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303 Stainless Turning--Speeds/Feeds?

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I'm turning a set of stand-offs for a vintage automotive luggage rack out of 303 SS. The stand-offs are 1.25" Diameter turned down to 0.625" diameter. I'm using an AXA-16 carbide holder with Terra Carbide 22-100-047 | TPG321 APC5T 60° Coated Triangle / Indexable Carbide Turning Insert.

IMG_1733.JPG
I'm getting decent results, but things seem happiest taking a 0.020" deep cut at the slowest turning and feed speed on my Logan lathe. I've heard that carbide likes to take a deep cut, so I tried deeper and faster cuts, but it just generates a lot of smoke and heat and long stringy chips. At the slower shallower cuts, I alternate between getting C-shaped chips and 2-4 inch strings. Should I just go with what seems to work? I tried steel cutting fluid and the blue water-based soap-like lube (Anchor Lube?)--both stunk to high heaven. Without any lube and cutting slowly with a 0.020" depth of cut things get warm but don't stink.
 
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Comments

#2
Do what works the best for you and your machine. It may not be the optimum feed and speed, but for a few parts who cares.
 
#3
Cutting speed for 303 should be around 150 sfm. Your nose radius is 0.016" so a depth of cut of 0.020" should give you a decent cut without chatter. 303 usually cuts easily but works best with positive rake cutters. If I'm not mistaken, isn't a TPG a negative rake insert?
 
#4
The AXA-16 is a positive holder. The TPG is flat on the top and has 11 degree relief.
 
#5
303 s/s cuts at speeds about the same as carbon steel, with positive rake tools, depth of cut should be much more than .020; speed it up! Perhaps to about 300 - 400 sfm. Of course, it depends on the lathe doing the work. 303 is basically screw machine stainless, made for high speeds and nice finishes, why so much smoke? cutting oil is not much needed, try water based coolant. If stringy chips, use more feed or advance the chip breaker on the tool; sometimes, we have to put up with stink, in life, and in the shop ---
 
#6
The AXA-16 is a positive holder. The TPG is flat on the top and has 11 degree relief.
Aloris labels it as a positive rake tool so I stand corrected but the insert beds with zero axial and radial rake and the top of the insert is flat so I'm not sure where the positive come in. I have one of those things, too, but haven't used it in quite some time. I usually use HSS for 303 because I want sharp.

If stringing is a major issue, try taking a deeper cut and increase the feed rate. If you hog off enough, that stuff will chip instead of string.
 
#7
303 s/s cuts at speeds about the same as carbon steel, with positive rake tools, depth of cut should be much more than .020; speed it up! Perhaps to about 300 - 400 sfm. Of course, it depends on the lathe doing the work. 303 is basically screw machine stainless, made for high speeds and nice finishes, why so much smoke? cutting oil is not much needed, try water based coolant. If stringy chips, use more feed or advance the chip breaker on the tool; sometimes, we have to put up with stink, in life, and in the shop ---
John,
That’s what I thought as well. I cut successfully up to 0.040” deep cut. There was a lot of smoke (maybe from Dykem or lube?). The surface finish was rough, but that’s not a big deal for roughing. The chip breaker is as close to the edge as it can be ~0.010”, but the corner sticks out maybe 0.025” beyond the chip breaker.

I will try running faster feed tomorrow.

Thanks!
 
#8
Aloris labels it as a positive rake tool so I stand corrected but the insert beds with zero axial and radial rake and the top of the insert is flat so I'm not sure where the positive come in. I have one of those things, too, but haven't used it in quite some time. I usually use HSS for 303 because I want sharp.

If stringing is a major issue, try taking a deeper cut and increase the feed rate. If you hog off enough, that stuff will chip instead of string.
Mike,
I tried HSS first, but struggled with geometry so took John’s advice on the AXA-16. The carbide works much better than my ground cutters, but that’s likely a grinding technique issue and I lost patience with figuring it out. I’ll get back to it soon.

The -16 holder has 1 degree positive I think (Axial? Lead?) rake and the cutter is flat.

Evan
 
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#9
Evan, the AXA-16 is fine if you have a rigid lathe but if not, there are better options. Stainless likes sharp positive rake cutters moving at continuous feeds without pause. You might consider an SCLCR tool which is definitely a positive rake cutter. I've used the AK inserts intended for aluminum on 303 with success. I tried it because it is ground very sharp, almost as sharp as HSS. The inserts don't last as long as they do with aluminum but they cut pretty well and left a nice finish.
 
#10
My CA16 tool holder has a 5 degree side rake and no lead angle, that is why they call it a positive rake holder; and it faces square, The first one that I bought back in the early 1980s did have a lead angle, apparently Aloris changed the design by the time I bought the second one. The first one was a victim of grinding the body away so that one could reach closer to the center ---- until the insert finally broke out of the holder.
 
#11
My CA16 tool holder has a 5 degree side rake and no lead angle, that is why they call it a positive rake holder; and it faces square.
I went and dug out my AXA-16 and you're right - it has a 5 degree side rake. I stand corrected, again. I don't use this tool much because I prefer the geometry of an SCLCR tool but I have admit that if you gotta' hog stuff off, its hard to beat.
 
#12
Here's the tool in its holder. I finished the other two standoffs. I did try both the uncoated as well as faster feed and speed. Neither worked as well for me as the 0.020" depth and slow feed.
IMG_1734.JPG
 
#13
I use my CA16 for nearly all the work that I do.
 
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