Posted by SillyOldDuffer on 12/05/2020 11:01:49:
Hi Shaun,
Part of the fun is learning the ropes!
An ML7 in good condition is a decent machine, but – like all machines – has to be used within it's limitations. Not serious in practice but the lathe was designed 80 years ago towards the end of an era when HSS tools dominated.
Lathes made before about 1900 were designed to cut with Carbon Steel tools. As Carbon Steels soften at about 200°C, early lathes are spindly affairs that cut rather slowly. No point in putting fast powerful motors on them because their bearings can't take the speed, and their frames bend. But, used slowly they produce accurate work.
Circa 1900, HSS hit the streets. HSS cuts without softening up to about 500°C, and can be worked 5 times faster than Carbon Steel, so 20th Century Lathes designed for HSS are much stiffer, heavier and powerful. During the 1930's it was found that carbides outperform HSS, and today's industrial machines are monsters, removing metal up to 30 times faster than HSS, and able to cut very hard materials. An ML7 isn't in this class, nor does it need to be! It's a precision machine, think scalpel rather than axe, used to make accurate parts rather than hack metal at maximum speed. Power – ¼HP is a bit low, ⅓HP reasonable, ½HP plenty and ¾HP over the top. Substitute patience and skill for brute force!
HSS can be sharpened on an ordinary bench-grinder. Mostly these are sold with grey wheels, coarse on one side, fine on the other, which is fine. Being a clumsy oaf, I'm not good at it, but grinding HSS just needs practice. Carbide inserts are an alternative; you can get HSS inserts, but the sharp carbide intended for non-ferrous metals works well on steel at ML7 speeds. They're available in bewildering variety, but the types sold by hobby suppliers are a good place to start. Inserts remove the need to sharpen, and I value their easy convenience. (About 80%)
Generally easier to get good finish with HSS because it can be sharpened. Carbide likes to cut blunt, and it produces an excellent finish when used to specification. But this is too much for most hobby machines, making it necessary to experiment sometimes.
Experts prefer to buy blanks and particular tools rather than sets, but I found a set to be a good way to start. With hindsight, a tangential toolholder is attractive, and Eccentric's Diamond Type comes with a jig to simplify sharpening even more.
Perhaps the best book on lathes available is Sparey's The Amateur's Lathe. Written in the 1950s, when the ML7 was new, the only disadvantage is it doesn't cover developments like carbide inserts. Highly recommended!
As you suggest, not all QTCP are well-made. My main objection though is value for money. First there's the tool-post itself, then the holders. I'd need 8 or 9 at about £20 each. Say £200, which is a lot of money compared with a handful of shims, especially as I don't change tools much. I've got better things to spend the money on, but others find them indispensable. Not necessary for a beginner, maybe later.
Dave
Thanks for that info.
I may well just use the lathe without a fancy QCTP for now anyway.
I have just finished machining a new feedscrew for my lathe today, using the cheap chinese carbide tools off ebay, they didnt do the greatest job and I had to improvise with shims(see photos!) but considering this, im still quite impressed with the finish.
I had to change tooling about 3 times, the parting tool i bought was supposed to have had the correct holder for an ML7, but it still needed heaps of shimming. This is the parting tool ive got, it seems to have a nice sharp carbide blade that has not gone blunt, but it takes ages to cut a part off!

I still really dont know alot about the different types of tooling, im really still learning at this stage.
I did have trouble making too deep cuts, probably taking off about 1-2mm max in one pass is about the most it can handle. Also it would also seem to slip rather than cut at times leaving uneven surface (see photo) I wasnt making a very deep cut when this happened, so not sure what was going on here.
All in all the finished part seems OK considering. Will be great to get some decent tooling anyway.





Edited By Shaun Belcher on 12/05/2020 12:29:00