17.5" reincarnation: part 2 - Page 2

mental4astro (Alexander) · #21 26-03-2010, 11:40 PM

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!!!

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!

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.

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 (Peter) · #22 27-03-2010, 12:30 AM

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 · #23 27-03-2010, 12:38 AM

Great news Alex and well done mate

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

mental4astro (Alexander) · #24 27-03-2010, 12:47 AM

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 (Frank) · #25 30-03-2010, 03:51 PM

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 · #26 30-03-2010, 09:16 PM

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

Andrew

ps the wooden tighteners are a very nice touch.

mental4astro (Alexander) · #27 30-03-2010, 10:37 PM

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 (Alexander) · #28 09-04-2010, 12:08 AM

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!

En1gma (Robert) · #29 09-04-2010, 06:07 AM

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 (Adam) · #30 09-04-2010, 08:40 AM

Great looking progress there Alex

mental4astro (Alexander) · #31 12-04-2010, 05:31 PM

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,

.

I'll let you know how it goes.

mercedes_sl1970 · #32 12-04-2010, 07:31 PM

Fabulous. Good luck with the first night.

Andrew

GrahamL · #33 13-04-2010, 10:49 AM

Great job Alex

quite compact compared to how it used to look .

enjoy mate!

Satchmo · #34 13-04-2010, 06:32 PM

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

Paddy (Patrick) · #35 13-04-2010, 07:56 PM

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 (Ian) · #36 15-04-2010, 11:01 AM

Very nice indeed Alex. Well done

mental4astro (Alexander) · #37 28-04-2010, 02:01 PM

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 · #38 01-05-2010, 10:38 AM

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 (Alexander) · #39 05-05-2010, 11:08 PM

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 · #40 10-05-2010, 10:25 PM

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?