17.5" reincarnation: part 2

[mental4astro]

Well, the time has come to quit talk'n and start cutt'n to rework my Odyssey II.

After much consultation on the matter of design and material selection, I've finalised the design to a modified 'Albert Highe' tri-pole truss scope.

My change to his original design is the use of a more conventional solid timber mirror box. I'm just not satisfied that the original light-weight mirror box is stiff enough for a 17.5" mirror. It should also see the centre of gravity dropped down much further.

I've got the 50mm drawn aluminium tubes, 15mm hardwood ply, made braces for the spider & have had them powder coated. I've also made a couple of router jigs for the various arcs and circles needed to be cut.

I spent the last couple of hours scribing the various panels onto the plywood. Because of its unique design, my intention to make 750mm diameter bearings may not be feasable. Their ultimate diameter I will need to determine once the OTA has been completed. My intention here is to also make them removeable.

Cutting will finally start tomorrow. It got me all giddie to see the shape of the single sheet secondary cage scribed onto the plywood.

What do you think of renameing the scope 'Odysseus'?

[DavidU]

Great stuff. I can't wait to watch your progress.

[norm]

Good luck with the progress Alex. Looking forward to the updates.

Cheers Norm:thumbsup:

[AG Hybrid]

Very Nice Alex! :)

I remember when I helped you load that big dob up in your 4WD back in October. That was a lot of work!
But that looks great, and i guess you wont need that elastic rope hook as a counter weight any more. :D Looks like it can be folded up like a accordion now too!

[mental4astro]

Thank you for the encouragement, gentlemen. The first cutting session went slowly, as to be expected. Though no disasters.

I should clarify, the completed scope at bottom is one of Albert's three-pole scopes, not mine. I've used it to give an idea of the direction I'm going.

[lacad01]

How about "Cyclops" :P
Hope it all works out well, can't wait to see it in action :)

[mental4astro]

All the OTA panels have now been cut, as too where the clamps cut out today. Hickny helped me out here with the clamps, giving me use of some very nice power tools. Ta mate, :thumbsup:.

We also put together the mirror box. It has been reinfored with triangular brackets, should be able to jump on it now. The bottom panel holding the mirror cell is being held in place with cross-dowel connector bolts and a couple of side screws to allow access to the mirror (pic. 1). This should only be a rare occarance. I used epoxy glue to fix the cross-dowels in place to prevent them from rotating.

The second pic shows the secondary cage being cut out with the router jig I made. The jig shows the various centres measured out for the various radii. Tricky part here is to keep in mind the out-side and in-side edge of the router bit. The third pic show the finished 'cage'. The teat on the top is the continuation of the stop of the top strut. All three poles stop on the underside of the cage.

The fourth pic shows the completed clamps. The were made by joining three layers of the 15mm ply. Because of the size of the scope, for me the clamps make or break this design. Having such a long clamping surface makes for less flex. I'm looking at using very fine emery paper on their pole contact area to provide an exceptionally strong grip when engaged.

I'll paint the cage and clamps before fixing the clamps to the cage to avoid having the paint 'glueing' the moving part of the clamps to the cage. The clamps in the centre of the image are larger as they sit on the outside half of the cage and the top edge of the mirror box.

[tnott]

Glad to see you are underway with your project. Not sure what you mean about the emery paper - never seen anyone bother to do it before - though sometimes wooden pole blocks can expand and contract a little with changing weather, making the poles a little harder to slide in or requiring a bit firmer clamping.

In my experience, the drilled holes in the blocks would have more than enough friction to hold the poles tightly in place. Adding emery paper on the inside of the pole blocks would seem to me to be complicated, problematic and unnecessary.

Of the top of my head- you'd probably have to drill or sand the holes slightly oversize to make the paper fit. The layer of paper and glue might make the fit more "spongey". The paper would likely get torn off in the process of putting the poles in and out. If the paper did not go all the way around the pole, go the whole length of block or had any bumps or wrinkles in it, you would have a less snug fit around the pole than a precisely drilled piece of wood.

Good luck!

[mental4astro]

Tnott, I've been mulling over the emery paper. What you've mentioned has all popped into my head. I'll see how I go without it first.

One set back. I'm having to recut the clamps. The first batch was too loose. I used a 2" forstner bit after having measure one end section of one pole to gauge the pole diameter. No other section of pole length is within 1mm of the cut hole. I'll be using a 50mm forstner now. Amazing what a 1mm disprepency can do.

