Difficulty getting a square line around a board

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    So this sounds so dumb especially since it is probably the most basic of tasks to do but I’m still having trouble with it for some reason. I wish someone could watch me and tell me what I’m doing wrong because I can’t figure it out.

    So this is the task of getting a square line around a board for shoulder lines on a tenon. (it’s not the square I’ve tried 3 different types and styles and I end up with the same result each time) (this also has happened on many boards that have been both hand planed and also machined square)(the boards I’m using are 2.5-5″ wide nothing super wide or anything)

    The short story is that when I use the knife to cut a line around a board I always end of off by a 32nd or slightly more maybe just under a 16th sometimes but that might be on the high side. And I’m always ‘off’ the same way each time. Not sometimes to the left sometimes to the right.

    I’ll describe how I do it and maybe someone can give me some pointer because I have tried practicing and messing around with my technique I can’t get a better result and can’t figure out why.

    So I start with a reference face and edge and I always measure off that. I use the square in my left hand and I’m using the knife with my right. I have the reference face up and the edge is on the bottom closest to me. I make my first mark from the top to bottom by drawing the knife back. I turn the board ‘up’ so the near edge is now on top. Turn the square and use the reference face and click the knife in the mark and draw it down. I then rotate the board around so the reference face is facing me and the reference edge is now on the bench and I click the knife into the mark (which is now on the close side) and line my square and make my mark. Finally I put the reference face down on the bench and register the square on the edge and from the further away edge (which has the edge mark) click my knife in and line up my square. When I look down at the near edge my square has shifted left and my marks don’t line up by a small amount.

    When I look at all my other corners the mark couldn’t be any more on the line. Something is happening and I can’t figure out why there is always this difference in the same way every time. I’m starting to think my eyes are crooked.

    Any suggestions on what I could try to resolve this?


    Have you checked that your square is truly square?

    Using a board with a true edge place the stock of your square against it and mark a line. Then flip the square and mar a line starting at the same point. The lines should match if the square is square.


    A traditional marking knife is flat on one side and beveled on the other. Knives like the Stanley knife have bevels on both sides. Both are fine, but you need to be aware that, if you place a bevel against the square’s blade, then the actual mark will be made some distance away from the square unless you tilt the knife blade. See the attached sketch. I am wondering two things. 1. Is your square really square (see Bill’s note) and 2. Are you changing how much you tilt the knife as you draw it down? Or, you may change the tilt between when you register and when you mark. Or, you may change from one side of the knife to the other at some point without changing the lean. I suggest you pay attention to tilting the knife so that there is zero stand-off from the square’s blade and then mark around the wood with the lightest possible marks, done as gently as you can and with just one knife draw on each face or edge, just to see what happens. If that makes things better, then work to deepen the lines.

    Joe Kaiser

    I agree with Ed. Assuming your board is square, make sure your knife is positioned accurately.

    Seattle, WA

    Matt McGrane

    It sounds like you are using proper technique. The advise given above is spot on. I’ve had problems with this too, and it may have been because I was knifing too deep a line. I tend to blow out the corner at the end of each knife cut and that makes it hard to find the knife nick to start the next cut. Read Ed’s advise about going lightly, make some test lines and see how it comes out.

    Matt, Northern California - Started a blog in 2016: http://tinyshopww.blogspot.com/


    Thanks for the tips I’ll be trying this more this weekend and I’ll report back on what I figure out


    So here is what I’ve learned by taking your tips and experimenting a little.

    I have a piece of 8″ wide S4S scrap that I used to to make some lines on. I was noticing that when I pushed too hard on the knife (this is magnified in soft pine) I’d tend to angle it more causing the knife wall to undercut the beam of the square causing me to be inconsistent when registering the knife on the other edge. I’d start by going super light at first but then noticed I was lazy or careless when I went with the heavier passes causing this to happen. I am also now focusing on locking my wrist and moving my whole hand and arm backwards when I draw the knife. Again I was probably being lazy and pulling by using wrist action causing it to be an inconsistent angle on the knife bevel.

