How do you Saw large panels Dead Square?

[sitefive]

Or the question is how do you mark them to saw them totally square?
Have been making a few tabletops recently, where I cut off the ends off after gluing everything up to make it all nice.
even I'm somehow able to make the both sides the same length they are not totally square, and always there is some 0.3-0.5cm deviation once you join the tabletop with the base together...
I have some 40cm large carpenters square however even with it Im not able to mark the line precise enough since the tabletops usually are around 1m wide, The best way I have come up with is making a pendulum out of heavy screw and let the gravity show the way- this has given me the best results so far...

Anyone can aware me how is this done the correct way?
Thanks.

 

[adidat]

What are you using to cut the boards, if it's a table saw getting the fence square can be tricky even on a top of the range felder. We made up a sheet of hardboard that was perfectly square and clamped the edge parralel to the edge of the sliding table and moved the fence accordingly.

Using a track i hold my 12 inch engineers square to the back of the track and clamp it gentley then check again re adjust if necessary and tighten up the clamps.

Adidat

 

[marcros]

you could clamp a straight edge down and use a router and bearing guided bit. these are the best that i have used http://www.radiantools.com/products/1/3 ... mm_x_51mm/

 

[No skills]

Assuming your not having any problems cutting two edges parallel I would either invest in a very good large framing square or make up your own large square to mark 90 degrees across the top. If you make your own you could make it so you can clamp it to the work piece and run you saw along it as a guide.
I must say since owning a track saw I have found cutting sheet goods very accurately both quick and fairly easy.
Fwiw

 

[sitefive]

Don't have a table saw and have no intention of buying one because of the limited space I got,seriously I would get laughed at if anyone were to see where my workshop is #-o , Duing it freehand with just a regular saw
The problem is not the cutting part but just marking both the lines so they are totally 90degrees square. The cutting part honestly is the easy part.


btw are these the largest framing square there are? 40x60cm
http://www.toolstation.com/shop/Hand+To ... are/p84150
I guess 40cm reference edge is much better than 12cm I got from my carpenters square.

 

[RobinBHM]

I would start by making one long edge your datum edge.

Then measure across at each end to check the opposite edge is parallel.

To cut the ends square, mark the length you want on your datum edge.

Use a triangle solver to work out the diagonal

http://www.cleavebooks.co.uk/scol/calrtri.htm

There is also a triangle solver app for android and apple

Mark the diagonals where they land on the opposite parallel edge and check the length is correct, then cut.

I keep a large piece of mdf, that has been cut with dead square edges to check things like tabletops etc.

Squares are not the best way to check large components.

 

[sitefive]

I would start by making one long edge your datum edge.

Then measure across at each end to check the opposite edge is parallel.

To cut the ends square, mark the length you want on your datum edge.

Use a triangle solver to work out the diagonal

http://www.cleavebooks.co.uk/scol/calrtri.htm

There is also a triangle solver app for android and apple

Mark the diagonals where they land on the opposite parallel edge and check the length is correct, then cut.

I keep a large piece of mdf, that has been cut with dead square edges to check things like tabletops etc.

Squares are not the best way to check large components.

Damn good idea in theory,however just checked it in practice and I have to admit I probably can't measure well enough for it to be precise within 1mm it needs to be.

btw are these the largest framing square there are? 40x60cm
http://www.toolstation.com/shop/Hand+To ... are/p84150
I guess 40cm reference edge is much better than 12cm I got from my carpenters square.

 

[No skills]

The average shop brought frame square is not very square, there are large squares available that are better something like 0.9mm tolerance over 1m.

If you don't want to go the math route as per Robin then why not make your own square?

 

[katellwood]

Pythagoras 3, 4, 5

 

[No skills]

I haven't brought myself one yet but I was going to get..

hedue framing square from fine-tools.com

Got it wrong, it's 0.5mm over 1m

 

[dzj]

0.5mm over 1m?
Good enough for a tabletop and for most other things too.

 

[RobinBHM]

The easy way to mark the diags is to make a rod, say a strip of mdf or straight batten. Hook the tape over the end, mark at 100mm and length plus 100mm. Use a 2h pencil or a marking knife to square the lines across the rod.

Its always handy to make a square, could be just a square of 6 or 9mm board. There are plenty of ways to mark out a 90 degree line; 3, 4, 5 or 1, 1, sq rt 2, triangle solver, a pair of dividers, reversing a square and halve tge error.

 

[skipdiver]

Mathematics are your friend. Trust them, they are universal and unchanging.

 

[Phil Pascoe]

Pythagoras 3, 4, 5

5, 12, 13 - or others.

 

[Woodmonkey]

Am I missing something here? Hold a straight edge against your square, mark the edge and cut it. Even if you are a couple of mill out it will not be noticeable on a metre wide table ( this is one reason why your table top will overhang the base by say 10-15mm… a few mm difference in size will not be noticeable)

 

[sitefive]

Am I missing something here? Hold a straight edge against your square, mark the edge and cut it. Even if you are a couple of mill out it will not be noticeable on a metre wide table ( this is one reason why your table top will overhang the base by say 10-15mm… a few mm difference in size will not be noticeable)

Got today the large 40x60cm framing square, seems much more accurate now than the small straight edge I had. Will have to test on the next tabletop and see how it goes.
well it is noticable to me, when it's all put together and it overhangs by 3-4cm no1 can really tell unless they took a tape measure and measured indeed, but still I know myself that I have that mistake there..

 

[mailee]

Got to admit I did wonder that too! After all it is wood work and not engineering and wood does move. I would have thought that was fine for a table top. :?

 

[MusicMan]

If doing Pythagoras triangles, note that most tape measures are not accurate enough. For 0.5 mm/m you need a EU Class II (printed on the tape near the start) at least, preferably Class I. Most of those in common use are class III or unclassified. Cisco are the only Class I measures easily available: http://www.thetapestore.co.uk/tapes-rul ... e-measures.

Many squares aren't, either. They can be checked by drawing a "square" line to a straight edge (e.g. factory edge of an MDF sheet) then reversing the square and repeating. The lines will usually deviate, and the average of the two is the true right angle.

No such thing as exact; there is always a tolerance (error). "Dead on" just means "I can't see the error". I agree with others that 0.5 mm/m in a table top is entirely within tolerance.

Keith

 

[Steve Maskery]

I've been reading this with interest.

I agree that a small try square is not ideal, as any error is magnified, and that your average tape measure is too much of an approximation.

However, you can get somewhere near "I can't see the error" without any measuring device at all.

This is embarrassingly awful videography, but I'd had the video camera approximately an hour and had to try it out. Have you heard of the Square of Thales? Well, that's my name for it, and no-one has ever told me it has a different name, so that is what it is called.
https://www.youtube.com/watch?v=A7RdAQj8nFc

You can make it any size and although it is best used in internal corners, rather than the external corner you need, it's not a difficult job to make it work for the job you want.

PS
I'm not sure why the video is so blurred, I'm pretty sure it was better than that when I filmed it.

 

[MusicMan]

Steve that is brilliant! I'd never heard of that (even though I was a professional metrologist for years). Many thanks for telling us about that device and I shall make one this week!

I am just in process of making a(nother) simple device for checking or setting the accuracy of any square and I'll post that when finished.

Keith