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Equipment Discussions >> Mounts

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Stew57
Carpal Tunnel
*****

Reged: 05/03/09

Loc: Silsbee Texas
Re: CGEM Declination axis shift new [Re: RTLR 12]
      #5719295 - 03/07/13 08:35 PM

I have installed a lot of thread repair inserts. They all require drilling out the original threaded hole oversize. Some applications do not have enough material to permit this. I do not know if this is a problem in this specific instance. It sounds like it is variable among samples.

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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM Declination axis shift new [Re: Stew57]
      #5719370 - 03/07/13 09:07 PM

Quote:

I have installed a lot of thread repair inserts. They all require drilling out the original threaded hole oversize. Some applications do not have enough material to permit this. I do not know if this is a problem in this specific instance. It sounds like it is variable among samples.




I would say that there is probably sufficient space diameter wise (but it might be close). Thickness is the problem though. There is just not much metal there for the insert to grab onto and it has to be completely below the surface for things like the worm housing bolts. I just replaced a worm housing adjustment set screw and it was a lot easier to simply drill it out and tap it to the next size up using tapping/cutting oil that trying to install a thread insert would be (not to mention the small size of that one). I agree that thread inserts are also not a job for everyone. You could easily make matters much worse since there isn't much metal to work with in the first place.


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RTLR 12
Post Laureate
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Reged: 12/04/08

Loc: The Great Pacific NorthWest
Re: CGEM Declination axis shift new [Re: EFT]
      #5719448 - 03/07/13 09:49 PM

I've have installed the inserts on the worm gear housing mounting threads for 8 mounts so far. All have turn out perfectly well. The use of SS thread inserts in aluminum castings is a very common practice. From an engineering standpoint it makes much more sense than just drilling and tapping the aluminum to a larger size. Although drilling and tapping to a larger size is a much more simple procedure, in my opinion it just isn't the right way to solve the problem of weak aluminum threads.


Stan


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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM Declination axis shift new [Re: RTLR 12]
      #5719664 - 03/07/13 11:43 PM

Quote:

I've have installed the inserts on the worm gear housing mounting threads for 8 mounts so far. All have turn out perfectly well. The use of SS thread inserts in aluminum castings is a very common practice. From an engineering standpoint it makes much more sense than just drilling and tapping the aluminum to a larger size. Although drilling and tapping to a larger size is a much more simple procedure, in my opinion it just isn't the right way to solve the problem of weak aluminum threads.


Stan




The problem with the original threads is not the aluminum but how it is threaded. Most mounts are just fine, but you can tell when they either used a dry tap or a worn tap because the threads are not good and smooth and sometimes even pop out. Cast aluminum taps poorly with a dry tap. If done correctly, the cast aluminum taps just fine and I have never seen anything to suggest weak threads when a good tap and lubricant is used and I have done this a fair number of times now. The threads are always clean and strong. The only time when things might be questionable is if the holes happen to be located in an area with significant casting bubbles but I have not encounted this personally.


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RTLR 12
Post Laureate
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Reged: 12/04/08

Loc: The Great Pacific NorthWest
Re: CGEM Declination axis shift new [Re: EFT]
      #5719755 - 03/08/13 01:08 AM

Did you ever compare aluminum castings. Take a good quality German or Japanese casting and compare it to the Chinese casting of the CGEM. There is a big difference in the purity of the aluminum and the quality and properties of the casting. It has very much to do with the aluminum and not just how the threads are cut, but what they are cut in. I find the aluminum of the CGEM to be very brittle and full of impurities. That's why drilling or cutting it needs to be performed properly and with care. This is also why I choose to install the SS inserts. I think we are on the same page here, we just have different solutions to the problem. I can completely understand the situation from your perspective, as the installation of Heli-Coils is not propitious to your business.

Stan


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orlyandico
Post Laureate
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Reged: 08/10/09

Loc: Singapore
Re: CGEM Declination axis shift new [Re: RTLR 12]
      #5719829 - 03/08/13 03:52 AM

Stan, I don't see the need for insinuating that helicoils would not be propitious for Ed's business. After all, if his customers want helicoils, he can always charge them the difference - the tool doesn't really cost that much.

Probably, in his view, proper threading with a larger-diameter bore is good enough (there will also be more thread engagement with a larger bore) and his customers are happy with that. If he had a lot of returns where customers were PO'ed because their threads stripped, then most likely he'd already be putting in helicoils (and charging the difference).


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RTLR 12
Post Laureate
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Reged: 12/04/08

Loc: The Great Pacific NorthWest
Re: CGEM Declination axis shift new [Re: orlyandico]
      #5719972 - 03/08/13 07:57 AM

orlyandico,

I suppose you are right about that. I only charged $15 ea to install Heli-coil inserts in my shop. Not a prohibitive amount. I see some shops that charge as much as $25 per insert. That would be $200 to do all the inserts for the worm gear housings for both axis. I'm sure Ed could come in somewhere in that price range. The problem with using a larger bolt is that it requires a larger bolt head. In the case of the worm gear housings you now have created more labor time to accommodate for the larger bolt head. This weakens the casting of the worm gear housing. Maybe that's a trade off, but I would prefer to go with the original factory engineered fixture size. I don't like having to alter the design of the housing and I was never a guy that was comfortable with a mechanical 'good enough'. I have found that when you alter something in such a way, it leaves you open to more customer dis-satisfaction that satisfaction. In my opinion it's just not being professional, but that's how I ran my business.

