- bruski, Roller, Cutter and 3 others like this
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Posted by Swarfmonger on 29 July 2020 - 06:22 PM
Posted by brk on 29 July 2020 - 12:01 AM
I also added a slot down the length of the acme screw and made a brass finger to engage it to keep it from turning. Here are a couple photos, one with a flash to help show the groove.
I have a thrust bearing under the brass piece that is under the finger.
Posted by Swarfmonger on 26 June 2020 - 06:16 PM
Posted by Sparky_NY on 09 January 2020 - 02:31 PM
I will follow your instructions.
It is not obvious to a newbie that such experienced techniques are so critical.
If I understand your comments, I drill the hole and then ream prior to proceeding to the next hole (no movement of the work). It appears that a relatively short length reamer will be required to preclude large movement on the Z axis. My DRO is one of the Chinese version that displays position to 5 decimal places so the hole location should be accurately placed.
Not reamed, bored with a boring head. A reamer will still follow a drilled hole that is not true. A boring head will true up any walking off center the drill bit did which is pretty much guaranteed to happen with deep hole drilling like this.
In general terms, when holes need to be very accurately sized and exactly on location, boring is the accepted method. Drilling a starter hole to get most of the meat out is how to start of course, just leave enough material for the boring bar to true things up.
I went through the same problems you are experiencing. If I recall correctly, Cutter is the one that suggested boring the holes as the best method. He was absolutely correct ! The hole positions were orders of magnitude improved.
Making the bolt carrier in 2 pieces also helps a lot, the depth of the holes are much less than one piece. Although its 2 parts instead of one, its actually easier that way with better results.
Posted by barrelguy on 10 November 2019 - 05:15 PM
I am a machinist with 60 years experience in the trade who started a couple of guns 3 years ago. With my machining experience I decided I didn't like the idea
of silver soldering or welding these parts together. I used dowel pins and screws instead. I have disasembled these guns at least 100 times in the last three years
to re-work, modify, tweak, or re-engineer the parts to make the gun work. I couldn't have done that with a soldered up gun.
Just food for thought.
Posted by brk on 01 July 2020 - 03:37 AM
I machined my bolts for the extractors from Gbull and found a little interference with the drum and the feed lips I made. Before the extractors were in the bolts, the bolts all cleared the magazine and feed lips, but with them installed, there was just a little interference. I missed this when I drew up the feed lips. The magazine would have needed just a little clearance with or without the feed lips. I had to put a small radial (or arc) cut in the lower 1/16" sheet brass cover of the magazine and then add a 1/16" x 1/16" relief in the feed lips. I could have gotten by with less clearance, but did not want to do it twice and figured a little extra clearance here wouldn't hurt anything.
Extractors from GBull were very accurate to each other but were a little off from the .dxf file. I did have some extractors from Cutter from years ago when I bought the bolts and forgotten I had them (actually I had misplaced them). Cutter's matched the dxf but varied a little more than Gbulls. Gbulls didn't vary more than about .001" He said he had them wire EDM, Cutter's were milled. I checked them out on a optical comparator I made a dummy bolt and made a few samples on the cuts/cross hole for the extractors. If I put the cross hole on location for the heel of the extractors, Gbulls extractors were about .067" from the face of the bolt to the underside of the extractor. Cutters were much closer to .055". I decided to move the cross hole toward the rear and used Gbulls since his were already hardened. I figure I could use Cutter's as spares and may just need to take a little material off the heel to get those to the.055" from face of the bolt to underside of extractor. This way gave me the most options with extractors from two sources.
I advise anybody that is going to fit extractors, make a dummy bolt first to get the setup right and tweak to get what you want. I had a total of 23 bolts and got them all machined without scrapping any.
Here are some pics
Posted by Cutter on 12 June 2020 - 12:27 AM
Posted by drhardin on 20 May 2020 - 03:08 PM
Thanks for all you do.
Posted by Cutter on 19 May 2020 - 10:46 PM
With the two piece carrier. I would have to buy another piece of brass, I can only get 1/2 the carrier out of the new piece that I have ready to go. Plus I have to buy an additional hex bushing part for the extra 2 press fit sockets. The counterbore I was using was a 3 flute 27/64 .4219 (within tolerance) but bored a .434 hole, opps your fired! Curious why would an endmill produce a better hole? How would a shop do this with strict adherence to the print without f-up? I was a machinist 40 years ago with some schooling, and only 2 yrs experience. At that time all the work went to Japan, and shops wanted 5-10 yrs experience, they could get it easily. So I went another direction, but I kept my tools. I knew I'd finally get back to it.
Posted by Dave on 01 February 2020 - 07:00 PM
Posted by Larryx on 29 January 2020 - 12:11 AM
I will use the steel bar. It is drill rod from the drops of a company that makes of all things, drills.
Posted by maccrazy2 on 12 October 2019 - 10:02 PM