Crayford focuser gearing rough.

[Coastliner]

Hi All, I am in the process of fitting a motor to my focuser on my SW150PDS which is a Crayford-type (may even be Crayford). The bit in the pic. is the 10:1 gear. I notice that when I rotate the shafts the bearing feels as though there is a bag of sand in there. I have lubricated the three ball bearings on the rhs to no effect. Any ideas? Or does anyone know where I can get a relacement bit?  I would have expected the bearing to glide, but it really does feel rough. On the lhs there is a slotted washer which I would like to undo but it is Locktited, and I do not have the neccessary tools to undo it properly.

[Astrobits]

When I made my 10:1 reduction knobs I also found that they were very rough. Amazingly, once the knob is fitted to the shaft they became quite smooth. Try it.

Nigel

[Coastliner]

Nigel, I have not come across anything as weird as this in a long time - as you say, reattach the 10:1 focuser knob and all is fine. Merely slackening off the allen key causes the roughness to return. I've jst tried it on my fully assembled ed80 focuser - slacken the allen key, leaving the knob in place, and the mechanism goes rough.

 

[Steve Ward]

Much easier to fit the motor to the other end , the control the motor gives you counters the 10:1 ... 

[Coastliner]

Deliberately fitting it to the 10:1 bit for finer focuser control.

 

[steppenwolf]

Quote

Nigel, I have not come across anything as weird as this in a long time - as you say, reattach the 10:1 focuser knob and all is fine.

I have discovered the same thing - it defies sense to me!

Quote

Much easier to fit the motor to the other end , the control the motor gives you counters the 10:1 ...

My own 'jury' is currently out on this one - the manufacturer of my auto-focuser (SharpSky) has recommended that I use the 10:1 reduction drive to take advantage of the additional 'resolution'. In fairness, there does not appear to be any backlash on the focuser's (Feathertouch R & P) 10:1 reduction unit so that is how I currently use it.

[Coastliner]

I may have found out what is happening, although it still seems weird. The X10 knob is very heavy for its size, and googling for something like "Ball race vibrations" brings up some heavy but interesting stuff. So, I think what we are feeling, when the x10 knob is removed is vibration which gets damped by the heavy knob, which has to be tightened onto the shaft. If you just hang it on there the roughness returns.

 

[Astrobits]

Hmmm...  I suspected something like that but didn't bother to follow it up.

Thanks for the ( possible ) explanation.

Nigel

[Dave In Vermont]

I've also noted similar phenomena. And yet when I am actually using it in the field - all I care about is the ability to 'dial-in' as fine a focus without any vibration issues causing a 'bump' to need of time for dampening. And no such issue has happened.

I've relegated the issue to the "If it t'aint broke - don't fix it." category.

Dave