Stan


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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM Declination axis shift new [Re: RTLR 12]
      #5720139 - 03/08/13 09:46 AM

Quote:

orlyandico,

I suppose you are right about that. I only charged $15 ea to install Heli-coil inserts in my shop. Not a prohibitive amount. I see some shops that charge as much as $25 per insert. That would be $200 to do all the inserts for the worm gear housings for both axis. I'm sure Ed could come in somewhere in that price range. The problem with using a larger bolt is that it requires a larger bolt head. In the case of the worm gear housings you now have created more labor time to accommodate for the larger bolt head. This weakens the casting of the worm gear housing. Maybe that's a trade off, but I would prefer to go with the original factory engineered fixture size. I don't like having to alter the design of the housing and I was never a guy that was comfortable with a mechanical 'good enough'. I have found that when you alter something in such a way, it leaves you open to more customer dis-satisfaction that satisfaction. In my opinion it's just not being professional, but that's how I ran my business.

Stan




I have never seen a mount that needed more than two holes fixed. There is plenty of room to move to a larger size and still have room to spare. There needs to be so that the worm housing can move for adjustment. Were that not the case, then I certainly would use inserts. Modifying the housing to fit new bolts would not make sense. I have never seen a need to do this preemtively on any mount.

I understand that the casting used in these mounts is not of great quality, but I have never seen any problems with properly tapped holes in it. Maybe the difference is that I do not machine tap holes so that the ones I do are smooth and strong.

I certainly wouldn't mind another $120 in what I consider to be almost pure profit, but charge for this type of thing? I don't think so. Maybe if I was doing as a separate service that people specifically wanted, but I consider minor repairs like fixing a couple of badly threaded holes to be part of the tuneup service that people pay for. I could certainly offer it as a specific service to replace all of the bolt holes with inserts, but I would personally consider it a waste of people's money and I prefer to not spend my customer's money in that fashion. If someone is dying to have something like that done, I'm happy to work something out with them, but I have never been asked and until someone convinces me that it is necessary, I would try to talk them out of it. That's how I do business and that's what I consider to be professional in the mount tuning business. You were in the machining business I assume and your business and means of profit were different than mine. Maybe that just makes me a stupid business person.


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RTLR 12
Post Laureate
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Reged: 12/04/08

Loc: The Great Pacific NorthWest
Re: CGEM Declination axis shift new [Re: EFT]
      #5720277 - 03/08/13 10:57 AM

Ed,

I would never call you a stupid business person. I think very highly of you, your business and the way you conduct it. If this was implied by anything I have stated, I sincerely apologize to you and everyone here on CN.

Stan


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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM Declination axis shift new [Re: RTLR 12]
      #5720701 - 03/08/13 02:57 PM

Thanks Stan. No problem. I appreciate your take on this from a machinist's point of view.

Ed.


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Carl Lydon
journeyman


Reged: 01/12/13

Loc: Stamford, Ct
Re: CGEM Declination axis shift new [Re: WarmWeatherGuy]
      #5722579 - 03/09/13 04:20 PM

Hmmm, I think one alen bolt for the dec head (just below where the dovetail is) is already stuck, A mayhave over tightened it, as you Gus said might happen. Anyway, though that was lose before i don't think that's where the current wobble is coming from. I do think that using the mothers to rotate thendec , then releasing the clutch and rotating the opposite way might get me back onto a tighter part of the gear, so ill try that next.

I'm planning on going to NEAF, I wonder if there's a celestron rep there that can tune up the mount and save me the cost of shipping?


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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM Declination axis shift new [Re: Carl Lydon]
      #5722619 - 03/09/13 04:40 PM

Quote:

Hmmm, I think one alen bolt for the dec head (just below where the dovetail is) is already stuck, A mayhave over tightened it, as you Gus said might happen. Anyway, though that was lose before i don't think that's where the current wobble is coming from. I do think that using the mothers to rotate thendec , then releasing the clutch and rotating the opposite way might get me back onto a tighter part of the gear, so ill try that next.

I'm planning on going to NEAF, I wonder if there's a celestron rep there that can tune up the mount and save me the cost of shipping?




Celestron does not tune up mounts and the reps that will be at NEAF are sales reps. They will not touch your mount. If something is broken, Celestron will repair it (30 working days for warranty, 60 working days for nonwarranty) or replace it (30 working days if under warranty). If it is not broken, you are likely to get the mount back with nothing done to it. If it was working originally for a fair amount of time, then it is likely that nothing is broken and it simply needs to be cleaned and tuned up.

Back to the original problem and assuming the worm housing is tight, if the "wobble" is back and forth in the direction that the axis turns, then it is a backlash issue caused either by the worm spacing (most likely) or the worm being loose (less likely). If the motion is not in the direction that the axis turns, then the problem is most likely that the axis nut is loose so that the taper bearing does not have enough preload to hold the axis shaft in place. Much less likely is a defective taper bearing.


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MHamburg
scholastic sledgehammer
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Reged: 06/21/06

Loc: Brooklyn, NY/Berkshires, MA
Re: CGEM Declination axis shift new [Re: EFT]
      #5732078 - 03/14/13 11:32 AM

I would just like to post a public heartfelt thank you to Ed Thomas for the great tune-up he did on my CGEM. I just got the chance to remount the scope on its pier and run it through some mechanical paces. (Of course the sky clouded over when I planned to do alignments!) I recommend hypertuning to all CGEM owners.
Michael


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Stew57
Carpal Tunnel
*****

Reged: 05/03/09

Loc: Silsbee Texas
Re: CGEM Declination axis shift new [Re: MHamburg]
      #5732314 - 03/14/13 02:08 PM

Ed does quality work and is a nice guy to boot.

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