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How Do I Re-plate Plastic Dial Knobs?

12/05/2010 7:17 PM

My club collects vintage radios. The finish on the plastic knobs are usually tarnished be-yon repair. I think they are aluminum plated, but I may wrong. They have a bright polished silver look. Does anyone know of a method to re-finish them?

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#1

Re: how do i re-plate plastic dial knobs?

12/05/2010 7:27 PM

Send a picture.

Is the metal thing an insert? Is the plastic molded around the shiny part.

If it's plated, it's probably chrome over nickel over aluminum or brass. What does the back of the knob look like? silver or brass?

More info

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#3
In reply to #1

Re: how do i re-plate plastic dial knobs?

12/05/2010 10:10 PM

the back is black plastic. there does'nt appear to have an undercoating. it looks alot like the plastic trim that you might find in a car interior. it looks like chrome on plastic.

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#5
In reply to #1

Re: how do i re-plate plastic dial knobs?

12/05/2010 10:15 PM

it's plastic with what appears to be a chrome finish. i've seen the same thing in car interiors. i vaugely remember reading an artical on vaccuum plating, biut i'm not sure if it applies in this case.

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#23
In reply to #1

Re: how do i re-plate plastic dial knobs?

12/09/2010 12:50 AM

is there something 2 be learned from the process of brozing baby shoes

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#24
In reply to #23

Re: how do i re-plate plastic dial knobs?

12/09/2010 10:26 AM

I'd say it's much the same as the other plating on non-conductive processes discribed herein. If we are talking about direct plating on plastics and not onto metal inserts, which I'm still not clear on. If I missed that part, sorry.

Does this look anything like one of yours?

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#2

Re: How Do I Re-plate Plastic Dial Knobs?

12/05/2010 8:10 PM

You might have better luck thoroughly cleaning them then using a spray paint made specifically for plastic. Once you get a good primer coat down, you can use a metallic paint to bring back the metalized look.

http://www.krylon.com/products/

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#7
In reply to #2

Re: How Do I Re-plate Plastic Dial Knobs?

12/05/2010 10:30 PM

thanks for the input. no one that I've talked to have had much luck in getting an original looking finish. our club collect rare vintage radios, and it's important that everything is original looking. there are no after market parts that are suitable

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#4

Re: How Do I Re-plate Plastic Dial Knobs?

12/05/2010 10:12 PM

i agree a picture is needed. if that does not help I would take it to a machinist and have him / her look at it. good machinist are amazing with ability and knowledge,and could make you one. if you want to keep the knobs and put a new finish on them look in the phone book for industrial finishers. a freind of my family has the designation for thier company. they do many differant types of paint,textures,coatings,silk screen,powder coat, electrastatic,alumininizing,crinkle,anodizing, and so on. i would think a place like that could help you or point you. good luck. cool hobby.

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#10
In reply to #4

Re: How Do I Re-plate Plastic Dial Knobs?

12/05/2010 10:48 PM

i agree with you on the bad engineering. i erected structural steel for years, and there where many times that i wished the engineer was there helping me put the building together. that would be a better lesson that four years in college.

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#6

Re: How Do I Re-plate Plastic Dial Knobs?

12/05/2010 10:21 PM

does anyone know if they may be anodized. can plastic be powder coated?

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#9
In reply to #6

Re: How Do I Re-plate Plastic Dial Knobs?

12/05/2010 10:47 PM

A vacuum-deposited aluminum coating may be what you need, but it can be expensive to do. Here are a few options:

1. Contact your local university Physics department and ask if they have a vacuum coating chamber capable of coating a piece of plastic with aluminum. They might do the job for you for a nominal fee. Maybe you can just buy a couple dozen pizzas and offer a 'free' lunch for their help.

2. Contact a company that coats mirrors for amateur astronomers. (Clausing in Illinois comes to mind, but there are others). They might give you a cheap rate.

3. Contact a large coating company like Dontech or Metavac or JDS Uniphase and see if they would be willing to partner with you in this preservation process. You'll get the best help from them in terms of prep and advice on materials.

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#8

Re: How Do I Re-plate Plastic Dial Knobs?

12/05/2010 10:42 PM

when they powder coat they spray on the powder and put the part it in an oven @ 350 to 400 for 1/2 hour. I don't know if your plastic could handle that temp or if the coating would stay on the plastic. the plastic may be Bakelite. you know a knob machined out of brass that has his masters voice,nipper,RCA, GE,ham logo,d-104 symbol would look cool stamped on the face of the knob especially when it gets a bit tarnished. tell people they are OEM and your club is the only one in existence that is known to have these formally thought existing parts. LOL. cqdx

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#11

Re: How Do I Re-plate Plastic Dial Knobs?

