TPG322 wierdness

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Batmanacw

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I was having issues with finish on my Mulliner Enlund lathe with TPG322 inserts on 12L14. The USA made no name inserts were tearing the surface pretty bad on 0.005" per rev 0.005" to 0.010" per side cuts. Especially at my top speed of 417 rpm. I tried different corners to no avail.

It took me a long time to get smart enough to try a different brand of insert. The original insert had a frosty looking TiN coating. The new insert had a shiny TiN coating. Night and day difference. I was able to take a 0.003" per rev and 0.010" per side, while not shiny, it was very smooth. Super shiny at 417 rpm is hard to do at 1 1/2" diameter.

Now I'm looking for shiny coated and uncoated inserts. Lol!
 
I know I'm "old school", retired in 2000, but I'd be using HSS on 12L14... And .010 depth of cut? If you want a good finish you've got to cut metal, not scrape it.
 
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Iscar's IC907 coating is outstanding for working with 12L14. It takes shallow cuts well and the SFPM required is much lower than the online calculators say that you need. Little Machine Shop's speeds and feeds calculator says that you need 3440 rpm on 1" 12L14. I get a very nice finish at 700-750 rpm. It definitely needs to be fed fast enough to get a good finish but that is a reasonable rate as well.
 
The only time I've had poor finish on 12L14 is if I have a chipped insert. I usually use TCGT or TCMT. Sometimes the chip in the insert is not visible unmagnified. But using a 10x magnifier shows the edge flaw.

I've turned 12L14 at 500-700 RPM 1" diameter on a mini lathe using TCGT inserts (uncoated cheap one's) and gotten smooth good looking finishes. It's quite forgiving. I also use TCGT inserts on my 10x22 and get beautiful finishes on 12L14 as well. At this point if the finish gets weird, I simply change the insert edge first, because that's usually the problem.
 
Sometimes all it takes is a coupla licks with a diamond file to make an insert cut like a champ. With the cost of inserts these days, I always touch mine up before I flip to a new edge or change them.
 
It turned out that my quick change tool post was teetering on the T nut. Once I corrected that the finish got a ton better. Nothing shiny. Just smooth with no nasty tearing. The 417 rpm top speed is brutal. The addition of light cutting oil helped a bunch too.

I might spend the money on a 5" pulley. I'll loose some torque but not enough to matter.
 
@Batmanacw one trick to try is to buy some inserts that are ground *sharp* for cutting aluminum. You should see a step up in surface finish.
 
Dabbler said:
@Batmanacw one trick to try is to buy some inserts that are ground *sharp* for cutting aluminum. You should see a step up in surface finish.
Click to expand...

I have a CCMT insert holder on its way for this lathe which will end up being my main tool. I have lots of aluminum inserts for that one. I'm also looking into buying a larger pulley to get to 515 rpm or on the high end.
 
Old school here - HSS on 12L14 very nice finish.
 
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