labelling

I addition to painting I have labelled the axis spars by stamping them with these metal stamps (in our case intended for making aluminium plant labels). Obviously this is optional!

How to make a caltri

This example is made of boxwood but any dense hardwood will do. The spars are 15mm square by about 150mm long, but obviously you can change this. The only tricky bit is the joint, which is shown at left with an exploded diagram. The joint is glued but uses a 20mm long #4 screw through the green (y) spar and each of the other two to secure it whilst gluing and give additional strength. The screw hole is pilot-holed and clear-holed and countersunk as is usual in hardwood.





The dimensions of the cut-out sections on each spar in the images above are:-

Green (y) - 10mm across and 15mm along the spar
Red (x) - 5mm across and 10mm along the spar
Blue (z) - 10mm across and 10mm along the spar

I did these with a spindle moulder with a tenon carriage but you can cut them carefully with a fine saw.

Note that the green spar will end up a little (5mm) shorter after assembly, and I have then trimmed them all to the same length (and relieved the edges with a sander).

What is a Caltri?

One of these.

It consists of three 15*15*150mm boxwood rods fixed mutually at right angles, varnished and then painted red (x), green (y) and blue (z) as you see. It is useful to engineers and scientists considering three-dimensional co-ordinate transformations. You can do this with the thumb and first two fingers of your right hand, indeed this is traditional, but the caltri is easier! Obviously one could also do a left-handed version if needed but usually you will not want this.

Why 'Caltri'? well it looks a bit like an abbreviated caltrop (albeit with 90 degree rather than 120 degree angles) and adding the 'i' seemed a good idea to represent the three arms.