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rabbithutch

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Posts posted by rabbithutch

  1. I wouldn't fancy doing it with a hand drill either but I've got a drill press so I'll probably use that if I do decide to have a go. I reckon it might be easier to use that than it would be to fix my sander to my workbench too. My sander is a funny shape and I can see it being a right pain to get (and keep) everything square. TBH I don't really know though. I'll have to see what I think is best if I do decide to do it.

    Thanks for the advice btw.

    Just a bit more . . .

    You can use a drill press but you need to be very careful about how much pressure you apply. Drill presses are not designed for pressure applied at 90 degrees to the armature. You should expect to take very small amounts off the edges of the bearings and make multiple passes of ever lighter pressure. I ruined a drill press (admittedly an inexpensive Asian one) in this pursuit. That's why I suggested a belt sander.

  2. I might be getting confused about what a lathe does, it's been a few years since I last used one, but I was thinking more along the lines of making a jig for the circle to spin on and using the drill, with some sort of attachment, to sand the wood. Instead of attaching the wood to the drill.

    Something a bit like this but with a drill instead of whatever it is they're using.

    Sanding Jig for Circles

    I've got a router to cut the circles out. I was just thinking of using the drill as an easy way to finish them off and make sure both bearings are exactly the same.

    You are correct. I was afraid that someone might try to center a piece on the shaft of a drill and shape it. The approach that you depict would work. The tool shown is a rotary bench sander and would be ideal - much better than a drill or a drill press (Is a 'pillar' drill the same tool?). If you have no bench sander, then perhaps a belt sander on its side and affixed to the workbench would do just as well. I've used a belt sander in this way and see no reason why it wouldn't work for the job at hand. The last tool I'd use would be a hand drill and then only as a last resort.

  3. To some extent the measurements are academic as they need to be designed to suit the tube for which you are making the base, the position of the balance point / length of the tube and of course observer height.
    Of course you are right, Shane. I was asking about dimensions so that I might get a better idea about why you chose them and a better sense of the overall proportion. There are a lot of variables to consider and I thought that a discussion of dimensions might shed some light on the considerations and educate us about your decision making process. I know nothing about 6" Newts (and very little about any other scopes) and so have no idea of the length of the OTA or about balancing weight among mirrors, finders, focusers, eps, etc.
    My main concern is always stability and I feel anything less than 12" at the base is basically unstable.
    I'm surprised that a foot print of only 12" on a side could be deemed adequate, but then I'm thinking about the bulk of my 8" dob.
    groundboard

    a circle with feet set at 120 degrees and as far out as possible. this could be any shape really but a circle remains hidden at all times. e.g. a square would have corners sticking out when the rocker is turned. (toes, dark etc). teflon pads on the upperside 1.5"x1.5"x3mm fixed above the feet. mine is 13" diameter.

    All makes perfect sense. I'm in the throes of making a triangular sub-base to fit under the manufacturer's circular. The motivation is to use all-thread rods through nuts fixed in the base at each intersection to be used to level the base so that I can use a digital angle gauge to get more accurate bearings. I move my scope about with a small handcart with the OTA bearings sitting in the carriage. Of course I brace the OTA against sudden shifting. Adding the extra bit of weight for the triangular sub-base doesn't concern me, but I wondered if moving it about while on the bearings is a bad idea.
    Rocker

    basically four rectangles and a square base. square piece at the bottom to match the groundboard plus maybe 1/2".

    sides need a circular section cut to match the bearings attached to the tube. needs to have a large enough curve to be able to fix teflon pads at 70 degree points from centre of arc. as mentioned match the height to the observer's height. I literally got him to hold the scope up to his eye while seated at about the mid point and measured to the ground.

    front piece should be measured to reach as high as possible but to allow the scope to drop down to a few degrees.

    back piece high enough to provide support and low enough to let the primary end of the mirror pass plus a few inches for balancing if required.

    Carriage construction seems straightforward, but I'm curious about why you the proportions you did. It seems tall to me, but you said that the dimensions were custom fitted for someone seated while viewing.
    alt bearings

    just circular sections maybe 1.5-2x the diameter of the tube. they can be half circles too. obviously need to be matched to the circular sections on the sides of the rocker.

    The scope appears to allow you some leeway in choosing the pivot point on the OTA. I will have to examine my Orion to see if it can be changed. I thought, perhaps, that the engineers at Orion had done the geometry and physics and chosen the optimum pivot point making assumptions about the average weight of finders, eps, etc; therefore I had not considered possible mods. I would like to know how you chose the pivot point and whether that decision influenced the size of the alt bearings or the height of their pivot center above ground.
    hope this makes sense. really, like an equatorial platform, you need to match the dimensions to suit your own circumstances - one of the main advantages of making one yourself and the reason why I suppose, manufacturers use more 'generic' dimensions?
    Yes, of course, your post makes great sense. My curiosity and lack of knowledge - and maybe a bit of obsession and compulsion on my part - prompted my questions.