    When I went back to my project pieces the problem came back. Extremely frustrating I know… What I noticed was that the reference face wasn’t as flat as I thought and the square edge wasn’t square to the whole width of the board. If you can picture when I checked for square the stock of the square went on the face and the beam came in contact with the edge. If I checked this way then everything appeared square but it wasn’t when I flipped the square around to rest the stock on the edge and the beam across the entire face that I noticed the problem. My board sloped off towards one edge.

    I’m not sure how this happened (probably just my inexperience) but I did it along an entire board which I then cut down into smaller sections so the error was present on all boards. (all with the same reference face and edge marks)

    I think what happened was that this sloping off in the last inch and a quarter on the face of the board caused me to get an angle on the square when I squeezed it to the board to get the line on the edge which was square to the section of board I had referenced but that wasn’t what I wanted. I quickly flattened and squared it and when I corrected the problem the line rejoining in the end became better.

    This sloping off on one side was about half as much on one board than the other board and when I compared the discrepancy on the square lines between boards the discrepancy was proportional to how much the board was off from the edge.

    Thanks for your help and maybe this can help someone else in the future. This took me a lot of thinking and imagining what is happening in order to resolve and say that this was causing my problem. I still don’t fully believe it but I think the combination of being more careful with the knife and having a flat square board will help in the future.


    Sharpen the knife. Lighten the pressure. And cut the fibers not plow through them . When i did this my shoulders looked a lot more like Pauls and less like i cut them


    Be sure that your stock faces are parallel to each other and reference the square from the same edge/side. A small angle of error will magnify with increasing stock width.


    David B

    The one thing that I struggled with at first is knowing when to flip your combination square over so that the stock is flat against the reference face but the knife mark you are lining up is on the other side of the board(usually the 3rd line). But then it clicked and I understand why Paul is always flipping the board and combination square over/around–it’s not just for the camera.

    If you can’t get anything to square up I’d think the square itself may be the culprit. Like someone else said. Check your stock against a square edge and draw a line across the board, then flip your stock over and draw the exact same line from the same face. If they are square it should be accurate enough from my exoerience.

    • This reply was modified 6 years, 4 months ago by David B.
    Michael B

    I’ve run into the same issue a few times due to a couple of different factors. The first was my combination square wasn’t fully tightened. It felt tight enough, but running the edge of the knife along it when marking was pushing the ruler edge away ever so slightly. This error was compounded on each face, so the resulting mark was about 1mm out.

    The other main factor was I the way I was holding the square – my fingers weren’t in the right position to securely hold the square against each face. I think Paul mentions how he holds his square in one of his videos, which made me double-check my technique. Now I spread my thumb and forefinger along the length of the ruler, pushing down firmly. I use the remaining fingers to pull the square edge firmly against wood edge.

    Thomas Angle

    I find that if my lines do not line up, my board is not square.

    Arbovale, WV

    Proverbs 18:13
    13 He that answereth a matter before he heareth it, it is folly and shame unto him.


    I keep noticing the mention of a board being square. I don’t think being square will effect the issue you are having as much as PARRALLEL (am I spelling that right?) sides. You could have any shape like an octagon or something with no sides at 90 degrees. It’s the parrallelness (now I’m making up words) that matters.

    Good luck,

    Steve Giles

    That’s exactly what I was thinking Kevin.

    (Parallelism? Lose one of the ‘r’s at least!)

    Sven-Olof Jansson

    With all known apologies for a, perhaps late, comment that also suggests further cluttering up of already full work benches.

    A base square (also known as a T-square) of sufficient precision simplifies squaring around corners. Those of accuracy on par with Starret’s combination and sliding squares, are also priced at the same level. Their thick blades make under-cutting less of an issue when using a double bevel marking knife, and next to an impossibility with a single bevel one.

    As base squares are less inclined to flip or fall over, they are likely to stay in place while looking for that disappeared marking knife, or when a drill bit is to be perpendicularily positioned.

    Sven-Olof Jansson
    London, UK; Boston, MA

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