Finally able to get good finish on mild steel

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compact8

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I have never been able to get good finish when turning mild steel ( the kind used for making bolts ) no matter what RPM or feeding speed I used. Using sharper inserts produced slight better results but still the surface was not shiny. Before long I accepted that the metal is to be blamed because there is no such issues on aluminium or stainless steel. Today, I did it again without doing any finishing pass and much to my surprise, the finish is very good. It turns out that the DOC was just too small ( < 0.1 mm ) in the past. Today I dug deeper to 0.5 mm in the final pass and it made a big difference.

Just want to share this experience with other beginners like me.

0.1 vs 0.5 DOC mild steel.JPG
 
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Good find and share!
Especially with inserts you always have to find the sweetspot between RPM/surface speed, depth of cut and how much you feed per revolution.
Sometimes even how you angle the insert(rotating your compound etc) can make a huge difference in how it cuts and how the cutting forces affects your machine and material.
Changing to another insert or material and you will have to try to find this sweetspot again, it can be a lot of work.
This can then be different from machine to machine as they'll have differences in rigidity, affecting how the cutter performs.
Definitely more complicated than it can seem sometimes. :grin:
 
I have found that light finish passes toast the finish quality (on my setup) Also, RPM I have been running too low. 12l14, 4140, 1018 were hopeless for me until I started using a .025" final pass. God help me if the part was a few thou large...really have to compensate for deflection and hope you're right. It seems feeds and speeds are not a rule book, just a starting point. Sadly, it took YEARS to figure this out....not sure about you.
 
GunsOfNavarone said:
hopeless for me until I started using a .025" final pass.
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This DOC is very close to that used in my case which is .02 inch. Your experience confirms the importance of DOC in determining the finish on mild steel

GunsOfNavarone said:
Sadly, it took YEARS to figure this out....not sure about you.
Click to expand...
About 20 years in my case …… For a very long time I have accepted that mild steel is bad in regard to finishing until I found this by accident a couple of days ago.
 
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compact8 said:
Interesting concept. Will try it out after I have got a grinder. Right now I am limited to carbide tools.
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What insert are you using? DOC has a strong relationship with the nose radius, so it will be interesting to see the correlation for your setup.
 
jwmelvin said:
What insert are you using? DOC has a strong relationship with the nose radius, so it will be interesting to see the correlation for your setup.
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The insert is Kyocera DCGT070202-TN60. nose radius is 0.2 mm. Material is cermet uncoated, for cutting steel and cast iron.
 
compact8 said:
The insert is Kyocera DCGT070202-TN60. nose radius is 0.2 mm. Material is cermet uncoated, for cutting steel and cast iron.
Click to expand...

Thanks. So have you tried cuts larger than nose radius but smaller than the 0.5mm you know works?
 
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