Mixing fractions and decimal units in an imperial drawing

[Brian HParticipant @brianh50089]

I have an old book called " The Boilermakers Assistant" published in 1904 and this has measurements such as 7 3/8 -1/16 and this is consistant throughout, it is always -1/16. A very easy system to use in fractions.

[Brian HParticipant @brianh50089]

To answer Jason regarding sheet metal thicknesses, I've always been used to SWG or the American equivalent and this was working on aircraft parts.

I've also worked on Airbus parts in metric but cannot remember how sheet metal was specified but I suspect metric.

[Neil WyattModerator @neilwyatt]

Click the Machine DRO ad at right, they have plenty of imperial measuring equipment including M&W rules.

Neil

[SillyOldDufferModerator @sillyoldduffer]

My old book (ICS Geometrical Drawing Mechanical Drawing Sketching Projections Development of Surfaces, London 1907) gives the following advice, which is consistent with earlier posts.

This drawing (part of a commutator) is an example of mixed fractional and decimal dimensioning:

Of interest is that decimal dimensions omit zeros before the decimal point, i.e. .063" rather than 0.063"

Here's the text (from 122 onwards) :

Fans of imperial fractions may note the very last sentence. It addresses a disadvantage of that system. Extra calculations are needed to convert thousandths into 64ths and use of a table is recommended to avoid doing them.

I have a 1947 book that pretty much repeats the same advice about dimensioning. Does anyone know when fractions in drawings were phased out in favour of decimal inches?

Dave

[Sam Longley 1Participant @samlongley1]

Posted by Ajohnw on 06/11/2016 10:21:16:

. Think I have used it twice but it was more or less given too me.

John

–

That reeks of — " I borrowed it & never returned it !!!!!!!"

Which we have all suffered from in some form or other over the years

Only thing I would like to do that with would be the mother in law – but it never seems to work– Like a damned pigeon !!!

[AjohnwParticipant @ajohnw51620]

Posted by Sam Longley 1 on 06/11/2016 13:09:45:

Posted by Ajohnw on 06/11/2016 10:21:16:

. Think I have used it twice but it was more or less given too me.

John

–

That reeks of — " I borrowed it & never returned it !!!!!!!"

Which we have all suffered from in some form or other over the years

Only thing I would like to do that with would be the mother in law – but it never seems to work– Like a damned pigeon !!!

No. Some one begged me to have it as I kept refusing. The price was a tenner and it took some persuasion to get me to buy it. Must admit the couple of times I've used it a rule would have been a bit dodgy.

I need to mark out a 3 4 5 triangle on the floor. Should I use mm or m ? Think I'll use feet – the type on a tape measure.

John

–

[AjohnwParticipant @ajohnw51620]

Posted by Neil Wyatt on 06/11/2016 11:13:38:

Click the Machine DRO ad at right, they have plenty of imperial measuring equipment including M&W rules.

Neil

This is a toolroom style 6" rule Neil – not those stupid things with mixed graduations along their length.

~kAAOSwcUBYHtXG”>http://www.ebay.com/itm/Starrett-C304SRE-6-Semi-Flexible-Steel-Rule-with-4R-Inch-Graduations-/232135140790?hash=item360c5525b6:g~kAAOSwcUBYHtXG

I like to have 2. One rigid and one flexible.

John

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[Sam Longley 1Participant @samlongley1]

Posted by Ajohnw on 06/11/2016 18:04:28:

Posted by Sam Longley 1 on 06/11/2016 13:09:45:

Posted by Ajohnw on 06/11/2016 10:21:16:

. Think I have used it twice but it was more or less given too me.

John

–

That reeks of — " I borrowed it & never returned it !!!!!!!"

Which we have all suffered from in some form or other over the years

Only thing I would like to do that with would be the mother in law – but it never seems to work– Like a damned pigeon !!!

No. Some one begged me to have it as I kept refusing. The price was a tenner and it took some persuasion to get me to buy it. Must admit the couple of times I've used it a rule would have been a bit dodgy.

I need to mark out a 3 4 5 triangle on the floor. Should I use mm or m ? Think I'll use feet – the type on a tape measure.

John

–

Make sure you use a calibrated one, they vary in length by quite a bit. Try comparing 2 different makes of 5 metre tape.

When BS 5740 ( think that was the No.)was first introduced there was a lot of fuss over calibrated tapes in the building industry – now long forgotten. But certainly the old carpenters boxwood 3 ft rules varied by over 3/16 inch as we used to compare them in the joinery shop when arguing about fit of various components.

