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Criterion Dynamax 8

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#201 apfever

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Posted 04 June 2015 - 05:50 PM

NO PICTURE HERE BECAUSE:

 

You are going to have to press apart one whopper of a tight assembly. The RA shaft with gears is not only a tight press into a bearing race, it's pressed in with cyanoacrylate (Super Glue).  You must jig this in a press correctly, and carefully, with supports in the right place, or you're just about guaranteed to shatter the cast arm base.  This pressure needed took me to the point of "OH Lord, you gotta be kidding me", and when the glue gave way the shock shook the shop.

 

The factory used a 3/4" thick steel plate with a custom hole bored in it. Think about that.

 

I want to jump around the process a little to show you how it is assembled, and get you familiar with it so you have an idea of what is coming apart, maybe violently, with a hefty specialty bearing and shaft shooting out the bottom of the press when it breaks free. Have your padding under the press to drop the RA shaft and bearing onto, just in case.


Edited by apfever, 04 June 2015 - 05:54 PM.


#202 Gil V

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Posted 05 June 2015 - 05:27 AM

After all this, did you get the mount pressed back together? Gonna be your biggest challenge. At the factory, it was done with a single, relatively quick pull on a manual Arbor press.

#203 apfever

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Posted 05 June 2015 - 07:20 PM

Lost internet for 48 hours. Just came back. I'll be busy for a few days recouping the down time.

 

Thankfully I have NOT pressed it all back together. I need to use the parts to show the assembly and jig set up. I also want to show all the mods from extra set screws in the gear retaining ring to trueing the setting circles, refelting, better gear assembly and more. Gil has seen some of these.

 

The RA shaft does press in the bearing but not ridiculously so. I can do a couple of test runs to feel out the preload. The biggest issue was getting that dang super glue to break, which covers a large surface area around the shaft. 

 

I replaced the safety bolt on the RA shaft end with a longer SS one, and deepened the tap in the end of the shaft. A lubed cap bolt and heavy washer may be sufficient to set the preload with precision control. I'll have it all worked out before wiping the drop of glue on for final assembly.


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#204 Gil V

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Posted 05 June 2015 - 09:38 PM

We would set up the whole assembly, put the bearing loosely in place, squirt a liberal amount of authentic Superglue around the entire bearing ID, and then press the whole thing together immediately after application of glue. Wear safety glasses, and press that bearing with one good stroke. The right amount of force, just until it "pushes back". Really a matter of feel. I wish I could tell you the pressure used, but I can't. It was a gear driven tabletop arbor press, the press was probably 30" tall.

#205 Gil V

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Posted 05 June 2015 - 09:42 PM

Then put in the screw and washer and tighten just to the point that the washer begins to deform.

If done properly, the mount will spin nicely with no play. Grab the polar shaft from the bottom and give it a spin!! Should not freewheel, should actually be stiff enough so it's not all that easy to spin the shaft just by grabbing it with your bare hand.

#206 Gil V

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Posted 06 June 2015 - 08:53 AM

Another thing - when you tighten the screw in the top of the polar shaft, you'll have to hold the lower end of the polar shaft in a vice (or something similar).

#207 apfever

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Posted 06 June 2015 - 11:24 AM

Another thing - when you tighten the screw in the top of the polar shaft, you'll have to hold the lower end of the polar shaft in a vice (or something similar).

 

The standard here is to drill a matching hole in a block of wood (scrap 2X4). Cut the block through the middle of the hole (band saw here for little kerf).  Then clamp the shaft between the blocks in a vice. This can be tightened as much as you want with no damage to the shaft, until the blocks break. It's best to cut the blocks from end to end instead of across the 2X4. This gives a much stronger grain unless you chance into a board that is quarter sawn in which case get another board.



#208 Dirko

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Posted 04 August 2015 - 08:46 AM

Hi there everybody this is Dirk from Europe and I have to say congrats Chuck, that's a beautiful Criterion Dynamax you have there.

 

I also own a D8 which  I purchased in the late seventies, unfortunately the drive base seized up on me so it won't rotate anymore.

 

Seeing the great work by apfever on his D8 I was thinking if I could do this also with your help.

 

I also have the Criterion drive corrector which worked fine on 220 volts which is standard over here in Europe.

 

I'll post some picks of the unit later this day after work.

