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Metric or Imperial Lathe - What do I want?

opensourcefan

opensourcefan

OSF
I've been using imperial for most fabrication type stuff for ever. Looking for an imperial lathe is causing me trouble, I can find metric much easier.

Really for the cheapo China lathes were talking lead screws therefor indication differences for the most part. They have the gearing to cut both metric and imperial threads.

So... Can I deal with metric dial graduations? It's nice that this forum is Canadian, looking forward to the responses.
 
opensourcefan said:
I've been using imperial for most fabrication type stuff for ever. Looking for an imperial lathe is causing me trouble, I can find metric much easier.

Really for the cheapo China lathes were talking lead screws therefor indication differences for the most part. They have the gearing to cut both metric and imperial threads.

So... Can I deal with metric dial graduations? It's nice that this forum is Canadian, looking forward to the responses.
Click to expand...

So, I was in the same quandary before I bought my 12x36 Imperial. It can do metric with a gear change but the threading dial doesn't work on metric. It isn't a huge issue but it's an issue.

In hind sight, I am glad I hung in there for imperial. It turns out that maybe 95% of my work has been imperial. Had I gone the other way, the threading dial would have been useless.

I do not think the handwheel graduations are a really big deal. One could always keep a calculator handy. They even sell conversion calculators. Any android phone can be equipped with a conversion program/app. But living without the threading dial would kill me in the long run.

So my opinion is that you need to look at what your work will be. If the majority will be metric, I'd go metric.

As far as the graduations go, you can always install DROs. They will convert for you. That is easy on the carriage, but the Cross-Slide, Compound, & Tailstock Quill will be a challenge. If it were me, the carriage is a no-brainer, but I'd go to great lengths to do the Cross-Slide too.
 
My first lathe was a metric SouthBend 10K. One of the first things I bough for it was a
digital caliper. With the caliper you can switch back and fourth between metric and imperial.
Most of the work I did on the lathe was imperial. I used that lathe for 15 years before I
upgraded to a BusyBee 12x36 which has both metric and imperial markings on the dials.
 
terry_g said:
upgraded to a BusyBee 12x36 which has both metric and imperial markings on the dials.
Click to expand...

Can you post a photo of what that looks like?

I'm thinking that the extra metric or extra Imperial (depending on your perspective) might be something one could add to an existing set of dials. Now THAT would be handy!

Alternatively, I would not be averse to having interchangeable dials. The problem of course is the end point. Most cranks are designed to provide a set continuum of graduations - eg 1 turn per 10th or one turn per 2 millimeter so one can count turns to achieve a bigger number. I have no idea how that gets handled with both systems on a dial.
 
@Susquatch Get @RobinHood to send you a short video of his *sweet* Colchester toolroom lathe - it has a metric converting cross slide that is really 'dope'...

All you do to convert the slide to reading metric is to rotate the 'shield' that has an opening for the graduations, and then it truly advances .1mm per revolution instead of .100 inch per rev. it is direct reading and is a joy to watch!
 
DRO's are useful in their own right so that gives you dual units capability. To me, an equally important issue is your measurement tools. You are constantly going back & forth between physical micrometer reading & adjusting the machine dials accordingly to hit dimensions within a tolerance & required finish. Yes, vernier's can do this to an extent & most people own a set. But its not really considered a super accurate way of measuring things on lathe & many setups cannot accommodate them. So now its either calculator time unless you have a dual read mic or a metric mic. That will get you a certain way down the path, sooner or later you need to measure larger diameters or bores (so bigger outside mics, different internal mic), plus depths, threads.... so that's even more measurement tooling. This can add up to a significant multiple of the machine itself.

There is always a workaround, home machinists are really good at that, more so when on a limited budget. But to me it's kind of a systems approach which is the machine plus this other $$ stuff. Having said this, you can make do, enjoy what you are doing & upgrade or switch at some point in the future. I've also seen really good deals on metric measurement equipment, less than the IMP counterpart even same brand & condition etc. Not quite sure why. So that would be the 'mostly cold turkey' metric shop. I think depends on your projects & aspirations.
 
