Any graduated marking gauge that you can set to the radius will do. Still need to drill the hole precisely but that's at least one working solution for marking. I made a third line just to verify (I was worried about the center notch in the gauge but the effect was negligible). Prior to making the jig, I was at least able to find the center using an Incra IG32, by setting it to 1" (the radius): It's not really sensitive to imperfections in the roundness, and since I have to go to a friend's shop to use the drill press, I only had to use the press once and now I can use my handheld drill at home for drilling the dowels. Then I just stick it on the end of the dowel and use it as a drill guide: My final solution was to just use a drill press to drill a 2" hole with a forstner bit partway through a block of wood, then a 5/16" hole the rest of the way, centered on the pilot hole from the forstner bit: Use a punch to mark your center and then guide your drill into that hole. That will keep it perpendicular to the table. Keep in mind that you still need to clamp it to the table but the deeper the hole the less error you will get from the dowel moving. The depth of your block, if possible, should be close to the length of your dowel. Hopefully your table moves down far enough. Take a deep block and drill a hole, with the press, that is the same diameter as your dowel. This might not work for your case but in general I would recommend using a drill press for something like this where accuracy is important. Might even be able to make a home brew version of this depending on your acceptable tolerance. Press it up against the dowel and draw your line. If you need to be perfect every time and plan on doing this a lot than a center gauge, or similar tool, is the way to go. This is what I would do as I don't need to do this to often.Ī center square, or similar tool like the one in Jason's answer would work very quickly and efficiently and would take less time and be less error prone. The point where the two diameters meet is your center. Repeating this process a second time (starting from another point.) will get you a second diameter. Drawing a line between those two point will get the diameter. The sides from this angle will bisect the circumference of the dowel. Draw a right angle and the edge of the dowel. ![]() Something simpler, that requires a square (or anything with a known 90 degree angle), called Thales' Theorem. ![]() That seems like more work than it is worth though. This picture makes way more sense than my words. The point where all those lines intersect is the center of the circle. Then draw 3 perpendicular lines from the center of those lines. Since your dowel is big enough you can do this by hand relatively easy.įirst would be to make 3 lines on the outside of the dowel the cross 2 different points along the circumference (each line).
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