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Restoring a Criterion Dynascope Deluxe Mount

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#76 apfever

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Posted 26 December 2018 - 04:31 PM

see post 42 and 44 in this string also.

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#77 mfoose

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Posted 27 December 2018 - 09:43 AM

Thanks apfever, that picture is exactly what I need. 

 

So, here is what I have to work with. If you notice, the DEC perfectly matches the RA except the gear is hand driven rather than by a motor. This would make what Geo31 suggested very easy to do (replace it with a reversible motor and hand control).

 

Now to find a motor and hand control set-up or make one myself.

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Edited by mfoose, 27 December 2018 - 09:44 AM.

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#78 Geo31

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Posted 27 December 2018 - 10:20 AM

Oh yeah, I'd definitely add a reversible motor.  You'd probably have to build the hand box, but that's not hard.  I'm no good for the schematic, but that shouldn't be hard to find.  I think Criterion klugged this together anyway, so I personally wouldn't have concern about originality (although I'd paint the box wrinkle black as well).  It would look period correct at least.


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#79 DAVIDG

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Posted 27 December 2018 - 11:15 AM

Looks like Criterion was following  the same technique as Cave when it came to the gearing in the clock drive. So it is most likely a 1 rpm motor with small 10 tooth gear that drives a 144 tooth gear that drives the main gear which has 100 teeth.

   For the Dec drive you want a reversible motor. The question is what speed and if you it to be AC or DC ?  Hurst makes reversible AC motors that would fit . They are bit expensive but you could find a used one on Ebay. If it  is 1 rpm then the slew rate is going to be slow. Good for imaging but maybe a bit slow for centering an object in the eyepiece vs the manual control setup on the scope now.  

    If you go DC you can vary the speed. There are a couple ways to do that. The best is Pulse Width Modulation. You can buy kits or complete drives boards on Ebay to  do PWM.  Even simpler is to just vary the voltage to the motor but you loose torque but it can work since you have huge gear reduction that increase the torque. 

    Here is link to  a PWM controller on Ebay for only few dollars I used these to the control the motors on the spectrohhelioscope at Stellafane https://www.ebay.com...W2Y4S:rk:2:pf:0

  Here is a  link to just one of many examples of a motor that might work.https://www.ebay.com...5.c100005.m1851

  By the way I would replace the power cord and the wiring for the RA drive. Use a modern day molded 3 prong grounded cord and ground the scope. I would also fuse it at 1 amp. The odds of a short are  low but not zero so a grounded cord and fuse could make the difference between a small problem or big one.

              - Dave 


Edited by DAVIDG, 27 December 2018 - 11:24 AM.

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#80 mfoose

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Posted 27 December 2018 - 11:28 AM

Oh yeah, I'd definitely add a reversible motor.  You'd probably have to build the hand box, but that's not hard.  I'm no good for the schematic, but that shouldn't be hard to find.  I think Criterion klugged this together anyway, so I personally wouldn't have concern about originality (although I'd paint the box wrinkle black as well).  It would look period correct at least.

I agree. I am not concerned about originality, but I am using the wrinkle black to make it period correct. Before I paint the whole mount I am testing the primer and paint on the pier cap. So far I have used 3 light coats of self etching primer and one light coat of camouflage black that I had around. Soon, I'll apply VHT black wrinkle finish, but I am waiting for the weather to get better. Hopefully in the next week I will. 



#81 mfoose

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Posted 27 December 2018 - 11:31 AM

Looks like Criterion was following  the same technique as Cave when it came to the gearing in the clock drive. So it is most likely a 1 rpm motor with small 10 tooth gear that drives a 144 tooth gear that drives the main gear which has 100 teeth.

   For the Dec drive you want a reversible motor. The question is what speed and if you it to be AC or DC ?  Hurst makes reversible AC motors that would fit . They are bit expensive but you could find a used one on Ebay. If it  is 1 rpm then the slew rate is going to be slow. Good for imaging but maybe a bit slow for centering an object in the eyepiece vs the manual control setup on the scope now.  

    If you go DC you can vary the speed. There are a couple ways to do that. The best is Pulse Width Modulation. You can buy kits or complete drives boards on Ebay to  do PWM.  Even simpler is to just vary the voltage to the motor but you loose torque but it can work since you have huge gear reduction that increase the torque. 

    Here is link to  a PWM controller on Ebay for only few dollars I used these to the control the motors on the spectrohhelioscope at Stellafane https://www.ebay.com...W2Y4S:rk:2:pf:0

  Here is a  link to just one of many examples of a motor that might work.https://www.ebay.com...5.c100005.m1851

  By the way I would replace the power cord and the wiring for the RA drive. Use a modern day molded 3 prong grounded cord and ground the scope. I would also fuse it at 1 amp. The odds of a short are  low but not zero so a grounded cord and fuse could make the difference between a small problem or big one.

              - Dave 

Right you are Dave. Here is a picture of the 1rpm motor with 144 tooth gear in the back ground. Same setup on the DEC, but minus the motor.

 

I will take some time and mull this over. However, I am leaning towards your PWM suggestion. 

