Singin' Barrels

[Snag_one]

I've been working with a nice young 'smith here on a few projects , 2 in particular I'm excited about . Right now we're working on a barrel for an SVD rifle for him , later we'll be demilling an RPD .
But right now I'm having a bit of a problem profiling this Green Mountain barrel blank <24" x 1 3/8 -.311 cal> - it wants to sing while I'm machining it down . So far the only cuts that didn't chatter are ones I made with a brazed carbide . I tried Saturday with a very sharp M42 cutter and my follow rest - no joy . <<aside - I just mounted some small roller bearing on the rest , in order not to have rub marks on the barrel and will be doing so on my steady also>> I do understand that my lantern post isn't the most rigid setup , but I've never had a problem like this before even when turning long pieces of large rebar .
The lathe is an older Wards 94TLC2136 <Logan> in pretty darn good shape , lantern post , QC box geared 4:1 from the spindle . We're turning between centers with center-drilled brass "mushroom" plugs in the bore . I did notice that the blank was a few thou larger in the middle when cutting without the follow rest as expected . I'm not really worried about finish at this point , but I'd really like to have this problem sorted out by the time I'm doing finish passes ...

Snag

 

[toolman]

I can't guarantee that it will work for you, but I had one like that a few years back that I calmed down by turning several grooves in a piece of brass that would just fit in the bore without touching. I then installed suitable-sized o-rings in the grooves, sprayed the bore with silicone lube, and slid the rod into the bore, making a harmonic dampener of sorts. It worked on that one, but I've never tried on anything else.

 

[Inflight]

I just place my left hand on either the chuck or the work while turning. This applies a little extra drag that keeps the part from singing, as you describe.


Matt

 

[TIGL]

I just place my left hand on either the chuck or the work while turning. This applies a little extra drag that keeps the part from singing, as you describe.


Matt

That strikes me as being awfully dangerous...

 

[John Hasler]

I've been working with a nice young 'smith here on a few projects , 2 in particular I'm excited about . Right now we're working on a barrel for an SVD rifle for him , later we'll be demilling an RPD .
But right now I'm having a bit of a problem profiling this Green Mountain barrel blank <24" x 1 3/8 -.311 cal> - it wants to sing while I'm machining it down . So far the only cuts that didn't chatter are ones I made with a brazed carbide . I tried Saturday with a very sharp M42 cutter and my follow rest - no joy . <<aside - I just mounted some small roller bearing on the rest , in order not to have rub marks on the barrel and will be doing so on my steady also>> I do understand that my lantern post isn't the most rigid setup , but I've never had a problem like this before even when turning long pieces of large rebar .
The lathe is an older Wards 94TLC2136 <Logan> in pretty darn good shape , lantern post , QC box geared 4:1 from the spindle . We're turning between centers with center-drilled brass "mushroom" plugs in the bore . I did notice that the blank was a few thou larger in the middle when cutting without the follow rest as expected . I'm not really worried about finish at this point , but I'd really like to have this problem sorted out by the time I'm doing finish passes ...

Snag

I've heard of sticking blobs of modeling clay on the chuck to damp vibrations. Never tried it, though.

 

[twowheelinjim]

Your best bet is to watch your feeds and speeds. Try taking smaller cuts. Check run out and adjust the work piece. A little patience goes a long way.

 

[hothead]

I taper quite a few G M and Douglas blanks.
The Lathe i use to taper is an MSC Vectrax 13-40 with taper attachment.
I run coolant and take fairly heavy cuts to start. I set the feed to the fastest setting the machine has.
to start your only removing steel , dont have to be class a finish. I run at 105-260 rpm .
when i get close i set the feed rate back some and take less cut. at this point you can feel what
the bbl wants for a good finish. Last cut i put Good insert in and have a cut of no less then .010 per side.
Too light a cut and too slow a feed will always give chatter. to remove chatter run fast feed and it will walk over it
in a cut or two.
the finish i get are equal to the finish on most factory contoured barrels. I have never had a barrel that didnt finish well.
I dont use a belt sander just 10 minutes with wet paper of various grits and its done.
Green Mt. are good barrels never had one that didnt perform. I bought 30 Douglas cm blanks at an auction of an old gunsmith that
passed. some of those are pretty funky steel but they do shoot well. I still feel guilty, I gave $20 for each bbl.,
so a little more feed rate and rpm under 350. ( sometimes need to run at 105 rpm ) It works for me.
your singing barrels just need a little more tempo.
HH