where to get Crayford focuser repaired

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John999R United States of America
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where to get Crayford focuser repaired

#1

Post by John999R »


I was having issues trying to get my new Advanced ZWO focuser to work. I tried many times, but concluded it was likely defective. However, I decided to venture into an area I probably should not have and thought my OTA Crayford focuser might have been or contributed to the problem. I noticed the focuser wasn't snug against the OTA body and the focuser tube wasn't centered with the OTA tube. I went ahead and adjusted a few focuser body screws and managed to tighten up the focuser to the OTA body and centered the focuser tube relative to the OTA tube. However, after I did that my fine focuser knob wouldn't function. It would spin but the coarse knob wouldn't spin with it. The coarse knob was OK and unaffected by the adjustments I had done. I went one step further by disassembling the fine focus knob, removing the inner brass "thing", the item with the fine teeth ring that I assumed meshed with the coarse knob. I was able to turn it out and in, but no matter how it moved the results were still negative. The EAF initially would rotate in fast mode very slowly for about 5 to 8 seconds then stop with the focuser alarm sounding. One revolution of the coarse knob took 15 seconds and I thought that didn't seem normal. The slow mode was hardly detectable but that didn't matter to me. No matter how many times I pressed the fast mode button on the hand controller the results were the same, the focuser just stopped each time. I did download the appropriate software prior to starting up. I did hear some talk about a firmware update and in fact I tried to download what appeared to be an update on the ZWO website, but I'm not sure whether the update succeeded or not or if in fact the update was even required.

The Crayford focuser is to an Astro Tech 106 APO refractor (first generation with gray/white body). After I fiddled with it some more without success I detached the EAF focuser and tested it without any weight on it whatsoever. It still didn't work and it was then I concluded it had to be defective. I had a JMI focuser connected before without any issues and decided to switch to the ZWO imaging system because their focuser had a higher payload limit.

I looked around today for anyone that fixes Crayford focusers and didn't find anything. I'm upset at the vendor I bought the EAF from, I've left three email messages and two voice messages over the past 1.5 weeks, all without a response.
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Lady Fraktor Slovakia
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Re: where to get Crayford focuser repaired

#2

Post by Lady Fraktor »


Most of these focusers are made by a small group of companies, if you post up some images so we can see what it looks like we may be able to help you out.
You did not remove the fine focus knob while adjusting things?
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Re: where to get Crayford focuser repaired

#3

Post by helicon »


Yes it would be nice to see a pic or two so we can try to help you out
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Re: where to get Crayford focuser repaired

#4

Post by SkyHiker »


The EAF doesn't rotate very fast, that speed of 1 rotation per 15 seconds could be normal. I don't have my system set up right now otherwise I'd try it to verify.
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Re: where to get Crayford focuser repaired

#5

Post by Richard »


Oh dear another toothless problem
These focusers rely on friction , if one adjust a bolt here and there then you will mess it up unless you know what you are doing , if you take it apart and think one needs to introduce grease then its a no no , if the fine adjust does not work then you have not put it together correctly or not adjusted correctly
I have never been a big fan of these focusers , a well make rack and pinion will last for ever , these friction ones when they get dirt etc give all sort of problems , problem is no one makes good Rack and pinion and all the higher end scopes have this toothless wonder
In your case just try and clean the friction surfaces with alcohol, meths , but no oil based cleaner
Some pictures will certainly help but if some parts are slightly out of spec , bent parts it will be difficult to see , when one adjust too much
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Re: where to get Crayford focuser repaired

#6

Post by John999R »


Lady Fraktor wrote: Sat Feb 12, 2022 4:36 am Most of these focusers are made by a small group of companies, if you post up some images so we can see what it looks like we may be able to help you out.
You did not remove the fine focus knob while adjusting things?
Sorry for not getting back sooner, but I have a correction to make on my original post and also a positive update. I stated I removed the fine focuser and found the brass mini geared "thing" inside it. That was not the case, the brass gear is located inside the coarse knob and it faces the OTA. What I couldn't figure out is what gear mechanism did the small teeth engage? I assumed they must engage something, after all, they are gear teeth, albeit very small. Inspecting inside the tube where the focuser knob shafts are inserted, I saw nothing in terms of another set of gears, so for now I moved on.

