Boot
member
Reged: 06/04/07
Posts: 15
Loc: Lions Head, Ontario
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The Meade corporation has broken a cardinal rule of machine design as far as their (my) LXD75 mount goes.
The rule is this:
Screws should be made of a softer material than that into which the threads for said screw have been tapped.
Why? Beacause if anything gets stripped, it is the easily-replaceable screw, NOT the body of the device.
What am I talking about?
The LXD75 mount is cast from rather soft aluminum (or something too soft...). The "secondary lock knob", on the other hand, is made of a much harder metal. The result is that the threads in the mount are stripping-out rather than the screw threads.
I will now learn how to tap threads.
I need to drill-out and tap some larger threads into the mount, then replace the secondary lock knob w/ a larger, matching SOFTER screw.
Am I the only one out here finding new ways to break things?
Edited by Charlie Hein (06/29/09 12:45 PM)
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4947
Loc: MA
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>>>Screws should be made of a softer material than that into which the threads for said screw have been tapped. <<<
That not a rule I've hear of or seen applied. Screws have to be hard so the heads don't strip, much harder than the aluminum much equipment is made of. The only reason that a hole will strip is if the fastener was over torqued, the thread have corroded or galled, the joint was subjected to well over the intended load, or repeated disassembly/reassembly cycles have worn them out. If you do strip out threads, it's common to fix them using Helicoil inserts or similar. This generally produces a stronger thread than that in the native material. In some applications in engines and such, Helicoils are used from the outset to improve strength.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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Ed Kessler
scholastic sledgehammer
Reged: 05/17/06
Posts: 828
Loc: Millersburg, PA
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Use a high quality bolt with threads that are not rough or sharp, and some lithium grease.
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Ed Kessler
Televue NP127is, Borg 101ED,
Coronado SM60, 1961 Questar Standard (updated with new optics and a Powerglide II Retrofit, 2009)
16" "Jeff Counsil Dob"
Vixen VMC200L
Pentax XO, XP, SMC Orthos, Vernonscope Brandons
Televue 2-4mm Zoom, 13mm Ethos, 22mm Nagler, 35mm Panoptic;
TAK 32mm MC Erfle; 25mm and 15mm Zeiss Microscope Eyepieces
sic itur ad astra (Just to look profound!)
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vegasMike
professor emeritus
Reged: 05/24/04
Posts: 605
Loc: Las Vegas
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Take a look at this vendor "Scopestuff". THey have heard your (and others) cries. http://scopestuff.com/ss_l7sa.htm
In the case of my previous LXD75, repeated tightening and loosening destroyed the threads. I bought a Vixen mount after that. Vixen, whom Luigi has poignantly called, "a casting shop", yet in my mind, a damn good one.
I wish you luck my friend.
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Can't afford an APO but I used to get my mail at one...
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 2704
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I agree with Luigi. A screw softer than the aluminum mount would be too soft.
And if you made the mount out of steel to match the hardness of the screw, it would be a lot heavier.
If you DO want a harder thread, buy a Helicoil kit. When you drill out the old thread, use the Helicoil to go between the screw and the mount material. This way, when you screw things in, they screw into the helicoil.
If you ever strip the Helicoil, you can unscrew it from the hole and replace it.
The only downside is that there needs to be enough room in the metal to support the bigger hole required by the Helicoil.
And have no doubt about the strength. When professional shops find stripped scew holes on cars, this to me is what the BEST ones do to repair it. This way it allows you to keep the same size hole and tread of the original screw rather than having one hole that is bigger tread size than the other.
The kits are not all that expensive, and if you think this will be an on-going problem, the Helicoil will be THE way to solve it.
Regards.
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 2704
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Oh, and this. The problem is likely NOT the soft metal, but most likely rough threads on the screws chewing up the metal.
The solution to this is to get a threading die and chase the threads using a die. You can buy a die kit from harbor freigt.
