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Help to fix EQ5 - Mount Modifications (Bearings/housing etc)

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#1 cjr


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Posted 09 October 2019 - 08:02 PM

Hi guys,


As the topic states i am looking to modify an EQ5 that i have been using for a while to see what i can get out of it. I have an EQ6-R on order as a replacement mount so i don't mind how this goes, obviously like it to be successful but if something goes wrong its not the end of the world. I'm not an engineer so i could be off in my thoughts which is why I'm here.


Basically i was looking to service the EQ5 so that i had a good reliable portable mount for astrophotography but after tearing it down a lot of the internals are less than to be desired.


Basically seeking a bit of advice or an open discussion about how to proceed in making this mount perform a bit better as a learning experience and to get some solid information together for others that may want to do the same.


In breaking down the mount the way things are shimmed and the lack of the correct bearings are my main concerns. Other than the standard de-burring, polishing and re-greasing i am trying to workout what i could do to make the mount perform:


RA Axis - bearings that handle the axial and radial loads

  • The standard bearing that is in there is not really fit for purpose. I am looking at machining out a small amount of the housing or machining up a housing that can press into place and fitting a tapered roller being on the upper end of the shaft.
  • On the lower end of the shaft doing away with the thrust bearing (which is OK but could be done better) and also fitting a tapered roller bearing into place. I would look at machining out the housing to fit a larger bearing then machine up a replacement retainer that currently secures the shaft compresses the thrust bearing, I would machine up a part with the inner outer threads and also a collar so that the bearing could be pressed on that.

DEC Axis

  • Machining out and fitting a tapered roller bearing the end of the Declination housing.
  • I cant really see of any way to fit a bearing into the worm gear side of the declination shaft I'm hoping that the above will still provide a noticeable improvement.

Worm drive

  • Both ends of the worm drives currently have bearings on them (i think the older eq5s didn't) but this seems like its all OK so i was going to just replace with a quality bearing de-burr re grease and reassemble.


Any opinions or advice is appreciated or other items to highlight that i can look into making the mount perform better is great too.


Cheers, Cody.

#2 m. allan noah

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Posted 10 October 2019 - 06:23 AM

I wonder what makes you think the original bearings are 'not fit for the purpose'?



#3 roscoe



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Posted 11 October 2019 - 07:18 AM

So...here's my thoughts and solution to the manufacturing tolerances in my vintage CG-5 mount:

Sleeve bearings, or pretty much shafts running in machined 'holes' in the housing, are more than capable of handling the weight and rotation of any scope you can lift atop the mount, bearings only come into play as necessary at much higher shaft loading or speeds than any of our normal uses.  Always keep in mind that the crankshaft of an automobile engine, which runs at far higher speeds and thrust loads than any mount, runs on plain old split bushings, for hundreds of thousands of miles....

The problem with my vintage CG-5 was that the holes were a bit too big for the shafts - so there was side-play.  The famed oriental glue-grease worked to minimize the slop, but...it was still there.  My 'backyard'  solution, which worked wonderfully, was to use an old mechanics' trick:  The housing on my mount is aluminum, which can be induced to distort fairly easily.  I took a center punch, and punched fairly significant 'dents' into the housing back about 1/8" from the edge of the hole, probably about 8-10 dents around the rim. This caused the hole to close in a bit, enough that I had to tap the shaft into the housing, which, when lubricated, gave me essentially zero-clearance, and removed the wiggle in the shaft (I did both the RA and the dec axes....)

Since I am a visual observer, I just tightened up the worms until they ran reasonably smoothly, and called that good.  The worms and gears would need to be lapped in (run with fine grinding grit in oil) to make them run any smoother, and still, I don't think that their small size and lack of precision would satisfy any serious astro-photo work.

The advanced mechanic-trick, if more bearing surface is needed than can be offered by merely having the rim area distorted slightly, is to drill a series of holes around the housing, and drive into each hole a pin that is a couple of thousandths larger than the hole, which will distort the sides as deep as the pin goes in.  This solution often needs the shaft and housing to be 'lapped', honed with fine grit, to restore any sort of useful clearance, so the shaft will move without a wrench on it....  I'd start with the punched dent method first....

As I think upon the project, it is likely that I fabricated some custom shim-rings as part of the rebuild, probably using oiled stiff cardboard for stock.

I did my mount probably 10 years ago, it still seems fine....  Also, before I found a source of damping grease, I used thick-and-sticky wheel-bearing grease to lube my mounts, a solution half-way between regular greases and true damping-grease.


In the end, my mount ended up with no play at all at the tighter sections of the worms and gears, and very slight play in the looser segments.  Not for me worth tearing it all down, lapping everything, and spending the time to clean all the lapping compound off everything afterwards.....


However, all that said, if you have access to a lathe, and have good machining skills, adding bearings or bushings, and making custom shims, and lapping the worms and gears, will certainly improve the mount's performance.

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