What do we really mean when we say we work in “X” units.

[chris stephensParticipant @chrisstephens63393]

Hi Guys,

Let me start by saying I am not advocating any particular measuring system, I am asking “what do we really mean by saying I work in (say) metric units”

It clearly does not mean that I use metric drills or milling cutters, because they are just tools, you don’t use a file and say you are using it it in metric.

 

It surely can’t just mean that I am using a metric scaled Mill or lathe, because those machines are used to make something to a size and as we know any particular size can be expressed in whatever units you like, physically it is the same. I am looking for a deeper meaning than this.

 

The only thing that I can think of that really makes a difference is the size of raw materials that we start with and then only because we might, say, have a single size collet that such stock will fit. We might also legitimately say we use Imp reamers because we need a hole to fit an IMP piece of ready made ground stock. This though is just a fact of standard sizes, rather than “I only work in IMP units”.

 

Another factor that might have some bearing on the matter is a set of plans that we wish to follow. Here again, other than using a few stock sizes that we can change to suit our measuring equipment, all dimensions that have to be cut to size can very easily be swapped, by simple use of charts or a calculator, from one system to the other. If we are not using plans but scaling a model from full size, then if we are using 1-12 as our ratio a particular system might seem to have the edge, but again any size can be defined in anyway you wish..

 

Might I suggest that what we mean by saying “I work in “X” measuring system” is that there are a few stock sizes that I use and they just happen to be measured in even numbers of mm’s or fractions (or decimals) of inches. If we are turning to a size it is only psychologically nice to turn to whole numbers. It feels nicer to turn to say an Inch rather than 25.4mm or turn to 25mm rather than 0.984″, because of the simple numbers involved, but the accuracy needed does not change at all.

 

 I offer the above as a start for an intellectual discussion not a soap box for bigoted or biased dogma. I just want to know what people really mean by saying they use whichever units. I don’t suppose that even the most ardent fan of, say, metric would refuse to buy a piece of 1″ round stock because it was sold as IMP.  In addition, I hope that we don’t, again, risk having to buy 6.35mmBSF bolts, because of someone else’s dogma.

 

 Over to you., and please keep it friendly

chriStephens 

[chris stephensParticipant @chrisstephens63393]

Just a Sunday afternoon diversion

[KWILParticipant @kwil]

Have you not noticed that when you pick an article up and run a rule over it, if you measure between centres of say two holes, it is either exact metric say 10mm or  exact 1/2″,  except for gear shaft centres etc.

[John HaineParticipant @johnhaine32865]

What I mean is that I use tools calibrated in either metric or imperial – actually almost always metric – and tend to think in metric units unless I’m doing woodwork.  When you buy material which is nominally either “X mm” or Y inches” it never is unless sold as precision ground stock. 

[Speedy Builder5Participant @speedybuilder5]

I would have thought that if you were tooled up with imperial drills, reamers micrometers etc, its a little more difficult to tap a metric thread – as I have found out moving to France.  Sure we can all have a calculator to hand and convert any measuring system back to the tools we have, but reamed and tapped holes must be made with the correct tools.

 

My lathe has an imperial leadscrew, so without a 127/100 gear wheel, its difficult to cut a metric pitched thread (Near equivalents must be used).

 

Living in metric land has a few problems for the imperial tooled engineer – even BSP is slowly being phased out in favour of metric pitched fittings (Quite rightly so).  But interestingly enough, if you come accross antique French threads, they are of Whitworth form.

 

I wouldn’t say one is better than the other, but be aware.  In the French building trade, centimetres are the preferred unit and not Milimeters as in the UK. My suprise when I ordered a small pane of glass 60 x 120 for the front door.

[chris stephensParticipant @chrisstephens63393]

Hi Kwil,

That’s the sort of thing, but even metric users don’t always use whole or convenient numbers. Some just equally space things, are they then metric or imperial, if odd numbers are used? 

Does using one or other system mean that you have to use whole numbers?

chriStephens 

[blowlampParticipant @blowlamp]

To me, “X” would be derived from any drawing or plan I was working to.

So even if all my machines were imperial but the drawing was metric, I would class myself as working in metric and view the conversion process as being a necessary evil.

 

Martin.

