Upgrading a Lightbridge

[Helen]

I've talked about this before, but never actually got around to doing anything but minor mods. But now that I'm about to get the mirror recoated it seems a good time to get the rest of the scope in good shape too .

My ultimate objective is to get the scope set up so that it is easy to move around, through single doors and over slight steps without having to carry it. I've got a hotech collimator, so tweaking collimation following any bumps shouldn't be a problem.

My target date for completion is SGL5 (well we had so much fun with Kev with it last year it would be a shame not to take it again ).

There have be lots of great ideas for mods on this site (and others) so I'd like to tap into that experience please.

I've got a few ideas.

Adding wheels to the base.

I've seen the great wheel barrow mods, there's still a necessity to lift some weight. The design that really appeals is a wheely-bin approach - just add a couple of wheels at the back and then tilt the scope centre of gravity over the wheels and away to go. To do this though requires the wheels to be on the outside of the base, and if I want to get through doors then I think I'll need to square off the base. I've seen that done for a bigger lightbridge, and OO Dob bases are very compact. The size would depend on what bearing I use (see below!) So question 1 - does anyone see a problem with making the base square?

Az bearing

At the moment the scope has a bearing which consists of two metal plates with a (needle?) bearing disc between them. At some point one of the metal disks got out of place and the centre got a bit deformed when the bolt was tightened. The disk also don't seem perfectly flat. The movement is OK, but not particularly smooth. Question 2: are these bearings good? if so, should I just flatten and clean? or should I look to upgrade?

Balance

The friction brake is a fiddle. I'm thinking of adding a counterweight bar to bottom. I know John did this. Question 3: What's the best way to attach any bars - should I screw or stick? and should I keep or change the Alt bearing? (I'm assuming keep)

Flocking

There's far too much white/silver on the scope and the inside of the lower OTA is badly scratched from the mirror cover. Q4: what is the best flocking material?

Focuser

The stock crayford won't come to focus with 2 inch eyepieces as there isn't enough out focus - pretty poor really given the scope comes with a 2 inch eyepiece! (As an aside: its easy to see why beginners give up when they get a scope they can't focus with the supplied kit, and for which the instructions say you won't need to collimate despite it being a truss tube that has been shipped halfway round the world..). To add to the frustration, the extra travel needed for focus is too much for a shorter extension and not enough for a long extension. So maybe a focuser with extra travel might be answer? Q5: any recommendations for the best way to do this?

Shroud

The Meade shroud for it is too big and so sags into the lightpath . I'm thinking of making one from neoprene.

Anything I've missed??

I'm rather looking forward to this now!

Thanks

Helen

[acey]

Q4: what is the best flocking material?

The Meade shroud for it is too big and so sags into the lightpath . I'm thinking of making one from neoprene.

For flocking, Protostar is the standard recommendation, available here: Telescope Parts UK. Black felt from craft shops is also used and is cheaper - just got to make sure it doesn't deposit fibres on the mirror.

For the shroud - why neoprene? It'll be even heavier. They're usually made from nylon. Sagging is better prevented by hooping the shroud in some way.

Good luck with the mods!

[Andrew*]

Hi Helen,

I never knew you had a LB - what size is it?

Q1

I don't think there's a problem with this. Round bases always line up, so they look better than square bases. That's probably the only reason LB bases are round, and large.

Q2

I'm looking to going down the teflon route for both bearings TBH. I don't like either of the LB bearings. I'd use a 12" vinyl record runnin on teflon pads for azimuth, and ebonystar running on 1mm thick teflon strips for altitude.

Q3

I made an adjustable dob counterweight very simply and cheaply:

http://stargazerslounge.com/equipment-discussion/67351-dob-ota-counterweights.html#post1106073

Q4

I used black hobby felt. It does shed a little fibre, but this doesn't have much effect IMHO. Protostar is the good stuff, but more expensive of course.

Q5

The focuser thing is annoying. I had this problem and eventually found a short Lumicon 2" extension tube. I don't use it anymore, so if you're interested, just drop me a PM. You could try it out FOC. I have a 1.25" eyepiece needing a lot of in-focus, and 2" eyepieces needing a lot of out-focus, so unfortunately just have to do a lot of racking in and out, removing and replacing extension tubes. Bit of a pain...

More travel would resolve the above problem, but create the problem of the focus tube entering the light path.

Re: the shroud. I had my wife sew one from doubled up black polycotton fabric. It was excellent, except for the fact that I measured it wrong.... If you're handy with a sewing machine this would work fine.

My LB has been sitting unused for months unfortunately, as I just don't get the time to do these things and get it properly usable. Plus the ED120 is just too nice!

HTH

Andrew

[Helen]

Some brilliant ideas here already - I love this place

Thanks guys

Keep the ideas coming...

Helen

PS Andrew - perhaps I could try the adapter at SGL5 If I'm not sorted by then

[Doc]

Hi Helen.

I'm sure even if you do fit wheels ouside the diameter of the base on a 8" it will fit through a standard door. Have you thought about a potato sack trolley, the one's delivery drivers use. If you could put casters on the base to raise it up a touch then the trolley would slide below the base and then you could secure the lower oTA with a bungee chord and then tilt the trolley back.

My 16" LB still uses the lazy susan bearings and the movement is spot on, dead smooth and I don't think could be improved. So the standard Az bearing does work. Also it still has the original felt Alt bearing and once again movement is really good. I think if your scope is perfectly balanced then the original bearings are perfect for the job. I never have to use the friction brake.

My counterweights are secured on the bottom of the mirror cell. I drilled 3 large holes in the bottom and secured round weights with long bolts and nuts.

The standard focuser is rubbish you need to upgrade. I have the revelation focuser and it's pretty smooth and takes 2" eyepieces.

Best Light shroud I think is the Astrozap one. it's hooped and doesn't intrude into the light path.

Hope this helps.

Look back through the DIY section under Doc and you will see all the mods I've done.

[John]

I think this must be the nice 8" LB I had a look through at SGL4

If you want some teflon sheet for bearings this e.bay supplier might be worth considering:

ptfe teflon plastic sheet 95x100x1.5 dobsonian mount on eBay (end time 23-Mar-10 11:16:27 GMT)

There is a trick with the stock focusser to get some more outward travel - unscrew one of the two screws underneath the focusser a few mm - I can't recall which one so you will have to experiment. I found focusser travel OK except for the Ethos 13mm which the above trick gave me enough travel to sort and the supplied Meade 26mm QX eyepiece which has a very odd focal plane and needs to hang halfway out of the focusser to reach focus (nice one Meade ).

I used black foam pipe insulation to blacken my truss poles (anyone remember Rambling Syd Rumpo (Kenneth Williams) ? "... me truss poles I must be blackening oh ..."

I've got loads left if you wan't to try some although I suspected it of intruding in the light path a little.

HTH

[Helen]

Thanks both. Yes, its the 8 inch we used John Its actually Jean's, but we've swapped with my ETX as she was finding the scope hard to handle. I'd love to get to a point where its so easy to use for her she'll want it back!

Helen