westmarch
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Posts posted by westmarch
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Mods, this might get better advice if it was moved to AP section.
John
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Terry,
I think you have to temper your expectations. You are beyond the lower latitude that this design is optimised for but that does not mean it is not functional.
1. EQ Platforms are not going to give you EQ6 level tracking.
2. If you are looking at DSOs, you are never going to be using high mag so a bit of drift in a wide FOV is not a game changer. If this is not enough for you then try the following:
3. Shim the southern pivot.
(a) Your bottom platform should be level.
(b) Get a digital inclinometer/protactor. Only costs about $£10. Put it on the top platform and zero it.
(c) Incline the southern end of your upper platform with wood packers until your inclinometer shows a 4 degree elevation.
(d) Measure the distance between the upper surface of the bottom platform and the lower surface of the top platform. That is your target elevation for the southern pivot.
(e) Get a longer bolt and put it through the southern pivot bolt hole. Now mark it at the measurement that you made in (d). Cut it and round off the end.
(f) substitute it for your original bolt.
If you started off with segments designed for the minimum latitude that Reiner Vogel specified (46 degrees), then your 4 degree shim will have converted it to a 42 degree platform.
This, combined with Michael’s suggestion of trimming the speed, should give you a more stable target acquisition.
I can’t however emphasise enough! Check that you are happy with the stability of this setup at full tilt before committing your precious Dob to it, unsupported.
Good Luck!
John
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Hi Terry,
Acurate segments are key to getting smooth tracking. At a relatively low latitude such as 39 degrees the VNS design will struggle. If the segments were designed for a higher latitude, you can shim the platform to compensate slightly. This involves lifting the south pivot by no more than 4 degrees. Again you may run into stability problems at full tilt so be careful.
John
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12 hours ago, Time Traveler said:
Can someone show me what the vns segments measure for latitude 39 degrees?
Hi Terry,
Reiner Vogel does not list a VNS segment for 39 degrees, probably because you start to get into problems of platform instability at lower latitudes. As you get nearer the equator you have to consider substituting a circular segment as the southern pivot.
For 39 degrees you would probably be better considering a poncet type design. There is a discussion about latitude and design type here (towards the end of the thread):
https://www.cloudynights.com/topic/689330-equatorial-platform-cutting-aluminium-segments/
John
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I’ve used a double survival bag in the past during star parties. Probably the cheapest solution if you are only leaving your kit outside for a few nights.
John
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You do know that most UK libraries have these for free on their ebook app. Ours is called Libby. Use it before it gets cut.
John
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Hi Peter,
Excellent piece of improvisation and if stuff like this is not for tinkering with then why do we have so many cloudy nights?
If your dob feet can not be fitted into anything on the platform, try drilling two holes through the dob base and platform and using a long bolt with a lock nut on the platform, followed by wing nuts to secure the dob base to the bolts. I am sure there are any number of other solutions.
I hope you have many dark nights to enjoy it.
John
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This website is probably the highest resolution mapping of the moon.
John
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welcome to the forum,
lots of advice here and wishing you many clear skies.
John
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37 minutes ago, PeterStudz said:
Just started on mine. Just one question - in the instruction documentation by@westmarch the southern pivot bolt is given as M20 - that’s rather wide/large bolt! - I’m guessing it should be something like M8, possibly M10.
Just finishing off the segments. I stuck down the paper template to the aluminium with some craft glue to make things easier for me. Will soak it off in WD40 when done. My woodwork is OK but I’m a bit rubbish with metal.
I’m a bit late to the party but this has got to be one of the best, if not the best, threads in the DIY forum.
Hi Peter,
It is a wide bolt and intentionally so. The Southern pivot carries a significant part of the weight of the whole rig. You can use a smaller bolt but risk it eventually digging out a pit in the softer aluminium block. I wanted to avoid the risk of judder from that.
Good luck with your build.
