My interest is building an MX5 based roadster, probably a Vodou plans one but this question relates to those and the main book plans.

The suspension brackets are fabricated from flat 3mm plate, drilled and bent, and the plans seem to imply you mark it out, cut it out, drill the holes and then put the two bends in it.
Then repeat 23 times.

Good luck with getting 24 accurately bent brackets with the two holes (drilled before bending) perfectly in line with each other.

After studying the plans the dimensions of these brackets appear to lend themselves to be made out of 50 x 50 x 3mm box section, with the open section cut out.
Once the basic shape is made you'd drill the holes slightly undersize and then ream the two inline.

The side of the box section cut out would be the side with the weld in it.
The bends you will end up with will be far more accurate than would normally be achievable in a home garage or workshop environment.
The bends will have been formed in a way that will ensure accuracy first time (no overbend, underbend, bit more, nearly there, pull it back, that will do!) and will have been done in a way that should avoid excessive working of the steel (rolling). That has to be better, doesn't it?
Bending 3mm plate is hard work, even if you get it right first time, every time, 24 times.

So is using box section stock for these brackets a bad idea?
Am I missing something?

Not a bad idea at all.
Remove the side with the weld seam as you said

That's what I did (see pics on my build diary...1st page about a 1/4 way down).

Only issue to be aware of is to make sure you round off the sides enough for the dampers...I left mine too square so had to come back and round over the edges a bit more (page 5 near the bottom ). But other than that it's all good

If you have a bench still saw set up and a simple wooden jig to hold the parts, cutting off the surplus should be easy. Also, if you don't already have one, I'd recommend buying a pillar drill with a vice on the table. This makes jobs like this much easier and a lot more consistent once the vice has been bolted down, your just swapping out the blanks and the holes will always be in the same place. Once finished with it you can resell it and will only lose a small amount of money if anything, although I'm sure you will use it many times. The more time spent making good simple jigs, the less time will be spent correcting mistakes.

Also don't skimp on the drill bits, buy good quality cobalt ones and they last for ages.

Thanks for the responses.
Glad I'm not going mad and missing something obvious.

As regards radiusing the brackets once cut and drilled I'd knock up a quick jig and clamp it to my linisher / bench belt sander and just wizz them around centred on the holes and done with it.
Just because it's not immediately visible doesn't mean it shouldn't be nicely finished.

I already have a reasonably equipped workshop - pillar drill, small lathe, decent benches, vices, selection of welders etc. but short of a project to use them on at the moment.
Hence looking at building a roadster.
It's a good excuse to buy more tools too! A steel cutting chop-saw looks like a necessary buy for this project, as does a hobbygas bottle kit for my MIG.

What you suggest will work and I have often done it. Just be aware that the box section has a residual stress in in from the rolling process and will distort somewhat once you cut the 4th side out. You will have to massage the bracket back to square.

Don't forget to add a little fill in gusset behind the brackets where the corner of the brackets overhang the angled tube at the front end. Brackets have been know to crack though here.

[Edited on 25/5/24 by Fred W B]

[Edited on 25/5/24 by Fred W B]

To save time. I bought a trial batch off Ebay. They are good and cheap enough.

Having watched metal bashers make stuff, would they not be made...

Steel strip
Holes punched
U shape formed on a press
Accuracy and fast repetition to keep the cost down

...just thinking aloud BTW.