Help/Ideas for turning 2⅛" 303 stainless with low power

[MrWhoopee]

I wo
I wonder if it got lost in shipping and went to scrap?

Sounds like aerospace "excess inventory". Who else can afford to scrap something like that because it costs more to keep it on the books?

 

[OCJohn]

I think that’s the case. They have a lot of titanium as well. The 303 took some digging. Most of the SS they had was 304 and 316.

 

[MrWhoopee]

I think that’s the case. They have a lot of titanium as well. The 303 took some digging. Most of the SS they had was 304 and 316.

Wish I had a scrap source like that, just not willing to live in southern California to get one. Maybe something near Boeing.

If I may ask, how much did that chunk set you back?

 

[OCJohn]

A little over $100 @ $2.50/lb. Not exactly free, but better than anything I've seen online.

 

[OCJohn]

Without flood coolant in 303SS I would run about 200 SFM (about 300 RPM on 2.5'' material). My go to insert for SS is the Mitsubishi DiaEdge DCMT xx.51 MV where xx is the size, I assume 21 for your tool holder. Your feed rate at 0.0015 should be good for finishing at about 0.005 DOC. If your machine is rigid enough, a bit more aggressive on the roughing cuts would be in order.

I have cut about 1/4 mile of 303 SS in the last 6 months or so and these inserts have proved to do a nice job.

I just tried 0.004 DOC and cut only about a half inch before the spindle stopped. (Better finish, though!)

I assume you're cutting 0.005 with more than 250w?

 

[JimDawson]

I assume you're cutting 0.005 with more than 250w?

Well a bit more..... OK a lot more . But I'm surprised that your machine stalled at 0.004 DOC. You were in low gear?

 

[mattthemuppet2]

DCGT will take less force to cut at the expense of insert life. I used CCGT inserts quite a bit with stainless on my Atlas 618 (similar size lathe) and it worked pretty well. Still slow, but doable.

 

[ttabbal]

For HSS, start with the mega thread here on HM.

Models for grinding HSS Lathe Tools

In a recent thread by @Darkbluesky, http://www.hobby-machinist.com/threads/lathe-accessories-tools-ideas-of-what-to-buy.62043/#post-511618, @ttabbal joked about sending me blanks to be ground into lathe tools ... he was joking! But it got me to thinking ... yeah, I know it's not a good thing...

www.hobby-machinist.com

For smaller machines, a very sharp HSS can help a lot. The ground inserts are great as well. With inserts, try to run a DOC of about 2x the tip radius (should be on the insert package). A good HSS grind can peel off tenths.

For feed rate, with carbide try running faster. I know it's a bit counter intuitive, but sometimes carbide just wants to run hard. And make sure RPM is in the right range for the material. Also try to keep stickout on the tool particularly low. Getting what rigidity you can is only going to help.

Ground "for aluminum" inserts will work well for steel, but they do wear down faster.

 

[Aukai]

Jim is this the one your using, or 2.5 304,308?

 

[macardoso]

I highly recommend "aluminum specific" insert geometry for cutting stainless with low power. These inserts are xxGT ot xxGX (DCGT, CCGT, DCGX, etc.). They have a razor sharp ground edge and make cuts with much less horsepower. The tool life is not great but acceptable. I buy these inserts from AliExpress for about $1 each so the cost isn't bad.

In terms of geometry, the smaller the included angle (DCMT vs CCMT) the lower the cutting forces, but also the weaker the insert and the smaller the depth of cut. VCGT is on the far end of the spectrum and is a great choice for low rigidity machines or poorly supported workpieces.

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