What to get: Imperial or metric

[duncan webster 1Participant @duncanwebster1]

The argument that building to scale in imperial is easier does not seem very strong to me. 5"g locos should be built to a scale factor of 11.3:1, you don't do that one in your head. Just as easy to multiply the dimension in inches by 2.25 and call it millimeters. Same argument goes for any other scale factor, for 1/4 scale multiply by 6.35 and so on. If you're using a calculator it's just the same either way. It is almost impossible to get black plate in imperial, so if you try to stick to imperial you get all sorts of strange sizes to compensate. Over the years it will become increasingly difficult to get round bar in imperial.

I have metric lathe and imperial miller, but both have DRO, so I'm bi-lingual. The only downside of metric lathe it screwcutting imperial, but it can be done as others have explained, and if I had Imperial lathe I'd have the same difficulty screwcuting metric.

[Brian GParticipant @briang]

If buying a new "imperial" lathe I would want to check very carefully that it was actually imperial, and didn't just have 1mm screws and 0.025mm divisions numbered to 40 like a mini lathe. It just feels like a bodge.

Brian

[not done it yetParticipant @notdoneityet]

I can instantly envisage what 3/8” looks like – but 9.525mm? – I’ll get m’book then !

The simple argument to this is that any metricated person woud never even think of what the imperial fraction would be for 10mm! Even if they came accross a 9.525mm measurement and converted it to inches, they would come up with a decimal answer of 0.375, not 3/8.

Come to think about it, who would dial in 3/8 on an imperial lathe without first convertig it to thousandths? Try 25/32 or 31/64 and see what I mean? So only decimal inches are really used on the lathe or milling machine, anyway.

[JAParticipant @ja]

Posted by Brian G on 26/08/2016 16:26:29:

If buying a new "imperial" lathe I would want to check very carefully that it was actually imperial, and didn't just have 1mm screws and 0.025mm divisions numbered to 40 like a mini lathe. It just feels like a bodge.

Brian

Do I read you right? Are you saying that 0.040" = 1.00mm? Surely, if you are, this is completely unacceptable. Any lathe or milling machine with such an arrangement should be avoided (like the plague comes to mind).

JA

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JA on 26/08/2016 17:10:29:

Do I read you right? Are you saying that 0.040" = 1.00mm? Surely, if you are, this is completely unacceptable. Any lathe or milling machine with such an arrangement should be avoided (like the plague comes to mind).

.

JA … Robert Blackshaw mentioned the same thing on page_1

Yes it happens.

Whether, or not, it is "acceptable" is a matter for debate … it's a nasty fudge, but you could work around it.

As John Stevenson likes to say: "fit for purse" sometimes beats "fit for purpose"

MichaelG.

[ROBERT BLACKSHAWParticipant @robertblackshaw40066]

If I was buying a Myford with this arrangement I would not be happy about this, but the fact is that .1000 is .025 mm give or take a nats cock, so to me an imperial machine can be used as metric. if need be. The lathe cost £700 new and it has done all I've asked for it, my milling machine has .025 and .020 which I found confusing so have DROs on it but I have not on the lathe as I find it quite easy to use.

[JAParticipant @ja]

Posted by Michael Gilligan on 26/08/2016 17:54:17:

Posted by JA on 26/08/2016 17:10:29:

Do I read you right? Are you saying that 0.040" = 1.00mm? Surely, if you are, this is completely unacceptable. Any lathe or milling machine with such an arrangement should be avoided (like the plague comes to mind).

.

JA … Robert Blackshaw mentioned the same thing on page_1

Yes it happens.

Whether, or not, it is "acceptable" is a matter for debate … it's a nasty fudge, but you could work around it.

As John Stevenson likes to say: "fit for purse" sometimes beats "fit for purpose"

MichaelG.

Apologies.

But I don't think I could work round it.

JA

[John HaineParticipant @johnhaine32865]

Posted by John Alexander Stewart on 26/08/2016 14:39:09:

I'm not UK based.

I'd go with metric.

It is the future for world standardization.

The future? Has been the word standard everywhere except the USA for decades!

[Neil WyattModerator @neilwyatt]

Posted by duncan webster on 26/08/2016 15:50:53:

The argument that building to scale in imperial is easier does not seem very strong to me.

It depends on the scale; my engineering models are 1:12 aside from 1:16 for 3.5" gauge and some of my boats.

I'd also add that designing models in imperial is easier. Oh yes! Very easy to make things that add up to sensible sizes in close approximation to reality with such a range of sensible steps available.

