View Full Version : Anodizing my mill table (some pics)

04-13-2006, 11:57 PM
I finally finished anodizing the table for my mill project. Since I couldn't make the true cold (hard) anodizing work because of bath heat problems I settled for semi-cold anodizing which is able to build up a much thicker layer than decorative anodizing. It is perhaps three times thicker than decorative anodizing but not as thick as hard anodizing. It will do just fine to protect the aluminum table.

This is my anodizing setup. It's outside well away from the garage and anything else that matters because of the fumes it generates.


The hobby welder and the rectifier box are for providing enough current for cold anodizing. They work nicely too for warming up the bath when it is too cold for regular anodizing. There is a small battery charger in the left background that I use for regular anodizing. I have an assortment of high power resistors and ribbon wound pots for adjusting current.

These are two of the rails from the table in the anodizing bath. I monitor the current with the 30 amp DC lab meter in the background.


This is the table completed but without the linear bearings attached. I did some more work on the top of it and it is now close to optically flat, better than .0001" all over and in all directions.



04-14-2006, 12:08 AM
The one thing I wish I knew how to do better in the home shop is to get anything as square and flat as possible without having a surface grinder. The table looks great, you should point us in the right direction to learning how to get something that flat in all directions.

04-14-2006, 12:33 AM
Holly Cow! That's way too nice to do any work. It appears you'll be building a glass display case too. ;) :D

04-14-2006, 12:47 AM
Man,that looks like the buffet line at the last company picnic:D

Nice job,I am impressed.

One question,have you ever had trouble with screws not wanting to fit afterwards? Company I worked for did routinely until I finally convinced them to use H4 or H5 limit taps.They used to chew up taps regulary trying to open them back up after the anodize.

04-14-2006, 01:08 AM
Nice setup and nice work, Evan. I can't wait to see the whole thing together. You must be getting antsy too.

04-14-2006, 06:06 AM
Nice work Evan i wonder how you can get it so flat and square... i guess i need more practice.

John Stevenson
04-14-2006, 06:23 AM

This is the table completed but without the linear bearings attached. I did some more work on the top of it and it is now close to optically flat, better than .0001" all over and in all directions.

Yup looks good to 0.00001" from here.

04-14-2006, 08:51 AM
Evan, Beautiful work but just as I was about to joke about a "No-Mar" clamp set for the top, it occurred to me that you may have to restrict horizontal motion (due to the highly finished surface) as well as vertical clamping.

After reading a PM thread on washer solvent disposal which is degenerating into a sad southern CA "no machine shops here" commentary, your images of the chemical plant in the pines is a breath of fresh air ;)


04-14-2006, 09:06 AM
I didn't intend for the surface to come out that polished looking. It went in with a matte finish but I forgot about the electropolishing effect. Because the anodizing times were much longer and slower than for regular anodizing the polishing effect was enhanced. I still don't expect it to be a problem.

As for toxicity, there is nothing in the process that you can't safely throw on the ground. It even acts as fertilizer.

04-14-2006, 09:14 AM
I forgot to answer Wierd's question. You note that the screw holes are facing up in the bath. The anodizing is somewhat like electroplating in that it tends to "throw" line of sight. With the holes facing up there isn't much buildup in them. If they were through holes it would be different. In that case I would plug them with aluminum wire. The wire I use is electrical wire, pure aluminum and soft as butter. It forms its own thread when you wind it into the holes.

04-14-2006, 11:07 AM
Here in Iowa, It would be fun to see the reaction if the police drove by, and seen that set-up

04-14-2006, 12:19 PM
I think there were some guys in Utah not long ago that were able to get cold fusion with a setup like that.

Nice work, and yes, do please detail the saga of achieving flatness, squareness, trueness, and the resulting covetousness.



Alistair Hosie
04-14-2006, 12:20 PM
As usual very nice work Evan my dear friend very nice work Alistair

04-14-2006, 12:41 PM
an other Excelent piece of workmanship..

Allan Dimmock
04-14-2006, 01:27 PM
Our side of the pond, EU regulations say you should only do that sort of work in a Gothic castle, preferably during a thunder storm.

Frying tonight ! :)

I'm astonished at that finish. Excellent !

John Stevenson
04-14-2006, 01:37 PM
You forgot to mention the leap year and Alistair's bit with the sheep.

Cecil Walker
04-14-2006, 01:38 PM
Beautiful work Evan, I can only echo what everyone else has stated.

04-14-2006, 03:06 PM
Anodizing is easy and fun. That anodized finish makes the final difference on a lot of parts between a really nice looking "home made" part and a "where did you buy that?" finish.

"It would be fun to see the reaction if the police drove by, and seen that set-up"

Here too. That's why I have nearly all of the containers clearly labeled with the words WATER-DYE SOLUTION etc. Don't want the meter reader to get any strange ideas about what I am cooking.

04-14-2006, 05:21 PM
Evan, Keep some piles of sheep wool nearby, preferably dyed in several colors. :D

John Stevenson
04-14-2006, 05:29 PM
Leave my bloody sheep dog alone, don't want a different colour.

