Saturday, November 27, 2010

Criterion Dynascope RV-6 Project: "Naval Jelly and Elbow Grease"


With the scope disassembled, it was easy to see that removing the rust that had built up over the many years of direct weather exposure was not going to be an easy task.

Worse yet, the majority of the original paint job was a loss as well with brittle flaking and loose chips falling free at just the slightest touch.

I needed a safe product (and procedure) that could simultaneously remove rust and all other debris from each part leaving me with, more or less, a clean surface ready for a fresh coat of paint.

Enter... Zud, Naval Jelly, steel wool and lots of hard scrubbing!

My grandfather, who was an expert at these type of things (guru of grease, Grainger-aholic, wholesaler extraordinaire), had first recommended Naval Jelly to me when I was just a teen and I have been using it ever since.

It is a strong and safe phosphoric acid based pink jelly that you apply to a surface and let sit for a while before scrubbing off to reveal a new, rust free look.

Better yet, it tends to eat through just about anything including old paint, dirt and other grime making it perfect for the sort of application where you are not trying to spare any of the original surface.

Before and in-between coats of Naval Jelly I decided to scrub each parts surface vigorously with Zud, a Bon Ami-like, heavy duty powder cleanser, in order to remove any obviously loose debris.

In order to facilitate the de-rusting/stripping process, I secured and old box that I used to contain all the mount parts once they were covered in jelly.

This made it easy to cleanly transport the parts around and worked to keep my workspace clean of the arrant blobs of jelly that tend to drip from the surfaces as they "cure".


Though most parts of the clock drive and setting circles are made of aluminum and brass, the hardware is not and corroded right along with the rest of the mount leaving nasty stains on many of the rust proof surfaces as well as resulting in the seizing of some set screws.

Covering these parts with ample amounts of Naval Jelly I sought to remove whatever stains and grime had infected them as well as free up any stuck hardware.

A typical aluminum pan worked to contain these parts as they were being jellied and, as with the box of mount parts, kept the work area clean.


Each coat of jelly was given roughly 24 hours to "cure" after which time I coated each part with Zud and scrubbed until the jelly was no more and all lose material was removed.

I used steel wool to scrub the mount parts but a typical scrub-top cleaning sponge for the clock drive parts so as not to mar the surface of parts that would not eventually be painted.

On several occasions I actually scrapped away the debris from the mount parts using a screwdriver as these surfaces needed some serious attention and would inevitably be completely painted so there was no fear of them being marred by scratching.

After a few of iterations of this process the surfaces of most parts began to look very clean and paintable but there was still a serious issue.

Some rust was simply out of reach of the jelly and my scrubbing.

The entire inside of the pier, for example, was covered in rust yet it was virtually impossible to cover it with jelly much less scrape it clean after the jelly had done its work.

Further, there was rust in nooks and crannies that were equally unreachable... I began to realize that, while the Naval Jelly approach worked to remove most of the rust that was easily accessible from the surface, I needed another approach if I wanted to really rid this mount of all rust.

Next up: "Evaporating the Way"

Friday, November 12, 2010

Criterion Dynascope RV-6 Project: "Disassembly and Decisions"


After getting the scope home and performing a deeper inspection of the various components, it was obvious that this project was going to require a complete overhaul.

Rust had infected virtually every oxidizable surface including all hardware, the whole interior and exterior of the pier, and both axes with particularly bad pitting and corrosion covering the declination axis and its various collars.

Worse yet, the declination axis was actually frozen in place, apparently corroded so badly that it refused to rotate in its housing.

It was clear that the only way to approach this project was to completely disassemble the scope down to independent parts, remove the rust, scour away the grime and lose paint, replace hardware that was too far gone, and completely repaint and re-assemble.

After making a quick run to the hardware store for a few hex keys, some cleanser and an ample supply of naval jelly, I started the disassembly working first on the clock-drive then the axes and then the pier.

Most hardware was still functional coming lose after a little work but a few screws, namely the ones holding the mount head to the top of the pier and the various collars to the declination axis, refused to budge.

