Criterion Dynascope RV-6 Project: "Clock Drive and Cork Clutch!"

At the conclusion of my last post, I had finally solved what was sure to be the most problematic issue for this restoration project, namely acquiring and fitting a new Synchron motor to the original worm gear thus allowing for proper function of the clock drive.

With that task complete, I was ready to reassemble and rewire the clock drive, but first I had some minor cleaning to do and there was also a small matter of an old, torn and rotten cork clutch ring to contend with.

The Criterion RV-6 clutch system is pretty simple really... there are just four major components; the R.A. gear, two clutch plates and a ring of cork.

When sandwiched all together ( ... in the proper order of course), the mechanism allows you to freely move the telescope along the R.A. even while the motor is switched on.

Then when you let the telescope go, the friction between the clutch plates and the cork ring allows the motor to continue moving the telescope with the proper motion to track the sky.

My clutch plates and gear were pretty dirty from all the years out in the weather, so I decided to scrub them down and even go a few rounds polishing with Brasso which worked very well in restoring a near factory finish for each component.

Next, I needed to fabricate a new cork clutch ring.

First, I turned to Amazon.com for a roll of cork sheet which I found available in various thicknesses.

I choose the thinnest I could find, 1/16th inch, based on my guess as to the thickness of the original ring... mind you... the existing old rotted and torn ring didn't provide much help in this judgement as it was very worn and flat.

It did, though, serve as an excellent guide in tracing a new ring which was done
swiftly with just a simple ball-point pen.

After tracing, I simply cut out the cork ring and checked the fit against the clutch plate... it was very snug so I made a few more minor cuts to the inner portion of the ring and eventually the fit was just right... a little snug but not to tight.

Next, using my original photos I took prior to dis-assembly as a guide ( ... as well as the labels in the egg carton where I stored all the various nuts and screws),  I reassembled the entire motor drive part-by-part.

This clock drive isn't really as complicated as it seems at first... you just reattach the gear/clutch to the R.A. shaft using the hex bolts in the back clutch plate, screw in the worm gear/drive motor assembly using the proper bolts through the drive box plate and then attach the pressure bolts/plate ( ... two bolts and small plate that work to press against the worm gear in order to make the connection between the worm and gear tight).

There is likely to be a little tuning required ( ... such as adjusting the pressure applied to the worm, adjusting the pressure to the clutch, making sure the alignment of the worm is sufficient, etc.) but for now, the drive is generally ready for use.

Of course, there was still the small matter of re-wiring the motor so it can be plugged in!

For that, I tuned for some guidance to a detailed RV-6 restoration site hosted by Company Seven which shows quite clearly how to reconnect your drive motor adding a ground so that the motor can make use of a typical three-prong power cord.

After giving the Company Seven images a good looking over, I headed off to the local Radio Shack to purchase a 6-foot Enercell power cord, a pack of wire nuts and a pack of assorted ring tongs.

First, I clipped the head off the power cord ( ... the opposite end of the cord from the prongs of course!) and stripped the three internal wires down a bit in order to allow for contact with the motor.

Then, I soldered a ring tong to the ground wire ( i.e. the green wire) and I was now ready to connect the cord to the motor.

Connecting the plug to the motor was pretty simple, though I must admit, I'm only really certain of the ground wire at this point as there was no indication which lead from the motor should attach to the positive lead of the power cord.

I attached the ground wire ( ... using the tong) to one of the screws of the worm gear pressure plate ( ... as was demonstrated by Company Seven), and the two motor leads to the two remaining plug leads using two wire nuts.

I plugged the motor in and it hummed pretty nice but the real proof will come with First Light... or should I call it the pre-First Light... as I expect that it will take an entire night just to tune the clock drive in order to get the tracking reasonably close.

This "tuning" may include swapping the motor leads ( ... if the motors motion runs the scope backwards) as well as tweaking all the various clock drive and clutch couplings in order to get the motion correct.

