20" f/4 Dob build

[Gina]

Great stuff!

[fwm891]

Francis - what holds the two things together though - just the weight of the mirror and gravity or some retaingin mechanism?

Cheers

Mike

Mike - I put a small retaining screw down through the plate into the adjustment bolt with plenty of side clearance through the plate. The screw was filed to length so it bottomed in the threaded hole without tightening on the ali plate, so the plate could 'rock' but not fall off - it that makes sense!

If you enlarge my photo you can just see the retaining screws in the centre of the ali plates

[swamp thing]

Its coming along nicely Steve,Ive sourced a 20" mirror set and im planning to build a truss tube dob in the summer im hoping it will be done ready for the autumn.

Have taken my 16" to mid Wales a couple of times, man you've got some great skies there. Hopefully be taking the 20" when finished. Maybe meet up with a few of you guys n gals and do some observing.

Great stuff!

Thanks Gina

If I can make my build a quarter as interesting as yours, I feel that will be a success.

Regards Steve

[Gina]

Blush

[Matthew]

Have taken my 16" to mid Wales a couple of times, man you've got some great skies there. Hopefully be taking the 20" when finished. Maybe meet up with a few of you guys n gals and do some observing.

Your more than welcome to join us anytime Steve.

[swamp thing]

Managed to locate the missing box section and flat bar that I had previously cut and put "somewhere safe".

This was then marked and drilled in the relevant positions, except for the flat bar, as the fixing holes in this are easily accessible after the tailgate is assembled.

The whole assembly was tacked then welded together keeping a careful check for square and trueness all the while.

I mocked it up with the support triangles and it looks as though everything has come out ok.

Now I'm waiting on the nuts and bolts etc that will make up the collimators, the side pins and the split bolts for the sling.

These should arrive tomorrow or Wednesday.

I used some thick gauge box section so the collimators have a fair amount of tapped thread inside the box to prevent future problems. This thick gauge should easily be compensated for by the ally triangles.

I will have to source a cooling fan at some point. But TBH just looking forward to starting on the UTA and the scope proper.

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[Moonshane]

looking really excellent mate!

[swamp thing]

looking really excellent mate!

Cheers buddy.

Looking forward to doing some woodwork as this is more up my street than the metalwork.

Regards Steve

[Moonshane]

One lesson I'd pass on is give yourself enough time to do everything well. Probably teaching grannie to suck eggs but there's nothing worse than messing things up as you have to end it for the day in the wrong stage. It's surprising how quickly it all starts to come together though once you get things moving.

I can assure you it's all worth the effort in the end.

[swamp thing]

Don't worry mate, I've set myself the sum total of no deadlines. It's ready when it's ready, that's it.

Have enough deadlines at work don't need em at home.

Besides its not my only project on the go. My mobile observatory is still underway. And slowly getting there.

Regards Steve

[Moonshane]

cool - looking forward to seeing it one day and even meeting at future star parties etc!

[swamp thing]

Likewise.

If I ever get any work that is predictable that would help.

Don't know whether I'm coming or going at the moment.

[jam1e1]

looks good Steve! will bring sample of that black matt up next time so can see if any good for light shield

[swamp thing]

Nice one Jamie. That's if we ever get some clear skies, yeah?

[steelfixer]

Steve - Looking good but can you answer me a question.

The mirror supports are off set on the frame so how does all this fit into a round tube?

Thanks

Graham.

[swamp thing]

Steve - Looking good but can you answer me a question.

The mirror supports are off set on the frame so how does all this fit into a round tube?

Thanks

Graham.

Hi Graham

The tailgate I'm constructing is for a square mirror box.

The upper tube assembly will be circular and the mirror and rocker boxes will be square.

Check out

http://www.obsessiontelescopes.com/telescopes/20/20-f4.jpg

This looks something like what I'm trying to achieve.

Regards Steve

[steelfixer]

Cheers for that I now have an understanding.

The pic sure is some scope.

I look forward to seeing yours when its built.

Thanks

Graham

[swamp thing]

Hi

Nearly finished the mirror cell now.

The sling split bolts were a riot to cut, having to hacksaw slightly off centre with one blade, then put two blades in, then run one blade down the slot while the other one widened it. Definitely an exercise in patience.

The side pin positioning bolts have off centre drilled cams made of hickory to allow for variation when positioning the mirror. They are topped with eye bolts sandwiched between shake proof washers these will be the retaining clips. The ends of the eye bolts being covered in cable heat shrink to protect the mirror in the advent of contact.

I cut a plywood template (1/2 thickness) to allow measurements to be taken and a full scale rehearsal run of installing the primary. The side pin cams allow very accurate positioning of them whilst the sling is easy to adjust with the split bolts.

I cut two rings of 0.5mm plastic to hold the mirror support pads in the correct position whilst allowing the full floatation movement. These rings are held in situ with double sided carpet tape. I've made the outer ring a little large. This I will rectify before final assembly.

The three collimation bolts will be finished with T bars welded to them after the cell has been disassembled for painting them reassembled.

I will source a small 12v cooling fan in due course this will fit between the rungs of the tailgate, blowing centrally on to the primary.

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[Moonshane]

this is looking like a top quality job Steve. and going much more smoothly it seems than mine - you appear to know what you are doing!!

[spaceboy]

You can't really appreciate how much work that goes into dob build until you see threads like these. Great progress Steve!

[swamp thing]

this is looking like a top quality job Steve. and going much more smoothly it seems than mine - you appear to know what you are doing!!

Appear being the right word buddy. I'm fumbling around in the dark as much as the next person. The KB book has a few holes when it comes to accurate measurements, I've also had to find studding rather than bolts for the collimating, split pins and side bolts as the equivalent metric ones aren't available fully threaded.

You can't really appreciate how much work that goes into dob build until you see threads like these. Great progress Steve!

Thanks Nick, it's getting there. TBH sourcing some of the materials is proving the hardest bit. The Yanks are much better geared up for building stuff like this it would seem. The stuff KB state as "available in any hardware store" is like finding rocking horse poo here.

Regards Steve

[spaceboy]

These guys have all sorts West Midlands Fasteners, Parabolt, Lindapter, Rawlplug, Fixings may be worth a try if you are struggling to find what you need.

[Moonshane]

Hi

Nearly finished the mirror cell now.

The sling split bolts were a riot to cut, having to hacksaw slightly off centre with one blade, then put two blades in, then run one blade down the slot while the other one widened it. Definitely an exercise in patience.

I am really daft sometimes. Never even considered cutting with two blades. I'll remember that one.

[swamp thing]

Nice one buddy. Trying to find fixings that KB recommend ain't easy when your in Euroland.

blumming metric system, bring back real measurement.

[spaceboy]

I have only had to have the odd imperial bolt off them but they have or can get what ever imperial, BSF and whitworth threads you need as far as I'm aware. But as I'm sure you know these are not as cheap as metric counterparts.