Dobsonian mount for 300PDS ?

[wisedraco]

Hello!

I want to made a dobsonian mount for sky-watcher 300PDS OTA.

Until now i newer making an dobsonian mounts, and also must say, my woodworking skills is not good at all, but, i cannot see another variants. I think to build something like a find in russian ( ukrainian actually) forum:

  http://www.astroclub.kiev.ua/forum/index.php?topic=27456.0

but on bearings i want to use a roller wheels, like as in user "8kids" from this forum, dob.

plan to use both-sided laminate 18mm plywood.

any suggestions? maybe anyone have an plans for something like this?

also i plan a brake with changing pressure like as in fabric skywatcher mounts...

[8kids]

I used some rollerblade wheels on this mount with some felt pads as a friction brake. The side bearings are bolted straight into the tube rings, but I don't think it's any better than using Teflon pads.

[wisedraco]

btw, i think, if you align a tube rings with locks to one side and up from ota, and mount to rings locks a handlebar, then it is a much more easy to operate with scope and carry it around...

[wisedraco]

I used some rollerblade wheels on this mount with some felt pads as a friction brake. The side bearings are bolted straight into the tube rings, but I don't think it's any better than using Teflon pads.

can you give all your mount dimensions?

especially inside width and side bearing diameters, who is bolted to ota tube rings?

ideally, if you give it in centimetres...

[John]

One of our members made a dobsonian mount for my 300mm F/5.3 Orion Optics tube. Here is a link to some information on it:

http://stargazerslounge.com/topic/176078-back-in-the-dob-mob-again/

I would think that a similar design would work well for your scope as well.

There are some more photos of the mount and scope in this thread as well, this time on a commercially made equatorial platform:

http://stargazerslounge.com/topic/186625-my-12-orion-optics-dob-with-equatorial-platform/

[8kids]

The width was determined by the tube rings plus the 18mm plywood, in my case that was 42cm wide. The bearing diameter is 56cm. I've recently changed back to Teflon pads due to a dodgy bearings in my rollerblade wheels. I have the lowest point of the bearing 50cm from the floor but you can change the height by making the bearing box higher or lower.

When I get some time I'll try and draw it up with dimensions.

[wisedraco]

ok. i take some calculations, and think, sideboards ( rockers?) can be make a 65 centimetres high. altitude bearings with 42 centimetred diameter, box side size on external edges - 46 centimetres, and base plate in a round shape with diameter 68 centimetres.

inner size between rockers in box be a 42 centimetres, as 8kids says.

make from plywood 18mm thick, also plan to make 2 larger altitude bearings - 50 centimetres diameter - first complect ( 42 cm) is for use on rockerbox on teflon pads, edge on edge, larger - 50 cm - to try make a construction as 8kids - with roller blades of inside of rockers.

any suggestions?

[8kids]

That should be o.k.

I have now replaced my rollerblade wheels. I had to reduce the width of the rocker box to match the alt bearing width (42cm). You can see the base of the dob which has a lazy Susan bearing underneath.

I hope that helps you Wisedraco.

[wisedraco]

what is you ?rockerbox? height?

use tha same alt bearings of 56 cm diameter?

where, from the bottom of scope, is scope's balance point?

what is scope height on a mount?

what is clearance between rockerbox bottom, and scope tube bottom?

what do you think, i must build an 42 cm diameter alt bearings, or better to be on 42 cm?

42 cm is inside width of rockerbox, i understand right?

[8kids]

1, Height of the rockerbox is 42cm in the middle. It's higher at the ends because of the curve.

2, You can make the bearing any size you want, you'll just have to make the rockerbox higher or lower to suit your viewing preference.

3, The balance point will depend on the eyepieces, extension tubes etc that you use. From the bottom of my scope to the centre of the alt bearing is about 53cm.

4, The whole thing is 167cm from the floor to the top of the scope.

5, Clearance under the scope is 11cm.

6, The size of the bearings etc depends on you. If you make the bearings smaller you will need to make the rockerbox taller.

It depends on what height you like the eyepiece at the Zenith. I'm about 180cm tall so this scope suits me.

Hope that helps.

