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New Q needs DEC/RA loosening

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#1 Simoes Pedro

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Posted 28 November 2019 - 03:23 AM

Dear all,

 

my new Questar 3.5 just arrived yesterday. Unfortunately, both RA and Dec axis are too stiff. Just to put this into perspective, the electric motor cannot drive the RA axis.

 

There is a series of excellent tutorial videos on youtube, addressing Questar maintenance. This likely belongs to a member of this forum. Anyone?

 

Videos #6 and #7 of the series teach you to disassemble both RA and DEC axis. However I need to know the size and type of the set screws in these videos. Does anyone know this information? There are 4 set screws to unlock.

 

  • RA axis adjustment knob.
  • RA axis holding nut.
  • Same for Dec axis.

 

Thanks.

 

Joao

 

 



#2 Erik Bakker

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Posted 28 November 2019 - 03:55 AM

Joao,

 

That's not what a new Questar should need. Especially a brand new one, just out of the box and tested for acceptance prior to delivery to the customer by Company 7. I recommend you contact them and let them solve this for you. Start with giving them a call and discuss the issue with them.

 

Hope that all is well with your new Q soon!


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#3 Loren Gibson

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Posted 28 November 2019 - 07:40 AM

Erik is right. Don't do anything with your Q until you consult with the vendor about this.

 

That said, I'll comment on a couple things. There naturally is drag in the motions due to the nature of the slip clutches, which do not have manual clamps. How stiff is yours? On mine the motions are stiffer than, for example, a mount with manual clamps, where there is next to zero drag if the clamps are released. I bet the perception of stiffness is more noticeable due to the very light weight of the objects being rotated. But that's the nature of the Questar Standard's design; there has to be some resistance to the motions.

 

As to the drive motor not successfully tracking, if we assume that the motor is good (I would think that would have been checked before shipping), that suggests that the RA turntable nut needs to be tightened, not loosened. Loosening the turntable nut will reduce the pressure and the static friction at the slip clutch interface, which is not what would be needed. If it's determined that you need to tighten the turntable nut to fix the tracking problem, it probably requires only a small amount of tightening. 1/8 turn can make a big difference in the pressure applied at the clutch. (Adjusting the clutch pressure does not require removing the knob for the RA slow motion.)

 

The setscrews require a very small size of Bristol spline key. I was mailed two of them by Questar. One of them has a shortened length in order to be able to "squeeze" into the turntable nut's setscrew. (There is reduced clearance between the flats of that nut and the sides of the depression it sits in, requiring a shortened key.) My turntable nut has two setscrews, both of which need to be loosened in order to turn the nut.

 

The maker of those videos you watched on youtube is indeed a frequent poster here, to our benefit.

 

Hope this helps.

 

Loren



#4 munirocks

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Posted 28 November 2019 - 07:54 AM

Make sure you are using the correct Dec knob. One Dec knob is the Dec lock, the other Dec knob (on the other arm) is for Dec movement. Don't get them mixed up. Make sure the Dec is unlocked when you try to move it (the locking direction can be counter-intuitive). It should only be locked for shipping.

 

Are you sure the RA motor is not moving the RA? It only rotates 1 degree in four minutes. The RA reading should not change during this movement. The RA ring should rotate against the shiny base. Put some tape on the shiny base and mark the tape at some RA point reading and see if the RA ring moves relative to the tape.

 

If you establish that the RA motor is actually rotating the scope slowly like it should then maybe the stiffness is further up the chain. My RA movement is a bit stiff which makes the RA knob slip a bit, but the motor works fine because that is lower down in the drive chain. When I use the RA knob it helps if I slightly push the knob in the direction of movement while rotating it.


Edited by munirocks, 28 November 2019 - 09:16 AM.

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#5 davidmcgo

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Posted 28 November 2019 - 12:06 PM

The motions will loosen up In feel with use for manual slewing.  Also, the RA drive is not affected by the friction you feel when slewing the fork, so I think something else is going on there.

 

Definitely call Questar on this or your dealer before you open anything up.

