Cutter kit (the budget one)

As is common, you’re totally misunderstanding the point of a “heatsink” inside the unit

no i’m not, I know this! i didnt mention anything about fanned heat sinks… the heat sink I made was actually a cylindrical support (26mm of seatpost!) with cut outs to get round the switch and power inlet. This ‘spacer’ was then sandwiched between the back of the alu LED disc and the back surface (where switch and power connector go in) when the front screwed flange was screwed down it was all locked solid. I imagine that made a good as/better thermal path than a nearly-fitting slug of alu with compound filling the gap. however ,i couldnt get the driver to fit down the bore of the 27.2 dia seatpost chunk so just left it out as an experiment.

on the table in the kitchen, the housing got hot. riding outside the housing stayed tepid-warm.

and

since that air’s got nowhere to go it won’t help much with cooling your LEDs

is misunderstanding how heat is conducted through air… air doesn’t need to ‘go’ anywhere to extract heat from a solid.

I dare say that air is nothing like as good at conducting heat as alu, but it certainly conducts some. I totally admit more testing needs to be done with it, esp with regards to what temp the LED board gets too – the next plan is to strip the unit after 5 mins static indoor use and see what temp the board gets to relative to the body. I may have some direct contact between LED board and housing across the base of the board where i filed a flat.

by no ill effects, I mean the driver board didnt thermally cut out… maybe it doesnt have a thermal cut out.

Apologies – was making assumptions from your wording. The point being that heatsink isn’t really the correct term for what you’re using – though I accept it is now common usage. I agree what you’ve planned should be a decent thermal path – compression fit is always much better than just a contact fit.

air doesn’t need to ‘go’ anywhere to extract heat from a solid.

To extract a decent amount of heat it does – by new cool air coming into contact with the heatsink as hotter air leaves. With a fixed volume of air the heat extraction is very poor – air is a very decent thermal insulator when it is prevented from moving (is what sleeping bags use!)

I doubt the driver board has a specific thermal cutout, but then heat transfer to that will be almost as poor as transfer to the body. The chances are your LEDs are dimming due to heat (though you’ll not notice as it’s gradual) and you’ll also be decreasing their lifespan. If you’ve not got even a decent contact fit then heat transfer will be very poor.