16" f4 Orion Optics UK Dobsonian Project

[spaceboy]

Getting there Shane. I bet the excitement of first light is starting to brew

[Moonshane]

oh yes mate!! it's starting to look like an OTA now. Might get the focuser on tomorrow and if the cell comes back before weekend I may even have the bones of the base done too.

[johninderby]

cheers John, yes, after seeing yours I was going to ask my neighbour to make me some for the caps - she's a whizz with a machine and she'll do anything for a wine bribe. well, not anything obviously!!

Sounds like a plan, although give her the wine AFTER she's made the dust caps otherwise they might come out fitting a 1.6" dob or a 160" one.

[Moonshane]

ha ha - do you know her?

I can always find a large headed Frenchman I suppose if all else fails!

[spaceboy]

When you making a start on the base?

[Moonshane]

I need the cell back to enable me to get the whole OTA including finders, mirrors, rings and alt bearings and even a mid weight eyepiece (probably 13mm Ethos although I might actually use my 26mm Nagler as it's easier to correct bottom heaviness in the field than top heaviness - sometimes an extra set of batteries in the Telrad can do this between say a 26mm Nagler and 13mm Ethos) so that I can get the balance point sorted out. this will dictate the height of the rocker sides and I can then fabricate the base. the pieces of ply are all cut to size, I just need the height of the sides. I could guess but I don't want to steal defeat from the jaws of victory at this late stage!

to answer your question, hopefully this weekend.

[George]

hopefully this weekend.

Part of the welding was done today, hopefully will be finished tomorrow

[Moonshane]

awesome - cheers George!

I know it's difficult at present so I really appreciate your help mate - you're a diamond! (and another on the list of people I owe some eyepiece time once the scope is done ). as you can see I still have lots to get on with so I am certainly not being held back at all

just blacked the edges of the secondary with a sharpie pen and the back of the mirror with some matt black enamel paint. can you tell I want to squeeze every last bit of contrast out of this scope?

rather than having a bolt going in an out of the thread in the secondary fixing block, I am going to epoxy a piece of M6 stainless rod in place and then have a nut on top of the spider. seems a lot safer to me. I may even fit a 'safety rope' too but this may be overkill. that said, the secondary only falls on the primary once.

is it worth blacking the edges of the primary I wonder?

[George]

I'd say blacken anything that has the slightest chance of reflecting stray light.

A permanent black marker should suffice.

[Moonshane]

cheers George. may as well then!

[Astrokev]

I use the Astrozap breathable dust covers on my OO dob. Keeps the dust out but lets the moisture escape so you can put the covers on as soon as you bring the scope in.

http://astrozap.com/scripts/prodView.asp?idproduct=248

The Astrozap ones aren't cheap, but if you can get some of the right breathable material and convince someone with a sowing machine to make some up for you it shouldn't be too expensive.

John

Useful link to Astrozap John, thanks. Are there any distributors of these in the UK d'you know?

[johninderby]

Useful link to Astrozap John, thanks. Are there any distributors of these in the UK d'you know?

FLO does some of the Astrozap stuff so they should be able to order them in, but not sure how long that would take. Perhaps we'll have to "convince" Steve to bring some in.

John

[Moonshane]

hi all

pretty much gone as far as I can for now.

tube rings back on - check

spider fitted - check

shane's knobs fitted - check

telrad base fitted - check

optical finder base fitted - check

focuser base fitted - check

tube end rings fitted - check

dob knob fitted - check

edges of secondary blacked - check

cut to length and glue in central bolt to secondary holder - check

black out edges of large 50mm washer for secondary holder back - check

cut down three stainless m8 all metal lock nut (to ensure there's no chance of them hitting the bottom of the primary) - check

jobs left to do :

rebuild, adjust and fit the focuser, when the drawtube comes back. this is on it's way back from John's after he kindly turned off the small ridge that prevented the Paracorr going all the way in. in fact - this just arrived as I am typing!

paint and finish off the cell. need to hammerite everything with smooth satin black and then build up.

fit the primary mirror in the cell.

add all accessories and establish the balancing point which will allow me to confirm how high up the OTA the alt bearings need to be, which will in turn confirm how low I can get away with making the rocker box.

construct the rocker box

construct the ground board

fit the (etched) 3mm thick teflon pads in place on the groundboard and rocker sides - will be glued with impact adhesive

fit the formica to the bottom of the rocker box with impact adhesive - I will be using a square sheet about half an inch less in size all round than the rocker box.

fit the formica to the alt bearings, again with impact adhesive. as luck would have it, I found a roll of worktop end trim at a relatives recently which has a more texture finish then the one I planned to use. see pics. this will provide a better bearing surface with less 'stiction' than the other material. I have just enough too.

fill, prime, undercoat and top coat (satin black) the alt bearings, rocker box and groundboard - hopefully will be using a borrowed spray gun for this to speed things up a lot.

put it all back together, collimate and then use the backside out of it!

oh, next project, make another equatorial platform for this scope!! should be just a couple of weekends in due course but not rush.