Just oil the bold or screw and screw the die down the length of the screw or bolt a couple of times to uniform the threads and knock off any burrs.
ANY screw or bolt that has rough threads will damage just about any thread you put it in if the material is softer.
I bought an inexpensive set of taps and dies many many years ago and ANY time I encounter a bolt or screw that will be removed or turned frequently, I always chase the threads smooth. THIS is the key to not only eliminiating the problem you have, but getting these kinds of connections to work SMOOOTHLY! Having a screw or knob with dress threads greatly improves the smoothness when you DO have to turn or make an adjustment.
Good luck.
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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Boot
member
Reged: 06/04/07
Posts: 15
Loc: Lions Head, Ontario
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Thanks for the advice, guys. I've been away for a few days. But now that I'm back in town, I plan to hunt-up a Helicoil kit w/ the proper range of thread-sizes and go for it.
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The life of a repo man is always intense...
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gnowellsct
professor emeritus
Reged: 06/24/09
Posts: 733
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I saw the head of an LXD75 crack open when it fell over onto soft grass, and got some criticism after saying it looked to me like pot metal, but whatever it's made of, billet aluminum it ain't, and it's considerably less sturdy than the Vixen line which may be cast but is good quality machining.
I think the Chinese mounts have their place but when you find that issues of build quality are begining to annoy you, it is probably time to be thinking about a Losmandy or a Vixen or some other step up.
regards
Greg N
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"Aperture will get you through times of no money better than money will get you through times of no aperture."
featuring selected astrojunk:
bunch o' widefield eyepieces
bunch o' narrowfield eyepieces
couple o' Barlows
couple o' scopes
couple o' mounts
couple o' tripods
and a pier 'n' stuff
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NewAstronomer
Post Laureate
Reged: 09/03/04
Posts: 3020
Loc: Scranton, PA U.S.A
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Quote:
I think the Chinese mounts have their place but when you find that issues of build quality are begining to annoy you, it is probably time to be thinking about a Losmandy or a Vixen or some other step up.
FYI for Vixen I think the Portamount is made in China, while Sphinx SX EQ line and above are made in Japan.
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Chris
279mm f/10 C11 SCT
250mm f/4.8 GSO Dob
70mm f/6 SV70ED
Atlas EQ-G + EQMOD
SVP Intelliscope & ST-4 Autoguide Mod
Vixen Portamount on the way!
DBK 21AU04
Olympus e-500 DSLR
Meade DSI-C
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GaryML
sage
Reged: 02/16/09
Posts: 324
Loc: San Diego, California
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Quote:
Quote:
I think the Chinese mounts have their place but when you find that issues of build quality are begining to annoy you, it is probably time to be thinking about a Losmandy or a Vixen or some other step up.
FYI for Vixen I think the Portamount is made in China, while Sphinx SX EQ line and above are made in Japan.
THe Vixen Porta series are Chinese. The Sphinx, Sphinx D, GP2, and GP-D2 mounts are all made in Japan. The HAL-130 tripod often sold with these mounts is made in China.
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Sky conditions in San Diego, California:
Vixen VMC200L 8" corrected Cassegrain telescope on a Celestron CG-5 Advanced Series GT mount
Pentax eyepieces and Televue eyepieces & diagonal
Fujinon 16x70 Binoculars on a Manfrotto 028B/501HDV tripod
Celestron SkyScout
______________________________________________________
Avatar: Gemini North on Mauna Kea, November, 2008.
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gnowellsct
professor emeritus
Reged: 06/24/09
Posts: 733
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I wasn't thinking of the Vixen Chinese stuff. GN
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"Aperture will get you through times of no money better than money will get you through times of no aperture."
featuring selected astrojunk:
bunch o' widefield eyepieces
bunch o' narrowfield eyepieces
couple o' Barlows
couple o' scopes
couple o' mounts
couple o' tripods
and a pier 'n' stuff
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Trebor777
Hazy
Reged: 01/04/08
Posts: 1164
Loc: Connecticut - U.S.
