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Ball bearings in equatorial mounts

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#1 Gianluca67

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Posted 31 January 2010 - 06:56 AM

Can someone help me understand how manufacturers mount ball bearings in equatorial mounts to reduce friction? I am a bit confused. Do they use them instead of plastic washers you can find in cheaper mounts (for instance under the ring nuts of the RA and DEC shafts) or there are other possibile locations inside the mounts?
Thank you
Gianluca

#2 jrcrilly

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Posted 31 January 2010 - 10:30 AM

Can someone help me understand how manufacturers mount ball bearings in equatorial mounts to reduce friction? I am a bit confused. Do they use them instead of plastic washers you can find in cheaper mounts (for instance under the ring nuts of the RA and DEC shafts) or there are other possibile locations inside the mounts?
Thank you
Gianluca


I've also seen bearings at the ends of worm shafts.

#3 Eddgie

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Posted 31 January 2010 - 02:30 PM

While I have often heard it said that some mounts use plastic bearings, I have not ever actually SEEN plastic bearings being used in a mount. There IS plastic there, but in every case I have ever seen, this plastic acts as some kind of non-load bearing spacer or as a clutch or drag mechanism.

The Meade LXD55 is a classic example. I have heard people say that it uses plastic bearings but nowhere in the mount are there any plastic bearings. Both the Dec and RA axis uses two bronze bearings that support each shaft assembly, one on the end where the weight shaft and polar scope goes in, and one on the worm wheel at the other end.

As I write this, I am LOOKING at the bearings. I have spare, and I quickly pulled the shafts out (takes 2 minutes) to confirm there were no plastic bearings anywhere.

I often see people reference plastic bearings in mounts, but I personally have never seen a plastic bearing in any astro mount I have ever taken apart.. They are just about always either bronze plain bearings supporting bearing rings cut into the shafts or castings, or roller bearings. Plastic lacks the compressibility and wear resistance that lubricated bronze does, and for that reason, any assembly that is expected to carry anything more than a very small amount of weight will use plain bearings or roller bearings.

Any plastic washers that are encountered are normally there for spacing purposes or to act as a clutch of some kind.

Hope this is helpful.

Regards.

#4 Eddgie

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Posted 31 January 2010 - 02:34 PM

And to answer your question of course, which I faild to do, they replace the bronze bearings with ball bearings. This usually entails modification to the mount so that the ball bearing assembly can replace the bronze bearing and be captive.

For the CG5 for example, the updated assembly used a sealed roller bearing at the bottom of the RA shaft, and near the worm, they used a thrust type bearing cage (where the bearings are loaded from the front and back of a ring rather than around the outside of the ring like a common roller bearing.

Regards.

#5 Peter in Reno

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Posted 31 January 2010 - 02:47 PM

It's not related to EQ mounts but Celestron CPC series uses 122 nylon ball bearings at the outer part of the base. But it also uses metal bearings at the R.A. shaft. Meade ETX scopes use plastic bearings.

Maybe that's where people hear about plastic bearings: from fork mounted scopes.

Peter

#6 Eddgie

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Posted 31 January 2010 - 03:06 PM

Ha ha ha.. You foold me in your original post when you said Equitorial mounts.. I thought you meant equitorial mounts because you talked about RA and DEC shafts which equitorial mounts have.

You were really talking about equitorial mounts without those things. Pardon my confusion.

Sorry.

#7 Gianluca67

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Posted 31 January 2010 - 04:06 PM

So to use ball bearing in a mount like the Vixen GP DX which I think it is very similar to the original CG5 would be impractical as there are lots of modifications to be made. However to understand how ball bearings are mounted I am interested in learning which actual modifications were made in the new CG5 which uses ball bearings.

#8 Eddgie

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Posted 31 January 2010 - 04:18 PM

Have you tried astronomyboy.com? He had several pages of instructions on how to tune the CG5, and he also shows some pictures of the newer version with ball bearings.

It is a significent design change. Beyond the capability to reverse engineer I think.

I am not sure why people feel that these mounts require ball bearings. The plain bearings are fine. If it is tight, doing the Astronomy Boy tuneup can make a very big difference in their smoothness. I basically did the same modifications to my LXD55 and the movement was much smoother. Tracking and pointing though did not improve one bit. Still, if you are using a standard Vixen or Celestron without motors and with slow motion controls, I could see wanting to improve the mount to eliminate as much friction as possible.

Good luck..

#9 PJ Anway

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Posted 31 January 2010 - 07:26 PM

The higher quality equatorial mounts use tapered roller bearings. I recently refurbished my Takahashi mount and it had three on the R.A. shaft and two on the Dec. shaft. Tapered roller bearing provide larger contact area (as opposed to spherical (ball) bearings) and they handle axial forces (thrust) better.

#10 Gianluca67

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Posted 31 January 2010 - 11:29 PM

I have seen astronomyboy.com and I will do a complete lubrication of the Vixen GP DX shortly as I bought it 8 years ago. Concerning ball bearings I agree that the design change is well beyond my capabilities so I will not go further with this project.

#11 TxStars

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Posted 01 February 2010 - 03:32 AM

The old Meade DS series of EQ mounts used on the DS-10 and DS-16 used plastic sleeves in both R.A. and Dec.






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