A strange thing happened the other night with the focuser on my SV80ED. It's one of the standard Chinese 2" Crayfords and is just over two years old.
Basically, I took the scope out of the case and attached it to my mount. When I turned the focus knobs the focuser was rough and "grinding". It was the same with the coarse and fine focus knobs. It's particularly strange as it was fine when I last used it about 10 days ago.
I removed the focuser, checked for anything obvious (nothing) and put it back together. I did check the little grub screws around the shaft and adjusted them slightly to make sure they were all evenly tightened.
The coarse focus knobs are a lot smoother now but not perfect. However, the fine focus knob seems to turn ok for about a third of a turn then it hits a "bump", i.e. it stiffens slightly then "falls" over the bump before feeling normal again. It's doing this approx 2-3 times per rotation of the fine focus knob.
I'm at a complete loss as to how this has happened. The scope hasn't been dropped or mistreated in any way. In fact, I treat my scopes with kid gloves at all times.
I've emailed Stellarvue for advice but thought I'd throw it open to the many experts here as well. Maybe a trip to Bintel's technicians is required?
Every Chinese Crayford I IMPROVED by adding shrink tube to the pinion shaft - gave the thing grip and actually holds more than a fly's weight.
I DETEST Crayfords - any flavour. Whilst Feathertouch are the best, I still found they slip enough.
R&P all the way, especially Vixen's dual speed version (which I prefer significantly to Takahashi's)
Try the shrink tube Morton. It works. Not as smooth as a standard Crayford, but at least it will hold something and actually move when it is supposed to.
You can buy it from any JayCar , Dick Smith Electronic Stores ..etc
It is very small ' dia ' tubing used in Electronics for covering wiring ... such as ' two wires soldered together ' ....it is ' shrink wrapped ' around the exposed wire to insulate it from causing shorts......
I've used it in Electronics myself ......used a cigarette lighter to gently ' shrink ' the tubing....
Every Chinese Crayford I IMPROVED by adding shrink tube to the pinion shaft - gave the thing grip and actually holds more than a fly's weight.
I DETEST Crayfords - any flavour. Whilst Feathertouch are the best, I still found they slip enough.
R&P all the way, especially Vixen's dual speed version (which I prefer significantly to Takahashi's)
Try the shrink tube Morton. It works. Not as smooth as a standard Crayford, but at least it will hold something and actually move when it is supposed to.
Heat shrink is a great idea Lewis! Will give it a go.
If you get a tight diameter shrink tube, apply some vegetable oil to the pinion shaft before so it slides on easy. Then heat gently with a cigarette lighter or a hair dryer.
Is the focuser the same diameter as the standard ED80? You may need to tap some extra holes to accommodate?
Bo
I think the Stellarvue is narrower. I considered replacing it with a cheap GSO model but not sure it would work without some sort of adapter.
According to the Stellarvue website, if I'm reading it correctly, their new R&P models have an 88.5mm screw thread, which is about 3.5". Not sure if any others focusers would fit.
Interesting tip Lewis re shirk tubing, I must give it a try. Just a question, would the veg oil not eventually dissolve the plastic tubing?
I had a single speed crayford on my ED80 and have since changed it to a R&P as it holds the DSLR better (IMO).
Bo
For those that asked for pictures, here you go. Stellarvue asked me to send them so they can attempt to troubleshoot.
I also have some more info:
Ignoring the fine focus knob, I can get a reasonably smooth setting on the coarse focus knobs, but even here there is a mild 'sticking' once every turn. The fine focus continues to 'bump' three times per turn.
Looking carefully at the part that contains the bearings it looks to me as if the axis of rotation is slightly out of alignment, which would seem to explain the grinding issues. I can't see any way to adjust the alignment and have not tried to do so. There is nothing that is obviously 'bent'.
Anyone know if Bintel can deal with this? I forgot to call them today.
Is there any chance the bearings are being pinched by a retaining nut/washer that's on too tight?
Possibly, but I can't see anything that looks adjustable beyond what I've already done.
The other question is how this happened, as the focuser was working fine before. The only thing I can come up with is that I store the telescope case on its side rather than flat, and it seems the way I put the scope in may have been putting weight on the fine focus knob. So maybe over time something has shifted. Or, worst case scenario, something is now bent.
Focuser is stuffed
