Dave
I think you misunderstood, or didn't read closely enough
OR BOTH
I've already got the back plate to affix the fan and speed controller to, so I don't need the aluminium sheet.
I've already amrked out the places where I have to cut to allow access to collimation screws and where the fan's going to go. I'll figure out the controller units pozzie after that.
What size fan and where do I get a variable speed unit?
What about vibration dampening? Power considerations?
Got any pics of where you attached the temp sensor on your primary? It'd need to be out of the direct line of fire of the fine, wouldn't it?