Moonshane

ps one unexpected advantage of this design and size of scope is that as you remain seated in the same position throughout the whole of the observing session, and the alt bearing is positioned just where your hands are, I found that you can drive it through space like a car using the alt bearing as a steering wheel!

here's the last of the finishing bits and the whole thing set up. used it the same night and it's excellent! he's delighted with it.

added some iron on contiboard end trims to the alt bearings. work well with the 3mm teflon pads added and nailed in place.

also added the keeps and some flocking as a liner to reduce friction and possible damage to the finish when he applies it.

as you can see, being a tidy worker is not one of my strong points!

hope this inspires others to have a go even if they do it their way

I think it was a case of me misunderstanding it and trying to overcomplicate things. Sorry for hijacking the thread and thanks for all the advise.

It's still raining here so you can all blame me for causing it. If I hadn't bought the wood yesterday we'd have all been guaranteed clear skies for at least another week.

hey mate, this is an open thread and all comments and contributions are welcome and useful!

In my view, the decision on where to place the teflon supports is independant of the curve depth and diameter of bearing. I think it's angular position that is important. The decision is, I believe, driven by the following considerations -

1. the material used to make the bearings and the structural integrity of the circularity (ie. is the bearing a solid circular piece, or a hollow ring such as a section of pipe or similar). A ring would be more prone to deformation (ie. losing its circularity) than a solid piece.

2. the weight of the OTA being supported. Heavier = more likelihood of deforming the bearing, depending on the answer to point 1 above.

I guess the overall aim is to use contact points that provide the lowest pressure at the point of contact, without deforming the bearing. The position obviously needs to be wide enough so that the OTA doesn't "roll off" the supports when the altitude is adjusted.

For my next 6" Dob (currently being planned) I was intending using 110mm drain pipe end caps for the bearings (larger ones are available on-line so may consider these instead). Couple of quid each and would not require any fabrication on my part.

no reason not to at all. the principle according to Kriege and Berry is that the smaller the bearings the higher the sides need to be (good when it comes to a 6" tube) and the less friction there is in the bearing teflon combo. again this might be good but I prefer more friction (albeit less 'stiction'.).

again the 65-70 degree spread of the alt bearings is just the optimum according to their research. obviously any other angles can be used but there will be differences in characteristics.

Hope you don't mind me suggesting ... but you might find that thin aluminium sheet works better than an LP. Its easy to work and will give you a better more rigid base. The buttery smoothness of Al is really nice - and it won't shatter at lower temperatures.

this seems like an excellent suggestion but I thought that there was a fair degree of stiction with smooth surfaces?

I've just noticed this and my V was 90 degrees and the teflon pads were 90 degrees apart as well, and I'm pretty certain the alt bearing sat on the teflon at 90 degrees too. I can't tell at the minute because my scope no longer has the original side bearings on it and I've removed the teflon from my last base.

edit: I've just checked the plans for my dob and the bearings definitely sat on the teflon at 90 degrees.

this is certainly possible. I think it's due to the relationship between the depth of your curve and the diameter of the bearing. according to Kriege and Berry the optimum spread is 65-70 degrees although this assumes a shallow section of the curve.

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.

this is a much better idea. just to be clear I agree with a router being the best too for the job (and have one) but was trying to think of ways to do this if you don't have one. yes, any kind of sander on the side would be good with this sort of jig - or just buy a used router for £25-30!

One tool I would recommend buying when building the base is a sash clamp, or two. They're not really needed, my previous two bases were made without them, but they do make constructing the box part of the base so much easier. They don't have to be expensive either, mine cost about £8 each.

Buy Axminster Aluminium Sash Cramps from Axminster, fast delivery for the UK

I hadn't thought about using a drill as a lathe either. It's not a bad idea really. I'll have to try it when I get round to sanding my side bearings.

I'm sorry to read about you all being made redundant too. I've been unemployed for the last few months so I know how you all must be feeling, although I was self employed so I didn't get any redundancy pay.. In the long run it could be a good thing for us all though. I've been using the time to go back to college and gain some qualifications. I think the main thing to do is to try and keep yourself busy.

good call mate re the clamps. thankfully, my father in law has a box full of these and I'll be able to borrow some so will be very useful.

cheers for the encouragement re job hunting. let's hope I/we get something soon

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.

all good points Kevin and you are spot on. might be better make a wooden arm of the circle radius and then cutting the piece in half and bolting a sander down to the workbench. always more than one way to skin a cat!

I've used a drill for sanding small parts.

ouch. sounds painful!

ha ha

have a go matey. seriously, all you need is care, a hand saw and a drill and I am sure you could make one.

an angle grinder would be good as a wood turning lathe to smooth the circle for the bearings with sandpaper. I bet if you have a woodworking shop nearby, they'd cut you a circle for not much cost. the alt bearings are really the only critical part.

cheers matey.

the way I look at it is this. if you can get the materials for maybe £20 for the average base - OK maybe £30 you can have a go and if it goes in the skip afterwards at least you've tried.

you can get the wood all cut to size at the place you buy it from for either nothing or a few quid too.

none of the measurements are critical really, just that they need to be the same - eg the sides need to be the same size and shape, the sides need to be as wide as the base, the groundboard which is hidden need be no particular shape. you can use straight V cuts as mentioned by Kevin for the top of the sides. you could even rough cut a circle with a standard hand saw and then if you have a drill or grinder, use this as a 'lathe and sand the circle into shape, cut it in half and you have your bearings.

there's always a number of ways to do things and this was a great learning experience for me and will be useful when it comes to making the other two scopes I have planned.

I have just completely finished it and it works superbly.

easy to balance (the rings are a real help there) and lovely action.

I'll post some final pics later on as I need to tidy up now before my wife gets home and we go for some lunch!

hi Kevin, yes, I totally agree.

as long as the teflon pads are at about 70 (not 90) degrees apart (imagine a 70 degree piece of pie from the centre of the bearing radius) then the shape of the cut out at the top of the side bearing does not matter. effectively, be it on a curve or a V, it's in the same place. so the angle of the V would need to be 110 degrees to ensure they are 90 degrees to the alt bearing surface.

Scogyrd did this on his thread but not sure what his angles were.

I have to say the LP and teflon combo is beautifully smooth. no stiction and perfect 'stoption' too. it moves when you want and stops where you put it.

I have found some contiboard end tape in the shed (the iron on stuff) and this will work well with the teflon pads for the alt bearings. will iron this on shortly and then show some pics of the whole thing. even with no teflon it slides beautifully in the saddle.

the whole thing is rock solid and I'll be making another one for my 6" f11 in due course.

wow, you CAN make anything out of plywood.

I am even thinking about making an alt az mount for a refractor and a car.

Howdy, Shane!

Great design and great execution on the dob mount!

Any chance we could get dimensions?

cheers Bob

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.

My main concern is always stability and I feel anything less than 12" at the base is basically unstable. It's broadly in 18mm ply. quality of ply is not essential if you are painting but if you are staining/varnishing then you'll want better 'furniture' quality timber.

the design is literally :

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.

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.

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.

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?

I've not searched yet, so may be readily available, but where did you get your teflon?

hi Kevin

I generally get mine from Ebay - just search Teflon sheet

the one I used for this was 3mm thick and Kriege and Berry suggests 1.5x1.5 inches square for smaller dobs.

I think you can get 'etched' teflon too (and I'll be buying this next time) and this is better as it will take a good quality epoxy from what I read.

quick update. added teflon pads, tacked and driven below surface - didn't have 'etched' teflon so glue no use. rounded off the sharp corners to aid smooth rotation. will see how the record/teflon effect works in the morning. obviously the pads are attached directly over the feet to ensure the weight is transferred to the ground directly. makes for a more solid mounting.

glued on the record to the bottom of the rocker and went round to father in law's (he has a pillar drill) to sort out the alt bearing holes.

will put up more pics of the finished thing tomorrow. will just need painting (by Steve!).

Very neat and tidy solution. So much better and safer than carrying dobs individually. I always think that one day, it'll slip in my hands when I carry the OTA on mine But with your dob mount, it looks secure and definitely makes it's easier to 'lug' around. Seriously think that you should submit this design to some manafacturers, and get them to re-design their dob base. It would certainly make it better to carry with the handle/cut-out! You're a genius dude.

ha ha wouldn't go as far as genius but yes, I'm close

your comments have actually made me think of an addition I will make tomorrow - some finger sized cut-outs in the alt discs. this will make it much easier to pick up the OTA. I am sure you'll be fine carrying the dob - main this to worry about is things under the feet I suppose.

Sorry to hear about the redundancy Shane. I have been out of work for a while now but like you my wife has a good job with a good company so in the end we decided it would be best if I looked after the kids. I won't lie I'd much rather be back in work, for one it would be easier than having to look after two energetic children all day . I'm sure you and Kevin will find some thing soon.

cheers matey. mine are too old at 16 and 13 so no chance of that. applied for a few so will wait and see.....

Don't buy formica Shane have a word with a local kitchen fitter and grab one his sink or hob cutouts.

They've only got to pay to dump em otherwise.

Regards Steve

cheers Steve, good suggestion but I'm not a fan of the weight or the materials in worktops and much prefer ply. BUT as you say, a ready made solution!

Shane,

Excellent work, you are very handy with the tools.

I am beginning to wonder whether to make a base like this for my dob, I am getting hacked off with the footprint of the circular base...

it's highly recommended. if I'd have been making a 12" scope base, I bet it would have only been a couple of inches wider, maybe less.

definitely easier to move about and less storage taken up too.

Excellent choice!

cheers Kev!

I don't know how I missed that bit.

Your mount does look good though, it looks a lot neater than mine.

he he no probs mate. hey if it works, it works. the best thing with this one is has cost me the grand total of £2 at the current time as I already had the wood in the shed.

same here mate so thanks for the tip! and here it is - 12" version of 'Good Life' by Inner City - not seen the light of day for about 20 years!

That's you and me both, mate!

Regarding the formica for the base, I've read of someone who used an old vinyl LP. Worth considering if you have any old disks lying around. Certainly cheaper than buying formica.....

.....and if you stick a needle in the rocker box, you could listen to some music at the same time!

quite positive and actively applying for jobs etc - want a new career so in seek and justify all my skills mode currently. got a decent package though so have some time and it may even work out well. my wife has a good job too and I think will be the main breadwinner for a long time to come!

you're a genius mate with the LP. I do actually have some still in the loft so bonus!!

this will enable me to get it finished while Russ and I work on a joint purchase of some laminate/formica.

Nice looking mount! I like the piece of wood you put at the back to help keep it square, where have I seen that before?

I plan on making a similar mount for my dob soon. I've already bought the tube rings and made the side bearings but I've just spent a fortune on my MOT and I didn't quite have enough plywood left over from my last build so it's been put on the back seat for now. One day I'll finish it though...

ha ha

cheers mate - I did mention somewhere that my mount was inspired by you and OOUK of course

good luck with your own build!

Shane, just got to say that is wicked!

cheers mate

quite pleased with it. just need some formica now

I thought to myself, I wonder...........and as an added bonus (and this was pure luck) the scope sits nicely within the base with the alt bearings attached, making for a quite compact and neat package - allowing it to be carried in and out in one. nice.

just call me Joseph!

nah, I am very amateur when it comes to woodwork but I broadly know what I am doing and this is (genuinely) the first time I have used a router so I am pretty pleased.

Now I know how it operates, I'll be making templates and then routering off those for my 'half cartwheel alt bearings' and rocker cut outs when it comes to the 16".

here's today's efforts (redundancy has it's benefits sometimes.....).

made some 'keeps' to prevent lateral movement.

checked the fit with some rough blocks and a single ring - spot on

I have as mentioned previously, built this with the knowledge that he may eventually buy an 8" tube so it is a little oversize but this adds to stability.

I then put the tube in and it seems to fit together well.

no worries. will do - if you want pics of anything specific let me know soon as I may be taking it to Steve next week sometime.

did I say this was my practice run from 'free' materials which will be a good learning experience for when I use expensive double bonded exterior ply for my 'proper' one.

yeah I am using teflon and was going to use formica (ebony star or something with the same orange peel texture anyway). I'll be paying for the latter so as he's getting this mount for free, we'll try it with just teflon and a varnished surface for now but if my and Russ's plan to get some locally pays off at the right price then I may add this to the base later on.

I'll certainly be using Teflon and formica for my 16" when this is done - hopefully start on this soon,

after this experience cutting (the cut-outs not the circular sections) freehand pretty accurately though, with a jigsaw, I will probably make a template and router the shapes out for my biggie.