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mattyfatz
Pooh-Bah
Reged: 12/27/06
Posts: 1296
Loc: Boise Idaho
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I would like to replace my stock 1.25inch focuser with a high quality 2" focuser. I have a Vixen RSF130 5" aluminum newtonian optical tube. The current focuser is installed with three screws. It is a cheap platic thing.
For something like a Moonlite or JMI focuser I will need a bigger hole for the focusing tube and different screw holes. How should I meaasure & cut the opening for the focusing tube (hole saw?)? Should I remove the primary and secondary first? What type of screws should I use (anybody make a screw that doesn't reflect light?)?
Thanks for the advice
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**Matty**
Stimulating the economy, one piece of equipment at a time.   
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grendel
sage
Reged: 04/12/09
Posts: 250
Loc: Canterbury, Kent, UK
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I cut new holes in the opposite side of the tube for mine, then I can put the old one back if I need to.(plate over the old hole using the original bolt holes.
Grendel
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Wes James
Post Laureate
Reged: 04/12/06
Posts: 3459
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I don't know how thick the tubing is on your Vixen... to enlarge the hole, I'd probably mark the circle with a circle template and a scribe- then open it up using a Dremel hand grinder- or something similar. I would definitely take the glass out of the tube... no telling what could happen. Too easy to be safe the first time. It could also be done with drills and a file... drill a series of small holes around the circle just inside the template- then clean it up with a half-round file.
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Wes
Atlantic Beach, FL
Some bino’s from Miyauchi 5x32 Binon's up through Garrett 20x110 Signature's,
Some telescopes from a Stellarvue 80mm NHNG up through a couple of 8” reflectors…
And a wonderful 4.25" Delmarva Shiefspiegler!
Some good friends, made here on C/N.
Oh- several cats and a wonderful wife!
Anyone want a cat???? :-O
"When your work speaks for itself- Don't Interrupt" -Gamble Rogers
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DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1989
Loc: Hockessin, De
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I've done this a couple of times using a hole saw that has multiple saw diameters. They are sold for installing locks and door handles. You first partially drill a hole in a piece of wood that is the same size as the hole in the tube. The hole saw as center drill bit which marks the center of the hole. Now you clamp the piece of wood inside the tube and align it so the partial hole in the wood is concentric with the hole in the tube. Now change the hole saw size to the larger diameter hole that you wish to cut. The center pilot hole in the wood will align that hole saw will the new larger hole and make it concentric with the original smaller one.
- Dave
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
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mattyfatz
Pooh-Bah
Reged: 12/27/06
Posts: 1296
Loc: Boise Idaho
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All sound ideas.
Thanks
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**Matty**
Stimulating the economy, one piece of equipment at a time.
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arpruss
scholastic sledgehammer
Reged: 05/23/08
Posts: 858
Loc: Waco, TX
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I strongly recommend taking out the mirrors. It would be very easy to bump the secondary, and you really don't want metal shavings on the primary.
I once enlarged a 0.965" focuser hole to a 1.25" focuser hole for a friend by using a flat file and a round file. It was very loud, took a lot of hard work, and the result was very messy (but it works fine, and that's what matters). Mind, that was steel, not aluminum, and aluminum would be easier. I think if I were doing it again, my first choice would be a grinding stone in a drill (don't have a Dremel).
If I were to use a hole saw, it would have to be a very fine-toothed one. I would worry about a holesaw getting bogged down and imparting very nasty torque to the drill, the drill operator and/or the workpiece. (I once got whacked in the forearm with a piece of wood or maybe particle board torqued by a hole-saw. Ouch.)
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Coulter Odyssey 13.1" split-tube
Coulter Odyssey 8"
Home-made 7.8" F/4 dobsonian travel scope
Home-made 68mm F/5.3 achro (typically used as finder on 13.1")
Skymaster 15x70
BPTs4 8x30
32mm Plossl, 30mm Rini, 27mm Kellner, 13mm Hyperion, 6mm TMB/BO Planetary, Owl 2X Barlow
Palm TX with AstroInfo and RescoViewer
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Igor
super member
Reged: 04/20/06
Posts: 126
Loc: Croatia
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Hello Matty! I too have a 130f5 newtonian although it is Sky Watcher not Vixen like yours but mine have this plastic 1.25" focuser too. Could you tell me which 2" replacement focuser you have and where did you get it? Thanks.
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GSO 250/f5 dob
Skywatcher Explorer 130p @ EQ3
Baader modified 350D and bunch of old M42 lenses
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grendel
sage
Reged: 04/12/09
Posts: 250
Loc: Canterbury, Kent, UK
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I replaced my plastic focuser with an old meade one, but I got a 2" revelation crayford that is sweet for a good price at telescope house in the UK, that one is now on my 12.5" instead of the meade one.
Grendel
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