The positive update is the fact I got the EAF to work. By inspecting the Crayford focuser ramp, I detected a thin smear of lubrication oil on the ramp and that is when I remembered oiling the focuser shafts over a month ago and I guess I applied too much oil at the time and it got on the ramp. I reasoned that a Crayford focuser needs some friction to function so I decided to clean up as much of the excess oil, at least the stuff I could access. Using body solvent instead of a water-based degreaser, also Qtips and micro towels, I spent a considerable amount of time cleaning the entire mechanism, especially the Crayford ramp. I don't know if I mentioned it, but I was able to tighten the focuser body to the OTA and center the focuser tube to the OTA tube. The adjustments I made were arbitrary and it seemed I had a little luck going my way.

I then reassembled the coarse and fine focus knobs to the OTA and reattached the EAF. Using the hand controller, I started from the focuser zero position while the OTA was at an incline pointing in the direction of Polaris, latitude-wise. I did all this while inside the house. Since it was at zero, going backward was uneventful, but a good sign was the fact it did not stall or stop as I continued past the 5cm scale on the focuser tube. About 100% of my focusing stops on the 5cm focuser scale mark so I decided to stop the focuser travel at around 55mm. The real test was moving forward when there is a load on the EAF. I was happy to see I had no issues going back to the zero position and this corroborated my theory there was too much oil on the ramp and associated parts of the focuser. During this initial test, I had nothing hanging off the focuser, but on the second run, I attached my DSLR and repeated the run. Again, the EAF performed as it was designed to do both forwards and backward without any hiccups. I guess you could say I was relieved and excited at this development. However, I still have some further verification tests to conduct, more payload, etc. :popcorn:

At this time I still have the issue with the fine focuser knob not functioning manually, I can still use the EAF in both fast and slow modes since it's attached to the left side coarse knob. I still need the help getting the fine focus to work, the knob spins, but it doesn't engage the coarse knob nor will it move the focuser tube. I checked the tightness of all the grub screws, just to rule out the knob just spinning in place around the coarse knob shaft. However, as I turn the fine focus knob it will feedback a 'thumping" sensation with each revolution. I have no idea what that is.

The fine focus knob is secured by a grub screw to the focuser shaft which protrudes from the center of the coarse focuser knob. I know I tightened this grub screw down as far as it could go without damaging it (I don't think). I would like to find a replacement grub screw because it's pretty clear to me the fine knob is just spinning around the shaft. I'll check with Astro Tech or maybe Ace Hardware, they seem to have a wide assortment of bits and bobs.
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Re: where to get Crayford focuser repaired

#7

Post by John999R »


SkyHiker wrote: Wed Feb 16, 2022 12:05 pm The EAF doesn't rotate very fast, that speed of 1 rotation per 15 seconds could be normal. I don't have my system set up right now otherwise I'd try it to verify.
After I found success with the EAF, I agree with you now.
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Re: where to get Crayford focuser repaired

#8

Post by John999R »


Richard wrote: Wed Feb 16, 2022 2:06 pm Oh dear another toothless problem
These focusers rely on friction , if one adjust a bolt here and there then you will mess it up unless you know what you are doing , if you take it apart and think one needs to introduce grease then its a no no , if the fine adjust does not work then you have not put it together correctly or not adjusted correctly
I have never been a big fan of these focusers , a well make rack and pinion will last for ever , these friction ones when they get dirt etc give all sort of problems , problem is no one makes good Rack and pinion and all the higher end scopes have this toothless wonder
In your case just try and clean the friction surfaces with alcohol, meths , but no oil based cleaner
Some pictures will certainly help but if some parts are slightly out of spec , bent parts it will be difficult to see , when one adjust too much
Thank you, I found out what you said the hard way, but I learned something too. Actually, the outcome was better than expected.
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