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#82 mfoose

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Posted 27 December 2018 - 04:50 PM

For those who want to learn more, here is a video link for a quick explanation on PWM: https://www.youtube....h?v=YmPziPfaByw



#83 Joe Bergeron

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Posted 27 December 2018 - 05:43 PM

I enjoy watching you guys rescue and restore these old mounts and telescopes. Some of your efforts are really beautiful. Much respect.

#84 apfever

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Posted 27 December 2018 - 05:47 PM

OK, so a PWM system is more efficient than just using a simple potentiometer?  How about a potentiometer as half of a voltage divider to feed the base of a transistor, which would reduce the size of the pot to as small as you want using a high ohm resistor in the divider?  I'm interested in this for scope application as well. PWM vs simple pot or transistor control.



#85 DAVIDG

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Posted 28 December 2018 - 10:18 PM

 If you don't want to use a PWM circuit then a better choice then a transistor /pot would be a variable voltage regulator like a LM317. The issue is current draw  and torque. PWM gives you the most torque without wasting current that turns into heat. A typical battery powered hand drill uses PWM to vary the speed but keeps the torque high.

 

               - Dave 



#86 mfoose

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Posted 31 December 2018 - 06:30 PM

Since the RA motor is AC I would need an inverter to use in the field. This got me thinking about possibly using a drive corrector.

If I was to use a drive corrector would it matter how I configure the DEC drive?

#87 DAVIDG

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Posted 31 December 2018 - 06:48 PM

 The drive corrector is going to run off a 12 volt battery. So if the DEC motor is a DC motor that works off of 12 volts DC then you'll run it off the battery directly and the RA drive off the inverter. A number of the old AC/DC correctors had a outlet for 12 DC that the DEC motor would plug into. The reserve the direction the electronics just flip the polarity going to motor. 

   On the spectrohelioscope at Stellafane I used a 12 DC motors that had a build in gear box. They were powered by a PWM controllers I got off of Ebay for $4 each and then too a double pole double throw momentary contact center off switch. So the PWM set the speed and the switch controlled the direction. An DC/AC inverter powers the clock drive.

 

                          Happy New Year !

                            - Dave 


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#88 apfever

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Posted 31 December 2018 - 07:05 PM

The motors are probably steppers. I haven't looked. I suggest you set it up and check it out As Is first. You may find the stock rate to be excellent for visual, maybe OK for simple photo as well with good alignment.

The DEC and RA are two separate units. You can configure them individually however you want.  I have a few correctors here and some have slow motion control in both RA and DEC.  These can vary from unit to unit. I think my fancy one controls frequency for the RA and is variable voltage for the DEC control.  You'll have to check units and coordinate with what motors you have on RA and what you plan on using for the DEC.  I've always been fine with slo-mo floppies on these big guys for the DEC as it's not much of a shaky view with a floppy hand control like a smaller scope.


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#89 mfoose

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Posted 31 December 2018 - 07:41 PM

 The drive corrector is going to run off a 12 volt battery. So if the DEC motor is a DC motor that works off of 12 volts DC then you'll run it off the battery directly and the RA drive off the inverter. A number of the old AC/DC correctors had a outlet for 12 DC that the DEC motor would plug into. The reserve the direction the electronics just flip the polarity going to motor. 

   On the spectrohelioscope at Stellafane I used a 12 DC motors that had a build in gear box. They were powered by a PWM controllers I got off of Ebay for $4 each and then too a double pole double throw momentary contact center off switch. So the PWM set the speed and the switch controlled the direction. An DC/AC inverter powers the clock drive.

 

                          Happy New Year !

                            - Dave 

Awesome Dave, just what I was looking for. 

 

I will be keeping an eye out for a drive corrector then, maybe a Criterion one to match the mount. 

 

I am also going to take up your suggestion for a DC motor with PWM controller.



#90 DAVIDG

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Posted 31 December 2018 - 08:57 PM

 I would stay away from the Criterion correctors. I have fixed a couple and they are just not well engineered. On one of  them I had to redesign most of the circuit because the way it was there was no way it would work. 

 

                       - Dave 



#91 mfoose

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Posted 31 December 2018 - 09:37 PM

Any drive correctors that are recommended?

#92 mfoose

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Posted 02 January 2019 - 11:22 AM

I bought a DC motor for the DEC and I got one of those $4 PWM controllers as well. 

 

I'm still going to keep an eye out for a drive corrector and if I can find one I like then I will use that. If not, the PWM controller and a DC/AC inverter will do the job.



#93 DAVIDG

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Posted 02 January 2019 - 11:41 AM

 The JMI units are nice units but just about any other except the Criterion ones. Most of the correctors will supply 12 volts DC that will run the motor and change the direction but they don't  control the speed of the DEC motor. The typical DEC motor was geared so they ran at typically 1 rpm or close to that range. So the drive corrector would power the motor and by pushing the buttons on hand box  reverse the polarity going to motor hence reversing the direction.

