Using Imperial Dimensioned Drawings

[Chris Parks]

How do others do this? Do you convert each individual component or abandon metric and just work off the imperial drawing? The problem then would be that our machines are metric, maybe there are other approaches I have not thought of?

[woodPixel]

I convert everything to metric. The only thing that irritates me is router bits.

Imperial is obscene. It needs to be strangled to death.

[derekcohen]

Hi Chris

I don't work from the drawings of others. I do essential measurements when I make my own. They would likely look nuts to most woodworkers - or drive them nuts :) - as they are in a mixture of imperial and metric. Many of my handtools (e.g. plough plane blades) are in imperial, while my jointer/thicknesser is metric. I grew up with imperial and in my teens switched metric. I have used both for many years, and switch reasonably effortlessly - whatever seems best at the time. For example, I am about to build a kitchen full of frame-and-panel doors, and plan to use a Domino 500 for the mortice-and-tenon joints. The frames are roughly 3/4" thick, so my jointer will end at 19.5mm (and I will remove the remainder with a smoother). Now I have an accessory for the Domino that centres on 3/4". One router is a 1/2" running a 1/4" slot cutter, and the other router is a 1/4" running a 6mm upcut.

I guess what I am saying is convert what you want and round off if you need. Or do as I do, and in this case switch to imperial. I doubt the metric machines will know the difference.

Regards from Perth

Derek

[elanjacobs]

I spent a day converting 4-pages of the most hyper-detailed imperial plans for a job a few weeks ago. This particular unit was getting AV gear installed in it that we didn't have access to, so we just went with their instructions of "do exactly what the plans say and it'll all fit".

I had to go metric anyway because of the CNC, but it did mean that I was converting every dimension exactly so 5 7/8" became 149 and not 150

[Kuffy]

I don't work from other peoples plans. But if I did, the first thing I would do regardless of metric or imperial, would be to fix the plans so I am not cutting wide boards down into strips or sending epic amounts of material straight up the dust chute. so 12" wide timbers become 290mm wide boards, 4" boards become 90mm wide boards, 3" legs become 65x65 etc etc. I do float between metric and imperial, often within the same sentence which drives my clients nuts because most of them operate with centimeters. what the hell is a centimeter!!!!!!!!

[derekcohen]

I don't work from other peoples plans. But if I did, the first thing I would do regardless of metric or imperial, would be to fix the plans so I am not cutting wide boards down into strips or sending epic amounts of material straight up the dust chute. so 12" wide timbers become 290mm wide boards, 4" boards become 90mm wide boards, 3" legs become 65x65 etc etc. I do float between metric and imperial, often within the same sentence which drives my clients nuts because most of them operate with centimeters. what the hell is a centimeter!!!!!!!!

Love it!

Regards from Perth

Derek

[Chris Parks]

I too was educated in imperial and converted to metric in my late twenties when the drawings for my workshop were done in metric and I had no choice and I would never go back to imperial willingly. I am forced to work from others drawings as I cannot draw in 3D/isometric due to some short circuit in my brain. I know a lot here would find that hard to believe but it a fact that some people cannot draw anything except a straight line with a ruler. I have just seen a plan for a small table I like but it is in imperial so I will convert it to metric and see what the dimensions come out like.

[derekcohen]

I was converting every dimension exactly so 5 7/8" became 149 and not 150

Why not just convert to a round figure, say 150mm. I do not understand the need to be exact, and make the measurements so much more difficult and fiddly.

Regards from Perth

Derek

[elanjacobs]

Why not just convert to a round figure, say 150mm. I do not understand the need to be exact, and make the measurements so much more difficult and fiddly.

Regards from Perth

Derek
'Cos this desk is getting AV gear installed interstate/overseas, so for the inconvenience of being exact now I can save myself trouble later. If things don't fit I don't want there to be any arguments about not following the plans.

[Glennet]

How do others do this? Do you convert each individual component or abandon metric and just work off the imperial drawing? The problem then would be that our machines are metric, maybe there are other approaches I have not thought of?Unless the dimensions are critical you can use the 24mm inch, a quarter inch is 6mm, half an inch 12mm and so on. That's about 5% smaller than the designer intended.Edit: I've found that the plans in woodwork magazines and such have errors, some major, more often than not. So it's worth checking them carefully.

