Switching to Metric in the shop, Is it even practical?

[Mike King]

I'm transitioning to metric. The transition is made much easier with the use of digital stops and readouts on my fence, thicknesser, calipers, etc. but these also greatly enhance my accuracy and repeatability. I just reset my planer to metric. Other things that help are dual scale rules and a unit conversion app on the iPhone.

[roger wiegand]

It seems perhaps the world is divided into those who naturally think in terms of halves, quarters, etc, and those who think in tenths, or percentages (eg a 1-100 scale). Hadn't thought about that before, there's an argument to be made for each. I'm mostly in the second camp, but have to admit I cut my oranges in half. When cutting watermelon I definitely think in terms of 2, 3, or 4 cm slices.

In the kitchen going over to weighing ingredients (in grams) vs volume measurement (in cups or teaspoons) has made me a much more consistent baker. And making 1-1/2 recipes worth of something no longer requires much thought.

[Jeff Roltgen]

I think it's too late for me. Acquired a CNC 12 years ago, and began thinking in imperial decimals. This lead to thousandths in accuracy as I draft, measure thicknesses and even widths with digital calipers. All the while, decimal/fractional equivalents have been burning clearer into my mind. Fortunately, in Sketchup, I can draft in the imperial system, yet, for instance, dictate "2.5mm" radius to draw in 5mm holes and their metric spacing without a complete conversion of the model as I work with the European hardware.

Then came my discovery of the wonders of European machines. However, since they were purchased through US dealers, spindles are 1.25" diameter, arbor on saw 1", scaled to imperial. Yes, one can change out analog scales, but what of digital motorized height readouts? Buy replacement spindles and arbor? New DRO module?

Perhaps, for me, the conversion to decimal thinking is as close as I'll get to the "simplicity" of metrics.

The whole thing feels more to me like a Mac vs. PC type of discussion.

They're just numbers, so if you're at ease with your current system and develop a habit of staying focused on accuracy, it may be simpler to stay the course.


YMMV

jeff

[Wes Grass]

I just assume that the 100 speed limit signs mean mph. That’s right, isn’t it?

Only on rural 2 lanes ;-)

I spent 2 weeks driving all over Scotland. Distances in miles, gas sold by the Liter. That little car I had got *TERRIBLE* gas mileage.

I'm pretty sure nautical miles would mess me up though. Probably easier to adapt to Km at this point in my life.

I ordered all my Felder stuff in inches, other than the shaper spindle. But the 'Parallel Cut' attachment was (is?) only available with a metric scale. No big deal, and I could probably find an insert of some sort if it starts being an annoyance.

My last job, I worked with several 'canucks'. None of them seemed to have any issue working with inches, and yeah, 4x8 sheets of plywood or MDF were a normal thing for them as well.

[Ken Kortge]

Lisa, I am in the process of moving my woodworking from imperial to metric. My reasoning was that none of the lumber or plywood is dimensionally as labeled anyway, so I have to measure and/or cut to needed size anyway.

First, live in a world of millimeters at first. Later talking in centimeters and meters may get easier.

Formulas, if needed (not sure why):
mm = inches × 25.4
inches = mm / 25.4

For general planning:
1x4: 19 x 89 mm
2x3: 38 x 64 mm
2x4: 38 x 89 mm
2x6: 38 x 140 mm

Plywood (rounded)
4x8 feet: 1219 x 2438 mm (1220 x 2440 mm)
1/4": 5.5 mm (6 mm)
3/8": 8.7 mm (9 mm)
1/2”: 11.9 mm (12 mm)
5/8": 15.1 mm (15 mm)
3/4": 18.3 mm (18 mm)

For your combination square, as others have said, almost certainly you can get new metric rulers (150 mm is similar to 6 inches; 300 mm is similar to 12 inches). I bought blemished PEC combination & double squares from Taylor Tools and bought the appropriate metric rulers.

Get a good metric tape measure. The FastCap True32 metric tape is very nice (about 16 foot - 32 refers to it having marks for a 32 mm cabinet system). I don't recommend using combo imperial/metric measuring tools - live in the metric world, but FastCap also has a good combo tape measure useful for fast planning & converting (my table saw is 36 inches tall - how tall in mm does my outfeed table need to be?)

Taylor Tools sells metric rulers, if needed.

If you want set-up blocks, Lee Valley sells a decent Veritas metric set.

Honestly, the only measuring tool I haven't found in metric (in the U.S.) is a wooden folding ruler with the metal extension - used to measure inside dimensions.

