Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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A fast SS 127mm refractor assembly
#2731858 - 11/02/08 08:11 PM Attachment (517 downloads)
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The reason i call this an assembly and not an ATM is because i am not polishing my own lens, making a lens cell, or fabricating a focuser. I am just assembling parts that i have ordered, i will post this so i can get some input and ideas from others to help me, and in return maybe i can help another refractor build in the makings.
I purchased a 127mm f/5.5 from Surplus Shed. It is air-spaced achromatic optics, fully coated, 127mm diameter with a focal length of 700mm. The entire lens housing is 130mm long and made of thermo-plastic. The coating are nice and it is a big son of a gun, i am sure from the price it will show its share of false color and have so softness on the edge but for the price it should be a fun scope, i am not expecting much. It will be used at low power as a Milky Way Buster and Satellite finder so color won't bother me. I purchased a 5" OD aluminum tube from a local supply store it is very nice and has good roundness. The focuser and adaptor plate were a scope stuff buy, the adaptor is the Adaptor Ring for Crayford Refractor Focuser on 5.125" OD Tubes. And since my OD of my tube is 5" and the adaptor is for an 5.125" i know i will have to do some magic to make it fit(later).
I figured out the size of the tube by making a "scope on a stick" and focused on some stars. I mounted the lens/cell on a board and mounted the focuser and adaptor behind it on an adjustable sliding jig. I used three eyepieces a 30mm, 12.5mm, and a 5mm along with a diagonal, starting out in the mid range of the focuser with the 12.5mm first. Then making sure i found the optimum position of the focuser using all the eyepieces, i marked its position on the board. That will be a rough tube length.(sorry no pictures of the scope on a stick due to the juggling act of making sure nothing came crashing to the ground).
Once i determined my tube length i cut the tube. Cutting aluminum tubing can be tricky and dangerous(aluminum tubing can fly around if the saw teeth grab instead of cut) so i borrowed my brother's metal chop saw. It did a great job, here is a picture of the metal chop saw and a different OTA i had cut.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2731873 - 11/02/08 08:16 PM Attachment (346 downloads)
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The cut isn't the most accurate cut but it is a safe cut(no flying OTA's). To square it up i wrapped a sheet of paper around the tube tightly so that the top edges of the paper met ensuring a straight edge. This let me see which areas were high and needed to be filed down. I sprayed black spray paint(leaving the paper ledger in place) to blacken and show the high spots when the paper was removed.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2731877 - 11/02/08 08:18 PM Attachment (289 downloads)
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now all that i had to do was file the blacken high areas and i had a square even tube.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2731884 - 11/02/08 08:24 PM Attachment (331 downloads)
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Now some easier stuff like mounting the lens cell. First i removed all the glass as so not to have any mishaps. I want to get it as square as possible but i am going to have to rely on the manufactures accuracy on this one due to the fact that the tube slides fairly deep into the cell so the is no play to collimate.
I slid the cell in place and marked the three holes,removed the cell, and drilled the holes using a drill press. I made a simple jig to get the holes straight.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2731892 - 11/02/08 08:27 PM Attachment (289 downloads)
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Since my tube is fairly thick i tapped the holes so i wouldn't have any nuts or washers inside the tube(less light scatter). Excuse my dried out dirty hands, earlier this morning i was using some strong degreasing solvent on my lawnmower engine, i was getting it prep'd to winterize.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2731906 - 11/02/08 08:36 PM Attachment (286 downloads)
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Then i worked on the other end of the tube. First i removed the lens cell for ease of work. And i had to conquer the problem of the adaptor being 5.125" inside diameter and the tube being 5" outside diameter. I had some scrap aluminum of the perfect thickness laying around so i cut it into a 0.75" strip and bent it around the tube by hand to give it some memory.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2731907 - 11/02/08 08:37 PM Attachment (299 downloads)
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I cut it to size and filed all the burrs off. Then i fit it into the adaptor plate. The adaptor plate is black and the aluminum filler strip is obviously silver. I marked each hole so when i disassemble it later i know exactly which way the strip,adaptor, and tube holes align.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2731967 - 11/02/08 09:05 PM
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It is late so i am calling it quits. I still have to mount the adaptor and collimate the focuser. I need to find out from some of you ATM'rs how to do a "ray trace" for knife edge baffles???? Mount finder scope, paint inside and out, make some rings(i have a good idea for those), and also a good idea for a dewshield.
