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All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"

Turning a thin walled barrel almost chatter free

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lloyd-ss:
I don't have a decent steady rest or follower for my lathe and turning long thin walled sections has always ended up being an exercise in how to remove the chatter marks after I was finished. (And I do have a good method for that!)

But this time it worked a lot better.  I was turning a 24" long .410 barrel to remove all the taper from the 10" closest to the breech.

I wrapped a 4' long 3/8" oak dowel with duct tape in a spiral pattern for a tight fit into the barrel.  I had the breech end in a live center in the tail stock.  Lightly chucked (Barely tight enough to hold) on the barrel with thick copper pads on the jaws.  10" of barrel were exposed.  The portion of the  barrel in the chuck had a little taper, so tightening up the tail stock taper-locked the barrel in the chuck.  Excess length of the dowel was sticking out through the head stock.  I found that by pushing or pulling on the end of the spinning dowel (bending it) I could control the chatter.  I slipped a loop of rope around the end of the dowel, pulled on it to get about 4" of bend in the dowel, and tied the rope off to the bench to hold the tension.  Finish cut was 300 rpm, .0025 IPR, and .003 DOC.  I was using a carbide insert set to have about a 45 degree lead angle that I lightly diamond honed to get a crisp edge.

I'd like to say it came out perfect.  Not quite, but almost.  Next time it will!

If anyone has other tricks on getting a nice finish on thin tubes, please chime in!

Lloyd

gene_sc:
Wow Lloyd that was some trick to fix da chatter. Thanks for sharing with us. I often make barrel shrouds from thin wall aluminum. Some are 24" long. When these shrouds are this long I need to make them in three sections. Yes they will chatter once you reach a certain spot and continue. It will ruin a project.

What I did to stop the chatter.. Either a rubber hose or dowel inserted in the tube stops the chatter. Has to be a good fit and not loose.

Works fer me....:)

Gene

chronic:
Thats cool, you loaded your work piece :)
I've done similar things like that at work, I used a broom handle inside a work piece supported on rubber bands to try and knock out some of the noise and it did work a bit! Still had to use super positive carbide inserts and low rpms.

Good old trick is to touch a lead hammer on your work piece near the cutter as you're feeding to cancel harmonics. I also wrap thin walled material with rubber on the od and feed up to that point, pull out then move the rubber over to the finished size, feed back in and keep going.
But if you're doing long thin work pieces, sometimes there is nothing you can do but section by section unless you get a follower rest.

Good work :) Chatter not worthy! Just cross hatch it when you polish and know one will know what you went through :D

Jawbreaker 38:
What nose radius was your insert? I fight these battles every day and have found that burying your nose radius completely is one of the best solutions, but in some cases it's not always possible. I also try to run the RPM's slow and feed as heavy as possible to stay ahead of the chatter, a positive rake makes a major difference as well. I've stopped in the middle of a cut and wrapped rubber bands on the material behind the tool to help absorb vibration. When boring deep holes I've wrapped rubber bands around the shank of the boring bar and around the outside of the part also.

lloyd-ss:
Thanks for the input everyone,  seems like its a universal problem


--- Quote from: Jawbreaker 38 on July 20, 2011, 02:16:54 PM ---What nose radius was your insert? I fight these battles every day and have found that burying your nose radius completely is one of the best solutions, but in some cases it's not always possible. I also try to run the RPM's slow and feed as heavy as possible to stay ahead of the chatter, a positive rake makes a major difference as well. I've stopped in the middle of a cut and wrapped rubber bands on the material behind the tool to help absorb vibration. When boring deep holes I've wrapped rubber bands around the shank of the boring bar and around the outside of the part also.

--- End quote ---

I used .016 radius triangular insert and honed it with a diamond hone to get a sharp edge on the top.  I also used a right hand holder so that the trailing edge was perpendicular to the part and the leading edge was at an acute angle to the OD of the part.

  What also helped a lot was some old fashioned maintenance: I cranked the compound back to eliminate overhang, tightened up the gib screws on the compound and cross slide, and fixed the excess clearance that I had on the bar under the far side of the carriage that hooks under the rear way.  That was long overdue anyhow.

Lloyd

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