    The PWM module is nice because that will allow you to control the speed without having  to gear down the motor.  So if your using a motor that is not geared down, and you want to use a drive corrector your going to have to modify it. The drive corrector would need to have the PWM wired in and the output of the PWM circuit would be wired back into the drive corrector before the switches on the hand controller . Now when the buttons are pushed on the hand box the signal from the PWM module go thru those switches and out to motor. 

   Just be cautious of any vintage drive corrector you might buy. They are at least 15 years old if not older and the output transistor typically go bad in them. I'm in the process of rebuilding a Celestron controller for a friends C-14 that had the transistor fried.

 

                    - Dave 


Edited by DAVIDG, 03 January 2019 - 09:33 AM.

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#94 mfoose

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Posted 18 January 2019 - 10:21 AM

It has been a couple weeks since my last update. 

 

I have not brazed the cracks in the cast aluminum yet. Over New Years I was talking to a friend, who is a mechanic, about my dilemma. He has a nice set-up at his shop with everything I need to work. We plan to meet tomorrow morning to see how much we can get done before noon. We have limited time available in his shop so we may need to do multiple sessions. 

 

In the mean time I have found time to paint the pier cap with the black VHT wrinkle plus. I did the steps as directed on the can: "Apply at least 3 heavy coats in a crosshatch pattern. First coat vertically, second coat horizontally, third coat diagonally allowing 5 minutes between each coat. A relatively heavy film thickness is required for the product to wrinkle." However, I found it difficult to gauge if I sprayed enough on some areas and when the paint did wrinkle, about a day later, some areas were not as wrinkled. I had to do two touch-up sessions to get it how I like it and I may touch up one last area, but right now I am pleased with the results. It looks better in real life compared to the pictures.

 

After brazing the cracks in the other pieces I will prime and then paint them as well. It will just depend on the weather. Here in Southeast PA we just started a cold and snowy pattern. Between the cold and the wind it could be difficult to find a day to paint outside.  

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Edited by mfoose, 18 January 2019 - 10:23 AM.

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#95 DAVIDG

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Posted 18 January 2019 - 10:48 AM

 The cap looks great, just understand that the paint is soft for about a week maybe more in the colder weather.  So be careful in handling  it in for awhile You  can bake it to harden more quickly. 

 

                  - Dave 


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#96 Geo31

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Posted 18 January 2019 - 11:26 AM

That looks GREAT!

 

Really looking forward to this restoration.  Just have patience.  Impatience will lead to rushed decisions and rushed work.  When you get done you want to be proud of your hard work.  Truly enjoy the process.  I know how easy it is to get antsy to be done.  I'm almost done with my RVC-6N, but the weather hasn't been cooperating and I still have to send the Sky Micro to my friend to machined the adapter base.  It's killing me.  But I'm loving the process and each finished step I can look at it and say, "Yeah, the patience was worth it."

 

Truly enjoy.  Love those scopes.


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#97 Geo31

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Posted 18 January 2019 - 11:27 AM

Oh, and be prepared to chase the threads with a tap.  May or may not be required.  If you can find someone with the right sized tap, it will make threading the new bolt in much smoother.


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#98 apfever

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Posted 18 January 2019 - 12:22 PM

Chasing painted threaded holes.  It's pretty common having to chase a painted hole with a cleaning tap or regular tap, especially a hole with a heavy coat. 

One thing to try is to run a nice bolt through the hole with some lube after the paint has dried but well before the paint has had substantial cure. There's a huge difference between 'dry' and 'cure' which I'm not going to launch into. A 'nice' bolt is one with good threads and a friendly starting end with no issues. Butter has been a good choice of lube lately on this end. 

 

Wiggle the bolt around once you get it all the way in, if it goes in snug but smooth. Also consider that the paint will still shrink a little while curing if the bolt is a little snug. It's easy to check and may let you keep the finish in the threads.  

 

Exposed cosmetic paint can be worked around shortly after 'dried'. Anything under pressure should be allowed to cure at least a week to avoid a sticking situation. Paint to Paint contact is the worst situation and most likely to stick together if under pressure and left for any length of time.  My Edmund HD grey resto has parts painted over a week ago, and I don't care if I have to wait that long again before subjecting them to some substantial force and pressure. 


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#99 mfoose

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Posted 18 January 2019 - 01:48 PM

Thanks for all the encouragement and advice!

 

I won't be touching the pier cap anytime soon. I have sitting in the warmest and most secluded place I can find. However, I may be chasing the threads with a bolt. I will need to look into this more today. 

 

I am not in a rush to complete this mount and plan on tackling it a part at a time. 



#100 Geo31

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Posted 18 January 2019 - 07:08 PM

Thanks for all the encouragement and advice!

 

I won't be touching the pier cap anytime soon. I have sitting in the warmest and most secluded place I can find. However, I may be chasing the threads with a bolt. I will need to look into this more today. 

 

I am not in a rush to complete this mount and plan on tackling it a part at a time. 

And that may work just fine.  For the pier cap, that is what I did on the RVC-6N, mainly because I didn't have a tap that size.  I took it slowly.  Other painted threads I chased.

 

Again, looking forward to following this.




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