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Penguin Pete

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About Penguin Pete

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  1. Sam, I made a carbon spider and it was easy to work and is rock solid. Image here; http://stargazerslounge.com/diy-astronomer/146066-diy-octagonal-wooden-8-dob-project.html The batten was 0.45mm x 10mm. It is only under slight tension, obtained by gluing carbon rod on the side near the end of the batten and wedging this into blocks inside the OTA. At the mirror end, the batten is simply glued into saw cuts. Not sure if your design will allow this but it's ever so simple. The mirror is placed centrally and the alignment is dealt with by the focuser mounting block. I have a feeling that a single rod of carbon would twist too much.
  2. Hmm, thanks, interesting idea as that large expanse of black plastic always bothered me and that would be quite quick and easy. Rebuilding it in wood would be another idea but I'm not sure I've got time for that.
  3. I've posted this in the DIY forum too but since you asked Telrad, here it is.
  4. Thanks for the nice comments. Here's a shot of the underside of the base, as the feet rather disappeared in the long grass of the previous photo.
  5. Finally fished the base. Many thanks for your helpful ideas everyone.
  6. Be sure to clean or sand any part that is to be glued since it is usually coated in release agent. Use a dust mask as the dust is not good. Masking tape on the areas to be cut makes life easier - a junior hacksaw works well. Another nice thing about carbon is it is already black.
  7. Here is a link to a source for carbon batten Carbon Fibre. I have used the 0.5mm x 10mm batten for my 8" dob and it's solid as a rock. The 0.8mm stuff is very strong indeed.
  8. I'd love a little advice from anyone who has used a dob. Is weight an issue for the base? I don't need to move it far for use and am thinking that leaving it on the heavy side might help keep it solid in use. Secondly, I have searched these forums and it seems that a good angle between the teflon glides for the altitude bearing is 70°, perhaps better than 90°. An thoughts? Many thanks, Pete
  9. Well, it shouldn't have too much problem with rust :-) I have limited experience in this sort of thing but wood doesn't like sudden changes or extremes of humidity. One problem is that it can become permanently compressed if it becomes very wet whilst being held rigidly and is unable to swell. Then, when it dries out it cracks. This is unlikely to be an issue in a decent shed or observatory though I would have thought. Would heat in the summer be an issue? I don't know how hot they get. In general I imagine that if it's suitable for a mirror it's probably ok for the wood too. Walnut is dimensionally pretty stable and ply should have little problem.
  10. Astrokev, I've looked back through my notes and found a simple formula for calculating the angle the light cone makes entering the scope: True field = apparent field/magnification. So, using your lowest power eyepiece, in my case a 33mm eyepiece with a field of 72° in a 1200mm scope gives 72/36 = 2°. I now remember being baffled by that program too but did find the excel spreadsheet calculator and other info here very useful: Oldham Optical Telescope Design page
  11. Astrokev, I just put a 45° on one edge and let the other edge over hang. You only need to be careful with gluing the rings onto the first piece (lining them up against the 45° edge) and then to make sure it is on a dead flat surface before continuing with the next piece. If you look at one of the early photos I think you can see the piece overhanging ready to accept the next one which will be bevelled. Putting a 22.5° bevel on each edge is more like coopering and struck me as harder to do if using baffles. As for the theory of tube diameter, I do remember being advised just to make the opening at the front of the telescope an inch wider (in radius) than the primary. Calculating more precisely probably just enables you to reduce the tube diameter a little if you are really trying to keep it to a minimum.
  12. Many thanks for all the nice and encouraging comments, and to Telrad for the photos of a an interesting base design. Nice to see and quite a few interesting ideas there. Astrokev, to avoid vignetting when using a wide angle eyepiece, the ring at the mouth needs to be wider than the one nearest the primary as the light enters the scope in a cone shape rather than parallel. I can't honestly remember how I calculated it - I can't run "Newt" on my Mac but it may have been with this program; Newtonian Baffle Calculator. Yes, the opening is 10" and the baffles give more strength at the primary end. If I were to do it again I would put one more baffle between the primary and secondary as it needed careful assembly with such a long gap either side of the 4th ring. Finished strength isn't a problem though, and with the flocking the baffles are really more about ease of construction than cutting out stray light. Focaldepth, it is oiled with "Osmo Poly X Oil" available in the UK from Brewers (a paint shop) and flooring suppliers etc. It contains some hard Carnaube wax and only needs two or maybe three thin coats. It dries with a lovely natural look to the wood and is very hard wearing. Gina, thanks - I'll look through old threads more for other ideas - I didn't see many in my first quick look.
  13. I've posted these pictures elsewhere but this forum is probably more appropriate. It was supposed to be a quick & fun project but I had some nice walnut wood and so it seemed worth putting some extra effort in. I still need to design the base so if anyone knows of a particularly nice looking design I'd love to see it. Many thanks in advance. The photo of the moon & Saturn is a composite of two to bring them closer together and it wasn't properly collimated at that point (still isn't - I'll cross that bridge when I've made the base!).
  14. Haven't had much time to work on this but the altitude bearing cradle is nearly finished and next I'll make the base for it.
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