As requested by a member of the WWUK Facebook group, just a quick video showing how to reliably and accurately ensure that your woodworking squares are truly square. / woodworkinguk
I use a piece of 3 or 4mm aluminium plate with a dead straight edge (checked against a known good straight edge) but stick blue masking tape on the plate and cut it just shy of the edge. The take your sqaure and scribe down to cut the masking tape and peel off either side to reveal an edge. The turn your square and overlap it very slightly and cut a new edge to leave a sliver of masking tape which will clearly reveal any deviation from square. Much better than using a piece of wood and trying to see the cut line.
One possible flaw with this method is the edge of the plywood may not be perfectly straight. Any deviation from straightness of the plywood would translate to non-parallelism of the two vertical lines.
Hi Matthew I have done the technique that you showed in this video with a Swanson speed square. The lines were dead on. When i used an engineering square though, on the side of the Swanson that i drew the lines with, i can see little bits of light peaking through when holding it up to a light. Does this basically mean that the engineering square is more accurate, yet because the original lines that i drew with the speed square were dead on, the speed square is alright in it's own regard? Or is it okay that there are bits of light? I couldnt see light unless holding it up to the ceiling light. Cheers
Its a great method whichi use myself, but its not the most accurate way to check for squareness. One more accurate and measurable way is using a surface plate, feeler gauge, test indicator and surface gauge stand (how machinists measure for squareness). I guess there are even more accurate ways, but, in any case, using the marking knife method is certainly accurate enough : )
Not sure about that technique... the knife will follow the previous line. The first technique with a 0.5mm mechanical pencil works for me. As its double the error, I think its good enough for woodworking.
I clearly demonstrate in the video that the knife does not follow the previous kerf unless you are absolutely square. If you are cutting tenons into cabinet legs where a cabinet side might be a metre long, if your square is out by half the width of your pencil line, that would put you 2.5 mm out at your next mortice. Depending on the thickness of stock you are using, that could mean the difference between fitting and not fitting. When I built my workbench with 120 mm thick stretchers, an error of 2.5 mm would have been a disaster. A knife line is precise. It's exactly why shoulder lines are cut with them. Everyone is free to do what they wish of course, but it isn't like I'm presenting anything revolutionary here. I think the vast majory of cabinet makers check squares with a knife.
@@MatthewSmall If you're square is pretty accurate, but is still slightly out towards to the top, i.e the lines start out the same but then deviate, the knife is going to follow the existing line unless you have some engineered jig. If I was using a knife, I would shift it over a tad to definately avoid the issue. Sorry, but we're just going to have to agree to disagree. I think you're also thinking in absolute certainties. Even if you manage to get your tenon to engineering square tolerances, your legs are not perfectly straight. They might be the minute they came off the planer, but not a few hours or days later.
@@SirBenJamin_ I'm sorry, but that is simply not true. As I demonstrate in the video, even when the second line is imperceptibly close to the first, it will still cut a new kerf and you will still be able to see and feel it. Disagree all you like, but I've presented solid evidence to back my argument up whereas you haven't presented anything but your opinion. And you are free to think what you want, but in my experience, evidence always beats opinion. As for the engineering square part, engineering square would be measured to an error of hundredths of a mm over a metre span, not in mm integers. Whilst wood certainly does move and absolute square isn't always important (again, as I pointed out in the video), when you are cutting proper joinery like mortice and tenons or dovetails, absolute square is crucial, otherwise you get gaps along shoulder lines where the mating pieces don't meet or they don't sit in the same plane as each other, which puts everything else out through accumulated errors. If you're working with sheet goods, that's not going to be a problem, but it is a very real problem with traditional joinery. All of this is explained in the video. If you don’t want to use this method, that is absolutely fine. I’m not telling or asking you to, but it is a perfectly valid method that is used by a lot of people and has been used by countless people over the years. Add to that that there are real and empirically based reasons as to why this method is preferable and that leaves a situation where you are free to choose a differing method, but you shouldn’t be trying to dissuade others from using it based on your intuitive bias.
@@MatthewSmall With all due respect, I can see in the video the point I am trying to make. If you look at @4:01, the the knife kerf you made is a very wide, and is pretty much the same width as the pencil line on the left.
Yes, you're right, but you're missing the point. With a knife line, the width of the kerf is irrelevant. What is important is that it is a single kerf that is cut with the flat edge of the blade against the square. If your next line runs against the side of the square and also in the same kerf, then it's square. If the kerf is wider at one end than the other, you will usually be able to feel where it deviates and it also means that you're not square. The width of the line DOES matter with a pencil as there is no definitive point on the width of the line that is the reference. Even the edges are fuzzy in comparison to a knife line. Also, that wasn't the point you were trying to make. Your point was that you think a knife will simply follow its previous kerf. That's true if you use heavy cuts, but providing you're marking as you would with a shoulder line, using repeated light cuts, it won't follow the previous kerf unless it is genuinely square. I'm also not saying that using the pencil method is bad or wrong. It's not. It's just that using a knife has an advantage when it comes to accuracy and the fallibility of the human eye and our perception. If you have perfect vision and experience of judging line widths, then using a pencil can be just as accurate as a knife line. The problem is, is that not everybody sees the same, your vision can change from one day to the next, your perception can change from one moment to another and from different angles. A knife removes all of those sources of error and so is not only at least, if not more accurate, but also entirely repeatable, regardless of the time between measuring.