[wisedraco]

Thanks. looks like a sideboard curve is no more than 5 - 7 cm, as so full height is about bellow 50 cm.

i bought and cut plywood yeasterday. plan to make altitude bearings 50 cm diameter, rockerbox sideboards is cutting to 65 cm height, but now, based on your dimensions, it is like too tall....

i consider of balance point of ota a 65 cm from bottom, who too looks like too much. try to make altitude bearings, and then like to try and measure, what is my rockerbox optimal height.

i also about 183 cm height, but i think, the lowest is eyepiece, the better - on stability, mobility, and also seating height take on consider...

btw, what paint you use to painting your rockerboard? on alt bearing working side the same? how its slipping via teflon? wearing? where can get an teflon pads? furniture store? yesterday i go to one building materials store, and cannot find any teflon / ptfe pads...

in what way you control altitude and azimuth bearings stiffness ( for that not rotate too freely)?

sorry for my bad english...

[8kids]

I bought my Teflon/PTFE from ebay.

I originally used dulux weathershield black satin pain, as seen on the bearing when I refurbish the mount  I'll use the same paint again. I don't know the equivalent paint in Latvia.

The bearing should have some formica applied to the edge, I haven't got around to that yet. The scope is retained on the rockerbox by the two small circles of timber which have Teflon on their face you can see one in the top picture. The stiffness takes care of itself when the scope is in balance the movement is very smooth.

I wouldn't worry about your English, by the time we have finished this thread you will be fluent. On the other hand my Latvian is non existent.

[wisedraco]

ok, thank you for a help.

I do not think, at finish my english be a much better, because my english state is about unchanged for many years, sadly.

About latvian - i think, it is a better to switch to russian - it is a far more common, widespread, than latvian

ok, going to wait to salary - then i can have made out my alt bearings on CNC machine at workshop, and then i can continue this construction, and maybe appear a new questions

[8kids]

No problem.

[wisedraco]

The width was determined by the tube rings plus the 18mm plywood, in my case that was 42cm wide. 

Hello!

need some clarification - your rockerbox is 42 cm wide on outer edges, not inner?

in my plans i draw rockerbox width 42 cm wide on inner dimension, therefore outer dimension is 46 cm...?

it means, i must shrink my box width to about 38 centimetres, or, better ( imho), must use a distancer wood scrap between alt bearings and tube rings on each side?

PS if not a secret - why you use a metric system?

as i understands, you live in united kingdom, and there be use a imperial system...?

[8kids]

Yes the rocker box is 42cm wide on the outer edges.

My original mount had roller blade wheels so the rocker box was wider. If you measure your tube ring width and add the thickness of you bearing material you'll get the dimension you need.

There is no secret, I thought you might prefer the metric system. I actually use feet and inches normally, and quite often a mixture of the two.

[wisedraco]

ok, thanks.

with integer numbers on inches i be more or less ok - 4" = 100mm, 10 - 25 cm and so on, but on small numbers, like a 3/8" and so on i not so comfortable

i think, i build my dob on my early plans, because most of details is already shortened \ sawed to early plan size.

try to use another plywood piece as distancers for right wide on altitude bearings...

[8kids]

Good luck. Post some pictures if you can.

[wisedraco]

i plan to post there a lot of information, including sizings and pics, when i was finish "my" dobsonian mount ( based mostly of your used design with oversized alt bearings and relatively small rockbox).

[wisedraco]

partially finished. a bit too tall, and some another problems, but...

hope, my plans be a bit understandeable....

[wisedraco]

some more assembled 300pds pics.

plywood 18mm, double laminated.

handle is mounted via alluminium bar, handle length is 320 mm - a bit shorter, than distance between tube rings bolt holes ( 360 mm).

[wisedraco]

weights are: OTA with rings and so on - 30.5 kilogramm!  really heavy to operate.

dobsonian mount: 16.1 kg. a bit lighter, but also not as near, as my, for sale, orion optics europa 200f6 ota (9.5 kg) on also homemade plywood dobsonian (8 kg)...

[8kids]

Are you going to add some feet? I f it's too tall the great thing about a homemade base is you can easily chop a bit off. Have you had a first light yet?

They do weigh a bit, but you'll soon develop those arm muscles.

[wisedraco]

there are already a three feet - glued Hockey puck .

sadly, but i cannot it chop a bit - my sawings not make a ideal, spheric and perpendicular edge.

really, yes - if i make that dob again, i choose a side stands not 650mm, but about 550 or even 500mm.

i do not first light - i live in city, apartments. looks like first i must buy a car again

about  muscles - there is not problem with muscles, but with back, due to larginess of OTA. if that ota  weight is packed in compact, like a weight ball, that problem is significally less, but due to ota size, moving there around time from time must be in inconvenient poses, and thats is danger for back...

[8kids]

Just keep your back straight and you shouldn't have too many problems......they are heavy though.