12/05/2010 11:01 PM

Once again, we have everybody's favorite process or material being touted.

Fact is, if it's an old radio, the knob is phenolic resin molded over a plated brass insert. Or maybe just a plastic knob molded with a D-hole and machined for a set screw. Bakelite ring a bell?

Vacuum deposition, powder coating and even anodizing were not available when these radios were built.

A picture please. Front and back.

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#12
In reply to #11

Re: How Do I Re-plate Plastic Dial Knobs?

12/05/2010 11:45 PM

we collect vinage radios. mostly from the 60's through the 70's. antique radios don't have much value. i believe it's because during the "golden days of radio", there were so many made

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#17
In reply to #11

Re: How Do I Re-plate Plastic Dial Knobs?

12/07/2010 6:49 AM

Vacuum aluminizing was available in 1940 & might have been used if these radios are from that era.

I know that our local aluminizers are able to fit small quantities of parts in with other larger runs at a reasonable cost so it might be worth pursuing.

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#13

Re: How Do I Re-plate Plastic Dial Knobs?

12/06/2010 10:05 AM

You need to make the part conductive first in order to plate it. Caswell plating has the stuff to do it. http://www.caswellplating.com/index.html

There are systems for home / small users

hope this helps

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#14

Re: How Do I Re-plate Plastic Dial Knobs?

12/06/2010 3:22 PM

You might take a look at this. It's an adhesive back foil.

http://www.bare-metal.com/bare-metal-foil.html

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#15

Re: How Do I Re-plate Plastic Dial Knobs?

12/07/2010 12:16 AM

What about the paints used on plastic models?

Silver with a clear coat over it to provide protection.

Regards

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#16

Re: How Do I Re-plate Plastic Dial Knobs?

12/07/2010 2:28 AM

Thermosetting plastics like Bakelite respond well to the old-fashioned "electroforming" process. Detergent wash the knob after picking off all traces of the original metal coat.

Take a soft artist's brush and a paste floor wax. Lightly wax the front surface of the Bakelite knob that requires metal plating and run the wax coating a little round the rear to a metal pin that you have inserted in a drilled hole. If you don't mind the entire rear also being plated, use a brass shaft in the knob hole - but do remove the original grubscrew.

Dust fine powdered graphite onto the waxed surface. Be sure the graphite reaches all the way to the metal pin. Dab the graphite around with a fresh artist's brush.

Make the graphited, waxed knob the cathode in a simple copper electroplating bath and obtain a flash of copper on the knob. Remove and rinse. Follow up in a nickel plating setup.

Voila! Electroplated plastic radio knob just like the original. If the knob shape has plenty of texture, the electroplated coating will be plenty firm enough.

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#18

Re: How Do I Re-plate Plastic Dial Knobs?

12/07/2010 8:04 AM

As someone mentioned, you need a plastic primer, available for cars from such stores. Then a chrome spray from the same source.....looks like real chrome.....

Check here:-

http://www.newfantachrome.eu/videoteca/spray/

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#19

Re: How Do I Re-plate Plastic Dial Knobs?

12/07/2010 9:00 AM

The knobs if plastic were plated with a process called "plating on plastics" which means the parts are first cleaned then placed in a electroless copper plating bath to make them conductive after which the part is acid activated then put into an electrolytic nickel plating bath and finally into a electrolytic chrome plating bath. (besides many rinses between processes) This is not something you could refinish yourself properly without special equipment. I am certain you may find web sites saying you can but the electroless process would be replaced with a spray conductive paint and the nickel and chrome via brush plating. Your best bet is to find a metal finishing company on line that does plating on plastics.

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#20

Re: How Do I Re-plate Plastic Dial Knobs?

12/07/2010 9:02 AM

The knobs are probably chrome plated. If you really want to do the work yourself, then you can certainly make a new hobby out of it, but I, for one, would send the plastic knobs off for chrome plating to ensure that I get a professional finish that would be as good or better than the original.

Here's a company that can do it for you:

http://www.cvvacuumplaters.com/

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#21

Re: How Do I Re-plate Plastic Dial Knobs?

12/07/2010 11:20 AM

There are many companies out there who do this type of work. Here is one with a good explaination of the process.

http://www.muellercorp.com/chromeplatingplastic.htm

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#22

Re: How Do I Re-plate Plastic Dial Knobs?

12/08/2010 5:09 AM

ABS can be chrome plated at specialist plating companies. You could contact one of these to see if they could help.

Also you could consider rapid prototypes with metalised coatings for new replacements - there are several companies how offer this service but the costs can be quite high.

If the parts are plastic they will not be anodised as the anodising is a chemical reaction of the aluminium base metal i.e. no base metal no anodised finish.

Finally you could consider asking a small engineering company to make copies of the parts in metal that can then be plated.

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