Accurate Measurement

[JOAMdude]

Does anyone know how to measure things accurately?

I know that on rulers and tape measurers the marking line is like one centimeter.

do i measure at the end of the line or the middle or the end?

does anyone know what im talking about and can help me?

[Rick500]

If you have a good enough measuring device, the engraved lines will be so thin as to make the question meaningless.

For situations where the marked line is thicker than whatever you're using to mark the piece, I would use the center of the tape's marked line. (You'd want to start your measurement at the center of a marked line as well.)

[dh7892]

Digital calipers are a good idea. They're not too expensive either.

[Jon]

Depends what exactly I'm measuring. But if it involves a lot of lines, chances are I'm sketching out a full scale drawing. If that's the case then a sharpened pencil, an accurate center line, and a square are my best friends for keeping everything accurate and precise as possible.

[doug]

One of these are your best friend! They have little slots for everything and a machanical pencil makes the accuracy complete. I don't know how anyone ever lived without one...

Incra tools rock! Get them at a whole lotta woodworking supply shops or direct at woodpeck.com.

-Doug

[Jon]

Indeed, those rock! That's my primary tool for measuring in the 0-6" range.

[Woodenspoke]

I would guess it depends on what you are measuring. The incra are good as Doug suggests even though the holes are small and a good sharp pencil is necessary. If its a fingerboard fret positions than you really need to go all out crazy accurate. But if it is just laying out your instrument any good ruler will do. A set of rulers, 6", 12" and 24 " (or metric equivalents) are recommended.

Always start your marking using the 1" position and not the edge of the ruler and of course add one inch to the measurement. I never found it necessary to get crazy laying out patterns or anything else 1/32 is close enough (or 1/2mm). I buy my fingerboard templates so I dont have to get crazy.

[doug]

All tools have limits...that's why we needs so many!

These would be useless for fingerboards as noted, but laying out exact positions of stuff or whatever you need on the button is way easier with those rulers. There are several aspects of guitar making that need more accuracy than a tape measure provides (to be on the safe side anywway).

For waht it's worth... mechanical pencils help a lot because the line width always stays the same. A little bit here, a little bit there all adds up.

-Doug

[isaac]

I use a type of calipers, however it is not digital. It can measure up to X.XXX " and is quite accurate. A digital one would probably just speed up the process.

[vikingblood]

What about fret scale rulers? Are they better for fret distances than incra?

[SwedishLuthier]

Not really when it comes to accuracy. The main difference is that you do not have to think were to draw. And for me that is a big enough bonus

[vikingblood]

Ok I am getting some of those incra tools. Now how do you measure something like 1.231 (just an example)? Do you use the 1/32nd, 1/64th or 1/100th of the Pro T-Rule? I really don't know how to use these precision rulers.

[Mattia]

Convert to milimeters and quit messing with fractional inches. Or use the decimal inches if you've got decimal measurements.

I'm tempted to get myself a few incra tools, but for now, simple steel rules marked to 1/2mm are good enough (coupled with a dial caliper, cheap, home-made stand, see harbor freight for the units, for acoustic plate measuring). Fret spacing gets done with laser CNC cut stainless steel fret slotting templates, so I simply don't think about that at all. Calipers would be handy to have, but I make do with the dial caliper, generally.

[mammoth guitars]

+1

Always use a thinline mechanical pencil (.5mm) when marking positions or lines.

[Mattia]

Right, line marking (forgot to comment on that): I tend to use normal pencils (varying from 2B to 2H) for various rough sketches, marking, etc., might use the mechanical for precise outlines, but for marking things that need cutting or drilling, nothing can beat a marking knife. Most woodwork suppliers have them, perfect, sharp, precise lines (fill with chalk if it's not visible enough) that will tend to also help guide any cutting implements slightly (chisels and the like in particular).

[vikingblood]

I just bought some gear, digital caliper and a little machinest rule with 32nd and 64th markings and decimals equivalents on the back. First fret according to one of the guitar building books I got is 1.389 (24 3/4) scale. The closest measurement on the rule is 1.390 is that good enough? Or should I use the caliper to get it right on?

[Rick500]

One of these are your best friend! They have little slots for everything and a machanical pencil makes the accuracy complete. I don't know how anyone ever lived without one...

Incra tools rock! Get them at a whole lotta woodworking supply shops or direct at woodpeck.com.

-Doug

Just ordered one of these along with a new drill press table from woodpeckers.com... looking forward to getting it. So far I've done my best with "normal" scales and rules, but I drive myself nuts trying to get my marks perfect.

Edited April 28, 2008 by Rick500

[doug]

Incra tools ROCK! They are absolutely essential for neck taper layout, and for tuner hole locations.

Just a quick reality check:

Now, that being said.... we can only get just so "close" with non-CNC woodworking. Cut me a board 1.389" wide (the first pass) on a table saw using just the .5mm pencil line. Even the time tested marking knife has it's limits.

In the context of high precision, the width of a .5 mm mechanical pencil is a mile. The cut could be made either side of the line, or in a best case scenario split it. What is "close enough" for woodworking in this case?

Good layout is extremely important. Once a solid baseline is established, we can judge tolerance. Great tools are a must if a high level of accuracy is required.

For fret slotting I only use CNC made templates. I can't imagine trying to layout a whole fingerboard then run the risk of making a slot just a little off.

-Doug

[fryovanni]

I love those rules for marking, just makes life easy. Good measuring tools allow me to have confidence when cutting. That allows me to ruff cut closer(less work finishing up). It also is really helpful for making and checking jigs. Other tools like machinsts squares, machinist square and thickness blocks, straight edges, calipers and so forth are all great.

Rich

[Rick500]

Speaking of calipers, I just bought a $14 digital caliper from eBay and I'm just amazed at how accurate it is. I was skeptical until I got it and measured some known dimensions repeatably dead-accurate. I'm impressed.

[ToneMonkey]

I have to get me some of those Incra Tools, even if I don't use them I'll just have them hanging around looking cool.

Personally I use a mechanical pencil (have been known to use a biro once or twice of pencil lines didn't show).

Inches are just a pain in the arse for measuring anything with a tolarance of less than 1/2 an inch, metric all the way, it's a lot easier to count to 10.

[Hey]

It seems there's a lot of doubt about the possibility of cutting a fretboard using scale positions measured by hand. Of the three guitar books I've read (Siminoff, Hiscock, Koch), none said it was impossible to do that job by hand (though one, Hiscock, did say you should forget winding a pickup by hand). Hiscock just said the job would have to be done to the "highest degree of accuracy possible," without specifying what that would be. Koch says you need to be within 1/64".

Here are my calculations, for a 25.5" scale guitar:

At the first fret, an error of 1/32" would result in the note being off by 2.2 cents. 100 cents is the difference between two semitones, while the just noticeable difference for pitch is 6 cents. So, that's well within the just-noticeable limit.

At the 24th fret, an error of 1/32" would result in the note being off by 8.46 cents. So, that's outside the the just-noticeable limit, but not by much. An error of 1/64" would put it back in that limit.

[Rick500]

Doh! My Incra 18" marking rule is here:

Yeah, that's a big crease in my precision Incra rule.

[anderekel]

Ouch, that sucks rick.