Back in the day, carpenters would reference the "factory edge" as a starting point. After copious years of cutting, one learns that removing the factory edge is the most important step to getting straight and square panels. We must turn a questionably 4'x8' [or 49"x97" sheet] into an accurate panel.
How to straighten sides if all four are not square?
- Thread starter mikewaters
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Hi Mike,mikewaters said:
When I read your 2nd post about the checks you had made of not having a bowed track etc I assumed you would therefore have a straight edge. However some (including myself, just this weekend) have been able to introduce some slight sideways bowing/deflection (especially on joined rails) from accidentally pushing sideways during the course of the cut. These days I not only make a mark at either end of any long cut, but also in the middle. One of the posts above suggests using a string as a means of checking, but I save myself the effort and use a laser line. [big grin]
Anyway, if you follow those steps above it doesn't matter if the first cut actually introduced an angle that wasn't there before, as the remaining 3 cuts will fix it all up.
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If you are relying on the 20 mm holes of the MFT3 to be in a perfect 96 mm square centre to centre pattern then this may cause some of your error.
Festool make no claim (as far as I am aware) that the pattern of holes on the MFT3 is in any way accurate. I think we have assumed that as they are being produced in an industrial production process (and are CNC'd) that they should be spot on. I am sure that many MFT3 tops will be pretty good but this may not always be the case.
Also, the diameter of the holes in the MFT3 top can vary from one top to another. This has caused huge problems for bench dog manufacturers who have either had to work out the mean diameter across a selection of MFT tops or use tapers to account for the variation in sizes.
With any cutting station, be it an MFT3 or custom made top, that relies on bench dogs to position the wood and the guide rail, you need to perform a 4 (sometimes called 5) cut test to verify its accuracy.
Peter
Festool make no claim (as far as I am aware) that the pattern of holes on the MFT3 is in any way accurate. I think we have assumed that as they are being produced in an industrial production process (and are CNC'd) that they should be spot on. I am sure that many MFT3 tops will be pretty good but this may not always be the case.
Also, the diameter of the holes in the MFT3 top can vary from one top to another. This has caused huge problems for bench dog manufacturers who have either had to work out the mean diameter across a selection of MFT tops or use tapers to account for the variation in sizes.
With any cutting station, be it an MFT3 or custom made top, that relies on bench dogs to position the wood and the guide rail, you need to perform a 4 (sometimes called 5) cut test to verify its accuracy.
Peter
kevinculle
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The advice as to technique above is fine, but if I found a factory sheet of plywood to be as far out of square as you indicate I would find a new supplier. Like others have noted when working sheet goods it is always a good idea to process the piece such that all factory edges are replaced with clean square straight cuts. But I have never seen a sheet of quality plywood out of square by more than a pittance...certainly not by 3/4"!!! Imagine the roofing or floor deck you would end up with if you you used such sheets as received, you'd potentially have 1 1/2" gaps!
Wooden Skye
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Are you clamping the rail? Even though you say your technique is correct, you could be moving the rail unknowingly at the end of the cut, since you mention the second measurement is off and I assume that means end of cut.
mikewaters
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Awesome that you got the help you needed! [smile]mikewaters said:
If you're processing sheet goods a lot and want to make quick square cuts, you might want to look into the TSO Products Guide Rail Squares (GRS-16, & GRS-16PE). You can see a lot of YouTube reviews as well. I purchased one a couple of months ago and it seriously makes things so much faster than marking up both a start/end point (often the end point being out of reach and needing to walk around to the other side and back) lining up the rail to a square etc. I highly recommend this, and I am only a home hobbyist. I got the "PE" version where you can reference both off the near edge as well as the far edge, and have definitely referenced off the far edge.
mikewaters
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eddomak said:
I actually have one. I had trouble make sure the rail was straight the entire way.
Cheese
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morts10n said:
Amen...
Mike, as others have said, I'd also seriously recommend purchasing the TSO GRS-16PE as it makes the squaring process so much easier. I purchased the GRS-16 because it was released first, however I find the PE version to be a lot more convenient to use.
Sanderxpander
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I know the problem is already solved, but I still like to offer that I think of it as cutting a square from an uneven piece of wood, rather than "fixing bad angles". You could cut a perfectly square piece of paper out of any misformed scrap with a good T Square, so why not with a saw? Helps my process to think of it that way.
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