For a laugh one year we listed him on the electrol register as Graham White [ grey and white :D ] and we now get mail for Graham White.

I want to see what happens when he gets called for jury duty ;)


04-14-2006, 05:35 PM
Beautiful job,Evan.But I bet Alistair is disappointed,it's not GREEN!:D.

04-14-2006, 07:25 PM
Nice work, Evan. Roughly what thickness does the anodizing add to the part? Is it easy/hard to control thickness with this process?


04-14-2006, 07:33 PM
Using a warped straightedge I see! Just kidding; Excellent job.

04-14-2006, 07:53 PM
Very nice.

The idea of a hard aluminum mill table is not bad as long as you dont torque the hold down bolts down like crazy. (thats true with a cast iron table too)

I have seen pallet changers on cnc mills using aluminum sub plates that work just fine.

I have not run a cnc mill in 15 years , I would love a light duty cnc mill at home. I would do like david colfer and clamp a long arm to the table for torch and plasma pattern cutting off to the side. thats a home shops dream tool. :)

04-14-2006, 10:44 PM
The thickness of the layer is dependent on many variables including temperature, voltage, current, area of the part, electrolyte strength, electrolyte agitation, aluminum alloy, current type (filtered, pulsed, ramped...) as well as additives to the electrolyte. In other words, for the home anodizer it's a crap shoot.

The voltage and current are not directly related as you may think. As the layer grows thicker it provides more insulation and requires higher voltage to produce the same current. The ultimate maximum thickness is determined by the rate of buildup vs the rate of dissolution in the acid. Lower temperature means less active electrolyte and less dissolution and a thicker coating, but much more slowly.

I had to put my anodizing activity on hold today. It's one of the hazards of working outside up in this part of the planet.


04-14-2006, 11:19 PM
Evan: Great as always, but the set-up made me chuckle. Home work at it's best.

04-15-2006, 08:30 AM
Just to answer some of the questions about how I get it so flat:

If you ask my wife or kids (all grown) they will immediately tell you it's a clear case of OCD. I must admit to sometimes polishing parts that will never be seen but I put it down to attention to detail. A lot of attention to detail. Excuse me, I think I must go polish something...

04-15-2006, 09:09 AM

Short summer?

Nice looking part for the mill, are going to treat/color other componets?

OCD is in the eye of the observer, just be careful of what you polish in public...

Peter N
04-15-2006, 03:27 PM

Thats very impressive, I'd be happy to get that flat with my surface grinder (mind you, that thing was old and worn when Gods dog was a puppy:D ).

IIRC didn't I read that you intially hand filed the surface on this? Even more impressive then.


04-16-2006, 07:46 AM
Boy, late to the party as usual!

Evan Bayuteful work! I have some questions for you, specifically about dye and sealing methods? Also some clarifications.

First for those who don't know, they're are two types of common anodizing processes, Type II and Type III. Type III is the "hard ano" that Evan was referring to - basically it can only be dyed black, and is basically damn near impossible for the hobbyiest/DIY'er. It requires very, very high current densities(vs. the 4-12amps/sq foot for Type II), and loooww temperatures. Type II on the other hand works between 65 and 78F, easily maintained with an enclosed box and a surplus airconditioner.

Now for my questions - Evan were you using commercial ano dye, or were you using the frugal method of clothing dye? Also what temp were you keeping the dye at to achieve the results you did? About Sealing, did you use Nickel Acetate, or did you just dunk it in boiling water? And finally, did you use desmut, and what did you use to do it? The reason I ask is because I have a strong suspicion that you can use Ferric Cloride(the stuff they use to etch PCB boards, and available in Radio Shack), as a substitute - unfortunately, nobody I've asked can give me an answer on this.


04-16-2006, 08:34 AM
basically damn near impossible for the hobbyiest/DIY'er

Yep. I have the voltage and current but not good enough cooling.

You can however do a weak imitation of hard anodizing by using lower than normal temperatures and a weaker electrolyte. The final thickness is in part controlled when an equilibrium is reached between oxide formation and dissolution. The weaker electrolyte and lower temperature allows a thicker film to be achieved, albeit much more slowly. I anodized the parts for about 3 hours to a total current density of about 24 amp-hours per sq ft with the bath at about 45-50 degrees F.

I use commercial clothing dye with sometimes a little addition of ink jet printer ink as well as permanent writing ink. That gives better color fastness. Not much of my stuff is going to sit in the sun so fading isn't an issue. I seal in boiling water only followed by a complete wipedown with lanolin. Lanolin makes a very good final sealant for anodizing. It is composed of a variety of fatty acids, ester and alcohols which are able to penetrate the pore structure of the surface.

I don't desmut 6061 as it doesn't contain that much copper but I can confirm the ferric chloride is an acceptable desmutting agent for high copper alloys like the 2000 and 7000 series.

level head
04-16-2006, 12:25 PM
hey evan what linear bearings are you using on the x,y table