Tips for Accurate Measuring and Machining

[DonRotolo]

Originally Posted by Pat Fairbank

My favorite set of low-tech tools for laying out holes and lines consists of a combination square, a blue marker, a scribe, and a center punch. When marking a hole, for instance, you can set the combination square to the X and Y distances to the hole from the edges of the workpiece, and scribe two lines to establish the point (use the blue marker to provide some contrast before scribing). Then mark the hole with a center punch, and drill with a center drill before the actual size you want, as twist drills tend to walk.

Requoted for truth.
If you use a sharpie with a 1/8" thick tip to mark your spot, the best accuracy you'll get is 1/8". Instead, use the marker to mark nearly the spot, then use a scribe or other sharp object to mark exactly the spot.

If you make a cross or X with a scribe, you can 'feel' the intersection of the lines with your center punch, ensuring you hit the mark perfectly.

Measurement and markout is a skill and the techniques can be learned, just put in some effort and don't settle for 'close enough'. After a while you'll get fast at it too.

[GeeTwo]

A neat trick that works for some applications is to use perforated breadboard to line things up. The holes are already present at 0.1" apart, so if you can work out your spacings on that grid and fit pieces within a relatively small area, it's great. Just mark which holes to drill, and line up on these as pilots. If you're going to do multiple copies of a piece, use a 1/16" bit as a pilot for your stock, then follow up with the actual size hole. This trick is especially useful for making "control panels" and similar applications where you want everything to line up evenly, but exactly WHAT the spacing is isn't critical. OBTW, use the stuff WITHOUT solder pads for this!