[Sub MandrelParticipant @submandrel]

Hi Chris,

 

The engine I’m building now is in Imperial units.  In this case I mean

 

*   It’s at 1″:1′ or 1/12 full size and the original was built with most dimesions as inches or large fractions of inches.

*   >90% of the dimensions of my design (taken from an engraving) are to the nearest 1/16″.

 

The only ‘stock’ size so far is the thickness of the material the frame is fabricated from – I don’t recall if it is 1/8″ or 3mm

 

Everything else so far has been machined all over so I don’t think the ‘stock size’ theory applies strongly. The piston and valve rods will be 1/16″ and 1/8″, but that’s because these scale to 3/4″ an 1 1/2″ at full size. Tool sizes have an influence (mostly number drills and BA taps).

 

Neil

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Units and systems of units only have significance within a social group where the members of that social group need to communicate with each other . For example a lone individual could make a table to suit his needs without any dimensions at all – a general idea of size and parts made to fit each other would do the job perfectly well . If however the one individual wanted to publish his design for others to make then it would is nescessary for him to establish a system of dimensions based on a repeatable reference standard available to all .

 

The reference standard in our earliest days was always something commonplace like the average height of a man or the length of a walnut or stride . As time went on the standards became more accurate and the idea of a parent standard and repeatable copies of it developed . Thus were born all our common dimension units inch , yard , metre and many others .

 

In modern times saying ‘I work in Imperial/Metric’  just means that we have chosen our personal reference standard – the actual sizes of things don’t change – just the way we communicate .  

 

The actual system of subdivision of units in the Imperial system comes from simple practicality  – 1/2 of something , 1/4 of something etc are just intuitively useful  and most of the other subdivision systems like decimal have some origin in practicality . .

Edited By MICHAEL WILLIAMS on 07/11/2010 18:36:54

Edited By MICHAEL WILLIAMS on 07/11/2010 18:51:10

[Steve GarnettParticipant @stevegarnett62550]

Michael’s right – most tools don’t work in particular units, we do. We either use what’s written, or convert it to what our social group might use if we really feel the need to.

 

You can get into slightly interesting situations with taps and dies and their associated holes but generally even that isn’t really an issue with most construction, if we’re honest. When we complain, we’re just being bloody-minded and awkward, really.

[Bill PudneyParticipant @billpudney37759]

“X” is what you think in.  Everything else is a compromise.

cheers

Bill Pudney

 

[dcostaParticipant @dcosta]

Hello.

 

In each moment humans use the measuring system most adequate to his means and environment.

 

A while ago somebody sent to me the following text about measuring units (and in some sense  measuring systems). I think it illustrates what measures have been for people.

It looks to me that the text has some historical imprecisions. I beg You, please,  ignore it.

And smile… 

 

 

Here is the text:

 

The gauge of railways (distance between two rails) of the United States is 4 feet, 8.5 inches. Why was this number used?

Because this was the gauge of English railways,  and the American railroads were built by the British, this measure was used to …
Why do the British use this measure?

Because the British companies that built the cars were the same who built the wagons before the railroad and used the same gauge of the wheels.
Why was that measure used (4 feet, 8.5 inches) for the carts?

Because the distance between the wheels of carts would fit into the ancient roads of Europe (not only continental) that had this measure.
And why were the roads this measure?

Because these roads were built by the ancient Roman empire during their conquests, and these measures were based on the chariot pulled by two horses. And why are the measures of the chariot were so defined?

Because they were made to accommodate two rear horse!

Finally … The American space shuttle, the Space Shuttle uses 2 fuel tanks (SRB – Solid Rocket Booster) that are manufactured by Thiokol in Utah.

The engineers who designed these tanks wanted to make it wider, however, had the limitation of the railway tunnels through which they would be transported, they had their measures based on the gauge line, which was limited to the size of the English coaches who had the width European roads at the time of the Roman empire, which had the width of two horses ass.

Conclusion: The most advanced example of the engineering world in design and technology is based on the size of the Roman horse’s ass!

Note: The text was translated from portuguese  language using Google translate.

