An accumulation of errors

[Todd Burch]

Measuring precisely has always gotten the best of me. Inside measurements, outside measurements - nothing ever seems to be just dead on. I mean, we work with wood - so you can always cut it again, sand it down some more, or glue another piece on to compensate.

Do you all get frustrated with plan measurements versus actuals? I do. Lots.

One thing I enjoy about using SketchUp is the accuracy. If you design a cabinet 36" wide, and another 20" wide and a third 40" wide, and you put them all together in SketchUp, you get a run that is exactly 96" long. But in reality, if you (if "I") make a 36" wide cabinet, and a 20" cabinet, and a 40" cabinet - no how, no way, will the accumulated length be 96".

Is it me? Do you all see this too? Is this one of our dirty little secrets that we can't measure to save our lives?

I have learned that when I need utmost accuracy (and that is not too often...), I "replicate" my cuts to test for accuracy. For instance, if I need a rail that is 16" wide, I'll cut 3 of them, line them up, and then measure for 48". If the sum adds up to 48", I know (that I know that I know) that one rail is indeed 16" long. Who else does this? What do you do?

Todd

[Van Huskey]

I build as I go and measure as I go, good thing I don't build cabinets or built-ins for a living! I just make each new piece fit the last ones... :o

[Stephen Cherry]

I just make each new piece fit the last ones... :o


Van-- you should be a wooden boat builder. I've read a few books on the Chesapeake boat building tradition, and it seems that parts were "fit to the boat". Many of these boats were built without plans.

For fitting parts, I was looking for an expandable double bevel, and I finally found a reference to one that was made about a hundred years ago. Didn't find anything made today.

One thing that I have been doing is going digital. I've got a couple of the wixey tools, and my table saw has a digital fence. If I set a board to be 14.000 inches, it comes out 14 on a ruler every time. Next up will be digital height on a planer, which will be nice.

[Chris Parks]

My rules for measuring:

Use the same rule each time

Never use a tape unless absolutely necessary

If after marking you need to extend the mark put your pencil, knife whatever you are marking with on the mark you made when measuring and then bring the square, straight edge etc up to the pencil. Do not eye the mark, put the square down then bring the pencil to the mark.

If squaring to a measurement I lay the straightedge, rule etc down and place the square over it to the desired measurement and mark off. I do not measure, make the mark then work from that mark as there are two extra steps to introduce errors.

Where possible throw all measuring devices in the corner and use a measuring stick. It is amazing that you can build something and starting from one measured piece finish it without knowing the dimensions you used.

Use a knife or a chisel sharpened pencil that is flat on one side

Buy an Incra rule with holes in it.

Practise like everything improves skills and measuring is a skill like everything else and the more you do it the better you will become. Go into the workshop, grab a bit of timber and practise, do that every day for a week using the exact same dimension exercise and note the difference from the first day to the last. When you start you will have an error of so much and when you finish your error should be a lot less if any.

[Victor Robinson]

The tape measure is the devil. I'm still looking for a good, accurate T-rule between 24-48" that doesn't break the bank.

+1 on the Incra rules.*

[glenn bradley]

Do you all get frustrated with plan measurements versus actuals? I do. Lots.

Not usually but, I usually make individual pieces and don't (or just haven't) do built-ins.


One thing I enjoy about using SketchUp is the accuracy. If you design a cabinet 36" wide, and another 20" wide and a third 40" wide, and you put them all together in SketchUp, you get a run that is exactly 96" long. But in reality, if you (if "I") make a 36" wide cabinet, and a 20" cabinet, and a 40" cabinet - no how, no way, will the accumulated length be 96".

You and me both buddy.


Is it me? Do you all see this too? Is this one of our dirty little secrets that we can't measure to save our lives?

Like you said; its wood, it moves. Accepting that there will be variations an hour after you have cut the perfect piece is part of being happy in this medium. I strive for as perfect as I can get when measuring, marking and cutting. I find this minimizes the effect of the movement. I try to sequence my assembly so that many parts are fit to the piece. I never cut out all the parts and expect a piece to assemble correctly. Designing for movement will also minimize your anxiety. "You're not being the ball Danny" :)

[Larry Edgerton]

I don't even try. Houses are never perfect, even mine. Walls are not straight. Studs vary 1/8", drywall doesn't get screwed tight, so forth and so on.

I don't do euro cabinets, so I always have a face frame to work with. I make each box an 1/8" small and extend the face frame with a scribe point. Most times I do not build individual boxes, so one cabinet may be 8-9' long. Old school, but I install everything I build so no problem. This helps as well. As said, I don't do any production work, and don't want to, so I have been to the house that they are going in, looked at it with a level in hand so I know where I need to leave myself wiggle room. This is all part of the map I take back to the shop. Always leave wiggle room.

For example, you check a wall where a cabinet run will end with a level, and it is 3/16 out of plumb. So you build your run to the longest measurement and leave at least a 1/4" scribe point at this junction and plane to fit on site. To make the planing easier I dado out the back half of the scribe point before assembly.

People get too caught up in exact numbers, when what you are really after is not an exact number, but rather an exact fit. No one measures a cabinet when it is installed, and once installed no one can see that there are gaps between boxes as long as the face fits.

Larry

[John Coloccia]

Buy an Incra rule with holes in it.

My Incra is off by a bit less than 1/32".