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mattyfatz
Carpal Tunnel
Reged: 12/27/06
Loc: Boise Idaho
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2732283 - 11/03/08 01:00 AM
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Looks good so far. I'm glad you had the "perfect piece" of scrap aluminum in your shop. I never do. As for the "ray Trace" its kind of hard to explain without pictures. I can send you some pages from SAM BROWNS ALL ABOUT TELESCOPES that describe it pretty well. PM me your email and fax if you can.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: mattyfatz]
#2733389 - 11/03/08 05:57 PM
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Thanks Matty but i have been searching through the archives and i think i may have it, with the exception of one hang up. If you look HERE How do i select a desired size for the illuminated field and draw it at the focal plane? I am keeping in mind i will probably be mostly using a 30mm Tele Vue plossl, or a 26mm Meade smooth sided Super Plossl.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2733684 - 11/03/08 09:00 PM Attachment (292 downloads)
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Since i was at a bit of a road block with the ray tracing, i decided to paint some shiny surfaces with Ultra Black Krylon paint. These are surfaces that may reflect and bounce light around in the tube, some may think it is overkill but it can't hurt being safe. The red arrows show the surfaces painted, masking off these parts can be a bit of a pain, i hope it pays off?
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2733688 - 11/03/08 09:02 PM Attachment (243 downloads)
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I also scuffed and painted the retaining ring for the cell it had a sheen to it that i didn't like(it will now match the inside of the future dewshield). It still needs a second spray.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2733703 - 11/03/08 09:11 PM Attachment (280 downloads)
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The lens cell had that ugly brown Synta color, so i sanded it down and primed it, it will be a satin black to match the rear focuser transom.
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beanz4
member
Reged: 08/23/08
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2747793 - 11/12/08 09:57 AM
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More updates please, really looking forward to see what else you have done with your scope.
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reodds
member
Reged: 05/04/06
Loc: Merrick, New York
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Re: A fast SS 127mm refractor assembly
[Re: beanz4]
#2747859 - 11/12/08 10:52 AM
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Brian, perhaps you want to wait to complete your scope, and make the tube out of carbon fiber!
Or make this one, and use it as a template for a cf tube, whic would be a major weight saver over metal.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: reodds]
#2748533 - 11/12/08 06:05 PM
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Sorry Beanz4 i have been directing my attention to another build HERE. The baffles on the 127mm will be similar but i will need more. I need better weather to do a test run with a 32mm Meade SWA and then i can do a ray trace with those measurements. And as you can see my sky clock is white so i will just have to wait. 
Roger i was thinking of a cf tube for this project but getting a mold tube the exact size for the lens cell and focuser transom is tough. I want to see how yours comes out then i will try it with a Newt, i have a few mirrors laying around in wait. I do have some cf sleeving that i bought for the dewshield and heat shrink to match, but that was going to be later in the post, plus i want to do a cf laminate for the rings and maybe incorperate the finder into the cf mix.
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oneslowz28
Witty Title
Reged: 11/14/06
Loc: Aiken , Sc
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2748579 - 11/12/08 06:28 PM
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This is coming along great. Keep up the good work.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: oneslowz28]
#2757090 - 11/17/08 09:20 PM Attachment (269 downloads)
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Quote:
This is coming along great. Keep up the good work.
I wish that were so. I was drawing a ray trace tonight to plan my placement of baffles and i made an alarming discovery. The drawtube is pinching the optical light path! I picked my desired field size using a 2 "32mm Meade SWA eyepiece at focus. And i set the drawtube distance at focus using a diagonal(diagonal is not drawn in)and the optical path in red is pinched dramatically by the focuser drawtube. At first i thought i could shorten the drawtube but with this GSO model it can't be shortened(internal roller bearings ride on drawtube to stabilize). I have a longer section of aluminum tube for another OTA but it wouldn't help because the focuser drawtube would still be at the same position. My only hope is using a 2.7" focuser, i do have one but it will be a pain to mount. ANY IDEAS? Are my drawings correct? I am new to this so any help would be appreciated, please excuse my drawings i am not a draftsman.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2757092 - 11/17/08 09:22 PM Attachment (245 downloads)
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A close up at drawtube. red is desired optical path for a 32mm 2" and green is pinched path.
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Happy-Idiot
Stuck with it
Reged: 04/06/06
Loc: 3rd Rock
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Re: A fast SS 127mm refractor assembly
[Re: Happy-Idiot]
#2757095 - 11/17/08 09:24 PM Attachment (243 downloads)
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You can see with the green how little of the lens i am using. A glorified 80mm! 
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