 

Grtnx Dirk



#209 Chuck Hards

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Posted 04 August 2015 - 09:35 AM

Welcome to Cloudy Nights, Dirk!  And thank you for the compliments on my DX-8.  If anyone can talk you through this repair, it's Gil and Neil.  Looking forward to the photos.



#210 Dirko

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Posted 04 August 2015 - 12:15 PM

Hi there Chuck,

 

Thnx for the kind welcome, yes I understand from reading the posts that Neil is the person who disassembled his Dynamax which is a brave thing to do, congrats to him for completing his task.

 

So I understand that Gil is the person who worked originally on our great telescopes, I think that`s really cool to have him in this forum.

 

I have taken some pics, hope they show.

 

 

 


Edited by Dirko, 04 August 2015 - 12:17 PM.


#211 Dirko

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Posted 04 August 2015 - 12:26 PM

So here are some pics

 

 

 

 

Attached File  WP_20150804_001c.jpg   50.13KB   11 downloadsAttached File  WP_20150804_003c.jpg   63.75KB   9 downloads


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#212 Gil V

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Posted 04 August 2015 - 05:34 PM

Good looking scope. What is the serial number?

PM me if you want to communicate directly. Neil is the expert on the right tools and fixtures, I can help with proper disassembly instructions.

You've come to the right place. Describe your RA problem in detail.

#213 Dirko

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Posted 05 August 2015 - 06:44 AM

Hi there Gil,

 

Thnx for the welcome Gil the serial is 3709 and yes the scope looks good and also when looking through it, it really performs very good but the drive isn`t.

 

So I used it for many years from the late seventies to the late eighties but then de drive base seized up, thats when I switched to a Meade, but it wasn`t as bright as the Dynamax, so I was a bit disapointed with the Meade brand.

 

It stood for many years at sheds and attics but I didn`t want to part with it because the look of it is really unique.

The drive base is kind of locked up, it rotates but vey very stiff, I tried to rotate it for many hours in the hope of redistributing the grease within but with no succes.

 

 I think it needs the same treatment that Neil gave to his, I will start with removing the tube from the mount like in his photos, any help from you Gil by PM would be very great since you worked on the scopes in those days.

 

I made some new pics because I wasn`t happy with the 2 pics I posted before, I also made some new pics of the corector an the base serial nuber, hope you can tell me something about that Gil.

 

 

Thnx,

Dirk

 

 

 

 

 

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#214 Dirko

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Posted 06 August 2015 - 06:29 AM

I removed the centercap and disassembled the Dec arm from the base to remove the tube assembly.

Then the washer and screw were removed which are on top of a Timken bearing.

 

Then the underplate was removed to expose the underside, at the center there are two countersunk bolts wich I removed and then I could separate the top of the base from the under side of the base which only houses the motors, switch and light.

 

So now I have to think of a way to remove the top Timken bearing with the Ra shaft which is pressfit and locked with superglue according to Neil and Gil.

 

I see there are arrow  marks on the inside of the base and a number F-129, maybe Gil can shed some light on what they mean ?

 

I hope Neil is willing to advise me on the tricky part how to to do it, since I dont want to break anything.

 

 

 

 

 

 

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#215 Gil V

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Posted 06 August 2015 - 02:27 PM

Second time I've seen this, so I'll state this again.

The 10-32 socket cap screw and fender washer (under the Dynamax 8 engraved cover plate) are only to be removed when disassembling the upper base from the RA gear assembly. If you don't have to do that, do not remove the screw!

That is a safety feature that is meant to keep the base together in the event the press fit fails.

We put that hardware in immediately after pressing the mount together, and only removed it as a prerequisite to pressing the mount apart.

I gave the same warning to Neil before I understood the capabilities of his workshop. I do have to dispense advice carefully, as I cannot assume the abilities of an owner to work on their scope.

Edited by Gil V, 06 August 2015 - 05:48 PM.

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#216 Ben H

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Posted 22 August 2015 - 12:50 PM

Did anyone ever organize a Dynamax serial registry? 

My baseplate # is 2727, in the "all grey" color tones. 

I know Gil says the corrector plate #s don't matter, but for posterity corrector plate # is 760814.

I've been super busy lately buying 21 acres out in the country and beginning work on our first home but now that summer is coming to an end I want to get the DX in top operating condition for fall/winter. I'll be taking a look at replicating Dave's work with centering the optics. 