[mental4astro]

Hi all,

At last the clamps have been sorted. And it all works really well. The poles fit nicely and the whole rig is very rigid. No need for Emery paper. The clamps now donot need to be closed all the way to grip like Tarzan.

In the pics you can see that the base of the mirror box contains ply wood rings which provide an assistance to the clamps to maintain alignment. This way the whole mirror box serves to provide rigidity to the rig, not just one surface.

Next step is to begin painting the clamps, mirror box and cage ring before glueing and screwing the clamps in place. This is followed by placement of the spider and determining the size of the focusing board. Then, the primary's placement and finalizing the length of the OTA poles.

[tnott]

Looking Good!:thumbsup:
A lot lighter than the original setup.

[Wavytone]

Looks like you're making good progress, Alex.

One question though - in that example photo at the start, there's a big black stray light shield. Are you planning to put that outside the light path, or hard up behind the secondary and well inside the light path, as on your 10" ?

The reason I ask is that on your 10", while the shield works, the diffraction it caused on bright objects (Jupiter) was pretty bad and personally I think the scope will work much better if the shield is outside the light path. But the best would be a lightweight closed cylinder for the top end, if you can manage it...

[mercedes_sl1970]

Fabulous project!

[mental4astro]

Hi Wavy,

This is one for a light baffel outside the light path as you suggest. Yes in my 10" the diffraction spike is big, but at the same time I'm rarely looking at bright objects. Tnott mentioned he uses a signwriting corrugated plastic board as a light shield on his scope. I'm contemplating using the same for the baffle. Thoughts?

By the way, I've changed the focuser on the 10 to a 2" focuser, also low profile helical. The change in image quality was immediate. M42 looked like billowing smoke.

Thank you all for the encouragement. Blue Skies told me "it will take longer than you think". I initally thought "no way! I'll get it done by the end of January". Tick-tock, tick-tock!

[mental4astro]

After a detour, and work, I was able to get a bit more done. Painted OTA, installed the mirror, spider and focuser. Looks so cool just like this- a real scope!

Little more tweeking of the focuser needed to better align. Gee laser collimators are unforgiving!

I'm assembling the OTA first on these short struts to reduce any excessive pressure from the screwing of components. Once completely satisfied I'll do the final pole length determination.

Also cut out the mirror box cover. None too soon either! First thing I did before installing anything. Already paid for itself! :ashamed::scared2:

Man, I thought the mirror was dirty! Gawww, I've seen a couple of CLEAN mirrors lately, and this one is in real need of a clean. Won't do it until finished. Kept it covered all this time though! Don't need more dirt to then remove, :rolleyes:.

[hickny]

Alex,
It looks like the hard work and effort are finally paying off. Cannot wait until first light. We may have to drink something other than home brew.
Keep the pictures coming. It is inspiring me for my mod later this year.

[Bruceaust]

Well done Alex,

Looks like a giant compared to my reborn 8".



I cut mine on my "little one" on my CNC Machine ( I love my CNC too!). It made my project very straight forward for me. I commend the job you are doing now, but if I can help in the future please don't hesitate to contact me. I hope this does not sound like to much of an advert - I really do enjoy building stuff.

I look forward to seeing your completed project; it certain looks impressive.

Bruce

[mental4astro]

Ta, gentlemen.

Bruce, you are a good man to know!

CNC, eh! Have you seen Greg Babcock's 24" beauty?

http://www.synrgistic.com/astro/

That one should get your spindle spinning, :rofl:.

I've got some other projects in mind, might give you a PM when the time comes.

Mental.

[mental4astro]

Peter, I'd be very happy to toast first light with one of your home brews, mate, :thumbsup::cheers:.

[tnott]

Looking mighty fine and going well! When is first light?

I just suggested to a 16" Lightbridge owner this weekend that they consider this design to make it more portable, rather than the traditional truss dob setup. I reckon the Highe/Plettstone/Dobstuff design is my favorite one for scopes 10-18 inches. Only disadvantage is that you cannot use a shroud if you want one (most experienced ATMers don't).

Just to clarify, for the baffling on my scopes opposite and just below the focuser, I have used thin black polypropylene from a plastics place, covered in Protostar adhesive flocking. Works well and holds it shape there.

For the big removable tube around the primary mirror on the 22", this stuff was too floppy to hold shape. Instead, I used black plastic hollow core signboard bent along its length around in a circle. If you try and bend it the other way it kinks, unless you slice the outside along the hollow tubes underneath with a stanley knife. It's very stiff and holds its own weight well.

