Hi Neil

You buy the size that fits your toolpost. I bought a Myford size quick change toolpost (QCTP) for my lathe. This can take 12mm cutters and because it is adjustable vertically, 8mm and 10mm too. Some 1/2" fit but if they are a tad oversize then they need milling down.

John

I have to agree with both John and Phil - but "give" (or lack of) in the tool to some degree depends upon the cut you are taking.  On my ML7 I often use 1/4 square cutters for fine work but if roughing out, a 10mm or 12mm square with carbide tip. Also with things like a qc toolpost, there are various elements of "give" before you even get to the tool. I hesitate to admit it in public but if I occasionally have a "dig-in" when parting off, the lathe (ML7) stops, the qc toolholder flexes downwards and the parting blade (1/16 thick) remains intact! Theoretically none of that should happen but it does, and parting-off is probably the most testing cut anyone is likely to take. In those circumstances there is a lot to be said for rigidity not just in the tool but also in the toolholder. Like Phil says, it all comes down to compromise!

I think the best tool for my Boxford is about 1/2". I bought a parting off tool that was a bit over that (about 15mmx5mm) at the car boot sale on the weekend and when I put it in the lathe earlier I had to grind the top down so the cutting edge was centred on the bar I wanted to cut off. Now I've got a proper parting off tool though it flies through really easily. I think it may also help that I'm getting the hang of grinding the cutters.

I'm itching to get out and try some accurate screwcuts now I've got some more tooling. I picked up a dial to check the work is centered on the weekend too so my toolbox is slowly growing! Might have found a fixed steady too - I want to try threading large diameter pipe which has to grip on the outside edge of the jaws.

I was thinking about buying a couple of those 6mm tool holders, are they any good? The idea of using another tool as packing is a good one, if I ever buy any I'll try it.

I'm quite soft on kit and don't tend to push it. It's only a hobby so there's no rush and as you say the Boxford isn't that big anyway.

Nick Kempley wrote:

Particularly useful for odd shapes where you don't want to go grinding bigger cutters

That was my thought. I'm looking for a couple of these holders at the moment, hopefully even a 90 degree to do internal threads in pipes. The grinding of a half inch cutter is a pain compared to say a 6mm. Even the difference between 3/8 and 1/2 on my little grinder is quite obvious.

I've been away over the weekend so am a bit behind on the ebay scene. I'll go and have a look now.

Use this type of holder all the time on the Boxford at School they work really well, but one not being used  always gets in the way if  you mount two in the 4 way tool post.
Ashley

Although I share Nicks approval of toolbits and toolbit holders, using them in an interchangeable (QC) toolpost system doesn't really make sense, especially on a small machine, as overhangs, projections and general bulk do stack up burning up space which no small machine has to spare.  I've mentioned before that, in my view, the best way to exploit these devices is by basing a proper system around the idea of changing bits in "fixed" holders using a tool height gauge to simultaneously set bit projection and height.  Working in this manner relatively slim two slot tool carrier blocks can be used minimising interference from the resting tool when the other is in use.  I found it helpful to adopt 25° (ish) off straight in as the standard position for the topslide which also gets the handles nicely out of each others way.  Two blocks would do nicely for a starter set.  One carrying bent to the right and bent to the left holders for normal turning and facing duties respectively the other nominally for parting tool and boring bar although its doubtful it there is any advantage to leaving the boring bar mounted at all times.  With a slot waiting and tool height gauge for set up mounting a boring bar is fast.  The T-slotted top slide on the Boxford makes it trivial to change toolblocks if they are made as complete assemblies with Tee nut, stud and locking handle.  Built up construction works just fine for the block and Tee-nut. A person more refined than I would arrange some form of indexing so the turning tool carrying block could be swivelled 180° to change from turning to facing duties and the parting tool block accurately mounted exactly perpendicular to the lathe axis.  I happily used a variant of this proposal for many years in my SouthBend driving days using pairs of welded shank tools in rapid interchange 4-way post, Tee nut & stud assemblies.  20-20 hindsight says toolbits and holders would have worked a little better.

Once you have a nice collection of toolbits ground to the correct angles this is the system least likely to tempt you into using a less than ideal tool for the job as mounting a different bit is no fuss.  Even if you have a QC set-up with plenty of holders only the uber organised have enough tools mounted never to fall into temptation! ( I've usually got only 6 or so of my Dicksons filled.)  Toolbits have the advantage of being much easier to grind to defined shapes using templates than  welded shank tools.  Despite doing it on numerous occasions I've never subscribed to the idea that twisting a tool post to change the cutting angles is a satisfactory way of going about things.  Standard HSS tool blanks are long enough for two, sometime three, cutting bits so building up a set with all the right angles is affordable.

Clive