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LXD75 mount serious problem

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#1 HomerPepsi

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Posted 12 October 2013 - 02:56 PM

So after 8 Years of owning my LXD75 SN-8 I decided to install warp drives and give it a good scrub down and polish.

After completing everything I needed to adjust my Right Ascension worm as I could not get the sweet spot between binding and jiggle (where as I could easily do it before). Turns out the center push screw had cracked. See images.

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So I called meade and asked if the had any worm housings and they only have motors. Should I accept my loss and sell the mount as damaged whole, piece by piece or find a cost effective solution (I don't want to dump much more money into this thing)?

Thanks for your help!
Aaron

#2 scott4comp

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Posted 12 October 2013 - 05:56 PM

JB Weld ?

#3 HomerPepsi

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Posted 12 October 2013 - 06:33 PM

First thing I thought of as well. Now, better to salvage the original piece or make and thread a new hole with the cement?

#4 skycamper

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Posted 17 October 2013 - 04:07 AM

I don't think this will ever be as strong as it was before it cracked. I think it would crack again. Im surprised at this but things get weak after years of use I guess. You can try the JB weld option though.

I think a better option is to find this piece used or another mount head from parts. These should be easy to find by placing an ad here or astromart, looking on ebay and such.

Another option would be to part this mount out and replace it with a vixen GP or GPDX head. That should fit on the LXD tripod and the LXD75 motors bolt right on with one small shim on the DEC and a shorter bolt on the RA drive. I think a Vixen GP head alone can be found for $150-$175. Or buy a used LXD75 or Celestron GP scope and sell off the tripod, scope, accessories and keep the head to use. A LXD75 head alone can be found for less than $150.

But try the JB weld first and worry about other options later.

#5 Cliff Hipsher

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Posted 17 October 2013 - 09:59 AM

This is an inherent shortcoming with cast aluminum. The casting and cooling process tends to encourage the formation of a very granular crystalline structure within the part. This granularity inhibits the uniform distribution of tensile and compressive forces. After repeated stress cycles the part breaks.

Another problem is that the nature of the failure and the low quality of this casting make welding an expensive and most likely a futile exercise. The same holds true for using epoxies or other adhesives.

#6 Geo.

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Posted 17 October 2013 - 10:56 AM

I have the Dec assembly from an LXD55, but I don't know if that part is the same. The GP will fit your tripod, but the Az alignment pin will have to be modified. Budget $250 for a GP, unless you are lucky. Head sold for $300+ on eBay last week.

#7 maugi88

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Posted 17 October 2013 - 11:22 AM

Cast can be welded by a professional. Its difficult but It can be done. It has to be heated slowly then welded then cooled slowly. Prone to cracking.

I would take it to a local metal shop for sure they should be able to fix it for you for less than $30.00
$40.00 if they have to re-tap the threads.

I know my local metal shop would.

#8 maugi88

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Posted 17 October 2013 - 11:24 AM

DON'T use jb weld until a pro says its hopeless.

there are probably stronger epoxies out there anyway.

#9 Cliff Hipsher

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Posted 17 October 2013 - 11:58 AM

DON'T use jb weld until a pro says its hopeless.

there are probably stronger epoxies out there anyway.


Its not the strength of the epoxy that matters, its the nature of the failure. Look at what he has to work with, not much if you ask me, and then look at how the part is being mechanically loaded. This thing failed under a tensile load, most likely due to a crack that propagated from one or more voids in the casting. If you do get it epoxied back together, there would be a very thin, very weak layer of epoxy between the two parts. As soon as you loaded the threads the part would fail. Gare-on-teed....

Fellas, I've seen this sort of mechanical failure a bazillion times, and it cannot be repaired. Period. End of Story...

#10 jrcrilly

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Posted 17 October 2013 - 01:07 PM

look at how the part is being mechanically loaded.


There's practically no load on that part. The screws are used to shove a small, lightweight piece of aluminum back and forth to position it. The load is on the bolts that secure it once positioned. It was probably damaged by someone trying to use the adjustment screws while the mounting bolts were tight. That can be prevented by not doing it again.

#11 maugi88

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Posted 17 October 2013 - 07:53 PM

Just saying don't gum it up with epoxy until a professional welding shop says its done for. Aluminum has to be uber clean to weld. Cast aluminum is a pain to begin with. Cast aluminum with epoxy all over it is no more than a paper weight.

If the pros say its toast then it doesn't hurt to try whatever. If its toast you cant hurt it more by trying epoxy. Just a few bucks for epoxy and time. Course if you epoxy it and it falls apart with thousands of dollars worth of payload it might cost a little more.

#12 Cliff Hipsher

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Posted 18 October 2013 - 06:12 AM

My father was a boilermaker and high pressure welder for the AT&SF RR. I've been welding and cutting since I was 10. That's over 50 years of breathing welder smoke and dodging hot slag. The part is toast.

#13 maugi88

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Posted 18 October 2013 - 10:26 AM

My father was a boilermaker and high pressure welder for the AT&SF RR. I've been welding and cutting since I was 10. That's over 50 years of breathing welder smoke and dodging hot slag. The part is toast.


Not going to argue with someone with 50 years of experience. I guess a pro has said the part is toast.

Wonder how much getting a new one milled would cost.

#14 Christopher Erickson

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Posted 18 October 2013 - 01:32 PM

In the hands of an experienced user, AlumiWeld aluminum brazing rods can be used to build up the broken-away piece and then the hole can be re-drilled and re-tapped.

http://www.alumiweld.com

I have used Alumiweld to fix many broken aluminum parts on motorcycles and cars. Even cracked motorcycle engine blocks.

Search for Alumiweld on Youtube to see how it is generally-used.

The BIG SECRETS to using Alumiweld is first getting the dirt, oil and thin layer of aluminum oxide removed from the surface to be brazed. Next, heat the PART, not the rod. As soon as the heat of the part melts the tip of the rod, it will bond and flow properly. You will need to use a ceramic tile on one side to help shape the puddle of Alumiweld the way you want it. Afterwards, you will file on the repair with an oiled-file to shape it back into square. Then re-drill and tap the hole. Use Break-Free CLP as a filing, drilling and tapping fluid. And note that it is a metric thread in the hole.

Or you could send me your broken parts and I could use them as a pattern to machine you a brand-new part. It is a complex, 3-D object that would require several hours to hand-machine. That translates to about $250 for the raw aluminum and machining time. Probably not worth it unless you really, really want to salvage this particular mount.

#15 HomerPepsi

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Posted 28 October 2013 - 12:16 PM

All right fellas! Thanks for all the input, I have a few ideas, in mind, I'll post pics and results when I complete the repair.

Thanks for all the help :D

Aaron






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