TONGKW
scholastic sledgehammer
Reged: 01/16/07
Posts: 866
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The single arm Alt-Az mount of my NexStar 6SE appears to have excessive backlash on the altitude axis as there is a free movement (play) of about 1/16” up and down when I rock the OTA by hand. There is no backlash on the azimuth axis however. May I know if other owners of this mount also have problems like this.
Regards
K W TONG
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C8 + CG-5GT, TSA102 + HEQ5, MK67 + Kenko NES, NexStar 6SE, WO ZS 80FD + Mizar K mount, C5, Mini Borg 50, PS
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jrcrilly
Refractor wienie no more
Reged: 04/30/03
Posts: 30716
Loc: NE Ohio
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Quote:
The single arm Alt-Az mount of my NexStar 6SE appears to have excessive backlash on the altitude axis as there is a free movement (play) of about 1/16” up and down when I rock the OTA by hand.
That's normal for all the single arm Celestrons. There is no worm drive so the backlash in the transfer gears appears at the OTA.
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John C
Battle Cry of Reno
http://www.wadsworthobservatory.com
My Cloudy Nights gallery
AT12RC
AT65EDQ
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Bob Griffiths
Getting Grouchy
Reged: 10/10/05
Posts: 10103
Loc: Frederick Maryland
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Yep its normal...just adjust your backlash settings and when powered on the "play" will be eliminated..
Bob G.
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CPC1100
Nexstar 8i + GPS & Rays Brackets
Denk S1 power switch
Orion 100 mm Refractor
Meade LXD 55 ...AR-5 127 mm Refractor
Gerbring heated clothing in the winter
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TONGKW
scholastic sledgehammer
Reged: 01/16/07
Posts: 866
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Despite after adjusted the anti-backlash settings many times I still get the 1/16” free play on the altitude axis of my NexStar 6SE mount. Thus during the changing of eyepieces or whenever the OTA is touched, the OTA could be moved either up or down by 1/16” resulting in the lost of the GoTo alignment. Feeling frustrated I open up the outer cover on the mount and after careful examination I find the 1/16” free play is actually due to the driving shaft being supported only by a single bearing on the outer end and no bearing on the inner end, such that the driving shaft would wobble from side to side whenever the direction of rotation is changed and this shows as the 1/16 free play of the OTA. A photo below shows the single bearing on the outer end of the driving shaft and the inner end can be seen with the OTA removed. I would think it is good engineering practice to have the driving shaft supported by two bearings.
Would other owners of the NexStar 6SE please tell me whether they have similar problems.
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BBishop54
sage
Reged: 06/08/07
Posts: 247
Loc: Upstate N.Y.
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I havent noticed this but I have this scope and the next time I use it I'll look for the problem you speak of.
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David Bishop
Nexstar 6SE
The conquest of space is worth the risk of life.
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Tel
Postmaster
Reged: 03/31/06
Posts: 7764
Loc: Wallingford England
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I don't get any altitude backlash on my 8i but there is about 2mm on the azimuth axis. I guess this represents backlash between the teeth of the spur gears and the fact that there's no friction clutch on this axis to absorb it.
I think I once mentioned this to Bob G. and he confirmed a similar amount of slack on his 8i. (Was this correct Bob ?)
However, I recently measured the amount of play on a friend's new 8SE and there was none. Anyone any views on the reason apart from a certain degree of wear ? Hasten to add that it causes no real practical problem to me.
Tel
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Truth is the cubed root of Verbosity.
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b1gred
Enginerd
Reged: 04/01/04
Posts: 16902
Loc: Castle Rock, CO 6677' MSL
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I think this is one of the reasons they say to 'approach gotos' from below...
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"Dark Skies & Great Viewing"
RandyR / W0RDR
GPS 9.25 XLT/Sky Align /FeatherTouch
TV85 w/FeatherTouch
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Claudia
member
Reged: 03/05/06
Posts: 35
Loc: Frankfurt, Germany
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I observe the same thing as you, TONGKW: no play in azimuth, 1/16'' in altitutude. Have my 8SE since about half a year now and can not remember if it has been like this from the beginning - don't think so but I am not shure. Baader Planetarium say it would be normal.
I am rather unhappy about this because I am loosing GoTo adjustment from time to time just for this reason (in particular if I am not careful about front or back heavy mounting of the telescope) - actually this is the only thing which I consider really bad about this otherwise great scope .
Claudia
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eric_zeiner
Phoenix's Dad
Reged: 12/09/06
Posts: 8040
Loc: Georgia USA 34 31'57.18N 83 53...
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Yeah Randy you are right. I was out last night and if I approached from the top my alignment would ultimately drift down and away to the left(FOV)but if I approached from the bottom it was good to go. I hadn't noticed this before but I was doing mostly planetary and star viewing last night.