 

Best regards

Dias Costa

 

 

 

 

 

[TerrydParticipant @terryd72465]

Posted by MICHAEL WILLIAMS on 07/11/2010 18:24:54:

Units and systems of units only have significance within a social group where the members of that social group need to communicate with each other . For example a lone individual could make a table to suit his needs without any dimensions at all – a general idea of size and parts made to fit each other would do the job perfectly well . If however the one individual wanted to publish his design for others to make then it would is necessary for him to establish a system of dimensions based on a repeatable reference standard available to all .

 

The reference standard in our earliest days was always something commonplace like the average height of a man or the length of a walnut or stride . As time went on the standards became more accurate and the idea of a parent standard and repeatable copies of it developed . Thus were born all our common dimension units inch , yard , metre and many others .

 

In modern times saying ‘I work in Imperial/Metric’  just means that we have chosen our personal reference standard – the actual sizes of things don’t change – just the way we communicate .  

 

The actual system of subdivision of units in the Imperial system comes from simple practicality  – 1/2 of something , 1/4 of something etc are just intuitively useful  and most of the other subdivision systems like decimal have some origin in practicality . .

 

Just remember that there are decimal divisions in the Imperial system just as in the Metric.  Some Imperial proselytisers seem to have forgotten this and talk about the difficulty of deciding on the position of the decimal point as though Decimal and Metric are one and the same thing.

 

When in France (I live there for much of the year) I ask for a half or quarter kilo of cheese or ham etc, I may even ask for 100gm, everyone is happy with that.  Fractions and decimals are used colloquially just as in the Imperial.  These are not mutually exclusive units of expressing quantities.

 

Most of the work we undertake in Model engineering is decimal, and will involve the same problems as in Imperial.  In another thread someone spoke of a drawing giving a measure of 68580mm which he had to convert and had difficulty of deciding on the position of the decimal point.  Well whoever produced the original was using the wrong units for a start (should have been metres as a architectural drawing) and surely it’s not that difficult to decide that you move the decimal point to the left by three places to divide by a thousand, I learned that when I was 9 yrs old.

 

Whatever you want to use is ok, just don’t use cubits if you are working collaboratively

 

By the way, apart from sheet materials, building products are now made in metric multiples.  So a 4″ x 2″ is actually 100mm x 50mm now etc.

 

Terry

 

Edited By Terryd on 07/11/2010 23:12:01

[Ramon WilsonParticipant @ramonwilson3]

Hi All,

Some really good replies to Chris’s initial question but heres another view based on experience(s) (with a small ‘E’ I must stress) .

Personally I believe its a matter of ‘preference’. If I may elaborate…..

 

As someone ‘brought up’ with imperial it came as quite a sharp learning curve to have to use metric at work. I took a job in a small jobbing shop where some machines were metric – French Somua mills, another imperial – Cincinatti, the Bridgeports dual(DRO) and the lathes imperial. It was the norm when using the Somua to convert any imperial drawing dimensions to metric and carry on – it helped of course to have metric measuring kit available. On the Cincinatti if the drawings were in metric the reverse occured and on the BPs one worked in whatever the relevant drawing featured (As a jobbing shop the drawings came from many sources). It quickly became apparent – for me that is – that metric seemed very much the ‘easier’ system to work and if anything slightly more accurate but I accept that for some that may be open to debate.

 

I then took a job in a factory where all the machines where metric or had DRO fitted and the drawings came universally in metric also, ergo metric was the system in constant use. Material sizes came in all forms, both imperial and metric, and really had very little relevance to the working ‘system’. I would however go home and use the Myford and Linley mill which at the time were both imperial!

 

At some stage a DRO was fitted to the mill and since then is used constantly in metric. I find it no real burden to convert imperial dimensions to metric before work begins even though technically theres no reason to actually ‘have to’.  It’s not a bad way to help to find yourself ‘about the drawings’ and possibly pick up the odd mistake. Note however this is direct conversion and not ’rounding up’.

The Myford? well with no DRO on that I’m afraid I’m still stuck with using imperial but it would be the same again if DRO was fitted and if it was replaced (ooh I wish)  it would definitely be a metric machine.

