It's a great book and full of everything you need to build a big one (including some very important phsyics regarding truss designs).
There is nothing wrong with the design with regard to optical performance, and I can unload mine, set it up, have it collimated, aligned and working faster than an EQ6 owner takes to put their tripod together!!!
Not so good if you don't have a trailer/van and ramps - they are not light, but there are plenty of hybrid designs to fix this if need be.
Nice looking scope .. i gave some thought to a two pole truss when I was planning mine.. theres some very good designs out there.. though not many in larger scopes .. wonder if theres a good reason for that ?
good luck .. like all atm projects if something dosn't quite work the way you want the first time you'll make it the second
I remember seeing an article in a very old copy of 'Sky and Telescope' (US ed.) regarding the rigidity of two "pole" elements when clamped in various ways.
It was this article that convinced me in adopting the design I used.
Thing is, the larger the scope gets, the larger the pole members need to be to securely deal with being pushed and pulled in azimuth. Also, the higher in altitude you're looking, the greater the force needed the move the bugger, creating problems in alignment. The site I noted below shows how the this bloke sured up the poles to deal with this.
the dob I'm looking to rebirth still is of the original 'Sonotube' construction.
One idea I've had is to cut off and reuse the top section of the tube containing the spider and focuser and rebuild the rest, reconecting the "cage" with either three or four poles.
Three poles lightens the overall weight, marginally, four poles may stress the integrety of the remaining Sonotube a lot less than the benefit of the reduced weight.
Anyone know of the strength of these Sonotube contraptions, their machineablity and suitability for this reworking?
I've also being designing on paper clamp ideas for attaching the cage to the mirror box. I am open to suggestions to ideas that would not direct clamping stresses to the tube, or greatly reduce any residual stresses.
I'm sure you could use the sonotube as the upper cage. However, I think you would need to reinforce it with wood or aluminium rings so it was strong enough to hold the clamps without warping. If you have to add these reinforcing rings then the sonotube is not doing much more than providing a stiff (and heavy) baffle.
I like Albert Highe's 3 tube designs. In case you are not familiar with them here's a link:
Your insight and this site has changed my approach!
Now I'm toying with the idea of hybridising Albert's design!
Albert's design seems a little light in support for the alt bearings. My idea is to incorporate the Sonotube section containing the mirror and float into where Albert has his "fibreglass" tube, and add some more bracing for the alt bearings. I realize this makes the thing heavier, but Albert's mirror box design I'm otherwise following.
I've ditched the Sonotube cage, though I'm yet to finalize my cage design.
My idea is to incorporate the Sonotube section containing the mirror and float into where Albert has his "fibreglass" tube, and add some more bracing for the alt bearings.
Hi
Sonotubes were part of the reason big dobs had a lousy reputation for soft images in the early to mid eighties. Thin aluminum sheet or 1 to 1.5mm Aircraft Ply is much better thermally
I know a fellow who built a very good 18" F4.5 version/rendition of the Highstone scope , and only got it stabilised to his satisfaction with fine wire guy ropes to tension it up. He said he would build a standard truss next time around. I think they are fine for a 12" but pushing things with an 18"
One thing I did with my 10"er was to make sure the two struts had a long clamping area, if that make's sense. If the struts are just "pinched" in place, they will not hold their square securely.
The whole length of the mirror box holds the struts in place, and the cage also has long grip.
I think this is important for small numbers of struts, without resorting to 'string' setup. This is the compromise mechanically. I could be wrong.
The increased bracing I was thinking of may be through the clamp coupleing of the struts, and an extra ply planel behind each alt bearing.
I could just be blowing smoke!
The cage also would require larger clamping area. These could extend down three or four inches.
This Sonotube OTA has been reworked already. Have to reconsider its viability in this project, and not be so romantic.
One thing I did with my 10"er was to make sure the two struts had a long clamping area, if that make's sense. If the struts are just "pinched" in place, they will not hold their square securely.
The whole length of the mirror box holds the struts in place, and the cage also has long grip.
I think this is important for small numbers of struts, without resorting to 'string' setup. This is the compromise mechanically. I could be wrong.
The increased bracing I was thinking of may be through the clamp coupleing of the struts, and an extra ply planel behind each alt bearing.
I could just be blowing smoke!
The cage also would require larger clamping area. These could extend down three or four inches.
I think the 3-pole setup of Albert Highe is a good one for this size scope. I would use at least 40mm or even 50mm diameter tubing. If you look at the designs you can see that the top of the altitude bearing is clamped to the pole, reducing the unsupported length. It is a well tested design used formerly by Plettstone and currently by Dobstuff. My 10 inch version is very rigid.
The Tridob is a good approach but quite complicated to build.
The Obsession UC (a la Greg Babcock et.al.)design is also a good one but requires quite a few steel parts to be cut, bent, drilled, tapped and welded.
I understand that others who have tried the 2 and even 1 pole approach for this size scope have had problems with the poles springing about.
After seeing these cyclops's, I feel very pedestrian in my ideas.
I am, however, still now inclined to the three post 'Albert Highe' design. It will make most use of the components in the existing scope, and this design does not gain or lose too much more in compactness or portability, other than the 'Moonsilver' version. Oh man, it really is, well, oooohhhh...
.. i gave some thought to a two pole truss when I was planning mine.. theres some very good designs out there.. though not many in larger scopes .. wonder if theres a good reason for that ?
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