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Eric R. Zeiner
Refractors:
Carton 60/1000
Swift 863 Aerolite 60/810
ATM 60/360
Sears Mod 6335 76/1200
Bailey Alt/Az Pipe Mount on DIY Pier
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"Where there is life there is hope"
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Tel
Postmaster
Reged: 03/31/06
Posts: 7764
Loc: Wallingford England
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HI Eric, according to Mike Swanson's book and contrary to the default setting (Negative), the GOTO approach at least where the 8i 8iSE and 8SE are concerned should be set to positive when operated in the northern hemisphere. This ensures an altitude approach with this series of 'scopes from below the chosen object.
Whether this transcribes to the 6SE I don't know for sure but if the 6SE is back-end heavy like the 8 series then the answer is very probably yes, so I'd advise setting the GOTO approach to positive if you haven't already done so.
If it doesn't work in eliminating the drift you mention, nothing lost -- you can always revert back !
Best regards,
Tel
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Truth is the cubed root of Verbosity.
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eric_zeiner
Phoenix's Dad
Reged: 12/09/06
Posts: 8040
Loc: Georgia USA 34 31'57.18N 83 53...
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Hi Tel,
I do have my goto approach set positive and I just think the drift is something I must live with but as I said as long as I follow the process I have been using then as you say nothing lost. BTW, thanks so much for the Auto Two Star advice, it worked like a champ 
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Eric R. Zeiner
Refractors:
Carton 60/1000
Swift 863 Aerolite 60/810
ATM 60/360
Sears Mod 6335 76/1200
Bailey Alt/Az Pipe Mount on DIY Pier
Some really nice vintage EP's
"Where there is life there is hope"
Copper Mines Observatory
Carton Scope Club
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Tel
Postmaster
Reged: 03/31/06
Posts: 7764
Loc: Wallingford England
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Hi Eric, following on from the above, I checked out the 6SE manual last night and it does indeed advocates a negative GOTO approach setting as with my N8i.
It would therefore seem that the same characteristics apply both to the 6SE as to my N8i and as I took Mike Swanson's advice, both should then be set instead, to positive (You've in fact proved anyway that this works for you as it does for me so a positive setting is the way to go ! ).
BUT ! if as you mention, you're still experiencing some object drift, do you put this down to the spur gear backlash, which is very sensitive on the altitude axis ? If so, this can be corrected and generally applies only when you adjust an object in the FOV using the HC.
Alternatively, is this a slower process whereby the chosen object progressively drifts from the FOV as you observe which I would think relates more to a slight tracking problem ?
Best regards,
Tel
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Truth is the cubed root of Verbosity.
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eric_zeiner
Phoenix's Dad
Reged: 12/09/06
Posts: 8040
Loc: Georgia USA 34 31'57.18N 83 53...
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Hi Tel,
I think that I need to try the Precise goto feature along with perhaps some more accurate alignment techniques to include using Polaris as my starting point for the Auto Two Star. I think with all of these factors combined and a little more precision on my part from the alignment aspect, I should be able to eradicate this problem. As an aside, from a visual standpoint this is no big deal but once I start doing AP, then it will be a problem.
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Eric R. Zeiner
Refractors:
Carton 60/1000
Swift 863 Aerolite 60/810
ATM 60/360
Sears Mod 6335 76/1200
Bailey Alt/Az Pipe Mount on DIY Pier
Some really nice vintage EP's
"Where there is life there is hope"
Copper Mines Observatory
Carton Scope Club
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Tel
Postmaster
Reged: 03/31/06
Posts: 7764
Loc: Wallingford England
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Hi Eric, if you're not sure, perhaps let me point out that precise GOTO has nothing to do with initial alignment but is a very useful feature particularly when you're imaging.
If I'm trying to teach you to suck eggs please forgive me but "Precise GOTO" works as follows. Say for example, you want to centre the Bubble Nebula in your EP prior to imaging but you can't see it visually in real time.
You then call upon "Precise GOTO" which will slew the OTA automatically to the nearest bright star to the Bubble's position and request you centralise that. Once done, you just press "Enter" and the OTA slews back to the "Bubble" placing it in the centre of the EP. If you couldn't see it before you still won't be able to but your camera will !
Alternatively, if you want a more general improvement in accuracy within the area of the sky you wish to investigate then use "Sync". The procedure is very similar. If for instance you want to survey the area around Lyra then "Sync " on Vega. You will be asked to centralise Vega in your EP. When done and "Sync't" other objects in Lyra and its close surrounding area should at each slew, be pretty central in you EP.
Again Eric, forgive me if you are already aware of all this. It was just the way I interpreted your post.
Best regards,
Tel
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Truth is the cubed root of Verbosity.
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b1gred
Enginerd
Reged: 04/01/04
Posts: 16902
Loc: Castle Rock, CO 6677' MSL
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Good tip "Tel" (again)
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"Dark Skies & Great Viewing"
RandyR / W0RDR
GPS 9.25 XLT/Sky Align /FeatherTouch
TV85 w/FeatherTouch
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