Slipping Focuser

When I was out testing a new solar astronomy gear configuration a few days ago, I had a problem with my focuser slipping.  This was caused by two factors...  first, this new configuration put a lot of weight on the focuser...  and second, at the time, I was viewing the sun at its highest point in the sky at noon.  This orientation made it easier for the focuser to slip downward toward the ground.  

When I brought the gear back indoors, I tried to adjust some of the setscrews underneath the focuser but, honestly, I had no idea what any of the setscrews did.  You would think that you want all of them as tight as possible but that is completely wrong in this case.  I had to do some research.

While in bed that night, I did some research on my Kindle.  I found a thread in an astronomy forum about adjusting this focuser.  I wanted to get out of bed right away to fix this focuser but I wisely memorized the page and then went to sleep instead.  

The next evening I pulled out this little telescope and placed it down on a towel on our coffee table in the living room.  We were watching television so I figured I would work on this focuser while watching television with Sheila.

So, here is the underside of this focuser...

First, I loosened up the setscrews inside the red circles in the photo.  These are the focuser adjustment setscrews so loosening these removed all tension from the steel rod that runs between the focuser knobs.  I thought this would be a good idea before disassembly and it actually turned out to be a good idea so that there was no tension/pressure on these setscrews when I reassembled the focuser.  

Then I unscrewed all the setscrews inside the white circles in the photo.  After unscrewing these setscrews, the focuser just lifts off the telescope.  There is a small O-ring on each of these setscrews inside the focuser so be careful not to lose them.  Mine stayed in place.

While I had this assembly open, I looked more closely at how each of these setscrews inside the red circles in the photo affects the operation of the focuser.  The two outside setscrews control a leveling plate that runs across the steel rod running between the focuser knobs.  This rod applies friction to the focuser drawtube.  The connection between the focuser knobs and the drawtube is not geared.  This connection is controlled strictly by friction.  You want the pressure to be even so there are two leveling screws, one on each end...  the outside setscrews inside the red circles.  The center setscrew applies the tension to the steel rod and pushes it up against the focuser drawtube allowing the steel rod to have some friction against the drawtube.  This friction is what moves the drawtube in and out as you turn the focuser knobs.  

I noticed that there was a dark oil on my drawtube.  Since this drawtube works by friction, I cleaned off the oil.  I didn't see a need for oil here.  In fact, I felt that oil would only allow the focuser to slip more easily and I was trying to eliminate slippage.  

Everything else looked good so I reassembled the focuser.  

Once reassembled, I slowly tightened the two outside focuser adjustment setscrews.  I tightened each a little at a time, then switching to the opposite outside setscrew...  until there was very light pressure applied...  in other words, until they were very lightly snug.  Then I also lightly snugged the center setscrew.  Now all three focuser adjustment setscrews were applying pressure evenly across the steel rod that is in contact with the drawtube.

Being at this point of being snug is just the starting point for the adjustment process.  At this point, the focuser drawtube is loose and can easily move in and out without the use of the focuser knobs.  We don't want it this way.  We want some friction between the steel rod and the drawtube so we need to make some adjustments.

I loosened each of the two outside setscrews a quarter turn...  then tightened the center setscrew until just snug.  I kept repeating this until the tension on the drawtube was just right.  Depending on how much you loosened these setscrews before disassembly, you may need to do this sequence of adjustment upwards of about a dozen times.  

After all this cleaning and adjusting, my focuser now holds very well.  There is no more slippage and the focuser operates very smoothly.  That was a very successful bit of maintenance!  

Honestly, I was afraid that my focuser may have been unable to handle this heavier load of solar astronomy gear which would mean that I would have to either buy a better focuser or buy a different telescope that has a better focuser.  I definitely did not want to go down that road for two reasons.  First, I really like this little telescope so I didn't want to replace it.  And second, I didn't want to needlessly spend money on another little telescope that would likely only be used for this sole purpose of solar astronomy.  

My focuser wasn't bad before this maintenance but I have found that this focuser seems to be quite good when finely tuned just right.