|Project by GnarlyErik||posted 12-02-2012 06:54 PM||3538 views||13 times favorited||4 comments|
Sometimes layout situations call for a radius, or a series of radii which makes using trammel points tedious. Here is a large compass you can build in about thirty minutes or so. Over time I have made three or four different sizes, but this size seems handiest for my use. It has arms of a little over two feet long, giving a range of use from less than a 12” radius to over 36”.
The pictures explain everything; after all, a compass is not complicated. The main concern is having the cross arm fall in the same plane for each arm. You can be fancy and relieve the arms where they hinge, or simply glue on a block the same thickness as the arms to one of the arms. See picture #3. Alternatively, you can put a spacer under the pivot for the cross arm.
This particular compass uses copper rivets and roves because I happen to have some on hand, but machine bolts with nuts will also work fine. I use a flat washer between the arms where they hinge. A spring clamp is used to hold the cross arm securely in use, and to hold the entire apparatus together when stowed.
This costs almost nothing to own, which makes it appealing to me! It is also very simple to make your own trammel points – or simply use a long flat stick with a notch in one end, and a nail through the radius center point.
-- "Never let your dogma get run over by your karma!"