If you buy a measuring wheel from Screwfix & measure the same 30 metres twice you will often find it varies by up to 1.5 metres each time you run the 30 metres

[JasonBModerator @jasonb]

John you can get the same thing from MSC by either Mitutoyo or the SPI EZ-View for half the price and no need to import, I have a couple of the flexi EZ-View ones 6" and 12"

[GeorgineerParticipant @georgineer]

Posted by Martin Connelly on 06/11/2016 09:09:18:

[… ] Micrometers, vernier calipers, dial calipers and electronic calipers do not usually show fractions on their imperial scales. [… ]

True in part. Look on 'a well-known auction site' for fraction calipers.

George

Edited By Georgineer on 06/11/2016 18:44:30

[Clive FosterParticipant @clivefoster55965]

When emeshed in these fractions / decimal / metric controversies its easy to forget that the underlying philosophies of the systems are different. The imperial fractional system is based on integer (whole number) divisions of what ever base unit is considered suitable. In the real world outside of machining levels of precision that's a very useful way of working. If you need more than one base unit to span the distance in sensible numbers you "and" them together. Such as 5 miles and 387 yards and 2 feet and 8 inches and 11/16 inches. Apart from being immediately and obviously absurd, feet and yards should never be mixed, its clear which component defines the accuracy. The 11/16 which implies ± 1/64 accuracy, two steps down on the divisor chain. In the real imperial world you should never use more than two base units anyway. Its miles and yards, feet and inches (with fractions if need be).

The beauty of the basic imperial system is that its relies on sensible size baseline units, thats why there are so many of them, with minimal faffing about to produce stuff that fits. Don't forget that imperial was developed for and used by essentially innumerate folk. For example you can set a roof on an imperial house pretty much without calculation. Heck if you are an American working to 4 ft module you can build the whole darn thing without maths. Setting a roof in metric can give even the pros pause for thought. The guy who helped me build my workshop got into heaps of trouble until he gave up being modern & metric.

Thou's and the like came in to align inch divisors with base 10 maths. Which has its points but inevitably leads to irrational numbers and incomplete divisions. When adding up you have to have enough decimals which soon leads to absurdity with fairly precise work generating a conflict between design figures and tolerances. Fractions are exact by design. Strictly you should and out the different divisors too 11/16 being 1/2" and 3/8" and 1/16" but folk familier with the working do it automatically in their head. As ever textbooks make the easy hard.

Metric of course is an additive and subtractive system working up and down from a baseline unit with suitable mutlipliers to keep the number of digits in bounds. If you don't keep your brain engaged it rapidly becomes absurd. Being aligned with the base 10 number system can make maths easy but it becomes hard to spot errors. I'd like pound for everytime I've had to explain the absurbity of the metric equivalent of that 5 miles example.

Clive.

[Sam Longley 1Participant @samlongley1]

I would suggest that you can just as easily build a house on a 1 metre module than a 4 foot one & your friend building your workshop probably got into trouble because he was possibly trying to think in imperial as well as metric. Clearly not a tradesman experienced in metric units & not a reason to reject the metric unit. I have used both & have difficulty with imperial units. As a joinery manufacturer I often had to go onto my shop floor & do some setting out or to explain something. Messing about in 1.8's. 32.s etc was a nightmare & millimetres was far more accurate for setting out. My older machinery was all converted to metric scales until renewed with new plant to avoid errors. My joiners & machinists understood it easily as well.

In my early years on site I used to use a steel square to set out roofs ( A roofing square) for the carpenters & mine was in metric configuration. This was far easier than our old contract managers imperial one as one could simply multiply by 10 when scaling rafter lengths etc.

I can assure you that the mix of feet & yards has caused lots of problems as the units are so close. We had a lorry load of DPC that lasted years because the site ordered yards instead of feet ( then the secretary typed it as rolls but that is another story) & motorway curbs that were a yard long not a foot. The list went on.

That is why the industry (construction) chose millimetres & metres. There can be little confusion between the 2 being such a big difference in size

The problem comes when people try to think between the two systems. Once they are tuned to think metric & forget imperial they find it easy. Do mnot think of a room in feet , think of it in metres. Unfortunately in the construction industry problems arise because in schools kids are taught to think in centimetres as well & carry that forward in future life.

Edited By Sam Longley 1 on 06/11/2016 19:53:13

[Nick WheelerParticipant @nickwheeler]

Posted by Sam Longley 1 on 06/11/2016 19:52:38:

That is why the industry (construction) chose millimetres & metres. There can be little confusion between the 2 being such a big difference in size

The problem comes when people try to think between the two systems. Once they are tuned to think metric & forget imperial they find it easy. Do not think of a room in feet , think of it in metres. Unfortunately in the construction industry problems arise because in schools kids are taught to think in centimetres as well & carry that forward in future life.

