Chatter Problem

Hi guys. I'm trying to maching a small item on a lathe. It's going to be a depth gauge, folloeing the directions givien the the Machinist's Bedside Reader. The material is some sort of mild steel, pedigree unkonown. I have ground a full radius tool from a peice of HSS. I have ground a 45 degree cone on the end of the tool and a 10 degree rake (?) angle on the top surface. I have tried speeds of 200 RPM to 1000 RPM. The work piece is about .625 Dia. X 2.5 in long. Every time I try to machine the OD I get a lot of chatter. Any ideas? Thanks

Reply to
Kelly Jones
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"Kelly Jones" wrote in news:DMWdnVQ9XI8RZwHenZ2dnUVZ snipped-for-privacy@comcast.com:

I'm not sure if I'm following your grind on the tool. Part of the problem is that your bar is sticking out over 4x its length, so deflection will be an issue. Once you have anything over 3-4x the diameter hanging out of the chuck, you need to think about supporting the work, usually with the tail stock. The other thing you need to do is keep the cutting forces low. This means lower speeds and feeds, lighter depth of cuts, and a free cutting tool geometry.

For the tool grind a positive lead creates more pressure, as does a full radius. A positive side rake and back rake will help lower forces. I would use a tool with zero lead, 5 degrees of end and side relief clearance, 12 degrees of side rake, and 10 degrees of back rake. Grind the tip to 80 degrees by grinding the ten degrees from the front. Stone the cutting edges and stone a small radius of around .005" on the corner minding that you maintain the 5 degree angle all the way around. This tool will cut freely in most steels at light DOC. Run around 900 rpm and feed at .0015"-.0025" for best results. Make sure the tool is dead on center to slightly above. No more than a thousandth or so. Try a .01"-.02" radial DOC to start.

Reply to
D Murphy

Reduce the radius. Big radius is prone to chatter, lots of tool in the cut. I very seldom use any radius, if the tool is sharp and the feed right, finish will be good. As an alternative, you might try taking lighter cuts, my guess is it won't help much.

Rich

Reply to
Richard

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You gotta fix this to have a chance. Chuck in closer for this cut? Time to build/buy a follow rest?

Karl

Reply to
Karl Townsend

Are you using a live center in the tailstock?

Nick

Reply to
Nick Müller

The tool bit grinding is pretty critical. You also need to check the crossfeed and spindle for backlash. Didn't see any mention of the make and size of lathe. A 10" or 12" lathe wouldn't even tremble, but one of the small toys would be prone to chatter, in my experience. Bugs

Reply to
Bugs

Reply to
Kelly Jones

Ok. I think I follow: I currently have a full radius on the tool and a 45 degree "side relief" all the way around. The angle of the top of the tool top the plane of the ways is about 5 to 10 degrees. This doesn't sound like what you describe. Sounds like you are suggesting grinding two tools, one for a left hand fillet and one for a right hand fillet, instead of trying to make one tool cut both sides. I can do that. Hadn't thought about breaking the edges of the tool though. I was thinking that the sharper the better. I can radius the tool edges too. What's "DOC"? I was putting the tool dead center to slightly low. I can fix that too.

The lathe is a 12 X 36 import, only a year old. It shouldn't be to lathe's fault, just my inexperience. Thanks for the help.

Reply to
Kelly Jones

DOC = Depth Of Cut

Reply to
Karl Townsend

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