how square should square be? - Router Forums
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post #1 of 41 (permalink) Old 11-18-2015, 10:09 AM Thread Starter
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Default how square should square be?

My never ending quest for flat square wood is progressing. very slowly I have to admit, but progressing.
anyway, now i have to ask if i'm on the same page as the rest of you.

i have a sliding table on the front of my router table, and have made a wooden jig that allows me to quickly clamp flat pieces to run them across the cutter to make flat sides.

So, i start with a 9mm thick flat piece of hardwood about 6" (150mm) roughly square,
i run the piece across the cutter to get a flat edge. By turning that wood once and repeating the cut, i get two sides at 90 degrees. but if i do all 4 sides, one from the next, i dont get 90 degrees at the end of it.

After a lot of trial, i realised I had to do 5 sides to get rid of any tolerances from the first cut.
I'm close, the final angle is ONE degree adrift, which means I'm a quarter degree out on each cut.
Without a complete redesign and lots of time and effort, my wooden jig is as good as I can get it.

Remembering my complete ignorance of this kind of thing, am I there yet?
Or is it normal to get all four completely square?
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post #2 of 41 (permalink) Old 11-18-2015, 10:25 AM
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Obviously the closer the better. The main thing is if there are no gaps in any joints when you put your boxes together. If you can't see a problem then for all practical purposes there is no problem. If the 1/4* is causing a problem then instead of starting from square one and risking even worse results is it possible to shim some part of your procedure? The shim might only need to be a couple of thicknesses of paper.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #3 of 41 (permalink) Old 11-18-2015, 10:37 AM
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What happens if after you square the end if you use the same side to square the opposite end ,then run the other side? Like Chuck said a piece of paper or tape might correct the "problem", if it is a problem. Wouldn't be a problem for me. Maybe the "dial indicator guys" might have a solution.

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post #4 of 41 (permalink) Old 11-18-2015, 10:38 AM
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Well now you have opened a can of worms! I remember a recent discussion about whether dial indicators have a place in a woodworking shop. Some of us are hardly more than carpenters. If a cat can't crawl through the crack, it's close enough. Others are much more demanding, requiring joints you can't even feel. The way we get there varies from the artist who carefully planes a joint until it fits just right, to the technician who carefully sets up machinery to make "perfect" cuts every time. "Close Enough" depends on who you are and what you are building. It's not a destination, it's a journey. Your own definition of "Close Enough" will change as your skills progress. Meanwhile, just keep finding ways to get closer.

We should be careful to get out of an experience only the wisdom that is in it and stop there lest we be like the cat that sits down on a hot stove lid. She will never sit down on a hot stove lid again and that is well but also she will never sit down on a cold one anymore. - Mark Twain
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post #5 of 41 (permalink) Old 11-18-2015, 12:02 PM Thread Starter
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The jig is like all my stuff, as basic as basic can be. No way to shim the leading edge without starting all over with a different design.

I thought a little while ago (while I was in the barbers chair) about reversing the wood after the second cut, I'm wondering if that will reverse the angle? if it did i would be dead on. I shall try that as soon as I can.

I have an engineering background which is why I'm trying for such close tolerances, but I've already learnt the hard way that wood moves about a lot.

The effect I really want to achieve is almost marquetry, where the box is made of different woods, and the floor has panels of different colour woods. this is why I am trying so hard for accuracy. Yes, I aim high (lol)
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post #6 of 41 (permalink) Old 11-18-2015, 12:13 PM
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Sunnybob,

As soon as you said 5 turns it made me think of William Ng and his method for squaring TS sled fences. If I understand it right the process requires one to compound the error X number of times then measured with calipers. The error is measured over the length of the cut not at the vertex. If your calc of .25 at vertex is correct then at 6" sides, you are out of square opposite the vertex approx 13/512" + or -.
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post #7 of 41 (permalink) Old 11-18-2015, 12:22 PM Thread Starter
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ok, youve blinded me with science, where do i get a tape measure in 512ths? (G)
I reckon do two sides rotating the wood. The flip the wood and do the other two sides. i think that equals plus minus minus equals zero.
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post #8 of 41 (permalink) Old 11-18-2015, 12:50 PM
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Originally Posted by sunnybob View Post
ok, youve blinded me with science, where do i get a tape measure in 512ths? (G)
I reckon do two sides rotating the wood. The flip the wood and do the other two sides. i think that equals plus minus minus equals zero.
How is the sliding table indexed to the main table? As Ghidrah states, the 5-cut method is typically used for checking squareness of a sled, and it checked by measuring the "taper" of the strip left after the 5th cut. For your router table, where you're just truing up the edges of a piece of wood, the adjustment has to be made in the mechanism which locate the sub-table which slides past the cutter. Look at how this table is referenced relative to the cutter, and see if there is a way that you can make this adjustable, adding/subtracting paper shims is a good (low tech) way to accomplish this. I have an old Delta shaper where the wooden fences are shimmed to the table top with strips of playing card - I always meant to take it to work and have them skim it on the mill but never got around to it, the strips of card have worked for over 20 years with no problem.
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post #9 of 41 (permalink) Old 11-18-2015, 01:01 PM
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Wouldn't doing the 'do 1 side then flip and do the opposite side' simply give you two pairs of parallel sides? Basically a parallelogram with the corners not necessarily at 90deg?

This is reminding me of my SiL working with me doing the new 2x2 spindles on his back porch. I wanted to do the center spindle then use a 2" spacer to set the adjacent ones consecutively going in both directions away from the center.
Nope. Apparently that's not accurate enough; he had to do each one by measuring top and bottom to a 32nd" ....zzzzzzzzzzzzzz
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post #10 of 41 (permalink) Old 11-18-2015, 02:13 PM Thread Starter
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Tom, you might be on to something there. Its a very basic system with wooden slats sliding between two ally rails. i always push the unit towards the cutter to take out the very minor slop in the slider. I could just about get a thickness of paper on the front edge of the rail which might tip the whole sled enough.

Dan, TWO sides, not one.
Cut one side, then use that as reference to cut side two. This now has a quarter degree angle. use side two to cut side three. This now has a half degree angle. Flip the wood top to bottom and do side four, this has removed a quarter. do side three again, and your back to 90 degrees.

Thats my theory, based on nothing more than hope. i shall try to prove or disprove it tomorrow morning, but we are going away for 3 days, so it depends what time the packing is finished.

Ordinarily, I would agree that this is very small potatoes, but i want to match five different shapes into one box base, so I'm testing myself.
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