Thermal conduction relies on physical contact, which is easiest to guarantee with two flat smooth surfaces. Theoretically, two zig-zag surfaces that perfectly mate will give a better conduction as the contact surface area is increased. However, reality sets in and making two perfectly mating zig-zag surfaces is not easy. Easiest is two flat surfaces.
I recommend lapping the star and pill to remove any bumps that may be on those surfaces. Pills are really a pain because most have a lip around the edge. You need a rod with a flat end to get at the mating surface. A plate glass surface is best, but just a clean, smooth desktop will do (I often use a large aluminum heatsink). Use a randomish circular sanding motion.
As an eye-opening test, paint the surface of the star (or pill) with water-based paint and set the star on it. Then, look at the bottom of the star. The places where paint transfers to the star is where physical contact occurred. Usually the result is not much contact at all. Wash the paint off before it sets.
This is where the Thermal Interface Material (TIM) comes to the rescue. It fills the gaps to improve contact. TIMs usually have no where near the conduction of the star or pill materials, but they are much better than air.
It does, and that’s why I ‘wiggle’ the star around some to spread the TIM underneath. A good portion will squeeze out the sides, which is a good thing.
I have a few different types of TIM, and I find the thicker, pastier ones harder to get thin.
I find that Sharpies dry too quick. Paint has issues too, as it doesn’t go on in an even coat.
Pills surfaces are surprisingly non-flat. Probably should not be surprised though… most budget lights aren’t exactly precision machined
With the Sharpie, color in the area with dots, not scribbles. Even when dried it will still transfer.
Sharpies are great for stuff like fitting a reflector into a light it wasn't meant for, to see where a cut needs to be made when you can't see what's hitting where.
So, how DO you lap the emitter end of a pill when it is countersunk? I filled in the emitter end of a Defiant AAA light, but now I’m trying to figure that out. Here’s what it looks like now:
That piece that I added is kind of rough, and I was hoping that I might be able to use some kind of wheel on a Dremel, but I don’t see any that are completely flat (they all have a screw in them).
I used to have to lap hydraulic components to ensure a perfect seal at high pressure. We lapped on a machined piece of stone (granite?) with a full sheet of very fine wet-or-dry sandpaper and heaps of kerosine to stick the paper to the stone, and to stop the sandpaper clogging. I was taught to apply zero downward pressure to avoid sanding on an angle, just the weight of your hand is enough. I was also taught to sand in figure 8’s, rotating the component 1/3 of a circle every few figure 8’s to ensure even sanding as well. Hope this makes sense?!
I got Roche F8 from FastTech just so I could swap out the emitter. The pill and body are integral and deep. Dead center, under the star was a deep conical depression. It looked like the spindle of the lathe was attached to that spot (directly under the emitter). There was nothing to be done but fill it with arctic silver. There were screw holes, but no screws. I put some in , tightened it down and it seems to transfer heat well.
As I understand it, lapping is what you get at certain, uhhh, “gentleman’s clubs”. You have to pay extra for it, and the surface seldom stays flat… :party:
I find that Sharpies dry too quick. Paint has issues too, as it doesn’t go on in an even coat. Pills surfaces are surprisingly non-flat. Probably should not be surprised though… most budget lights aren’t exactly precision machined !http://i00.i.aliimg.com/img/pb/088/585/407/407585088_409.jpg!
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I just want to share this information:
Our Noctigon boards are actually lapped before the plating process to remove grooves that exist on the copper substrate.
You don’t even need TIM to make it sticking for a short time. Once i found a better video with much better surface tension effect, but i can’t find it anymore.
I almost agree w/ you…. BUT after many pills w/ craters or peaks at the center I wholly endorse at the very least a careful pill sanding to insure at least some degree of “flatness”. I’ve used wood dowels to make sanding sticks w/ a small sandpaper disk glued to the end. Only takes a few minutes to remove peaks or begin to level craters.
Maybe everyone can relate to lapping by the ceramic washer-less faucets that are available nowadays. 2 pieces of ceramic are lapped so fine that stop water from flowing without any washers or o rings.
I think that for badly machined pills it’s worth doing, although if it’s that bad then sanding isn’t really going to make much difference as sanding is a pretty inefficient way to remove material and there’s a tendency to deepen the low spots by accident. You’d be better off using a cylindrical roughing stone on a Dremel first, followed by sanding to remove the coarse marks.
For two relatively smooth surfaces, I think the difference will be largely undetectable by eye, even if it does help by luxmeter. That said, it’s not going to stop me from doing it
+1
A small granite surface plate is overkill but a nice investment if you use it often. I bought mine years ago for fixing gasket surfaces on small parts. I don’t know about using kerosene. Granite is somewhat porous so I only use tape and water.
This star i lapped today with 1500 grit, 6000 with abrasiv toothpaste, 6000 without toothpaste and finally 8000 grit paper (yes, the toothpaste is more abrasive than the 6000 paper, you can hear and see it). I made this photo and you see the blades of the shutter are not perfectly parallel to eachother, so still not a perfect flat surface.
