Mercury arc rectifier

[Radio Fixer]

"metamerism" is very interesting Jeffrey, I had not the term before. Come across the effect though when trying to match touch ups and resprays on old radios. I just used to use cloudy daylight and accept that under other light sources the match might not be so good.

As for the panel you dont say how big but clamp and a file might be as good as the sander.

Gary

[ppppenguin]

It's about 36 inches by 12 inches. So about 48 inches to cut down slightly. Tedious!

[Mark Hennessy]

If you could find a local woodworker with a table saw, that would be a trivial operation. They are quite happy to remove a tiny fraction of a mm if needed. Most sheet plastics cut really well with standard or fine woodworking blades in my experience, though I'd probably do a quick test, just in case.

[Mike Watterson]

I've used my flatbed tile cutter (spinning wheel in dish of water) to cut plastic, thin metal sheet, hardboard and plywood. Bought for quarry tiles.

A plane might work too.

[Mark Hennessy]

A router guided by a straight edge would also work. More measuring and setup, but routers are much cheaper and easier to store than a table saw. Depending on the exact type of plastic, it might be best to do it in multiple passes.

[Mike Watterson]

A router guided by a straight edge would also work. More measuring and setup, but routers are much cheaper and easier to store than a table saw. Depending on the exact type of plastic, it might be best to do it in multiple passes.

I think a cheap router is likely better than a table saw for this.
You can clamp a plank as a guide.

[ppppenguin]

I've got a router so that's probably the answer. I'll clamp the original metal panel to the plastic, the screw holes are ideal for this as they will be needed in the plastic. Then clamp a guide bar suitably inboard. If the router cutter gently touches the metal it shouldn't do much harm to either the cutter or the metal.

There are a couple of rounded corners which I can cut with a fretsaw and sand to final finish. Or dare to rout freehand with the metal panel to stop me going too far.

[BusyBee]

I only do small pieces for projects but I tend to use a file for almost any type of material as I don't have the machine tools. It's very tedious but acurate enough.

Tracy

[Mark Hennessy]

As you have the original panels, you don't need a straight edge, and you can also do the rounded corners at the same time. Just bolt them together and use a straight cutter with a guide bearing, e.g. https://www.screwfix.com/p/bosch-1-4-sha...-7mm/994fw

That's just an example - for that money you could buy a selection box of router cutters that includes one.

If the panels are aluminium, a router will cut through them with ease, so make sure only the bearing is able to contact the metal.

There is a slight gap between the bearing and the cutter, so you'll need a shim between the two pieces - otherwise you'll end up with a sharp ridge on the plastic, which could be hazardous during cutting and obviously afterwards.

Anything will do within reason. The minimum thickness is just a case of assessing the gap - usually 1 to 2 mm - and adding sufficient margin to make sure the bearing is always in contact with the original metal panel - between 1/3 and 2/3 of the bearing thickness (most often 5mm), so 4 to 5mm would be a good start. The maximum thickness obviously depends on the length of the cutter.

[ppppenguin]

I think I've got one of those cutters. The panel is steel so an occasional touch from the router probably won't harm it. Good idea to add a spacer, I've got various thin sections of wood including a load of slats from an old venetian blind which are good for making shims. Almost impossible to run the roller on a 1mm or so thick panel that's in contact with the plastic.