Accuracy of a Square

[George Bokros]

I have a framing square that I just checked for accuracy. It is off ~1/64 over 23 1/2", should I accept that as accurate? I did the draw a lineflip and draw a second line test and there is 1/32 between the two lines.

Thanks

[Art Mann]

That may be the best you can do with a framing square, although there is a technique to adjust the angle a little if you want to fool with it. Framing squares are used for framing houses and that amount of accuracy far exceeds any house building requirements. To get really good accuracy, you are going to have to pay more and you needn't even look at a big box store. I have taken two identical framing squares off the rack and put them up next to each other and found 1/8" or so difference over the whole length.

[George Bokros]

That may be the best you can do with a framing square, although there is a technique to adjust the angle a little if you want to fool with it. Framing squares are used for framing houses and that amount of accuracy far exceeds any house building requirements. To get really good accuracy, you are going to have to pay more and you needn't even look at a big box store. I have taken two identical framing squares off the rack and put them up next to each other and found 1/8" or so difference over the whole length.

Where do you suggest to get a more accurate square the size of a framing square.? I want to use it to set up the track saw for cross cuts of sheet goods.

[scott vroom]

A bit pricey.....but they claim to be .001 accurate at the angle. http://www.leevalley.com/US/Wood/page.aspx?p=32587&cat=1,42936,42944&ap=1

[George Bokros]

A bit pricey.....but they claim to be .001 accurate at the angle. http://www.leevalley.com/US/Wood/page.aspx?p=32587&cat=1,42936,42944&ap=1

They claim .001 radian or 1/32 doing the standard square test and my framing square is least that accurate. My question is, is that accurate enough for woodworking?

[Garth Almgren]

In the instructions, they say that translates to 1/32" over the length of either leg.

[lowell holmes]

Well, if you center-punch the square at the outside or inside corner, you can move the tongue in or out. This should correct the square. I can't believe these old woodworkers didn't come up with that. :)
The center punch should be placed really close to the corner you decided to adjust. Watch this- https://www.youtube.com/watch?v=azMBpXqDJW0

[Phil Thien]

They claim .001 radian or 1/32 doing the standard square test and my framing square is least that accurate. My question is, is that accurate enough for woodworking?

Right, yours is a little more accurate.

Hopefully obviously, the edge on which you reference your square needs to be perfectly straight. Any deviation from straight on that edge will translate to measurement errors.

Also, I've found drawing two knife lines to be a bit more accurate than two pencil lines.

But to answer your question, 1/64" over 24" is perfectly acceptable for most anything you'd do in woodworking. I'm trying to think of something where that wouldn't be accurate enough but nothing comes to mind.

[scott vroom]

In the instructions, they say that translates to 1/32" over the length of either leg.


Mmmm....if the 16" leg is off 1/32 then wouldn't the 24" leg be off by an amount greater than 1/32? So how can they claim "1/32 over either leg"? Or am I just geometrically challenged?

[jack forsberg]

Well, if you center-punch the square at the outside or inside corner, you can move the tongue in or out. This should correct the square. I can't believe these old woodworkers didn't come up with that. :)
The center punch should be placed really close to the corner you decided to adjust. Watch this- https://www.youtube.com/watch?v=azMBpXqDJW0

while i agree with the punch the video show it being done in the wrong place IMHO. It should be in a line that is a miter. And a cold chisel is way faster as a spreader.

[George Bokros]

Made a mistake in original test. I am off 1/32 not 1/64.

Guess I am as accurate as the Lee Valley square.

[Al Launier]

I agree & wondered myself, but decided to cut them some slack as I felt they may be suffering from a Senior Moment as I frequently do. ;)


Well, if you center-punch the square at the outside or inside corner, you can move the tongue in or out. This should correct the square. I can't believe these old woodworkers didn't come up with that. :)
The center punch should be placed really close to the corner you decided to adjust. Watch this- https://www.youtube.com/watch?v=azMBpXqDJW0

[Rich Riddle]

Made a mistake in original test. I am off 1/32 not 1/64.

