grendel
sage
Reged: 04/12/09
Posts: 243
Loc: Canterbury, Kent, UK
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Well I have ordered a Carton 60mm x1000mm f/l lens, and am going to make up the refractor in some cardboard tubing from where I work, this has got me to thinking - I have 2 sizes of tube available, 85mm OD -76mm ID tube and 58mmOD - 50mm ID tube, this has me thinking 2" crayford focuser, with a very long draw tube, so I can space the bearings out further for better precision, over the next few weeks I will be looking at this and seeing how practical a solution I can come up with for this cardboard crayford, on a refractor.
Grendel
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 371
Loc: UK
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WOW! I am interested on how you make out on that one. Let's have details.
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grendel
sage
Reged: 04/12/09
Posts: 243
Loc: Canterbury, Kent, UK
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I am looking at using some sliding mirror wheels as the bearings, they will be mounted to the outer tube and spaced quite well apart to allow for good alignment of the drawtube, I have calculated that a 2" ID drawtube can be 750mm long before it even starts getting into the light path.
Basically the outer part of the focuser will be the main tube of the scope and the f16.7 focal ratio should give great views of the moon and planets, I have had good reports of the performance of scopes with these carton objectives. once I recieve the objective I can start building at the moment I am working on it in CAD.
Grendel
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neo
professor emeritus
Reged: 02/12/08
Posts: 614
Loc: Iasi, Romania
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Hi Grendel,
Sounds very interesting...I've never heard making a cardbord focuser before  . One concern would be if the draw tube is strong enough when pressure is applied. I was thinking to treat it with some epoxy just to be sure.
Good luck with your project and ...lots of pictures 
Alex
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Russian 15x50 binos
Home made 8" f/5 Newton on eq mount
Home made 70mm f/6 (Rodenstock Rotelar lens) Apo refractor
www.astronomy.ro
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 371
Loc: UK
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Try using 2 inch diameter, or thereabouts plastic tubing for rain gutter down pipes, available at your friendly hardware or DIY store.
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grendel
sage
Reged: 04/12/09
Posts: 243
Loc: Canterbury, Kent, UK
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Well thats something I will find out I guess, I already have the cardboard tube (its a waste product from the drawing office I run) and in my experience its a lot stiffer than the equivalent sized pvc tube. I was planning to use car spray paint as I have in the past, a couple of good coats of primer and a few white topcoats seals the tube from water, and some matt black down the inside seals that and raises some fluff on the side walls.
I have tested my 2" to 1 1/4" adaptor and its a good tight fit in the end of the 2" tube, so that sorts out the eyepiece end of the drawtube. The plans are coming on apace , I have the wheels in place and the bearing pivot axis is just outside the tube which makes things easier to construct mounting blocks to fit on the outside of the tube
Edited by grendel (10/04/09 04:47 AM)
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grendel
sage
Reged: 04/12/09
Posts: 243
Loc: Canterbury, Kent, UK
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another viewpoint, I still have to cut the holes in the tube for the wheels to run. 3D drawing and rendering is a real brain twister as you have to be able to think three dimensionally and thenyou have to remember the right tools to create the effect you want.
Grendel
Edited by grendel (10/04/09 05:06 AM)
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grendel
sage
Reged: 04/12/09
Posts: 243
Loc: Canterbury, Kent, UK
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virtual progress:-
Grendel
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grendel
sage
Reged: 04/12/09
Posts: 243
Loc: Canterbury, Kent, UK
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the focuser will have 2 sections one fixed, and the other sprung loaded to push the axle against the drawtube.
Grendel
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timo4352
super member
Reged: 04/16/07
Posts: 160
Loc: Northeast Ohio
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I love the ingenuity. And I love building stuff too - especially with free materials.
Have you thought about some type of seal at the focuser end?
Tim
--------------------
Orion 3.6CA Reflector
and 2 homebrew scopes --
8" Hubble Bubble ballscope
8" F/8 CHief - nearing completion 
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grendel
sage
Reged: 04/12/09
Posts: 243
Loc: Canterbury, Kent, UK
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Not yet, maybe some bit of plumbing fitting?
I'll have a dig round my scrap box, maybe just a cut out wooden donut to fit in the middle.
Grendel
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 371
Loc: UK
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Very ingenious, I look forward to seeing the finished product.
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grendel
sage
Reged: 04/12/09
Posts: 243
Loc: Canterbury, Kent, UK
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well mark one focusing block was made today, it highlighted 2 problems,
1. I need an 85mm hole saw, not an 83mm one
and
2. I need to go get my pillar drill from my mother in laws (or go there to use it) to drill the holes for the long tension adjusting screws (the holes are a fraction off alignment as I just hand drilled by eye on this mark one version.
This version is binding a bit and too tight on the tube, but thats not a problem really as I was only trying it as concept at this stage.
Grendel
Edited by grendel (10/08/09 06:01 PM)
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 371
Loc: UK
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Looks good.
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John Carruthers
Skiprat
Reged: 02/02/07
Posts: 2270
Loc: Kent, UK
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Hi Pete, may be easier to mount the wheels on a 90 deg V ?
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Jc
ATM 10" F6.1, 1/25th wave spec (max wavefront error +/- 1/12.6 in zone 4 of 6, sodium light )
6" F7 spec
127mm F9.4 Refractor
10 x 50 bin
ETX80 (finder)
Canon 20D
PST
DSI 1
and a curious mind
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grendel
sage
Reged: 04/12/09
Posts: 243
Loc: Canterbury, Kent, UK
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John C
I may use a similar segment of a block like I have for the focuser.
Grendel
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