Do you have a router? If the alloy plates are very close to size.... attach them to the pattern, and run a flush trim bit around them. Then remove the pattern and knock the edges off with a rounding over bit. High speed. thin cuts and wear a jock. The rounding over part is easy, the trimming part can be dangerous if trying to remove too much material.
Since you are a wood guy...
Thanks for that,
Yes I`ve got a Router, actually got eight at the moment & that made me look on Youtube to check the possibilty of using one.
I made the first pattern out of ply then used that to make the first plastic one which I cleaned up by hand & used that to make the second one using a bearing guided cutter to follow it.
Then once I`d checked the fit I used the same setup to router the Aluminium brackets.
I used double sided tape to attach them each time but should really have put the router in a table to get better results instead of free hand like I did.
Cheers
Dave