Turning Cast Iron with HHS

outsider347 said:
By now, you probably figured out the question

Tool bit dulling in about 15 rev of the work. every HHS tool that I have dulled

So got the books out & re ground to the following spec
8 deg F clearance
10 deg side

5 deg Pos top rake

80 deg tool included angle
speed at 50 ft /min


Im attempting to machine a back plate for my new 4jaw All purchased from Shars

Suggestions appreciated
Click to expand...

You may have to slow the feed down more. The material is dusty you might want to use a shop vac while turning. I hope someone has a good idea how to help you. Bill C.
 
When I make mistakes,I just hurry back to delete them,hopefully before too many have seen them!!!!:) I just turned 72,things sometimes get remembered wrong.
 
Remember,in the many years before HSS was available,cast iron by the tons was turned with nothing but plain carbon steel tools,all they had. You just have to be able to turn at very low RPM to cut it. Most modern lathes just do not go slow enough. My 16" lathe will swing 25" in the gap. It came with a 60 RPM slowest speed. That is just ridiculous for turning large diameter steel or cast iron. I put an intermediate pulley in the lathe and run it at half speed to get down to 30 RPM. I don't miss the halved top speed. 30 RPM is still much too fast. If my lathe was 3 phase,I'd get a VFD and run it a lot slower for large jobs. I had a Promaster at work that would do 11 RPM. It swung 19" across the bed,though it was listed as a 17" lathe. I forget what It'd do in the gap. I appreciated the 11 RPM,though.
 
I agree with George. when turning that hard crust off from cast iron, the slower the spindle speed, the better. Also i don't know if it was mentioned before, but also if you can take a deeper cut on the first pas, it will get you below that crust, and will cut much better.
 
The large facing lathes many years ago had a worm gear turning a big spur gear that rotated the faceplate. The worm gear was powered by the lines haft,which was not a high speeds affair. They must have turned 1 RPM or less when facing large castings with carbon steel tools.
 
This thread is pretty well beat to death but i'll add my 2 cents worth.

When using HSS, top rake should be zero, maybe a little on the negative side. Well rounded nose radius,>1/32". Always cut dry for us home shop users. Keep your surface feet per minute around 20, yes 20 SFM. Heavy feed! even with carbide.

Now days, do what everyone else is doing move up to carbide tooling for cutting cast iron.
 
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