Anodizing - part 2

Heating things up

All of the chemicals I purchased online at Caswell Plating have their own specific temperature ranges for best results, so it is crucial that I be able to accurately control the heating of the different solutions I’ll be using. My best option for this task is to rely on a PID (Proportional Integral Derivative) temperature controller.

PID testing

Since I have never used one of these units before, live testing on some benign substance was imperative before I started messing with acids, so I filled one of my buckets with 4 gallons of water and started with one of the eBay Chinese 1500W/120v heaters.

Test #1: 120V 1500W (12.5a) heater, in plastic lid. This had the advantage of being able to use a regular 15a outlet. 

Original setup with plastic lid

Unfortunately, the water temperature never got any higher than 140℉ at the top, remained in the 50s at the bottom, and it took over an hour to do so. Unacceptable! 

I need MORE POWER!

Test #2: 240v 4500W (18.8a) heater, in plastic lid. I disconnected my air conditioner, and hooked the heater up to the 20a outlet. 

One 240v/4500W heater flanked by two 120v/1500W Chinese heaters

HOLY CRAP! That’s some power! The bucket was glowing orange from the part of the element sticking out of the water. The experiment was terminated after melting the lid, and briefly getting electrocuted once or twice.

This plastic is obviously out of its league

Unfortunately, this heater died an early death, possibly due to overheating of the parts sticking outside of the water (the ones glowing), and I was unable to do any further testing with it. 

Obviously, there is a definite need to keep these things as submerged as possible. 

Test #3: I decided to double up on the Chinese heaters, even though I knew my electrical system might not be able to handle it. Using two 1500W heaters at 120v would draw 25a, more than my 20a well pump outlet could supply, but I irresponsibly decided to try it anyway, relying on the circuit breaker to prevent burning down my house. 

Stupid… I know.

Anyway, I fabricated a steel holder for the two heaters, as not to melt any more plastic lids. This holder allowed the shorter heaters to be nearly fully submerged without touching the bottom of the bucket.

A CNC mill comes in handy in so many ways!

These heaters will need to get further down into the water (not in photo)

Fabricating an improved heater support

Splendid!

This actually worked great... initially. 

When the circuit breaker started tripping, and the electrical cords became warm to the touch, I decided to put an end to this madness before I burned the house down for real.

It started to look like doubling the voltage, ergo halving the amperage, was the only real way forward (that would explain why there are so many more 220v units for sale). 

So, back to the store I went. This time to pick up a 220v 3500W, and a backup 220v 4500W. Both of these heaters extended the same length into the water as the eBay ones, about 10" (25 cm), compared to the now defunct 13" (33 cm) long one.

If these don't work, it's all over.

Test #4: I chose the 220v 3500W (14.6a) for this test, and it proved to be a good choice at last.

Capturing the beginning of the test, water temperature is 85℉ at the top (and bottom)

25 minutes later, I had 4 gallons of boiling hot water!

A little while later, we-are-smoking!

PID boiling 4 gallons of water

Temperature data for test #1, #4, and the newest 4500W unit (note test #4 started at 84℉)

One important side note, is that I used a long ruler once or twice in all of these tests to mix up the water, because the heaters create layers of different temperatures, with the hottest water near the top of the bucket, and the coldest near the bottom. 

This worked well with a bucket of water, but I wouldn't want to be forced to stir some toxic acids if I don't have to, so some device that agitates the water would be a definite advantage.

I have not figured out what to use yet, but you'll be the second to know when I do.

Anodizing - part 1

Setting up shop

One of the collateral tasks of building any airplane, including a composite one, is making sure that metal parts are protected from corrosion. Although aluminum is not as susceptible to corrosion as chromoly steel is, it will still eventually succumb to this oxidizing plague, especially if the plane is kept in a coastal location.

   

I have previously used Alodine to protect my aluminum parts, and I have liked the results, but while effective, it has had a few issues that have forced me to search for an alternative.

Chemically etching the main gear fwd attachment point (the gasses were atrocious).