It is probably overkill and might be too heavy or thick for the baffle behind the secondary on the top end though. But you could just try whatever you can get your hands on the easiest.:)

[mental4astro]

Hi all,

What an eventful week it's been for me. First the Spooks, then the poles final length attained, and now, IT'S ALIVE!!! ALIVE!!! :clap: :clap: :atom: :atom:

The first step to this point was working out a method of attaining the pole lengths accurately. With a bit of thought, the solution was in the scope itself. In building Odessius to now, I had been using three lengths of tubing that I would ultimately cut down again to get the final transport poles, leaving three off-cuts.

My solution was to use these new off-cuts to sit in the secondary cage, place the transport poles in the mirror box, and then get three length of stout dowel to fit inside these poles. The dowels would be fixed in the secondary cage and a scaled marked on the dowels at where the transport poles came upto. I calculated an approximate length of the final poles and marked the dowels with a scaled rule to where the transport poles finished. In this way, by sliding the mirror box up or down, you can read of the length of the poles needed. Not only did it work, but to exactly 1mm.

The first pic shows the scaled rule I marked onto one of the poles. Each pole's scale is slightly different to accomodate any discrepancy within each transport pole.

Cutting the poles was then done using a plumber's pipe cutter. Such a cool tool.

Tonight came the first assembly of Odessius and working out its centre of gravity. Hickny gave me a hand with this. We installed all the finders I would use- the 76mm reflector on its back, and a 50mm right angle finder at the secondary cage - and the heaviest eyepiece. Centre of gravity - Done!

Next we collimated it, and then had a first glimpse through it at the moon. The bloody thing works! Woohoo! :party: :jump2:

The pics show Odessius resting on a chair after we had a peek at the moon.

I am so excited that my experiment works! And it looks so cool with all the finders, angles, spider, bits and bobs. :cool: :love: :jump: :tasdevil: :D :eyepop:

Thank you, thank you, thank you Hickny for your help tonight, mate!!! My dear missus asked me earlier "do you really need his help?".

Now the next step is the rocker box and altitude bearings, and paint some of the new components on the OTA. Sweet.

[hickny]

It was a pleasure assisting, although I didn't realy do that much. It was exciting seeing it take shape and viewing the moon. Can't wait till the rokcer box is complete and the scope finally assembled. The process from conception to this stage has been a wonderful learning experience and I am grateful to have been invited along for the ride.

[norm]

Great news Alex and well done mate :thumbsup: Its been enjoyable reading the updates and progress reports.:)

What is the final focal length and did u end up offsetting the secondary?

Cheers Norm

PS: It must feel very rewarding to accomplish what you have done:thumbsup:

[mental4astro]

Norm, the final focal length was 1975mm. I did do the off-set, well half of it. After some confusion in fitting the spider, only in the vertical dimension down 2mm, an out only 1mm instead of the 2mm calculated. I wouldn't do it again though- really complicates things unnecessarily for a visual scope.

[telecasterguru]

Alex,

The scope is looking great. Now I need to get cracking on finishing and then putting all of my bits and pieces together on my 12" dob project.

Frank

[mercedes_sl1970]

Alex - great looking scope. I've really enjoyed reading about the project.

Andrew

ps the wooden tighteners are a very nice touch.

[mental4astro]

The wooden knobs of the tighterns were the easiest part. 54mm hole saw and a round rasp to gouge the grip. I made the grip really, really deep and rough to be able to handle them with cold, cramped hands in the depths of winter.

[mental4astro]

R & B has moved my world- with a new rocker box and alt. bearings!

On the weekend the rocker box was completed. Really cool to see how what is scribed onto paper actually works in reality! Heavy bugger though- the bearing sides and the base are two layers of ply thick each.

The altitude bearings where much more of a concern. I took great care to mark as much information and landmarks on the bearings before they were cut out. This paid of big-time when the time came to located them on the mirror box. They were cut from a doubled-up sheet of plywood with a router with an up-cut bit. Nice, big and deep.

The alt. bearings are removeable too. I used steel insert nuts in both the mirror box and the bearings. I managed to source these steel "Screw-serts" from PSM Fasteners in Marrickville- many thanks Matthew. I had concerns about the suitability of any other material other than steel for these inserts. The force required to wind them into place, and the constant winding and unwinding of the bearing nuts I doubt anything other than steel would not last.

Their placement was a simple task of threading on a nut and an insert onto a bolt and winding the insert in with an Allen-key. The tricky part is aligning the long axis of the inserts, and the alignment of the threads to make the winding of the bolt seemless.

The bearings were then coupled to the mirror box and mounted onto the rocker box. YOU RIPPER! All the parts fit neatly, and all the gaps and spaces are where they should be.

