Metric or Imperial Lathe?

[Roger JennerParticipant @rogerjenner32336]

Further to my earlier question about new or second-hand (for which I thank all those who replied) – should I go for a lathe defined as “metric” or one as “imperial”?

 

Do I assume that if a user is confident in converting from one unit to the other that this is not a major problem (with a suitable amount of care)?

 

Do I also assume that the main problem would be in screw cutting when it may be desirable to change the various gear wheels?

 

Thanks in advance.

[Roger JennerParticipant @rogerjenner32336]

[Richard ParsonsParticipant @richardparsons61721]

Roger Hi it does not matter really. Buy the best quality lathe you can get for your money which suits your current and future needs. You then have three options. Option 1 is to buy a ‘Number Box –a calculator- Well it is a box full of numbers- and remember 25.4 mm is 1”. 2. to make yourself (or buy) some dual standard dials. 3 Is to buy and fit some digital readouts. When you have decided and bought your lathe then post a list of the change wheels you have and the pitch of the lead screw. Someone will what extra change wheels you will need
Dick Parsons

[Gray62Participant @gray62]

Metric or imperial? it really comes downto personal preference.

There are always ways and means of creating metric threads on an imperial lathe and vice versa.

I am old school so I will always lean towards imperial machines. If you are buying an older English built machine, chances are it will have an imperial pitch leadscrew, many of the newer Chinese machines from suppliers such as Chester, Warco, Toolco etc are available in both guises and come with conversion gears to allow both imperial and metric screwcutting.

Other than that, there really is no difference and as already said, if you can stretch to fitting a decent DRO system, then you can easily work in both measurement systems.

[Clive FosterParticipant @clivefoster55965]

If you plan to do both metric and imperial screw cutting its better to start with an imperial lathe. The conversion set-up is a little easier with fewer gears and is, generally, more comprehensible. You also have the benefit of a thread cutting dial when doing imperial threads. Metric thread cutting dials are, at best, confusing to the occasional user. Many are downright incomprehensible and easy to set-up wrong.

 

If you get an imperial lathe with a gearbox don’t blindly follow the makers suggestions for metric conversion if a 100 / 127 conversion gear is required. For some obscure reasons most makes require you to ring the changes on the gearbox drive gear as part of the process. Very irritating as you have to adjust the positions of all the gears on the banjo for each change. Far better to copy the SouthBend system where the first, stud, gear is changed so you only have to fit the conversion gear and adjust the angle of the banjo for all changes. Actually most lathes will accept the conversion gear as an idler so it gets even easier.

 

If you end up with an imperial change wheel lathe best option is to use the Myford 21 drives 40 teeth conversion gear with change gears selected from an integer incrementing series rather than the usual by five increments. The set-ups become incredibly simple and easy to keep track of. Should you need to purchase gears for conversion purposes its easier and less costly to buy smaller gears than originally supplied. Means buying a full set and sorting out a way to span the extra distance but larger gears are costly and many machines have 14° pressure angle gears which can be hard to find. If 24 DP by 0.375″ face width are good enough for my Smart & Brown.

 

I discovered the relative difficulty of going the metric to imperial route and the threading dial conundrum after buying my metric Smart & Brown 1024 VSL. But I do have dual dials so normal working is no problem and the threading stuff is a minor irritation when set against the quality and capability of the machine.

 

Clive

[TerrydParticipant @terryd72465]

Hi Roger,

 

Personally I would suggest metric as a preference if you are comfortable with the system. One of my main reasons would be that imperial equipment is becoming more expensive as industry in most of the world is now metric .  Even that last real bastion of imperial systems, the USA is now officially metric and an increasing number (not all) of suppliers in that country are offering mostly metric equipment and advice. The only other countries still officially Imperial are Malaysia and Myanmar (Burma).

 

The same argument applies to materials such as bar, sheet and tube etc as well as components such as screws and rivets etc. These are much more easily available in metric sizes (and yes, scale headed hex head metric bolts are available). And before I hear the argument about our modern materials being simple conversion of imperial, that is simply false in most cases. One correspondent on this forum actually suggested that house bricks and paving slabs were really imperial and that slabs were having bits ground off to make them imperial. Of course this is ludicrous as well as false.

