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The base is not 100% flat

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#1 GR1973

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Posted 18 December 2018 - 06:09 AM

Good morning and happy holidays

 

 

When I tried to level my scope with a bubble level I found that the base of the scope is not 100% flat. It's not so wobbly but I can move it by pressing on one side and this change the bubble level. The turntable is snugged to the fork

 

arms  so no problem in this attachment.

 

Should the base be 100% flat ? 

 

Did any member find this with his Questar?

 

 

Best regards



#2 Loren Gibson

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Posted 18 December 2018 - 06:48 AM

Can you clarify a couple of things?

 

What is the base sitting on when you do this? Are you sure it's the base which is not flat rather than the surface you're setting it on? From your description, it sounds like you don't perceive any rocking, per se, only that you see bubble displacement. Is that correct?

 

Where do you place the level vial, and what part of the telescope/mount are you pressing on to observe the displacement of the bubble?

 

Loren



#3 GR1973

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Posted 18 December 2018 - 06:57 AM

I find little rocking when I press on one side of the turn table. 

 

The base was resting on a flat glass over flat table and I used the the bubble level at the center of front cover. I removed Questar logo and put it instead dead center. I checked the level on the same flat glass and found it centered also.

 

I concluded that the base is not flat from all these. I experienced this also when I observed and put the scope on flat wooden desk but I wrongly imagined that the problem is due non flat desk surface.



#4 Loren Gibson

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Posted 18 December 2018 - 07:20 AM

I would be rather surprised if the base wasn't machined flat. The base is, if I recall correctly, sand cast and then machined on the outside, and the sand cast "pebbling" is left alone on the inside. (Someone please correct me if I'm not remembering these details correctly.)

 

You're pressing down on an "edge" of the turntable, if I understand correctly. Note well that the turntable is attached to the drive base by means of a nut threading onto a stud beneath the center disc on the turntable. However, it is not just the nut being torqued down on the turntable. There are (on mine) two springs between the face of the turntable and the nut. When you tighten down on the nut, you're compressing the springs to apply pressure to the turntable in a way which, I would think, allows one to tune the tension to achieve a desired amount of pressure on the clutch discs, more easily than what could be accomplished than by just tightening down the nut directly against the turntable.

 

What I'm wondering is if the rocking you're observing in the level vial is a small amount of rocking allowed by the springs. How hard are you pressing on the turntable, would you say? Not in units of weight or anything, but something like firm finger pressure, for example? And, if this is the case, I wouldn't be worrying about this.

 

I may try to duplicate your issue on mine sometime, but it may not be today. I've got what feels like a real nasty ear infection, I think, and I need to get some attention for it.

 

Loren


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#5 Optics Patent

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Posted 18 December 2018 - 07:52 AM

It seems unlikely that the lower rim of the base housing is the source of the wobble.

 

The turntable is a moving part connected to the base only by a single but with a spring washer.  The turntable is separated from a precisely machines flat ring on the upper surface of the base casting by several Teflon sheets, a brass gear, a synthetic disc, and three stainless steel discs, all of which can rotate.  That stack has some compressibility, so pressing on one edge will cause some tilt due to the springiness of the hold down washer.

 

I have seen some improperly installed turntables that wobbled because the hub tension wasn't set right, or someone used the wrong hardware (a lock washer instead of a spring washer, believe it or not!), so if you suspect a problem then you can pull the hub cover and inspect the hold down hardware.

 

Besides that I'd advise against pressing on one side, as the scope isn't intended to be perfectly still in response to such inputs.  ("Doctor, it hurts when I do this."  "Then don't do that.")

 

Also, you can eliminate the base flatness question by putting three little shims under the rim to create a tripod.


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#6 GR1973

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Posted 18 December 2018 - 08:31 AM

It seems unlikely that the lower rim of the base housing is the source of the wobble.

 

The turntable is a moving part connected to the base only by a single but with a spring washer.  The turntable is separated from a precisely machines flat ring on the upper surface of the base casting by several Teflon sheets, a brass gear, a synthetic disc, and three stainless steel discs, all of which can rotate.  That stack has some compressibility, so pressing on one edge will cause some tilt due to the springiness of the hold down washer.

 

I have seen some improperly installed turntables that wobbled because the hub tension wasn't set right, or someone used the wrong hardware (a lock washer instead of a spring washer, believe it or not!), so if you suspect a problem then you can pull the hub cover and inspect the hold down hardware.

