Here at Gun Lab we do a fair amount of reverse engineering, most of what we like to make have no drawings. However when there are drawings or solid models available we will use them. With this said I have found that most of what is available on the internet or in books is just not correct.
A case in point is the MP-44 trunnion. I have all the drawings that I have been able to find on this part, a number of different sets are out there, and when compared with the actual part have found them to be lacking. Some are just wrong and in some cases I don’t think the person has actually looked at a part.
Over at weapons man he had a write up about reverse engineering a while back.
http://weaponsman.com/?p=21915
It was a very interesting write up and I recommend reading it.
Now back to the MP-44 trunnion. We were contracted a while back with making a limited number of new trunnions for the MP-44. He sent us a very good original one and we had a poor copy of one at the shop. Using these two pieces we started the project of reverse engineering it. The easiest thing to do was look for engineer drawings off the web. These are the ones that I found.
The measurements have been removed from these copies, however you can find them on the internet. I did use the basic drawing as a starting point. The sheets were cleaned and measurements were taken using a cmm, micrometers and pin gauges. Tolerances were set using not only the trunnion but also matching parts. When there was a doubt other parts were located to increase the measurement standards. This allowed us to come up with a reasonable solid model that we felt was accurate enough to start programing.
Even with this solid model and prior to making the parts we still caught a few errors that have been corrected.
Now comes the portion of the project were we start working on the machining of the part. A master cam programed was written to run the trunnion on the cnc machining center. It was determined that 7 set ups would have to be done to machine this part. This is a video of the master cam operation to complete operations 1 through 4.
With the program checked out we then ordered the proper tooling and set up all the off sets on the machine. Test material was brought in cut and machined to size to do a test run. This is the progress so far.The material was saw cut to size.
Then machined to the proper size and squared.
The first 4 ops have been completed. Op 1 and 2 cut the groves on both sides and drilled the ejector holes.
The next phase was op 3 and 4.
The parts are set up in the vises ready to machineThe barrel hole drilled and machined.
The hole for the bolt carrier is drilled, machined and then bored to a very nice finish.
The gas tube support is machined in.
Even now we are still not working on the actual parts. These are 6 test pieces that will be completed and set to the buyer to test on his kits to verify proper fit. In this case because of tolerances we went with a smaller bore diameter for the barrel fit, it is easier to remove metal then to add it.
that’s fantastic, did you find original prints or make your own off of an existing part?
We used original trunnions and reversed engineered them for the most part.
really cool. semi related, what rifle do you think has the strongest and most serviceable trunnion setup?
what is the weight of the trunnion ?
I am not sure. I will weigh it when I have an opportunity.
Your article on reverse engineering the MP44 trunnion was fascinating! I’d thought about making an MP44 knockoff in caliber 5.56 NATO and using an M16 magazine but when I looked at a copy of the blueprints I realized that it was much more complex then either the AK47 or M16, I gave up on the idea. The Germans tend to overengineer everything! Anyhow, good luck on your project.
Kerwin.
I agree with the over engineering.I would really like to build the complete rifle one day. Other projects take priority first though.
[…] he had something nice to say about us, in a longer post on reverse-engineering; to be explicit, reverse-engineering the MP44 trunnion. But forget what he says about WeaponsMan.com, how cool is it to be making an MP.44 trunnion for […]
I need to buy a mp44 trunion!