Why is the world of model engineering still imperial?

[SillyOldDufferModerator @sillyoldduffer]

Posted by Harry Wilkes on 06/03/2023 14:55:26:

Posted by SillyOldDuffer on 05/03/2023 20:39:47:

Posted by Harry Wilkes on 05/03/2023 18:23:14:

Posted by SillyOldDuffer on 04/03/2023 10:40:16:

Posted by UncouthJ on 03/03/2023 19:40:55:

Posted by Nicholas Wheeler 1 on 03/03/2023 18:32:39:

Posted by UncouthJ on 03/03/2023 15:49:00:

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Really? Even after slugs were explained? They must be very bright…

Dave

Of course they are give them a drawing and they can work in either imperial or metric ! Also I would suggest one needs to be bright to be a model engineer

H

No need to understand slugs if you only work from a drawing. Drawings don't expose what's wrong with Imperial, because inches and thou are easy. Have the youngsters been told what a slug is, and why understanding it is important?

Imperial only shows it's true colours when used to do serious calculations. That imperial is broken doesn't matter when handling tools but I hope no-one building stuff to a plan imagines that's all there is to engineering.

It's producing the plan in the first place that matters and Imperial turns nasty when engineers have to design anything involving calculations beyond simple weight and length. Designing bridges, rockets, aircraft, motors, pylons, ships, cars, tower blocks, chemical plant, satellites, and machine tools all require significant mathematics, and in this field Imperial causes endless trouble. Beware thinking Imperial is fine because it works on a beloved Myford; unfortunately that type of engineering doesn't make the shortcomings apparent.

The economic future of the country depends on engineers who can do the maths, not on perpetuating a fading system that makes design even harder than it already is. That's why youngsters shouldn't be told Imperial is OK. Although friendly enough in a shed and on the shop floor, Imperial develops cloven hooves, hairy legs and horns in the drawing office and laboratory. Plus a strong smell of Sulphur!

My guess is most fans think Imperial is just inches, feet, pounds, and ounces. Far from it, full Imperial is seriously complicated, and it hurts when used on grown up problems. For example, if youngsters are going to be Imperial engineers rather than artisans, they'll have to learn the relationship between British Thermal Units and Horsepower, and a host of other complications arising from inconsistencies within the Imperial system. That the sums are considerably less error prone if BTU and HP are dumped in favour of Watts doesn't seem to matter to chaps who think it's patriotic to drink pints!

My advice is that engineering has no place for sentiment or laziness. Professional engineering isn't a hobby. Therefore Imperial has to go, sooner the better. Not understanding the trouble Imperial causes by being internally inconsistent for random historical reasons is no reason to promote it.

Dave

[Martin KyteParticipant @martinkyte99762]

Posted by Dave Halford on 06/03/2023 17:04:04:

Posted by Baldric on 05/03/2023 18:34:28:

Posted by Dave Halford on 04/03/2023 11:22:53:

There's also the world of telecom's equipment.

American 19" wide racks use a height unit of an U which is 1.75" or 44.5mm by 482mm wide

European ETSI 21" wide racks use a height unit of an SU which is 25mm or 1" ish by 533mm wide.

So what should be Metric isn't always.

I was not aware of that, I wonder why someone decided.to create a new standard when it means a lot of equipment won't fit. I am sure you can get narrow 19" racks, that just leaves less room for cables down the side of equipment.

Well, you can get 21 to 19 inch adapters should you have mixed equipment. Going the other way is impossible as you can't remove the outside edge blades/cards

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

[Dave HalfordParticipant @davehalford22513]

Posted by Bdog507 on 06/03/2023 14:53:52:

Hmmmm! Devil's advocate time 😁😁

I believe James Watt's original calculation was indeed 550 lb/sec or rounded up to 33.000 ftlb a minute. It became known as the mechanical or imperial.horsepower….but there's this thing known as a metric horsepower or PS which is slightly smaller at circa 542 lb/sec or circa 735 watts.😄😄

Cheers.

Stewart.

Edited By Bdog507 on 06/03/2023 14:54:23

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

[Dave HalfordParticipant @davehalford22513]

Posted by Martin Kyte on 06/03/2023 12:19:07:

The thing you are measuring is not intrinsically metric or imperial, your choice of measurement systems is. Horsepower is not imperial neither is it metric but based on the output of a horse. Actually the rate at which said horse could raise a weight of 550 lbs or 250kg through a fixed distance of one foot in one second. It may perhaps be better described as an equine system of measurement if you really want to ascribe it to anything.

regards Martin 🥴

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

[JAParticipant @ja]

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

[Dave HalfordParticipant @davehalford22513]

Posted by Martin Kyte on 06/03/2023 17:18:19:

Posted by Dave Halford on 06/03/2023 17:04:04:

Posted by Baldric on 05/03/2023 18:34:28:

Posted by Dave Halford on 04/03/2023 11:22:53:

There's also the world of telecom's equipment.

American 19" wide racks use a height unit of an U which is 1.75" or 44.5mm by 482mm wide

European ETSI 21" wide racks use a height unit of an SU which is 25mm or 1" ish by 533mm wide.

