Issue with fine focus knob on SW130PDS

[AstroMuni]

I was trying to attach an EAF to the 130pds by watching this video https://www.youtube.com/watch?v=b19IQXB8Hz4 and noticed that he had swapped the knobs. So I unscrewed the coarse focus knob on the same side as the fine one in the hope that I could swap sides. I didnt manage to unscrew the fine knob so in the end just tightened it but now I have a strange issue. When I rotate the coarse knob the fine knob rotates but when I rotate the fine knob this has no effect on the spindle even after >10 turns. How do I fix? 😞

Help please.

 

[FrenchyArnaud]

When I build my DIY EAF I came accross the same issue.

The problem is that the metal core inside the plastic fine focus knob is dislodged and the plastic outer case of the knob just slides freely around the core. When you turn this knob, due to friction the plastic turns around the core without moving it, when you turn the coarse knob, core and casing both turn in sync because no force is applied between them.

You need to pull the casing out cautiously, unscrew the tiny allen screw to free the core, then when you have both parts in your hand, a drop of superglue on inside the edge of the plastic then push the metal core back in (making SURE the screw thread and the opening in the knob casing are aligned!) 

[Enceladus Dan]

I recently put an EAF on my 150PDS, I swapped the fine and course over as I wanted the EAF pointing away from the front. I just spun the whole plate with the knobs and the pin. I took out the focus lock thumb screw and the hex screw that doesn't adjust anything and swapped them over. 

The whole plate then fits the other way round. 

Clear skies 

Danny

[AstroMuni]

34 minutes ago, FrenchyArnaud said:

You need to pull the casing out cautiously, unscrew the tiny allen screw to free the core, then when you have both parts in your hand, a drop of superglue on inside the edge of the plastic then push the metal core back in (making SURE the screw thread and the opening in the knob casing are aligned!) 

The bit that puzzles me is how did the fine knob get dislodged? I unscrewed the coarse one and realised that unscrewing the fine knob wouldnt do the trick as that side is different to the other side (i.e it has some kind of extra screw).

I cant seem to pull out the fine focuser knob at all. I tried a few allen screws that I have and none seem to fit 😞 Grrr.... One to take to The Repair Shop (read local astro club) as I am no DIY expert.

[AstroMuni]

15 minutes ago, Enceladus Dan said:

The whole plate then fits the other way round. 

Will do that once I fix the fine knob. I will need appropriate screw driver for those screws. Out of interest which ones did you remove - just the 4 in the corners?

And what exactly is the function of the countersunk screw (the video uses that hole for attaching the EAF)

[Enceladus Dan]

Also note once the EAF is fitted the knobs can't be used while the motor is fitted, if you plan to always use the EAF and the fine knob slipping on the pin isn't effecting anything else, it could be left alone. 

Clear skies 

Danny

[Enceladus Dan]

Here is a pic of the bottom, 

The 4 corners hold the plate to the focuser, the 3 down the center are focus stop thumb screw, tension adjuster (take slip out) bottom ( counter screw) has no mentioned function but i think it levels the plate as it presses againt the focuser housing.the 2 either side of the tension screw level the Teflon Bush against the pin. 

The 4 corner ones hold the EAF bracket in place, will probably need new longer one. I bought m3 x 25mm long and took few mm off the end. To turn whole plate round I swapped the thumb screw and counter screw over and spun the whole plate 180 degrees. That way the fine knob was facing to the open end of the OTA. 

Danny

[Enceladus Dan]

Mine fitted. 

[Enceladus Dan]

If you take the whole plate off, be careful as there is 4x small rubber o rings. 1 on each screw. 

[AstroMuni]

On 18/03/2023 at 19:40, Enceladus Dan said:

Also note once the EAF is fitted the knobs can't be used while the motor is fitted, if you plan to always use the EAF and the fine knob slipping on the pin isn't effecting anything else, it could be left alone.

If I leave it like that I will forget about it altogether, so best fixed when I remember. Also not sure if I need this to gauge backlash. I recall seeing in the manual something to do with watching the knobs.

Its also interesting to see that you have fitted the EAF using 4 corner screws instead of just 2 supplied with the EAF. Different ways to skin a cat 🙂

[Enceladus Dan]

I think backlash is for rack and pinion focuser, ours are friction between a pin and the flat side of focuser tube. There is constant connection if the tension is too low the tube slips. 

I used 4x bolts as these were the original mounting  holes for the focouser plate, the other holes are for focus lock, tension adjust, and Bush leveling. 

[Enceladus Dan]

his was the video i used as reference to fitting mine, the scope is different but has the same focuser as mine.