mapstar

I'm hoping that mean's SGL will have another build thread to read

Hi Sporadic, I can understand everyone wanting to know how it is done, being very open about the rest of my build. It took quite a bit of head scratching and is the only part of the build that I am going to keep under my hat for now sorry to say. I have further plans for it in the future which will become apparent as time goes by. Hope that doesn't offend anyone

It is rather strange to comprehend!

Thanks Gina Its taken quite some time but finally finished

Sorry Neil, Here is the mirror box fully painted Awaiting the mirror being fitted. I put Velcro on the side of the mirror itself and straps on the rear of the box to secure it, in case it decided to fall forwards at lower elevations. Here it is with the cover and the raised blocks to put the UTA on when it was stacked for transport Finally with the glass fitted. The surface having condensation on it due to storing in my garage/workshop. It shows the collimation set up and the wiffle tree supports All ready for the stars

Now all the components were finished it was time for an outing. Here's the scope packed into the car ready for some dark site action I made a secondary cover out of an old hat with a bit of Velcro on it. Works rather well and the fleecy liner is nice and soft Unfortunately I forgot to take the proper camera (I've always maintained that I'm not into astro photography!!!) The stack is 650mm high and fits the boot quite nicely. All the components can be lifted. Obviously the mirror box is the heaviest at around 30kg. The mirror cover I'd fitted four blocks to so the UTA would sit on top above the collimation Knobs. I used a couple of cheap belt straps the type with clip in plastic buckles to keep it all from rattling and moving about through the rocker box holes and around the UTA Next up the fully built shots once I manage the pics

It was time I finished a few of the components and I'd decided a few months ago that the scope would be painted black. I chose a range of paint called Protek royal exterior black, with the clear coat also of the same paint. These paints are water based and don't have any nasty chemicals in them. I've heard a couple of people mention that mirror surfaces can be tarnished by the vapours of certain paints, although I have no evidence to corroborate this so thought I'd play it safe. I had to order the paint direct but I will say that the delivery was despatched the next day arriving the next morning. In all excellent service and highly recommended Here's the UTA during finishing and also the ground board and cross brace. The inside of the UTA was painted with Wilko exterior blackboard paint again water based. I gave the ground board 3 coats before like the UTA giving them both the clear finishing coat. The rocker box took me quite a while seeing as it is a complicated structure. Photo in progress. The bearing's were also painted and the bushes glued in for the 8mm attaching knob's to slide through. I then refitted all the hardware and glued on the formica to finish off the rocker, ground board and bearings Through the attachment hole's on the bearings I glued in some stainless 10mm (1mm wall thickness) bushes to accommodate the 8mm threaded attachment knobs to stop the wood wearing everytime the scope was assembled/dis-assembled for use Just the spider/secondary holder and focuser to fit to complete the build up. More soon Thanks for reading

Thanks for the comments all. I will continue with a little more soon.

Motorising it is all pie in the sky at present Ian

Thanks Raymond. I'm not planning on motorising the scope at present although I think if it were to happen it would be the stepper motor and raspberry pie/encoder route? I will probably experiment with the carbon fibre a lot more in future builds as I've learnt quite a bit already and would like to work a lot more with the different techniques. More updates soon

O.k. so moving on from all that light hearted banter I shall continue the thread. The most troublesome part of the build was trying to keep the Upper Tube Assembly weight down for balance purposes. My secondary weighed 650g on it's own, so having all that weight to start with would cause problems. The original design I had chosen was an aluminium plate and to use silicone but I went off the Idea as it can cause astigmatism in larger secondaries especially when bonded to something with differing thermal properties to that of low expansion glass. So I opted for a design like the Astro systems holders which are considered by many to be the best way of holding a large secondary. Here is Mike Lockwood's thoughts on the design http://www.loptics.com/articles/mirrorsupport/mirrorsupport.html Unfortunately my actual minor axis is 131mm (130mm coated area) and Astro systems do not do a holder to fit. With the space required around the glass for expansion and contraction (.5mm) the size was 5.177" and the maximum size the 5" astro systems holder would expand to was 5.05". In metric I was 3mm oversize. So I set about trying to make a holder myself from .5mm thick steel. I'm no fabricator and the lip proved just too difficult to fold over and keep flat (to be fair it looked like next doors dog had chewed it on). I also took the drawings to two local fabrication firms but came away with a 9 week wait from one and 7 weeks from the other! I had a thought and contacted one of our fellow SGL colleagues. After a few emails and message exchanges I sent a Wood template of the secondary across country for someone else to also take up the challenge. During the wait I started to also experiment with a different method/material which was a complete first for me. Carbon Fibre A couple of weeks later and I received a package with the steel secondary holder from the helpful SGL member. It was a quality crafted steel holder and beautifully finished in matt powder coat. There was just one problem it weighed half a kilo. Unfortunately it was going to be too much. Half a kilo at the top would mean I needed to redesign the bearings and rocker or find some other way to reduce weight up top. I had four attempts with carbon fibre until I struck on a technique to make it work as I wanted. Apologies for all the writing as I know you guys will be wanting more pictures, so here it is not quite perfect cosmetically but it works brilliant Reflecting the SIPS unit in the focuser (orange cover fitted) The secondary sits inside on the flat lip supporting the full edge. The carbon fibre holder weighs a scant 74g and its thermal dynamics are much closer to glass than steel/aluminium. It is also a solid tube and front ring so much stronger than a split tube. My intention is to replace the countersunk allen cap screws with dome head ones but I've not got around to it yet. The dew heater inside is packed behind with foam to stop the secondary moving. I could take a little more out of the lip around the edge but the minor axis now measures 128mm so I have lost 1mm around the edge which wouldn't make any difference. All this had taken a long time but progress is never simple on something you've never done before I had also been doing a little painting too and in the background on one of the shots the dew heater vane wiring can be seen clipped to the inside of the UTA. More soon

Damn bet me to it! Although it's a good job it wasn't Ian as no one would've got a piece!