In metric you have to cope with preferred sizes* which make sense for designing tools, but for models the steps are too large in bigger sizes and you have to machine things to size in which case it makes no real difference whether you use mm or thou.

Neil

Edited By Neil Wyatt on 26/08/2016 19:52:23

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JA on 26/08/2016 19:10:08:

Apologies.

But I don't think I could work round it.

JA

.

I think you do yourself an injustice … I'm quite sure that you could; it's just that you don't wish to.

Our predecessors made wonderful things, using lathes with no dials; measuring or [more likely] comparing as they went. A dial that even roughly approximated measurement would be a luxury to them.

Of course, accurate dials are a great convenience, [but …]

MichaelG.

[duncan webster 1Participant @duncanwebster1]

Posted by Neil Wyatt on 26/08/2016 19:43:25:

Posted by duncan webster on 26/08/2016 15:50:53:

The argument that building to scale in imperial is easier does not seem very strong to me.

It depends on the scale; my engineering models are 1:12 aside from 1:16 for 3.5" gauge and some of my boats.

Neil

so do you divide by 12 in your head in which case you'll get decimal inches? Or perhaps you convert feet and inches into decimal feet and just call it inches. I think not. You'll do it on a calculator, and finish up with decimal inches which no doubt you round to conventional 1/32 or 1/16. Just as easy to to it in metric.

Same argument for 1/16 scale, to convert say 11 ft 7 inches you have to work it out in inches (139), then divide by 16 to get 8.6875, then convert the 0.6875 to 11/16.

[JasonBModerator @jasonb]

"It depends on the scale; my engineering models are 1:12 aside from 1:16 for 3.5" gauge and some of my boats."

If you were making a metric model you would not choose 1/12th scale in the first place you would more likely choose 1:10

This actually makes the difference in increments, prefered sizes, call them what you will much the same, the smaller 1/12th model would use increments of 0.031" and the metric one increments would be 1mm so that 6" full size crankshaft would be made from 1/2" stock size on the imperial model or 15mm stock size on a metric model.

[MuzzerParticipant @muzzer]

Posted by Neil Wyatt on 26/08/2016 19:43:25:

In metric you have to cope with preferred sizes* which make sense for designing tools, but for models the steps are too large in bigger sizes and you have to machine things to size in which case it makes no real difference whether you use mm or thou.

I suspect preferred sizes are becoming a thing of the past in many areas. Many things nowadays are designed in CAD, then moulded, cast or machined, so that nominal sizes are of no relevance – the positions and dimensions of features can be whatever feels right. Indeed, I suspect many young (CAD) engineers wouldn't have any idea what we are talking about. Obviously, subcomponents like fasteners, bearings and components that are made from simple bar stock will remain the exception.

[Russell EberhardtParticipant @russelleberhardt48058]

This side of the Channel we have 127 mm scale locos instead of 5" scale. What's the difference? You can measure in Barleycorns if you like. The system of measurement you use can be anything, what is important is the actual size of your parts not the rather arbitrary number you give to it.

I have an imperial lathe and two metric mills and have no difficulties with that.

Russell.

[Brian GParticipant @briang]

Posted by Michael Gilligan on 26/08/2016 19:55:40:

Posted by JA on 26/08/2016 19:10:08:

Apologies.

But I don't think I could work round it.

JA

.

I think you do yourself an injustice … I'm quite sure that you could; it's just that you don't wish to.

Our predecessors made wonderful things, using lathes with no dials; measuring or [more likely] comparing as they went. A dial that even roughly approximated measurement would be a luxury to them.

Of course, accurate dials are a great convenience, [but …]

MichaelG.

To be honest, working round it isn't that difficult for diameter at least – I wouldn't cut far without using a micrometer anyway, and on a 10 thou cut the error in the graduation is only 0.000157", still less than 1/2 a thou on diameter.

Brian

[Neil WyattModerator @neilwyatt]

Posted by duncan webster on 26/08/2016 19:59:32:

Posted by Neil Wyatt on 26/08/2016 19:43:25:

Posted by duncan webster on 26/08/2016 15:50:53:

The argument that building to scale in imperial is easier does not seem very strong to me.

It depends on the scale; my engineering models are 1:12 aside from 1:16 for 3.5" gauge and some of my boats.

Neil

so do you divide by 12 in your head in which case you'll get decimal inches? Or perhaps you convert feet and inches into decimal feet and just call it inches. I think not. You'll do it on a calculator, and finish up with decimal inches which no doubt you round to conventional 1/32 or 1/16. Just as easy to to it in metric.