Hickny's help on the weekend and today was invaluble. The extra pair of hands made the tedious repetitive winding and unwinding of the bolts, whilst balancing the large bearings much easier. The extra head helped keep mine cool at times too.

I just might make first light on the 17'th. Fingers crossed!:question:

[En1gma]

Woot!!!!

I can't help but imagine your scope on one of the following tv shows

australias next top model
biggest loser

that scope is such a change and seeing it in person is just mouthwatering

your the man.. Man

cheers rob

[lacad01]

Great looking progress there Alex :thumbsup:

[mental4astro]

At long last, Odessius is ready for its first trial run.

This last weekend was spent cleaning up details- lots of them.

I assembled it for the first time today. Oh, it moves soooooo smoooooothly. Waxed the bearings too.

Took a few pics. I reckon he's quite handsome, ho,ho,ho.

Tonights trial run is to iron out any bugs in preparation for its true dark site test on Saturday, :cloudy:.

I'll let you know how it goes.

[mercedes_sl1970]

Fabulous. Good luck with the first night.

Andrew

[nightstalker]

Great job Alex :) quite compact compared to how it used to look .


enjoy mate!

[Satchmo]

Nice work. You'll need a baffle plate behind the secondary mirror.

[Paddy]

Very elegant. Many nice touches, but I quite like the way the mirror cover just folds up and locks onto the truss. Nice minimal top end too.

[stringscope]

Very nice indeed Alex. Well done :thumbsup:

[mental4astro]

I've had a few sessions with Odessius now, none at a dark site yet though. I've made up a couple of make-shift buffles for now from foam board until I get some Corflute stuff.

My first finding on its movements are:

* Azimuth movement is really smooth and buttery
* Altitude is too sticky, and has a biggish 'pop'.

I've set the altitude Teflon pads at 70* and made to the perscribed 15lb per sq inch, and the laminate surfaces have been waxed.

Any suggestions on how to reduce this stickiness and pop? Should I reduce the angular separation between the pads or increase/decrease the size of the pads?

Mental.

[Rod]

Hi Alex,

You may not want to try this but when I had a similar problem, I replaced 3 of the altitude pads with roller bearings. One pad added a enough friction, you may find two bearings and two Teflon pads works well for you. If you used pebbly Formica, you'd need to replace that with smooth laminate or metal.

Are you using virgin Teflon? If not, try that first.

BTW. It's a great scope. You've put a lot of thought into it.

Rod.

[mental4astro]

Thanks for the idea, Rod. I've been thinking about your suggestion for some time now.

I've found a possible reason for the extra stick- uneven bearing surface.

Because the router I have is a light-duty unit, I had to do the cutting in stages, rather than one cut, once. This ment that the router bit wore unevenly, narrowing at its tip as it was the part most doing the cutting.

As consequence, the load being taken but the Teflon pads is of a higher weight per square inch than perscribed. The solution is to shim the pads to provide a more even gluiding surface.

The test being that the azimuth movement is much more buttery as the weight/pad size ratio is true in this case. No uneven surfaces here.

I'll keep it as is a little longer as I have to install a few new dew heating straps and controller, plus baffles.

Even 'as is' it is a beauty to use.

I've been considering installing 'brakes' to both axis. They really would only be used at public viewings as most folks at these sessions have no idea how to use a scope and nearly always make a grab for the eyepiece and at the same time bump the scope of the target. The brakes would be to reduce wasted time recentering the target. Might not be worth the effort, though.

[tnott]

You could try having the pads closer together and see if that helps.

The altitude motions on my 22 are fairly firm due to the large diameter of the side bearings and continual strips of teflon, but I have not had any of my dobs pop or stick. Not sure why this is happening in your case.

Did you use a pebble-textured laminate?

[mental4astro]

Hi Tnott,

Yes, I did use pebble-textured laminate. It was the colour "Sapphire" from the "Dimensions" range from Laminex, their most textured range. The 'Quarry' range from Formica is now discontinued and hard to source as off-cuts, and the Wilsoncraft stuff, such as EbonyStar, is expensive, AND it means getting a full 3mX 1.8m sheet- enough material to start commercial production, :shrug:.

There is no problem in trying out a smaller separation between the pads too. I made allowance for this by making the separation an orthodox 70 degrees, so reducing is not a problem. First I might look at evening the contact platform, though. This I think is the reason for the pop as I'm not achieving the 15lb per sq inch at the moment.

I hope to get this puppy out to a dark site this coming weekend for the first time. Well, oneday this should happen.