Why is the world of model engineering still imperial?

Why should one invent a new rack size. There is no law to say it has to be an integer number of whatever you choose to measure it in. It’s still one rack width in parsecs.
regards Martin

Ive used a few and I can’t ever remember measuring one. The more useful measure is the horizontal pitch (hp) of which you can get 84 in the card cage

Edited By Martin Kyte on 06/03/2023 17:24:00

Which is fine till someone confuses electrical KW with mechanical KW on electric motors.

It might be an imperial horse if it's height is measured in hands

Dave

Slugs - I am sorry, Dave, the SI system is no better. I would like to have 4.45 Newtons of potatoes, please.

No system can cope with the person in the street's measurement or understanding of weight and the basic problem it brings.

JA

Slugs were being abandoned when I was at college. All the Slug was was a cheap laugh.

Edited By JA on 06/03/2023 17:29:21

Never used that pitch, it seems you were using a Euro measurement in 19" imperial racks.

You can tell ESTI 21" from 19" by the cage nut pattern Etsi is regular even spaced and 19" being imperial has a repeating pattern

95 hp’s in a 19”rack and yes I’m talking about euro card subracks.

What on earth (or anywhere else for that matter) is 4.45 Newtons of potatoes. If you use the appropriate unit which is Kg you will get the same mass of spuds wherever you are in the universe.
regards Martin

But most people measure weight rather than Mass because it is easier to measure, even though they then use the wrong SI units.

As I said earlier, confusion twixt mass and force, and I did mean reduced gravity on the moon, not zero, thanks Martin. When I was young (long ago) we had things called poundals, beloved of academics, scorned by most everyone else

Come on Keith when have you ever heard anyone asking for spuds in Newtons.
regards Martin

Edited By Martin Kyte on 06/03/2023 18:32:42

Having mulled over the original OP's statement. I have come to the conclusion that he is wrong in his belief that the model engineers world is metric.

Only a few of the oldies are still working in imperial. Most of us, me included, are perfectly happy to work in either metric or imperial, whilst the younger members are working in metric units.

Andrew.

But most people measure weight rather than Mass because it is easier to measure, even though they then use the wrong SI units.

Consider a balance with adjustable arms. A known mass M1 is on one side and the mass to be measured M2 on the other. Adjusting the fulcrum so the balance beam is horizontal the downward force on one half is given by GxM1xMe/r^2 and on the other GxM2xMe/r^2

For the beam in balance the ratio of the first equation to the second is L2/L1 where L1 is the first arm length and L2 the second. Cancelling the gravitational constant, the mass of the earth and the radius of the balance to the centre of gravity of the earth gives the simple equation

M1 = (L2xM2)/L1 as M2 is known M1 is calculated by the simple measurement of the two lengths. So the balance measures mass and is easy to do.
Spring balances also measure mass by the same comparative technique. This time the calibration extension is by the standard known mass and the mass in question found by the ratio of extensions.

So I contend that the majority of people measure mass not weight.

I thought I would just post that for fun.

regards Martin

Edited By Martin Kyte on 06/03/2023 21:10:29

Edited By Martin Kyte on 06/03/2023 21:11:14

And the someone comes along with a spring balance. I believe they are very very common.

Really this thread is going nowhere. Perhaps I should blame Isaac.

JA

"Really this thread is going nowhere"

I'm sorry i asked! :0(

Most balance scales I have seen have the iron weights marked in lbs/oz or grams/Kg so on one side of the scale you have a known weight not a known mass

I had a look back at the last two issues of ME, of the articles that had dimensioned drawings with them 3 were imperial, 2 metric and another had one drawing in imperial and one in metric. so the world according to ME mag is only about 55% imperial

Paul, it is a pity you bought a "kit" of barstock rather than just drawings, at least then you could have decided to do a full metric conversion from the start but as you now have the materials it is a bit of a shame to put them to one side. It would be interesting to have a look at the drawings and see if a few changes to metric stock for things like the piston rod would work out more economical to change to metric so you could use metric threads on that and any screws you have to supply anyway so they could also be metric as unlikely to be affected by the supplied stock sizes. As an example a Stuart Victoria would only need three pieces of round stock changed and then could be made with all metric threads and fixings, infact even one of those could still be used as it's close to the metric size.

Unlike the other "kits" the e-bay seller has on offer I don't know where the design originates from so can't look at the drawings but if you wanted to PM me I'd take a look and suggest a course of action that may be the best if you want to stick with metric

when i wer' a lad we had a fruit & veg shop called Newtons, lots of people came in and asked for potatoes.!!!!!

Thankyou for the offer Jason, I am becoming accustomed to the ME environment and accept that I have to invest in some imperial tools, I guess one issue is the ready availability of imperial drills, screws, bolts etc.

There are a few elements which I may choose to metricate but generally I'll keep it as it is.

Edited By Paul McDonough on 07/03/2023 10:11:49

Totally agree with you Paul but you have to remember that it is cold in the workshop at the moment and all the members are sat in front of the fire with nothing better to do. Model engineering is imperial because 99% of drawings are done in imperial, we all bought mics verniers etc years ago when they were imperial, we pick up tat from boot sales etc that is mostly imperial, we buy ex industrial machines, old Colchester Bantams and Bridgeport’s that were imperial. I was working up to ten years ago in the aerospace industry, all our drawings were imperial, all our measuring gear was imperial, the fifty year old Hardinge lathes that we were expected to hold half thou tolerances on were imperial, half of this country is still imperial.

Jason is either being deliberately provocative or deliberately obtuse. His lumps of cast iron should be marked as lbm (pounds mass), what they weigh will depend on the local gravitation constant. A beam balance is a comparator, it compares the stuff on one side with a set of known masses, a spring balance actually measures the force of gravity acting on the mass you've hung on it