Etching zirconium oxide with hydrofluoric acid

I am currently working on a project where I need to replace a standard mouse ball with a non-metallic equivalent. Normal mouse balls are built from a steel core that has been coated with a thick layer of rubber. I can't use any metal in my project, so I must find a replacement. The main requirements are:

Ball must be very dense
Ball must be non-magnetic and non-conductive (ie non-metallic)
Ball must be coated with rubber or naturally have a high friction coefficient
Outer diameter 7/8"

My first solution was to use 7/8" glass marbles. These are not easy to find, but they are available. The problem is that the marbles are not perfectly spherical, and they are not nearly as dense as the original mouse ball. The lower density means the ball weighs less and will not track smoothly on the mousepad surface, since it sometimes skips and hops. I was able to etch them with hydrofluoric acid, spray them with primer paint, then coat with with spray-on rubber. They worked OK, but I have a better solution now.

I found a source of 7/8" dia zirconium oxide balls (http://www.ortechceramics.com/). This stuff is a ceramic, but 2-3 times as dense as glass. It's non-metallic, and the balls have very high sphericity. The problem is that the balls come very highly polished, and the paint will not stick to them. I tried etching them with standard glass etching cream, but there was no effect.

I found that a local lab supply company (http://www.lab-proinc.com/) sells 50% hydrofluoric acid (HF). I bought some and initially made a small 10% dilution. The ZrO2 showed no etching after 1 hour of full submersion in the dilution. I upped the concentration to 20%. Still no effect after 30 minutes. Finally, I submerged the ZrO2 in straight 50% HF. After 10 minutes, I could see the shine starting to disappear from the balls' surfaces. After 20-30 minutes, the balls appeared to have enough etching so that they would hold paint well.

Hydrofluoric acid is scary stuff. There are reports of it penetrating skin painlessly then dissolving bones and causing blood toxicity. Standard nitrile or latex gloves only provide splash protection -- ie if the HF is spilled on the glove, immediately remove the glove, and get a new one. HF will penetrate the gloves if left in contact for too long.

I was surprised to see the 50% HF was actually 'fuming'. When I left it in the open container, I could clearly see vapor droplets coming off the surface. If I blew across the surface of the HF, more vapors were produced. I am not sure if it is reacting with water in the air/breath or what. I didn't expect 50% to be fuming.

More Cosmiar 12.5mm f/1.4 sample images

Cosmicar 12.5mm at f/1.4




Cosmicar 12.5mm at f/8

Adapting a Cosmicar 12.5mm f/1.4 c-mount lens to the GH1

The micro four thirds (and standard four thirds) camera format makes it possible to use old c-mount lenses with decent results. The lenses with shorter focal lengths will not cover the image sensor fully, but it seems that anything 25mm or longer will have full sensor coverage. These lenses are very cheap (eg $30), and the quality is surprisingly good.

This is the cosmicar 12.5mm f/1.4. I got it here:
http://www.surplusshed.com/pages/item/l10128.html

One problem is that the fast, short focal length lenses have a very wide barrel. In fact, it is too wide to fit into the micro four thirds -> c-mount adapter. I machined both the adapter and the lens so that they would fit together and also achieve infinity focus.

The lens has a brass mounting plate with the C-mount threads on it. It comes off very easily by removing the three screws around the periphery.


I used a lathe to cut an angle onto the edge of the brass mounting plate.

I cut the same angle onto the C-mount adapter. I bought mine from an eBay seller called rainbowimaging.


I'm pretty sure infinity focus has been achieved. If you think this image looks soft, it may just be the overall characteristic of the lens. It is $30.

The real benefit of theses lenses is that they are very fast (f/1.4) and wide, so they are ideal for indoor video. The 16:9 format works a little better with the image circle produced by the lens.

This has been very helpful in choosing lenses:
http://spreadsheets.google.com/pub?key=p9kkgjwEQQQ-HJwvNDobeEw


Also note that this is my second attempt in adapting the cosmicar to the camera. I had bought a c-mount adapter previously and machined it without machining the lens. I eventually machined away so much material (accidentally) that the adapter became too weak and broke immediately. I then realized that some material must be removed from both the lens and the adapter to make it work.

DIY heated computer mouse

I modified my standard, cheap Logitech optical mouse to include a small heating element. This really helps out on those cold nights when I am too cheap (or energy-conscious) to turn up the thermostat.



I opened the mouse, and located ground and +5V locations on the circuit board. I added two strings of 1/4w resistors that each have 4 10-ohm resistors in series. Each string is 40 ohms, so at 5V, this comes out to 5/40 = .125A or .625 W. The total heating power is 1.25 watt, and the total current (250mA) is well below the 500mA limit for each USB port.

DIY Steadicam construction

A steadicam is a device that is built to reduce the camera shaking and rotation that is associated with hand-holding a video (or film) camera. Everyone has seen the Blair Witch style footage where the camera is bouncing around and being shaken to death by the person holding it. Even the most trained camera operators cannot hand-hold a camera and walk without the footage showing some shaking. The steadicam greatly reduces the amount of shaking and provides much smoother footage.

The name "Steadicam" is actually a trade-marked name thought up by the Tiffen company who invented the first one. However, like Xerox, the name steadicam has come to mean any camera stabilization device. A very popular model is the Tiffen Merlin Steadicam. It looks something like this:

This is a copy of the Merlin that I built from junk parts that I had lying around the shop. In this photo, it is shown holding my friend's HV20. The construction has been detailed in other places on the internet. Here are the best places to start looking

http://www.youtube.com/watch?v=4pLBUC-O1js

http://rafgodlewski.wordpress.com/2009/05/02/diysteadicam/

http://www.diycamera.com/stabiliser/index.html


The water bottle on the bottom of the stabilizer can be filled and emptied to adjust the amount of mass at the lowest point of the system. Ultimately, it may be best to replace the mass with metal (washers or similar), but the water is great for adjustment and testing. The gimbal joint is a Traxxas 4949 "half-shaft" for large RC cars. I have two radial ball bearings inside the handle -- these are similar to skateboard bearings in size and quality. The aluminum plate is 1/8" thick and I drilled it to accommodate different camera mount positions. The aluminum square tube is 1/8" thick 1"x1" with a slot cut lengthwise along the bottom for balance adjustment.

The curved piece of metal is a large sector from a lazy susan bearing (aluminum). The handle was made from 1" aluminum bar stock.


Areas for improvement:

Instead of drilling a bunch of holes in the top plate, it would be better to cut a series of horizontal slots. I found out that the side-to-side balance is critical and having a slot would allow much finer control than jumping to the next hole. The front-to-back balance can be adjusted via the slot in the aluminum square tube, so it will be fine to move from one horizontal slot to the next in the top plate as long as fine horizontal adjustment is attainable.

The friction of the bearings and gimbal must be as absolutely low as possible. The traxxas gimbal has 3mm pins, and the corresponding holes in the plastic gimbal parts are a little tight. I happened to have a reamer of just the right size to loosen the fit. In its original form, the tight-fitting pin will transfer too much motion to the camera. Likewise, the ball bearings in the handle must be super low-friction. Using sealed bearings will probably not work because the rubber seal will create too much friction. If I were building another steadicam, I would focus even more on getting a super low-friction bearing system.

I might try experimenting with making a longer balancing arm. If the lower mass hangs further below the pivot, less mass will be needed, and the longer pendulum will favor slower oscillations. It seems like win-win, but the device may be more difficult to carry and use.

Panning control should not be ignored. I found myself gripping the traxxas shaft with my finger tips to control the camera pan, and this worked pretty well. Adding a knurled wheel might be nice.