Probably comes from the days when the machine shop planer would strike out the dimensions not required, so that there was only one set left.

Provided parts were fitted to each other, would there be any need to measure more accurately than the 64ths divisions of a rule? Until recently the only way I would have been able to set the lengths of those axles would have been with a surface gauge and a 4R rule

Just because we can buy instruments graduated to 0.001mm doesn't mean we have to (or that the measurement will be that accurate). I spent a large part of my career explaining to engineers that specifying unnecessarily tight tolerances wastes time and generates an excess of either scrap products or concession notes, adding to the cost without benefiting the customer.

Brian G

As far as limits and fits are concerned, back then, certainly in my 50 years of draaughting BS or ISO standards were rarely used. Some companies used the Newall system but most older engineering companies, and a lot of these were established around 1900m had established their own standards which they continued to work with until they needed to standardise. The reason for standardisation was the decline of the "make all" factory, where the raw materials went in one end and the finished goods came out the other with no subcontracting. Since, probably the second world war, industry changed and manufacturers did what they did best and let some one else make the other bits. So now we have drawings with all the information on to make a fully interchangeable part so that everybody who reads it has the same information without query.

I'd not be too worried by multiple dimensions as long as they are coherent and reasonable easy to follow: as others say, simply highlight the relevant ones, or make a copy with them alone.

More to the point is having drawings without errors! I wonder how many projects have come to grief over that.

Oh, I use things like drill or milling-cutter shanks as gauges, bits of old plastic bank-cards – our town never had trams so no tram tickets – and the like; though I do measure them with a micrometer. Actually that's reciprocal. Ground cutter-shanks are good for verifying micrometers. I set my mill's DRO read-heads using a plastic feeler-gauge cut from an expired caving association card. I do need use the firm-joint caliper and rule sometimes.

'

What I have noticed elsewhere on this forum is something of a corollary to this thread. This is the fretting about model-engineering drawings not published to the very latest industrial presentation to ISO-rhubarb, rich in tolerances, correct line-thicknesses, proper boxes of precise material and finish codes, "approved by " and revisions lists, etc.. A certain point-missing, one thinks…!

Besides, model-engineering often means replicating in miniature, machines originally built using rules, stiff-joint calipers and genuine blue-print copies of linen tracings of beautifully-made pencil drawings.

I could live without the suffix " bare " though. So-many-sixty-fourths are fine and solved by the Tracy Tools conversions poster… but is that an Imperial Doncaster "bare ", an ISO-approved Thetford " bare "… ? Perhaps I'll use the " just-about-fits bare " .

Maybe we are spoiled – though no, I don't pine for the chain-drill, cold-chisel and file, despite sometimes needs-must.

The Apple store offers various calculators for fractions – but how can one tell which are FREE and which require payment?

I have not been able to set up my iPhone for payments – and it has NOT proved a problem to date.

MC

Perhaps one of these!

**LINK**

FC

Same people do an Android version **HERE**

https://play.google.com/store/apps/details?id=com.digitalchemy.calculator.freefraction&hl=en_GB&gl=US

I tried clicking the link at the end of the film but nothing happened!

I wondered if it's possible to buy one of those rulers in the United Kingdom

MC

I'm sure publishing to a hobby audience had far more to do with it than engineering best practice!

Model Engineering Plans are often eccentric by professional standards, for all sorts of reasons. They range between excellent and downright misleading. Using the same drawing to redimension similar parts is asking for trouble in manufacturing, but not a bad idea for economy minded hobbyists wanting to build the same engine in different scales. It does require the hobbyist to be wide-awake though!

I never trust hobby plans entirely, and always do sanity checks before making anything. Safer to assume model engineering plans are flawed than to blindly trust them! The check might be a basic sketch, or a full 2d CAD redraw to confirm many dimensions, or modelling whole parts and assemblies in 3D CAD. 3D Modelling is useful because it often suggests how parts might be machined for real, as well as confirming their shape and dimensions. (In a sense 3D CAD modelling really makes parts, rather than representing them 2D on paper, which is error prone.)

In my limited experience sanity checking reveals fairly quickly how good or bad the plan is. Although cluttered the PottyMill plan I found on the internet proved sound, as was Stewart Hart's properly laid out original I came across much later. Same can't be said of some of the plans in old ME's, where the number of question marks often suggest a full review is necessary! Mistakes are fairly common, more difficult are missing dimensions and reference points, and parts that can't possibly fit together. LBSC plans are inconsistent, ranging from crystal clear – the famous words and music – to unsatisfactory outlines, probably never built, and perhaps only published as suggestions rather than practical designs. To be fair to amateur plans, draughtsmanship isn't an easy profession, and drawing offices usually cross-checked and reviewed everything with a team, corrected mistakes promptly, and applied proper version control. More work than most of us have time for.

No matter: I'm a gentleman dilettante who likes making things, indulging interests, who has no need to earn a living from my tools. Iffy plans are deeply frustrating if get-on-with-it perfection is expected of them, but all part of the puzzle solving fun once you understand they are often flawed. And they often are…

Dave