That's exactly what my grandfather told me, thirty years ago – work in what you're given, and never try to convert. While I think in metric, imperial measurements aren't a problem.

Clive, I'm afraid you're going to have to explain the absurdity of your 5 miles example again, as I can't see how 11.45km is even remotely complicated? Whereas converting the mixed imperial units into one number to get that 11.45km was a pain.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Clive Foster on 06/11/2016 19:17:36:

…

Fractions are exact by design.

…

Clive.

To their amazement the ancient Greeks came unstuck with that notion when they tried to solve this simple example. Given a right-angled triangle with two sides of length 1, what is the length of the diagonal expressed as a fraction?

Fractions are an excellent tool but they also have serious limitations. I'm not suggesting decimals are perfect but they are considerably more general.

Dave

 

Edited By SillyOldDuffer on 06/11/2016 20:56:38

[JasonBModerator @jasonb]

Posted by Clive Foster on 06/11/2016 19:17:36:

Thou's and the like came in to align inch divisors with base 10 maths. Which has its points but inevitably leads to irrational numbers and incomplete divisions. When adding up you have to have enough decimals which soon leads to absurdity with fairly precise work generating a conflict between design figures and tolerances. Fractions are exact by design. Strictly you should and out the different divisors too 11/16 being 1/2" and 3/8" and 1/16" but folk familier with the working do it automatically in their head. As ever textbooks make the easy hard.

Should that be 15/16" being 1/2" and 3/8" and 1/16"

[Neil WyattModerator @neilwyatt]

Posted by Ajohnw on 06/11/2016 18:24:50:

Posted by Neil Wyatt on 06/11/2016 11:13:38:

Click the Machine DRO ad at right, they have plenty of imperial measuring equipment including M&W rules.

Neil

This is a toolroom style 6" rule Neil – not those stupid things with mixed graduations along their length.

You greatly confuse me at times, you post said you could do with another 12" rule…

But you mean like this Mitutoyu one: http://www.machine-dro.co.uk/mitutoyo-fully-flexible-steel-rule-150mm-6.html

Neil

[SarahJParticipant @sarahj]

Hi Guys,

Thanks for all your replies. I haven't been on my computer since I posted my question and was surprised at all the responses. I'll have a good think about what appropriate tolerances to put on the drawing, I've got a lot of posts to go through and have a good read

I'll do a bit more on the drawing and then post a picture of it. I bought a set of castings for a Stuart Progress and you don't get a plan, but a facsimile of a construction booklet from 1913. I started to do some sketches of the components, but then decided to do drawings of the components instead. Being a Stuart engine I thought it appropriate to do them in imperial. One of the features of doing the drawings in CAD is that I can do a reprint with some of the dimensions in decimal, so it's easier to use with digital calipers or a micrometer.

Again thanks for your responses.

Regards,

Sarah

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 06/11/2016 20:58:48:

Should that be 15/16" being 1/2" and 3/8" and 1/16"

.

What's two hundred and fifty thou' between friends ?

MichaelG.

[Mark P.Participant @markp]

When I was an apprentice at Ruston Gas Turbines we had an old boy in the pipe shop who used “wipers”(rags) as a measurement eg a bit of 1/2” pipe 3 wipers long!
Mark P.

[AjohnwParticipant @ajohnw51620]

Posted by Neil Wyatt on 06/11/2016 21:10:31:

Posted by Ajohnw on 06/11/2016 18:24:50:

Posted by Neil Wyatt on 06/11/2016 11:13:38:

Click the Machine DRO ad at right, they have plenty of imperial measuring equipment including M&W rules.

Neil

This is a toolroom style 6" rule Neil – not those stupid things with mixed graduations along their length.

You greatly confuse me at times, you post said you could do with another 12" rule…

But you mean like this Mitutoyu one: http://www.machine-dro.co.uk/mitutoyo-fully-flexible-steel-rule-150mm-6.html

Neil

Sorry Neil. The ones I looked at had the silly markings.

The other useful markings are across the end of the rule. I have a rigid satin chrome one like that and 2 narrow flexibles that don't have this feature. I now have a 12" hardened rigid one on it's way to me. When I looked for one to link to I had a look around. The price of those vary a lot and I feel $26 for nos is pretty good. Shipping a bit expensive but ………

John

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[JasonBModerator @jasonb]

If you want to follow the Stuart style of drawings than just fractions and no tolerances are needed. The odd "ream ##" is all that is needed. Have you seen any other Stuart drawings to compare with?

J

[Howard LewisParticipant @howardlewis46836]

Coming in late, without having read all the responses, for what they are worth, here are my comments:

If you call for a 3/16 BSF thread call it that rather than than 0.01875 BSF. 3/16 BSF is what everyone else will call it rather than the decimal size.

