I've been working on a CNC project for quite some time. One of those I'm going to finish this someday projects...
I changed my motor controller over to an Arduino based design that uses the Pololu motor control modules (very common in the 3D printer arena). They recommend heatsinks and forced cooling for long life of the modules - naturally.
The modules I got had nice little alum heatsinks like you see on motherboard chips and the like but no means to attach them. And since this was a pretty critical component I figured the attachment method should be pretty good.
I found a zillion different methods but the one that looked the best and most reliable was an epoxy made by the Arctic Silver people. They are the guys that make the best heat sink compound for computer CPU's. They actually have an epoxy. The official name is: "Arctic Silver AATA-5G Arctic Alumina 5g Thermal Adhesive Epoxy Set" -- most places have it in larger tubes for about $30. I found it on everyone's favorite water auction site, eBay.
Here's a link to the 5 gram tube set I bought, the vendor was "Super Star Click" if that link doesn't work. It was $6.53 and you're only supposed to use the slightest amount and clamp it good. Plus, even though it has silver in it it is non-conductive(huh?). Which might help if some squeezes out in the wrong place...
Just thought I'd pass this on. I'm thinking a 5g tube will glue on a lot of heatsinks.