Noob question about reading drawings

[JohnDi]

Picked up Bob Lang's book on Craftsman furniture. It includes measured drawings.

The curved pieces have the radius marked, but I have no idea how to translate onto a pattern.

Could anyone explain in lay mans terms how to go about this?

[Tpt life]

Drive a pin (for 45" it could be a finish nail in the center of one end of a sheet of plywood. Measure a string or use your tape hooked on the nail to put your pencil at 45" and strike the arc it makes. The sheet of ply is helpful at this measurement because you can clamp a board to the sheet. This board can be cut to give you a template to lay on your workpiece. You could also build a custom pair of dividers ( like a mathematical compass) to set points at 45" and strike an arc.

I used to run 45-60' radii for arched garage door tops by driving a pole barn spike into an asphalt drive and pulling a long tape from the spike to my work pieces.

[Bob Lang]

Including the radii was something I argued against when my book was first published in 2001. I lost that argument (and the one about including cutting lists). In these pieces, arcs don't start at the end of the rail, there is a flat of 1/2" between the shoulder and the start of the arc. If you have trammel points and want to swing perfect arcs, you need to make a full-size lay-out. Swing an arc down from each end (those points that are in 1/2") so that the two arcs intersect somewhere below the rail. That intersection will be the center for the arc at the bottom of the rail and you can use that to draw the arc your need..

 

In real life, that's a lot of trouble to go through without much benefit. The distance from the top of the rail to the high point of the arch is 1-3/4", a difference of 3-1/16" from the overall width in the rail. It the shop, I would make a pattern of the rail from plywood, mark the end points and a vertical centerline and drive a finishing nail at the peak of the arch. Then I would bend a thin piece of wood across those three points and trace the arch. It likely won't be perfect, but no one will ever know as long as it is a fair curve. You can also do this is SketchUp, or other CAD programs. On the computer you specify each end of the arc, then the rise to the top (called the "bulge" in SketchUp), and print a full-size pattern.

 

In the current edition of the "Great Book of Shop Drawings for Craftsman Furniture" the distance to the top of the arch isn't listed in the drawing you're asking about. In the original versions, we included a small scale with each drawing so readers could check things like this with a pair of dividers or a couple of tick marks on a scrap of paper. There was an argument about removing them from the latest edition, and like most arguments I have with publishers I lost. On the last page of the book is a mention of my personal website, and you can get in touch with me by e-mail through there if you have any questions.

 

Bob Lang

[Tpt life]

I answered the question as asked and am not sorry I did. But since the master has answered, I want to add one thing to the discussion. If you follow Mr. Lang's advice and use a flexible strip, one other advantage follows. Sometimes a circular arc is less pleasing to the eye than a parabolic arc. With the flexible strip you learn to trust your eye.

[JohnDi]

Bob, thanks for taking the time to reply. I Had no idea you were a member here, and feel honored that you answered my question.

Using a flexible strip sounds like the way to go. The addition of the measurement from the top of the rail and the distance from the ends helps me make sense of the arc. Now I can apply that thought process to the other drawings when making the curved cuts.

C your reply was how I had interpreted the way to draw the arc when I saw the drawing, thanks.

[Bob Lang]

Arcs and angles are much easier to think about, and make, if you ignore the numbers and work from easily found points.

[wdwerker]

1/4" MDF is cheap So I draw an initial arch with a thin strip and 3 finish nails and cut it out, then sand to the line. Use this to draw a new arch in one color, flip it over and draw in another color. I usually find that the arch is slightly lopsided but this can be a good thing. Now you can choose between the lower lines and the higher lines. My preference is the higher lines if it will be above eye level and the lower lines for an arch like the one on the table.

This gives you a more symmetrical arch pretty quickly. If you are going to use the template multiple times wipe some glue or finish on the edge to harden the MDF to handle more wear.

[Byrdie]

Thanks, Bob, for being an active participant here and supporting your product.  I believe this kind of effort is what makes the woodworking community different.