Once the clock drive is provably functional, there is just the simply matter of cleaning out the inside of the OTA ( ... there are many cobwebs in there!), cleaning the primary and secondary mirrors and swapping out the broken focuser with a reconditioned one that I bought on eBay, but for now it's sensible to spend some quality time really testing the clock drive motion.

Next up: "(pre)First Light!"

Best to all,
BBG

Criterion Dynascope RV-6 Project: "Dead Motor, No Shaft!"

Recall from the first post in this series that the person I purchased this old scope from kept the pier, including the RA motor, outside in the rain and snow for the better part of thirty years and that, while loading the pier into my car, a significant flow of water came streaming from the motor box.

Needless to say the original Synchron 6-RPH motor, irreparably damaged with corrosion, would not make the slightest peep when plugged in to power.

I was clearly going to need to find a replacement motor and after Googling around a bit I determined that the exact model was still being sold from Herbach and Rademan, a company specializing in electro-mechanical and scientific supplies.

At first, I thought this would be a simple swap-out, "out with the old, in with the new" type of replacement but after comparing the motor I received from H&R to the old corroded Synchron, I realized that I would have a problem connecting the new motor to the worm gear of the clock-drive.

The shaft on the new motor was too long and didn't have any ability to make the connection with the worm gear which appeared to use a simple "tongue and groove" type of fitting.

After Googling some more, I discovered the excellent Criterion Dynascope Yahoo user group which, aside from being an great resource for Dynascope related issues, lead me to contact Ken Poshedly, an extremely nice and helpful group member who had solved this problem already and was happy to help others.

During his Dynascope restoration, Ken had a fitting made by a machinist that could be fastened onto the shaft of a new Synchron motor to make the connection to the worm gear.

Lucky for me, Ken didn't just have one fitting made, he had many (I believe he said something like 50 or 100) and he was selling them at cost (... just a couple of bucks) to anyone that needed them and, even more lucky for me, he still had a couple left.

I sent Ken my order and he sent me back two of the shaft fittings along with a hex tool for tightening the fitting onto the shaft and some great installation instructions he had printed up.

Sadly though, after tightening Ken's fitting onto the new Sychron motor shaft and attempting to reassemble the motor-worm mechanism, I discovered that the diameter of the fitting was slightly too big to fit inside the worm gear housing... there must have been some slight differences in my RV-6 and Ken's... drat!

Further still, the mini hex nut used to hold the fitting onto the shaft was sticking out from the side of the fitting even after being fully tightened further exacerbating the diameter issue.

Finally, the shaft, particularly with the fitting installed, was just too long to fit correctly when reassembled.

What to do?

After some time pondering this major set-back, it occurred to me that I might seek the help of a local clock repair shop... surely they would have the skill and the tools to deal with such an issue.

Lucky for me it was recommended that I bring my troubles to Jim Peghiny of the "Clock and Watch Shop" in the Auburndale section of Newton MA. 
 
Jim is not only a great guy, but a true expert and craftsman with over 30 years of experience repainting intricate clocks and watches.
  
He took an immediate interest in my project and was fully acquainted with Synchron motors (... apparently they are routinely used in some clocks) an even knew a thing or two about Criterion so I handed over all the crucial parts (new motor, old motor, shaft fittings, worm gear) and upon leaving his shop, I had the distinct feeling that my problems were solved.

A few days later Jim called to tell me that the fitting was now the correct diameter and that he would like to shorten the shaft to make it the correct size as well as glue (with some sort of epoxy) the fitting to the shaft instead of using the hex bolt.

I was elated!... I had just assumed that Jim was going to get the diameter of the fitting right but now he was going to whole route, making the complete mechanism correct end-to-end.

Of course, I quickly gave him the go-ahead and he said I would be able to pick it up the next day.

Well, when I got to Jim's shop I could see that he took great care in getting the mechanism right as he had fully assembled the pieces and even hooked up the motor to test how it functioned powered.

The mechanism was now perfect and it cost just $15 for Jim's work. 

In this day and age for that much work, care and attention to detail to cost just $15 seems undervalued to say the least so I thanked Jim and assured him that I would be bringing all my future clock, watch and telescope repairs to his shop.