Are you intending to make just one machine? Or will do you want someone else to make lots, so that the parts are interchangeable?

if the first, then why bother with drawing tolerances, they are not necessary for a one off. You ream/bore the hole, and turn the shaft/piston/whatever to fit. (Depending upon the tooling, and the machine, the chosen dimension could turn out to be exact, undersize, oversize, or even tapered).

For production by someone else, you may well need them, even for a one off.

For mass production with interchangeability of parts, tolerances ARE needed.

Howard

Edited By Howard Lewis on 07/11/2016 11:50:57

[SillyOldDufferModerator @sillyoldduffer]

Posted by Sarah Frazer 1 on 06/11/2016 21:11:25:

Hi Guys,

…

I bought a set of castings for a Stuart Progress and you don't get a plan, but a facsimile of a construction booklet from 1913. I started to do some sketches of the components, but then decided to do drawings of the components instead. Being a Stuart engine I thought it appropriate to do them in imperial. One of the features of doing the drawings in CAD is that I can do a reprint with some of the dimensions in decimal, so it's easier to use with digital calipers or a micrometer.

…

Regards,

Sarah

That's important information Sarah.

Firstly, it's probably not a good idea to go metric if you are building an imperial model using imperial parts and imperial tooling. All you are doing is adding the risk of conversion errors. (But be aware that someone with an all metric workshop and a metric mind-set might disagree with this. For them it might well be easier to do all the conversions.)

Secondly, many of us work by producing a sketch or drawing of a component before starting work on it. Simple components may only need a sketch but in my opinion anything remotely complicated deserves a dimensioned drawing. Another advantage is that making the drawing often clarifies how to approach making the part. What you are doing is a very good idea.

Thirdly, as the drawing is for your own use, you don't have to adopt 'industry best practice' . In particular, as others have suggested, you won't need to put formal tolerances on the drawings.

Unless you're already comfortable with imperial fractions, I'd suggest decimal notation throughout. This is because digital calipers work that way and you can use one to check the size of drills etc before making a cut.

Another useful trick is to keep a pre-prepared table of conversions needed by the project handy in the workshop. For example, if a plan calls for many 1/8" holes, it's helpful read that 0.125" is 1/8" or 3.2mm rather than stopping work to do mental gymnastics.

By all means share some of your drawings with the forum. I'm sure you'll get lots of advice!

Good luck,

Dave

[Martin ConnellyParticipant @martinconnelly55370]

Mark P.

Bay 1 pipe shop?

Martin

[Nigel McBurney 1Participant @nigelmcburney1]

When I was apprenticed 1958 to a small company making scientific instruments ,the drawings were the same as those I I had seen in model engineer magazines, boat and model aircraft books,so had no problems with simple fractional drawings with little tolerancing and holes specified by drill size or ream size, tapped holes were specified as so and so BA,whit or bsf,or brass, the only gauged threads were for eyepieces which had a internal standard.though their was little tolerancing,you were expected to turn fractional lengths to within 5 thou by rule and we did. The rule when producing dwgs was as dimensions get longer avoid using the smaller fractions,there was no dwg manual in the drawing office you just learnt company practice as there was no need for interchangeability except eyepieces and everyone got on with their jobs making good products at an economic price. I then moved to a company making very early automated typewriters and drawings used the decimal system with general tolerances specified on the drawing,never had any problems,and there again a small company with no drawing manual/standards. A further move was quite a culture shock,a big multinational still using imperial and as I was too find out ,a vast amount of specifications and standards covering every thing,and then it went metric. Plus there were volumes of specifications for our suppliers,no personal judgement allowed,just work to spec,plus a very good knowledge of the specs so you could pull a flanker on the inpection and quality personnel who got into a mode of looking for faults rather than, was the part acceptable for production,what that mode of working costs!!.At home I have some all imperial machines,one all metric and I find that I think quicker when working imperial and produce parts quicker.Though looking at the original post ,perhaps we should look at in a way like this the model we build mainly based on vintage items were made to a what is regarded a crude imperial system,the originals worked well some like locomotives were a bit crude ,but had vto work with steel weeks on a steel track and had a reciprocating engine with a sprung crankshaft,I think we get too tied up with measurements and take less interest in the geometry, the coupling rods on a loco have to be free and a bit sloppy to work,but no one seems to get into looking at the geometry , are the axles all parallei to each other,are the cylinder bores parallel to the frames,probably far more important than the actual spacing of the axles.And by the way the US imported rule I bought is crap, .it was divided into thirty seconds and the i/8 ,1/4 and 1/2 lines were all the same length as the 1/32 lines difficult to read,now at the back of the drawer.

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