Why are my tools too high?

I recently aquired a Myford ML7 lathe which is in good condition and as far as I know, pretty much as it came from the factory. I bought an inexpensive set of basic cutting tools (12mm) as all the tools that came with the lathe were too small, mostly 8mm. When I check the cutting height with the centre point they are all slightly too high, maybe about 1mm.

So do I have the wrong size tools or is there some adjustment I can make on the lathe?

Hello Chas,

Welcome to the forum, they usual size for an ML7 is 3/8" or 10mm, shimmed up with thin metal if required.

Neil

All my tools are 5/16 or 1/4 with shims stuck underneath

Roy

Rigidity, my ML10 I use 12 mm tools as I machined off about 1.5 mm from the bottom. easy enough with milling cutter and the tool on it's side in the tool post.

Perhaps a headstock riser is required? with right riser you could use 25mm tools?

Regards Ian.

3/8" is the 'design' size, but I am sceptical that a Myford can deliver a cut heavy enough to cause issues with an 8mm tool.

Neil

What toolpost is fitted to the machine as they can determine the max tool size that will work and how the height is adjusted

Neil it also depends on how far your tool sticks out, a thicker one will be less prone to chatter as the tool overhang increases regardless of actual cutting load.

Rik, by "too small" the OP probably means to small to come upto ctr height

Edited By JasonB on 04/06/2017 10:19:39

Whilst the tool capacity for the Myford toolpost(s) may be advertised as 1/2", it probably refers to using the "Boat" type tools which allow the toolbit to rock to allow adjustment in height.

If you're using 1/2" HSS blanks for rigidity, then just grind the cutting edge a little lower.

Obviously it's a bit more of an issue with carbide tooling, either brazed, or inserts. In this case you need to mill or grind a bit off the bottom to lower the cutting edge proportionally.

it's obviously less of an issue with the single tool holders where the base of the tool bit sits directly onto the topslide.

In my case, I made something similar to this many years ago. Obviously the issue is that the bit of metal below the slot for the tool needs to be of a suitable dimension to prevent it bending under load, and it's this thickness which restricts the tool height.

I got round this by losing that piece altogether and machining a plain rebate rather than a more conventional slot. i.e. there is no bottom to the LH edge of the toolholder. I then cut and welded a short length of ex-bed angle iron in place. This provides a very thin base to the toolholder, but it's still rigid as one now has a square hole for the tool, rather than a three sided slot. I can now use 1/2" tooling without issues.

Sorry for all the external links, but the relevant parts are on my other lathe 30 miles away, so I can't photograph them at the moment.

+1 for Clives suggestion to mill off a couple of mm from base of tool

Mick

Thanks for all the replies. To clarify a little, I thought, perhaps niaively, that the toolpost would be designed to accept a certain size standard tool without shims. I have a couple of 12mm tools that came with the lathe and have obviously been reground, that are pretty much spot on centre height so I bought a set of 12mm tools expecting the same result. I have used the 8mm tools with shims but find it quite a faff to get the height right - I understand people strip down feeler gauges to get the fine adjustment so I'll give this a go. Also I had thought that I would mill off the extra height to get my new cutters just right which would make them handy for everyday jobs and whilst I'm at it, I would make some accurate 1 piece shims to use with my smaller cutters.

Thanks again for all the advice, I feel I'm much better informed on the subject now

Edited By ChasF on 04/06/2017 11:33:27

That's the best way to go. I would suggest even going down to 1/4 in or 6mm toolbits. Far less material to remove when grinding and with a solid packing underneath will be rigid enough.

Russell

You do not need to use feeler gauge material for shims. It doesn't need to be that accurate for most turning until you get down to turning 1/8 or the very centre of a bar that isn't going to have a hole in it anyway. Just collect bits of thin aluminium, hard plastic (credit card), drinks can, paper even for the final thous. Cut to size and stick in a box, Then setting height becomes a ten second job and some people keep the shims with the tool using a rubber band.

Hi Chas

If your tool is too low, face a piece of bar for a couple of mm then measure the remaining sprig. Shims of 1/2 that diameter will put your tool on centre. It may work the other way if too high but I havent tried it ( you will have to be careful that you dont knock the sprig off as the tool will be pushing into it.

Roger form OZ

Shims can be made by cutting up biscuit tins, or sardine / fish tins, The material of often about 0.010" so makes for fairly accurate adjustment.

Coca Cola tins can be used, but you are starting with curved material, and being aluminium based, soft, and liable to collapse in the longer term.

Howard..

In my view, an essential accessory is some sort of quick change toolholder for the Myford, such as the Dickson type or clone. Then use 8mm tools, no need for shims, adjustable and repeatable height. Or make something similar, such as Mike Cox's here.

I bought a Dickson system when I got my Super 7, have never had a problem with tool rigidity down to 3mm sq.

+1 for John Haine recommending a QCTP.

Before selecting a toolpost check the cost of extra toolholders. The Dickson toolpost is a fine tool but the price and availability here in the US is a show stopper. I have Aloris clones on my two lathes. I am highly satisfied with them. The Chinese made toolholders that fit them are inexpensive and quite satisfactory. The grub screws in those holders, however, are junk

I've superglued appropriate shims to each tool ready for use, saves faffing about every tool change.

Pallet strapping is thin and hard, 2 usual thickness, .020' and .025"