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Rick Woods
Post Laureate
Reged: 01/27/05
Posts: 4104
Loc: Inner Solar System
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Quote:
It seems to me a fork mount ought to be fairly simple to make very solid. And yet everyone here seems to agree that their factory forks for the various scopes are less than optimal. I don't get it, the forks on the LX's look pretty danged beefy for example.
The problem is the RA bearings. The design is bad. Look at the Mathis mounts - see the big honking cone at the base of the RA axis? That's what allows them to have the big, properly spaced bearings. There's not enough room in the base of M or C forks to give them the stability they need when mounted equatorially, especially the big ones. The 14" LX200 mount is beefy, all right, but it's that darned base that makes it wiggle!
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- Rick
14" LX200GPS
8" Meade 826C
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MtnGoat
scholastic sledgehammer
Reged: 02/18/07
Posts: 825
Loc: Columbia Gorge, WA
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ahhh, that makes sense. you'd think one side or the other would use that to trump the other guys
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"Ignorant people think it's the noise which fighting cats make that is so aggravating, but it ain't so; it's the sickening grammar they use." Mark Twain
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Jeff Young
Post Laureate
Reged: 08/04/05
Posts: 3050
Loc: Ireland
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Rick is correct -- the problem is in the RA bearings. Mass-market forks use radial bearings which only locate the axis in 2 dimensions. There's no positive control over the 3rd dimension.
Even the big Meade 16" fork mount vibrates badly when on a wedge. (In alt-az its rather substantial weight is directly over the RA bearing providing better control.)
GEMs, in contrast, normally use radial bearings and thrust bearings. The thrust bearings positively locate the 3rd dimension (along the axis of rotation). One could also use conical bearings, but I don't know of anyone that does.
Cheers,
-- Jeff.
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Nikon 18x70s / UA Millennium Colorado:
Solarscope SF70 / TV Pronto / AP400QMD Coronado SolarMax40 DS / Bogen 055+3130
APM MC1610 / Tak FC-100 / AP1200GTO Tak Mewlon 250 / AP600EGTO
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mclewis1
Thread Killer
Reged: 02/25/06
Posts: 2354
Loc: Colorado
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Quote:
HEY DAVID: The 12" Meade is 75 pounds, OTA & fork only.
If your 14"R is only 69 lbs, then the mirror must be missing. The weight of the OTA/Fork is 116 pounds. HAL
Sorry HAL but Davids correct ... that OTA is just under 70lbs (those big forks and base easily make up the other 45lbs).
Interestingly the C14 OTA is around 50lbs so if the mount is questionable (not able to move up to a Titan/NJP class of mount) then that would be another reason to choose the C14 over the M14. But personally I would be hard pressed to pass up those R optics.
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Mark
C11, C6, APM/TMB115, and AT80ED
Tandem mount CGE and CG-5A, WO EZ-Touch and AT Voyager
25x100s, 8x56s, T-Mount Light, and Mark 1 eyeballs
Modded 350D, SPC900, Mallincam
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Hal Pollner
Reged: 08/30/05
Posts: 6161
Loc: Southern California Desert
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HEY MARK:
I was referring to the OTA PLUS the Fork assembly, so I'm still correct!
This is what you would have to carry to the Tripod for mounting. (I'm not considering a GEM here...)
HAL
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sang33ta
professor emeritus
Reged: 07/08/08
Posts: 529
Loc: UK
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If you buy a 14" Meade you'll get fed up of carrying it out and build it a little house in the garden so budget for this http://www.ccastronomy.org/photos_home_observatories_smith.htm 
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Hioptic 152mm f12.5 Maksutov
Celestron Advanced CG5-GT Mount (Mr Noisy!)
Meade 4000 Super Plossl Set
Casio QV-2900UX
Got fed up of waiting for Meade ETX-150 so put this together for £500/$1000
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rmollise
Pooh-Bah
Reged: 07/06/07
Posts: 1360
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Quote:
This is fascinating stuff.
It seems to me a fork mount ought to be fairly simple to make very solid. And yet everyone here seems to agree that their factory forks for the various scopes are less than optimal. I don't get it, the forks on the LX's look pretty danged beefy for example. The pix of the massive LX16 forks look like they would be bombproof.
It's not so much the forks, it's the drive bases they are mounted on, and, even moreso, what you hafta do with that-there fork: tilt it over on its side to polar align. A hefty wedge is de rigueur, and even then you have an unstable situation. The 16? If you could get one, it's not so much the forks, but the OTHER bombs that will have you cryin' real tears.
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Uncle Rod
Watch for Rod's New Book:
Choosing and Using the New CATs--coming soon!
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tim53
sage
Reged: 12/17/04
Posts: 306
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Quote:
I checked out the mount but couldn't get the price..I'm not paying them 12 bucks just to look at ads. For now.
that does look like a monster of a mount and very capable. However, it still entails my basic problem...I spend mucho dollars only to still need the OTA to use it with. Leaning ever more to just figuring out how to mount the Z12 since then I only need the mount.
Well, I probably shouldn't buy it myself (am still waiting to hear about a Tak EM-500 that someone closer to the seller is interested in as well), so I'll tell ya.
He's asking only $2K for the Mathis mount. If it's anything like the modern version, it's about 200 pounds without the pier or the OTA. That sucker won't move. (which is only a problem if you WANT to move it!).
I checked the company who made the goto upgrade for it, and though they're using servo motors now, the goto kit is currently about $3K by itself.
Probably my biggest trepidation regarding that mount is that I'd need to build an obsesrvatory for it. Less big a deal, the software is only PC. I have one, but I prefer the Mac. So it's not a big problem, compared to the nonportability.
Would hold my 12.5" Cassegrain (and maybe the 6" f/10 and 6" f/15 Jaegers piggyback!) pretty much fine.
-Tim.
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"We`re just waiting looking skyward as the days come down.
Someone promised there`d be answers, if we stayed around."
-Orchestral Maneuvers in the Dark, "The Romance of the Telescope"
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David Pavlich
Postmaster
Reged: 05/18/05
Posts: 6309
Loc: Mandeville, LA USA 30.38 X 90....
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Quote:
HEY DAVID:
The 12" Meade is 75 pounds, OTA & fork only.
If your 14"R is only 69 lbs, then the mirror must be missing. The weight of the OTA/Fork is 116 pounds.
HAL
Oops...forgot to mention that it's the OTA only that weighs 69lbs. My error...
David
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A few scopes and mounts.
Proud Member; PAS NOLA,
Life expectancies would go WAY up if green vegetables smelled like bacon...
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Al Canarelli
Pooh-Bah
Reged: 12/06/07
Posts: 1443
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Oops...forgot to mention that it's the OTA only that weighs 69lbs
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I've often wondered...why are Meade SCTs so much heavier than Celestron's? I'm not talking a few pounds, it's more like almost 30 lbs. I've weighed my bare C-14 OTA on a good scale and get just about 40 lbs.
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