The Mapstar Scope build

[mapstar]

Morning all (working shifts any time of day could be morning!)

Just to finish off the bit on the Az bearing I completed the assembly with teflon pad and top lock nut which would be inside the rocker box bottom.

Next up was to make a start on the UTA (upper tube assembly) and finally some woodworking (I can hear the cheers) .

Apologies to those that already know if I quote what the abbreviations and measurements are as not everyone reading this will be familiar with the terms and after looking around there are very few details on builds? 

The structure I made from 12mm and 18mm (1/2" and 3/4") baltic birch ply and after quite a bit of research ordered the wood and made a start.

The focuser was to be a moonlite CR2 so I set it all out making sure there was enough adjustment in the secondary. All the woodwork was double dowelled into the upper and lower rings. I put a rebate around the inside of each ring for some 3mm (1/8") aero ply (Rustysplit build) to be glued and nailed. Inside diameter was 650mm and the outside of the rings 750mm (I tend to work in metric sorry)

The depth of the UTA was 200mm (8" old money) overall 

I then added the aero ply which was held in with brad's and yet more glue. The focuser board being a wide area and flat I had to make a jig with the router to get a curve on the inside for a decent glue area when the Aero ply was added.This proved a proper fight to get it in as the open time of the glue was only ten minutes. 

This made the structure really strong and importantly light. I'd added two finder boards which later I added to as the finders weren't available at the time.I also added 4 reinforcing points again dowelled onto the lower ring where the steel insert nuts would be screwed into for the trusses.

After everything had set solid I gave it three coats of varnish between several cups of tea!

Next up was cutting the spider vanes to length, drilled the ends for the sellock pins so I could put the vane mountings on (first pics) sprayed and finally fitted the spider

The secondary was 120mm minor flat so a kendric dew pad was fitted before the secondary went on with an offset of near as dam it 6mm (this was at the end of the bulid more later)

I later added two more boards for the finders (meade 80mm and TV starbeam)

More pics to follow and next bit of the build is the LOA (Lower Optical Assembly or mirror box)

Think the kettle has just boiled!

Damian

[Uplooker]

Excellent work, yet again Damian. Can i ask why you mounted the focuser in the orientation that you did, as shown in the last picture? I have seen others do the same, I think it was SimonfromSussex. What advantages did you hope to realise?

Ian

[mapstar]

Thanks Ian

I didn't mount it any way in particular?

just mounted it so that the dual speed was on the right hand side (right hand user) that's all and that is was not too near the bottom so as to give clearance for adjustment when focusing.

The focuser can be mounted any way I suppose just whatever fits your need's? I will be having a feather touch with SIP's on mine eventually as you can mount it any way on the UTA adaptor plate.

It won't be for that reason but It's a neat light option for one with a coma corrector but does bring different issues with the focal length as others have found. Yet to deal with it so it may cause problem's working out truss lengths?

Hopefully that answers what you were thinking Ian? Unless I've missed what you were on with?

Damian

[Uplooker]

Hi Damian,

It was really the way that you had mounted the focuser so that the axis of the focus knobs were perpendicular to the OTA rather than parallel / inline with the OTA. Just curious, no right or wrong. Mmmm...... SIPS, outa my price bracket

Ian

[mapstar]

Yeah I know what you mean Ian about the feathertouch ,it wasn't exactly planned for mine either until my mirror went from F4 to around F3.7!

I think it was just a case of it being a bit more compact mounting it that way and you can use both knobs as it sits below the rim of the UTA and inline you couldn't as one would be up against the lower ring.

Scope building is difficult but mirror grinding that's just frustrating, difficult, time consuming and requires the dedication and patience of a saint! Oh and a bit of luck too.

Damian

[Daniel-K]

that UTA is look good be bice to see it finished !

[Uplooker]

Ah, Ok it was practicality rather than preference. As i said,  I had seen the focuser mounted that way previously and was just curious as to the reason why. I have to say that it is evident how much planning and thought seems to have gone into this build - and you agreed to do it after a conversation with someone at a show!!   Or is that the other build you are doing and this one is for the Chairman of your Astro Soc?

I also have to say that having made my own Dob mount (which in my opinion is mediocre) and having read the threads that you, Crashtestdummy and Simonfromsussex have posted on mirror and scope making it is encouraging me to attempt something similar. Alas, it will be sometime off as i struggle for time as it is, but your are all certainly enthusing me.

Ian

[wookie1965]

This is looking like a really great build cant wait for the whole picture.

[mapstar]

Ah, Ok it was practicality rather than preference. As i said, I had seen the focuser mounted that way previously and was just curious as to the reason why. I have to say that it is evident how much planning and thought seems to have gone into this build - and you agreed to do it after a conversation with someone at a show!! Or is that the other build you are doing and this one is for the Chairman of your Astro Soc?

I also have to say that having made my own Dob mount (which in my opinion is mediocre) and having read the threads that you, Crashtestdummy and Simonfromsussex have posted on mirror and scope making it is encouraging me to attempt something similar. Alas, it will be sometime off as i struggle for time as it is, but your are all certainly enthusing me.

Ian

Think you have summed it up there Ian and that's why I wanted to put together a full build thread. It has taken a lot out of me to be honest.

It might encourage others (or scare them to death?) and after seeing so many make theirs I obviously got the bug myself.