#217 Ben H

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Posted 22 August 2015 - 04:15 PM

The secondary is most definitely not centered. When looking down the baffle tube the secondary is noticeably low, and a laser strikes noticeably high. Pretty much confirmed at this point I will be taking the OTA apart at this point, I'm just trying to ascertain exactly how to do that. 

 

Also need to figure out what tools I'll need. I know Dave used digital calipers to find center, but I don't have any. I could probably get them, just trying to think that through. 

DcQP0IE.jpg



#218 apfever

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Posted 25 August 2015 - 11:55 AM

Hi,  Neil (apfever here)

 

I'm on vacation, been gone for a while, been gone even longer according to the phsyc.

 

Put that bolt and washer back on, that were under the top label cover. leave it installed till you are ready to press the RA shaft out.  I have a ton of pictures on how to press that shaft out, but those are not available to me now.  It took a whopper of a stress load on my 20 ton press to get it to break the super glue hold. You have to support the assembly directly on a round base that just clears the big seal master bearing, and rest on the top hat section that houses the setting circle and gear assembly. I suggest you DON'T DO ANYTHING till I get back and show pictures. I'll be headed back this weekend, and will need a day or two to recoup. If you don't brace the assembly on a press just right, you will break it - guaranteed.  if you try to brace the blue base casting in ANY WAY, and not the special top hat assembly, you will shatter that blue base - guaranteed.

You will need tons of pressure. The idea of knocking it out with a hammer will require such a shock load that I would never try it. 

 

Do not remove those set screws in that seal master bearing. If that bearing moves on the shaft, I can get you to reset it correctly but it has a trick twist to get the screws to seat correctly on a groove lip in the shaft, and it must be correct. The best thing to do is leave that fancy seal master bearing alone. 

 

I internet at a library, and will be back with procedures on this early next week. 


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#219 orion61

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Posted 25 August 2015 - 01:09 PM

Most of the Dynamax RA problems I have resolved have been able to do so without Pressing the shaft out.

Mostly it has just been the grease has gotten hard and stiff, that causes the issue it is between the 2 RA drive/clutch plates that compose of the clutch, it can get so stiff you can hardly move the fork arms in RA.. The silver Allen screw on the opposite top side of the RA cap from the clutch flip lever is used for fine tuning the RA clutch after you clean all the old hard grease from between the 2 RA Drive gears/clutch plates. The slow motion knob is only engaged to the top RA gear/clutch plate. It has a small Teflon, or plastic tip so it doesn't dig a groove in the top clutch plate, when you fine tune the RA drift with the clutch lever partially engaged. They are both "toothed" The RA lock presses them into one another and the Bottom Gear is engaged to the drive motor. There is a locking collar that slides up and locks/adjusts the RA clutch plates.

I have used penetrating oil, and also used Gasoline and stiff brush. I once used #1 Diesel fuel.

Once you get that Mount freed up you will see why some people really love them.

Criterion intentionally drilled the Dec Slow Motion adjustment shaft holes "higher" so it bends it up from the slow motion arm. This makes turning it kind of stiff. I found it out on my first Dunamax, I thought the threaded rod was bad. When I took it out to replace it with

all-Thread I found the issue. You can open the holes up just a bit if you want to make it turn easier. It makes it hard on Dec motors if you put one on it.

I hope this helps clarify the issue and helps save you work. If this isn't the problem and the bearing is frozen, then you will be forced to press it out. Fortunately I haven't had to do it. IF the RA has slop in it when the Clutch is engaged (very annoying) you need to unplug ONE of the power leads from just ONE of the motors, let it run for a few seconds or until it takes up all the slop when locked.. This works for spur drive dual motor systems on Celestron C8's too. The reason for the dual A/C Motors is just that, to take up slop. It will run off one motor fine fut the gear reduction has play.. hence the dual motors so the drive gear is pushing a bit, and the other motor is dragging a bit so between the both it takes up all the slop!!!!I would certainly try every other option before I went to the extreme of pressing it out.

friends

Larry "Duane" Beach


Edited by orion61, 25 August 2015 - 01:29 PM.


#220 Gil V

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Posted 26 August 2015 - 02:31 PM

Agree with Duane. Pressing a Dynamax mount apart is a repair of last resort.


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