Guess I am as accurate as the Lee Valley square.

And you're $68 to the good (plush shipping). I have a Empire square as accurate as the Lee Valley model. Short of purchasing an engineering model, which would prove very expensive, you are likely as good as it gets with what you have.

[Greg R Bradley]

1/32" off is 0.031" off over 24" or 0.015" off over 12".

I use a Woodpeckers 26"/16" square to set my MFT. They claim theirs' is accurate to 0.001" per foot. I've found the Woodpeckers to be more accurate than required as there is more than that amount of flex in the track and the mechanism that keeps the saw on the track. Using one that is accurate to 0.005" over 24" that also has a short leg at least 12" long seems fine with what I've done.

You are 15 times the maximum error on the Woodpeckers unit. Somewhere in between is probably "good enough" in that you don't really need the accuracy of the WP unit but yours' seems "not good enough". I guess it depends on what you are building.

Another factor is that a thin square like the one you are using works poorly for setting up a MFT.

Another note based upon my experience: The legs being long are a huge help in setting up a MFT accurately. In other words a super precision square that is only 12"/8" isn't much good. Woodpeckers current MFT Square probably is optimum for use as much for the 1" thick outside edges as the 17"/17" leg dimensions. Way too single purpose and too expensive to be justified for me.

[Robert LaPlaca]

Might want to check out Chappell framing squares, just remember accuracy costs.. http://chappellsquare.com/product/framing-squares/

[Walter Plummer]

Just wondering if you measure from 15" on the outside of the tongue to 20" on the outside of the blade do you get 25"? The old 3-4-5 pythagorean trick.

[ken masoumi]

The best bang for your buck(in my opinion) is a drafting square,the are inexpensive and very accurate,I bought one for under $20 and check all my woodworking squares against it.

[Rich Riddle]

The best bang for your buck(in my opinion) is a drafting square,the are inexpensive and very accurate,I bought one for under $20 and check all my woodworking squares against it.

I always thought a drafting square was shaped like a T and a carpenter's square was shaped like an L.

[Lee Reep]

Mmmm....if the 16" leg is off 1/32 then wouldn't the 24" leg be off by an amount greater than 1/32? So how can they claim "1/32 over either leg"? Or am I just geometrically challenged?

Scott, you are correct. Since 16" is 2/3 of 24", then the 24" leg will be inversely greater -- 3/2 (1.5) times the error, or 3/64".

Lee "I just love math" Reep

:p

And to the OP, you might get in on the Woodpeckers Framing Square One Time Buy, if it is not too late to order. They aren't cheap -- about $200 with shipping (for the 26" model).

UPDATE: Order deadline was late January, but some dealers may have ordered some for selling to those that did not get in on the deal. Good news is that Woodpeckers seems to re-run the framing square "One Time Deals" ever couple years.

[Andrew Hughes]

Last time I bought a framing square at the Borg.I grabbed a bout a half dozen and took them over to the sheet goods took about 10 mins to eliminate the bad ones. The Swanson framing square will set you back wopping 10 dollars.Aj

[Greg R Bradley]

I always thought a drafting square was shaped like a T and a carpenter's square was shaped like an L.
Exactly.

Most people that say that they bought a drafting square for this purpose actually bought a drafting TRIANGLE. Problem is they only go up to about 12" and even 12"/12" is hard to find and around $35 if you can find them. They are very thin so great for checking other squares and some layout work but pretty useless for the OP's use. A great amount of accuracy for a low price but some serious limitations on function.

[Chris Parks]

Where do you suggest to get a more accurate square the size of a framing square.? I want to use it to set up the track saw for cross cuts of sheet goods.

I wouldn't use a square at all, I would use a version of a story stick. Use a home made version of Festool's parallel guide system.

Set the track as close as possible to the line you want to cut to

Using two sticks of wood longer that the distance to the edge of the sheet set up the track parallel to the edge of the sheet at the measurement you need.