[ian]

How do others do this? Do you convert each individual component or abandon metric and just work off the imperial drawing? The problem then would be that our machines are metric, maybe there are other approaches I have not thought of?
I never "abandon" any measurement system, I just use the rule appropriate to the dimensions on the plan. But for me, a component's length, width and thickness are arbitrary. 50 mm (or even 49 mm) is close enough to 2" (= 50.8 mm) as makes no practical difference.

Except for my Japanese chisels and 3 or 4 blades for the plough plane all my hand tools are imperial.
But all that really matters is that tenons fit into their mortices and that reveals are uniform.

For me, the only machine with a frequently used gauge is the table saw, but for critical cuts I don't rely on the scale, so I always measure from the outer edge of a tooth to the fence or stop.


and, unlike Kuffy, I don't down size 3" components to 65 mm, etc without checking with a scale or full sized drawing that I'm happy with the change in proportions.

[ian]

I spent a day converting 4-pages of the most hyper-detailed imperial plans for a job a few weeks ago. This particular unit was getting AV gear installed in it that we didn't have access to, so we just went with their instructions of "do exactly what the plans say and it'll all fit".

I had to go metric anyway because of the CNC, but it did mean that I was converting every dimension exactly so 5 7/8" became 149 and not 150
I'm rather surprised that your CNC controller doesn't accept imperial dimensions

BTW, I get 5-7/8" = 149.2 mm

[AlexS]

Use metric, it's a dozen times easier.:D

[chris0375]

I avoid imperial at all costs. Try converting imperial sectional properties (for steel ub sections for example) to metric. It's ok when you are only dealing with a distance or weight or volume but when you are combining units and have mm^4 converting to and from unit systems is a serious drain on productivity.

The Americans always justify imperial by saying that imperial units are easier to use for everyday things and are friendlier. That's all well and good but it's an absolute disaster for technical design, manufacturering, research etc

[wheelinround]

Chris I to grew up with Imperial during tech years it began to change one thing that came up during that time is USA imperial rulers & tapes are different standard (teacher had one to show) USA 1" is longer than Imperial UK 1". I've since seen the same thing.

During my latter years working off my apprenticeship we were working in both, then as vehicle maintenance man for a number of companies who had vehicles built long before metric buying imperial tube and other fittings etc became a nigh mare.:~

Give me back Imperial any day just because European's can't count past 10 why should the rest of the world suffer. After all there are 12 months to a year, 360 degree's which equates to 1hr 60 sec's , 24 hours, 12 loaves 13 if you get bakers doz LOL. 12", 1ft, 36"

In industry I still hear terms used by people who were born well after metric came in which are imperial.

Chris somewhere on this forum many moons ago this topic raised its head and proof was made Imperial IS far more accurate than metric.


Hey Kuffy I always work on 3" being 75mm so your are short changing there or trying to save timber :p

[IanW]

This discussion has been had so many times over the years! I was raised on Imperial & converted to Metric in near middle-age. Having converted, I much prefer to work in metric, but don't get too excited if I have to work in Imperial - all measuring units are just arbitrary choices that someone made a long time ago!

All woodworkers should grasp the difference between precision & accuracy. For example, if you wish to make the parts for multiple identical pieces of furniture, which all have to fit in their allotted places, you need precision. Dimensions will have to be taken off carefully made drawings, and followed - that's what precision is about.. If you make one piece to fit neatly in a given spot, that's accuracy, and it's what we mostly need.

In making a 'one-off', there are two ways to tackle it. For sure, you can follow a 'cut-list' and make each part according to the plan, in which case, precision is necessary, and you will either have to work in the units of the plan, or convert them to what you are more comfortable with. It's a risky way to work, you will introduce small errors by converting, & Murphy's law says they will always be additive & never self-cancel. And never forget there are frequently errors on even the most carefully-drawn plans, though I suppose CAD programmes are less prone to such things?

As Derek said, there are only a few basic dimensions to even the more complex pieces of furniture, and these determine all the rest. I look at the 'minor' dimensions on a plan, be it yours or someone else's, as merely suggestions - does it really matter if a moulding is 18, 19.02 or 20mm wide? Rounded dimensions that are 'near enough' are usually fine in these situations. When I'm building a desk or chest of drawers, I couldn't tell you exactly what most of the minor dimensions were, because the parts were either marked directly off where they had to fit, or sizes transferred with marking gauges, calipers, etc., or simply rough-cut & planed/pared to fit. Usually far more reliable than using a rule or tape, and often quicker (I can still make stuff-ups when I try, of course! :doh:).