Oh no Ian will be on that comment like a rat on a bag of scraps

Admittedly it's already had it Calvin but that will be included at the end

Great stuff Calvin, looking forward to meeting up again

Thanks for the comments and compliments guys. I'm still refining bits but it's been another learning curve in many ways. I am really glad you're all enjoying the read, as I don't want to bore anyone with too much detail. Just a few more bits to do and then the shots of the complete item. Gotta think of a good location this time for some arty back drops

I knew the focal length of the mirror and so it was onto calculating the truss pole length, also adding 6mm above the end of the focuser tube where the longest length eyepiece should come to focus. The scope would be using a Feathertouch Focuser with the SIPS system. I calculated the truss poles and because they were going to be welded ends I made a frame up from wood to test that the images came to focus. The weather had other Ideas and it was another 3 weeks before I got a clear enough night to test the assembly. Here's the feather touch before fitting The SIPS unit has a specific set up method detailed on the instruction CD that comes with it. It is adjustable in/out on a thread (under the part with Televue on it) by the range of about 1".Having set this thread half way I found I needed to add length to the tune of 45mm between the Lower optical assembly and the UTA before I could focus using my longest length eyepiece 21mm. With the thread being set halfway I still had a range of adjustment once the truss poles were welded up. With this measurement set I cut the truss poles and had the ends welded on. Here's a couple of the machined ends before welding. The smaller machined diameter would fit inside the tube I made a jig with the correct hole centres for the M5 bolts to go through. I took them off to the same company in Sheffield (JNC) that welded the cell up. I spent a couple of hours then covering them in heat shrink. I bought 41mm flat to shrink onto the 22mm poles. The poles would be joined at the top and bottom. At the top I used bicycle skewers but on all eight poles fixing. Here's how the top fixing looked with the link bar in between. Underneath the two springs are two 8mm diameter spacers these would rest against the inner cup of the top mount copying the way an actual bicycle hub fixes into the forks. It should not rest on the spring and the thickness of the spacer should be smaller (approx 4mm) than the thickness of the top mount (5mm) attached to the Upper Tube Assembly The lower would be a triangular plate to locate on the LOA corner mounts. An M5 allen cap bolt on each would provide the pivot point but also allow the truss to be locked up when the scope was finally set up creating a solid assembly. Below is how they looked once all fitted together complete I was finally on the finishing straight. There were a couple more things to finish off like the secondary holder, formica gluing for the bearings and the final finish.

Cheers Mike and thanks for taking a look and commenting. Take's nearly as much time to write it all up as make the scope Trying to get detail in that people may find useful is difficult, as some are more accomplished tinkerers than others . Glad you're enjoying it though

I didn't Derek but the author of the book I use has all the testing of laminate and teflon combinations. Ebony star quarry effect was the ideal. I knew what texture I needed, and I took a piece of teflon with me. The guy in the shop obviously thought I was a bit barmy! I spent months looking for the best match it works really well and is very smooth

Thanks Gina

Here's another shot of the rocker 'box' with the extra hole's cut in the bottom, the central bush fitted and the teflon refitted until I came to finishing it. To complete the base and bearings I needed some laminate/formica. The last scope used quite a textured surface and was replaced by bearings eventually due to the scope being motorised. I wanted something smoother this time as the scope would only be used manually. Finding a suitably textured material and supplier proved to be quite a long task. The wilsonart ebony star that so many books mention is no longer available so an alternative was needed. I actually went through a book of over 500 samples at a supplier I chanced upon whilst travelling on the motorway. I don't normally look at the side's of trucks but I noticed one with International Decorative Surfaces on it (mental note to self was left). I checked them out and fouund a branch only half an hour from me. The laminate I ended up with is superb stuff and is actually from the brand Formica. It's full designation is:- Formica Pattern range StarDust HGP Quarry F1782 CW They also do two others called Lava Dust and Grey Dust. It's the quarry finish that makes all the difference though. It just so happens that these three are that finish Here it is being cut and ready for attaching to the rocker bottom Just the same to do for the alt bearings and then glue it on. I use Evo stik 528 Instant Contact Adhesive (this used to be made by Dunlop) to attach the Formica to the surfaces. It is the best I've used as contact adhesives go. I have a little bit left over so may need to build some more scope's to use it up

Nothing a cuppa won't sort at this time in the morning!

I try Derek, but at present think job worries are putting paid to that?

Yeah seems like years ago now though.

Ha ha, thought you may spot the catch