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Steady rest, live center, or other way ??...

56type

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#1
OK, here's what I have so far...Picked up a Yugo AK barrel awhile back that had some galling where it had been pressed out of the trunnion (common on these barrels). Seems the way to fix that is to weld up the galled area, rough grind it close to final dimension with a dremel, then place in the lathe to turn to finished dimension. Here's where where I'm running into trouble...

I've got the barrel centered in the 4-jaw chuck on my Atlas 10100 lathe to within 0.0005, needle on DI barely moves when rotating the 4-jaw by hand. The barrel itself is 16.1" in. total length with about 2" in. of that in the 4-jaw. The problem is the remaining 14"in. of barrel hanging out in space. At the chamber end where the cutting needs to be done it's 0.019 runout according to the DI. The magnetic base of the DI was locked to the bed ways for both measurements (up at the chuck & 14"in. away at the barrel chamber journal).

Question is how should I go about bringing the chamber journal end of the barrel into center so I can trim the high spots of the repaired (welded) section to match the OD of the chamber journal ?????..... Would using a live center do the trick or am I going to need to find a steady rest, or am I missing something entirely about dialing this in to get the barrel to run true so I can re-cut the repair back into spec. ??

The OD of the chamber journal is a press (interference) fit to the trunnion so it has to be held to 0.001 - 0.002 tolerance for the press fit. Thanks.
 

Bob Korves

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#2

56type

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#3
Unfortunately the barrel won't fit thru the spindle. Which method would allow me to dial in the chamber end for best accuracy ?? What I'm essentially trying to do is take a series of small skim cuts to bring the repaired section back into the same OD as the rest of the barrel chamber journal. I do have to keep it to within 0.001-0.002 to maintain the correct press fit with the trunnion that the barrel is pressed into then pinned in place.
Thought about trying one of these but was unsure if it was the best tool for the job at hand, or if I should try to find a steady rest and use that.http://littlemachineshop.com/products/product_view.php?ProductID=1704&category=
 

Bob Korves

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#4
Unfortunately the barrel won't fit thru the spindle. Which method would allow me to dial in the chamber end for best accuracy ?? What I'm essentially trying to do is take a series of small skim cuts to bring the repaired section back into the same OD as the rest of the barrel chamber journal. I do have to keep it to within 0.001-0.002 to maintain the correct press fit with the trunnion that the barrel is pressed into then pinned in place.
Thought about trying one of these but was unsure if it was the best tool for the job at hand, or if I should try to find a steady rest and use that.http://littlemachineshop.com/products/product_view.php?ProductID=1704&category=
A tailstock center will make it difficult to move around to dial it in true. A steady rest, properly set up, adjusted, and used will allow you to dial it in far from the chuck. It not so good an idea to force the barrel over with the steady rest to make up for the poor chuck jaw clamping alignment you are getting, but it is not really very far (.019") considering the length of the barrel. It would be more correct to use a center and a drive dog at the spindle end and eliminate the barrel bending. Study up on the use of a steady rest before trying to use one. There are some important details to learn that are not necessarily intuitive.
 

56type

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#5
Thanks Bob, I appreciate the help. These rifles were never known for tight tolerances but the trunnion/chamber journal is one of those areas it has to be right. So I need to get some drive dogs & a steady rest for it along with a center. What was puzzling was after dialing in the barrel so close at the chuck end was having it go 0.019 out at the chamber end. I expected it to flex like crazy since it was just hanging out there but with just plunger pressure from the DI I guess I didn't expect that much out from the chuck reading.

I'll try to pick up a steady rest from ebay if I can turn one up. Is there anywhere that still offers a steady rest for the Atlas 10100 6" x 18" ?? (so I can avoid a bidding war if at all possible).
 

francist

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#6
As far as I know, there are no aftermarket steady rests being marketed for the 618. Sometimes you find an old one, but they're not always easy to come by. Couple of places to try are mymachineshop and an eBay seller "antfarm".

-frank
 

56type

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#7
As far as I know, there are no aftermarket steady rests being marketed for the 618. Sometimes you find an old one, but they're not always easy to come by. Couple of places to try are mymachineshop and an eBay seller "antfarm".

-frank
Thanks, I'll check them out.
 

Bob Korves

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#9
So I need to get some drive dogs & a steady rest for it along with a center.
Actually, a center will not work with a steady rest. Centers have to be used at both ends. The chuck can hold it, you might want to use small pieces of aluminum, brass, or copper between barrel and chuck so it can flex some there instead of flexing along the barrel length.
 

dulltool17

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#10
Make center-drilled plugs for chamber and muzzle end, them spin the barrel between centers, muzzle at headstock, chamber end at tailstock.

This is commonly done in turning- think "crownsaver" for the muzzle end. Alternately, you could just use a 7.62 x 39 case as a center in the chamber. As you said, tolerances on AK variants are pretty loose.
 

56type

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#12
Make center-drilled plugs for chamber and muzzle end, them spin the barrel between centers, muzzle at headstock, chamber end at tailstock.

This is commonly done in turning- think "crownsaver" for the muzzle end. Alternately, you could just use a 7.62 x 39 case as a center in the chamber. As you said, tolerances on AK variants are pretty loose.
Sorry but I'm having a bit of trouble picturing it...Not sure how the plugs would work exactly. If I put the 7.62 x 39 case in the chamber (minus the fired primer for the center), it would seem the barrel would be rotating on the thin walls of the case with the live center in the primer pocket, correct ?? Could you better describe the muzzle end plug & how it would work without spinning in the bore ?? Thanks.
 

Silverbullet

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#13
It would be riding on the brass , what better to not Mar the barrel or chamber . The live tail center will spin freely and if it's aligned with the head stock there shouldn't be a problem it it's not lined up on the bore where the center is it never will be .
 

dulltool17

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#14
Yep, Silverbullet described it pretty well. Brass cases are thicker as you get to the rim, so it really isn't " thin" brass.
The plug at the muzzle end needs to be close to a light press fit. Once you are done with the operation, you pull the case and use your cleaning rod to tap out the muzzle plug. This is an operation that requires a bit of patience.