I am still fairly confident about a mid July first light but I am not worried if I go over a bit.

pics below of all the jobs done. any queries as to how or what I did, just ask.

cheers

Shane

[Moonshane]

last of the pics today - just fitting the focuser.

[George]

You have a PM....your cells ready

[Astrokev]

Hi Shane

Been a bit busy lately so haven't had much time to keep up with things. Apologies if the answers to these questions are in the thread somewhere.....

Did you make the secondary holder. If so, what did you use?

What did you use to fix the secondary to the holder?

What are Shane's knobs for?

[Moonshane]

hi Kevin

in the end, as I was buying the secondary mirror from OOUK, I also bought the holder and spider and OOUK, kindly offered to secure the mirror to the holder using silicone.

Shane's knobs are tool free secondary mirror adjusters made from female plastic nuts with a brass insert and M4 stainless rod epoxied in place.

I have now fixed the focuser and the Paracorr fits a treat - thanks John

also, received the primary cell back from George - thanks matey - and all nice and shot blasted too!

checked for fit (not helped by the usual OOUK lack of roundness) but will be fine. need to paint this and build it up now for balance testing over the weekend and maybe a start on the rocker and groundboard

cheers!

Shane

[Moonshane]

hi all

yesterday I managed to fit the focuser and the secondary successfully and also test fit the cell. The Paracorr fits spot on now. pics show this and the whole OTA which is really starting to look like a scope now.

today as it forecast rain in the PM I decided to get the cell prepared fully for painting (tomorrow weather permitting) and subsequent construction on Sunday.

Then next week I can get the rocker/groundboard constructed and paint next weekend if time allows. maybe even first light too!

today then I sorted the cell out. I realised that I needed to ensure that the mirror was a good fit but did not wish to risk the glass at this stage. Therefore I routered a circle out of some scrap chipboard of the same size (400mm) and used this during the checking and fitting process.

George had kindly arrange some welding for me and I decided to use T nuts, tacked to the inside for the attachment bolts (M6) and primary collimation knobs M8). you can see these in the pics. I also used M6 rod connectors for the mirror clip bolts, again tacked to the cell.

I had actually miscalculated very slightly and had to grind back the mirror clip bolt holders as much as possible and the 'mirror' now fits a lot better. I'll line these metal bolt holders with either teflon or some plastic attached with contact adhesive to ensure there's no possibility of damage to the mirror edge.

I made the clips from 3mm stainless and drilled holes for the cap head bolts. these will also have 3mm teflon glued to the underside for the same reason.

at the bottom of the cell I decided after discussion with others to have two pads of 15mm wide teflon which I cut to fit the gap between the mirror and the cell wall. This will provide protection and support to the mirror when observing at low elevation or traveling.

so next will be paint the cell and then fit the whole OTA together for balance which I think I will base on my heaviest eyepiece as it's much easier to correct a bottom heavy scope in the field than a top heavy scope.

pics as usual.

[Moonshane]

last of today's pics

[Astrokev]

hi Kevin

in the end, as I was buying the secondary mirror from OOUK, I also bought the holder and spider and OOUK, kindly offered to secure the mirror to the holder using silicone.

Shane's knobs are tool free secondary mirror adjusters made from female plastic nuts with a brass insert and M4 stainless rod epoxied in place.

cheers!

Shane

Cheers Shane.

[Moonshane]

no worries mate.

if I were making one myself, for a light secondary, I would probably use plastic water piping (like the stuff for sinks etc.

the one I have is a cast alloy so maybe some ali pipe of a suitable diameter would be better for bigger mirrors?

[spaceboy]

Your certainly making good progress! Now that's what a scope should look like!

[Moonshane]

cheers Nick

being in between jobs (got one though starting 1/9/2011) does have its advantages sometimes.

I think I have managed to find some etched Teflon sheet at 1mm and 2mm thicknesses which is a real bonus. might slow progress by a day or so though but well worth using the right stuff.

yes, all scopes should look like this, big, white and sat on a dob base ....mmmmmm.....nice.

I have to say that even without the primary in, the OTA is pretty heavy. I won't be chucking this about like the tiny 12" I had previously! it will be well worth it though with 77% more light grasp than the 12"!

[spaceboy]

I have to say that even without the primary in, the OTA is pretty heavy. I won't be chucking this about like the tiny 12" I had previously! it will be well worth it though with 77% more light grasp than the 12"!

This did cross my mind. Just hope the enthusiasm don't wear off and the thought of having to lug that mighty thing out in to the garden means it doesn't get the star light it deserves. I know dobs are nothing to set up compared to EQ based scopes but none the less it's going to be a lot of effort in comparison to what you have had previously especially if it's a case of setting up only to have the clouds come over and having to pack away again. How is it for maneuvering through door ways and stuff ?

[Moonshane]

don't fret mate. I am making some barrow handles / air filled wheels and will wheel the whole thing through doorways and to the back patio doors. then it's a short hoik and outside. then put the OTA back on the rocker to put in position. it will all easily fit through a doorway - designed it carefully to ensure this was the case.

it will cool a little slower than the 12" but I can be doing some doubles with the 6" while it does. clouds, yeah cannot do much about them