Lay one stick on the sheet butted up against the back of the track

Using a clamp and a block of wood clamp the block to the stick against the edge of the sheet you are measuring from, this sets the distance from the edge at one end.

Taking the now set gauge, use it to set the distance on the other stick by laying it on the first gauge you set and clamp the block.

You now have two gauges set to exactly the same length without measuring anything or using a square and the track will be exactly parallel to the edge of the sheet and it took about two minutes to do it using scrap timber.

Set both on the sheet butted up against the edge, the track butts up against the other end and cut the sheet parallel to the edge.

You could finesse the idea by using sliding adjusters and thumb screws etc but I wouldn't bother

[ken masoumi]

I always thought a drafting square was shaped like a T and a carpenter's square was shaped like an L.


Exactly.

Most people that say that they bought a drafting square for this purpose actually bought a drafting TRIANGLE. Problem is they only go up to about 12" and even 12"/12" is hard to find and around $35 if you can find them. They are very thin so great for checking other squares and some layout work but pretty useless for the OP's use. A great amount of accuracy for a low price but some serious limitations on function.

This is the drafting square I'm talking about,they are great for verifying squareness of other squares (try ,woodworking,etc.),I thought the ones that looked like "T" are T squares and the triangle shaped are "drafting squares" ,at any rate,this the one I have :
http://www.modulor.de/en/Drafting-Graphic-Office/Drafting-and-Graphic-Supply/Drafting-Set-squares/Drafting-and-cutting-set-square-Plexiglas.html
http://www.modulor.de/out/pictures/generated/product/2/320_240_85/khdo_2_zeichen-und-schneidedreieck-plexiglas.jpg
The op mentioned:I have a framing square that I just checked for accuracy.that's why I thought the above square/triangle would be a good tool to check the accuracy of his framing square.

[william watts]

Heres a modification to a aluminum framing square that I find very handy. Add a straight piece to the tongue by cutting a deep kerf in a wood piece and drilling some oversize holes in the square to allow for adjustment. Then use the draw/flip method to adjust for square. I like this setup better because it is easier to hold to the edge of the work piece. The extra hole is a hang hole

I have used the center punch method to adjust a steel square and it worked well. An aluminum square is so soft it just deforms at the corner and does not change the angle.





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[George Bokros]

Heres a modification to a aluminum framing square that I find very handy. Add a straight piece to the tongue by cutting a deep kerf in a wood piece and drilling some oversize holes in the square to allow for adjustment. Then use the draw/flip method to adjust for square. I like this setup better because it is easier to hold to the edge of the work piece. The extra hole is a hang hole

I have used the center punch method to adjust a steel square and it worked well. An aluminum square is so soft it just deforms at the corner and does not change the angle.





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You can achieve this by using a set of stair gauges on the arm without having to modify the square. The arm is then able to set on the sheet goods and the stair gauges are against the edge of the material.

Stair gauges
http://www.homedepot.com/catalog/productImages/400/f0/f0f384f9-0b9e-40fd-9954-8b40a2fe1d96_400.jpg

[Roger Pozzi]

Well, if you center-punch the square at the outside or inside corner, you can move the tongue in or out. This should correct the square. I can't believe these old woodworkers didn't come up with that. :)
The center punch should be placed really close to the corner you decided to adjust. Watch this- https://www.youtube.com/watch?v=azMBpXqDJW0


What lowell said! ;)

[Larry Edgerton]

while i agree with the punch the video show it being done in the wrong place IMHO. It should be in a line that is a miter. And a cold chisel is way faster as a spreader.

I use a ball peen hammer. Why be gentle. Tap, tap, tap.

To come up with square all you need is an edge that is straight on a piece of plywood. Put the square on the edge, draw a line, flip the square and draw another line in the same spot. That will show you what you are off. Now adjust. Take it easy and shoot for the sweet spot between the two lines. If the square is less than 90, inside needs to be stretched, if it is more than 90, the outside. Easy.

