PM-1660TL

[erikmannie]

With carbide, and looking up 2" 12L14, the calculator says 1500 RPM?

This is cold rolled steel, but clearly I need to increase RPM.

 

[mmcmdl]

Cut at the tailstock and cut at the headstock . Measure the difference . Your finish will depend on feed per rev and your insert radius .

 

[erikmannie]

It took a long time with the slow feed rate & RPM, but this is what it looks like after the .001” deep dry pass at .0022” per rev.

The diameter at the tailstock and was .0035”smaller than the diameter at the chuck.

I’m going to use all of the suggestions in this thread today.

 

[mksj]

You feeds, speeds and DOC are not correct for the type of insert. The SFM would be in the 300-400SFM range which for 2" diameter works out to 600-800 RPM, you should be in the feed rate of around 0.007-0.010 IPR, the minimum cut in particular with a molded edge insert is 1/2 the nose radius. The nose radius also dictated the maximum recommend feed rate

Below is 4140 3" turned at around 600 RPM using a CCMT 32.51 insert, the first 1/2 is at an IPR of 0.004 and the second part is 0.008. The DOC was something around 0.050".

The change in diameter has nothing to do with leveling, it has to do with the tailstock alignment. This also can change with material, insert , depth of cut, etc. So once set it may need to be tweaked slightly to get an even diamter cut over that distance or longer. The lathe should be leveled accurately and then checked periodically, you should not have to twist the bed for alignment. That is a last resort after you have eliminated everything else. Headstock alignment is checked with an unsupported stock, typically that should be no more than 5X the diameter, but there are other approaches to testing it. My experience with several of lathes from this manufacturer is that they are spot on from the factory.

 

[erikmannie]

At this point, the surface finish changed in this way as it got close enough to the chuck.

One could say that it went from a calico-type look to striations.

 

[mmcmdl]

You're going to get vibration out near the tailstock , that is what you're looking at . Don't be afraid to throw a feed rate on that machine . You're trying to baby a nice size lathe .

 

[erikmannie]

Well, working at 1200 RPM is more exciting. I immediately realized that the flood coolant was a no go. I did a .025” deep (radius) dry cut at a feed rate of .007” per rev. The chips were flying everywhere, and they were hot!

 

[mmcmdl]

Well, working at 1200 RPM is more exciting. I immediately realized that the flood coolant was a no go. I did a .025” deep (radius) dry cut at a feed rate of .007” per rev. The chips were flying everywhere, and they were hot!

That's what chips are suppose to do . Come off like corn chips and remove heat from the stock .

I find it interesting also that a lot of folks on the site are looking for cylindrical ground finishes on a lathe . IT's not going to happen .

 

[erikmannie]

This is the finish after that:

 

[erikmannie]

That's what chips are suppose to do . Come off like corn chips and remove heat from the stock ...

...and into boot onto my bare ankle to teach me take the time to put on socks (and long pants, for that matter).