By adopting a logical work flow, you should only need to establish the major dimensions in whatever units you are most comfortable with, work out your stock requirements from that, & there should be little or no need to convert anything after that....

Cheers,

[aldav]

Chris, you should have known that you were opening a can of worms when you posted this. You didn't do so for your own amusement, did you? :rolleyes:

I quite happily work in both and like Kuffy am apt to quote both metric and imperial dimensions in the one sentence - you do generate some totally blank expressions on peoples faces though. I have never resorted to the "24mm inch" and as long as both these measurement systems are operating side by side I can only see that suggestion creating problems.

For those not aware centimetres are the female metric system!

[Kuffy]

Hey Kuffy I always work on 3" being 75mm so your are short changing there or trying to save timber :p

Yep, savin timber. Where do I get a DAR 3" blank? From a 4" rough sawn blank. Thats 7 cubic inches up the chute! I quoted 65mm because most of the time I laminate leg blanks from 6x1" roughsawn. 3 layers and I can always finish at 65mm. I can finish bigger, but I plan for guarantees.

[Chris Parks]

Honest, I never had any idea what would happen except I thought someone might admit they had the same 3D imagination handicap as me. I try and avoid Imperial if I can mainly due to dealing with fractions, I have tried to forget everything I ever learned about fractions for good reasons.

[labr@]

....though I suppose CAD programmes are less prone to such things?


A CAD drafter I know often says that CAD doesn't lie - but he also acknowledges that the operator can get it wrong and that things like rounding errors can cause problems when decimal places are not shown on dimensions. Let's face, it computers are all about doing things faster - so the real difference is that you can make 10 times as many errors in the same amount of time .:rolleyes:

Like many others I was schooled during the era of change and can use both systems. I tend to think in / feel one system better depending on the circumstance. For instance when talking about the beam of a kayak I need to convert mm into inches to get a feel for how wide it is but with small things like fastener sizes it's better in mm.

Oh, and Aldav - you shouldn't be so sexist! Even if you ARE right.:U

[Chris Parks]

For those not aware centimetres are the female metric system!

Mrs P. has an imperial system and just ignores metric totally. How many years have we been measuring in metric? If they ever stop making dress making tapes in imperial she is going to be unable to make anything.

[elanjacobs]

I'm rather surprised that your CNC controller doesn't accept imperial dimensions

BTW, I get 5-7/8" = 149.2 mm

It probably does, but it's set in metric as is AutoCAD where I had to draw it. I rounded the 0.2, didn't need to be THAT extreme

[ian]

Have you checked if your version of autoCAD accepts imperial measures?

I do most of my drawing using CorelDraw. If you set the drawing dimensions to imperial you can create a shape that is 5-7/8" long (provided you enter the length as a decimal, 5.875") and then with just a few mouse clicks you can turn the entire drawing from imperial to metric.

I'd be very surprised if autoCAD doesn't have a similar function.

[Lappa]

When I was building my finger joint jig from American plans it has all these fractions like 5/16", 7/16" etc. etc. on the end of the dimensions. I reread the article and saw that it was a German guy that designed the jig. Quick conversion and obviously the original plans were in Metric changed to Imperial for the US market.

[DavidG]

I grew up with both systems. Electronics (Wave length etc) has always been metric and life taught imperial.
As a result I can work in either and simply use 25.4 mm/in for conversion where required.
I still find my self going in to bunnings to get a 3.6m of 4/2

[Chris Parks]

I simply cannot do pressure in metric, no way no how, it is never going to happen. I suppose that is because I don't work in it often enough for it to become familiar to me.

[A Duke]

:roflmao:
Hi,
You guys were lucky, where I grew up we had Cape measures thrown in and a few others like Rods an Perches.
Anyway have fun, that is what it is all about.
Regards

[AlexS]

Back in '73, when Australia was about to go metric, I produced a conversion table for units that we commonly used at work - cubic feet per second to megalitres per day, etc. As it was a comprehensive table with units that most tables didn't show, it was widely distributed within the organisation. The only problem was, there was one error in it. Although it was quickly recalled and a correction issued, some erroneous copies lived on in circulation.
Fast forward 30 years, and I'm back working on contract for the same organisation. There, in the branch where I used to work, are several copies of the incorrect table, still in use.

I wonder how many dams are about to fall over because of that one little error.

