Joe Abbott's Weblog

Letters home to mom

How not measuring can make you more accurate

Posted by joeabbott on December 21, 2013

imageFor a long time now I’ve realized that I can’t measure accurately. At least not repeatably accurately. Sure, I can get in the ballpark and even pretty close, but invariably when making measurements and cuts, one board will be ever-so-slightly different than the other. In some cases by 1/32”, in others a 1/16”, but in all, going by tape-measure-and-pencil methods, I’ll get parts that are just a bit different.

Now this normally doesn’t matter but when it does, I’ve created some practices to avoid having an Island of Lost Toys sort of collection of parts at the end of a day of cutting. Sometimes I can cut two parts at the same time. Usually this is a chop saw operation or other place I can safely zip through multiple pieces at once. Another practice is to set my table saw fence at a given dimension and then cut all parts that will be that dimension before changing the saw configuration.

But neither of those practices would have worked for me yesterday when I had to break down four sheets of 4’x8’ panels into various parts. The cut list is shown here and I wanted to be sure I was as close to “the same” as possible for all parts. What did I do? I measured once and used that measurement for all parts! Here’s how I did it.

Make it easy on yourself

imageI started breaking down the plywood panels by laying a 1” thick piece of insulation on the floor and dropping a panel onto that. I set my saw depth to just a bit more than 3/4” (the plywood thickness) so, when making the cuts, I’d go through the panel and then just a bit into the foam insulation. The panel is fully supported, it’s easy on both the wood and the saw, and I don’t have to worry about catching cut-off parts. It’s a great system.

Measure once

I say “measure once” but you can make multiple measurements to be sure that the one location you’re measuring is in the exact spot. I went back and forth a number of times to make sure the marking I made at the 24” point (half a 4×8 panel when ripping length-wise) was in the right spot. But, once I had that spot marked, I called it good.

Once I had that point, I placed my saw rail up in such a way that the saw blade would split that pencil mark exactly down the center. Take your time, make sure you’re eyeballing it correctly, and then know that this is the point that will define your measurement.

Let a stick tell the story

imageAt that point I find a bit of scrap material that is longer than the remaining distance between the back of my saw rail and the edge of the panel, mark it, and cut the scrap. I then have a way to easily and quickly butt the stick up against the edge of the panel, butt the saw guide rail against the other end of the stick, and know that sawing to that line will give me a repeatable size.

There are a few details here that I should elaborate, but that’s as easy as it is: create a physical block that allows me to repeatably create a cut a distance that’s my accepted length.

Now, I don’t trust myself to make a single cut and have the stick the exact length that I want, so I’ll cut it just a whisker long and then continue to sneak up on the final length: something that butts up hard to the edge of the panel and the guide rail to allow me to cut to a line. When sneaking up I use a “trick” to get a whisker’s thickness cut off the end of a part using my miter saw: I’ll hold the blade down (so it’s below the table surface), I place the piece I’m going to cut in-place with the end I’ll cut against the saw blade, I then raise the blade, engage the motor, and cut.

What’s happening here is that the carbide tips on the blade are a tiny bit wider than the blade itself. By placing the end of the part to be cut against the blade and then chopping it, I take off the difference between the edge of the carbide and the edge of the saw blade. Again, I’m just looking for a whisker’s breadth!

You need two

imageAt one time I tried to use a single stick to define the guide rail placement. I’d use my golden stick for one edge, then use it to set the other, find that setting the second side changed the position of the first side, correct the first side, go back and change the second (as it now moved), etc. It was tedious.

So now I make two sticks.

You can try to make one stick and then a second, or just cut two at the same time, which is the method I use. Either way I recommend using your fingers to tell you if both ends are identical. Remove the fuzz from the edge of the sticks, place them so their ends mate, and then feel the faces of the wood. Your fingers are remarkably sensitive and will more readily tell you if you have identically lengthed sticks.

In the end, with the two sticks of the same length, I will place the guide rail in the rough location it should go, place the sticks against the edge of the guide rail, and sneak the other end of the sticks up to the edge of the panel. Move slow. Be careful, and when the sticks are butted against the rail on one side and the panel on the other, make your cut! And do it again and again and again.

Leave your tape measure on the bench and keep cutting!

Cutting a long panel

imageimageMy guide rail is something like 52” long, so when I need to make a long cut (say ripping a 96” long piece of plywood), it’s still easy. Set your guide rail up to make the first half cut, cut it, then move the guide rail down the panel, use the sticks to set it in location, and make the second cut! If you push everything snugly up against each other (that is, the guide rail against the stick and then the stick’s other end against the panel edge), you should be golden.

Another option I’ve used is to cut the first half of the panel, then use the saw and one stick to set the rail for the second half cut. That is, move the rail in about the right location for the second cut, place the saw on the rail and lower the blade (do not have the saw running) into the cut with one hand, and then use your second and third hands to position the other end of the rail correctly. I joke a bit as it can be fiddly, but with a little practice you should be able to set your marks. The key is: use the stick to set one end using the proper technique (butting up firmly against the rail and edge) and allowing the saw to tell you exactly where the other end should go.

Keep ‘em handy

I used to create a quick stick, use it, and toss it aside … leaving me to scramble through scraps when I needed to make a cut of that length again. I’m more organized now and usually make all the cuts of a given length at one time, but I both mark the sticks with helpful descriptions, and I save them all until the job is done. Then I toss them out; they’re easy enough to create that I don’t want to have a warehouse of random measuring sticks just in case I need another 18.25” cut.

A possible improvement to the stick could be to add a t-cross piece to one end so you can be sure to have your stick perpendicular to the edge (or, if not perfectly perpendicular, at least the same each time). This could also take the guesswork out of determining if one end of the stick is exactly butted up against the panel. It’s a fine addition but not one I’ve used.

What if you don’t have a guide rail?

imageIt may sound flip but … get one! Seriously. I have a Festool saw, which was ridiculously expensive, and yet it’s the best power tool I own. Bar none. It’s smooth, gives great cuts, and with the rail gives me repeatable cuts. It really has made a hack like me able to bite off a project like our front room cabinets.

But, if you don’t have a guide rail now or just won’t get one, you can still use the stick method to avoid measuring multiple times … instead of cutting a stick that measures from the edge of the panel to the edge of a guide rail (you don’t have), cut a stick that measures from the edge of your panel to the cut mark!

I’ve used this method a bunch when I’m doing something quick or not using my guide rail. I still recommend using some sort of straight edge to help you cut a straight line, but use what techniques you find best there. The key is, let a block of wood be your measurement and not rely on eyeballing a measurement off a tape measure!

Coda

That’s it. Instead of relying on a tape measure, your eyes, and the ability to hit a pencil or strike line in exactly the same location repeatedly, I transfer the responsibility for keeping a measurement to a physical object and keep that handy as my golden reference. Fast and easy!

Hope you can use this technique yourself and, if you have a neat measuring trick you use, please share it! Thanks for dropping in!

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