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Threading problems??

Saturday I chambered and fitted another barrel for my 6.5 1000 yard light gun and all went wonderful until I went to cut the threads on the chamber end. I do my chambering between centers and use a Gre-Tan flush system. My normal procedure is to turn down the tenon but leaving it oversized by .050 then ream the chamber and then I put the live center back in the chamber to finish turning down the tenon and cut the threads.

The blank was 32 inches so it was using up a fair amount of the 48 inch bed. When I turned the tenon down things were good. Then I started to cut threads and noticed some chatter. I made sure everthing was tight and solid and proceded. The threads continued to chatter and when I was done the job was totally unacceptable so I cut off the tenon, rechambered and started over. The second time I double checked rigidity and even set the steady up past the mid point on the barrel not tight but just providing enough contact to prevent flex when I ran the live center into the chamber end. This time things were alot better but there still is some evidence of chatter in the threads. I am using a CARMEX tool and insert. I had no evidence of chatter when turning down the tenon just in the threading operation.

I chucked the barrel in the 4 jaw to do the muzzle brake work and did all of the threading and fitting with no chatter. Things were great.

Any ideas? All thoughts appreciated.

Daryl Kopriva
 
Daryl Kopriva:

Chatter comes from misaligned tool/work, to much overhang from chuck or steadyrest, wrong feed/speed, wrong tool geometry, wrong cutting fluid, ect.

If you are cutting in the headstock with a spider, use a piece of 4 gauge aluminum or copper wire between the chuck jaws and the barrel. I use a piece of split copper waterpipe on the end under the spider. Make sure your work is running concentrically and coaxialy by taking dual readings on your indexing rod/pin.

Use a testbar near the length of barrel to align yor tail stock. Then use a 60 center to align your steady rest. work with no more than 2 inches extended past the steady rest. Keep the steady rest well lubricated. Let it run for a minute or two then tighten up as the feet wear into the shape of the barrel.

Using the wire gives the barrel a smaller softer bearing surface in the chuck jaws. This allows the tapered barrel to flex without bending or bowing.

I cut threads with Brownells DO-Drill or Dark High sulfer thread cutting oil. If you can do it without loosing control at a higher speed it will give you better quality threads.

Good luck
Rustystud
 
Thanks Rustystud. I've never encountered this problem with heavier tapered barrel's but this one was a little lighter contoured and I think was flexing more. I have a barrel here to test with and I'll put the copper wire in the jaws. I always use the wire when working on the part of the barrel I don't want to mark up but in this case I was going to cut the end off and didn't care about the marks so I didn't use it.

Daryl K
 

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