Author Topic: Lathe cut question  (Read 96 times)

jpigg55

Lathe cut question
« on: December 04, 2019, 05:21:56 PM »
I was turning some mild steel today and noticed some "Rings" left on the steel.
The steel is Unknownium from the local scrapyard that seems to have a little residual magnetism in it from them handling it with electromagnet cranes.
Anyway, I wasn't sure if these were caused by a dull cutter (self ground HSS) or the chips building up on the back relief from the residual magnetism.

I ground a steeper relief angle and re-sharpened it which got rid of the rings, but I got to wondering if it was the back relief or cutter sharpness that caused it.
For future reference, can anyone tell me if this is caused by one or both of them or something I didn't consider.
SB 9A, Clausing 8520, Sanford MG 612

chips and more

Re: Lathe cut question
« Reply #1 on: December 04, 2019, 05:49:27 PM »
I suppose with the finer the swarf, the easier it will be hold onto that residual magnetism? So depending on what the chips look like will or will not show the rings, because of chip size? Maybe try and degauss the metal first? Is the finish OK? Are you still making good parts? Just have a curiosity? If you have a big chip and also little chips like filing size with the same cut. Maybe you are cutting and also rubbing? Can you show a pic of the cutter?

34_40

Re: Lathe cut question
« Reply #2 on: December 04, 2019, 05:52:53 PM »
I was turning some mild steel today and noticed some "Rings" left on the steel.
The steel is Unknownium from the local scrapyard that seems to have a little residual magnetism in it from them handling it with electromagnet cranes.
Anyway, I wasn't sure if these were caused by a dull cutter (self ground HSS) or the chips building up on the back relief from the residual magnetism.

I ground a steeper relief angle and re-sharpened it which got rid of the rings, but I got to wondering if it was the back relief or cutter sharpness that caused it.
For future reference, can anyone tell me if this is caused by one or both of them or something I didn't consider.

I've got some of the same steel and it's done the same thing, made "rings" during a cut.  It also cuts "stringy" at times.  To counter this I usually have to make sure I stone the cutter as sharp as I can and don't take small cuts unless it's a spring pass.  And I use the smallest back rake I can.. HTH.
Clausing 108, Clausing 8520, Atlas Horizontal, Lincoln stick and mig welders

Carpenter84

Re: Lathe cut question
« Reply #3 on: December 04, 2019, 07:10:30 PM »
I dunno, I'm thinking it's not the steel and more so maybe chips in the rack or the lead screw. The rings look pretty evenly spaced.
That's my thought anyways.
I used to get subtle changes in my finish, it was because my machine was loose
Shawn

First 9x42 column mill,
Enterprise 10x28 lathe,
Ko Lee 6x12 surface grinder,
Airco dip/stick 160 welder,
Fully stocked wood shop.

woodchucker

Re: Lathe cut question
« Reply #4 on: December 04, 2019, 08:37:15 PM »
can't see your tool clearly to see how it's ground.


2 things come to my mind.
the tip of the cutting tool doesn't have a radius and is leaving those marks
the swarf is cutting those grooves  from rubbing.


put a radius on the cutting tip , provide more relief on the cutting tools trailing edge. it may be dragging the swarf.
Jeff
Clausing 8520   SB Model 9a - power hacksaw, Milwaukee band saw in a table.  Delta Rockwell Surface Grinder (not online yet .. being rebuilt where am I going to stick this)
For pics: https://imgur.com/user/woodchucker/posts

jpigg55

Re: Lathe cut question
« Reply #5 on: December 05, 2019, 08:17:36 AM »
Initially, I had a large radius on the cutting edge, maybe too much.
It was only the fine swarf sticking to the metal as I took lighter and slower cuts when closing in on final diameter and that's when the rings started to appear.
I also didn't have a lot of back relief which allowed the swarf to collect on the trailing edge of the cutter due to residual magnetism. Larger chips would fall away when hogging off material.
I did grind more relief and less radius, stoned the edges and rings went away.
Just got to wondering later what might have been the cause. Wasn't sure what the cure was, sharper tool, less radius, more back relief, or combination there-of.
SB 9A, Clausing 8520, Sanford MG 612

woodchucker

Re: Lathe cut question
« Reply #6 on: December 05, 2019, 01:49:23 PM »
Initially, I had a large radius on the cutting edge, maybe too much.
It was only the fine swarf sticking to the metal as I took lighter and slower cuts when closing in on final diameter and that's when the rings started to appear.
I also didn't have a lot of back relief which allowed the swarf to collect on the trailing edge of the cutter due to residual magnetism. Larger chips would fall away when hogging off material.
I did grind more relief and less radius, stoned the edges and rings went away.
Just got to wondering later what might have been the cause. Wasn't sure what the cure was, sharper tool, less radius, more back relief, or combination there-of.


I can tell you that more radius equals nicer finish.  I have played with radiusing tools, and found that more equal better finish. I haven't seen where it is a problem. But I have not worked in titanium , iconel or other tough material.
Jeff
Clausing 8520   SB Model 9a - power hacksaw, Milwaukee band saw in a table.  Delta Rockwell Surface Grinder (not online yet .. being rebuilt where am I going to stick this)
For pics: https://imgur.com/user/woodchucker/posts

Machinists Gazette

Re: Lathe cut question
« Reply #6 on: December 05, 2019, 01:49:23 PM »