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Rack and Pinion Focusing - How To Improve.

Greg

By Greg
in DIY Astronomer

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Greg

Greg

Posted
Posted

The focusing unit on my 8" Newt is pretty poor, jerky and rough. I decided to strip the unit and re-grease it in a hope to improve things.

A very valuable modification, using quality grease I have improved it no end. The focus is now a lot smoother and is a lot easier to obtain a sharp focus on difficult objects.

I have documented the procedure below - with photographs.

Disclaimer.

The author cannot be held responsible for any injury, loss or damage to persons or property whilst carrying out the procedure.

Consider removing the main mirror (To prevent damage).

Ensure small children, pets and or grandparents are locked away before commencing the procedure.

If in doubt consult a qualified electrician.

May contain nuts.

the procedure is relatively simple, ensure you use quality tools that fit the fixings properly.

1. Remove the focus wheels - This makes removing the focus unit a lot easier.

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2. Carefully undo the screws holding the focus unit in place - be careful not to drop the nuts on the inside of the tube and hit the mirror!!

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3. Undo the 4 screws and nuts holding the unit in place and carefully remove the whole unit.

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4. Underneath the focus unit you'll notice 4 screws - These serve 2 purposes. 1. To hold the pionon gear in place. 2. To provide tension for the focus unit. (I'll get to this bit later!!)

5. Undo the 4 screws and remove the plate.

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6. Clean the rack and pinion unit using a cotton bud dipped in solvent - The grease they use at the factory is evil stuff - very sticky and difficult to remove!!! Patience works wonders at this stage!!!!!

7. Underneath the plate you'll find a metal spring plate - remove this. The pinion unit can now be removed for cleaning.

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8. The unit can now be removed from it's focus sleeve for cleaning and re-greasing.

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9. Re-grease the rack and pinion unit with a good quality grease.....I used Motrax 2000 bearing grease. It's a nice green colour and seems to give a nice viscosity when using the focuser - if you see what I mean.

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10. As Mr. Haynes would say re-fitting is reversal of removal!

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11. On the underside of the focuser you'll see a plastic plate - the focus lock adjuster fits into this - the plate can be adjusted using a 1.5 Allen key - basically this remove the slack in the focuser - it takes a bit of fiddling but it's worth it.

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12. After re-assembling the unit - place it back into the telescope tube and carefully re-fix the four screws and nuts - Don't drop them onto the mirror!!

Adjust the 4 small screws under the unit to reach the required focus tension (Personal preference) And away you go!!!

Easy Peezzy!!!

In next weeks lesson, i'll show you how to make a 9" Fluorite refractor using a cherry coke bottle and a toilet roll tube!

Greg

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Ant

Ant

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Posted

Very informative Greg! I wish I'd read that before I bought the crayford - could have saved myself a few quid!

Really looking forward to next weeks lesson - I've bought the cherry coke already (and I hate Cherry coke :lol: )

Ant

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Greg

Greg

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Very informative Greg! I wish I'd read that before I bought the crayford - could have saved myself a few quid!

ant,

It really does improve the action, but I don't think i'ts quite as good as a crayford.

Some credit should go to Tom.Yates as he talked me through it at the Welsh Star Party.

Greg

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FLO

FLO

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Posted

... when adjusting the focus on mine, it makes a pretty awful grating sound, like theres sand in there

Thats not right :? Have you told the supplier?

The Skywatcher R&P focuser has a dry/tacky grease that clumps easily. This gives a dry feel to the mechanism; not rough or grating!

The good news is that a strip down, clean and re lubricate - A.K.A. Greg's service - will probably fix it.

Steve :lol:

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JDWolf

JDWolf

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Thinking of doing this to my focuser soon, just got a couple of question.

1) Do i need to collimate after i have reattached the focuser to the telescope?

2) Didnt really understand want the the adjustment in number 11 is all about? Does adjusting these alter the slope of the focuser?

Thanks for your help

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Greg

Greg

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1. No as long as you don't bounce it around!!

2 . The plastic shim takes out the slack in the focuser - there are 2 teflon strips on the opposite side to this shim, when you have re-assembled the focuser you will need a small allen key to adjust this shim.

Once you have taken out the slack in this shim and adjusted the tension on the 4 small screws under the pinion your focuser will be nearly as smooth as a crayford - mine is!

Greg

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Grant

Grant

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Phattire had gone over his monthly bandwidth usage... probably because of how useful this thread has been to people!

So as a thank you from me, I've upgraded your account to a silver account, with alot more bandwidth :lol:

Cheers mate!

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  • 9 months later...
Caz

Caz

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Posted

I've been toying with the prospect of giving this a whirl for sometime, but not sure its something I should tackle! My focusser definately needs sorting, has done for sometime, and I don't want to spend money on a new focusser (crayford) if a simple re-greasing is all that is needed...

I'm quite good at taking stuff apart, but its the putting back together that worries me, just how simple is it to do this job? :?

Caz

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GordonCopestake

GordonCopestake

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I've re-greased a number of rack and pinion focusers and it's amazing how much better they are after a service. It's worthwhile doing if you have a syntaglue filled focuser. This guide is useful for refractor owners also as the focuser is almost identical apart from the bit where you remove the screws from the inside of the tube, on refractors there are 3 screws around the focuser collar which are easily removed.

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Caz

Caz

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Ok, I'll give it a try, I can't ignore it any longer, as it stands atm, the focusser feels like I'm turning a lid on a jar of Jam, ok, slight exaggeration, but its not good... :D

Wheres the best place to buy this gloop anyhow, Halford perhaps?

Caz

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Caz

Caz

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Caz

Only thing to beware of is not to let the tertiary frooble spring fly out

when you release the tube. :nono:

If it does, you'll need to re set it parallel with the gimble pinion.. :D

Spring? What spring? Gimble pinion? :D :D

I've dismantled the floojit, relativley simple, got the teflon grease from Halfords (£5 for a tube of grease :D), so I'm all ready to get stuck in!!! What should I use to clean the old stuff off, will a simple diluted washing up liquid do?

This spring, perhaps its still in place, hence not knowing about a spring?

Caz

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