    Thank you for taking the time to share your results with us and for taking our questions. You've helped me learn a great deal.

  4. Mmm, interesting idea using a drill as a lathe. A couple of points spring to mind though -

    1. Challange #1. Make sure the drill is well fixed to prevent any movement during working on the piece.

    2. If the diameter of the piece being lathed is large, this is likely to put a huge strain on the drill motor at start-up due to the large inertia. (the drill is designed to turn relatively small diameter tools with low inertia).

    3. Getting the piece to be completely square wrt the drill axis of rotation is difficult, and becomes more so as diameter increases.

    Not saying it's impossible, but I once tried to lathe circular plastic sheet material using a drill and all the above created challenges/difficulties.

    Oh, and wear goggles !! I recall an incident at school woodwork class once where a schoolmate failed to attach the cherished wooden bowl he was making onto the lathe correctly. Next thing, the bowl was through the window and ended up 20 yards across the field. Not pretty.

    I, too, would be very reluctant to try to use a drill to round anything as large as the bearings or the base. Most drill chucks do not run true enough to accomplish adequate rounding, to say nothing of the difficulties of fixing the drill and the wear and tear that the materials would cause to the motor and to the chuck and possibly to the motor armature.

    The best tool for this - probably even better than a lathe - is the hand held router. With a central pivot point and an offset from it to the inner edge of the bit set at the desired radius, geometry and the power of the tool will see you through. I've done this quite a few times. In a shop filled with all tools, the router would be my tool of choice.

    The most important part of Kevin's post though is the caution to wear eye protection. The cost of an accident is far too dire to be cavalier about this protection.

  5. The 8" dob - probably Orion 8XTi - seems to be the scope I lean toward more and more. I think it will give me the greatest cost-satisfaction combination.

    Knowing that I will, no doubt, invest in accessories for this particular scope probably doubling the investment (or more), I would prefer to have an extensible platform. Anticipating that the day will arrive when I will want to get into AP, I was wondering if it were feasible to consider buying an EQ mount with GOTO for this scope in the future, abandoning the dob mount. Or, is it the case that the sheer mass of the optics makes it unlikely to be able to buy a reasonably priced EQ?

    Are 8" newts on EQ mounts of approximately the same mass as an 8" dob? Is this mass issue the reason that Mak-Cass on fork mounted EQs seem to be so ubiquitous?

    Or, is it the case that most sales are of the entire kit making the market for secondary upgrades - such as the EQ tracking mount proposed - are not economically viable?

    Those without the funds limits that I face would probably just buy a new larger aperture scope, but I'm trying to figure out if I can extend my enjoyment of the hobby over time making gradual investments as my interests exceed the capacity of my original purchase. I'm a believer in buying the best one can afford, but I'm also a believer in looking past the immediate goals or ends for any purchase and using that to educate initial buying.

    Would appreciate hearing of any successes or failures from anyone who has been down this path.

    Thank you!

  6. Great forum! I might be the newest of newbies to astronomy and to the site. I just joined yesterday and made my first post demonstrating my great ignorance by making my first question about a telescope purchase. (Actually, it was the opportunity to get what seemed to be a bargain that rekindled my interest.)

    I've not done any skywatching to speak of for 30 or more years. I can find the constellations and even some of the planets without instruments. What I cannot do is read many of the posts here that interest me because I have not yet acquired the vocabulary necessary to understand what I'm reading.

    Would it be possible to create a page (or a sticky post) that gives us newbies a place to learn the terms? I've been trying to learn about telescopes and have been overwhelmed by terminology - some of which I think I know and still other which confuses me. What's the difference between refractor and reflector? Newtonian and Dobsonian? Plossi and Barlow? And I haven't even started on the confusing issue of tracking equipment.

    These are but a few examples of terms that apply to 'scopes, and I'm certain there are countless more that apply to other topics. A Glossary of terms would be wonderful. If it could be augmented by links, or pics ore other information, all the better.

    WELL! THAT WAS EMBARRASSING! :( I found the glossary. It was what I was looking for. May I suggest that it be promoted to higher rank on the forum. Maybe up there with Newbie Questions?

    Having complied with the request for feedback, let me now add my kudos for a wonderful site that I'm certain will continue to give me hours of entertainment and useful information. I live in the American Southwest - in the central part of Texas - and it is great to see posts from so many people scattered around out globe. I hope that I will progress in my journey to learn quickly and might someday become a contributor here.

    Thank you!

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