I think I just learned something.

 I am trying to bore a 5 inch diameter hole in 6 inch diameter
 aluminum bar stock about 5 inches deep.

 I was getting tool chatter.  At first I thought I needed a stiffer
 boring bar. My boring bar is about .75 inch in diameter.

 I discovered if you speed up the carriage feed the chatter goes away
 more or less.

 Some of you guys on here are expert machinist.

 Have you heard of this before ?

 Paul Lamar

 Paul, The spindle speed formula    RPM= Surface Feet per Minute x 4/
 tool Diameter SFM for aluminum is 400 & R is .002/.009 And the feed
 rate formula     Feed (rate per minute)= RPM x T (number of teeth) x
 R (chip load)

 Ray Hellstrom

 Thanks Ray,

 Interesting.

 Paul Lamar


 Paul, Are you using a carbide cutting tool? If so, a large nose
 radius can cause chatter. Also, I didn't mention that the depth of
 cut, which should be the adjusted with the speed to produce a
 continuous chip which forms due to plastic deformation of the crystal
 structure in the unmachined work surface and the shear occurs along
 the shear plane. As the cutting tool compresses the metal immediately
 ahead of the cutting tool, the deformation of the crystal structure
 elongates, the material above the cutting edge is forced along the
 chip tool interface and away from the tool.

 Ray Hellstrom


 No it is a sharp point.

 BTW do any of you guys know where I can get a six inch diameter
 steady rest?

 Paul Lamar

Paul

To the best of my knowledge, steady and follow rests are machine specific and not universal. I would start with the lathe manufacturer and get the model number.

Bolton tools sells inexpensive Chinese made ones. It may be possible if your ways are reasonably close to the ones they offer- it might work for you.

Alan Mullen
Colorado

My CC lathe is 40 years old. It came with a steady rest that is too small.

I will make one out of a 10" by 10" steel plate .75 inches thick. A 8 inch diameter hole will
be cut in the plate with flame cutter. More on this shortly.

Here is a picture of why I need it.

Paul Lamar

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