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My SM1120 came with a dual dial on the cross slide. The dial has 0-200 thou in .001 increments and 0-5mm in .02mm increments. I don't have the metric change gears but would like to find a set.
P1010866.JPG
 
Ah yes, very good point about my measuring equipment. I've been using imperial forever and I know what 1 thou is vs point something of a mm. I'm too old to switch my mindset now I think.

Love the idea of both graduations, that is cool but rare I think. A DRO is in my future, maybe that can fill the void.
 
Dabbler said:
@Susquatch Get @RobinHood to send you a short video of his *sweet* Colchester toolroom lathe - it has a metric converting cross slide that is really 'dope'...

All you do to convert the slide to reading metric is to rotate the 'shield' that has an opening for the graduations, and then it truly advances .1mm per revolution instead of .100 inch per rev. it is direct reading and is a joy to watch!
Click to expand...

That would be awesome to see @RobinHood !

But I really wanna know how you did it! In particular, how do you get a full revolution to workout in both units?

Same question for you @YotaBota! How the heck does that work?
 
@Susquatch - I guess I can't fully call her Miss Metric until I get her a working threading dial....alas..:rolleyes:

Looking at the set up it would appear that the feed screw is a 5 thread ACME so each rotation is 0.200" and that works out to 5.08 mm. Over the graduations in the dial that would be a 0.08 mm error or a hair over 0.003 thou - probably pretty acceptable
 
One of my lathes has just imperial the other has both.

DRO beats any graduations - on two machines (one mill one lathe) I have DRO & I don't even look at anything other then DRO.

When converting I usually think of 1mm as around 40 thou. Works very well for me - conversions are very quick either way.

I find threading to be of bigger issue for some lathes - with imperial screw there needs to be conversion of 254 -> 100 or 127 to 50 to get metric well aligned otherwise you get acceptable approximation only.
 
Below is the video link to the Colchester Lathe Inch/Metric Dials

streamable.com

Colchester Lathe Inch/Metric Dials

Watch "Colchester Lathe Inch/Metric Dials" on Streamable.
streamable.com

These dials were an option on these lathes, but my Master 2500 came with them. They are installed on the cross slide and the compound. They are labelled GMT.

Here is a drawing for them.

663CAE42-4C77-4E5B-97F0-34AA1F19A99D.jpeg


In a nutshell, here is how they work.

There are two co-axial dials, each is driven by a internal ring gear. One has 125T the other 127T. There is a common spur gear inside them. As you rotate the 125T dial, the 127T dial will take longer to make one full revolution, the ratio of difference being the imperial/metric conversion constant. You could also rotate the 127T dial one rotation and the 125T would rotate more than one full turn - the amount being, again, the imp/metric constant.

The shield is rotatable in either direction. There are tiny, spring loaded ball detents that locate it in either the metric position or, 180* opposite, the imperial position. Only one of the scales is ever visible when looking down from the operator‘s position.

The scale closest to the lead screw (either compound or cross slide) tells you what type of lathe you have. In my case, the imperial scale is closet to the lead screw, so it is an imperial lathe.

So in the video, I demonstrate how this works using the compound - the cross slide would be identical except that the dials are 5.00mm / 0.200” for one full turn. The compound is only 2.50mm/0.100” per rev.

First I show that both dials are at zero I turned the dial many times to get them to line up for demo purposes, as during use, you don’t care at all where the 0s are in relation to each other as the ratio is always the same. (The only way that this ratio could ever change, is if you have the gear jump a tooth - that would surely destroy the ring gears and jam the dial up - so you would know).

Then I go back to metric 0, followed by one complete turn on the handle back to metric 0.

Next I move the shield to show what the equivalent imperial reading would be for 2.50mm advance:

2.50mm : 25.4 = 0.98425”. And you can clearly see that the imperial dial has moved to that approximate position.

Then I turn the shield again to go back to metric 0.

If one were to start at imperial 0 and rotated the handle on complete turn (0.100”), then the metric dial would read 2.54mm. I did not film that (I can, if proof is required).

So, yeah, very clever, true imp/metric dials done by mechanical gear ratio. Fool proof, accurate and easy to use. No power required.
 
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