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JAY X

Painting rack case question
« on: December 21, 2016, 12:04:26 PM »
Hi All!

I just finished a prototype of my summing mixer,  https://groupdiy.com/index.php?topic=63515.0
and I painted the case myself. I just painted the case and the cover by the outer side, so inside there is no painting, to provide galvanic conection to connectors.

But now, if i want to make a small run, and have the cases painted professionally (powder coating), the cheapest option is to paint every thing... inside and outside.... and maybe loss the galvanic connection.... :P  it is a dilemma!!...

An option would be to scrap the paint with a file inthe holes of the connectors...
Another idea is to use masking tape to  block the inside rear connectors...
Next option is to have the case  with the cover screwed and then paint the case....

In any case i know that some manual scrapping is necessary for example for the chassis gnd point...

Any idea or suggestion is wellcome... :)

Thanks a lot, and merry christmas!!

Jay x





Re: Painting rack case question
« Reply #1 on: December 21, 2016, 01:10:00 PM »
If you decide to have it powder coated, use a kapton tape to cover the area you want to stay as a bare metal.
Most powder achieved a curing temperature at 200C, and the tape withstand up to 250C (some brands even go higher like 300C)

I use an office hole puncher on the tape to make tiny rounded stickers, then stick them to cover all of my M3 size mounting holes.

emrr

Re: Painting rack case question
« Reply #2 on: December 21, 2016, 01:57:17 PM »
I have honestly never had this problem.  I tend to buy off the shelf boxes, drill them, paint them, load them up with parts, I don't think I've ever seen a case where I couldn't measure case connectivity back to the AC power inlet ground, so I don't think it's that hard to deal with.  I'm sure there are cases which would be more critical. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounded g

Re: Painting rack case question
« Reply #3 on: December 21, 2016, 03:07:41 PM »
That's cool. I make my own boxes because off the shelf boxes are a lot more expensive, and they requires manual drilling.
I use kapton tape to cover holes that have self-clinching nuts installed, because I don't want the powder paint to melt and cured inside the thread.

JAY X

Re: Painting rack case question
« Reply #4 on: December 22, 2016, 10:12:36 AM »
Hi All!

Thanks for all ideas,

Kapton tape is a good idea...but quite expensive....I would need 428mm long and 43mm high tape...

I think despite it takes a bit more work, it would be best to have the case with  the top cover screwed on, and paint all with powder coating. Maybe some powder get inside thru the holes, even more with the new top cover i designed, with greater size holes. But maybe just some shadows get inside, preserving  more bare metal for galvanic contact.  Going to ask my supplier...

Jay x

Re: Painting rack case question
« Reply #5 on: December 22, 2016, 10:20:34 AM »
You don't need to cover the inside of your case, just the part where you need bare metal for chassis connection.

Note: 5 cm kapton tape is about $6 for 30 meters long where I live.

JAY X

Re: Painting rack case question
« Reply #6 on: January 16, 2017, 06:10:01 AM »
Hi All!

Recently i found there is a Vinyl Spray for painting cars...it forms a plastic vinyl layer over any metal surface. ┬┐has anyone try this?. seems interesting!

Jay x.

sahib

Re: Painting rack case question
« Reply #7 on: January 16, 2017, 01:40:16 PM »

An option would be to scrap the paint with a file inthe holes of the connectors...


Yes. It is the easiest and cheapest method. Masking takes time hence costs money.

Don't forget to use serrated washer to bite into the joint for better contact.