Cut telescope in half

[steve000]

So im sitting here thinking how am I going to transport my 12" 1.5m long reflector in my little 4 door lancer.....

I could cut it!

If I were to cut it in half then make 2 rings out of MDF to go around the outside screwed to the tube from the inside and use some bolts to reconnect the halves would it work?

My concern is the distance from the primary to the secondary.

See my dodgy MSpaint drawing for reference.
Red is the MDF ring. anywhere from 16mm to 32mm.
black is tube
white is bolts. probab M6 with wingnuts.

[asimov]

Certainly would work ok Steve. Naturally you'd have to collimate after joining again, but I'm sure that's a given. Go for it if you have the skills/Equipment!

[steve000]

Would there be enough adjustment in the secondary to counter 1-2mm shorter tube? (cut loss)

[alistairsam]

you'd have to adjust the primary, not the secondary to adjust for difference in length. if you adjust the secondary, it'll no longer be in line with your focuser unless you can move your focuser as well.
easier to adjust the primary.

[gbeal]

A simple solution I reckon. Cut it neatly, and (assuming it is a metal tube) get a ring attached to the inside of one of the sections. This then allows the other section to "slip over and not" this ring. Then use those "over-centre" latches, Bunnings here have them. About 4 around the tube would be sufficient.
And no, the "thickness" of the cut should not affect the focus etc at all. Make sure the cut is neat, straight, and tidy though.
Gary

[Draco]

I would love to know how this pans out since I am looking at getting a 12" next year. If it is cheaper to get a normal one and cut it in half than getting a truss one.. then hell ya ;)

[leon]

They only way you will know is to have a go, what is there to lose, and maybe you have started something.

It will work if you do a neat and square job.

Leon

[multiweb]

Most importantly remember the orientation of the tube. Worth marking before cutting..

[Wavytone]

Steve,

MDF is cheap but it's both heavy and nowhere strong enough for the rings, and if you put screws into the side grain, it will split and disintegrate. One way to deal with that might be to soak it in a watery glue that can soak in, and wait for it to dry, or better, choose marine plywood.

But... if you're going to make two rings strong enough for this to work well, you may as well make a truss.

Cut off the top end, fairly short and keep that. Cut off the bottom end, also quite short. The piece of tube in the middle (ie most of it) will be discarded (reducing weight too).

Devise some short poles or a truss to connect the top end to the bottom, there are a number of ways to do this. The simplest I have seen so far is a 2-pole truss which Mental (Alex) used for his 13" dob. In this:

- the two poles are aluminium tubes, fairly large at 2" outer diameter, which makes them quite stiff enough for this.

- the lower tube with the primary mirror has 2 wooden rings around it, at top and bottom. The top ring has 2 holes on either side and the two tubes slide through these. The bottom ring has two wooden plugs, and the poles are a neat firm fit over the plugs, which keep the tube and the poles aligned precisely. The plugs were the blanks from using a hole-saw to cut the holes for the tubes in the top ring (d'uh, stroke of genius).

The upper ring has small saw-cuts on either side of the holes, with a pair of coach bolts through the ring; tightening a pair of wing-nuts so you can clamp the poles by tightening the wing nuts. Its a simple, easy to make, secure and foolproof way to clamp the poles.

- the top end has just 1 ring and slides over the poles and clamps the same way. If you feel its too wobbly add a second ring as per the bottom tube assembly.

- the altitude bearings are plywood disks with laminex around the perimeter, and slide on the poles, so you can adjust the balance of the scope.

The result is quite elegant and very portable, his 13" would fit in my Honda CR-Z - and that is a VERY small car. The only thing to note is that you'll need to cover the primary mirror - or remove it and store in a box - to protect it from dust and grime.

Lastly, your present OTA is metal - no doubt heavy and its going to be a messy noisy PITA to cut this. if you are tempted to make the two piece above with the 2 poles, I'd suggest instead there is an even better alternative: leave your heavy metal tube alone and instead buy some 1.5 or 2mm 3-ply - this stuff rolls into a 14" tube quite neatly and if you have cut some rings, use these to hold it in place at exactly the right size to fit the rings (!) - then you can forget about the heavy metal completely.

[anj026]

This link shows a home made 10" f8 dob with a two piece tube.

http://www.rfroyce.com/amateur_telescopes_modpics_thurman_ t.htm

And here is a link showing a commercial two piece tube dob.

http://www.optcorp.com/discovery-12-5inch-f-5-premium-dhq-split-tube-dobsonian-1255s.html

[sheeny]

+1 for Gary's suggestion.

Make sure you mark the 2 halves so they always go back together the same way (should be easy if it has a folded longitudinal seam;)).

I wouldn't recommend MDF for the job. It's not appropriate for the dewy conditions you will encounter.

Do a search for pictures of Bird's newt as well, if you want inspiration. They are in IIS somewhere. He has a 2 or 3 piece tube depending on which mirror he wants to use in it.;)... and takes excellent images with it!

Al.

[steve000]

Hi all,

Hopefully someone can get something out of this but I have scrapped this project. I must thank everyone for their replies, great info.

Why have i scrapped it? After many years of thinking and drafts I have finally created some rings that allow the telescope to rotate, Wilcox rings if you may. Cutting the scope will get in the way.


These rings allow the tube to rotate on bearings for a near frictionless spin, not so much of a problem on small newtonions but on larger ones when you try and rotate it for a better viewing angle you will often also move the head slightly ruining any alignment on a goto (not polar but goto alignment) as most don't have encoders like the EQ6.

I have tried all combinations of Wincox rings and loosening the rings, teflon, other felts etc.. none have been satisfactory.

Manufacturing requires basic wood tools, ebay, bunnings and other local easy to get to suppliers. Im cheap so everything is made to be as cheap as possible leaving the maker to increase quality when wanted.

I'll start a new thread and put the link here. Dont worry I will do a instructable.

[Satchmo]

Birds tube which comes apart was made by Gary Mitchell in Sydney- he has shipped tubes that break into pieces for car transport , all over the country. They are made in aluminium and are very reasonably priced and very solid. i have seen even large reflectors like 18" F5.5 using these tubes. Gary does not have a web page but if anyone would like his business phone contact me PM.

He is a sheet metal worker by trade. He also makes very nice mirror cells for Truss dobsinains and he can make cells to fit in the round tubes too. Very talented guy...!

[steve000]

http://www.iceinspace.com.au/forum/showthread.php?t=106746