Best Metal to Chrome or Nickel Plate?

[verhoevenc]

So now for the inevitable noob to metal question: to what grit is aluminum or brass polished enough to be truly ready for plating?
Chris

[David King]

Chris,

I have a 1/2 HP, 3600RPM stationary buffer with 6" x 1/2" sewn cotton buffs. I sand with 500 grit 3M Gold then 1200 silicone carbide (wet) first and then rouge on the buff. That gives me a mirror surface with very fine scratches that disappear under plating. If you wanted to go a step further you could try Simichrome paste. There are lots of similar metal polishes, most of them are less expensive and easier to get.
Wear a dustmask, old clothes, a cap and a full face shield if you don't want a black stripe down your front. A pair of rubber gloves will give you a better grip, avoid buffer burns and keep your hands clean.
If the parts start heating up too quick you need to rake off all the old rouge from the buffs. I use a dull bandsaw blade all folded up as a rake.

[Bruce Johnson]

Yep;

Basically, the part has to be polished and buffed to a mirror-like shine. Any scratches, ripples, or defects that you can see in the bare part will show up after it's plated.

I do lots of engraved aluminum neck plates. I sand and polish every one. My usual sequence is:

1.) Hand sand with 600 grit wet/dry paper using oil, in a straight line, until all obvious scratches are removed.
2.) Hand sand with 1500 grit wet/dry paper using oil, also in a straight line, perpendicular to the previous direction, until all of the 600 grit scratches are gone.
3.) Buff with a sewn cotton wheel and brown Tripoli compound. Most of the buffing is done perpendicular to the 1500 grit scratches, so I can see that they are gone.
4.) Final buff with a sewn flannel wheel and white polishing compound.

Like David, I usually use 6" x 1/2" buffing wheels spinning at 3600 rpm. A 1/2 HP motor is marginal; 1 HP is better.

Some tips:

Try to start with aluminum plate that isn't all scratched up already! And be careful while drilling the holes, countersinking, filing the edges, etc. A gouge from a slip with a file can be 0.010" deep. That means that you have to sand 0.010" off of the whole surface, which is a lot of work. You can't just shine up the scratches. They all have to be removed by sanding the surface down.

In addition to getting the scratches out, you have to get the flat surfaces flat. Waves and dips show up clearly after plating. I use an aluminum block under the sandpaper. A rubber block can make the surface wavy.

It's much easier to do the sanding and polishing with the plate screwed down to a wooden block, one that can be clamped to a bench or held in a vise. It's also safer to buff it while mounted to the block. It gives you more to hold on to, and insulates you from the heat. Also, having screw heads in the countersunk holes prevents them from getting distorted and elongated from the buffing.

Be careful! Buffing metal requires some speed and horsepower, and if the wheel grabs the part, it can hurl it across the shop. Or embed it in your face. Don't do buffing with any kind of guard around the wheel. The safest setup is a completely open wheel with a lot of clearance around it.

Be aware that polishing metal parts isn't easy. It takes some practice and experience. And it takes time, even with the right experience and equipment. That's why it isn't cheap when you have someone do it for you.

[David King]

Maybe read the first three pages of this PDF doc from Caswell plating... http://www.caswellplating.com/buffs/images/Buffbook.pdf
Cutting and coloring were concepts that came naturally to me but if I'd read about them first it might have saved me a few minutes of gaining the practical experience on parts that needed to go out the door later.
Like anything in the finishing department it's all about preparation. Nothing should take very long if you just do the steps in the right order. If buffing a small part is taking more than 20 or 30 seconds then chances are you are screwing it up and need to go back a step or two.
You need a halogen bulb to be able to see small scratches. You need a fluorescent tube overhead to see if your parts are staying flat.
I enjoy polishing metal. There is something deeply satisfying about making things shiny.
If you have a local foundry supply house you can buy all the buffing stuff cheap.
If not, I use this place: http://baylandproducts.com

[verhoevenc]

Chris usually does things a bit different from us others (and usually he does his stuff very well) so I'm guessing he has a specific design in mind. Traditional hardware will probably not fit

It's been a long time coming but here's what they look like! I ended up getting them done in a steel alloy made in China. The chroming has some issues and they are re-doing the batch right now... But these were good enough for finishing the pickguard templates and taking some pictures!

Chris