[Chris Parks]

Against what standard?

[John Coloccia]

Against my Starretts. The problem is the rulers index against what looks like a cast aluminum hook, and the hook just doesn't seem to be precise. The rule itself is fine but it's useless without the hook. I've been meaning to try to get a replacement from Incra because I really love the concept, but I never get around to it. It's just an FYI to actually check the thing before using because you may get one that's like mine.

[Peter Quinn]

I use story poles and steel rules more than tapes these days. Steel rules don't seem to add as much fudge to the process. For built-ins that have to fill a defined space, like Larry said, it's about fit, the actual size is not relevant. You can't measure a 16' run of cabinets with calipers. Check the walls, check the floors, they may still move too before you get back. For built-ins you need scribes. It's about design IME. A break front that connects with tongue ang grooves gives you a way to actually manage a long run of built-ins and two or more places to adjust the fit in addition to the scribes at the walls.

For furniture, my concern for absolute measurements diminishes to almost zero. I rarely even use a ruler. As long as all parts are batch cut to the same length, I don't much care what the absolute length is. Drawers are fitted, make them a hair big and shave them down. Hand planes are great form sneaking up up a precise fit, power tools tend to take a little too much, a little too fast, and a little too easy for my comfort.

[Mike Cutler]

If I'm building cabinets for the house, which I currently am, the tape measure is fine for all the reasons Larry pointed out.
When it needs to be dead on I have a 72" Starrett. ( It lost it's NIST traceability and was headed to the dumpster when I retrieved it)

To quote my Machinist friend.

" I don't know why you wood guys are so obsessed about accuracy. The wood will be a different size when you finish all on it's own. It's not steel"

[Neil Brooks]

I've always liked what this article (http://www.woodworkstuff.net/precise1.html) had to say, on the subject.....

[Peter Quinn]

I've always liked what this article (http://www.woodworkstuff.net/precise1.html) had to say, on the subject.....

Funny, that is exactly the procedure most follow where I work. From rough stock to finished cabinets parts travel together on a cart, all labeled, numbered, batch cut. And on the bright side, if you cut something wrong, you cut a LOT of it wrong, so be careful for that! My favorite saying from a co worker is " hey this part is short, but only on one end!"

[John Coloccia]

If I'm building cabinets for the house, which I currently am, the tape measure is fine for all the reasons Larry pointed out.
When it needs to be dead on I have a 72" Starrett. ( It lost it's NIST traceability and was headed to the dumpster when I retrieved it)

To quote my Machinist friend.

" I don't know why you wood guys are so obsessed about accuracy. The wood will be a different size when you finish all on it's own. It's not steel"

Well, it depends what you're doing. For instrument building, it's not enough for things to look nice. You need to hit very specific dimensions. .01" is the difference between a wide nut and a narrow nut, for example. String clearances, relief etc are measured in thousandths of an inch. For smaller pieces of wood, you would be surprised just how stable dimensions really can be, and careful selection of species and grain pattern go a long way to preventing warps and other nasties. I have calipers and dial indicators all over my shop, and most things are checked with those as they come off the tool.

When I'm building jigs or shop furniture, on the other hand, I rarely even use a ruler. I simply eyeball it with a pencil and go. Sometimes things are a little crooked, or made from scraps with big chunks missing....whatever. It just needs to work and I don't have any time to waste making it pretty. :)

Part of the obsession with accuracy for me is exactly because I know the thing is going to move. If I need something to be a certain dimension, say .5" +0, -.010" in order to be acceptable, I'm going to do my best to nail a very specific dimension, maybe even depending on the time of year. In the winter time, when my shop is just a little dryer than normal, I might try to hit .492", knowing that it probably won't shrink much more but that it may expand in the summer. In the summer, I may try and nail .498", knowing that it will certainly shrink come winter time. This is how I size my neck pockets for bolt on necks, in fact....similar to fitting drawers. Loose in the winter, tighter in the summer, and the differences are measured in thousandths of an inch.

I hope that helps explain it a little. It would be crazy to try to nail that kind of precision for every cut. I'd never get anything done!

[Greg Cuetara]

i forget the exact saying but it goes something like...measure with a ruler...mark with chalk and cut with a chainsaw...seems to be why i can't ever get anything to fit right...

[Carl Beckett]

For furniture, my concern for absolute measurements diminishes to almost zero. I rarely even use a ruler. As long as all parts are batch cut to the same length, I don't much care what the absolute length is. Drawers are fitted, make them a hair big and shave them down. Hand planes are great form sneaking up up a precise fit, power tools tend to take a little too much, a little too fast, and a little too easy for my comfort.


This is a big part of it for me - and that is that 95% of the project doesnt matter the exact dimensions. They just have to fit each other.

So I make decisions on WHAT needs to be precise, more than HOW precise it needs to be. Do I care the width of a tenon - nope, as long as it fits nicely the mortise. Do I care if a stile or rail is 1/16" wide or narrow? Nope, as long as the finished door fits the opening.

So I measure to 'get close' - but make everything 'to fit the mating piece'. Heck, half my doors or lids or drawer fronts are not perfectly square/straight/etc - so to get a uniform gap I have to work a taper or curve or such on it.

Its all imperfect dimensions. And I think this is also part of what has me using hand tools more and more - to make these final adjustments by hand.