I am going to make a 'practice' pair or two out of some 2x4's, just to work out all of the joints and mechanics, and then make some good heavy duty ones out of some nice wood, likely hickory or ash because I have some stock in those, although I could use Osage Orange since I have some split stock in that laying around plenty seasoned. It is super tough stuff, and I wouldn't be worried about it breaking or wearing out!

I was thinking about using pole barn spikes with the heads shaped to fit up against grooves to keep the points from sliding down, with a pin above to keep them from pushing up, and secured to the wooden legs with fence staples. The pin above should be removable so that the points can be removed and changed. This would make them easier to work on if they get deformed, and also allow you to have multiple sets for different uses -sharp points for marking off hard surfaces, rounded points for use on soft ground or grass.

I am undecided whether the retaining arcs should use the friction stop method or be secured at their adjustment with a screw. The friction method would be harder to execute properly

Will, do you have some pictures of your 2' pairs? I would like to see especially how you handled the pivot joint at top.

For this I was thinking of having the wood especially thick near the top, with half laps cut out so that the legs overlap each other and run more or less even with each other. The other possibility is to have a third piece at the top with the legs joined to it independent of each other. This would need some kind of retaining mechanism to ensure that the legs would always be moving together at the same rate, rather than one leg pivoting.

The other possibility is to use a rounded bridle joint at this point, which would be the hardest option to cut out of 1 piece but likely the sturdiest in operation.

the interface between the two pieces is the most complex part, they need to be able to come together at the points, which will either require some complex cutting and reductions at the joint, or making the legs with a double curve to them.

Or I could do like it appears the two compasses pictured are done.

The legs appear to attach independently to a circular handle at the top with pivoting joints of some sort.