mm vs inches

[Michael Handrinos]

Hi all.

I'm looking at getting a couple of new rulers and wondered how many of you have made the switch and how you felt about it. Glad you did or wished you used the money elsewhere and stuck to inches

Thanks

[Cary Falk]

To me it doesn't really matter. It's all relative. Whether something is 200mm or 7.8" it is the same length. I use inches because that is what I like to use and I am more confortable with. My blades and bits are in fractions already. The math is easier with metric for people that can't do fractions. I do use metric(mm, microns, angstroms, mL, etc) at work. It's like watching the weather channel. They say it is 20 degrees Celsius outside and I don't know if I should wear a coat or shorts. I don't want to do the math to figure it out.

[Rod Sheridan]

Hi, I switched to metric when I decided to build some cabinets using the 32mm system.

All of my education through post secondary has been in metric, and of course Canada switched in the seventies.

Now when I design furniture I make pieces 20mm thick instead of 3/4" thick, 50mm instead of 2" etc.

When I purchased my new planer I ordered it with the digital height gauge in mm, so all I do is set it at 20.0mm and insert the wood.

A mm is a great size of unit for wood working as it's aproximately 1/25 of an inch.

Measuring devices are normally in 1mm graduations, which is easy to see, and easy to split if you need 1/2 of 1 mm which is about 1/50 of an inch.

Most tape measures are dual reading which helps with the adjustment process, for example if you want a desk surface 30 inches above the ground you can look on the tape and read 762mm so round to 760mm which helps with everything else.

My saw has a dual reading tape for rip and crosscut, it's far easier to set the fence or flip stop to 542mm than 21 11/32

It is far easier to design your furniture in metric as there aren't any fractions. This isn't meant to indicate that I'm not competent to work in fractions, most of my job is mathematics. It's simply easier and less prone to error to add whole numbers.

Of course if you use the 32mm system, it's all metric.

I suggest you try it out, don't try to convert back and forth, that's a disaster.

Measure a few items you use as design elements and convert them to metric (desk height, apron width, leg thickness etc), and round them to nice usable metric values. Write those down and keep them, soon you'll be thinking in terms of an apron width of 80mm, a leg thickness of 60mm etc, and you'll develop some familiarity with the system.

After all, you learned the Imperial system, you had to learn that legs that are 2 to 3 inches square are in the normal range of sizes for certain furniture styles.

Make a drawing in metric and use it to build something simple, you'll be amazed at how much you like it.

regards, Rod.

[John Coloccia]

I'll make the switch completely to metric one day, but a nice compromise for now is to dump all the fractions as use decimal points. Heck, you can use Miliinches if you want to. Just because everyone says 1 1/4" doesn't mean you can't think of it as 1.25". Thats what I do at the moment, and I get the best of both worlds: a) I don't have to convert everything over to Metric, including all of my tools, tapes etc, and b) I don't have to deal with fractions.

Sometimes fractions are convenient, but it's far simpler for me to work with decimal points most of the time, Metric or otherwise.

So you may want to pick up a ruler graded in 50ths on one side and 100ths on the other. 10th would be nice too but that's easy enough to do with 50ths.

[Fred Belknap]

Worked heavy construction most of my life and the plans were drawn in tenths of a foot. It takes some getting use to.

Fred

[Chip Lindley]

I'll make the switch completely to metric one day, but a nice compromise for now is to dump all the fractions as use decimal points.

Stanley does make a "decimal" tape measure! Using thousandths of an inch rather than coarse fractions (1/64" = .015625") allows for finer woodworking when the occasion arises. IMO, decimal measurements are more useful for machine setup and fasteners than for casework or lumber measurements. Were we to go totally digital, we still have to convert 15/32" plywood back to "thousandths"!

They say it is 20 degrees Celsius outside and I don't know if I should wear a coat or shorts. I don't want to do the math to figure it out.

Exactly! It is said you never master a foreign language until you "think" in that language. Converting mentally from one language to the other does not count. I can spread my fingers and show you 3 inches BUT I cannot show you how long 300mm is! Many of us will always "think" in inches, feet, pounds, miles, and degrees F. My grandchildren may be taught to "think" metric, but I never will!