I don't worry much about using commonly available imperial dowels, drill bits, forstner bits, and router bits. Just use whatever works best. Same with nails & screws.

Oh, and I can't find anything about metric angles (just kidding). Metric squares don't exist.

[Rich Engelhardt]

Do metric tape rules have red diamonds @ .4064 meters?

[Lisa Starr]

Thank you, Ken, for your detailed response.

As several have mentioned, I can probably purchase new rules for my Starrett Combo Heads, but it will be a fairly pricey endeavor. I could probably get by with fewer rules than I have now, but would really miss the 18", if I didn't have a similar replacement.

I totally understand that I need to commit to the metric world and not constantly convert numbers. It introduces error and defeats the reason for switching to metric in the first place.

Some of my rules are already 10th of a inch ruled on one side and I'm used to working in decimals, so I may have to look harder at that option. Haven't looked, but I imagine Woodpecker won't offer things like my 16 x 24 square in that type of rule, but will offer metric.

I use .03937 as my conversion factor, inches/factor = mm or mm*factor = inches. but imagine the results are the same.

[Jim Becker]

Something else to consider, Lisa...in a good bit of woodworking, your overall dimensions are whatever they are in the measuring scale you choose to use. All the intermediate parts really need to be sized by "actual" to account for variances in materials, etc. Example...a stretcher or component between two others. I cut it proud and then "sneak up on it". That doesn't require measuring; just careful cutting of the component.

[Wes Grass]

Do metric tape rules have red diamonds @ .4064 meters?

LOL.

Older Canadian I worked with told me plans submitted for building a house had to be metric to get approved. Stud spacing, 400mm. And then the builder had to make them 16" so the drywall would line up.

I used to use .03937, but switched to 25.4 just because it's fewer digits to punch in. It's also *exact*, since they changed the inch to a metric standard, although .03937 is closer to perfect than anybody in the real world needs.

If I have to use Meters instead of MM, 39.37 is simpler to remember than how many digits/decimals am I dealing with.

[Cameron Wood]

I fully converted the shop (well except for some drills) about two years ago after decades of half and half. Wished I'd done it long ago. Decimal inches would probably work just as well, but none of the tooling I have does that easily. 50 year of lab work and I think first in metric for length, weight and volume at least. Other units are a mixed bag. I seriously don't miss dividing 17/32 by three.

My one strong piece of advice is never convert units. Work in one system or the other. Conversion is so fraught with error it's just not worth doing. If the plans are in inches I either draw new plans for a similar item in metric or work in inches. Just ask the space telescope guys how conversion goes.

In terms of thinking, a centimeter is about the width of your (pick the appropriate one) finger, and a meter is about as long as your arm. A tall beer can is around 500 ml. You don't need much more than that.

Those are some skinny fingers!

[Wes Grass]

And long arms. I'm only 27" ... substandard there too.

And who drinks beer from a can? What radii can I check with a 12oz bottle?

[Earl McLain]

I must admit, i snickered several posts up when @Jim Becker mentioned working with construction lumber in being Imperial. Let's see...a 2 x 4 is 1.5" x 3.5" (more or less, adjusted for warp & wane). The once we get to the 2 x 8, we have to adjust to 7.25". Granted, we don't normally have to put those edge-to-edge so that helps.

Just always strikes me as funny!! Until i have to sister up a header on a 2 x 8 stud wall!!
earl

[Mel Fulks]

And long arms. I'm only 27" ... substandard there too.

And who drinks beer from a can? What radii can I check with a 12oz bottle?

I’ll tell you who drinks beer from a can ! A guy who knows that when he used to throw glass bottles out of his car window, he got a lot of flat tires !

[Brian Holcombe]

I like it for fasteners and wrenches but not at all for building. Decimal inches are great for high precision and fractional inches for lower resolution work like construction. For precision in the construction world I typically work with a story stick rather than measurements.

[Howard Rosenberg]

Interesting question.

We went metric in Canada the year I got my driver's license.

If you tell me something is 6 miles away, I have no idea of how to gauge that. But I DO get what 10 kilometres feels like...

It's 100F outside. Cold? Hot? No idea. But tell me it's pushing 40C, I'll flash back to my years of living in Tel Aviv and feel reeeeeeally bad for you.......

Buy a quart of something? Ummm, that's +/- a litre, right?

Anything longer than 5 milimetres? Not a chance! Working on a 1.07 meter-long project? Cue blank empty stare....
But tell me you're working on something 42 and 1/8 inches long? Yep. Got it.

Obviously my biases are inconsistent - that's why I'd suggest metric might be useful for short measurements. Longer ones? Not so much.