FYI
I just picked up a Heathkit IM-28 on PayBay. It had a badly scratched and very foggy lens cover. The meter was barely readable through the haze. Not really usable at all. It Looked as if the lens had been cleaned with a solvent and melted - and then sanded or scraped to make it worse.

Others may have a better procedure but I just used my instincts and it all worked out.

I am told there are many types of plastic used in (non-glass) meter lenses. Acrylic and Styrene seem to be common. The IM-28 was styrene and therefore softer then acrylic.

With acrylic I would have been more aggressive and used more aggressive sanding with larger grit.

But here’s the styrene procedure. The lens is as clear as the day it was made. No fog, no scratches – perfect.

1 – Sanded with 600 Grit paper so that the lens was uniformly and evenly “fogged”. This required using a jeweler’s loop to make sure I had sanded “beneath” the deepest scratches. I was careful not to form a pattern. Using completely random motion.

2- Then went to 800 and then to 1200 grit sandpaper.

3 – Then I used Novus 3-2-1 Scratch remover and a small vibrating sander with a cotton cloth between the sanding pad and the lens. I applied the Novus to the cloth.

By the time I got to the Novus 2, the lens looked great. The Novus 1 polish made it shine.

I re-caped and re-calibrated.

Yet another fine instrument saved from the scrap heap!

Since the whole procedure is my own concoction, there may be better ones.

Would any one like to share?

Jim

That is a fine write-up.
It's a bold man who touches sandpaper to a meter face, but I suppose that's what I'm missing.

I've not really seen much positive result from the Novus #3 Heavy Scratch Remover. Now, I'm wondering if maybe I need to actually rough it a bit (if 800 and 1200 can be considered rough...) before starting with #3.

Picked up an RCA WV-120A Line Monitor this week (craigslist!) and there are still a couple of mild scratches evedent. Your 'strategery' seems right. Perhaps I need to rough around them and THEN use #3 Heavy....

Mike Yancey, KM5Z
Dallas, Texas

Yep

Tried the Novus 3 without first sanding and it was no go . . .

The 600/800/1200 sanding did the trick . . .

Jim

I do the same trick except I use water to carry the plastic out of the grit when sanding. Keeps it from clogging as fast. Then, instead of Novus, I use my Beall woodworker's polishing wheels. Tripoli, tin oxide (Beall calls it "white diamond"), and, finally, carnuba wax. I chuck them up in my hand drill so the speed's not so fast as to melt or tear at the plastic. After waxing, an anti-static treatment is in order.
I repaired a trench left by a cigarette recently. Cleaned the wound up carefully, filled with Norland 61 optical adhesive which is a uv-cured and water-clear resin. Then I took it down to a new plane with fine sandpaper on a cutting board, polished it and it went from virtually unusable to virtually pristine.

Yes!

Water! I should have thought of that. The sandpaper filled with plastic very quickly and if I didn't clear it, the clogs would cause additional stratches.

Water would have solved this problem.

Thanks

Jim

Hi!!!
In addition to water, naphtha (lighter fluid) can be used... The naphtha is also used with the finer grit polishing agents to even out the distribution of the grit for a better, more evenly charged polishing cloth...

The oxide papers should be used wet, with very frequent rinses to remove plastic dust, and so the cutting action is less aggressive, and prevents heat build-up which will cause the work surface to get sticky, and hold grit, dust, polish unevenly, and even burn from friction... I have even used papers in a tray of water with part submerged... And I prefer to do it by hand, to prevent heat build-up... But it takes a looooong time...

Always remember that the scratch is below the surface, which means that you are not really polishing the scratch, but taking down the entire surface to the level of the scratch... So the entire surface might end up convex or concave depending on how evenly the entire surface goes down to the scratch level...

Hey Mescalero, that optical cement process is really cool!!! I thought of trying that long ago, but never got around to it... Great to see it works well!!!!

For a while, I had been restoring several of those old, beat-up Uher Reporter portable R to R with those long styrene tape windows really trashed... Managed to make 'em look almost new... But a lot of work!!!!!

