Help with "help circle"?

[Johnno]

Hi guys. I hope you can help with some tech. drawing. I am on my way to making a snail and I was given some drawings which were referred to as a "help circle". I have never heard of that and I am wondering if it may be known by another name. The purpose seems to be to assist with ratios and as you can see at a radius of 114.6 every 1mm will = 2 degrees. How it works in practice I will figure out later just trying to track down what it is and where I can read up about its purpose. I can vaguely see how it will help, but need to get to the basic understanding of it and its purpose and why it would be referred to as a "help circle"? Thanks in advance if you can help.

John

JJvdEwi - Imgur.jpg (339.01 KiB) Viewed 6410 times

[Dave Booth]

Maybe they are calling it a "help circle" because it is drawn at a much larger radius than the actual snail. If you draw the circle with (for example) a 2" or 50mm) radius, and use your compass set at the radius to lay out six points on the circumference, you can draw six divisions of the circle. It is an easy step to bisect one of the angles to establish the points for the other six radial lines. Then, having done the layout on a large "help circle", you can reduce the radii to match your particular snail.

[Johnno]

I think you're right, Dave. I also am thinking the name "help circle" is archaic or someone's "pet" name for it.

Thank you.

Cheers
John