Lead screw dilemma

[Bodger BrianParticipant @bodgerbrian]

Metric or imperial?

[Bodger BrianParticipant @bodgerbrian]

When I bought my mini-lathe many moons ago, I wanted one with a metric leadscrew but only imperial versions were in stock at the time. Being the impatient type that I am, rather than wait I bought imperial but also purchased a metric leadscrew, half nuts & dial indicator, intending to swap them round but of course never did.

In the course of stripping & cleaning the lathe recently I realised that it would be ideal time to do the deed.

BUT…… I've also recently purchased a Cowells lathe, enabling me to cut metric threads if I need to, so why bother changing the mini-lathe?

BUT….. the Cowells has a smaller capacity, so I might need the mini-lathe for screw cutting on larger metric jobs.

BUT……. I don't think I'll ever feel the need to cut an imperial thread but if I do, I don't want the hassle of changing the leadscrew back again.

BUT…. I keep going round in circles!

What would you do in my situation?

(I should add that I'm aware that imperial threads can be cut on a metric lathe & vice versa but I don't want to faff about with odd combinations of change wheels)

Brian

 

Edited By Bodger Brian on 06/10/2016 22:01:25

[John Stevenson 1Participant @johnstevenson1]

Simples.

Buy a new metric Mini lathe

[HopperParticipant @hopper]

Posted by Bodger Brian on 06/10/2016 21:59:57:

BUT……. I don't think I'll ever feel the need to cut an imperial thread but if I do, I don't want the hassle of changing the leadscrew back again.

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.

[Danny M2ZParticipant @dannym2z]

Posted by Bodger Brian on 06/10/2016 21:59:57:

When I bought my mini-lathe many moons ago, I wanted one with a metric leadscrew but only imperial versions were in stock at the time. Being the impatient type that I am, rather than wait I bought imperial but also purchased a metric leadscrew, half nuts & dial indicator, intending to swap them round but of course never did.

In the course of stripping & cleaning the lathe recently I realised that it would be ideal time to do the deed.

Brian, I did the same when I purchased my mini-lathe (it came set-up for metric). Also purchased the imperial headstock gears and included was a suitable gear chart.

In 10 years I think that I have swapped leadscrews about 5 times when the (screwcutting) job absolutely demanded it.

As it's a bit fiddly to change things over (half-nut mesh etc) I found that the mini-lathe tended to remain in it's configuration until a job required swapping it back.

As for the X-slide and top slide handwheels and leadscrews, they do not require changing as the markings are only a guide so a micrometer and a pocket calculator are your friends.

The biggest problem is actually remembering which leadscrew is actually fitted if there is a long break between jobs – I usually resort to pulling out the calipers and measuring 10 threads ;-(

* Danny M *

[not done it yetParticipant @notdoneityet]

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).

[Danny M2ZParticipant @dannym2z]

Posted by not done it yet on 07/10/2016 06:57:31:

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.

Lol, you definitely live up to your name as you obviously have not owned a mini-lathe.

The topslide and x-slide handwheel divisions on a Mini-lathe are marked 0.001"/0.025mm. Obviously these are approximations, neither is accurate enough for precision work hence my reference to accurate measuring equipment. (Backlash takes care of any minor discrepancies ;-( )

As supplied, a mini-lathe comes with a comprehensive set of appropriate change gears/ threading dial indicator/ half-nuts and chart that are applicable to the type of leadscrew fitted.

I like your idea of indicating whichever leadscrew is fitted by marking the appropriate gearing chart, that's easily managed. Thanks for that.

As for threading; I found that certain camera lenses and filters require precision screwcutting of a very fine thread on a large diameter of typically 50mm+ lens. Dies are not (readily) available in the required sizes. Sometimes the lens is worth more than the mini-lathe (such as an IR quadrature) so 'near enough' is not good enough.

Actually, grinding the threading tool accurately was my biggest problem but Harold Hall's grinding rest made this a much easier.

If lead screw pitch was not so important, then the manufacturers would supply a 'generic' pitch and heaps of changewheels.

* Danny M *

Edited By Danny M2Z on 07/10/2016 09:30:56

[MWParticipant @mw27036]

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

[AjohnwParticipant @ajohnw51620]

The alternative is to work out conversion gears that have an acceptable level of accuracy. The ones that come with the lathe may be good enough so why not work out just how close they are.

The usual attitude to this area with novice Boxford users is that they want a 127 gear. Point out that the errors can be small when conversion sets are used and that lathes do not cut that accurate a thread anyway and they just say well it would be more accurate if I had the 127. The differences in real terms can be so small that it really doesn't matter.

