Homemade Self-Centering Scribe

You could use different length ratios for the arms to find lines other than the center line!:-) William

First, you have to follow the link provided to see the actual explanation for this tool. In it it is stated that the long ends of the tool have pins that contact the sides of the piece being measured. Then it is stated that there are also pins (sharply pointed) in the short ends that are used to scribe the center line. I see problems with this. First, the distance that is set on the long side is not the width of the piece. It is that width plus the diameter of the pins used there. So the distance on the short side is half the width plus half the long side pin diameter. Now, if you use a longer, flat end pin of the same diameter as used in the long arms, in one of the short end arms and a shorter, pointed pin in the other short arm, then the mechanism should compensate by the half pin diameter that is needed for it to work. Also, it would be best for the pins in the long arms to NOT be pointed. They should have a constant diameter so that that diameter is always added to the measurement. This should be explained in the article. And the exact method of use should also be explained.  Another point that should be emphasized is that the two pins should be aligned on a line that is perpendicular to the edges of the work piece. This should be the case for both setting the gauge with the long side pins and for scribing with the short side pins.