Squares do not stay good on site, so I have adjusted squares this way at least a thousand times. Takes all of a minute.

[David Kumm]

If you run a sliding saw, Brian Lamb's aluminum triangle is worth a look. 16x24 and accurate enough to use to set your fence and ensure the cut will be perpendicular on sheet goods. A little off is a lot over 96". Dave

[George Bokros]

If you run a sliding saw, Brian Lamb's aluminum triangle is worth a look. 16x24 and accurate enough to use to set your fence and ensure the cut will be perpendicular on sheet goods. A little off is a lot over 96". Dave

Where do I find this??

[Phil Thien]

Where do I find this??

If you're going to be using this to set a rail for a circular saw for longer cuts, I think you'd be better-off with a parallel reference than a perpendicular one.

I've seen attachments that go on rules and allow you to setup a couple of them for x-inches, and then slide your rail up to that.

[David Kumm]

lambtoolworks.com. I agree the triangle works best for slider setup. I also use it to check the first cut on a cabinet project to make sure the settings are still good. Dave

[jack forsberg]

lambtoolworks.com. I agree the triangle works best for slider setup. I also use it to check the first cut on a cabinet project to make sure the settings are still good. Dave

Dave i use the 5 cut method.

[George Bokros]

If you're going to be using this to set a rail for a circular saw for longer cuts, I think you'd be better-off with a parallel reference than a perpendicular one.

I've seen attachments that go on rules and allow you to setup a couple of them for x-inches, and then slide your rail up to that.

I want to set up the track saw rail for cross cuts on sheet goods.

[Robyn Horton]

lambtoolworks.com. I agree the triangle works best for slider setup. I also use it to check the first cut on a cabinet project to make sure the settings are still good. Dave

I like the lambtoolworks one but wish that they made a 12" version of it
I'm patiently waiting for Woodpeckers to have the 12" precision triangle made available again for my track saw

[Phil Thien]

I want to set up the track saw rail for cross cuts on sheet goods.

If I were going to use a track saw, I think I'd want both a good triangle or square, AND a parallel system.

For example, one of these:

http://www.senecawoodworking.com/products/parallel-guide-system-for-incra-t-track-plus

(Though I might make something myself).

[George Bokros]

If I were going to use a track saw, I think I'd want both a good triangle or square, AND a parallel system.

For example, one of these:

http://www.senecawoodworking.com/products/parallel-guide-system-for-incra-t-track-plus

(Though I might make something myself).

The only issue with the Senca system it it ONLY works with the green kool aid track saw

[Art Mann]

If (and only if) you trust the two sides of a piece of plywood to be parallel, then you can use a square that is pretty inaccurate to locate a track saw track for cross cutting. Use your square to mark a line that is exactly half the width of the sheet. Then, go to the other side and use the same square in the same orientation to draw a line from the end of the first line to the other edge of the plywood. Locate your track on the ends of the two lines right at the edges of the plywood. Even if the square isn't square, the errors of the two lines will exactly offset and cancel each other. The line you created this way won't be exactly straight but that doesn't matter if you are using a track saw

[George Bokros]

If (and only if) you trust the two sides of a piece of plywood to be parallel, then you can use a square that is pretty inaccurate to locate a track saw track for cross cutting. Use your square to mark a line that is exactly half the width of the sheet. Then, go to the other side and use the same square in the same orientation to draw a line from the end of the first line to the other edge of the plywood. Locate your track on the ends of the two lines right at the edges of the plywood. Even if the square isn't square, the errors of the two lines will exactly offset and cancel each other. The line you created this way won't be exactly straight but that doesn't matter if you are using a track saw

I believe the long sides of the sheet to be parallel to each other due the manufacturing process. The ends however may not be square to the sides. You need to cut the end off square to the sides. how do you locate your track saw for that cut?? You cannot measure from the end of sheet along each long edge and layout a cut square to the sides, if you do you will have a cut an equal distance from the end but it will not be square to the side if the original end is not square to the sides and I find that the ends are not usually square to the sides.