why are laser diode housings mostly brass or copper?

[-bart-]

Copper is used for good thermal conductivity.
Brass, allthough a coppercontaining alloy, conducts heat much worse than aluminium. https://en.wikipedia.org/wiki/List_o...conductivities

Bimetalic effects cause bending and warping. Objects that are homogenic and evenly warmed just expand. https://en.wikipedia.org/wiki/Thermal_expansion

[Bbe]

Pure aluminum you are unlikely to meet in metalworking, most often it is 6061 or 2024 alloys.

Brass, allthough a coppercontaining alloy, conducts heat much worse than aluminium

The difference between brass and aluminum alloys is not as significant, ~110 vs 160 W/m.K. Furthermore, if you will use anodized (colored) diode mount, you will get a worse result than with similar brass mount - oxide film has a lousy thermal conductivity.

If you choose between brass and aluminum - will be better if you'll take care of a good thermal grease.

[Draco]

aluminum to aluminum threads suck, they can gall and make for one nice unserviceable mass as well

[ghosttrain]

I understand the reasons now. But DTR seems to sell aluminum housings and EGB modules using those, as well as old DPSS modules seem to use aluminum. So I don't know if if in practice aluminum will really bend and cause issues. My aluminum heatsinks on several devices get in the 80C range, I don't notice them bending. At 100C I do though on 5mm 3d printer heatbeds.

[planters]

The practical effect of the differences in thermal conductivity of copper, aluminum and brass for the heating caused by several watts of heat into structures as large as a diode mount is negligible. When the loads become more intense such as the diode flange itself or in diode bars that move hundreds of watts then copper becomes useful and that is why you see it there. The state of the art is CVD diamond heat spreaders or graphene film interface layers.

Far more important than the thermal effects for low power projectors is mechanical stability. Steve is right about the need to produce thick (or thick like) robust structures. The alignment will drift due to flexure earlier then from thermal effects.

Brass is a joy to machine. It is even easier to machine than aluminum and the thread fit can be better. I think it is the aluminum oxide layer that creates the initial binding that soon leads to destructive galling when aluminum and aluminum parts slide together. You can use PTFE tape to defeat this effect or anodize the surfaces or use a different metal for one of the sliding components.

Copper is nasty to machine. It is even heavier than brass and it is very expensive.

[Draco]

is the reason for machining copper a nightmare because of it's malleability? or does it clog the tooling or grab on to it? I only have a basic understanding of machining so i am sorry is that is a newbie type of question.
the galling that aluminum does is outright engraging when it comes to threaded parts, in an earler thread on a 300mw green pointer i destroyed because the plate that mounted the diode galled with the housing, the jam is so bad i might as well have welded the parts to each other, i broke two pairs of pliers trying to in screw the plate with the diode, i atlest was able to save the crystal and the optics but the body is junk and i cant find another host. it was easier buying a whole new Chinese table top laser and build an adapter to run on batteries.
since then i have been using a housing that has a brass insert with threads so i can remove a diode from it with out destroying the diode, thats the only reason i dont use DTR's housings but it does make for a larger arrangement

[planters]

or does it clog the tooling or grab on to it?

It's a little odd. Lead is notorious for grabbing tooling, but because it is soft, if you control the feed and clean the cutting edge occasionally this is pretty easy. Hardened steels are obviously hard on cutting edges, but they tend to shatter off and so doesn't grab. Stainless steel's very low thermal conductivity screams out for excellent cooling flow and sharp cutting tools. Copper grabs a little like lead, but its strength means that when it does, only a little grab and the material will overload the strength of the tool.

There are some neat thread insert/ lead-screw pair kits that although more expensive than simply cutting your own threads when machining, they have the fit, feel and precision of high end optical screws. Some are press fit others are course threaded into a larger outer hole.