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