Aluminium frame assembly - what am I doing wrong?

[WannabeFramer]

I am assembling a small aluminium frame and can't work out where I am going wrong. It has perfect mitres when fitted without the brackets, but then each time I tighten the screws, the frame goes out of square. I can see and feel it moving out of square as I tighten the screws. I have tried holding it tightly, clamping it, bracing against a square. Each time the same. I am quite literally

I took a video to show what happens but I can't upload it.

What really, really obvious thing am I missing?

[theframer]

does it have the double plate hardware?
Are you using the 2nd plate if so?
Will it not tap back around when tightened up back into place.

[WannabeFramer]

I am using the fixing kit that came with it, one bracket for each corner. No, it will not tap back into place. If I slacken the screw off even a tiny bit I can wiggle it back, but it is then not secure.

This is with the brackets in loose:

7ca10bdb-56c1-4598-bb50-902ee9b8291a.jpg

Then tightened:

[Justintime]

Have you tried flipping the bracket over to see if it makes a difference?

[WannabeFramer]

You sir are a genius. Yes!! I was using the screws as they came in the brackets. Took them out, put in the other way and result!

This reverse way has Face stamped. Not sure which way it should be, but it worked.

IMG_0973.jpeg

[Justintime]