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Here's a pic of my Atlas EQ-G. Just a cheap Chinese casting.
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- Randy
Telescopes, Eyepieces, Mounts, Filters, CCD Cameras,
Astronomy Accessories, My Eyes, My Mind (Sometimes) and Hopefully Clear Skies.
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gnowellsct
professor emeritus
Reged: 06/24/09
Posts: 733
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Well Randy that's why I always wince inside when I see loads of folks urging someone on to the EQ6 and similar. I would rather have a non-go-to stepper G11 than a Skywatcher EQ6. In fact that is not theoretical, you don't see me selling the G11 to get an EQ6 with go-to. Seeing fractures on poorly cast material makes me cringe.
I think most people feel, however, that the go-to EQ6 is better to own than a non-go-to G11.
regards
Greg N
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"Aperture will get you through times of no money better than money will get you through times of no aperture."
featuring selected astrojunk:
bunch o' widefield eyepieces
bunch o' narrowfield eyepieces
couple o' Barlows
couple o' scopes
couple o' mounts
couple o' tripods
and a pier 'n' stuff
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jrbarnett
Eyepiece Hooligan
Reged: 02/28/06
Posts: 4349
Loc: Petaluma, CA
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How exactly would you do that with cast aluminum mount bodies? Screws are rarely made of materials softer than cast aluminum. Perhaps high-stress areas should use threaded stainless steel inserts into which the screws thread. But then you up the cost of manufacturing considerably on an otherwise budget-priced item.
Good luck fixing your stripped threads.
- Jim
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"I do not know what I may appear to the world; but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me."
- Sir Issac Newton
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BCB
Undercover Saboteur
Reged: 11/24/03
Posts: 5197
Loc: Look over your shoulder
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When a thread in ANY part strips out, there's usually one of a few things to look for..
Biggest one: over torquing (tightening, which boils down to people having gorilla hands, and not knowing their own strength)..
Second : A low percentage of cut thread (thread depth, peak to valley) in the part. This comes from the tap drill selected being too large.. Standard thread cut is approx 65%. Less than that, and you begin to really run the risk of easily stripped threads from not enough thread "overlap/contact..
Third: Worn cutting tools.. IE: drills cutting oversize, worn taps..
Just a few of the majors to consider. Most people will NEVER admit to stripping out a tapped hole, because they don't know what it feels like when the threads give out and strip.. They usually fail after repetitive over torquing, and give way quite easily so it's usually hard to feel it let go..
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Mark
Lost in thought. Please send search party!!!
Astro-Tech 111EDT
Orion 8" F5 Newt w/Moonlight CR-2 focuser
SVP mount w/Meade 497 Autostar GOTO mod
Treeline Observatory
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 2704
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Well, I don't know if it would raise the price CONSIDERABLY. I mean if they were going to do ALL of the holes, mybe it would raise the price $15 or $20. If they ONLY did the holes where a big load was going to be placed (like the Altitude bearing), it would only add a few cents.
Remember, they have to drill and thread the hole already.. To drill it a little larger and thread it with a little larger thread would cost almost nothing additional. Then to run in a Helicoil insert would cost them $2.00 plus labor (and let me tell you, labor in China is appallingly cheap).
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 2704
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Well, I am not so sure if this is JUST a casting issue. Castings can be quite strong.
This could also be a design issue in that when an Atlas is loaded with counterweights and before the scope it put on , the Counterweight shaft acts as a lever focusing all of weight through the fulcrum of the altitude bearing and the lug that the altitude adjustment screw bears on, and transfers ALL of that pressure to a point that is less than one half square inches in diameter.
Any flaw in the casting is going to show up, but even without flaws, there is a LOT of pressure on this one spot.
As much as people overload these mounts, I am surprised that we have not (YET) seen more of this kind of failure.
A casting might not have been the best choice here so that would make it a design issue.
It is true though that any flaw in the casting would make failure far more likely.
Regards.
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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