 

I find I can ‘think’ in metric just as easy as imperial but only at the smaller end ie thous and ’01s’. Its still in inches when it gets to feet and yards

 

When it comes to threads I just use whatever is called for and drills the same. I noticed at the Midlands show there were some small hex head metric bolts for sale – not as big a range as BA but perhaps something that will increase. It will certainly be easier and possibly cheaper to get decent HSS metric taps than BA I would think. Theres still a lot of bolts in tobacco tins and some decent wear left in the BA taps before a restock is in order though

 

That said I guess for myself at least I feel I can say that I do ‘work in metric units’ whenever possible and would certainly choose to do so at all times over imperial but in the end its down, as I said at the beginning, to choice – ‘preference’ – and for me I know which I would prefer – I just wish I could afford to up grade the Myford

 

Regards – Ramon

 

[John OlsenParticipant @johnolsen79199]

My workshop is bilingual….when I started with the Unimat about 25 years back I had all metric. I t was then a bit soon to be able to do that easily, so things like BA screws started to creep in, then I inherited my Dads Myford and things like Number drills arrived. Although it is notable that he had got heavily into metric for general purpose fasteners.

 

Ayway, I have quite often had to work to metric sizes on the Myford, and find that, lacking DROs on it, the best approach is to get the digital calipers set to the desired size and then  zero them. The job is then measured every so often , and of course the calipers tell you how much remains to be taken off. Just make sure you don’t go past the desired size, eg keep an eye on the sign on the calipers! (I only did that once!) For this of course, it does not matter much what the units on the machine are…I do much the same thing if using one of the shapers that does not have graduations at all.

 

I think the story about the Roman carthouses, while cute, is actually apochryphal. The early railways were plateways, with flanges on the outside and plain wheels…see Trevithicks loco for an example. They were laid to a nice even five feet or so . When the  flanges went on the wheels , it was no longer the outside size that mattered, it was the inside…for the same spacing and a rail head just under two inches wide you end up with 4 foot 8 and a half inches. Also the loading gauge for railways is pretty independent of the gauge, the American loading gauge for instance being somewhat larger than the  British.

 

regards

John

 

 

[Ramon WilsonParticipant @ramonwilson3]

You know guy’s, sometimes when the most obvious is simply staring you in the face it proves impossible to see the wood for the trees. Having posted last night I went to bed bemoaning the fact that I really would like a metric lathe and that I didn’t really want to fit a DRO. It was then the obvious struck – why not change the bloody feedscrews It has taken years for this stupidly simple fact to drop into place Aaaarrgh!!!

 

So this morning I’ve checked Myfords site and yes they are financially viable and I shall place an order forthwith. So thanks to Chris and his question it looks as if my wish has been easilly met and I will soon be able to say with real meaning – ‘I work entirely in metric’. Thanks Chris.

 

Regards – Ramon

Edited By Ramon Wilson on 08/11/2010 10:15:57

[John HaineParticipant @johnhaine32865]

The only thing to remember is that Myford supply topslide and cross-slide screws to metric, but not the main leadscrew!  I bought my S7 as metris when new and was puzzled when trying to part off to an exact length which needed several turns of the L/S which I assumed was 3 mm pitch…oh no, it’s 1/8 inch!  Now driven by CNC so it doesn’t matter…

[KWILParticipant @kwil]

I went down the route of metric leadscrews for a Myford S7, but fitted DRO instead + Derek Brown’s add on Metric system to still use the Norton Gearbox for either metric/imp. The metric leadscrews are in the box for a rainy day.

[The Merry MillerParticipant @themerrymiller]

I recently purchased an immaculate ML7-R-B from a fellow  I knew.

He had bought it brand new in 1984 from Buck & Hickman as a cancelled order from somebody else.

It had fitted metric indexable feed dials (0-40 divs.) on the cross slide and top slide.

I did some trial cuts with my metric hat on and noticed something wasn’t quite right. 

It had imperial feed screws. That really screwed me up (pardon the pun)

Without  realising it he had automatically been using the infamous “metrinch” system of measurement for 26 years.

He had never been involved in any branch of engineering when he bought the lathe otherwise no doubt he would have sussed it out  pretty quickly.

Any way all became normal!!! when I fitted imperial feed dials and I was able to put my imperial hat on once again.

 

As an aside , I use the metrinch system quite often especially when doing woodwork.

Also as I progressed up the engineering ladder via different companies I often had to switch hats but never had both on at the same time.

 

Len. P.