 

Metrication was first adopted in the British parliament in the second half of the 19th century (1872), and of course in the usual British way it took another hundred years of debate before the act was passed and enforced. No wonder we are now a second rate manufacturer and exporter when it takes so long to make any meaningful decision.

 

As an aside to the metrication argument it was amusing to note that one so called ‘Metric Martyr’, a market trader (don’t you love The Sun) argued that the kilogram wasn’t acceptable because it was easy to judge a pound of potatoes as it was about a handful. Was it really so difficult for him therefore to judge a kilo by taking two handfuls (and how about his female helpers, they must have had huge hands)? An anti metrication MP (Tory) argued against it, because the kilogram “is to heavy for the British housewife” (it is in Hansard)!

 

Anyway, apart from my digressions of course it is up to you and what you are happy with, personally I have worked with both systems for over 45 years and am comfortable with both. However I have the opportunity to sta rt a new workshop from scratch and am opting for the metric route for cost, convenience and simplicity. Take dies and taps as an example, although they are not always perfect for every situation I can get away with a set each of metric fine and coarse. I don’t have to get sets of BA, ME fine, ME coarse, BSW, BSF, Brass, UNC, UNF etc etc etc. The same applies to much other equipment.

 

Further although many designs and plans are in imperial there are very many metric and converted examples around. Plenty for me in fact and I can convert where necessary. I don’t have to produce yet another Stuart clone to go alongside the countless others and pollute the world.

 

My main advice to you is to enjoy your hobby whatever you choose without getting bogged down by meaningless arguments about standards.

 

Best regards, good luck and have fun (or is that too trite?),

 

Terry

Edited By Terryd on 27/02/2011 22:53:54

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Roger, it really depends on what units you yourself prefer to work in and are comfortable with. There are of course lathes with both graduations on the dials, the only differance being the screw cutting arrangement. If you intend to lean towards metric in the long term, why bother to learn how to use an imperial machine.

 

A lot of the lathes our farthers had, didn’t have any graduated dials on them at all. it was a question of measuring and putting on a cut of your own judgement, measuring again and repeating the process untill it came to size. You can replace or overlay an imperial dial with one graduated to ten divisions or multipuls of ten, and then take trial cuts on a piece of scrap to find out exactly what each division is in metric mearsure, thus giving you a better idea than your own judgement of the size of each cut.

 

It is clear that most of the world is going metric and most material that stockists hold is in metric sizes and imperial things will be harder to obtain, but that is not a reason not to continue using imperial if you so wish.

 

In the end they both make swarf. (but is it metric swarf or imperial swarf? can you tell which machine made it using a mike?)

 

Regards Nick.

Edited By Nicholas Farr on 28/02/2011 00:03:10

[mgjParticipant @mgj]

The answer, if you are going for a lathe of appropriate size is a DRO. Beyond that the truth is that a calculator is a wonderful thing, and digital calipers and micrometers can be set either way at the touch of a button. A dimension is a dimension, so the argument hinges on screwcutting..

 

However, I’d second the comments about imperial screwcutting on a metric lathe.

 

But against that, for most models, as opposed to toolmaking, the number of threads you have to cut as opposed to use a die are very few, and are in any case mostly convertible. So if you want a dead straight thread to retain a piston on a rod, even if the drawing specified imperial, it wouldn’t matter if it were actually metric.

 

I had to cut a 16 tpi buttress thread for for the brakes on my TE. Metre Maid calls for an 8TPI thread for the brakes, but shes getting a 16 tpi one – because I have the tap already from the last job! Neither would mind if they were 1.5 or 3mm pitch respectively.

 

So there are plenty of ways round either. So I’d suggest the biggest solidest lathe in decent nick that you can afford, and worry about the units afterwards. You will get used to them.

 

 

 

 

 

 

Edited By mgj on 28/02/2011 17:50:19

[Roger JennerParticipant @rogerjenner32336]

Thanks all, very useful advice.

 

I just to need to find a lathe now!!

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