If you never cut Imperial threads, change over to the metric leadscrew. Do you have all the metric handwheels and cross slide leadscrews and top slide leadscrews to match? If not, you will end up with a mishmash that will drive you crazy, so best to make the full conversion.

As for not wanting the hassle of changing back or changing change wheels to cut imperial threads, well Mr Stevenson had the only answer to that.

How many 'larger' jobs?

I swap around two change wheels and reverse the lathe for the odd screw cutting job on my (non-mini) lathe. And further, how many times (on a metric item), might an imperial thread make no odds? If you want to be a purist, go ahead and swap out lead screws, half nuts, etc. Of couse, maybe your mini lathe has no provision for swapping gears.

On the other hand, just get the job done. Following experience will tell whether it was the right decision or not and at least it would be easier/quicker swap

ping next

ti

me….

In your position I would stand still, stop turning round in circles, and do it. Make a decision for a ch

ange and get the job done. Then enjoy a lathe with metric lead screw and imperial cross and top slides? I would be changing those lead screws as well, if I were a purist!

On a final note, most threading jobs on a mini lathe might be handled with taps and dies, so even less need for continuous change-overs (and leave the alernative lead scew on view with a label on it denoting metric or imperial, or stick a label on your lathe, or colour your threading dial, or something else, to save having to measure up thread pitches all the time – if you change them regularly).

I had this problem with the sherline lathe, as you need a separate leadscrew for imperial/metric. I think some smaller clarke models do as well (sieg clone ones)

I was lucky in that it was equipped with steppers for PC control but it really depends how many jobs you want to do in metric. 

Michael W

Edited By Michael Walters on 07/10/2016 09:34:34

Buy or make one of these, then stop worrying and enjoy your lathe:

http://www.arceurotrade.co.uk/Catalogue/Machines-Accessories/Lathes/SIEG-C3-SC2-SC3-Mini-Lathes/C3-SC2-SC3-Mini-Lathe-Upgrades/Mini-Lathe-63-Tooth-Metal-Gearwheel

Neil

Sell the metric leadscrew and associated parts. Put the money under the bed – I mean bench. Keep an eye out for a secondhand metric mini lathe and purchase it. Make sure it is the same colour as the one you have – her indoors knows that you have only one "red" lathe! I have seen this phenomena with friends and motor cycles. As long as the new one is the same colour as the old one she will never question that it looks a bit "different" now. Sleep well!

Another way at looking at this is what threads do you need to cut. In general most people I suspect would use taps and dies up to at least 1/2 dia. That covers a lot of models of any type.

Many models are old designs and use BA and 40 and 32 tpi at different sizes. With the exception of maybe the 40 metric sizes can be used instead especially on BA. Newer ones may be metric.

That leaves odd balls. My interest is microscopes, cameras and telescopes. They don't use much in the line of different thread pitches. Then there are things like brass thread. Always the same pitch what ever the size.

The other aspect is that the list of metric pitches I posted covers many that aren't in the ISO standard. Imperial also only uses a limited number of TPI's. All people are likely to be interested in is sizes over 1/2" or so. The other limitation is the max pitch the lathe can realistically cut. if some one wants to try and cut helical gears then having the usual range of thread pitches on either an imperial or metric lathe is probably not going to help. It's really a job for a miller with a geared dividing head. Most millers I have used have the facility for this, heads too. Or cnc.

All of my machines apart from one are imperial but the vast majority of my taps and dies are metric plus some ME sizes with some larger 40 TPI stuff for fine adjustments as 0.5mm pitch taps are available at various sizes but not dies. I have a few whit and bsf and a couple of un series bought when I needed them.

I always used to worry about not being able to do this and that but eventually concluded that with things like threading gear much of it is best sorted out when needed.

However when I see a collet chuck at the right price and maybe one or two other more substantial items I may buy them even though so far I haven't had any need for them.

John

–

One advantage of a metric leadscrew is you can fit a handle to it and a dial with 40 graduations. it will give you more accurate 1-thou steps for Imperial use than a dial on an imperial leadscrew, unless you use 62.5 divisions…

Neil

< retracted >

For those with DRO, NO problem, with Top or Cross slides.

Filters for cameras are usuall 0.75mm pitch threads.

For a mini lathe (Seig C3?) the Leadscrew is 1.5mm pitch, and a Handwheel with 60 graduations, provides resolution of 0.025mm /division, or 0.00098425 inch/division in old money. (Personally the "425" bit won't matter to me too much, the "98" will be hard enough to handle) .

BA is really a metric system, although perhaps some oddball pitches, so better produced with Taps and Dies.

And, Yes, I have a 63T gear, but not yet used it. On machines with Norton boxes, such as Warco BH600, Chester Craftsman, or E T R BL12/24 the 120/127 compound gear allows fairly quick changeovers.

If all you normally screwcut is Metric, set up for metric and carry on. If you think that one day you MIGHT want to screwcut Imperial threads, buy a 63T gear "Just in case, it comes in handy one day" I did, still unused, but upto 1/2" I would use Taps and Dies for BA, BSW, BSF, BSB, BSP, UNC, UNF or ME.

I do have a very few Taps for Metric Fine, but unused (The "might come in handy one day" syndrome)

Have never needed to deal with electrical conduit, Cycle threads, or UNEF, and hope to keep it that way!

Howard