A Big Compass for Big Work . . .

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Project by GnarlyErik posted 12-02-2012 06:54 PM 4682 views 13 times favorited 4 comments Add to Favorites Watch

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 be run over by your karma!"

4 comments so far

View Ken90712's profile


17745 posts in 3702 days

#1 posted 12-02-2012 07:17 PM

Very cool. and effective

-- Ken, "Everyday above ground is a good day!"

View HillbillyShooter's profile


5811 posts in 2806 days

#2 posted 12-02-2012 08:11 PM

Great practical, economic solution. You never cease to amaze with your real life tools. Thanks for sharing. You, sir, are a one man learning center.

-- John C. -- "Firearms are second only to the Constitution in importance; they are the peoples' liberty's teeth." George Washington

View Underdog's profile


1403 posts in 2549 days

#3 posted 11-25-2013 02:01 PM

I like it! I have one made similarly in my shop, right down to the hose clamp for the pencil! Great minds think alike I guess?

Anyway, I’ll be making an addition of the adjustment stretcher to mine. It will help with the “creep”. I have a machine screw and wingnut on the pivot, but it’s still not enough to keep the compass/divider from slowly getting larger…

Great idea!

-- Jim, Georgia, USA

View GnarlyErik's profile


321 posts in 2648 days

#4 posted 11-25-2013 02:39 PM

Underdog – the Spring clamp may not look very elegant, but it sure does work just great!

-- "Never let your dogma be run over by your karma!"

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