John
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The platform really comes into its own when you are trying to spot DSOs that are on the edge of visibility - it gives you time to spot it with averted vision or wait until that moment of clear seeing.
John
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3 hours ago, mdstuart said:
You call that improvisation...what about my end stops.
Good Luck with those! 😯
John
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1 hour ago, mdstuart said:
..and action...is it moving?
I like the U bolt improvisation. Be interested to hear the first test result.
John
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On 24/06/2022 at 02:17, DWV said:
New guy here, I am looking to build one of these for my 8" dob, I pretty much have everything I will need here, but have a couple questions.
Could you extend the segments (following the same curve) to get longer times between resets, or would that put the platform/telescope on too much of an angle?
And would changing the angles on the top plate to bring it to the tip of the segment, change how it would work? (so you don't have that point sticking out)
Dave
Hi Dave,
extending the segments would mean that your centre of gravity could end up outside your footprint at the end of the travel and the scope would topple over.
You can make the top board bigger if you wish. I think most designs try to make the rig as small as possible to reduce weight and improve portability.
Good luck with the build.John
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I’m interested in your use of a UHC filter, I have been using an Astronomic filter on Bortle 4 skies and admit to being somewhat underwhelmed with it on emission nebulae. Which one do you have?
John
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I like your setup Peter and I have similar dew shields on my main tube and RACI. Despite this my RACI is always the first to dew up. Last week, I managed two hours before this happened. I put the scope into vertical position and placed an electric hand warmer, costing less than a tenner, on the objective end of the RACI. The dew cleared within five minutes and allowed me another hour at the scope.
John
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When I am trying to star hop through these areas, I tend to switch to my 40mm EP to use the fainter asterisms and continue to star hop. It also counteracts the LP. You do need something like Sky Safari to display fainter star asterisms and flip the field of view.
John
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Hi Phil,
can’t comment on the Poncet design you opted for but it looks like a solid build. A 14” is a heavy scope so your EQ1 motor might struggle but it looks as if you are nearly there with the work. I think it would be a shame to not try it out before changing the design.
The one piece of advice I would offer is to edge your chipboard with iron on tape. Once the board starts warping with dew entry into the exposed edges it quickly becomes useless .
John
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Ideally, the edge should feel smooth to the touch and be at right angle to the surface. Aluminium should be able to be filed smooth in about 5-10mins with the average flat file.
John
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Mark,
Spreadsheets have their place but you will struggle with sandpaper - really only for wood. You will find a flat file a lot easier. You will need it anyway, to to round off the tip of the bolt pivot that is going into that depression.
John
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On 01/11/2021 at 14:43, tony4563 said:
Does anyone know any company that makes the self adhesive digital setting circles for a Dobsonian?
Have you made one for yourself? If so, would you be happy to make one for me (would of course pay for materials and time)
Looking for one for my 12" GSO
Cheers
Tony
Hi Tony,
I have just had one printed for my 10” Dob and the company gave me a second one free. If you pm me, I will arrange to send it to you.
John
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Hi Lawrence,
There is a good website by Reiner Vogel with instructions on VNS segments.
http://www.reinervogel.net/Plattform/Vorlage Plattform 14 hoch.pdf
I dealt with the building of an equatorial platform here:
Hope that helps.
John
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Hi Mark,
Are you hoping to put the 20” scope on this build or is it for another scope?
John
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Hi Michael,
Excellent build and ingenious use of the Starsense add on. I must confess to being a star hopper myself but I have a mate who has one and swears by it.
Hope you have many clear nights to enjoy it.
John
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Larger Dobsonian
in Discussions - Scopes / Whole setups
Posted
If you can get your Dob away from light pollution, it is the equivalent of having 2-4 inches extra aperture.
If you have access to a dark sky area, a Dob that you can transport easily ticks all the boxes. For this, my advice would be something that you can comfortably lift and fit in your car. I find a 10 inch is the sweet spot and a truss dob just makes things easier.
John