Hi Dunc,

I have castings made to my own patterns and sometimes when turning hit hard spots. The only way I have been able to deal with them is slow the speed (back gear) use tungsten carbide tipped tools and if really necessary touch the tips up frequently on the grinder.

The same is generally true for getting through the hard skin. Intermittent cuts in and out of hard spots will destroy even my tungsten tipped tools – I suspect that is common experience.

Hope this helps,

Clive

Sounds like the iron is chilled, and therefor has a very hard skin. Try grinding a chamfer on an outside corner to let the tool start on the softer metal underneath. If you have one use a carbide tool, try slow revs.

Hi Duncan,

Don't act too fast! I have turned several flywheels and large items on my mini lathe with success of that sort of size or bigger in cast iron and steel.

This is a job where breaking rules and experimenting is fine.

Make sure you have it set to low gear. Don't set it as slow as possible, because that's about 1 rpm which is far too slow. Set it to about 1/3rd – 1/2 full speed in low gear. Believe it or not the higher speed will help it 'flywheel' past hard spots!

If it still stalls on the slowest possible feed, try using the topslide to manually feed very slowly.

If you still have hard spots it can't tackle, grind through the skin carefully.

Once you have a clear turned surface go over it on autofeed witha HSS tool for a good finish.

Fibnally don't put a small flywheel in a fire. I did this to a Lady Stephanie flywheel trying to get rid of some 'dish'. It came out looking like a pretzel and hangs on my workshop door to remind me not to be a prat.

Neil

I should have said dead slow on mini lathe is nearer 10rpm not 1 – they go slow, but don't go THAT slow!

I would go faster than 50rpm with a carbide tool – I reckon up to 200rpm or even more at 6" diameter.

Neil

If cutting cast iron consider not only speed, approx 2/3 the cutting speed in feet/minute compared with mild steel, but also top rake on your tool. If you are using something like 20 degrees top rake for mild steel the this will not cut cast iron very well at all. For hard cast iro, and if yours has chill spots it will be hard, then zero degrees rake is probably worth considering as a starting point. Carbide tooling obviously.

About 50 rpm would be a good starting point on a mini lathe I suspect.

Good luck.

You have my sympathy! If im right then you dont have a backgear, so slow turning is out. If your getting sparks then its not going to cut. Your only real option is to find someone with a big lathe and let them make light work of it. Thats what I had to do.

Had a job modifing some cast iron pullies 10 years or so ago, they were mostly chilled in the area that required work done, and with the hard ones I set up the angle grinder on the tool post, and did the job that way, it was quite adiquate. Good to hear you got yours done OK Dunc. Ian S C

I have a file with teh surface covered in little carbide blobs, not much use except for such tasks.

Neil

Tipped tool, 0.040 cut, get under the chill, it is no use skidding over it.

Its worth mentioning that the miniature lathes tend to use a variable speed drive. this is very good for finding the correct speed for materials. but from experience they have some major disadvantages the main on being that when you reduce speed using a belt drive or back gear the reduction turns the speed into torque so you can take deeper cuts and generally end up with a good finish. the modern model lathes just reduce power to the motor and you end up with both a speed reduction and torque reduction. To machine on these lathes it is best to set up a automatic feed at a very slow feed speed. this just means you will be able to get a cleaner finish on the cuts without stalling the motor.

Those RDG ones turn up quite well despite looking a bit rough on the outside, and very good value for money. I have used one of thos e"clarkson ones and several of the heavy 8" ones.

If the cast iron has been chilled it will,be incrediblyn hard. hard enough to ruin carbode tipped tools. Know of it happening on a transfer line; a very expensive error on nthe part of the foundry!

Might well well be worth heating and slowly cooling, before trying again.

Howard.