Just a measurement rambling

[Phil Mueller]

As I look through various woodworking plans, I notice a lot the use of small fractional dimensions. Often calling for pieces in the 16th and 32nds. Is this done just to challenge my eyesight, or would keeping things to 1/8s, 1/4s, 1/2s, etc, just ruin the entire design/look?

I have to admit, I round up or down to the next 1/8, 1/4, 1/2 etc., and have never been disappointed.

Is it a plan maker just showing off his/her precision? Is it an excuse to justify our expensive precise machinery?

In the grand world order of things, is a 32nd +/- going to be something I’m prouder of?

Yes, this is all just in jest, but really, calling for a table top to be 17 13/16” wide will be just fine at 17 3/4.

[Jim Becker]

For some kinds of components, I agree that more simplified dimensions are desirable, especially if folks are working in fractional inches. For some components, the "fit" is what it is.

One of the most enjoyable projects I did early on in my woodworking activities was a Shaker style clock using Norm Abram's NYW plan. It did not use "typical" material thicknesses like 3/4"...it would not have worked out proportionally. Many folks who design things take a similar track...the final product and how it looks is the most important factor, even if that injects some complexity.

And honestly, this kind of thing is a reason I use a different measuring scale for most projects so I can avoid fractions. :) My work also incorporates using overall measurements, but physically measuring everything else for exact fit, rather than some predetermined number. That may even mean "sneaking up on it" with repetitive trimming...without any kind of measuring.

[Richard Coers]

Actually, you can build anything without any measuring device beyond a story stick.

[mike stenson]

You can. I like to do a basic drawing to get proportions, but after that everything is relative anyway.

[Robert Engel]

Actually you can build an entire project without a measuring instrument.

[mike stenson]

Actually you can build an entire project without a measuring instrument.

Including a story stick. Although, it's hard(er) to make visually matching components

[Bill Dufour]

In metal working it is often the fault of the lazy CAD user. they will leave the tolerance setting to some default setting. This setting is often much more precise then needed. It may default to +- 0.001" when +- 1/16" would be fine. This can easily raise the cost by a lot. If you are making a clearance hole for a bolt does it really need to be bored to 0.001" =+ on diameter or is just a drilled hole good enough. If the bolt is a loose fit is that good enough?

I have seen fractional digital calipers that go to crazy extremes that I would never use in wood, like 1/64 and 1/128 of an inch. In metal work it is never fractions it is alway decimal inches.
Bill D

[Rod Sheridan]

Interesting question Phil.

I think 1/32” is a bit fine for woodworking dimensions, that said I design in metric for the most part and use 1mm increments as the smallest design measurement, however I often find myself using design dimensions in 2mm increments to simplify everything.

Regards, Rod

P.S. For example a leg in Imperial might be 2” square, so I make it 50 mm, likewise 3/4” thick material becomes 20mm. For accuracy I normally use +/- 0.1mm for furniture, a lot more for a fence��

[Maurice Mcmurry]

Much depends on what you are working on. A house, a cabinet, a piece of furniture, a clock, an engine.....
for general carpentry I use sixteenths, for cabinetry and furniture I use thirty-seconds, for anything fine or mechanical I use one hundredths and one thousands. My work turned a corner when I started to use a general brand thirty-seconds ruler in the shop. sixty fourths and one hundredths are too small for me to see without magnification so that is where calipers and indicators come in.

The General brand 6 inch ruler a has the decimal equivalents on the back, the 12 inch has 1/23 and 1/64 on one side and 1/10 and 1/100 on the other.
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[Jim Dwight]

I agree, as far as the look of the piece is concerned rounding to the nearest quarter inch should be plenty good on anything big. I wonder if they do not measure after the fact sometimes too. They might have planned a little different dimension but a mid-cut or the ability to incorporate grain they liked or something changed the dimension a little.

I also agree with Jim Becker's thought. The best was to measure is not to do it. Fewer mistakes that way. If you want another rip the same size, use the piece you already have. That kind of thing. Similar idea is the story pole. One of my most common mistakes is to cut something an inch long or short (long is the better way to mess up). That doesn't happen if you don't measure.

[Edward Weber]

I'm firmly in the measure as little as possible camp.
I use setup blocks, templates, story sticks and stop blocks much more than a scaled measuring tool like a rule or tape.
Back to the OP's comment.
It seems like some of those plans were measured after construction.
Maybe the top was originally supposed 17 7/8" or 18". After a few extra passes with the router of plane, it ended up 17 13/16”, so that's what went on the plans.
JMO

[al ladd]

I'm guilty as charged! I sell plans for a complex jewelry cabinet, and for a power feeder. Especially with the feeder I initially made the plans for those with digital fabrication capabilities, and a CAD/CAM interface doesn't bat an eye at 6.235"! In fact working with CNC tolerances make tiny amounts start to mean something concrete. For instance, in making inlay pockets and male pieces you can specify an offset for clearance, and .005" works well.

Starting with a digital plan, it's a fair amount of work going through after and deciding where less exacting measurements more easily read for the conventional tool workers will work as well, especially for components that need to match with each other. I get complaints about this, so it's something I know I should do. Thanks for the additional nudge!