[Lappa]

In my trade we have to deal with both measurements daily with some vehicles having both imperial and metric fasteners and eg. imperial engine measurements converted to metric in the specifications.
While most measuring instruments are available in metric and imperial, common feeler gauge sets are imperial based with both measurements on the blade ie. no 0.25mm feeler, its a 0.0254mm or 0.010" and no 0.04mm, its 0.038mm or 0.0015". You can buy Metric sets but they are generally metric only and in my game, we need both.

[elanjacobs]

Have you checked if your version of autoCAD accepts imperial measures?

I do most of my drawing using CorelDraw. If you set the drawing dimensions to imperial you can create a shape that is 5-7/8" long (provided you enter the length as a decimal, 5.875") and then with just a few mouse clicks you can turn the entire drawing from imperial to metric.

I'd be very surprised if autoCAD doesn't have a similar function.

It does handle imperial (fractional as well), but then I'd be left with funny decimals on everything and I'd have to cut all my timber components to match them. The CNC was just for the veneer board

[elanjacobs]

I still find my self going in to bunnings to get a 3.6m of 4/2
Yep, lengths are metric and sections are imperial

[rrich]

... USA 1" is longer than Imperial UK 1". I've since seen the same thing.

Don't feel like the lone woodworker. . . :D

I have seen tapes from the same manufacturer that are different. Some are off by as much as 1/8 over 96 inches.

The metric thing that bites me in the rear is my jointer / planer (thicknesser). The adjustment screw is metric and that makes it difficult to plane an Imperial dimension off a piece of timber. (IIRC one turn is almost 3/32".)

Getting back to converting measurements on drawings.

In Imperial there are many things that are implied and not explicitly stated. For some reason we have a fascination with ¾" which almost exactly is 19 mm. (19.05)

When converting drawings Imperial to / from Metric measurements my advice would be to design to your standards on the outside and then fit the internals. There is nothing that I could imagine that would need the accuracy of .4 mm or 1/64".

Repeatability is far more important than explicit accuracy. If you're building a serving table that is to be 39-3/8" high, nobody cares if it is really 1 meter high. The only thing is that all the legs need to be exactly the same length.

[elanjacobs]

Chris somewhere on this forum many moons ago this topic raised its head and proof was made Imperial IS far more accurate than metric.
How do you figure that? The inch is defined as 25.4mm exactly, so, technically, imperial is just metric in base-25.4 instead of base-10.

[AlexS]

Slightly off topic, but in the old Lands Department building in Bridge St., Sydney, there are brass plugs in the floor, where surveyors used to have to bring their survey tapes to check them. No doubt they, along with the beautiful internal architecture and cabinetry, will be lost when the building is sold and turned into a hotel or some such.

[ian]

Slightly off topic, but in the old Lands Department building in Bridge St., Sydney, there are brass plugs in the floor, where surveyors used to have to bring their survey tapes to check them. No doubt they, along with the beautiful internal architecture and cabinetry, will be lost when the building is sold and turned into a hotel or some such.
my favourite artifact with that building is the brass plug outside defining sea level.

[ian]

For those not aware centimetres are the female metric system!funny you should say that.

I think that Australia is one of the few countries that use millimetres, metres and kilometres and millilitres and litres.

Elsewhere, particularly in Europe and Canada, once you get over 10 or so mm dimensions start being quoted in cm, or dm.

The same is true with volume, a German beer glass would be 3.0 decilitres, not the 10oz (rounded to 285ml) used in Oz.

[rrich]

Slightly off topic, but in the old Lands Department building in Bridge St., Sydney, there are brass plugs in the floor, where surveyors used to have to bring their survey tapes to check them. No doubt they, along with the beautiful internal architecture and cabinetry, will be lost when the building is sold and turned into a hotel or some such.

In a previous life, I worked as a surveyor. In the back of the yard we had two concrete stubs about 12" in diameter with brass plates cast in. We had the USGS guys come by and scribe two lines exactly one chain (100 feet) apart into the brass. The USGS guys could measure off 1000 feet ten times and always be within 0.01 of a foot in a thousand. We would regularly go out and calibrate the pull required to measure 100 feet. It was just to make a muscle memory for the force necessary for an accurate measurement.

