Tooling and Surface finish

[Pevehouse]

Thank everyone for all your expertise. I will order up some different materials to practice with.

 

[Janderso]

This is dialing in 10 thou per cut at 400 RPM, using carbide . Correction on the size of the stock. It’s 1 3/8 . The finish looks pretty decent till I go to clean it up with sand paper. Maybe it’s going to look like that with the way I’m going about this . Not sure so I figured I would ask the pros. I just see some guys that can get almost a ground polish look just by taking a cut like this. Figured I have to be doing something wrong. Far that matter probably several things

Did I miss it?
What's your feed rate?

I'd be spinning at 600+ RPM with a .003" feed rate for a finish pass
Just 2 cents worth. Actually it's free.

 

[GeneT45]

Slow your feed down as low as it will go (as an experiment, but it's the easiest way to test if that's the problem). Also, looks like you're using a Dxxx insert - not the best for a fine finish, and completely unnecessary in the example you've shown. Do you have a Cxxx, or something with a larger radius at the tip? That pointed Dxxx is going to take a terribly fine (slow) feed to get a 'perfect' finish.

Lastly, as others have said, 1018 and the other mild steels are not renowned for producing good finishes (though I think you can improve what you have). For test purposes some aluminum (usually cuts beautifully) or 12L14 are excellent*.

GsT

*your insert doesn't appear optimized for aluminum, but in my experience you can still get a very good finish with a 'steel' insert if the feed and speed are correct.

 

[Pevehouse]

Did I miss it?
What's your feed rate?

I'd be spinning at 600+ RPM with a .003" feed rate for a finish pass
Just 2 cents worth. Actually it's free.

To be honest I’m not sure how to calculate my feed rate

 

[Pevehouse]

Slow your feed down as low as it will go (as an experiment, but it's the easiest way to test if that's the problem). Also, looks like you're using a Dxxx insert - not the best for a fine finish, and completely unnecessary in the example you've shown. Do you have a Cxxx, or something with a larger radius at the tip? That pointed Dxxx is going to take a terribly fine (slow) feed to get a 'perfect' finish.

Lastly, as others have said, 1018 and the other mild steels are not renowned for producing good finishes (though I think you can improve what you have). For test purposes some aluminum (usually cuts beautifully) or 12L14 are excellent*.

GsT

*your insert doesn't appear optimized for aluminum, but in my experience you can still get a very good finish with a 'steel' insert if the feed and speed are correct.

I’m not sure about the insert. It came with a holding set that came with the lathe. I’m not familiar enough with inserts to know all the different types. I have a grinder coming from grizzly today so that I can start learning to grind my own HSS

 

[DavidR8]

To be honest I’m not sure how to calculate my feed rate

If your machine has a quick change gearbox the feed rate will be indicated on the plate that's usually on the gearbox.
Might look something like this:

 

[Pevehouse]

If your machine has a quick change gearbox the feed rate will be indicated on the plate that's usually on the gearbox.
Might look something like this:
View attachment 473067

Ok, I think I had it set on 112. The fastest setting

 

[DavidR8]

Ok, I think I had it set on 112. The fastest setting

Actually 112 TPI would be the slowest feed rate equivalent to .0047 inches per revolution.
That said, I would attribute the poor finish to a) lousy material, b) surface speed too slow and c) nose radius of the tool is too sharp.

 

[GeneT45]

I’m not sure about the insert. It came with a holding set that came with the lathe. I’m not familiar enough with inserts to know all the different types. I have a grinder coming from grizzly today so that I can start learning to grind my own HSS

Just try something "less pointed" if you have it. The diamond tool in your picture is for getting into tight corners.

A picture of your gear setting plate would be handy as well. If that's really 112 TPI, you should be able to go about four times slower, but I've never seen those feed rates expressed as TPI. (For example, my lathe will only cut 60 TPI threads, but will feed as slowly as 0.0012" per revolution (of the chuck).

Feel like you're drinking from a firehose yet? ;-)

GsT

 

[DavidR8]

A picture of your gear setting plate would be handy as well. If that's really 112 TPI, you should be able to go about four times slower, but I've never seen those feed rates expressed as TPI. (For example, my lathe will only cut 60 TPI threads, but will feed as slowly as 0.0012" per revolution (of the chuck).

Feel like you're drinking from a firehose yet? ;-)

GsT

112 TPI is pretty slow. Four times slower is not likely. My South Bend went to 227 tpi if I recall correctly.