The tapered columns are slotted along their whole length to allow the laser cut side panels to slot inside them. So a fixture needed making.
The taper needed supporting on some sort of fixture, so I made a simple holding clamp out of aluminium bar, and made three small clamps to hold the column firmly in place.
I used a slitting cutter 1/6th inch wide to cut the slots, this gave a nice fit for the 1.6mm wide plate after I polished both sides. Taking very small depth of cuts of about 10 thou, I cut down to full depth. The fixture worked very well on all four columns.
It seemed a shame that it wouldn’t be used again so I adapted it to hold the four brass finials and column bases which also needed a slot cutting into them.