Designing Anodized Parts

What precautions should be taken or features added to a part that is going to be anodized in comparison to a normal part? Do bearring holes need to be made slightly oversize? what about tapped holes?

when a part is anodized the thickness of the finish could be anywhere from 1/32 to 1/16 of an inch, i would suggest sending out a part to the anodizer and measuring it when it comes back

30 to 60 thou over? :eek:

In our experience it’s been more like 2-4 thou over.

How much time should usually be allowed for anodizing parts?

So, how do you compensate for that? Do you make all holes that much larger? or do the anodizers mask them off?

A machinist I know said for a traditional basic anodizing, the dimension added (outside the existing material) is so negligable .0002-.0003" that it doesn’t need to be considered for most bearing press fits. If you are getting into hard anodizing, it is possible you could add a thou or two, and then it would need to be considered.

Most colored (Type II sulfuric anodize, which is most common) should be anywhere from .0002 to .0008 thick.

Type I anodize (Chromic) is usually only .0001 and typically has no dye added.

Type III (hard anodize) is typically thicker than the above two.

What I’m concerned with are; bearing holes, holes for shear pins and threaded holes.

So, if the anodizing is for cosmetic purposes (Type II- thanks for letting me know Travis), the effect is negligible?

This is usually correct. Dont worry about it at all if you are just doing a regular colored ano. If you are doing a hard anodization, find out exactly which process you are using and contact the people themselves. They will tell you the thickness which will allow you to change your part dimensions accordingly. It should be noted, however, that “thickness” in the anodizing world refers to the total amount of material affected by the process, both penetrating and building. This means an anodize that is .0002 thick penetrates .0001 and builds .0001.

If your bearing hole is exactly how you want it to be, I would mask it so it does not get anodized.

Don’t worry about the threaded holes and the holes for shear pins or roll pins.

Andy B.

No, Type II is what you want then. Type I is more functional than cosmetic, as it has no dye added.

If your so worried about the bearing holes, why not just ream them out when you get the parts back? You cold mask them off or cork them.


In my experience, masking is the best bet if you already have the hole to the exact dimension and location that you want it. You can sometimes mess it up through reaming.

In terms of lead time, if you’re friendly with the company and they don’t mind working hard for you, it can be done fast. For the central mass teams, Dav-Tech plating in Marlboro is really good. I’ve dropped stuff off at 8am and picked it up at 4pm. However, a typically company, depending on the color and batch size, will take 2-4 days.

Also, if you’re anodizing very small parts, make some spares. Tiny parts are known for getting lost in the tanks.

To really save some time and frustration, especially if you haven’t worked with anodize before i’d suggest reaming holes out after you get anodize back. That is IF you are very concerned.

We used A LOT of anodized parts this year on our bot 125 in technicolor

We left our dimensions the same and experienced no real huge problems with items not fitting. If your very concerned i’d go with cutting your holes slightly smaller than your actual dimension and then reaming them out after, it guarantees a correct fit regardless, and no one will see it.

Yeah…that is what we did, if the holes were too tight.

But anodizing is really great, it makes the overall appearance look way better and more professional. I’m almost positive that it played some small role in the success of numerous robots this year.

I’m curious how many teams that anodize their parts build their robot (or parts of it) first, then tear it down and send it off to be anodized.

I’d love to find the time and the resources to get our machines anodized, but usually I’ll be hard pressed to take something apart once we’ve put it together and I’m a bit nervous about sending off parts that may not even fit together.

We never assemble anything before powdercoating or anodize. We check dimensions and slip fits, but do not do any final assembly at all. There simply isn’t enough time, as you said.

anodize everything if something doesn’t fit make a new part and just polish it so it gets that lovely shine…chrome look goes with everything :slight_smile:

Anodize/powder first, assemble 2nd…check your general dimensions, but there isn’t time to go ahead and assemble and breakdown and assemble again.

I love annodizing too, but doing it on such a time constraint is hard.