Connection Trick

[sgunn911]

After a couple of failed connections, I bought some soft aluminum ground wire from radio shack. I then used a tap and die set to thread the end of the soft aluminum into the matching hole on the part, works every time!

Also, I have used aluminum screws and cut the head off. I can then attach two parts together if there is a similar size threaded hole on each part, I can get a lot more production by anodizing more parts at once.

I sell m2, m3, m4, m5, 2-56 and 4-40 sizes in aluminum screws if you cant find any.

Scott

[NeoMoses]

Thanks for the info, sgunn911. Just a reminder, though, the purpose of these forums are to provide information, not to sell products.

[Fibergeek]

That's awfully small Al hardware for the aluminum wire Radio Shack sells, which is 8 AWG.

You would have an easier time with larger Al hardware or much smaller wire. You can get 1100 alloy Al wire (the softest alloy) in small quantities, most any gauge from www.mcmaster.com. Larger quantities at cheaper prices from www.parawire.com.

[sgunn911]

The parts I anodize use mostly 3MM screws. If I use aluminum wire and thread it, I have to have at least .115" diameter wire which is 9 AWG. 8 AWG is .125" and is readily available.

The aluminum wire has to have a little strength to it, as the 1100 alloy will just twist and snap when you try to thread it (or at least in my case). I use the threaded wire to connect the first part, and then aluminum screws to connect other parts to the first one.

I am not trying to market screws on this forum, as I don't sell them for this application. It would actually be more of a hassle for me to sell them here, I was just offering a source since they can be difficult to find in certain sizes.

[Fibergeek]

With enough experience; you will find that NO mechanical connection will work every time, not screwing, bolting, wrapping, clamping, or racking. This is physically impossible, because you can't guarantee a totally liquid tight joint every time with any mechanical method.

The most insidious connection failures are the partial failures; the connection resistance increases with anodization time, but not to an outright open circuit. Who cares you might ask? The partial connection failure causes the current density to fall during the process, changing the pore structure, reducing the rate of coating formation, and tipping the balance in favor of dissolution. You won't see it coming if you aren't monitoring you anodization parameters as you anodize. This is the dominant cause of inconsistent results, it usually shows up in the dyeing.
This effect can be avoided if you are using Constant Current mode (CC) AND your power supply has sufficient voltage compliance to accommodate the degraded connection. This doesn't work with racking if the surface area of the rack is close to or larger than the surface area of the work, titanium racking helps but won't cure it. Sufficient voltage compliance becomes the sticky issue in medium to large setups. it requires substantially more voltage to be available and increases the thermal load on the anodizing tank, both get expensive fast.

What I would really like to know; where did you find aluminum machine screws with fine threads? I could really use 1/4 x 28 if I could find them. Not for my anodizing, I weld all of my connections now, which makes them a non-issue.

I understand your reasoning for offering to sell aluminum machine screws here, and I salute you for your willingness to help. Thank you.

[sgunn911]

I buy the screws in bulk for my RC business. They are all socket cap drive, and are easily transformed into a connector by cutting off the head. I won't advertise, so check with fasterexpress.com or custom-rc.com for the aluminum screw collections. Custom-RC.Com is not fully completed yet, but the guy will bend over backwards to help anyone.

I do have a CC system, but found that titanium has caused me more problems than aluminum for some reason. Right now I get about 95% success with connections using the tapping system, or you can just get a torch and melt the wire to an aluminum screw.

[Fibergeek]

If you deliberately damage the thread a bit on the screw it will improve the connection. You want a liquid tight joint, this can be obtained by forcing one or both sides of the connection to cold flow under mechanical pressure.

I tried a micro torch to melt the wire a bit to improve contact some years ago. Besides being tricky to do properly (not severing the wire) any substantial heat directed to the aluminum adjacent to the screw causes this area to oxidize quickly (in a few seconds) the humidity in the air provides the moisture. This leaves a pale spot where the heat was, since the natural oxide formed partially blocks anodization. Not a good idea.

Titanium racking will work well if all of your parameters are tightly controlled, especially keeping the surface area of the load constant. Suspending the work from titanium wire causes more problems than it solves, since it won't easily cold flow. Its too hard, not to mention too expensive.