So what should be Metric isn't always.

I was not aware of that, I wonder why someone decided.to create a new standard when it means a lot of equipment won't fit. I am sure you can get narrow 19" racks, that just leaves less room for cables down the side of equipment.

Well, you can get 21 to 19 inch adapters should you have mixed equipment. Going the other way is impossible as you can't remove the outside edge blades/cards

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

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

[Martin KyteParticipant @martinkyte99762]

Posted by Dave Halford on 06/03/2023 17:48:51:

Posted by Martin Kyte on 06/03/2023 17:18:19:

Posted by Dave Halford on 06/03/2023 17:04:04:

Posted by Baldric on 05/03/2023 18:34:28:

Posted by Dave Halford on 04/03/2023 11:22:53:

There's also the world of telecom's equipment.

American 19" wide racks use a height unit of an U which is 1.75" or 44.5mm by 482mm wide

European ETSI 21" wide racks use a height unit of an SU which is 25mm or 1" ish by 533mm wide.

So what should be Metric isn't always.

I was not aware of that, I wonder why someone decided.to create a new standard when it means a lot of equipment won't fit. I am sure you can get narrow 19" racks, that just leaves less room for cables down the side of equipment.

Well, you can get 21 to 19 inch adapters should you have mixed equipment. Going the other way is impossible as you can't remove the outside edge blades/cards

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

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.

[Martin KyteParticipant @martinkyte99762]

Posted by JA on 06/03/2023 17:26:59:

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

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

[File HandleParticipant @filehandle]

Posted by Martin Kyte on 06/03/2023 18:06:32:

Posted by JA on 06/03/2023 17:26:59:

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

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.

[duncan webster 1Participant @duncanwebster1]

Posted by Martin Kyte on 06/03/2023 18:06:32:

Posted by JA on 06/03/2023 17:26:59:

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

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

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

[Martin KyteParticipant @martinkyte99762]

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

[Andrew TinsleyParticipant @andrewtinsley63637]

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.

[Martin KyteParticipant @martinkyte99762]

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

[JAParticipant @ja]

Posted by Martin Kyte on 06/03/2023 21:08:22:

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

[Paul McDonoughParticipant @paulmcdonough43628]

"Really this thread is going nowhere"

I'm sorry i asked! :0(

[JasonBModerator @jasonb]

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

[HowiParticipant @howi]

Posted by Martin Kyte on 06/03/2023 18:30:53:

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

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

[Paul McDonoughParticipant @paulmcdonough43628]

Posted by JasonB on 07/03/2023 09:39:00:

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

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

[Bdog507Participant @bdog507]

Posted by Dave Halford on 06/03/2023 17:26:27:

Posted by Martin Kyte on 06/03/2023 12:19:07:

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

Beat me to it! 😄😄

[BazParticipant @baz89810]

Posted by Paul McDonough on 07/03/2023 08:56:07:

"Really this thread is going nowhere"

I'm sorry i asked! :0(

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.

[duncan webster 1Participant @duncanwebster1]

Posted by JasonB on 07/03/2023 09:39:00:

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

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

[Ady1Participant @ady1]

My favourites and still very useful are chains

Makes furlongs and acres easier to picture

[Clive SteerParticipant @clivesteer55943]

I believe that some "metric" ball races use Imperial sized balls and don't mention the issue of screw threads!

Most weighing devices are force balances rather than mass balances as they are relatively easy to make and more compact than a true balance. Unfortunately the wrong terms are often used by lay people so the "weight" used on the old style grocers "Scales" which is actually a balance is actually a reference mass. The later Grocers "scales" were a force balance where a spring extension measured on a scale indicated the weight being measured. Most precision laboratory scales are force balances where a current flowing in a coil of wire within a magnetic field produces a balancing force to the item being "weighed". These devices use a reference mass to periodically calibrate the "balance" to account for the local gravity and variations due to the Moon which is noticeable if you are measuring to 1 part in 10 million.

Other weighing devices such as kitchen and bathroom scales use a spring in the form of a strain gauge.

CS

[HOWARDTParticipant @howardt]

It doesn't matter, When the item has been made no one knows wether you used chains or microns. The fact the drawing used a set of numbers relating to imperial or metric systems only the drawing reader needs to know so they can interpret it to create the part. Converting between the two is simple enough for most engineers, it is just a number. Threads can be converted between the two quite easily, some special threads need a little thought as to why it is used before coming up with an alternative. Just for the record i am mainly metric, but use imperial for when connections are required to purchased pipe fittings.

[Martin KyteParticipant @martinkyte99762]

My point about spring balances and scales that rely on spring extension is that they rely on 2 readings. One with a known mass to calibrate the spring extension and a second with an unknown mass to make the comparison. The equations are the same as the balance beam and providing the device is in the same location as it was calibrated everything cancels except mass and length. Therefor they are mass comparators irrespective of what units you paint on the scale or the standard mass. Of course once you know the mass the weight under the same gravity is in the same ratio.

I know I’m splitting hairs but that’s where this discussion has gone. If there is no gravity term in the equations then you aren’t measuring weight.

regards Martin

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