[Greg Quenneville]

I think another thing that happens is a too literal adherence to design formulas. We have all seen those articles explaining the golden ratio and other pleasing proportions in design. The trouble starts when a fixed starting point gets multiplied by 1.618 and the designer is too dogmatic to let the dimensions relax a bit.

Also…metric. Or decimal inches. When you abandon fractions its all so much less trouble.

[Myles Moran]

I'm firmly in the measure as little as possible camp.
I use setup blocks, templates, story sticks and stop blocks much more than a scaled measuring tool like a rule or tape.
Back to the OP's comment.
It seems like some of those plans were measured after construction.
Maybe the top was originally supposed 17 7/8" or 18". After a few extra passes with the router of plane, it ended up 17 13/16”, so that's what went on the plans.
JMO

If the original builder was anything like me, that top was 17 3/4 when they started the project, seasonal humidity swings meant it grew a little and by time they were done and measuring for the plans, it was now 17 13/16.

[Maurice Mcmurry]

Jigs, fixtures, stop-blocks, and storyboards are important. I need careful measurements to create, maintain, and adjust them. Here is an example of one of the little scales combined with a fixture.

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[Zachary Hoyt]

When I'm measuring to cut slots in a fretboard I have inches measured to three decimal places, but in reality I round the last digit, and the fret slot is .023" wide. I have a ruler marked in hundredths (actually there's a line every 2/100) and now I use an old magnifying lamp I bought at a yard sale last year to see the marks better. For some other things I have to be accurate to a 32nd or less, but a lot of the details are flexible.

[Robert Hazelwood]

I am usually making my own plans, and unless the piece is very simple I'm not sure how you avoid having fractions smaller than 1/16. This is usually driven by a desired reveal, or clearance between sliding components, the need to center one part upon another, to evenly space items, etc. I don't set out to make a part be 39 23/32" or whatever but it's just what ends up happening, especially with multiple doors or drawer openings.

I find 32nds ok to work with and sufficient for most nominal design dimensions. I don't bother much with 64ths. At that point I switch to decimal inches, and it wouldn't be noted on plans, just left to fit in the shop.

[Myk Rian]

Interesting question Phil.

I think 1/32” is a bit fine for woodworking dimensions, that said I design in metric for the most part and use 1mm increments as the smallest design measurement, however I often find myself using design dimensions in 2mm increments to simplify everything.

Regards, Rod

P.S. For example a leg in Imperial might be 2” square, so I make it 50 mm, likewise 3/4” thick material becomes 20mm. For accuracy I normally use +/- 0.1mm for furniture, a lot more for a fence��
Too bad we didn't fully convert to metric way back in the 80s I believe.

[Maurice Mcmurry]

Metric certainly has advantages. I have always enjoyed Bicycles and working on Bicycles. I started out on USA one piece crank bikes and old school USA BMX bikes. Our son got the bike bug and is making a career of it. He will not allow me to talk Imperial at all regarding bikes.

[mike stenson]

Yea, there's nothing left that's imperial on bicycles. Thankfully.

[Maurice Mcmurry]

Most Ball bearings are Imperial even on Italian and French bikes. Ball bearings are also becoming a thing of the past.

[mike stenson]

Most Ball bearings are Imperial even on Italian and French bikes. Ball bearings are also becoming a thing of the past.
I haven't used a hub or bottom bracket that's used them in over a decade now.

I'm assuming you're talking loose ball bearings. Not sealed unit bearings.
name a single imperial tool used though. Last one I threw away was a 9/16" pedal wrench.

[Maurice Mcmurry]

I haven't used a hub or bottom bracket that's used them in over a decade now.

I'm assuming you're talking loose ball bearings. Not sealed unit bearings.
name a single imperial tool used though. Last one I threw away was a 9/16" pedal wrench.

Yes, loose balls or the ones in cage retainers. My language and bikes continue to be antiquated. It is helpful to be getting a handle on Metric in the auto parts store too.

[Rob Luter]

For thickness I think it has as much to do with material yield as anything. Any lumber I buy to a nominal size is usually on the low side of the allowable tolerance. For example If I need an actual 1/2" thickness I have to buy 3/4" and mill it down. If I resaw 4/4 wood I still have to mill it and wind up with less than 1/2". Usually 15/32" or 7/16". That being the case I always design for 1/32" to 1/16" under nominal for a finished thickness.

If you're using S4s or S2S lumber the same can hold true for widths. In Phil's example above I suspected the table width started out 17 3/4" after glue up and lost 1/16" from edge planing.

Sometimes lengths wind up to be odd sizes too. An example would be when you're trying to hold the outside dimensions of a box or case to an even 1/8" increment but you have to fit pieces in the interior and the thickness of the exterior parts is undersize per the first example above.

Or, the guy/gal drawing the plans is showing off.

[Scott Winners]

Boat plans are often out to 1/32 or 1/64 inch. My next boat is going to be metric. I don't mind converting quarters and eighths and sixteenths in my head, but that is my limit. One millimeter, about 1/25 of an inch, no fractions, ought to be a fine looking boat when it is finished.

[Maurice Mcmurry]

Scott Winners, I hope you post about your boat project.