hard anodizing, Machine-ability and thermal transfer?

[kitatit]

Hey guys,

I've got a couple of questions to help me decide on which surface treatment I use for my mini RGB projector.

As you can see from the pics the case is integral to the heat dissipating surfaces and I'm in two minds what type of anodizing to use.

My choices are normal black anodizing or the greyish hard anodizing.

The issue I can see using normal black is it abrasion resistance and it will be going in and out of my back pack when I fly to work on an iron ore mine (lots of fine abrasive dust around).

The issue with hard anodizing I'm worried about, is it not being able to dissipate heat effectively in this compact design, (it's about the size of a 15' notebook and 50mm thick)

Does anyone know how much this will compromise heat dissipation?

If I go for hard anodizing I could machine it off where I need heat transfer.

@ Chad or other machinists, Have you machined hard anodising? I know normal anodizing is hard on tooling. Would you use carbide or nitrided tooling? or maybe just sacrifice a HHS cutter?

I know this is a bit OTT planning, but I just want to make it the best I can.

Any thoughts or opinions?

Thanks Kit

[dnar]

My experience with hard anodizing is the thermal resistance is not much different.
You might experience radial "cracks" from any holes drilled AFTER the anodizing... It looks much worse than it actually is.

My 2c - go with black. Wear marks are not that bad IMHO. The case will always look $1,000,000 once the beam show commences.

Nice job on the 3D design. I hate you.

[taggalucci]

I saw this design when Kit was over in Melbourne and it''s nothing short of impressive! To get a set of scanners into that height is quite something.

I can't wait to see the finished product. I'm currently working on my contender for the micro-projector. Not quite the same form factor, but should be pretty compact (with significant power supply design help from Wayne).

[kitatit]

My experience with hard anodizing is the thermal resistance is not much different.
You might experience radial "cracks" from any holes drilled AFTER the anodizing... It looks much worse than it actually is.

My 2c - go with black. Wear marks are not that bad IMHO. The case will always look $1,000,000 once the beam show commences.

Nice job on the 3D design. I hate you.

Thanks Wayne,

Thats what I needed. Yep I'll go black. I won't have to worry about dimensions as much either.
If the corners get to worn out I'll just use a black Artline on it.

I saw this design when Kit was over in Melbourne and it''s nothing short of impressive! To get a set of scanners into that height is quite something.

I can't wait to see the finished product. I'm currently working on my contender for the micro-projector. Not quite the same form factor, but should be pretty compact (with significant power supply design help from Wayne).

Thanks for the props Tony. Damn! I wish I new Wayne before I committed to my power supplies. I'm using some little XP Power units so they are pretty small though. I'm not out of the woods yet, I might have to file a tiny bit off the PCB on the top scanner to fit it in.

Actually, Wayne, could you give us any pointers on building a driver for my GM-20 shutter? I wouldn't mind making up one with solder mask so it looks the part. Maybe do a board full if anyone wants one to.

Maybe I could do it in SMT so I can use my reflow oven again. Do you know how to make the Gerber files to give to PCB fab Co?

[taggalucci]

I've recently bought the parts to build this circuit...

http://www.photonlexicon.com/forums/...9465#post99465

[mixedgas]

It chews off and cracks when you mill it. The effect is localized, and you can hear the cutter complain, but you will not lose a cutter.

Steve

[chad]

It chews off and cracks when you mill it. The effect is localized, and you can hear the cutter complain, but you will not lose a cutter.

Steve

Kitatit,

In my experience mixedgas nailed it. You can hear it cutting, it sounds strange but a sharp tool can get through it. I use carbide for pretty much everything now days.

As for thermal I wouldn't worry too much about it. Remember anodizing is a Aluminum Oxide layer deposited on the aluminum base material, typically 5μm to 15μm thick. Black anodize is the same material, dyed then sealed, same with all colors.

Hard anodizing is usually the same process but much thicker, 12μm to 150μm. This gives it more wear resistance for extreme environments (your back pack isn't one of them) but will also provide much more of a thermal insulator because of thickness.

If it were my project I would just go with standard black and not worry about machining anything off after. The ~10μm thickness of Al2O3 is not going to make much difference in thermal performance. Everyday room temperature differences are going to do more to the thermal efficiency than a really thin layer of Al2O3.

$.02

By the way gorgeous little projector!!

chad

[BShanahan14rulz]

Does the "thermal insulator" property of anodizing nullify the radiative properties you gain from the change to a darker color plus the increase in surface area of the anodized metal?

iJel

[dnar]

Actually, Wayne, could you give us any pointers on building a driver for my GM-20 shutter? I wouldn't mind making up one with solder mask so it looks the part. Maybe do a board full if anyone wants one to.

Maybe I could do it in SMT so I can use my reflow oven again. Do you know how to make the Gerber files to give to PCB fab Co?

I have been thinking this might be sufficient. http://littlebirdelectronics.com/pro...er-control-kit

I'll get some in and try them out.

EDIT: I ordered 3 x MOSFET board kits. I will test with a GM20 next week when they arrive.

[csshih]

Does the "thermal insulator" property of anodizing nullify the radiative properties you gain from the change to a darker color plus the increase in surface area of the anodized metal?

iJel

From what I've heard the anodized black aluminum surface is much better than a mirror polished surface.

Craig