Stripped Gears on Meade DS

[Tony H]

So I was busy playing with a Meade DS goto scope and adding cameras etc.  Then I found the limit of the cheapo plastic chrome plated focuser gearing and managed to strip the threads with the extra weight attached. 

Really clever I'm not!

I've trawled fleabay and the astro boot type sites globally and can find a few focusers that might fit but then again might not.

I can't seem to find an original, or even a complete scope that I can butcher of the same type.

I am wondering if anyone has attempted to remove the rack, which in this case appears to be glued to the focuser tube.  If so, what did you replace it with? 

I'm considering removing the glued on rack and trying a Heath Robinson Crayford idea with the rack being replaced with a quite hard piece of square form rubber in it's place.  I think the worm gear will gain enough friction against the rubber and may, if it works, provide a smoother focus operation than the original.

Thoughts?

[xtreemchaos]

its worth a try,ive stripped mine on my meade 90mm frac ,if it works let me know and ill try it.thanks for posting.  charl.

[Tony H]

I knew it was a cheap scope but seriously, chrome over plastic? Like a kiddies toy. 

I'm working on this right now.

Dweffo let you know how it goes.

Thankfully I now have a decent refractor and a Meade 130mm newt that work well so I'm still ok if there is a clear night.  :-)

[Tony H]

1st things 1st.  Don't rush into this. 

The focuser draw tube is very flimsy plastic on my version. I'm not sure about the one on the refractor series.

The rack is glued to this tube (tube is 2" dia with a plastic scrwed on top to allow 1.25" eyepieces).  The actual rack has very lightwieght alloy teeth (rubbish quality, hence stripped) and this is mounted on a thin plastic strip.  It is made to look like it is all one piece of metal.

If you try to remove it by prying or even sawing or pulling off with grips, there is a very real chance that the main focuser tube will split/crack and you'll have nothing to work with. Go slowly.

I've removed my rack now from a spare scope and used a hacksaw and then a Dremmel type tool to grind down close to the focuser tube. I'll finsih this with emery paper tomorrow.

I then plan to use an epoxy resin to glue to the focuser tube some quite hard sqaure section rubber that is the same size as the rack and the teeth assembly.  I'm using what was once a seal around a double glazed over-bath shower screen.

[Tony H]

Busy evening here. 3 attempts at replacing the rack with hard(ish) rubber were not all that successful. 

Turning the focuser up and down worked fine for the 1st few times then slippage sets in.

I tried slightly higher profile rubber to allow for a bit of bedding in, but there just isn't an easy way I can see to get enough friction to make this work long term.

It does work, but I don't expect it to last very long and I really don't want to keep taking the thing apart after each use and doing the work again.

I've found a few different rubber rollers and am now working on removing the rack (well the new rubber versions I now have), smoothing out the focus tube and then using the rubber rollers in place of the worm gear.

This will give me a friction roller against the focuser tube that I can control the tension on a little by adjusting the 4 screws that hold down the plastic plate that sits over the metal sprung shield above the worm.  If I can't get enough tension I can always use some shims in there to space it a bit closer.

Job for the morning I think.

[Astrobits]

Any progress yet?

I have a Celestron chromed plastic focusser that I bought about 20 years ago for a project that was never completed. It is designed to fit a newtonian tube of about 5" diameter. It is in "as new" condition never having been out of it's box for more than a few minutes. it takes 1 1/4" eyepieces with a 0.965" adaptor. Here's a photo:

I cannot see me ever using this. Would it be of any use to you?

Nigel

[xtreemchaos]

yer mate i cannot understand why meade lets themselves down by selling telescopes with not fit for perpuss draw tubes,my one broke just with normal use,the optics are great the tube is good but i cannot even class the focuser. best of luck.  charl.

[Tony H]

Any progress yet?

I have a Celestron chromed plastic focusser that I bought about 20 years ago for a project that was never completed. It is designed to fit a newtonian tube of about 5" diameter. It is in "as new" condition never having been out of it's box for more than a few minutes. it takes 1 1/4" eyepieces with a 0.965" adaptor. Here's a photo:

IMG_5376.JPG

I cannot see me ever using this. Would it be of any use to you?

Nigel

This would suit very nicely Nigel.

PM with how much you want for it and I reckon I'll modify that to do the job.

I ended up using 6mm bolts like in a camera bellows system.  Really not very smooth at all. 

I had thought of using this as is and possibly rough focusing then attaching a helical for fine focus.  Trouble is, I don't have a hellical and they seem a bit pricey for the application.

[Tony H]

Many thanks to Nigel for shipping me this unit.

There are some truly nice folk on this forum.

Payment winging it's way to you later this week.

Thank you again.