually referencing the offset from the centre of the pintle hole. The easiest way to confirm is to check it against the side plates - you'll find that it neatly aligns with the holes there.

As for #10, you're not alone with that problem. I believe that the cut is not a uniform depth. If you look at the last picture (the clean & bright trunnion) you'll notice that the cut is noticeably more shallow in the centre, but deeper towards the sides. I have found one image of a trunnion with the cut breaching through into the void below, but I'm wondering if someone just followed these prints without questioning it too closely!

I never noticed that in the picture, but you're right; the slot IS shallower in the center. Thanks all!

-WRM

 

...could be wrong...?

After building over 15-M2HB's...most from original WW2/Korea era trunions...seems that there were only minor varience's from mfg.-to-mfg. The one thing I did see was that almost all WW2-Korea M3 guns used an original M2HB trunion and just had a plate over the front sight bracket on the top front. One of the pic's here shows exactly that configuration. I did use a couple M3 trunions...and had to have Brian machine them to accept a machined front sight piece from TNW. It just screwed on with 2-cap screws.

 

Like many others that came before me, I'm looking for arsenal blueprints for the trunnion. I'm not sure why it seems to be so closely guarded, but I'm having a hard time locating it (I have the rest - almost). I have no intentions of making them (I probably could I guess, but it's likely cheaper to buy). I simply collect blueprints and want to make a dimensionally accuarate M2HB model.

I'm not asking someone to fork it over out of the goodness of their heart though (since you might have paid for it yourself); how about a trade? I have quality scans of the original prints for the AK-47 front trunnion that I'd trade. If you're a builder (or just a fan of AK's), you probably know that you can easily reverse-engineer the majority of the trunnion...with the exception of the 3 bolt lugs. This print tells all the secrets of getting it right the first time. (I can also provide info on how they're originally manufactured as well).

For the print I'm after, like I mentioned, I want scans of the original (the rest of mine are a mixture of Rock Island and US Army Armament Research and Development Command).

-WRM

Did you ever find the proper trunnion drawings. Apparently there is a 1934 Springfield Armory drawing?

Do you also know of anyone who has actual experience building trunnions, not just a machine shop but someone one with actual experience of taking a qualified forging to the final finished product? I talked to Bob Landies at Ohio ordnance that we have known for years today; good guy, and their production is full up. Any one else with actual experience?

 

I, like Caina-Longbranch Limited above, am interested if you have ever found proper trunnion drawings? I am about to start modeling one myself off of a NOS trunnion. If you need any dimensions or pics of it let me know and I will get those and post them. Good luck to all in the hunt.