Joe Heafner said:
This past weekend, I purchased a brand new Orion EON 80mm ED refractor. I've somehow managed to get the focuser out of whack. Could someone kindly give me VERY DETAILED instructions on how to get the focuser operating as smoothly as possible? Before I "fixed" it, turning the fine adjustment knob revealed zones in the focus travel. My attempts to "fix" this resulted in chaos and I don't know how to proceed at this point. There are so many allen screws! HELP!
I have worked on a few of the two speed Asian focusers, I imagine the EON is very similar... I have had good success reworking them but they are sufficiently complicated that an explanation is beyond the scope of a forum. Instead, I can only offer some basic suggestions:
- Patience: the key to working on any mechanical device is to understand exactly how it works. This takes time, looking, thinking, experimenting... Try to figure out what each screw does, what it adjusts, why it is there.
- Experiment: Understanding why the focuser is not operating properly is the key to improving the operation. This may require taking several shots at it.
- Take enough time and you will understand the focuser, understand the problems with the focuser and your scope will be back together better than new.
- These Asian two speed focusers are nice when the work, they are reasonably well made but they are not flawless. If you want flawless then you want Feathertouch or another high end focuser.
In general there are two issues, the preload on the Crayford "pinion" shaft and the adjustment/operation of the fine focus unit.
First do some testing to see exactly where the problem is, often the shaft is slipping and just requires more preload. Sometimes, there are adjustments not only to preload but also to the bearings. Adjusting these can help keep the shaft square.
The fine focuser uses three large ball bearings against a small diameter steel shaft to act as a planetary gear reduction unit but rather than gears, it uses friction. There is also a set of tiny balls that act as a thrust bearing. The adjustment of this unit is critical and not for the faint hearted. In the ones I have worked with, the adjustment was secured with Loctite so it took a bit to get it loose. Another problem is having the right tools, I made some work, like I said, not for the faint hearted. I do no recommend disassembling the fine focuser unless you are comfortable with your mechanical skills...
Obtaining proper adjustment requires trial and error, experimentation and understanding. Too much and make for a tight/rough action, too little means it slips... just right means YEAH
As a note: The fine focuser on my Astrotech 102ED was somewhat rough, I described it as "notchy", similar to a bicycle wheel bearing that is too tight. This scope was supposed to be the first in the US, here for review. After testing the focusers on the first ones, Astrotech decided to go with a Feathertouch mod.
Anyone, Adjustment helped but did not resolve problem. Finally I decided to go for broke. I again disassembled the fine focuser, purchased some fine grinding paste so I could "lap/polish" the balls and races. I put a small amount of the paste on the front section where the three large bearings ride, chucked up the unit in a small drill press and ran it for a few minutes. I then carefully cleaned off all the paste, lubed, assembled and adjusted it.
That seems to have resolved the problem, the focuser is now very smooth and very capable of handling heavy eyepieces, I test it lifting a 35mm Panoptic vertically, it works at 20x and it works at 300x+ so finally I am happy with it.
Anyway, I wish I could give you more help. I can't provide you with any short cuts or tricks. But if you patiently approach the problem with the goal of understanding it rather than simply fixing it, you will fix it too.
Jon