 

Dave


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#6 Optics Patent

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Posted 28 November 2019 - 07:17 PM

Agreed. Call the retailer.

#7 Simoes Pedro

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Posted 29 November 2019 - 12:00 PM

Company 7 claims the scope left working perfectly.

 

I need to know the size and type of the set screw heads. Any help on this is highly appreciated.



#8 Gregory Gross

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Posted 29 November 2019 - 12:57 PM

I would definitely *NOT* attempt to make adjustments to your new Questar yourself. Instead, give Questar a call. They'll talk you through whatever issues you're having.

 

On the very bottom of this page, Questar writes, "Drives and focusing mechanism are guaranteed for two years.... The Warranty is null and void if the instrument has been repaired by any unauthorized agency. Expert and prompt servicing of your telescope will always be available."

 

You run the risk of voiding this guarantee and putting yourself in a much worse position if you make adjustments yourself. Having a well-operating instrument for years to come is worth a bit more of a wait if you do indeed need to send the scope in for service.



#9 RMay

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Posted 29 November 2019 - 01:07 PM

I’m going to chime in for a moment just to say that I have also seen a newly delivered Questar that had a couple of issues: the focus knob is very scratchy when being turned and not at all the ‘buttery smooth’ movement we are supposed to expect, and that I certainly enjoy with my 35-year-old scope. Secondly, the three right ascension plates are not properly aligned under the base plate.

Frankly, I’m disappointed to hear of any Questar scope coming out of the factory not being in perfect condition when it’s first received in the hands of its new owner.

Ron

#10 Optics Patent

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Posted 29 November 2019 - 01:40 PM

To aid your communication I suggest clarifying “stiff axis.” Is it stiff when you turn either knob? Or is this about “slewing” when you grab the fork or tube to quickly aim it in a different direction.

In either event the stiffest or even stuck drive system will track when the motor runs because that relies on everything being frictionally linked.

Note that you can plug in the drive for an hour to see if it moved, but the RA ring turns with the fork so mark with tape on the base housing.

Let us know the details and we’ll see how our guesses compare to the Company Seven diagnosis.

Edited by Optics Patent, 29 November 2019 - 02:58 PM.


#11 BillHarris

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Posted 29 November 2019 - 04:06 PM

And remember, the Dec lock knob (on the left) is loosest when it's in the middle of travel-- all the way ccw is locked, cw is loose.

#12 munirocks

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Posted 29 November 2019 - 04:46 PM

I think you're getting way ahead of yourself. Re-read the above posts, do the checks, and report back.

 

Is the Dec unlocked? Do you know how the Dec lock works? Do you know how to tell if the RA drive is working or not? Until you clarify these points we're going to have difficulty helping you. 



#13 Optics Patent

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Posted 29 November 2019 - 05:56 PM

Bill that’s a good point. The brake of course is loosest with the knob screwed “in” but the knob is wobbliest when not snug at either extreme.

It’s a steel screw with fine threads received in a tapped thin wall aluminum casting so not a recipe for durability and close tolerances. One enemy of this interface is the dec brake knob set screw engages against the brake screw threads, deforming them. The deformed threads then remove material in the tapped hole if removed for service, leaving a looser fit. I advise repairing the threads before removing the screw. In a case with a very damaged screw, cut off the damaged end with a Dremel cutoff wheel and replace to preserve the arm. One of us here has a clever approach with two nuts that fit the screw, both to reduce thread damage and to gain the advantage to remove the screw. But with good threads it shouldn’t be hard to drive out.

A flat on the screw for set screw engagement prevents this but some have been mistakenly reassembled with set screws bearing on the threads.

#14 Gregory Gross

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Posted 29 November 2019 - 06:25 PM

Not to heap too much advice on the OP, but it's possible at least on my early 1960s Q to disengage the dec lock so far that the screw head on the inside of the side arm sticks out so far that it's in the travel path of the side of the scope itself as it moves up and down. So just enough turning to the clockwise (probably no more than a half turn) is all that is necessary to disengage the declination lock. Easy does it. All you're trying to do is loosen that screw head only to the point where it's no longer gripping the declination disk and holding the scope in place.




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