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sbwhart:
Hi Nick

Bin there done that got the grey hairs, look on it as a learning exercise, no blood spilt which is a good thing.

Deans advice was spot on :thumbup:

Have fun

Stew

Stilldrillin:
Ooohhhh....... Nick! :bugeye:

All part of the "fun" that is home machining! :wave:

No one damaged..... That`s the main thing! :thumbup:

Like wot Stew said, Dean`s spot on.....

I would have machined away the threads under the jaws, for a better grip . (Or held the bar t`other way round).

Very small centre drill hole, with centre in place to support, but no real pressure applied.

1" bar...... 250rpm
2" bar...... 120rpm
3" bar........ 70rpm

Part in to a depth of 1/2" or so, only. Then saw through the reduced diameter.

David D

NickG:
Thanks for the advice Dean and all.

Just for info, the lathe is a Harrison L5 - 4.5" x 24" or something. Very robustly built, although not as robust as Darren's, with 2 hp ph1 motor.

I've parted cast iron, gun metal and aluminium with no problems but this was steel to spec in attachment. It seems to machine nicely but fairly tough. There is about 3 1/2" protruding from the outer edge of the jaws.

I was going to hold it with the centre - I don't know why I didn't, just thought it would all be rigid enough. I'd say the parting blade was stuck out just over an inch. So in future I should make the initial cut with just a small bit sticking out then extend it, then it will be supported by the cut walls of the stock I guess the further you get in?

I will have to try some different smaller diameters of steel. I was going to make the thin cam disc from cast iron as I know I can part that but my try it from steel as an exercise. Not sure how much parting blade is left in there now!

I feel like I've had a good work out cutting the blanks by hand.

Should have mentioned before, I did do the 2nd oil cup - there are just 1 per engine, perched on top of cylinder.

Thanks for the advice, am coming back around to the idea of parting!

Nick

andyf:
I too have had problems with a "blade in a holder" parting tool. I reckon some of my difficulty might come from not getting the cutting edge dead square with the sides of the blade when I sharpen it, so the blade, being thin and thus having a bit of flex, gets steered increasingly off course, trying to flex more and more as it goes further in. The larger the diameter of the stock, the more the overhang of the blade, giving it more opportunity to flex. Then again, my problems may just stem from ham-fistedness and lack of experience.

I need to experiment to see if setting the blade short for minimum flex, going in say 1/4", and then pulling some more blade out of the holder will enable the sides of the 1/4" deep groove to keep the blade on course. At present, I'm using a parting tool ground on the end of a square HSS blank for greater rigidity, but I can only get just over 1/4" in with it before the saw has to come into play. But even that shallow groove gets me well on the way - in terms of cross-sectional area, a 2" dia, 1" radius bar is 3.14 sq inches. With a 1/4" groove round it, there's 3/4" of radius = 1.76 sq inches left to saw through, so 44% of the job has been done by the parting tool.

Andy

Darren:
I too had problems with HSS parting blades cutting steel. OK for brass and such though.

Then I bought an insert parting tool, different world. Now I part off under power and it can be quite a rapid speed too.
This one had left and right cutting edges so quite versatile as well.

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