 

 

 

[Ramon WilsonParticipant @ramonwilson3]

Well I’ve bit the bullet and ordered new feedscrews and dials. I didn’t realise that the leadscrew on a metric lathe was still imperial until I looked on the site this morning however I had already decided that a replacement would be too costly for the amount of use the  saddle feed gets. I see they do a metric handwheel for the leadscrew but assume this is probably 159 divs per rev but I shall leave this as is though and just convert if required.

 

Len, we bought a new Tos universal ‘metric’ mill, big beefy thing and a joy to use but it didn’t take long to realise something was wrong with it’s accuracy. Same thing, imperial leadscrews and metric dials. we ended up with a  fitter coming over for two days to strip it all out and replace – must have reduced the profit margin a fair bit!

 

Ramon

[TerrydParticipant @terryd72465]

Hi Ramon,

 

How does the cost o Myford metric screws, leadscrews and dials compare with  using electronic scales, I would imagine there would be some favourable comparison even if using the convenience of a DRO and you can use both imperial and metric depending on the project in hand at any one time.  Worth a passing thought n’est pas?

 

Terry

[Ramon WilsonParticipant @ramonwilson3]

Hi Terry, How is your rebuild going?

 

I’m not sure of current prices at the lower end of the market for DRO but the main thing was that I didn’t particularly want to fit one to the lathe. What I have ordered today though was just less than half what I paid for my (two axis) ‘ORTEC’ DRO for the mill  several years ago. I’m more than happy now (or will be once fitted) to be able to use it ‘conventionally’ and I’m well equipped with metric measuring kit. I can always retrofit the original feedscrews were it necessary I guess but can’t percieve of a situation that would deem it at this point.

What I can’t get over is why it took so bloody long to see the bindingly obvious!!!! (pardon the frencch)

 

Regards – Ramon

[TerrydParticipant @terryd72465]

Hi Ramon,

 

The builders are about halfway up with the walls, we’re now awaiting scaffolding but the weather has deteriorated!! The insurance company have been good so far.  I’ve bought a Warco 280V-F which appeared to be a good subs for my Boxford.  I also bought an ex demo Larger Weiss mill, both are being stored, but I hope to be in by Christmas given decent weather.  The concrete base of the garage has suffered some damage but that is to be repaired with an epoxy screed and painted so it should look quite good. And with an electric sectional door I should be quite cosy in there.

 

I’ll post a picture storyboard when finished as an inspiration I hope to others not to neglect good insurance.

 

Will post more later.

 

Best regards

 

Terry

 

PS  I can’t wait to be able to try and copy one of your engines!!

[chris stephensParticipant @chrisstephens63393]

Hi Ramon,

When you get your nice new screws and dials you will have to get used to the metric way of lathe dials. The norm is for IMP hand wheels to be marked in  actual travel of the cross slide but the Metric norm is for hand wheels to be marked in diameter reduction. It confused me at the MEX a few years ago when I was demonstrating the Metric Big Bore Myford on the SMEE stand, but in my defence it was before the cataract operations. I should have been used to it as my Colchester has the same system but my Myford is Imp, don’t ask about my Warco I haven’t figured that one out yet.

chriStephens

[Ramon WilsonParticipant @ramonwilson3]

Thanks for that Chris, I was used to it at work on Colchesters too but thats a few years back now – it will be interesting to see how well the transition goes.

 

It’s good to hear things are well under way Terry and that you should soon be back to some semblance of order. That must have been an awful shock and quite a setback.

 

Your misfortune prompted me to check my insurance carefully. I think I mentioned at the time I was with Norwich Union (now Aviva) but had forgotten that MoreThan had offered the equivalent cover so had in actual fact changed.

 

Just to be certain I contacted them only to be told that my cover was limited to £2000 for outside buildings. Instant raise of heartbeat and alarm bells ringing loudly. After several phone calls where it has to be said I was treated to very understandingly it finally resolved itself and yes I am covered but only because I took out the insurance before they brought in the £2000 limit. I do now have it clearly laid out in writing so am satisfied that it is in order. It was a nasty moment though and reinforces your advice to make certain of your cover.

 

Sorry to go off topic – had a good workshop day today making cutters. Tomorrow sees the start of rather a lot of cylinder head fin milling – long dormant project that has suddenly found it’s way from under the bench and on to the top and yes, all in metric of course

 

Regards – Ramon

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