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ETX 70 stiffness

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#1 dogeddie

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Posted 02 April 2013 - 02:45 PM

I picked up a used ETX 70 the other day for my son, and for some wide field viewing and terrestrial views for myself. The seller claims it was never used. I would tend to believe him. It looks brand new. I would guess it is from 2004-2005 or so. That is a long time to sit unused. The scope is very stiff in both axes, especially horizontal. It does slew and I performed a mock alignment, which it did well, but I have no idea on the accuracy. I just wanted to make sure it worked.

Is the stiffness on the horizontal axis normal for these scopes? I have had ETX 90 and 125s and don't recall them being stiff, but they are a different build than the 70. Thanks for any help.

#2 Christopher Erickson

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Posted 02 April 2013 - 08:33 PM

Since "stiff" isn't a rigidly quantifiable term, can you provide us with a bit more detail?

#3 Stew57

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Posted 02 April 2013 - 09:05 PM

The clutch on the RA axis never really releases fully. There is always a bit of drag. Perhaps this is what you are referring to?

#4 dogeddie

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Posted 02 April 2013 - 10:08 PM

It is possible that the RA clutch is dragging. I can improve it by loosening the clutch bolt, but then it doesn't hold tight enough to lock it. "Stiff" meaning harder to turn on its axis than the other telescopes I have had - ETX 125, 90, and LX 90. That is a hard term to quantify. Do I need a pipe wrench and a large extension to turn it? No. Would it make a good pinwheel? No ;)

I ended up taking the clutch apart and loosening the white castle nut, but it didn't seem to do alot of good in the end. Initially it seemed better, but by the time I tightened up the clutch enough to grab, it was stiff in its turning again. The base on this scope is different than the larger ETXs; I believe the scpoes horizontal movement rides on nylon bushings, and not grease. I can live with it, and this may be normal for this model.

I believe the early ETX 70 models had the same base as the larger ETXs, which was more robust - so those scopes probably don't have the same issues as the later cheaper built models like this one appears to be? Just wondering about other owners experience.

#5 Stew57

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Posted 03 April 2013 - 08:19 AM

Sticky nylon bushings and a clutch that always drag a bit is what you are feeling. The horizontal movement should ride on the thrust bearing if the castle nut is adjusted right. There is a very small sweet spot. If in polar mode the axis starts riding on the bushings. I replaced the bushings with roller bearings because of this. The quality f the ETX80 is certainly not great.

#6 dogeddie

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Posted 03 April 2013 - 10:51 AM

Thanks for the clarification. Seems the "sweet spot" eludes me
:p

#7 orion61

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Posted 08 April 2013 - 02:36 PM

Use PAO Synthetic lube. It is designed to work on plastic to plastic, or plastic to metal surfaces. I just posted about doing the same thing on my ETX 90 Astro. It came out superb, very smooth.

#8 dogeddie

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Posted 08 April 2013 - 03:28 PM

Thanks for the tip!

#9 dogeddie

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Posted 10 April 2013 - 07:12 AM

Use PAO Synthetic lube. It is designed to work on plastic to plastic, or plastic to metal surfaces. I just posted about doing the same thing on my ETX 90 Astro. It came out superb, very smooth.


I now have a new ETX 80 with the same issue. :( Exactly where do you apply the grease? Between the top of the white castle nut and the white bushing above it that it rubs on? Thanks

http://compare.ebay....dPriceItemTy...

Is this the stuff?

#10 dogeddie

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Posted 11 April 2013 - 12:17 PM

I spoke with the dealer (Highpoint Scientific) today and he opened up both boxes from new ETX 80s from their remaining stock, to see if he had one to swap out for me. He said - "We checked the two that we have in inventory and they were both very stiff as well and would not move smoothly in either altitude or azimuth. When trying to lock the axes down on both of the scopes nothing happened at all. It wasn’t any harder to move the scope either locked or unlocked but was just as stiff." So I am sending it back for a refund and will be satisfied with the ETX 70 I picked up cheap and shut up about the whole thing. Seems like it's just a flaw in most 80s.

On the other hand, I can't say enough good things about Highpoint Scientific. I couldn't believe they would actually go and open boxes up for me to check the scopes. I highly recommend them as good customer service is so hard to come by.

#11 rtanton

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Posted 11 April 2013 - 12:40 PM

Another alternative plastic to plastic or metal to plastic lubricant is Novagard G661. It has been used for this type application for many years starting with GE in the 70's. It also goes under generic product names as silicone dielectric grease (Radio Shack, Home Depot, and auto parts stores). As it contains fumed silica filler is NOT a good choice in metal to metal applications.

Russ (formerly with GE Silicones)

#12 thanar

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Posted 19 June 2013 - 12:00 PM

Hello,

I have had an ETX-70AT for a couple of years now. For as long as I remember, the horizontal axis has been exceptionally stiff. However, sometime last year, stiffness led to erratic tracking, since the axis would rotate in little "jumps" while tracking.

I decided to do some research to try and fix the issue. Read numerous threads, including much on Weasner's Mighty ETX Site , where I stumbled on Xephius' ETX Repair Guide. This last one proved to be quite a valuable asset.

I managed to fix the issue on my ETX for now; however, I believe I will be needing spares of the nylon bushings that cover the thrust bearing axle, since there is a noticeable GAP despite the bushings and grease in this axle setup, even on regular (non-polar) mode. The gap that exists, actually TILTS the telescope's main body plain, hence it makes contact with the bottom base, which produces friction between the bottom and main plastic cases, if you understand my writing. The lower (close to horizon) the scope, the greater the tilt and friction, since the center of mass moves away from the bearing axle.

So, the final question is, anyone knows where I could get some replacement nylon or plastic bushings for the bearing axle? Or any online store that would provide all kinds of bushing and would ship just a couple of them?

I also have a question for Stew57, who says he's replace the bushings with roller bearings. How did you manage that? Unless you are referring to the part of the bushing that stays in contact with the white castle nut that holds the whole set-up firm.

#13 Stew57

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Posted 19 June 2013 - 12:09 PM

CN article
http://www.cloudynig...hp?item_id=2794

Guide for bearing modification
http://www.weasner.c...earing_mod.html

At some time Meade changed the base internals. I believe it was during the production of the ETX70. My ETX80may be the same as your ETX70 but it may not be depending on when your 70 was produced. I saw somewhere on Weasner's site a person had used a needle thrust bearing the diameter of the base to fix the problem you have. it would not help polar mode at all, but keeps the upper base from rubbing on the lower base.


I will hunt for the old nylon bushings and other unused parts from my modifications. If I can locate them I will PM you for your address and ship them to you. It all depends on how well they were hid from my wife. If not good enough they were tossed! :o

#14 thanar

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Posted 19 June 2013 - 12:38 PM

Wow! Thanx Stew for the great reads! I will dive deeper later on and see if I can use some of your ideas!






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