Wow! Rulers Are Not the Same! Recommend An Accurate Straight-Edge?

[Blake Porter]

Oh my gosh! Have you ever lined up various rulers in your workshop to see if they match up? I just did and was shocked to see they don't match.
Can the good people here offer me suggestions as to a manufacturer of an accurate straight-edge ruler?
I'm thinking I need an accurate 36-incher.
Thank you

[Jim McConkey]

First, be very aware that rulers and straight edges are two entirely different things, and are not necessarily found together on the same instrument! If you need a straight edge, buy a straight edge. Our sponsor LMI sells some inexpensive acrylic straight edges designed for guitar making. I think they are flat to 5/1000ths over the length.

For rulers, you can't go wrong with Starrett, but you will pay a hefty price. Do you ever work in metric? If so, seriously consider a meter stick instead of a yardstick. I have a meter rule with metric on one side and inches on the other, made by Swordfish, available on Amazon and elsewhere for a very reasonable price ($30-ish). I double checked a couple of the inch etchings with a micrometer, and they weren't more than a couple thousandths off. Way more accuracy than I will ever need.

This discussion probably belongs in the Tools section, so after you see this I will move the discussion there.

[Blake Porter]

Thanks!

[Paul Breen]

Not sure how long a ruler you need/ want but I use a 6" machinist rule frequently and like the flexible variety. My first one, which I still use, is a General brand. General is a cheaper brand commonly sold in hardware stores. I saw a Starrett on Craigslist and bought it thinking I would improve on accuracy. Turns out that the General's tick marks lined up perfectly with the Starrett and was a bit less money, more expensive is not always better. It is handy having more than one rule though, as I frequently misplace them. I also bought a metric version for violin projects. Reference values for violin family stuff is always expressed as metric.

I have found that most of what I would want a good ruler for, can be dealt with using a 6" machinists rule or dial caliper. I also have an 18" steel rule that I don't use much, or just use a good tape measure for anything longer. I never count on accuracy from a yard stick and they are not made to double as a precision straight edge. Get straight edges made for this purpose.

[Christ Kacoyannakis]

I noticed this long ago, as well. For some reason I was comparing rulers, and I noticed that the cork backed ruler I had purchased from Staples, which is great for cutting a straight line, because the cork doesn't slide as easily, was WAY off from other rulers. I now only use that for cutting straight lines with a razor, or non-critical measurements.

[Bob Gramann]

Wow! I have many rulers of many lengths in my shop that I select for convenience for the task at hand. I never thought to compare them. Now I know that my inches and centimeters are many lengths. I guess it’s no wonder that measured things don’t always fit tight. I will have to be consciously consistent on using only one for all phases of a task. There may be a Starrett in my future. I almost wish I didn’t know this.

[Karl Wicklund]

You know, I've known this in the past but I forget it. So easy to just assume the tool does the job it's meant for. I'm in the same boat as Bob with things not quite fitting sometimes. The danger with measuring more consitently is that the only thing left to blame is my own sloppiness.

[Jim McConkey]

@Paul, when doing things like laying out a non-standard fretboard, a long rule is invaluable. Guitars are more or less standardized, but other instruments are not. The cumulative errors trying to use a short rule would be unacceptable. I build folk and world instruments, and a good yard/meter rule has been absolutely necessary.

Like Christ, I have a 15" cork-backed ruler, BNR-15 from Bates. I don't know what brand Staples sells. I checked and it is almost dead on with my best rule. Just for grins I also held it against a real straight edge, and one side was a U shaped, deviating by about 1/32" in the middle, and the other side was curved, almost 1/16", both over 15". If you really need to layout a straight edge, use a purpose-made straight edge!

From years working with FDA regulators on surgical equipment, I have learned never to assume that an instrument is correct and true out of the box. We always had to prove it before we could use it (and re-prove it yearly!). If you really want to shell out the money, there are certified standard suppliers out there who provide the certification for you, but these are generally way out of a hobbyist's price range.

[Clay Schaeffer]

These people deal in cosmetically blemished rulers and have decent quality for reasonable prices. I have bought several rulers from them and have always been happy with the product and service. They offer several different sizes and types.
For a 3 ft rule:
https://www.ebay.com/itm/Blem-Cosmetic- ... SwajVUO~g7
Or a 600mm (2 ft) rule:
https://www.ebay.com/itm/PEC-Blem-Cosme ... SwAb1cx1Z3

[Alan Carruth]

You can, of course, make a straight edge by planing or sanding a piece of wood or plexi. The trick is checking to see whether it's really straight or not, especially if you don't already have a straight edge. If you plane two pieces they could go together perfectly because they have mirror image curves. If you make three at a time, and check each against both others, you won't have that problem. Wood rules can, of course, warp over time, and while plexi stays straighter, it's also softer and wears faster than metal. Still, it's at least a temporary solution to the problem.

[Paul Breen]

Agreed Jim, that a long accurate rule could be handy for laying out non-standard scale length finger boards but not essential. I make custom fingerboards infrequently, two last year, and use a dial caliper to lay out the marks. I mark fret to fret dimensions and then verify them in groups that my 6" dial caliper can reach, at different locations along the board. I don't think anyone offers rulers that have an accuracy a dial caliper offers, 100th of an inch is the most graduations I have seen on a ruler.

[Blake Porter]

Thanks Clay Schaeffer, I just ordered a 36"

[Bob Gramann]

I ordered one, too. Thanks.

[Clay Schaeffer]

You're welcome!
For fretboard layout I like the 2 ft. (600mm) rule. It is graduated in millimeters and 1/2 millimeters on one side and inches on the other (32nds and 64ths). I like using millimeters and 1/4 mm is about as fine as I can see anyway (the space between the 1/2 mm marks).
I also bought an 18 inch rule (English/metric) for my combination square from them and several 150mm (6 inch) pocket rules so I can hopefully stumble on another one when after I forget where I put the one I was using.

[Bob Gramann]

I’m waiting until my new rule arrives to see which, if any, of the rules I have I can keep. I’m hoping that some are correct so I don’t have to replace all of them.

[Carl Dickinson]

I got a 24" Woodpeckers straight edge. Measurement marks are very accurate. It is pricey...@ $50, but it is a straight edge not a ruler. I've gotten the measuring stuff from taylortoolworksllc too and been very satisfied.

[Clay Schaeffer]

I noticed the 600mm rule I linked to above is metric on both sides. For one that has both metric and English graduations here is a link:

https://www.ebay.com/itm/Blem-Cosmetic- ... SwajVUPAfV

[Peter Wilcox]

I always measure once and cut twice, so accuracy is not a problem for me.

[Carl Dickinson]

Hah! I did that recently cutting a neck to length so now it's a butt joint rather than mortise and tendon.

[Gilbert Fredrickson]

IGaging 24" or 36" Precision Straight Edge! They have a flat edge and a tapered edge with lots of precise little markings.