How do I make a jig for this?

[the snooper]

Why put flanges on each shelf ? 3 for feet then just put threaded bar through the lot pulling it together you could cut circular grooves I to each shelf to locate the tube

 

[zeppelin builder]

Because of the bump on the flange, actually measuring when they're square is surprisingly difficult...

put a large square on the back of the flange and measure off the blade to tube at the ends of the blade


or look up flange square ,small bit of angle to sit on the pipe and a inverted u shape welded to it that , like an upside down u with unequal legs welded to the angle edge ie like top of a roof

 

[Aesgarth]

Thanks everyone for your suggestions. I managed to make a jig that worked on the 4th or 5th attempt. I used a bit of angle iron which I eventually got perpendicular to the base plate with a little bracket to make room for the flange underneath.

Why put flanges on each shelf ? 3 for feet then just put threaded bar through the lot pulling it together you could cut circular grooves I to each shelf to locate the tube

This is what the customer wants. I will be putting a bit of threaded bar through the whole lot to keep the upright bits straight.

 

[Aesgarth]

Not quite finished, but you get the idea....

 

[Aesgarth]

Finished and delivered to the customer. One upside to the social distancing thing is I just left it on the drive, the customer had to get it into the house.

 

[waddycall]

Looks great!