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Please provide some context, some helpful hints, and other information if you can!

I have two projects that are making me think this:

  1. When you make frames with a homemade jig, it is often the case that the jig is at 44.8º through the center of the 90º. You can compensate with this by making one cut on one side, and the other cut on the other side. No regular person can notice this 'error' because of how you compensate.

  2. I am making a bed frame. Think of an 'H' with a top bar on it. When cutting the mortises on the top part to secure it to the two verticals (middle bar is already complete) I clamped the top bar to the completed 'H' to measure it was square. Did the measure 6 times cut once thing, and somehow when going back to dry fit, the top part of the frame isn't 100% square. Im measuring 62.75" and 63.125" .

Obviously I am a bit of a perfectionist, but when I frame a house, I can make a 40' wall vertically square and plumb to less than a eighth" before securing. So there has to be some acceptable tolerances depending on the circumstances. Is there a formula? a percentage? something else?

So what is your tolerance in your area of work? How do you handle errors? Know any tricks?

  • I am unsure if this is too broad or opinionated. Projects vary and people tolerance for error varies. With wood working there is some leeway because, depending on you materials and location, wood will change as it ages and you need to account for an accept that. I don't think there will be one all encompassing answer for this. You need to make sure your tools are square. When it comes to gaps you can fill these up . You can make gaps on purpose with tenons and fill them with keys. Also need to be sure that each tenon is made for each mortise (one at a time if you are worried about fit). – Matt Nov 15 '15 at 16:56
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    You've identified a good category of questions but I agree with Matt that currently the question is too broad in scope. Different types of projects can allow for different tolerances. It also isn't entirely clear which question you're asking. You touch on how to determine appropriate tolerances and how to work with errors which seem like two related but distinct questions. – rob Nov 15 '15 at 20:57
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The things I have learned that have been working fine:

  • Dry fit always, then trim until it's good enough. You can stop at good enough.
  • Err on the long side since you can't add some back after you remove it.
  • Measure to what you've actually built instead of what you've designed.
  • Order your cuts so that things that match can be done in bulk. If you need two 20" rips set your table saw fence then make both cuts. Don't do one, change settings, then change back to 20" for the second later. You can also cut things at the same time. If I need two pieces of equal size I'll rough cut then stack them on the saw or put them side by side on my sled and cut them together.
  • Use your square to double check things copiously.
  • Make jigs and sleds to help with repeatability where appropriate.
  • A shooting block is great for trimming miters. Veritas makes a shooting sander too if you're not comfortable with a hand plane.
  • When gluing, prep your clamps and stuff ahead of time so you're not running around or adjusting clamps while your glued pieces fall apart. I sometimes do a dry clamp fit to make sure e.g. my clamps aren't going to pull things out of alignment.
  • Also, this one's important: If you're making a lot of mistakes, take a break. You might be hungry, tired, or just frustrated. Sounds silly but sometimes you need space from a project, not just for sanity, but for safety too. Frustration can make you careless.

I don't have a lot of experience but those have helped me.

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It really depends on the project. If you're gluing up a wide panel, acccumulated error from a series of non-square edges can become significant, unless you take steps to counter that by balancing the errors against each other. A joint might not come together well, showing gaps. On the other hand, in some places the difference may not be visible, or may be unnoticable, or may be something you can close up with a block plane or a bit of sanding. As with length measurements, tolerace for error really depends on the design and size of the project.

Rule of thumb: The more accurate you are to start with, the less fine-tuning you'll have to do later. Do your best and don't stress about the rest.

  • +1 for balancing errors, especially for designing so that your errors tend to cancel each other out. – dlu Oct 18 '16 at 4:49

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