Simple Beam Compass......

[brino]

Hi All,

I recently realized that I have receiving more than I've been giving on this site.
I will try to do better.

This is not an in depth tool build, because it is a simple tool.
Sometimes I need to draw a circle bigger than my two-leg compass can handle.
I wanted something that was adjustable in a huge range of circles.
I also wanted to make it from what I had on hand, rather than buying anything.

I had some T-slot track left over from a previous project. The extruded aluminum track and hardware look like this:
http://www.leevalley.com/en/hardware/page.aspx?p=61986&cat=3,43576,61994,61986

I made up two hardwood blocks, with a small shoulder on one side to slide in the t-slot groove.
They were drilled thru that shoulder for a bolt, drilled thru at 90 degrees for a pencil or point, and finally slit on the table saw.





Here is a shot of all the parts minus the t-slot track.


I did not have thumb screws so I used some regular hex heads bolts, but then got tired of needing a wrench to adjust them, and so MIG welded some washers on for "wings".
They are not my best welds, but they work.....I was in a hurry.

The little "plate nuts" slide into the t-track slot from the open ends.
The extra washers simply help adjust the length of the bolts so that when tight the end of the bolt does not drag in the bottom of the slot.



Now I can draw circles almost up to the length of the t-track.....if required I suppose I could even connect multiple tracks together if I needed to.

-brino

 

[Tony Wells]

AKA trammel points. Good job!

 

[brino]

A couple improvements I would consider if doing it again:

I would make both the centre of the pencil and the centre of the pin a known distance from the edge of the wood block, say exactly 1 inch.
Then I could put a measuring scale like this on the t-slot track:
http://www.leevalley.com/en/wood/page.aspx?p=70539&cat=1,43455,53293
It would be very easy to set instantly to any length.

Or use a aluminum track like this:
http://www.leevalley.com/en/wood/page.aspx?p=73516&cat=1,43455,61994
with the measuring tape protected in a shallow recess.

-brino