Can anyone help plan for a cell

[radioactive]

I am making a 10" dob using a f4.5 mirror a 2" oval secondary and I have the spider sorted the 2" focuser rack and pinion type also and now I have obtained the tube it12" sono type (cardboard) what I really want to do is try and keep the weight down I want to build a mirror cell but am at a loss how to do this can anyone help me by giving me some sort of plans and how to do it Description Please?

I have sent a picture on of the state of the tube and also shows the spider sat on the top to help give a size feeling to the picture not the bannister rail as well
thanks a lot chaps

[Orion]

Hello Martyn,
There is so much out there on the net about making 10" telescopes.
Besides the web sites there are also books on the subject one of the all time favourites is a book by Richard Berry...
http://wvi.com/~rberry/mybooks/bk-byot.htm
This book describes in detail on how to build a 10" telescope.

Another well known book is The Dobsonian Telescope well worth having a look at...
http://wvi.com/~rberry/mybooks/bk-tdt.htm This book has large and smaller aperture telescopes and much more.

By doing your home work a telescope is not hard to build.;)

[Vermin]

Also there is a very good cell design freeware program called 'PLOP" that will give accurate information on cell support dimensions (i.e. where to hold the mirror to avoid flex etc...) but not how to mechanically construct it.
Link to the program is here:
http://www.davidlewistoronto.com/plop/

[janoskiss]

Plop just tells you where you should place your support points for optimum mirror deformation (within the thin plate approximation). But you don't really need the program, because the results for most common scenarios have been tabulated. Just look it up here:
http://www.atmsite.org/contrib/Holm/Plop_optimized_cells/index.html

Also check out Toshimi Taki's wesite (plop principal author):
http://www.asahi-net.or.jp/~zs3t-tk/

There appears to be as many ways to make a mirror cell as there are amateur telescope builders. Most books on telescope making will have something to say about mirror cell construction. You can find ATM books in most of the bigger libraries, or you can buy them from astro dealers like Bintel.

Good luck with the project! :)

[Roger Davis]

10" huh?
Okay, have you a router? and if you do do you have a radius arm? If not do you have a jigsaw? Most jigsaws have a position on the base plate where a radius arm can be fitted. If not, free hand with the jig saw would do.
Cut out a disc from 20mm ply to fit the inside of your sonotube. Determine the size of three holes to be cut with a holesaw from the disc at 120° (should be around 2"). This will eliminate around 50% of the discs weight. This becomes your backboard. Then cut out a second disc of 10" diameter to be used as the mirror board. You can lighten it in the same way.
Collimation. At 120° intervals fit three "T"-nuts through the wood with the topo of the "T" on the mirror side. Obtain three heavy duty springs to go between the mirror board and the backing board and using three bolts through the mirror board for collimation screws. OR three more "T"nuts on the backing board to provide push against the pull of the mirror board ones.
Support of the Mirror. You can use Plop if you wish, or the formula given in The Amateur Telescope Makers Handbook by Sidgewick to determine where the weight bearing points are to be located on the mirror board. From here there are a couple of methods of attaching the mirror to the mirror board. 1) you can simply place small blobs of silicon at the bearing points, about the size of a pea. Place three 5 cent pieces or washers of equal thickness around the edge. Put your mirror onto the board and let it cure for 24 hours.
OR take 9 brass thumbtacks and fit them at the nine determined weight bearing points and use three "L" shaped clamps at 120° on the mirror to hold it into place. You can drill three small holes through the clamps and squeeze some silicon into the space between the clamp and the mirror edge to buffer the mirror, alow it to cure for 24 hours.
Does that help?

[AstroJunk]

Have a chat to Orion Optics (the UK one!). I got a pile of stuff from them before I escaped to the sunny side. It may not be as fun as making it yourself but it will turn out cheaper in the long run. They were quite happy to sell me a tube and cell a few years back which were much lighter than anything I could do myself.

http://www.orionoptics.co.uk/acatalog/Dobsonians.html

Have a look at their latest dobs - a 150mm f11 no less!

[cristian abarca]

Hi I made a mirror cell similar to Roger's except that I made mine out of pine to keep the weight down and it cracked so I couldn't keep the telescope collimated. I redid the cell and made out of 5mm steel insted and now I have no problem keeping it collimated. using steel is a bit of overkill but you can use any material in between, the method is the same. here are a few pictures ( I have some more), of what i did and if you still want to build one let me know and I can guide you through it. I took these pictures because I want to do a write up on it .

Regards cristian

[Roger Davis]

I thought he wanted to keep it light Chris?
Even John Dobson used plywood in his mirror cells, albeit with loop pile carpet, the ultimate in multipoint flotation systems!

[cristian abarca]

I know Roger, I tend to get a bit carried away sometimes.

Regards Cristian