# Turning 303 Stainless  - what am I doing wrong?



## tcweb (Feb 18, 2019)

See pics attached, trying to face some 303 stainless rods.  I have a SB9 lathe, so only 3 speeds.  I've tried carbide bits and HSS.    A few don't look THAT bad, but there's always the nub visible in the center. 

Is 303 just this hard to get a good finish, or am I doing it wrong?  It the key light cuts?  Slower feed rate?  Faster spindle speed?  Radius incorrect on my tool bit?

The turning was done on a much more expensive lathe than my SB9, but I was hoping to do the finishing work at home.

-Tom


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## P. Waller (Feb 18, 2019)

Adjust the tool height until the nub disappears.
Your machine does not have CSS so turn the spindle speed to 11 in order to remove some of the dragging marks.
Use flood coolant.

303 is made specifically for ease of machining in production, compared to 316 it is has similar advantages as those between 1018 and 12L14/1215 steel as far as feed, speeds and finish.

From the pictures it appears that you are not turning it nearly fast enough with a carbide tool.


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## tcweb (Feb 18, 2019)

Thanks for the suggestions. I'll try going to my fastest spindle speed.  Or should I just punt back to using an HSS bit?

-Tom


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## tcweb (Feb 18, 2019)

Oh, and it's not a tool height issue. there's no nub, just an area that looks really crappy near the center.  It's not raised, it may even be recessed.  As if the material is tearing, not cutting.


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## P. Waller (Feb 18, 2019)

tcweb said:


> Oh, and it's not a tool height issue. there's no nub, just an area that looks really crappy near the center.  It's not raised, it may even be recessed.  As if the material is tearing, not cutting.


It is tearing at that point, as the tool approaches 0" in X the cutting speed approaches zero FPM.
There is a way to avoid unsightly tooling marks on the face of turned parts but you will not like that option I suspect.


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## tcweb (Feb 18, 2019)

Do tell.


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## P. Waller (Feb 18, 2019)

Cylindrical grinder.


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## mikey (Feb 18, 2019)

Tom, stainless tends to have more of a satin finish rather than a shiny finish when it is cut with a sharp tool. 303 is much easier to machine than 304 or 316 but all of them require sharp tools, coolant and continuous feeds or work hardening becomes an issue. 303 tends to be a bit gummy, hence the satin finish thing.

The circles near the center are a result of the surface speed falling off as you get toward center. You can minimize them by slowing your feed as you near the inner 1/3 of the face. I tend to run at higher speeds with stainless when facing. On a 1-1/4" diameter piece I am usually running near 1500 rpm and I manually feed toward center. As I hit the inner 1/3 to 1/4 of the face, I slow down the feed considerably. It doesn't completely eliminate the rings but it very nearly does. 

303 has a cutting speed of about 120 sfm but I tend to run slower when turning, about 80 sfm, because I prefer to use a sharp positive rake HSS tool with this material. I take lighter cuts so I can keep up with the feed and usually have no issues cutting it.


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## Karl_T (Feb 18, 2019)

tcweb said:


> Thanks for the suggestions. I'll try going to my fastest spindle speed.  Or should I just punt back to using an HSS bit?
> 
> -Tom



That would be my suggestion. Put a small radius on a super sharp HHS tool and it will be smooth as a baby's behind. use oil. Higher feeds may give better results.


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## tcweb (Feb 18, 2019)

Thanks all.  Cylindrical grinder sounds expensive.


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## P. Waller (Feb 18, 2019)

tcweb said:


> Thanks all.  Cylindrical grinder sounds expensive.


I suspected that you would not like the answer (-:


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## Karl_T (Feb 18, 2019)

You can always use the old machinist method - file sand polish.


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## tcweb (Feb 20, 2019)

Karl, I'm a big fan of file/sand/polish.

I sped up my spindle speed, and went to  a HSS 1/2" bit.   A little cutting oil, and my finish was much better.

Thanks everyone for some great tips.

-Tom


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## bhigdog (Feb 20, 2019)

Carbide cannot be sharpened to as fine an edge as HSS. For most types of non production home shop work HSS will serve much better, be less expensive and easier to use than tungsten carbide...............Bob


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