Crayford focuser in the cold

[Kirscovitch]

Sunday night is supposed to be extremely clear but also very cold. Lows around -10F.

Last night I was out with my SLT and as usual the rack and pinion focuser was very stiff after it cooled down.

Im just wondering what to expect when I take the dob out for her maiden run. Will the crayford be just as stiff and sluggish? I know this is a tension type focuser so if it gets too stiff will it even work in the cold temps?

[Peter Drew]

Should work ok, the Crayford works via pressure so it might be even better. 

[Moonshane]

I agree. I have never had problems with crayfords in the cold.

[Kirscovitch]

Thanks for setting my mind at ease. Also there are 2 screws underneath the focuser. I know one is the locking screw. When it's tight the knobs on the focuser turn but the tube doesn't move. I'm not really sure what the other one does though. Tight or loose it doesn't really seem to do anything.

[Moonshane]

could you upload a pic? the first one sounds like the locking bolt. the other is likely to be the tensioning bolt.

[Kirscovitch]

could you upload a pic? the first one sounds like the locking bolt. the other is likely to be the tensioning bolt.

The one I'm pointing to seems to lock it up. The knobs turn but the tube doesn't.

[ollypenrice]

Although I loathe Crayfords for imaging or on EQ mounts, I do quite like them on Dobs. Being horizontal their tendency to slip doesn't arise and you get a nice smooth action, even in the cheap ones, quite often. My temperature range is more extreme than most, say -15C to +23C and (believe it or not  )  I've no complaints about my basic Baader one on the big Dob.

Now I'm heading outside to curse at the abomination offered as standard by Lunt on the LS60 solarscope!! (I wouldn't want you to think I've gone soft on Crayfords...)

Olly

[Moonshane]

this should help http://www.teleskop-austria.at/information/serv-just-hu/pdf/Adjusting_Crayford_focuser.pdf

I think the two thumbscrews you have represent the stopping screw and the counter screw where what looks like the smaller one between the two thumbs in your pic is the tensioning screw.

[Kirscovitch]

this should help http://www.teleskop-austria.at/information/serv-just-hu/pdf/Adjusting_Crayford_focuser.pdf

I think the two thumbscrews you have represent the stopping screw and the counter screw where what looks like the smaller one between the two thumbs in your pic is the tensioning screw.

Ok I think I get what you mean by the stopping screw as when tight the tube doesn't move but the knobs turn freely. What does the counter screw do?

Or maybe I should ask what does "counter" mean?

[Moonshane]

I have not seen your particular focuser but the tensioning screw controls the 'stiffness' of the focusing (and prevents the drawtube slipping) the remaining screws basically balance the teflon pad so it is even and parrallel on all sides. counter means opposing.