Nose radius

[Aukai]

What nose radius for cast iron on the lathe? My facing, and register cuts did ok with light cuts. If I try to turn the diameter my tool presentation for approach angle is limited, as the cross slide is fully retracted, and I can get 10* max at this diameter. I've tried 5*-10* 100-700 RPM, and at .010 DOC I can stall the spindle hand feeding with inserted tooling. I'm sure I'm not doing something right. I have gotten a good shower of chips, then it slows up, and powders, then blows chips again. In the end it just is not cutting well, and I must have burnt the insert.

 

[mikey]

Pics of your set up?

 

[Aukai]

I did not get any, I took it all down to clean up the God-awful mess.

 

[mikey]

Last time I turned cast iron, I used my Aloris AXA-16 tool holder with TPGA-32.1 inserts, so a 0.015" NR. It is a flat topped insert with an adjustable chip breaker and cuts cast iron clean at about 400 rpm.

 

[darkzero]

For the cast iron back plates I made in the past few yrs I was using CNMG inserts with 1/32" nose radius. Larger nose radius seemed to do better for me than a smaller one on the blanks I bought. They were Grizzly SouthBend branded backplates that were listed as "fine grain cast iron" (whatever that is).

 

[mksj]

I would suggest using a sharper insert, on cast iron I use inserts that are also rated for aluminum so typically with a sharp ground edge with a positive rake edge. Something along the lines of a CCGT 32.51 or similar. I use Korloy WNMG 331 and Ceratizit CCGT inserts (see box labels below, red is cast iron). Speed will depend on the diameter and DOC. The sharper edge will do better with lighter cuts for surfacing as opposed to material removal, the bigger the nose the larger the minimum DOC but often the smoother the cut. No lubrication. If I am doing a lot of material removal I use the Iscar CCMT IC907 coating, they work on a wide range of metals and last a long time.

Can't recall ever stalling a lathe in a cut, let alone dropping more than a few RPM. If you are slowing it down then you are not cutting.

 

[darkzero]

at .010 DOC I can stall the spindle

Have you checked the belt tension?

 

[Aukai]

Sorry for the delay I'm prepping for Pediatric Advanced Life Support class tomorrow
I have this Korloy in my box, but have not used them, and the inserts that came with the lathe are 300 series but no labels.
Not after the stall, but I felt it was within tolerance before, something I'm doing isn't right, just by how it chips, and powders, then dies.

 

[darkzero]

Try the CCGT aluminum specific inserts. They should do well for finishing & a lot more free cutting but aren't great for roughing on ferrous metals cause they're fragile. I haven't tried them on CI but I have used them on steels & SS. CCGT are one of my favorite inserts, I have a bunch of them from various brands.

You should be able to tell if it's the belt slipping. Listen for the motor sound just before it stalls. If you are actually stalling the motor you'll hear the motor slow down. If you don't hear that it's mostly likely the belt slipping or something else.

I forget what lathe you have (PM1228?) but I can't imagine that you are actually stalling the motor not with only a 10 thou cut.

 

[Aukai]

That's the mill Will. I need to rough out 1.5" cuz you, and Mikey said. It pulls down on the RPM, and if I do not release it will stall.
I just went out, and the belt has more slack than before, and I re tightened it. The motor sounds like it stops completely though in operation,I'll try again and see.