Heading back home, I had the distinct feeling that I had just overcome the last show-stopper of this project.

The clock-drive needed reassembly and a new cork clutch but that was minor by comparison to the other issues I had encountered.

The optical tube assembly needed some serious cleaning and some repair (as we will soon see) but overall I did not anticipate any seriously problematic issues...

"It's all smooth sailing from here on out!" I thought.

Next up: "Clock Drive and Cork Clutch!"

Best to all,
BBG

Criterion Dynascope RV-6 Project: "Tap! Tap! Taping the Assembly!"

When we last left off I had just received the components back from the powder coater and, thrilled with the results, was excitedly readying to re-assemble the pier.

Recall though that in preparation for the new finish, I was forced to separate the saddle from the declination axis thereby permanently breaking the original factory friction connection between the two parts.

By this point, I had resigned to "re-attach" the two parts through the use of a hex-and-die tap... in fact, I planned to make three taps through the saddle head and oriented triangularly around the declination shaft so that the three inserted hex bolts would hold the two parts together firmly.

I say "resigned" because a cursory search on the web had me at least slightly concerned for the fragility of the aluminum saddle as it appeared not too uncommon for them to turn up broken.

But, be that as it may, there appeared to be no other way to re-establish the connection so off I went to the hardware store for a minimal "tap-and-die" set and a can of WD-40.

Without much of a plan, I began tapping the saddle settling on creating three taps that would together form sort of a triangle around the declination shaft.

Each tap went very well with a small depression mark setting the position for a pilot hole then followed by the thread cutting process all with the help of liberal amounts of WD-40.

The aluminum was quite soft and proved very easy to drill and tap and before you know it, I had three nicely threaded holes but now for the moment of truth... would the hex bolts hold firm to the declination shaft when tightened.
    

After tightening all three hex bolts I was happy (and very relieved/satisfied) to find that the connection was VERY firm with little possibility of slippage.

Now with the saddle issue finally resolved, I decided to continue assembling the main pier components with the goal of reaching the point at which I could begin to address the next "show stopper" issue... the corroded motor drive!

First, I reattached the "lunar lander" feet using new (but identical) stainless steel hardware and a slight modification from the original design, custom fitted washer-like pads (placed in-between the lander foot and the pier) made from a firm but compressible rubber-like material I had lying around (see below).

I simply cut rectangular pieces the same size as the side of the lander foot that meets the pier so that the washer would completely separate the two pieces but made sure that no rubber washer would show around the edges.

With the washers in place, I felt confident to REALLY tighten the feet to the pier without any marring the fancy powder coat finish and in no time the feet were all attached and I was ready to move on to the pier head.

Without much delay I was able to re-attach the pier head to the pier with the original hex bolts, the RA axis holder to the head with the original latitude bolt, the RA axis itself along with the RA setting circle and setting circle pointer, the DEC axis and finally the saddle with the three custom hex bolts.

Finally, during the re-finishing process the original green felt (... or what was left of it) that lined the optical tube assembly mounting rings had to be removed and now, needed to be replaced.

I ordered a nice, perfectly sized and self-adhesive felt in an identical shade of green from an Amazon store while the components were away being refinished and now I was ready to apply it to the mounting rings.

Applying the felt tape to the rings was as easy as measure, cut and stick though while it adhered reasonably well to both sides (clean aluminum and powder coated), it may need a more permanent adhesive at some point to ensure that it stays put.  

    
Now with the pier mostly re-assembled and such small details as the mounting ring felt complete, its time to move on to the next major hurdle in the restoration of this RV-6... the motor drive.

A sorry sight it is that motor drive... recall that it sat in water routinely for about 30 years so the motor and cork clutch were shot while the fasteners were corroded and the worm gear and wheel were all gunked-up.

Restoring the motor drive will bring some major complications for sure but for now I was happy with the results so far and even more enthusiastic about completing the whole project.  

  
Next up: "Dead Motor, No Shaft!"

Best to all,
BBG