[R-390] FrontPanelRestorationforChuck

[Glenn Scott via R-390]

Hi Chuck and others,
I hope this helps Chuck.
1) With regard to the layers on these panels, When I have chemically removed old paint years ago or in the last 5 or 6 years using soda blasting, I always go down to the Aluminum substrate. In fact I can't imagine a way to go through one layer at a time without a great deal of aggravation. 
The chemical stripping processes I used were messy and I ended up going back with a dental pick and brass brush to clean the engraves out. Soda blasting simply rids the panel of EVERYTHING at once. You should be ready to prime soon after you strip the panel since Aluminum starts to form oxides almost as soon as it is bare. As I mentioned in the article, I mix about a tablespoon of white vinegar to a gallon of water and wash the panel after soda blasting to neutralize and remove the remnants of the the soda. Then a second wash with acetone to get rid of any oils from handling; then. finally prime the panel. I like zinc chromate but other primers may work well to. I have not found one I like but a recommendation was made by one of the list members and I will try it soon. 
2) Bondo vs JB Weld  That is a good question. I have dealt with some nasty gouges and have NOT had any that I could not fill with JB Weld. Both are hard once cured and sanding it down is a chore. I have used bondo to fill and re-drill rack holes as you asked in your question 3.  If your gouge raises above the surface of the panel, you must sand it down to be flush. JUST REMEMBER, anything you can feel or see before painting will be visible after painting. Take your time and get your panel ready before priming and painting.
3) Using Locktight or Bondo to fill a rack hole is probably a fair to good solution. I have on a occasions  used bondo for reamed out rack holes. Herein lies the problem, if someone later plans to rack mount the receiver without supporting the receivers weight from the bottom, I would not be surprised to see a filler crack. I have seen many applications where the receiver was supported by the front panel only and as stout as it is, seemed to be an OK way to get by. However, this is NOT the recommended way to support a heavy receiver. It should have support from below. 
I have one rack where I rigged Teflon pads on support rails on the left and right side for an R 390, R390A and a R389 in the rack. The front panel rack holes are occupied with mounting screws with round black plastic disk behind the head of the screws to prevent marring but this is simply cosmetics. The receivers are held in place by the supports below each one. Removal is VERY easy.
4) the blue towels I use are available from any of the auto parts store. They are tough and fairly low lent.


Hope this helps. My email address is in the ER article and I will leave it below. Feel free to email me direct if you have further     questions. My biz number is on my webpage if you want to call.


Glenn WA4AOS
glenn at dsmlabs.com
www.dsmlabs.com


Glenn,

Thank you very much for your comprehensive article in ER.  I'm in the
process of refinishing my first engraved panel and have it stripped down to
what I think is the golden-brown Alodine coating. The zinc chromate and
paint stripped just fine.  Before proceeding I would appreciate your (and
others who might care to respond) thoughts on a few questions I have:
1) Is necessary to sand off the Alodine(?) coating before priming with zinc
chromate?
2) Is Bondo (or equivalent) a good substitute for filling small dings or
deeper scratches vs. J-B Kwik?  It seems like it might be easier to sand and
feather into the panel.  I suspect Bondo might not be a good sub on the
panel edges where mechanical strength would be an asset.
3) One of the rack mounting holes is "enlarged".  I'm considering filling it
with Loctite epoxy putty, sanding flush and re-drilling the hole.  Is this a
workable solution?
4) Don, you call for shop towels for wiping off the smeared acrylic
lettering paint.  Are these cotton terry towels or paper or something else?

This is my first venture, so I really appreciate the great knowledge of this
group.  Thanks to all!
---
Chuck, AE4CW