Jump to content


Photo

Improved dovetail for AT RC8 on Celestron CGEM?

This topic has been archived. This means that you cannot reply to this topic.
9 replies to this topic

#1 aekalman

aekalman

    Lift Off

  • -----
  • Posts: 5
  • Joined: 17 Feb 2010

Posted 17 February 2010 - 11:24 AM

Hi All. First post here.

I would like to mount my AT RC8 on my Celstron CGEM.

The RC8 has a Losmandy-style dovetail, which is not really right for the CGEM. The proper dovetail for the CGEM would be slightly narrower, and have much deeper dovetails so that the dovetail would engage over the entire height of the clamp -- the Losmandy only engages over the upper 30-40% of the clamp, and does not inspire confidence. IOW, the Losmandy dovetail is nowhere near as "deep" or "tall" as the dovetail that the CGEM is expecting.

Are there any plans to offer an alternate dovetail for this configuration?

Also, is there a name / standard that the CGEM dovetail adheres to? It looks to me from pictures that Celestron uses an extrusion (as opposed to a machined plate) as their dovetail -- an interesting approach to the problem. I suppose a compatible dovetail plate could be attached to the Losmandy plate on the RC-8, although I would prefer a complete replacement as the cleanest solution.

--Andrew

#2 TxStars

TxStars

    Apollo

  • *****
  • Posts: 1391
  • Joined: 01 Oct 2005

Posted 17 February 2010 - 12:04 PM

The Losmandy-style dovetail is the better of the two IMO.
But if you like the "Vixen" one I'm sure someone would be happy to swap with you.

#3 Eddgie

Eddgie

    Voyager 1

  • *****
  • Posts: 13209
  • Joined: 01 Feb 2006

Posted 17 February 2010 - 12:35 PM

While they are indeed slightly different, the CGE dovetail (which is what I call it based on the fact that it was introduced with the CGE mount about 10 years ago) and the Losmandy are more or less interchangeable.

The Losmanday Dovetail actually doesn't fit on the CGE as it is adjusted right out of the box. There is a screw that limits how much the clamping jaw can open on the CGE. IT is a very simple matter to either back out the screw a few turns to allow the jaw to open wider, or alternatly (and the approach I personally choose) replace the screw that limits the amount the clamp can open with a longer one so that the clamping jaw can open a bit wider but still have enough threads in it to engage into the hole in the saddle. It is likely that the CGEM has a similar setup.

I have a Losmandy saddle on my Meade LXD 750 and I use my $4000 refractor with a Losmandy dovetail on both the Meade mount and the CGE mount and never felt for a moment that there was anything to be concerned about. The fact that the dovetail sides and thicknesses are different really doesn't matter in practical use.

Regards.

#4 BlueGrass

BlueGrass

    Surveyor 1

  • *****
  • Posts: 1983
  • Joined: 25 Jul 2009

Posted 17 February 2010 - 11:34 PM

The CGEM saddle opens wide enough to accommodate D series plates without problem. It does not fit the D plate 100% but in my experience does provide enough contact surface on the beveled sides to grasp the plate and hold it tight. There is approximately 1/4" space below the plate itself but I've never had any second thoughts about mounting my C8 or the AT106LE on my CGEM. I've never had it slip or wobble once the saddle clamp is tight. I'm sure others with CGEMs have had similar thoughts and concerns.

#5 aekalman

aekalman

    Lift Off

  • -----
  • Posts: 5
  • Joined: 17 Feb 2010

Posted 18 February 2010 - 04:31 PM

Thank you all for your inputs ... I'm not comfortable or happy with the mismatch between the Losmandy D-plate and the CGEM mount, so it looks like I will be fabricating a new plate one way or another. I'll keep you posted ...

#6 mclewis1

mclewis1

    Thread Killer

  • ****-
  • Posts: 11071
  • Joined: 25 Feb 2006

Posted 18 February 2010 - 06:29 PM

Andrew, Order the replacement CGEM saddle from ADM, it fits real Losmandy D plates better and it's also compatible with the smaller Vixen style dovetail bars. It's a great upgrade to any CGEM. link

Oh and welcome to CN

#7 Jeff55

Jeff55

    Viking 1

  • -----
  • Posts: 564
  • Joined: 14 Apr 2005

Posted 18 February 2010 - 06:42 PM

I'll second the positive contact with the standard CGEM saddle and the Losmandy "D" dovetail...with 34 pounds of hardware on my mount the stock saddle holds everything tight and very secure. Also. the saddle does not mark up the dovetail at all.

#8 aekalman

aekalman

    Lift Off

  • -----
  • Posts: 5
  • Joined: 17 Feb 2010

Posted 18 February 2010 - 09:04 PM

Very interesting ... I had not seen the ADM website ... you mean this: http://www.admaccess...CGEM-SAD-BK.jpg , right?

Hmm ... I need to decide whether I want to do that saddle with the stock Losmandy plate under the RC8, or make a custom, much longer plate that can support a DSLR or FLI ML-series given the long extension of the RC8 ...

Thanks for the tip to the ADM website!

#9 th3umbra

th3umbra

    Lift Off

  • -----
  • Posts: 18
  • Joined: 26 Jan 2009

Posted 19 February 2010 - 01:37 AM

I got the ADM dual saddle so I could mount tubes with either Vixen or Losmandy bars. Got the saddle and called it done...

Posted Image

#10 aekalman

aekalman

    Lift Off

  • -----
  • Posts: 5
  • Joined: 17 Feb 2010

Posted 19 February 2010 - 11:16 AM

From the picture, not only did you get their saddle ... :)

Am ordering the saddle today.

--Andrew






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics