R = ((C/2)^2 + H^2) / 2H

Use alcohol to remove them. It won’t erase a dent, but it does get rid of the pencil lead. You won’t have the "ghost" lines as shown above.

That can get really anoying if you’ve erased a lot of lines. I know, I’ve done both.

I recently bought a tool that helps a lot. A large illuminated magnifying glass that sets on a stand on my workbench. This one came from an office supply store. I would need it to read the fine divisions on that steel rule, whether they be metric or Imperial units.

Bill

Straight Edges and Squared Ends are a biggie for layout. The board needs those made onto them before further layout can begin. Then try and lay out as much as you can from the one straight edge and square end. I have done a lot of surveying in my life and baselines are the beginning of everything. Most of the infrastructure we have in this country was laid out using Pythagorean Theorem, two tapes, a 6′ folding rule with engineers scale and a hand level. No lie.

Locating that 1" radius is easy. You are working from the corner, so using your compass as a divider, put the steel point at the corner and use the pencil side to mark the edge and end to the right and left 1" away from the corner.

Now flip the compass, and hold the steel point to the edge where the marks were made. At a right angle to the edges, draw a small arc 1" in from the edge. Where these two arcs meat is your radius point.

Flip the compass around and put the steel point on the crossing arc lines you just drew. put the pencil on one of the marks you made on the edge or end, and draw the arc across the corner to the other one.

For the partial circle, measure the section length that the circle makes into the board you are laying out. Half the section length is your radius.

Set a scrap next to your working board, that is the same thickness. Set your Compass to the section length, and from each end of the section of the circle, swing some small arcs where you predict the two will cross. That will be your radius point on the scrap. Then turn the compass around and set the steel point in the scraps "RP" and draw your arc from on end to the other on your work piece.

In any layout, if the circle has a constant radius, you will have a beginning and end on the curve, and the RP will be where two equidistant arc lines cross that are the length which equals the section length of the radius, and are at a right angle to the curve at those points. The section itself is a straight line (line BC-EC (Beginning Curve-End Curve) drawn from where a radius begins, and ends.

Bests,

Rob

It’s strange that you don’t want to use a measuring system that greatly reduces confusion and error. I can argue just as long and stubbornly for Metric units, and you won’t win either.

-J