Steve K

As for Novus #3, I have purchased it 3 different times over the past twelve years, and never got it to work. As far as I can tell, the batches I received contained little to no abrasive of any kind. I've had several discussions with one of their distributors and a company engineer, but no solid explanation yet. Yes, I shook/stirred/mixed it well. On the other hand, I have used Novus #2 (fine scratch remover), and #1 (plastic protectant and static diss) with no problems. We also use Novus 1 at work to protect and (dry) lubricate clear-plastic acrylic slider doors on lab weighing balances; otherwise the chemicals regularly spilled on them by students damage and haze the doors & prevent them from sliding in the metal tracks. Another source for the correct grades of sandpaper are the "Micromesh" sheets, available mailorder from Luthier supply houses or science instrument (mass-spec or SEM) suppliers, or auto headlite scratch repair kits. Meguiar's Plast-X seems to work well also; its abrasive is quite fine....not for the deeper scratches though.

edited/added on June 29: As a related type repair, I also work on pianos, where newer ones are often finished in thick polyester, which sometimes needs repair of scratches, gouges or cracks. The repair techniques are similar, also using micromesh sheets, abrasive powders and so forth. Professional-level polyester finish repair folks sometimes take a one-day training workshop, which includes a Konig-brand repair kit, which works fine....but the problem is that some of its repair chemicals in the kit have an expiration date & are very expensive to replace.

I have also used a Micromesh kit on some stuff too and that works well. Has alot of different grade abrasive pads down into the 4 digit range and then a bottle of polishing paste to finish up that is included in the kit. I wrote a review of it that appeared in QST one time. The Micromesh abrasives have a pad included that allows the rubbery abrasive sheets to conform to the surface.

Thanks for the tip, this thread should be moved to the hints and kinks forum.

-Sam T.

Maybe make this a sticky? Very useful thread.

Hi,

I started thei string and I have sure learned a lto . . .

So, I desided to try another lens on an older meter.

Here's the process I used.

I used 800, 1200 and then 2000 grit sand paper.

With the 800 and 1200 grit, I used a little Behlen Paraffin Oil to keep the sand paper from clogging.

With the 2000 grit I used water. Water might have worked just as well on the other two - not sure.

With each grit, I made sure not to follow any pattern and made sure I had sanded deep enough to be beneath the scratches. The jewelers Loop is best for that. It is really easy to tell if you are beneath the scratches or not.

Then I used Novus #3 and then #2 and polished with #1. The Novus I applied with a small vibrating sander and a cotton cloth. The meter lens was about 6X6 and I spent about 10 minutes with each Novus number.

I do not believe the lens was any clearer then the day it was made.

Note: I think Novus is basically a polish - it is not agressive and will not remove any scratches without being preceeded by something much more agressive.

Jim

Better yet, link to this in the "Hints & Kinks" category or have a moderator move it there.

To close this tread out, I did just a little more testing and investigation.

I mentioned in the first post in this thread that there are two types of clear plastic most common to meters and vintage electronics. Before the invention of Plexiglas in the late 30’s, glass was used exclusively when a clear cover was needed.

Plexiglas is acrylic and is very hard. Yesterday I experimented and tried to clear some scratches for a piece of Plexiglas. I found I had to be very aggressive. I used the same process as above, but finally went all the way to 220 grit sand paper. 220, 320, 400, 600 and then to Novus #3. The Novus #3 took twice as long.

So, from my experimenting and investigations, here’s the bottom line. . . .

Succeeding glass faces, molded clear plastic is used for most meter lenses starting in the late 50’s and it is mostly styrene. Styrene is soft and therefore molds easily. But also, it is easily scratched. The Heathkit IM-28 I started the post with is styrene and required that I start the lens sanding with nothing more aggressive than 400 grit.

Plexiglas is acrylic and can be bent and formed, but I have not found any “molded” Plexiglas. However, I assume it is possible and I just haven’t seen it.
If the lens is molded, it will feel soft and is Styrene. If it is flat, most likely it is acrylic.

Jim

I was recently given a circa 1959 Heathkit OP-1 'scope.Before even considering doing any work on it, I decided to open it up and search for invertebrate hitchhikers.Having found none, I decided to do some cleaning up before investigating what it might need before the first power up in who knows how long. Part of that cleaning up entailed removing the green tinted plastic over the CRT and the graticule.The tinted plastic is warped, shrunken and unusable.The graticule looked like it was exposed to long hours of high heat. It was cloudy, crazed and looking unsalvageable.Seeming like a nothing to lose situation, I decided to use one of the popular plastic head light lens refinishing kits, powered by a cordless drill.The results proved to be nothing short of miraculous ! The only blemishes not removed are pieces of metal still embedded in the plastic due to someone using a grinder in close proximity to it.Hard to believe such results could be obtained on a half century old piece of plastic. Try it. It will be the most impressive fifteen minutes to half an hour you will have in some time.

Dupont rubbing compound, cheap and you can forget about Novus.