Rather than stripping the hex screws, I decided to leave these troublesome parts alone and then revisit them again after a few courses of naval jelly had removed most of the rust that was preventing them from turning as they should.

The declination axis was a bit more concerning though as I could not tell if what was causing it to seize was a lot of corrosion inside the declination "T" housing or if there was just a little near the edges but with this too, I resolved to delay my concern until I had removed as much rust as I could.


The clock-drive looked surprisingly clean given that it had been submerged in water on and off for better than two decades but the motor was clearly suspicious with corrosion coming from the location of the power lines.

It seemed pretty likely that the motor was dead, a fact that I confirmed later after its removal, but the other parts all looked to be in pretty good shape with some minor rusting on the hardware and serious grime (possibly old grease) on the worm gear.

I took care to take many pictures along the way in order to document the proper placement and location of all parts as well as placing all small parts in the cells of an empty egg carton with each cell clearly labeled in order to identify the main component that they were associated too.


With the clock-drive removed, the RA axis slipped out from its housing still connected to the frozen declination axis which, for the time being, I would treat as one single troublesome part.

Removing the large hex bolt that held the mount head to the pier took some doing as it was firmly rusted in place but a slight jerky back and forth movement of the hex key eventually worked to break this bond.

After removing the "lunar lander" feet from the pier, and removing all other lose hardware from all parts, the initial disassembly was complete.

Next up: "Naval Jelly and Elbow Grease"

Friday, November 5, 2010

Criterion Dynascope RV-6 Project: "In the Beginning"


“Every new beginning comes from some other beginning's end.”  - Seneca

For the inaugural project of "This Old Scope" (TOS) I choose (for better or for worse) to attempt to rehabilitate a recklessly abused old classic Criterion Dynascope RV-6 that I found while perusing the listings at craigslist.

But first... I should mention a bit about myself.

I've been involved in amateur astronomy for nearly 30 years with my most active and focused period occurring when I was a teen during the 1980s.

From the outset I had at least as much interest in the telescope itself as I had for the typical amateur activities of observation, sketching, astrophotography and the like.

Whenever I would get my hands on the latest copy of Astronomy or Sky and Telescope magazines, I would immediately spend a good hour pining over the ads, the equipment reviews and the do it yourself projects before cracking into the general astronomy related articles.

Soon, I found myself with a subscription to "Telescope Making Magazine" plus the entire series of back issues, a copy of Richard Berry's "Build Your Own Telescope" and a 50 gallon drum in the basement for grinding my own mirror.

That said, I still have a tremendous amount to learn about mirror making, telescope construction and restoration so now that I'm a settled family man I'd like to revisit my love of the telescope by taking on a series of projects that I will fully document and chronicle here at TOS.

Hopefully in the process I will be able to rekindle my love of the telescope while producing a stream of useful DIY information for anyone with similar interests.

Now back to the project at hand!

As you can see from the photo above, this scope is a sad case indeed.

The man I bought it from was an interesting case too... In his late 40s as best as I could judge, I couldn't help but feel a tad bit melancholy as he recounted how his father had bought him the scope years ago and how he had left the mount out in the rain and snow year after year while always being sure to keep the optical tube assembly indoors.

Here was a classic scope... no... THE classic scope... a six inch Criterion Dynascope being treated like a cheap throwaway import.

Back when this scope was purchased (somewhere around 1972 - 1973), the standard RV-6 model cost roughly $325 which, adjusted for inflation, is about $1,598 in 2010 dollars... a notable investment in a special gift likely given under special circumstances.

Things sure don't always work out as one plans and this man's father had likely never anticipated such a lowly road for this fine instrument... but such is life.

After a few more pleasantries, I paid him the $100 he was asking for the scope and he offered to help me load it into my car.

As we wrestled with getting the mount into the back seat I suddenly noticed a significant stream of water flowing from the clock drive chamber... we locked eyes... "Not a good sign" he said self-consciously.

I reassured him that it was fine, I had anticipated the worst and if the clock drive didn't work, I would simply add it to the list of things that needed attention in order to restore the scope.

We shook hands and off I drove.

Next up: "Disassembly and Decisions"

Best to all,
BBG