[seanc]

Greg:

So you say not to adjust the voltage. Should I then turn it up to 30 volts and let it adjust itself?

Exactly. As long as the voltage is set HIGHER than the most it will actually have to deliver, that's enough. As you can see in your photos, the voltage has adjusted itself downward to 0.6 & 1.1v during plating. 3-4 volts is plenty until you get into real large parts.

How large of a power supply should I need to plate something in the range of 120 sq"? ...or say a 4bbl carb?

With the original formula, 120" would need about 8-9 amps, that would give you a current density of 70mA/sq-in. It'll work with a bit less, but the plate isn't quite as nice.

What brand and size power supply are you using?

I use a 16v/10A B&K bench supply. Any decent supply that can do Constant Current at the amperage you need will work.

The one you see in my pics are basically what Caswell sells but with a different name so I assume that it is the same internaly.

And it should be fine for up to the 3 amp max.

I used the fizzing as a guide quite by accident because that was when things worked the best. I tried calculating surface area but unless it's a basic shape I don't know how to do it and very little of what I have is a basic shape.

I sympathize, but I have found no shortcuts, and always pre-calculate at least to a rough estimate, then throw in a fudge factor.

Carburetors are particularly tough to calculate. I use graph paper to get an outline of the side, front and top views, and add the square inches that way, then double it to get inside cavities. Just depends on how many odd shaped protrusions & cavities it has.

From what I understand, commercial platers don't calculate surface areas either because of the complicated parts and the time required to figure out the surface areas. They just turn up the current until it slightly fizzes as well.

But commercial platers don't do mixed items, they do all the same item, in approximately the same amount, in a huge barrel, and they've already calculated the size of one item, so the multiplication is easy. They still have to do their preliminary homework.

What problems can I get into if I use fizzing as a guide? So far I haven't had any problems but then again I am very new at this and have LOTS to learn!

It depends on the size of the part. Too much fizzing on a small part will burn. Too little on a large part won't plate well.

It's tricky. The amount of fizzing you get will depend on many variables: the size of the part, the current density, the temperature of the bath, and the distance between part and anodes. Unless you control all of those from batch-to-batch, the fizzing will be different.

Larger parts fizz more than smaller parts, and it's not proportional. eg, a 10" parts puts out MORE than 10x the fizzing of a 1" part.

Higher current densities fizz more; Colder baths fizz more; greater distance between anode and parts fizz more.

In regards to polishing...if the part is plated with enough current, is polishing nessecary?

You want to polish the part BEFORE plating. The plated finish is only as good as finish on the part you start with.

Trying to polish afterwards is not really appropriate, since the plate is very thin, and you can easily polish right through it.

I experimented a little with some of the smaller parts by putting a very low current(.5amp) through them...so low that they were not fizzing either. I was trying to simulate the dull grey coating that I get when I try to plate larger items. After 5-10 minuites they to looked terrible

Yep, a result of insufficient current density.

Then I turned up the current until they fizzed and you could actually see the dullness going away and nice bright zinc either forming or being uncovered and the dullness went away.

So you hit the "sweet spot" at the lower end of the current density. If this works for you, then by all means continue. My concern here is that the initial plate, done at too low a current, might not stick well on the steel. Durability might suffer, I don't know.

Keep at it, and let us know what you find out!

Sean