 

Besides that I'd advise against pressing on one side, as the scope isn't intended to be perfectly still in response to such inputs.  ("Doctor, it hurts when I do this."  "Then don't do that.")

 

Also, you can eliminate the base flatness question by putting three little shims under the rim to create a tripod.

Thank you for your nice explanation

 

The point is even I move the base from sides it has minimal rocking and this appeared long time ago when I purchased the scope new from C 7

 

I asked them and the told me it's normal. and because of that many use the tabletop tripod or big tripod.



#7 Optics Patent

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Posted 18 December 2018 - 10:31 AM

If you rotate the base 90 degrees or other angles on your own "flat" table top does it get better or worse, or wobble in different directions?  That would determine which was the culprit (or both).

If this really bothered you, you could get a flat granite tile, adhere sandpaper to it, and sand it flat like grinding a telescope mirror.


Edited by Optics Patent, 18 December 2018 - 11:07 AM.


#8 GR1973

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Posted 18 December 2018 - 12:36 PM

If I rotate the base it gets better

The bubble level is dead center if it’s 180 degrees
(Finder mirror facing me).

I feel that the base is little bulged in the center and recessed in the periphery.

Edited by GR1973, 18 December 2018 - 12:39 PM.


#9 terraclarke

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Posted 19 December 2018 - 01:23 PM

If I rotate the base it gets better

The bubble level is dead center if it’s 180 degrees
(Finder mirror facing me).

I feel that the base is little bulged in the center and recessed in the periphery.

 

Could it have been pulled out slightly around the central 1/4-20 mounting hole during mounting on a tripod whose head was smaller than the Q’s baseplate? I worried about this happening to mine and so have always used a mounting plate that was larger than my Q’s base.

Attached Thumbnails

  • 279396A6-1A5B-43E6-BACA-B93001D767E4.jpeg

Edited by terraclarke, 19 December 2018 - 01:27 PM.


#10 GR1973

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Posted 19 December 2018 - 03:32 PM

It seems unlikely that the lower rim of the base housing is the source of the wobble.

 

The turntable is a moving part connected to the base only by a single but with a spring washer.  The turntable is separated from a precisely machines flat ring on the upper surface of the base casting by several Teflon sheets, a brass gear, a synthetic disc, and three stainless steel discs, all of which can rotate.  That stack has some compressibility, so pressing on one edge will cause some tilt due to the springiness of the hold down washer.

 

I have seen some improperly installed turntables that wobbled because the hub tension wasn't set right, or someone used the wrong hardware (a lock washer instead of a spring washer, believe it or not!), so if you suspect a problem then you can pull the hub cover and inspect the hold down hardware.

 

Besides that I'd advise against pressing on one side, as the scope isn't intended to be perfectly still in response to such inputs.  ("Doctor, it hurts when I do this."  "Then don't do that.")

 

Also, you can eliminate the base flatness question by putting three little shims under the rim to create a tripod.

 

 

I would be rather surprised if the base wasn't machined flat. The base is, if I recall correctly, sand cast and then machined on the outside, and the sand cast "pebbling" is left alone on the inside. (Someone please correct me if I'm not remembering these details correctly.)

 

You're pressing down on an "edge" of the turntable, if I understand correctly. Note well that the turntable is attached to the drive base by means of a nut threading onto a stud beneath the center disc on the turntable. However, it is not just the nut being torqued down on the turntable. There are (on mine) two springs between the face of the turntable and the nut. When you tighten down on the nut, you're compressing the springs to apply pressure to the turntable in a way which, I would think, allows one to tune the tension to achieve a desired amount of pressure on the clutch discs, more easily than what could be accomplished than by just tightening down the nut directly against the turntable.

 

What I'm wondering is if the rocking you're observing in the level vial is a small amount of rocking allowed by the springs. How hard are you pressing on the turntable, would you say? Not in units of weight or anything, but something like firm finger pressure, for example? And, if this is the case, I wouldn't be worrying about this.

 

I may try to duplicate your issue on mine sometime, but it may not be today. I've got what feels like a real nasty ear infection, I think, and I need to get some attention for it.

 

Loren

Thank you all for your explanations. You are right.

 

Please disregards my last two posts. 

 

The base is 100% flat. I grabbed the fork arms then I rotated the base and this did not make any change.

 

Now, I know the problem is in the connection between the turntable and the fork ( The central nut and their washers).

 

I made a little pressure on the turntable with my firm thumb and this made the bubble in the center.

 

If the Central nut become little loose this could cause this little rocking movement. 


Edited by GR1973, 19 December 2018 - 03:34 PM.



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