Turning cast iron

Hi chaps, I am attempting to turn the 6inch fly wheel for my glr "Tina" on my mini lathe , I realise that it's a big ask for a little machine but am trying light cuts in order not to stall the motor.

however IT'S SO HARD I've made a couple of stuart. Engines before and they were fine but I'm even getting sparks flying off the tool and can't seem to get into the metal. Any ideas ?

thanks muchley

dunc

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

1. Are you using a carbide tool?

2. Is your tool sharp and not chipped?

3. Are you ising a fairly slow speed?

4. Is the iron "chilled"?

Point 1. It's often best to use carbide on iron, particularly if the surface is a bit hard - it can sometimes be death to HSS if there's a hard spot or sand on the outside surface of the casting

Pont 2 - remedy obvious

Point 3. You need a pretty slow speed for a 6" flywheel - how slow does your lathe go? Try the very slowest speed you've got. I would say you could go as low as 60rpm if you can.

Point 4. GLR have a good reputation for providing good castings, but occsionally a bad one comes along. It might benefit from being chucked in a bonfire (or even a domestic fire if you have one) for few hours and allowed to cool slowly. This can sometimes soften a chilled casting.

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 there ,thanks for the quick replies. Yup I'm using a carbide tool, I'm running the lathe as slow as possible ( it's a bit of a juggling act. If I start too slow it just stalls when the tool hits it, not a lot of low speed torque on these wee chinese lathes ) so it looks like the casting will be going in the solid fuel stove overnight

Edited By Dismaldunc on 12/01/2013 16:53:44

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

All good advice IMO

Backgear, high torque, low speed 40-50 rpm

Maximise stiffness, tightening everything possible, very short tool length, use tailstock centre etc

Carbide tooling essential

I also put the tool in the parting tool rear position, upside down, this means that most of the iron filings and junk fall down the back of the lathe

good luck

Edited By Ady1 on 12/01/2013 18:08:03

If low speed just doesn't hack it just try higher speeds and tiny feeds with a carbide tool

Higher speed heat issues may mean you have to do the job for a minute or two then leave it to cool down so it could be an on-off job over a couple of days, a pain in the neck but worth it when its finished

Edited By Ady1 on 12/01/2013 18:21:10

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

I agree, but the OP mentions a mini-lathe so presumably it doesn't have a back gear; as the motor speed is reduced the torque doesn't increase. Consequently the power available decreases in proportion to the speed reduction.

The answer is to run as fast as you feel able to do so, to maximise the power available, as suggested by Neil.

Regards,

Andrew

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.

Hi chaps, well with a bit of faffing about and a combination of all your sage advice I have managed to complete one side and am pleased with the result. I ran the lathe a bit faster as per Neil, ground the corner off so I could get a start and finally hauled the flywheel round by hand until I managed to "cut the crust off" many thanks to you al once again.

i live on a Scottish island and am unaware of any other hobbyists, basically any activity that doesnt either feed you or earn you a few bob is looked at a a bit strange. I wish I had a pound for every time someone looks at one of my lovingly created engines and asks "aye that's nice...... But what does it do ? "

Dunc

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

OK _ I remember in the Bad !!! old days when a hard part of the casting had to be worked on with a FILE - ? can they stil be used

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

Neil

Hmm a "file" you say ??? ( looks it up on Wikipedia )

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

It was always known as a "Bastard" file - that was the type of cut not swearing at 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.

I have just turned up a 10" flywheel casting as a favour for a fellow model engineer who did not have a big enough lathe.

It looked as if the outer diameter had quite a few lumps and hard spots in it so I attacked it first with an angle grinder all the way round to get rid of a few thou of crust and any big high spots and it then turned superbly with an indexable carbide tip at around 20 rpm.

A decent file would suffice if you dont have an angle grinder, it just takes a bit longer.

Phil