My lathe has an imperial gearbox. This is what I need to do to cut accurate metric threads

 

Unlike Myford's I had to come up with this myself. When ever I post it I always say if used do check what it actually cuts. I have used less close approximations that came from the same spread sheet so all should be ok.

The one I have used a couple of times as well is this one

In real terms it's plenty good enough. Boxford kindly supply one of the gears needed as packing. Who ever bought my lathe also bought the 127 gear. It's not much of an advantage on one with a gear box.

John

–

Edited By Ajohnw on 07/10/2016 09:47:57

[Bodger BrianParticipant @bodgerbrian]

Posted by not done it yet on 07/10/2016 06:57:31:

How many 'larger' jobs?

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.

'Larger jobs' was just a hypothetical situation where a workpiece might be just that little too big to be accommodated on the Cowells.

You're probably right – I might be over-thinking this.

Brian

[Bodger BrianParticipant @bodgerbrian]

Posted by John Stevenson on 06/10/2016 22:08:44:

Simples.

Buy a new metric Mini lathe

My wallet is still hurting from buying the Cowells!

Brian

[Bodger BrianParticipant @bodgerbrian]

Posted by Danny M2Z on 07/10/2016 01:50:30:

The biggest problem is actually remembering which leadscrew is actually fitted if there is a long break between jobs – I usually resort to pulling out the calipers and measuring 10 threads ;-(

* Danny M *

I might be missing something obvious here but won't glance at the dial indicator tell you? 10 divisions, metric – 8 divisions, imperial?

Brian

[Russell EberhardtParticipant @russelleberhardt48058]

You should be able to cut accurate enough metric threads with your existing change wheels. There is a simple online calculator here

One or two additional gears might be needed if you need better accuracy.

"As for threading; I found that certain camera lenses and filters require precision screwcutting of a very fine thread on a large diameter of typically 50mm+ lens. Dies are not (readily) available in the required sizes. Sometimes the lens is worth more than the mini-lathe (such as an IR quadrature) so 'near enough' is not good enough."

In general filters etc., have rather short threads so a 1% error in pitch is not important.

Russell.

Edited By Russell Eberhardt on 07/10/2016 10:58:14

[Neil WyattModerator @neilwyatt]

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

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Neil Wyatt on 07/10/2016 11:27:18:

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

Yes, that will give sub 1% pitch errors for metric threads on an imperial lathe. Just remember to keep the half nut engaged and use reverse between each cut.

Russell.

[Alan Johnson 7Participant @alanjohnson7]

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!

[Bodger BrianParticipant @bodgerbrian]

Lots of food for thought here but I think the best advice was from Not Done Yet – stop turning in circles & do it.

If I'm honest with myself, I can't see me ever needing to cut imperial threads but if I do, I can either re-fit the original leadscrew or follow Neil's suggestion & buy a 63 tooth gear.

One last question; along with the metric leadscrew etc, I have a replacement sticker showing the change gear combinations for various pitches but I don't have a metric version of this….

Assuming that one is necessary can someone kindly either provide the figures or point me in the direction of a suitable image on the internet?

Thanks

Brian

[AjohnwParticipant @ajohnw51620]

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

–

[Neil WyattModerator @neilwyatt]

Posted by Russell Eberhardt on 07/10/2016 11:58:46:

Posted by Neil Wyatt on 07/10/2016 11:27:18:

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

Yes, that will give sub 1% pitch errors for metric threads on an imperial lathe. Just remember to keep the half nut engaged and use reverse between each cut.

Russell.

0.15% error to be precise

Neil

[Neil WyattModerator @neilwyatt]

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

[Michael GilliganParticipant @michaelgilligan61133]

< retracted >

Edited By Michael Gilligan on 07/10/2016 14:33:19

[Michael GilliganParticipant @michaelgilligan61133]

< retracted >

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Neil Wyatt on 07/10/2016 14:12:42:

Posted by Russell Eberhardt on 07/10/2016 11:58:46:

Yes, that will give sub 1% pitch errors for metric threads on an imperial lathe. Just remember to keep the half nut engaged and use reverse between each cut.

Russell.

0.15% error to be precise

Neil

I had assumed that the 63 wheel would be used in place of a 127 wheel (with a factor of 2 somewhere else in the train) so 127/126 = 1.00794. Just wondering if there is a clever trick to get your 0.15% not that I have ever needed better than 1% pitch error.

Russell.

[Howard LewisParticipant @howardlewis46836]

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

[MWParticipant @mw27036]

Yep, BA is practically a metric copycat. It was an early attempt by industry to tie up the U.K imperial system and metric system without actually switching to metric ..or maybe we were just too keen on big coarse pitch screws until we realized we could do with a quaint range of smaller ones..

Michael W

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