The AM Forum

I figured that with all the homebrewing going on here that this would be the best place to ask a few questions about dealing with panels and cabinets. I am starting to refurbish a 42 inch high rack cabinet and was wondering what the best way is to fill unused panel holes prior to painting. I was thinking about using a piece of metal tape on the inside and using something like JB Weld to fill the hole. No holes are very large,the biggest being about 1/4 or 3/8 of an inch. Also I am getting ready to build a high power tuner and need to paint the front and rear panels that are aluminum. Any ideas on how to prep the aluminum so the paint will not chip off easily? Any special type of paint or primer reccommended?

Yes for aluminum a light wet sanding with #600 or 800 wet/dry sandpaper followed by a thorough cleaning with Xylene.  Then prime with Zinc Chromate, followed by another light sanding then prime again followed by a very light sanding to rought up the primer.  Wash with water. 

Then you can paint.

If it is steel for the rack panel and ur into thickish material, not thin sheet metal, consider automotive Bondo?

For aluminum I understand that there are a few etching primers in spray cans that can be had, one from NAPA iirc. (for those who don't have a Zinc Chromate bath handy, or Alodine bath)  ;)

                  _-_-bear

I put a entire new front panel on it clamp drill n screw it together. I like light gauge steel. get em finished in gray or hammertone and your painting/primering is done and matched.

Now that's an idea I hadn't thought of.I do have lots of enameled sheet metal that I kept from an old deep freezer that I scrapped. I could just cut a new faceplate and put it on over the existing panel.Since it already is painted and baked on all I would have to do is repaint with my color of choice,probably grey hammertone. As for the rack,it is fairly heavy steel and the holes are not large and only on one side and one on the very top.I could always just put a bolt and nut in place and paint over it and nobody would ever know that the only purpose the bolt was serving was to fill a hole.  ;D

Tnx for the ideas.

As Bear suggested,  the automotive bondo stuff works very well. I grabbed a roll of the adhesive  backed aluminum tape sold at Home Depot and put that on the inside of the panel, then filled the holes with bondo. A little sanding and touch up then some paint and no one can see where the holes were. It holds up very well and ten years later there's no sign of cracking or deterioration.

There are hole plugs for panels, available from McMaster Carr.

The steel sheet metal panel on my HF-300 rig had a large number of 1/8" holes drilled in it when I got the empty cabinet.  I "leaded in" mine using acid core solder.  Sanded the solder smooth on the front side and then sprayed with black wrinkle paint.  You cannot tell where the holes were.  The interior side was brushed painted using black semi-gloss.  Small bumps are visible from the interior.

Bondo or JB Weld should work OK. 

One year I found a 1920's composition (hard-rubber?) horn type loudspeaker at Dayton for $5.  Some hammy hambone type had drilled four 1/4" holes and mounted a modern-day 6" cone speaker inside the flair part of the horn (unbelievable!), suspending it from wires attached to screws attached through the holes.  That probably explains why the selling price was only $5.

I filled in the holes with JB Weld, and after it had hardened, used extra fine sandpaper to smooth over the epoxy, both inside and out. I had planned to spray paint the entire horn to cover up the repair, but there was no need.  Enough composition material from the vicinity of the  holes rubbed off with the sandpaper to thoroughly cover the epoxy filler with a glossy finish identical to the rest of the horn.  It is faintly visible only by shining a light on the surface at a certain angle.

Where would be a good place to look for Xylene and Zinc Chromate?

At the AM Forum at Dayton last year, there was a presentation on restoring R-390/390A panels.  The guy recommended spray painting with something like Rustoleum, and then baking it in an oven for a certain length of time, which he said makes it rock hard and almost impossible to remove.  I took notes on the best baking temperature and length of baking time, but I didn't nail the notes to the wall immediately upon returning home, so I'm sure that information was sucked up long ago by the little black hole that floats around in my shack.

I prefer grey or black, or black wrinkle.  I think any kind of hammertone has to be about the ugliest finish ever used on radio equipment.

R-390, I did it this way. Sand down and clean surface with alcohol. Spray on green chromate for primer (from West Marine). Spray on Rustoleum Professional (comes in silver can) Machine Grey. Either let sit for a while, or bake at 150.

The pearls of wisdom at the R-390 site will have this.

Where would be a good place to look for Xylene and Zinc Chromate?

Don, any good automotive paint supply store should have both of these items.

mike

...maroon coloured scotch-brite pads, with water fer prep...east-west motion with the pad...this is called a water-break test....it removes any oils on the aluminum panel..rinse with clean water, or isopropyl alcohol, and let dry....it also allows the primer to adhere...zinc-chromite primer next...just a light coat...after cure, lightly abrade the panel with a clean, dry scotch-brite pad...remove any dust from the panel, with a dry soft cloth...place panel in an oven, at about 150*F....remove panel after about 5 mins, and apply paint, with the panel still warm...paint should adhere, and cure quickly...

..for filling holes, "dish-out" the holes...make them somewhat concave...mix up bondo, with swarf...apply in holes, let cure and sand...swarf is a term fer small, metal shaving that are left behind after drilling, filing metal...the purpose of the swarf in the bondo, is to actually create a structural bond in the hole...much stronger than just bondo...it creates a matrix that is strong...

..these procedures are how repairs, and painting is done in the aviation industry...they work...

..sk..

I sand my aluminum panels with 400 grit silicon carbide paper, then clean them with paint thinner and prime with a special aluminum primer and paint with Prylon fusion made to paint plastic. I usually leave it to bake in the sun for awhile. I have been using this method since 1999 with success.

Go to the hardware store and get metal plugs a little larger than the size of the extra hole. If it is a small hole put a screw in it. No one knows that nothing is attached to the other side unless you tell. If you messed up too bad, then cut a new panel and start over. My latest homebrew xmtr took 3 panels to get it right. I keep changing my mind on final tank. The homebrew rcvr took 2 panels. I quit worrying about extra holes on the chassis. The reason my audio driver has 3 pilot lights is I removed the tone controls and plugs looked bad, so I put in different color pilot lights, red, white, and blue.