Dennis & Brian's Build
Posted 19 February 2014 - 01:35 AM
First, cleanliness and deburring are mandatory. Second, building a good fixture saves a lot of time and makes for accurate parts. We decided to do a one piece bolt carrier so the first thing Brian did was make a fixture out of MIC 6 aluminum tooling plate to hold the bolt carrier and front and rear barrel plates. The fixture, shown below, only had the center hole for the hex sleeve and the .187 hole for the pin when we started making parts. The little plug setting in the lower right front replaces the hex sleeve for the front plate. Brian also circle ground an end mill for cutting the flat bottom holes. It is shown in the second picture and was used instead of a reamer for final size and to get the flat bottom. We need to turn the front of the bolt carrier, cut the flats and the groove to finish it. Oh, did I mention cleanliness and deburring are mandatory?
We did the ejectors individually instead of in a strip and slitting them. This was actually easier than I anticipated. Just time consuming. Of course, DRO’s were a major advantage doing them and especially the bolt circle function with all of the center drilling, drilling and reaming of the bolt carrier and barrel plate parts as well as on the ejectors
Posted 20 February 2014 - 06:22 PM
Yesterday we finished the bolt carriers. We had to put it back in the lathe and turn the front diameter and the groove. The thing I learned here is how to verify a piece is running true. The chuck in the pic is a three jaw adjust true. I don’t have one for my lathe so I use a standard four jaw chuck and place the indicator on top and center the piece and I am done. Brian showed me that even though you indicate the part on top it can be cocked in the jaws and still not be running true. In the second pic the indicator showed the part was cocked in the chuck and running out .003. So, you need to check both ways or indicate close to the jaws and again out on the end.
We then bolted the bolt carrier to our fixture and set it up on the Tomach mill, yea sweet, to mill the flats. There were three holes all together on both bolt carriers that the bolts would not go into after milling. So we had to put them back in a vise and mill an additional .003 off the flats on those three holes. No pic of that. Guess I was too concerned with the problem to take pictures. Then glass beaded it to debur and fitted all the bolts. The bolts are from Jerry/Cutter and were PERFECT! Thanks Jerry.
We decided not to use the tube on the main shaft but turn down a .500 piece and mill the hex. When we tried this we realized we would need a follow rest for the main shaft and the barrels. Most of the stuff Brian does is larger industrial stuff so he never had a need for a follow rest on his lathe. He designed and made a follow rest shown in the pic. He had some carbide pin gages which he used for the tips.
Again, I am just a home shopper who has the opportunity to work with someone with a lot of experience and I am just trying to pass on the little things I am learning. This is of course not the only way or even the right way but it is what we are doing. It also helps to have a will tooled machine shop.
More to come.
Posted 25 February 2014 - 12:13 AM
We milled the ejector slots for the front barrel plate on the Tormach. That went very well.
Next we wanted to mill the ejector slots on the bolts. We decided to do those on the Tormach so we came up with the setup shown to hold the bolts. The block in front of the rear jaw was milled and ground flat and a groove cut in for the bolt. The parallel on the right was milled square for alignment. Most parallels are not square on the ends. It was also not hard so it was easy to mill. We will try cutting the groove with this setup tomorrow.
Posted 28 February 2014 - 02:01 PM
Posted 06 March 2014 - 02:40 PM
Everything was going great until we decided it was time to see how all the parts fit together and worked. That created a great deal of confusion and aggravation. We spent the day making test bolts and a 4 inch test barrel to study loading and extraction. After much testing and correspondence with Jerry, aka Cutter, we came up with want we think will be a workable configuration and procedure for finishing the bolts and extractors. We decided to drill the pivot hole in the bolt and extractor separately. In order to get the bolt and extractor to load and extract without binding we did the following:
Drilled the bolt pivot hole .080 as shown on the drawings but drilled the extractor pivot hole .069 off the top of the extractor. This lifts the extractor flats .011 up off of the flats on the bolt.
Milled an additional .005 off of the rear flat on the bolt.
Cut a .026 x .250 radius on the extractor tip.
We experimented with Bic lighter springs and felt they were to strong so we ordered springs from Lee Spring.
We did get a day’s work in yesterday and got all of the above done on the bolts and extractors. We milled a pair of aluminum soft jaws from MonsterJaws to hold the extractor for both drilling and milling as shown in the pictures. We milled the same jaws to hole the bolt for drilling. Using soft jaws like this was a new experience for me but it really is a great way to accurately hold small parts. Brian picked up the DOM tubing and started to make the barrels. We ordered the barrel liners from Brownells and some snap caps for testing as we were not thrilled with using live rounds testing the bolts and extractors. As the saying goes, a picture is worth a thousand words so enough from me, here as some pictures.
Posted 06 March 2014 - 08:09 PM
Posted 06 March 2014 - 11:27 PM
Any suggestions on what to use other than brass for the housing. Also, any mandatory mods in order to get this gg to shoot reliably. I have looked at so many things on this site I am not sure what is actually necessary and what are just personal improvements.
Posted 10 March 2014 - 01:11 AM
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