Jump to content


Photo

Orion Atlas Counterweight Shaft shift w/ rotation

  • Please log in to reply
6 replies to this topic

#1 robininni

robininni

    Viking 1

  • -----
  • Posts: 777
  • Joined: 18 Apr 2011
  • Loc: Stephenville, TX

Posted 15 February 2013 - 03:36 PM

I just got my Atlas and have been playing around with it in the living room (waiting for a pier plate adapter from Dan's).

After putting my deforked CPC 1100 OTA and and ED80T on it using one of Orion's side by side mounts and then adding aonther 11 pound weight to the counterweight shaft for a total of 33 lbs., I noticed when rotating the declination fully around the counterweight bar would 'shift' at one point which could be seen and felt.

I didn't notice this when only using 22 lbs of weight and just my CPC 1100 OTA but then again I wasn't really looking for it and now I find it does it no matter how much weight is on it but it is much more pronounced with 33-44 lbs and using the counter weight shaft extension.

After further analysis, with no weights on the shaft, I can see that the counterweight shaft doesn't rotate true when spinning the declination axis around and around (done at a fast speed to be able to tell and see the counterweight shaft bar slightly wobble). When a lot of counter weight is used this untrue arrangement leads to a repeatable shift of the shaft at one point in a 360 degree rotation each time you pass the point.

I am thinking this won't be an issue when in actual use because the scope doesn't make 360 degree declination moves like I am doing, but is this normal for the atlas counterweight shaft as a function of how the narrow shaft is locked with a single compression lever rather than a 3 point type method to keep the bar centered and straight in its pass through hole?

I just want to make sure I don't have a factory issue with my new mount before I get it all set up and I know the Atlas is popular so many of you have one and can answer this for me.

Thanks!

Rob

#2 neptun2

neptun2

    Viking 1

  • -----
  • Posts: 807
  • Joined: 04 Mar 2007
  • Loc: Bulgaria

Posted 15 February 2013 - 04:05 PM

As i understand you use side by side setup with very different scopes as weight is concerned. The deforked cpc 1100 is much heavier than the ED80. In this case it is absolutely normal in my opinion to not be able to balance correctly in declination such setup. At least this is what i see.

#3 andysea

andysea

    Apollo

  • *****
  • Posts: 1449
  • Joined: 03 Sep 2010
  • Loc: Seattle, WA

Posted 15 February 2013 - 04:20 PM

I used to own an atlas but it's been a while so I am going by memory.
If I understand correctly, the counterweight shaft rotates with the dec axis.
Could the shaft not be true because it has a little play in it's housing and when you tighten it it's pushed off to the side wall? That's the only thing I can thing about.


Andy

#4 robininni

robininni

    Viking 1

  • -----
  • Posts: 777
  • Joined: 18 Apr 2011
  • Loc: Stephenville, TX

Posted 15 February 2013 - 05:32 PM

As i understand you use side by side setup with very different scopes as weight is concerned. The deforked cpc 1100 is much heavier than the ED80. In this case it is absolutely normal in my opinion to not be able to balance correctly in declination such setup. At least this is what i see.


Thanks for the help but it is actually balanced quite well by just adjusting to have the 11" scope much closer to the center. Also, the wobble occurs with just one scope, it is just less pronounced with less weight on the counterweight shaft.

I am really starting to think it is quite normal and totally a function of the way the counter shaft is 'secured' with the lever lock pushing it to one side and probably still allows some play in one axis where enough counter weight can cause a shift in this axis.

Rob

#5 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2544
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 16 February 2013 - 11:29 AM

It is actually quite common for the counterwieght shaft to not be completel true with the rotation of the DEC axis. Many mounts have this problem to some extent. In the case of the Atlas, you are correct that it is most likely a function of the clamping mechanism used to hold the collapsable shaft which may push it slightly off center. It can also be that the nut with the clamp is not made completely straight. Neither of these things is too much of a problem. While it does effect the balance of the DEC to some extent, the effect is fairly minor and the amount of off-balance is generally not noticeable when using the mount.

There is one possibility for this issue that is more problematic and should be resolved if it exists. That is if the preload on the axis taper bearing is insufficient to hold the axis shaft true. If the counterwieght shaft can actually be wiggled around when it is clamped tightly, then the preload may be the problem. That is addressed by loosening the 3 set screws that are resessed in the axis nut (where the counter wieght clamp is located) and then threading the nut further onto the shaft a small amount. You don't want so much preload that the axis gets stiff, just enough that the wiggle is gone.

#6 robininni

robininni

    Viking 1

  • -----
  • Posts: 777
  • Joined: 18 Apr 2011
  • Loc: Stephenville, TX

Posted 16 February 2013 - 12:29 PM

It is actually quite common for the counterwieght shaft to not be completel true with the rotation of the DEC axis. Many mounts have this problem to some extent. In the case of the Atlas, you are correct that it is most likely a function of the clamping mechanism used to hold the collapsable shaft which may push it slightly off center. It can also be that the nut with the clamp is not made completely straight. Neither of these things is too much of a problem. While it does effect the balance of the DEC to some extent, the effect is fairly minor and the amount of off-balance is generally not noticeable when using the mount.

There is one possibility for this issue that is more problematic and should be resolved if it exists. That is if the preload on the axis taper bearing is insufficient to hold the axis shaft true. If the counterwieght shaft can actually be wiggled around when it is clamped tightly, then the preload may be the problem. That is addressed by loosening the 3 set screws that are resessed in the axis nut (where the counter wieght clamp is located) and then threading the nut further onto the shaft a small amount. You don't want so much preload that the axis gets stiff, just enough that the wiggle is gone.


Wow, thanks! You really sound like you know what you are talking about. I will try using as is and I am thinking it will be fine, but if not, I will know how to fix it (or send it back to Orion :) ).

Thanks again!

Rob

#7 zerro1

zerro1

    Fly Me to the Moon

  • *****
  • Posts: 5854
  • Joined: 02 Aug 2009
  • Loc: Smokey Point , 48.12°N 122.25°W Elevation:512 ft

Posted 16 February 2013 - 11:14 PM

You really sound like you know what you are talking about.


Yes, Ed does have some experience with mounts...:poke:


There is a modification that can be done to the Atlas. The stock shaft is removed and the collar that has the lock clamp is bored out, threaded, and a larger 1" diameter shaft installed. I kind of like it for the fact that I can just use regular fitness weights and clamps.

Ed: you saw that mod on my mount when I sent it to you :grin:






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics