Dobson 250 trolley with setting circle

[AllanJ]

I made a trolley for my 250mm Dob using a bit of spare mdf that I cut to 22" diameter - an inch bigger than the dob base - and bolted on three 3.5" braking castors (I didn't want to put castors directly onto the mount). Then I printed off a setting circle from Rob Willett's website (here), glued that on and varnished it to keep moisture out. I stuck some castor cups on to prevent the mount's feet from sliding. For fine tuning the levelling I have a couple of levelling feet left over from installing a kitchen many years ago (never throw anything away if it might come in handy). I'll probably get a couple of clamps to lock the mount onto the trolley.

Rather than trying to orient the trolley, I point the scope at Polaris and note how many degrees off North the setting circle is. With the aid of a Wixey digital angle guage and alt-az readings off Stellarium (or printed from Astro Helper) I have been able to navigate very quickly to targets. Cheap and cheerful, but it works.

Allan

[Doc]

Well done Allan it's amazing how accurate this set up can be, it's very similar to what I have done on my dob.

[Rusty Strings]

Very nice Allan, what amazes me is that the manufacturers haven't done something similar.

[irishbloke]

Allan,

This is a great job. I have been wondering about how I could make up a setting circle for my dob too. I have been wondering about how to fit leveling feet but don't like the idea of damaging the dob base board. Your idea is a great work around!!! Plus the new board can be transported separately meaning wheels, leveling feet aren't sticking out of the bottom of the base which I imagine could make it arkward in the the car.

There's a couple of ideas being used on here, but yours seems to be a great model to see if I can get the setting circles to work.

Bottom line. I think I'll give this one a go.

Thanks. Brian

[brantuk]

Nice job there Allan. Be good to see that posted under "Dob Mods" thread in the Dob Users group. Feel free to click the link in my signature and join up

[yesyes]

Great job!

I keep wondering how one goes about making/cutting such large round bits. Do you just draw a circle and use a hand held jigsaw? Or do you have some machinery for this? Or did you have this made?

I'm doing a lot of DIY but always have problems with round things.... ;-)

[TheThing]

Good job Allan. It's very neat and professional looking.

[AllanJ]

Brantuk - I have joined the Dob Users group and posted a link as you suggested.

Brian - you are right about keeping it separate. I took it on its maiden outing to the Salisbury SP, and I had enough of a struggle to get the mount into my campervan as it was, without wheels as well!

Yesyes - I cut it as you said; on a scrap length of wood I drilled a hole for a nail to pin the centre at one end, and a hole for a pencil at the other, and rotated it to mark the circle, then cut it (slowly)with a jigsaw.

It may look professional, thanks Hugh, but its strictly amateur and probably doesn't bear too close inspection, with the varnish dripping down the sides, etc!

Allan

[twotter]

I do like that

[dobbie]

hi allan i to have a 250 flextube dobbie i made a board with leveling legs on then drew a circle on it with the degrees on but with not much success , how did u get to print a circle that size .. dobbie

[AllanJ]

Dobbie - I used a website with a program for printing various setting circles, etc, produced by Rob Willett.

Setting Circles

The basic functions are free, but to customise the size, etc, there is a small subscription.

Allan

[Wbarkingmad]

Hi Allan, nice one, an interesting approach. I went a different way and mounted a (brass) setting circle between base plate and rocker box. It involved cutting a hole in the base of the rocker box but the whole mount is already fairly modified. With a Wixey on the OTA, star-hopping is so much more straightforward. To what degree do you level the base plate?

[AllanJ]

Hi Pete, I was a bit (a lot) wary about cutting into my mount just yet. As far as the level of the base goes, since I have an auto tracking dob I try to get it as level as possible - I'm not sure how tolerant it is, but my scope tracks quite well when I get a good level and north orientation, as with any setup.

Allan

[Ogri]

Very nice Allan!

This has given me an idea that may be useful for height adjustment for those of us with bad backs (or those looking to prevent them), as well as for levelling.

How about two of the big circular discs as you used (maybe slightly bigger diameter to ease installing and adjusting a perimiter fixing mechanism more conveniently, without interfering with the standard dob base), then between the two circles for height adjustment, have 3 threaded rod adjusters set at 120 degrees around the perimeter for locking it solid and getting it level?

Could always put a level bubble into the top disc as well.

Just tailor the threaded rod lengths to suit what you need for comfortable viewing (the casters give useful extra height too!).

eta: actually nothing would need to be circular, as long as the existing dob base can be mounted securely and centrally to the top plate (easily done with clamps), 120 degree spaced arms would be fine.

PS. Oooooo thanks for that link Brantuk! I didn't even know there was a dob users group Now that I have one, I better mosey on over and have a look.

[WayBig]

Thats a nice looking piece of kit.

Regarding "levelling feet" - I've been trying to think of a way of doing this, since I recently fitted a few kitchen units that had twist up levelling feet. I haven't been able to find anything similar sold separately at my local B&Q or homebase.

Has anyone found anything suitable to make levelling feet out of?

Thanks

Chris

[ponytale]

here is my plan for my dob levellers , not constructed yet but this is my plan attatched

leveller feet.doc

[WayBig]

I was thinking of something similar - though not as complex - a bit fat bolt through each corner of a wooden base, with some sort of foot on it to prevent the end sinking into the ground, and a wingnut on the bolt, underneath the base - so raising or lowering the wingnut adjusts the angle of the base.

I'd prefer to put "cabinet feet" on the dob base though, if that's possible, so that I dont have another piece of kit to carry in/out.

[insomnia]

I will be starting my homemade setting circle base very shortly. I will get staples to print off a few copies of my setting circle (just in case I end up ruining the first 1) I have sourced my leveling feet from ebay, I will use a wixey, and I will use caster cups to hold the whole scope in position on the setting circle.

I want the job of finding night sky objects as easy and pain free as possible when using the setting circle.

I understand the idea of finding Polaris as a good guide star, but should the scope and 0 degrees on the setting circle be facing north before you aim for Polaris. I plan to put the dob base on a pre marked north to south marker line and have the 0 and 180 degrees over this line.

Is this just 1 of many ways to make a setting circle work effectively?

[Peter Drew]

Brantuk. I've just taken advantage of your link to the Dob Users link, I also didn't realise there was one. Thanks.

[brantuk]

You're welcome Peter - good to have you on board

[AllanJ]

Hi insomnia - the way I have been using it is not to worry about orienting the base exactly N-S but to note how many degrees off north it is once I have found Polaris. As long as you remember whether to add or subtract ....

By the way, an alternative to paying Staples to print a large circle is to print it on a set of A4 sheets and cut it to fit - takes a bit of fiddling about with the gluing, but probably cheaper.

Allan

I

I want the job of finding night sky objects as easy and pain free as possible when using the setting circle.

I understand the idea of finding Polaris as a good guide star, but should the scope and 0 degrees on the setting circle be facing north before you aim for Polaris. I plan to put the dob base on a pre marked north to south marker line and have the 0 and 180 degrees over this line.

Is this just 1 of many ways to make a setting circle work effectively?

[Wbarkingmad]

If its any help, my standard way of finding things is open up Stellarium, get the alt/az coords of the nearest easily identifiable target as a reference, and of the object in question. Set the dob up on the reference, then move in alt and az the difference between the two sets of coords noted from Stellarium. Works a treat for any baseboard orientation because you are only moving a few degrees relative to your reference. And its good for learning your way around the sky too. A Rigel (or similar) works wonders for this method too.

[martin_h]

Thats a nice looking piece of kit.

Regarding "levelling feet" - I've been trying to think of a way of doing this, since I recently fitted a few kitchen units that had twist up levelling feet. I haven't been able to find anything similar sold separately at my local B&Q or homebase.

Has anyone found anything suitable to make levelling feet out of?

Thanks

Chris

IT Solutions Cabinet Legs Pack of 2, 0000003232507