Tuesday, February 15, 2011

.50 BMG bolt work

 Okay, so the weather finally cleared up enough in my neck of the woods that I could get out in the garage and do some work without freezing to death. I wanted to get the extractor done on the bolt head, but found that the only end mill I had of appropriate size was broken. I ordered a new set of end mills, a new vise for my mill, and a handful of other odds and ends from a big name supplier whom I will not mention here as I want to remain civil despite their inability to keep track of their in-stock supplies. Suffice to say that they wanted to charge me for my order and not ship any of it until it came in around March 26th. I have had good luck with this company in the past, but I didn't care for the way they handled this one. I had heard a few good reviews about another business of similar nature named Wholesale Tool. They too sell good American and decent import tools at reasonable prices, and they have a shipping/store hub in Oklahoma. Good enough for me.
I went through and ordered the same parts as I had with the other tool supplier, but this time came out at a lower overall price, even with 3 day shipping via UPS. I received a phone call within 24 hours informing me that they did not have all the order in stock at the Oklahoma hub, would I mind if they shipped it 3 day UPS from another store located in Massachusetts, with no extra shipping costs to me, despite the difference in distance? Sure! They also informed me that I could get the order from Oklahoma within 3 days even if I elected to pay for normal ground shipping since it was so close to me. Apparently, these guys don't mind saving me some money. I will certainly be back to purchase tools from them if they stay true to their word.
So, the end mills should be here mid-week so I can get started on the extractor. Until then, I figured I would work on the striker assembly some more and make a bolt handle.

The bolt handle is really nothing special. I used a ~5.5" length of the .625 OD M2 drill rod I purchased a couple weeks ago for this. It was center drilled and chucked up in the lathe using a 3 jaw chuck and a live center. I turned one end down for 5/16" coarse threads about an inch long that would thread into the bolt, then reversed the part in the lathe and turned it down for 1/4" coarse threads that would thread into the knob on the end of the handle. I had to break out the calculator and figure out exactly what angle to set the lathe compound to, in order to go from a .625" OD to a .24" OD over a span of 3.5". I set the compound to the correct angle, then used the compound to turn this very gradual taper over the length of the handle. I also turned down a small section .25" in length, .51" in diameter behind the 5/16" threads so that the handle would fit in the .565 bolt slot of the receiver.



Finished part with 5/16" threads, about to run a die on the other end for the 1/4" threads.


 With all the threads cut, the lathe was sped up to about 1500 RPM and a piece of 100 grit sandpaper was used to smooth out all the tool marks before some scotchbrite was applied to polish it up and remove the sanding scratches.


Next up was the knob for the end of the handle. For this I used a piece of 1" OD 1080 hot roll steel I had laying around.
I started by center drilling the stock, then drilling it out in preparation for 1/4" threads. I then began  turning it down about .05" to remove the hot roll coating and get the outside surface completely devoid of pits and surface irregularities.


Next up was to decide what the appropriate taper of the knob should be. There was no math involved here, the exact angle was totally arbitrary. All I wanted was for it to look "right". I guesstimated about 35 degrees should work, and set the lathe compound to the appropriate amount. Ignore the scored threading marks on the stock, that was from using this piece of scrap as a test piece to determine correct thread pitch on something else I was working on.
 A few minutes later, I had this.
 The knob was then threaded internally,  a small section was knurled fairly deep, then the whole part was parted off. As I parted it off, I did it in small steps so I could get just the tiniest of tapers to it. This would allow me to use a file and sandpaper to give the end of the knob a slight radius. Once it was separate from the piece of scrap stock, I threaded the handle together to the knob, and chucked it up in the lathe for sanding and polishing. I used a small file to shape the end of the knob and give it a slight radius before using more 100 grit sandpaper to smooth out all the tool marks, then polished everything with scotchbrite. The photos are a bit misleading, as once I was done with the scotchbrite none of the parts needed actual buffing.

The completed assembly:



The completed assembly installed in the rifle:



 The above video was just a test of the video camera on my phone, this was just me milling flats on the bottom of the bolt sleeves in order to clear the sear.
Hopefully I'll have the sear completely functional tomorrow or the next day so I can dry fire the rifle. Once that is done and the extractor is complete, all the necessary parts go out for hardening.
More as I complete it.

1 comment:

  1. Not into blogs but stumbled onto this while researching .50 bmg plans. Can not seem to see how to email you directly. Have some of Homes other plans and the Maddi-Griffin bought from a friend. Do you have a forum or can you suggest one. Seems a lot of people hate both but have not found anything better. Have a Smithy I converted from a 1220 to a 1240 so can do pretty much anything I set my mind to. Just like to shoot. The bigger the bang the better!!!!
    Thanks and have a great day. mckeanwilliams@yahoo.com

    ReplyDelete