Of course, I can convert inches to mm. when necesssary, and vice versa. I must do it every day! All imported machinery uses metric nuts and bolts. But, most every other aspect of woodworking in the U.S. is in inches/feet. The building trades still use lots of inches and feet. A wall stud is 8 ft. long. A sheet of plywood or MDF is 4x8 ft. 12-2 wire comes in a 250 ft. roll! etc, etc.

A cubic meter of concrete? How many kilometers per liter does your new truck get? Until every quantity and size is offered ONLY in metric measurement, the two systems Will be obliged to coexist. Our infrastructure in the U.S. is firmly entrenched in the inch/pound system, in more ways than we can imagine.

[Rod Sheridan]

Chip, that's true, however Canada used the Imperial system until the seventies and then we switched. It's not that difficult.

As you indicated you're familiar with 70F, not 20C. I was also until I stopped using the Fahrenheit scale, and Chip, I have faith that you're clever enough to learn a new system, your posts demonstrate that.

Regards, Rod.

[Rod Sheridan]

Interesting Fred, a metric foot

regards, rod.

[Chris Padilla]

I have two metric left feet according to my European wife.

For my wife's sake, I've learned Celsius. It breaks down rather easily:

0 freezing
10 cold
20 warm
30 hot
40 really hot

Now you know.

[Brian Tymchak]

I bought rules with both cause I'm not about to convert completely over. Just need to handle the times where going metric makes life easier. For instance, last year, in using "real" baltic birch ply for some cases, I thought it was easier to layout dados using mm scales as the thickness of the panels is manufactured in mm. The inch measurements that BB is sold by in the US are approximations.

Grabbed this (without permission) from the Allied Veneer Company website:
---
Q: What thicknesses do you carry?
Thickness and unit quantities are defined as the following:
Thickness (mm) *Thickness (inches) Sheets per unit
3mm (1/8")- 130 sheets6mm(1/4")- 65 sheets9mm (3/8") - 44 sheets12mm (1/2") - 33 sheets15mm (5/8") - 26 sheets18mm (3/4") - 22 sheets
* Note - the Baltic Birch thicknesses in inches are approximate. For example, the most common thickness for drawer sides is 12mm or ½". However, a true half inch = 12.7mm. Baltic birch has been around long enough that the equivalency ratios stated above are considered the norm.
--------

[Rod Sheridan]

I have two metric left feet according to my European wife.

For my wife's sake, I've learned Celsius. It breaks down rather easily:

0 freezing
10 cold
20 warm
30 hot
40 really hot

Now you know.

Gee Chris can we tell you're from a warm area 10 degrees is cold??????

here's how it works for Canadians

-40 Intersection of F and C scales, good ice fishing hut weather

-30 Time to wear long underwear

-20 Nice winter carnival weather

-10 Time to zip up jacket

0 can't use the porch as a freezer any more, plaid shirt weather, no more jackets

5 motorcyle weather again

10 t shirt weather

20 Warm weather

30 uncomfortably hot weather

40 why would anyone live where it gets to 40?

regards, Rod.

[Jim McFarland]

I prefer metric for shorter lengths in particular. I use 150mm double square & 300 mm combo square and sold my 6" & 12" blades. Also easier to calculate & mark equal segments using metric IME. I'll confess I still use a 25' tape for rough-in type construction measurements though (easier for me to estimate 10' than 3,048 mm!).

[Paul Symchych]

I use both, depending on how critical it is. Starting with some harpsichords I built a while back I have since found that mm. was simpler than trying to add and subtract fractionals accurately and quickly. But, cutting a 2x4 to length... thats more intuitive for me in Imperial where being off by a millimeter isn't a disaster. So I think in feet and inches for the most part but often use metric for really accurate work
It isn't easy to get good rules or tapes with both metric and Imperial on them though.

[Will Overton]

I think in time we all must go to metric. So, not to be hypocritical, I have decided to be buried in a metric sized coffin.

[Chen-Tin Tsai]

As I am primarily a hand tool woodworker, I think in inches/feet. I can approximate an inch (width of a thumb) or a foot (length of my foot) and divide in half and half again. I think for something like wood, that's a natural, (once) living product, it's very well suited. Since furniture is built to be used by humans, which can easily be measured in inches and feet, it seem natural to me to measure it in inches and feet.