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New Celestron dovetail width is undersized.

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#1 mistyridge

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Posted 19 April 2011 - 07:26 PM

Has anyone checked out the width of the dovetail bar (orange bar)on their recent vintage Celestron SCTs. I went to slide my C11 onto another mount equiped with a Losmandy width saddle. It just slid off even though the saddle clamp were screwed down tight. It turns out the orange dovetail bare on the C11 is about 1/8" udersized. I just ordered a new Losmandy G11 that will not hold the C11. My older C9.25 had a slightly wider bar. What's going on? Is their a fix?

This also posted on the SCT forum.

#2 mclewis1

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Posted 19 April 2011 - 08:24 PM

This is very interesting. There are some comments embedded in another thread about a problem getting the ADM dual saddle to provide enough clamping capability on a Celestron dovetail bar. With the first instance of this situation the poster got Anthony at ADM to machine a bit off of the saddle allowing it to close a bit more. The assumption at that time was that it was a minor ADM problem. In general the fully moving side plate design saddles (ADM) haven't had any issues with variances in the dovetail dimensions the way that solid side plate saddles (Losmandy) sometimes do.

The extruded orange dovetail bar for the CGE/CGEM/CGEPro mounts has always AFAIK been the same as the Losmandy D plates (3" wide the inside of the angled cut). The angle of the dovetail has varied a bit between different vendors of similar dovetail plates but the width hasn't varied without causing problems. William Optics had an issue with the fit of their dovetail plates a while ago ... I believe it was suggested that this was due to metric measurements in the machining.

Perhaps Celestron now has a similar issue?

#3 mistyridge

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Posted 19 April 2011 - 08:43 PM

Mark I have three Losmandy width saddles plus all my other scope are equipped with matching bars all by different manufactuerrs. The new (less than a year old C11) slides right trough all of them. The C11 bar is 1/8" smaller. I was wondering if this is a isolated manufactuering defect or all that way.

#4 Bruce FitzGerald

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Posted 19 April 2011 - 08:45 PM

You will need to purchase a Losmandy or new Celestron dovetail. Celestron changed sizes sometime after my GP C8 was made (circa 1993) and my CGE Pro (2010). After putting the new Losmandy rail on the C8 OTA it fit perfectly! :p

#5 Cotts

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Posted 19 April 2011 - 09:27 PM

You will need to purchase a Losmandy or new Celestron dovetail. Celestron changed sizes sometime after my GP C8 was made (circa 1993) and my CGE Pro (2010). After putting the new Losmandy rail on the C8 OTA it fit perfectly! :p


Why in the wide world of sports does Celestron produce a dovetail that does not fit either one of the two 'standard' dovetail protocols? All we have in the hobby are the Losmandy 3" and the smaller Vixen dovetails. That someone has to fork out $100 for a new plate is just plain wrong. It's even worse that the dovetail in question looks exactly like a Losmandy but then comes up 1/8" too narrow. Are they purposely trying to mess with people's heads?

Unconscionable.

Dave

#6 mistyridge

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Posted 19 April 2011 - 10:28 PM

I agree this is just plain nuts. Someone over in China cannot read the plans and specs or C is just trying to get proprietary. I either have to get the saddles cut down or buy a new bar. I have not checkd with Losmandy.

#7 mak7

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Posted 19 April 2011 - 11:03 PM

Sounds to me as the though the bar does not meet standards and is therefore defective.

Have you posed the question to the dealer or Celestron support ?

IIRC, I have never heard of a Celestron dovetail being undersized. I have always expected they met the losmandy size standard as I have never heard differently unless it was specifically vixen size.
Brad

#8 jmiele

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Posted 19 April 2011 - 11:48 PM

Just a note the website states -
"•Includes dovetail rail compatible with CGE mount"
So not so sure they will agree it's defective. I found that on the optical tube C-14 page. So tomorrow I may be hosed myself with the C-14. Joe

#9 PHampson

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Posted 19 April 2011 - 11:59 PM

That's pretty rich - compatible with a mount they no longer make.



Paul

#10 skybsd

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Posted 20 April 2011 - 01:37 AM

Hello,
Sadly, inconsistent dovetail bar manufacturing measurements are quite normal, really.

Simple things like the width of the bars to the angle of the edges are often all over the place. Not just Losmandy, but also Vixen standard dovetails are often inconsistently made.

The simplest option is to get an after-market dovetail to replace the one your current bar.

Regards,

skysbd

#11 rmollise

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Posted 20 April 2011 - 05:27 AM

That's pretty rich - compatible with a mount they no longer make.



Paul


But we are also talking about dovetail bars they no longer make. Current ones _should_ be OK.

#12 Eddgie

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Posted 20 April 2011 - 08:23 AM

As far as I know, the CGE style dovetail has ALWAYS been narrower than the Losmandy dovetail.

Or... One could argue... The Losmandy Dovetail is too wide for the CGE mount.

Anyway, I had to take out the screws that limit the out-travel of the jaw on my CGE and replace them with longer ones to allow the Losmandy plate on my 6" refractor to fit into the saddle.

My CGE is about 7 or 8 years old, and the C14 is XLT, so less than maybe 5 years old, so this isn't a NEW Celstron, but the EdgeHD 8" I purchased last year had the same width dovtail as the C14. So, I don't think anything has changed.

So, as far as I know, they have always been different sizes.