Same argument for 1/16 scale, to convert say 11 ft 7 inches you have to work it out in inches (139), then divide by 16 to get 8.6875, then convert the 0.6875 to 11/16.

No I either do it a drawing program at 1:1 in feet and inches, then set the scale to whatever I need, typically with a precision of 32nds or 64ths. It's then easy to look at the drawing and drag any dimensions that don't round neatly to an appropriate guideline.

Or do it in my head 11 feet = 33/4 = 8 1/4 inches plus 7/16 = 8 11/16" – took as long to work out as to type, but I'm USED to thinking 1'-3/4".

In 1:12, 11 feet = 11 inches, 6 inches is 1/2" every inch is 1 1/3 sixteenths so you can say 11 inches 19/32 but over such a length 11 1/2" or 11 5/8" will probably be fine.

Now I could do that in metric but EVERY dimension needs to be tweaked or approximated, whereas with an imperial prototype most dimensions naturally fall on a convenient line. far more likely for the prototype measurement to be 11'6".

You may not be convinced, but this works for me although I would still recommend a new workshop is kitted out for metric.

Neil

[JAParticipant @ja]

Posted by Brian G on 26/08/2016 21:40:06:

Posted by Michael Gilligan on 26/08/2016 19:55:40:

Posted by JA on 26/08/2016 19:10:08:

Apologies.

But I don't think I could work round it.

JA

.

I think you do yourself an injustice … I'm quite sure that you could; it's just that you don't wish to.

Our predecessors made wonderful things, using lathes with no dials; measuring or [more likely] comparing as they went. A dial that even roughly approximated measurement would be a luxury to them.

Of course, accurate dials are a great convenience, [but …]

MichaelG.

To be honest, working round it isn't that difficult for diameter at least – I wouldn't cut far without using a micrometer anyway, and on a 10 thou cut the error in the graduation is only 0.000157", still less than 1/2 a thou on diameter.

Brian

Yes, this may all true and possible but I produce enough scrap as it is.

JA

[Another JohnSParticipant @anotherjohns]

Posted by John Haine on 26/08/2016 19:36:54:

Posted by John Alexander Stewart on 26/08/2016 14:39:09:

It is the future for world standardization.

The future? Has been the word standard everywhere except the USA for decades!

Fair enough, but I think you know what I mean.

E.g – wanted some heavy gauge electrical wire, sold by the length the local hardware store, a chain from the USA that is big here in Canada. Measured it in metres, converted it to feet for the purchase. Went to store, asked for so many feet, and the salesman said "hold on a minute – new measuring machine is in metric, I'll have to convert that".

Needless to say, I was not only surprised, he was also, that I could convert so quickly, in my head, from feet to metres!

John.

[Anonymous]

Posted by John Alexander Stewart on 26/08/2016 23:02:06

E.g – wanted some heavy gauge electrical wire, sold by the length the local hardware store…..

But how was the gauge specified, AWG or mm²?

Andrew

[not done it yetParticipant @notdoneityet]

The Americans have been using metric bearings for years, just requoted as imperial. Not sure if all bearings, but likely most.

[mark costello 1Participant @markcostello1]

Old stock bearings were made to Imperial sizes, new bearings made to the same sizes using Metric numbers. Oh for the old days. I can tell 27mm is bigger than 26mm, but what size that is beats Me till I get a chart.

[Mike PooleParticipant @mikepoole82104]

The most nonsensical thing about imperial measurements is fractions, if a drawing is dimensioned in thous then they are easy to add/subtract and relate directly to machines dials, a shame rules have fractions.

Mike

[Speedy Builder5Participant @speedybuilder5]

My Metric / imperial callipers are marked in 1/128" . Try that out !!

[Bill PudneyParticipant @billpudney37759]

Metric every time.

Fractions on drawings are a major pain in the neck to a caring draughtsman. To me as an old fashioned drafty, there was a deal of pride in producing a drawing that looked neat, competent and as if it had been produced by someone who was sober, most of the time. To get fractional dimensions looking "right" was/is an art in itself.

Decimal inches is fine except where some knuckle dragger uses inappropriate dimensions, for example three places of decimals on a casting, or on a drilled hole.

Metric makes most sense, except when the aforementioned knuckle dragger puts three places of decimals on a casting…………

But maybe it's just me!!

cheers

Bill

[JasonBModerator @jasonb]

The only time fractions are usfull on a drawing is when refering to a drilled hole, its a lot easier to go straight to the drill stand and pick up a 13/64th bit than it is to pick up a 0.203" one

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