Jump to content


Photo

Celestron 94216 Dovetail ... C8 to CG5 ????

  • Please log in to reply
13 replies to this topic

#1 NKemp

NKemp

    Lift Off

  • *****
  • Posts: 9
  • Joined: 19 Aug 2011
  • Loc: Minneapolis MN area

Posted 02 October 2012 - 08:00 AM

I have a Celestron C8 & CG5 mount. But I don't have the dovetail that adapts the two.

Celestron has dovetail #94216 :http://www.celestron.com/astronomy/celestron-8-inch-dovetail-bar-cge.html

That page is terrible at describing the product:
- It does not tell what it is used for
- The text is focused on what it does not fit
- It does not describe the product dimensions
- The support page links to a dimensioned diagram that does not include:
- The screw hole dimensions for the distance between the holes on one end of the OTA
- The size of the dovetail

It sorta looks like it would fit both the C8 & the CG5 mount but I don't find anything that indicates it will work and some indications that it may not work.

QUESTION: Will the 94216 fit on the C8 & fit the CG5 mount?
- The Screw hole spacing on one end of the OTA is 1.75"
- The Dovetail dimension needs to 1.75"

Thanks in advance,
Nick

#2 RTLR 12

RTLR 12

    Aurora

  • *****
  • Posts: 4558
  • Joined: 04 Dec 2008
  • Loc: The Great Pacific NorthWest

Posted 02 October 2012 - 08:27 AM

Nick,

The #94216 is a Losmandy (CGE) style dovetail. It does NOT fit the CG-5. You will need a dovetail bar like this.

http://www.admaccess...s_Dovetails.htm

Stan

#3 NKemp

NKemp

    Lift Off

  • *****
  • Posts: 9
  • Joined: 19 Aug 2011
  • Loc: Minneapolis MN area

Posted 02 October 2012 - 08:32 AM

Thanks RTLR 12,

Can you describe why it does not fit? What is different?

Thanks,
Nick

#4 ourobouros2k2

ourobouros2k2

    Messenger

  • -----
  • Posts: 489
  • Joined: 10 Nov 2011
  • Loc: okc area, oklahoma

Posted 02 October 2012 - 08:48 AM

Losmandy-d rails are much wider than vixen type rails. The Celestron dovetail bar that you have linked is only for CGEM, CGEM DX, CGE etc... with the wider saddles. CG5 requires vixen type dovetail.

regards
Andy

#5 NKemp

NKemp

    Lift Off

  • *****
  • Posts: 9
  • Joined: 19 Aug 2011
  • Loc: Minneapolis MN area

Posted 02 October 2012 - 09:12 AM

A side-by-side view of the ends of the two types would be helpful. The best I could find are views of adapters:
- http://www.togastro....y_to_vixen.html
- http://www.365astron...ndy-p-2216.html

With these you can see the difference.

When looking at the Celestron dwg of 94216 it is hard to determine the rail dimension (especially since it is not dimensioned on the print)
- http://www.celestron...79025_94216.pdf

#6 A. Viegas

A. Viegas

    Apollo

  • *****
  • Posts: 1062
  • Joined: 05 Mar 2012
  • Loc: New York City/ CT

Posted 02 October 2012 - 09:13 AM

Nick-

You need a "Vixen" size dovetail bar. This is just a piece of machined metal that screws into your C8 and has a rail for the clamp on your CG5 mount head to grab. The clamp on a stock CG5 is sized for the "Vixen" size bar.

You can buy the proper sized product at Scopestuff see here: Scopestuff dovetail for C8

The product #MDC8 is what you need. $79 including shipping. This dovetail bar comes with a mounting bracket that attaches to the bottom of the C8 like a rectangular ruler and the dovetail then screws onto that. All the screws are included. Its rather easy to do.

Cheers,
Al

#7 NKemp

NKemp

    Lift Off

  • *****
  • Posts: 9
  • Joined: 19 Aug 2011
  • Loc: Minneapolis MN area

Posted 02 October 2012 - 09:29 AM

I have the Vixen size bar that is the right length for the C8. The bar part that attaches to the OTA is not wide enough to take the 1.75" hole spacing on the OTA. As such, something like these radius blocks seem to be the answer: http://www.admaccess...dius_Blocks.htm

Or, get some aluminum plate and build an adapter which becomes an issue of "money" or "effort". :-)

Nick

#8 A. Viegas

A. Viegas

    Apollo

  • *****
  • Posts: 1062
  • Joined: 05 Mar 2012
  • Loc: New York City/ CT

Posted 02 October 2012 - 09:53 AM

the Scopestuff mounting plate or the ADM radius blocks are the easy answers.

#9 NKemp

NKemp

    Lift Off

  • *****
  • Posts: 9
  • Joined: 19 Aug 2011
  • Loc: Minneapolis MN area

Posted 02 October 2012 - 06:27 PM

Can you mount a Vixen dovetail on the 94216? Use the Celestron dovetail as the mounting bracket to adapt to the C8. It would have to fit between the 94216 "rails and maybe up a bit.