In fact, the Ci 700 (previous to the CGE) also used the narrower Celestron dovetail.

The simple solution for a CGE dovetail owner that wants to use the the scope in a Losmanday mount (and I have seen this over the years as well) is to use a long thin strip of metal along one side of the CGE dovetail to increase the width. You can use standard aluminum bar stock. Just drill a hole at either end of the strip and the dovetail, countersink the holes in the strip, and use machine screws to hold the strip against the edge of the dovetail.

So, I suspect that these have always been different, and most people simply assumed that they were the same. As far as my own experience shows, they were never dimensionally the same design.

#13 jrcrilly

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Posted 20 April 2011 - 08:32 AM

I've not experienced any incompatibility problems with a wide variety of Losmandy, ADM, and Celestron plates in various Losmandy-compatible saddles (CGE, BTTech, Losmandy). The only thing I've had to fight was using Losmandy plates with radius blocks in the CGE; the clutch knobs interfere with the radius blocks when end-loading the plate so it's necessary to modify the saddle a bit (as Eddgie describes) to convert it to a tip-in saddle. The plates themselves fit just fine.

It sounds as though there's at least one Losmandy-compatible saddle out there that's a bit wide and has trouble with the Celestron plates - but it's none of the above. That'd be more an issue with that particular saddle than with all the other stuff. We'd need to know just which mount it was that wouldn't clamp a Celestron plate.

#14 Eddgie

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Posted 20 April 2011 - 08:57 AM

Well, neither the Celestrion Ci 700 I used to own, or the CGE I currently own, would take a standard Losmandy dovetail.

Now the GGE and Ci 700 saddle design is a bit different than the Losmandy. The CGE and Ci-700 use a full lenght clamp rail so the entire clamp face moves in and out. The limit of out travel is governed by a single screw at the center of the clamp rail.

In both mounts, I had to replace this screw with a slightly longer one in order to use Losmanday saddles.

I was afraid that there was not enough threading left when I backed the screws out as required for the Losmaday plate, and though it bears no load, I decided to simply replace them with longer screws.

Maybe Celestron DID use longer screws on later versions and that could account for why newer Celestron mounts don't have this problem.

But back to the OPs remarks, while you or others might never have had incompatibility problems, the fact is that that all of the CGE dovetails I have ever owned have been narrower than the Losmanday plates.

I don't think Celestron changed the dovetail design. That was my main point. They have always been different, and the saddles are a bit different too.

And I know that others have had the issue as well.

Anyway, the simple solution for the OP is to make a full length shim. And as I said earlier, I have seen these on other Celestron dovetails, so it seems to indicate that other people also had the problem that their scopes were not clamping tight in Losmandy saddles.


He can of course modify the Losmandy saddle, but this would take some machine work, and in the end, a full length shim is a proven and cheap solution. It can be cut from strip stock available from Home Depot, and he doesn't even need to tap the dovetail. He can just drill though and use short screws with nuts backing them up.

Needs to countersink the screw though. Otherwise, it won't slide into the saddle. But this is easy.

#15 mclewis1

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Posted 20 April 2011 - 09:13 AM

There indeed has always been a bit of variation between the width of the extruded "CGE" dovetail bars and machined Losmandy D type plates. The Celestron bars have been a little bit narrower ... but there hasn't been an obvious problem with this (except possible with some of the earlier fixed side plate saddles). There are plenty of folks using those CGE bars in Losmandy and other fixed plate saddles. The moving side plate saddles (ADM and others) haven't been a problem.

Recently there appears to be another change to the the Celestron bars ... a further narrowing which has caused a problem with the ADM D type dual saddles (I can't imagine that there would be a problem with the standard ADM D type saddles as they appear to have lots of extra room to close on narrower bars). ADM seems to have instituted a slight change to their dual saddle to take care of these newer Celestron bars.

As mentioned above folks are going to have to be very careful with the new Celestron bars in other brands of D type saddles ... especially those with solid side plates. I'm sure Celestron will also point out that their bars continue to work just fine in CGE/CGEM/CGEPro mounts and likely something like "we never said it was Losmandy D plate compatible".

The bottom line - don't assume something will work just because it did historically ... stuff changes. If something isn't specifically spec'd to work with another product it would be smart to ask and get verification ... and it's always a good idea to practice additional insurance by using safety stops at the ends of dovetail plates/bars.

The best part of standards is that there are so many of them ... sigh.

#16 Figment

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Posted 20 April 2011 - 09:29 AM

I bought a new Edge HD 9.25 at NEAF this past weekend and the dovetail was over a tenth of an inch smaller than what I expected it to be.

When I tried to clamp it in my new ADM dual saddle the scope would slide freely.

I have been in touch with Anthony at ADM and I am getting a new dovetail from him. Oddly enough, he has one of the new orange cge dovetails at his shop and while it's smaller than expected, it's within the tolerances of his clamp and holds fine.

#17 mistyridge

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Posted 20 April 2011 - 11:51 AM

Yes the new Celestron dovetails are slightly smaller. I bought my C11 new in October last year. The 5 year old C9.25 that I recently sold had a wider bar. A shim o r new bar should solve the problem.

#18 jmiele

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Posted 20 April 2011 - 11:54 AM

My C-14 came today and the dovetail fits the AP DOVELM162 saddle perfectly..
It's also the Edge Tube on a standard C-14! Woot..bonus..Joe

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