One thing I would say is I never think of anything that someone has made is mediocre. Putting time and effort into creating something gives me far more satisfaction and respect than just buying It off the shelf and with big dobs there are few people that offer them?

I look forward to seeing your mount at galloway only thing is I'll be disappointed mine won't be ready for you to have a look at.

It was for the guy I met at the show who has been very patient, encouraging and become a very good friend along the way which is what I personally find happens a lot in this hobby.

Next installment tomorrow

Damian

[wookie1965]

Your coming to the peak star party arnt you Damian.

[mapstar]

Your coming to the peak star party arnt you Damian.

Yes I am wookie although my own build won't be as the mirror isn't even finished yet.

So it Will be the 200pds on the HEQ5 that's with me.

[wookie1965]

Yes I am wookie although my own build won't be as the mirror isn't even finished yet.

So it Will be the 200pds on the HEQ5 that's with me.

I will see you there then looking forward to catching up with fellow SGL ers.

Paul.

[mapstar]

I'm pitch 24/25 Saturn field Paul so pop down for a chat I will recognise you from last years event

Damian

[estwing]

Cracking thread mate keep it coming....

[wookie1965]

I'm pitch 24/25 Saturn field Paul so pop down for a chat I will recognise you from last years event

Damian

Im in Saturn Pitch 3 says Scott because my son payed for it with his paypal

Now back to your thread any more pictures I look everyday for updates its a great build.

[mapstar]

Morning all,

It had taken quite some time to get to this point and next was the real challenge of the mirror box. 

The box was to be quite a low profile affair and quite light as the design goal was under 50kg final weight without losing strength. It would be made from the same 12mm and 18mm baltic birch ply as the UTA. I used CAD again to work out the overall size of the box, which was to be an octagon so I could fit the lower dowelled mounting plates for the trusses in the corners.

Here's the initial cut of the box and lay up with the mirror cell. It worked out in the end to be 713mm square 

Once I knew everything was a good fit I added strengtheners to the corners all glued up with biscuits.All the hardware for fitting the cell was then put in, the 4 lower truss mounting plates, the cell top mount point and adjuster bracket mounting points for the collimation screws. These were bolted through from the outside with 8mm allen cap counter sunk screws so the ALT bearings would screw on flush when fitted.

To add strength I added several gussets around the top and bottom and then on went the top.I didn't go all the way around with the box top so the mirror could be lifted out easier. This wouldn't be a problem strength wise as the altitude bearings were to be bolted on either side making the thickness 40mm thick

I cut a hole through the back with a 6mm deep rebate for later mounting a plate with fans on 

And then some holes along the top and bottom again to lighten the box and also to provide something to lift it with.I chamfered the edges of the holes which made them easier on the hands.

When all the glue had set it was time to finish the box with blackboard paint, varnish and several more cups of tea!

I also bushed the holes where the threaded rods for collimation would go through. The rear hole was there just to give support laterally to the collimation bolts.

 

A refit of the cell and the LOA was nearing completion. Photo shows lower truss mounts also trial fitted onto the box.

The only job left to do was the ALT bearing mounting points which I made a jig up for once I'd made the two bearings. The jig consisted of three 30mm holes for the router guide bush and the holes for the steel insert nuts cut in each side.

 

LOA was finally complete so the feet went up and the kettle went on!!

Damian

[faulksy]

Absolutely spot on mapstar

sent from my fone using fingers

[crashtestdummy]

Just admit it,you saw my SIPS and had to have one

I can drop mine off with you when I'm next up if you need it for measuring up or for weight balance

[mapstar]

Just admit it,you saw my SIPS and had to have one

I can drop mine off with you when I'm next up if you need it for measuring up or for weight balance

Ha ha yeah its more weighty Crash but a better option than having tons of stuff stuck out the focuser to do the same job. It will move the focus point though as far as I'm aware so the poles will have to be be longer I will have to research a bit more on it?. 

[Daniel-K]

at 22" id rather have the parrarcorr  and use a riser plate rather than extending the poles. will you have to use a step if you use the sipps?

[Rustysplit]

Fantastic work Damian. This is really looking good. Keep the pics coming.....

[mapstar]

at 22" id rather have the parrarcorr and use a riser plate rather than extending the poles. will you have to use a step if you use the sipps?

Not sure how it affects it as yet Daniel but the focal length of the mirrors is around 2032mm (80") so I think the height at zenith will be about 7ft. Steps are a must to start with.

It is me that's grinding the mirror so figuring an f3.7 is going to be extremely difficult but to get the height down It would have to be like Simons at f3.38 and figured by a person with a lot more knowledge and experience than myself or Rich.

Tv's Parracor adds more weight overall which get's harder to balance as the ratio between top and bottom alters. O.k. if you've a mirror that weighs a ton but ours is around 17kg and I don't fancy adding weight.

I know people on here have experience with both of these and I will probably seek their advice. Needless to say it probably divides opinion

Price wise there is not much difference between the two options if you acquire them from the right place just with me the starlight system is better engineered being designed from the start that way.

I've time to think and dig about but need to get my head around it as Rich (crash) has already got one.

Damian

[mapstar]

Fantastic work Damian. This is really looking good. Keep the pics coming.....

Thanks Alan, more updates tomorrow.

[Uplooker]

Thanks Alan, more updates tomorrow.

You really are teasing us with this thread :-)

Ian

[Daniel-K]

my 16" sumerian will be up for sale if all these big dob builds carry on