Same part in the Alodining bath. 

Among the things I dislike are its high price, difficulty of acquisition, toxic fumes, dangerous nature of the chemicals, short shelf life, difficulty of disposal, weakness of the alodined layer, and the occasional mixed results.

Anodizing can also be done at home, but has some advantages over Alodining. Chemicals are cheaper, easier to find (battery acid), fumes are slightly less toxic (basically hydrogen and a few other unpleasant gasses), shelf life is longer, acid is very diluted (15% H2SO4) which is more easily disposed of, finish is much tougher, and wide variety of colors to choose from.

A quick look into titanium and aluminum anodizing

Anodized parts in different colors

Finally getting a small return on the cost of College tuition, I was briefed by my daughter (chemical engineer and PHD student/researcher) on the damages sulphuric acid can inflict on bare skin, and how one of her acquaintances had to take a semester off from school waiting for his flesh to grow back, after an accidental splash. 

The main drawback to anodizing is the more complicated setup, and procedure. 

Anodizing requires the parts to be perfectly clean, so a heated degreaser bath at 130℉ (55℃) is used. 

Aluminum degreaser

A heated de-smut bath, at 70℉ to 110℉ (21℃ to 43℃), eats the non aluminum metals off the surface, presenting a purer aluminum exterior to be anodized. 

Aluminum De-oxidizer/De-smut

The anodizing takes place in a bath of 70℉ (21℃) 15% diluted sulfuric acid, using a constant current power supply connected to a lead (Pb) or aluminum plate on one side (cathode), and the parts to be anodized on the other (anode).

Lead plate hanging off titanium wires

3 gallons (12 liters) of battery acid

Anodizing creates a non-conductive porous surface, that readily accept color from a heated dye (140℃ or 60℃). 

Golden orange and electric blue anodizing dyes

The surface can be subsequently sealed using boiling water, or a 202℉ to 210℉ (94℃ to 99℃) sealer solution (for better results), to lock in the color and corrosion protection.

Anodizing sealant 

The results are so dependent on cleanliness of the parts, and adherence to the steps listed in the instructions, that even a  single fingerprint will show up in the finish.

With anodizing the surface of the part actually grows slightly, perhaps by 0.002” (0.05 mm), and hardens, making it more scratch proof, though marginally weaker.

Armed with all these facts, I decided to go for it, and started looking for some sturdy 5 gallons (19 liters) buckets that I could use with heated acids. The ones I settled on are 30% thicker than the usual ones for sale at Home Depot or Lowes (0.090” versus 0.070”).

High Density PolyEthylene is resistant to many different solvents  

HDPE plastic can withstand pretty warm temperatures (120°C/ 248°F for short periods, 110°C /230°F continuously)

I also decided to purchase Gamma Seal water proof spin-on lids in order to safely store the chemicals when not in use.

Gamma Seal lids 

When the buckets arrived, I filled up one ½ gallon at a time, and recorded the water levels on the outside. Afterward, I recorded the distances from the bottom of the bucket to all the water levels.

Master bucket graduated in ½ gallons, and inches from bottom.

This would become my "master bucket", and I used the distances to mark the rest of the buckets.

Marking another bucket with ½ gallon graduations, based on distances from bottom.

I bought three 1500 watts immersion heaters from China that will be used to warm up the different solutions (I wish they had come with matching nuts).

1500W immersion heaters

Multiple PID temperature controllers will regulate the heating elements immersed in the various baths, keeping the solutions at the desired temperatures, or at least that is the idea. 

I ordered this one on eBay as a proof of concept, and will purchase more once I get it wired up, and get it working correctly.

Temperature controller

Because I didn’t want to poke any holes in my expensive colorful waterproof lids, I decided to use the ones that came standard with the buckets as “working lids” in which to drill holes as needed. Besides, I was going to toss them anyway.

Roughing out a 1.6" (4 cm) hole

Heater screwed into the plastic lid

Lid supporting the immersion heater

To prevent touching any of the parts after the cleaning stage, and to avoid getting near the various acids, I made a hanger for the parts out of leftover steel I had laying around from the computer stand project. It looks like a fishing pole for parts, with titanium wires.

I love having a welder standing by. Here I am welding a handle to the parts holder.

The “fishing pole” is not able to get too close to the lead plate, thanks to the two vertical tabs. This way the parts should remain well clear of the cathode, thus reducing  the possibility of short circuits.

This is as far as the part holder is able to go toward the lead plate 

The parts hanging in the empty bucket are scraps I am using for reference, though they will get anodized during initial testing.

Later, I decided to weld another retaining tab, recycling more scrap steel, to keep the parts hanger from being able to slide backward.

Using a welder this way is like working with a glue gun for metal

Multiple screws will allow flexibility in arranging parts

The little tab under the handle hooks the rim of the bucket, and prevents backward movement of the parts holder.

Using this hanger, I should be able to go from bucket to bucket, rinsing in between (in a water bucket), without ever touching, or otherwise disturbing the parts.

At least, that is the main idea. 

I plan on keeping a detail log of all the variables involved with each anodizing session, for the purpose of improving quality.

Anodizing bucket array

It remains to be seen how the implementation will work, but I am hopeful for good results in time, as I experiment, and tweak my anodizing recipe. 

CNC mill conversion - part 21

Fixture plate

There are many ways to hold on to stock material for machining. 

Up until now, I have been using typical devices such as vise, clamping kit, or adjustable clamps. They all have their pros and cons.

Stock held in the vise

Extremely versatile clamping kit

Adjustable clamp

The vise has always been my go-to device. It’s easy to use, but it is also limiting in many ways. It needs to be aligned with a dial indicator every time it is mounted, it raises the stock thus limiting Z axis effective travel, it leaves longer stock overhanging and unsupported (as in the first photograph), it is generally not very repeatable, and the parts held are not always completely leveled without the aid of a dial indicator.

The clamping kit is a lot more versatile than the vise, but has most of the previous drawbacks, on top of being more difficult to setup. If that wasn’t bad enough, the clamping kit is so big that it consumes half the space on the milling table. 

The adjustable clamps are pretty cool. Compared to the clamping kit, they are easier and quicker to use, and while they are smaller, they still take up a lot of real estate on the mini-mill small table.

Milling has thus far been a somewhat frustrating experience, mostly due to the difficulties involved with set up. It is not uncommon to spend more time coming up with creative ways to hold on tho the raw material than actually machining it.

A better way to go about it, is using a fixture plate.

Fixture plate

A fixture plate (also called a tooling plate) makes it easy to quickly mount things and be assured of perfect alignment. A fixture plate is a metal plate, clamped to the mill table, with many precision spaced holes, some threaded, and some for dowel pins. With it you can precisely bolt parts, vises, and other accessories to the table, and they'll be right the first time/every time.

With very high expectations, I decided to purchase one online…

Purchased from deepgroove1.com

… and mounted it on the the table.

The fixture plate did not come with T-nuts, so I had to make my own.

To create a visual representation of the surface area I can machine, I placed a permanent marker in the spindle, and marked the fixture plate with the outline of the effective travel of the mill. In other words, everything falling inside the black rectangle can be reached by the spindle, and machined, and after the last few improvements I made to increase the X and Y travel, this area has grown quite large.

Scope of the mill outlined in black

I mounted the two straight bars that came in the kit parallel to the X and Y axes, so that I will be able to shove parts in the corner, and lock them up with the supplied cylindrical clamps. These clamps are pressed against the part by the action of eccentric bolts.

Eccentric bolt vs standard

Eccentric bolt in the clamp

Stop bars and clamps setup for brake bracket

This method of clamping is very fast, and very repeatable. I practiced clamping on and off an odd shaped object, the brake bracket, and it worked beautifully.

Bracket clamped securily

Note the different size clamps

Bracket can now be removed, and precisely replaced in seconds.

How to use the fixture plate