[chambezio]

Rich, you talk about practicing for muscle memory. When I was an Apprentice I started on a multi story office building. The bulk of the excavation had been dug to 2 floors below ground. I was the "assistant" to the Foreman who was setting out for trenches and pads for the new building to sit on. I soon learned to hang on to the 100 foot tape well because he would pull it tight. Then in later years when I had an assistant to set out I would get annoyed because he wouldn't hold the tape tight for an accurate measurement.

After doing my Tech Coarse (Carpentry and Joinery) in Imperial then changing to Metric in 1973 I work 95% in Metric but its no problem to work in Imperial if need be. My hobby horse is hearing measurements talked about in Centimetres. It really gets up my nose (yeh I'm turning into the grumpy old fart my father was)

When ordering timber sizes my brain thinks of 4" X 2", 3" X 1½" etc but I write down 90 X 45 and 70 X 35mm.

[IanW]

..... My hobby horse is hearing measurements talked about in Centimetres. It really gets up my nose (yeh I'm turning into the grumpy old fart my father was)....

I don't get it, Cham., what's the problem? Just add or delete a zero, & Bob's your aunty. Ain't that the beauty of the 'metric' system? I'd need an abacus implanted inside my skull to manipulate the Imperial system units as easily .... :U

I'm glad someone decided we'd use the smaller units (mm & mL) as our basis units - they seem so logical & easy to work with, to me. But I can't convince the other half, who doggedly sticks with centimetres. Whatever floats your boat...... :U


..... When ordering timber sizes my brain thinks of 4" X 2", 3" X 1½" etc but I write down 90 X 45 and 70 X 35mm.

yep, we are of a similar vintage - there are some things they hammered into us in the old system that keep surfacing no matter how much I think I've suppressed them..... :D

Cheers,

[AlexS]

Rrich, I completed my survey training just as EDM was coming in, so all the practice that I had chaining wasn't put to a lot of use, especially as I was mainly working on water. This means that we can't drive pegs in to hold the ground still while we measure it, like land surveyors can.:D

[rrich]

Rrich, I completed my survey training just as EDM was coming in, so all the practice that I had chaining wasn't put to a lot of use, especially as I was mainly working on water. This means that we can't drive pegs in to hold the ground still while we measure it, like land surveyors can.:D

LOL.

After I got out of surveying and got into Computers, I had a contract job at Pt. Mugu Naval Air Station. A guy for the Core of Engineers was doing underwater surveying for costal erosion studies. They would use a 'Duck' vehicle with some RF ranging equipment. I had to write a driver in a PDP-8 that could collect the ranging data and time stamp it. Someone with SCUBA gear would be measuring the elevation of the bottom with a long Philadelphia rod.

They used my software for about a year. Then in some very heavy surf, a wave bounced the Duck so hard that the PDP-8 mounted in a standard 19 inch steel rack failed. The Field Engineers told me that the 19 inch rack was wrinkled on three of the four corners from the bounce. The engineers were able to extract the PDP-8 from the 19 inch rack and with a bit of twisting of the PDP-8 chassis the system was operational again. After that incident, the CoE engineer got an appropriation for a paper tape punch that attached to the RF ranging system.

[rustynail]

In a previous life, I worked as a surveyor. In the back of the yard we had two concrete stubs about 12" in diameter with brass plates cast in. We had the USGS guys come by and scribe two lines exactly one chain (100 feet) apart into the brass. The USGS guys could measure off 1000 feet ten times and always be within 0.01 of a foot in a thousand. We would regularly go out and calibrate the pull required to measure 100 feet. It was just to make a muscle memory for the force necessary for an accurate measurement.
What about temperature variation?

[ian]

What about temperature variation?surveyor's tapes chains and wires are temperature and tension corrected.
you measure the length of tape between the marks, the air temperature and tension on the tape and look up the tables -- more probably a phone app these days -- and there's your length, which is then adjusted for the angle between each end of the tape.

some quality pocket tapes are also have a temperature correction.

[rrich]

Absolutely correct.

The USGS guys would use "bats" and scales to assure accuracy. The bats had a spike that stuck in the ground to get good traction and a hook for either a clamp or a hook for the "chain". A plumb bob would be hung over the chain to define the point on the ground being measured.

BTW - The chain is really a flat tape about 5 or 6 mm wide. The chain is made from Invar, a nickel iron alloy, that is known for very little temperature variations.

BTW2 - For all of you non-surveying types out there, all chain measurements are made on the level. On very hilly terrain it may be possible to only measure 10 level feet at a time.