18" Telekit

[Marke (Mark)]

Yes Marc as you know it just so happens the misses won the 50% off
discount voucher for an Argo Will most certainly be going on when I am a bit further into the build

[barx1963 (Malcolm)]

Marke
I have stayed out of this thread up to now, but I will make a cuple of comments.
I recently purchased a 2nd hand Dob which is a 20" f5 which is a similar design to the Astrosystems one in that it has a closed back. The reason the original builder made this decision was that where he was living at the time suffered from considerable issues with exhausts, dirt and dust and he was concerned to full protect the mirror from damage. As such the mirror box seals completely with a cover even over the fan.
I have used the scope for 6 months now and while it can take a while to cool down fully a couple of action help mitigate this. I store the scope in an unheated (and in summer an uncooled room) which is as close to the outside temp as possible. I try to always setup well before dark. This makes setup quicker, collimation easier and gives more time for mirror to cool.
If there is a sharp drop in temp I do notice some deteriation in image quality due to some thermal effects, however the sheer light gathering power of the big mirror more than outweighs this in comparison to other scopes I have used. At the most recent SV camp I set up necxt to Paddy's open truss 16" (similar design to an Obsession UC) which would have cooled much quicker than my scope. The images in the 20" still easily beat the 16".
Obviously, I would get better images quicker and more consistently with an open back but it still produces great images. Sure I could have gone the SDM/Obsession route and ended up paying 3 times what I did, but overall, I am happy with it.
All this is not to disparage what John and Mark have said as I have complete respect for their knowledge and experience but to encourage you in this venture.

Look forward to hearing how your scope performs

Malcolm

[Marke (Mark)]

Malcolm thanks for that , I suspected as much and I will be using it the same way and actually the bottom 1/3 of the mirror box is open anyway. It will be set up hours before dark when I take it away and am sure it will be fine for our purposes and when needed there is nothing that cant be modified on the scope .

[Capricorn1(Tom)]

Hi Marke its good to have a project..wish you well with it....by the way I enjoy the megrez 88. Cheers Tom

[Hagar (Doug)]

Deleted by me.

[Marke (Mark)]

Originally Posted by Capricorn1(Tom)

Hi Marke its good to have a project..wish you well with it....by the way I enjoy the megrez 88. Cheers Tom

Tom thanks and glad it went to a good home

[Marke (Mark)]

Originally Posted by Hagar

Hi Marke, looking forward to following your chronicles on this build. I have thought about a big dob on a number of occasions. I think your idea of chronicling the build a great idea and whether successful or not it should be an interesting read.

Thanks Doug appreciate the support will catch up with progress over the weekend .

[bobson (Bob)]

Good on you Mark! The fact you have over 700 views already, means a lot of people are interested. Thanks mate!

cheers

bob

[Marke (Mark)]

Update:
Here is the progress so far , ground board done and most of the upper cage . I am pretty happy with the finish on the wood it came up nice with the urethane .
I am just waiting on the light shield for the inside of the cage , there was a bit of a hold up with it and should be on its way now . I can then fit the Moonlight and spider along with the secondary heater kit as shown in the photos .

The rocker box is now in the process of sanding - there is a lot of sanding !! . It went together pretty easy with care taken to make sure it was square .
I have routed over the finger joints and edges next step is to glue on the large sheet of laminate to the base - this acts as the bearing / friction surface. Once this is done I can start with the painting on it .

After this my next step will probably be mirror box and bearings - I can then take measurements to order the encoders for an Argo Navis

So far I can say the kit is great - 70% of the work involved is just the finishing and waiting for stuff like glue to dry. The manual while at 100 pages is comprehensive it is also a bit vague and the little BW photos arent a great help , really wish it was available as a PDF .

[Kunama]

Looks good so far Mark. At this rate you'll be ready for the new moon!

[multiweb (Marc)]

Yeah looking very good. Forget the urethane. Paint it pink and purple. C'mon! Brownie points.

[Marke (Mark)]

Originally Posted by multiweb

Yeah looking very good. Forget the urethane. Paint it pink and purple. C'mon! Brownie points.

Dude dont say purple ! If only she knew the focuser came in purple ... well lets just say it wouldnt be orange now

[Marke (Mark)]

Quick update as didnt get much time thru the week. Hoping to make some decent progress over the weekend will post some more photos tommow I hope.
Rocker box all done bar painting the inside bottom black , put the laminate on outer bottom where it runs on the ground board bearings . That was probably the scariest bit so far as you only get one go at putting on the big sheet of laminate straight but all good .
About to start on the mirror cell today and get the main parts glues on and while thats drying will glue together the mirror box more pics to come .

[Marke (Mark)]

couple more pics
The locating posts , travel pads and sling posts glued in .
This gets another sanding and will later be painted flat black after sealing.
The laminate added to the Alt bearings , tomorrow more sanding and
a coat of sealer .

[iceman (Mike)]

I've edited the part of Doug's post which caused offence to Mark S.

I've removed the other posts which flowed from there.

I think the OP has made it clear (within his right, it's his thread) that he doesn't want this thread to be a discussion of the pros and cons of different optics or cooling etc. If people have opinions or questions about it, start a new thread.

[iceman (Mike)]

LOL "our" doug was a typo. Have corrected/removed it.

[Marke (Mark)]

Bit more progress over the weekend
Base board bearings installed and sprayed the bottom of the rocker box
black , will put them together later when paint dries .
Mirror box glued and clamped square ( I hope ) this bit was a pita but I think we got it

[allan gould]

Mark
An excellent thread and I enjoy reading your progress to the final goal. Always thought of a large dob but shy away at the last moment.
Allan

[Marke (Mark)]

Thanks Allan my time has been limited to a few hrs after work working on it but is easier than expected just time consuming with sanding and varnishing. I will have some pics and update over the weekend again .

[Marke (Mark)]

Some more photos from my progress , hoping to get a fair bit done over the weekend .
Rocker box done and waiting , a nice touch is the centre bolt pre drilled
with a grub screw added to take an encoder along with pre drilled holes
for other addons like tracking hardware.
Mirror box is getting its final sanding before I start with the urethane... I do love the finger joints , it has reinforcing blocks in corners along with the mirror cell mount blocks .
Mirror cell getting its final coats before spaying the mirror side black and I can then start fitting the hardware to it .
The cell simply fits to the mirror box with 2 hinge pins and 2 bolts to allow to swing open to clean or remove mirror - I will add pics of this when I get to it .
Note if you feel the need the cell can easily be popped off and a steel open design swapped into its place at any time ( for those who just cant live without it :p )