Thoughts?

#10 HenryV1598

HenryV1598

    Sputnik

  • -----
  • Posts: 40
  • Joined: 01 Sep 2010
  • Loc: Houston

Posted 09 October 2012 - 01:47 PM

If you're not doing photography, just visual, and not loading the payload side down more than the OTA, diagonal, eyepiece, and finder, then you could make your own. I've made a few dovetails out of hardwood that work great. I mounted an old Meade 2080 tube on my CG5 for about $20. I simply cut a dovetail out of hardwood (in my case, oak) and attach it to a suitable metal bar which attaches to the scope. For my 114mm short-tube newt, I attached a set of rings to a hand-cut dovetail - basically cost me the rings plus $10. And for my 80mm refractor, I made my own rings from a 4" pvc coupling (cut in half), attached to wooden dovetail. All-told that rig is about $15 in materials. Its not ideal, but it works.

#11 dickbill

dickbill

    Viking 1

  • -----
  • Posts: 937
  • Joined: 30 Sep 2008

Posted 10 December 2012 - 09:58 AM

Grmmmfffff!
That's all i can say about those dovetails...Mine ordered was the 84217, the one to fit the c9.25. Well, no they don't fit. The dovetail is about half an inch too short.
I know it's because the newest c925 are sligtly longer than the pre-2004 c925, but still...it doesn't take a genius to understand that some old cg5-c925 users might want to upgrade their OTA to a losmandy-type mount.
Half an inch....in terms of engineering, i don't know how to call that.
Well, that or the saddle. The cgem saddle can adapt to smaller width than the standard losmandy width, but not as narrow as a vixen width. And since their is no intermediary between losmandy and vixen, i don't see the point of a saddle that can adapt to slightly narower losmandy-type dovetails, but not to Vixen type.

If i can't return it, I thought i would cut my new cgem compatible dovetail in two, drill holes near the end to screw some steel and fill a gap for about 1/2 inch. Nobody has done that?

#12 RTLR 12

RTLR 12

    Aurora

  • *****
  • Posts: 4558
  • Joined: 04 Dec 2008
  • Loc: The Great Pacific NorthWest

Posted 10 December 2012 - 12:05 PM

If you can return it, have you thought about getting the bar for an 11". You could then drill the required holes as applicable.

Stan

#13 dickbill

dickbill

    Viking 1

  • -----
  • Posts: 937
  • Joined: 30 Sep 2008

Posted 10 December 2012 - 12:33 PM

I can return it, no problem.
About the bar for the 11', its curvature wouldn't fit the c925 ota.
I guess i'm gonna stick to my current solution: a losmandy piggyback plate and ring system that i never used for its intendded purpose (too heavy for a c925-cg5) until i realized i could use the plate and adaptors in place of my vixen-type dovetail.

#14 Geo.

Geo.

    Mercury-Atlas

  • *****
  • Posts: 2843
  • Joined: 01 Oct 2008
  • Loc: Upstate NY

Posted 10 December 2012 - 04:20 PM

The C8 problem goes back to SN #1. The holes on the bottom of the tube were there for accessory fixture, primarily the counter weight system. Swinging the CWs around you wanted a wide base to take the load. Then came the SP-C8 and as far as I can find out, the introduction of the Vixen dovetail. Of course it was backwards. The dovetail was on the mount and the saddle on the scope. It was a pretty lousy solution the two #8 screws were fine for the rear CW bracket, but too light for the weight of the tube, especially when cantilevered out from the rear cell. They stretched and loosened until the thin aluminum rested on the saddle. Tube dimples are common on these SP-C8s. The original dovetail was 1.75" wide.

When the GP-C8 was introduced the dovetail and saddle assumed the current missionary position we all know and love. The Vixen provided 1.75" wide dovetail had a 2.5" wide flange that ran the length of the bar, fit the curvature of the front and rear cells and provided fitment points for the 1.75" spaced counterweight bracket holes.

After the GP was dropped in favor of the CG-5 Vixen continued to supply the dovetail bars for a while. Then Celestron found a cheaper bar without the flange. To use it they had to replace the counterweight holes with two drilled closer together. Some tubes have just the two close holes others have both sets of holes. Like dimensioned lumber, the nominal 1.75" wide bar shrunk to 1.7" and is now called the univeral mounting bar.

Losmandy's D bar is 3" wide. Celestron's CGE/CGEM bar is about 0.125" narrower, but the CGEM saddle will accept the Losmandy bar. I've milled adapters to fit the 13" universal bar on C8s, but have found it easier to buy the Orion Atlas 3" saddle, machine off the bottom flange, bolt a short length of 1.7" bar to it and fit 3" D or CGE bars to may scopes. The Atlas adapter then converts any 1.7" saddle to a 3".

Machining an C8 dovetail bracket from 5/16th plate.

Attached Files








Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics