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Carton 100mm f/13 Refractor Project

johninderby

By johninderby
in DIY Astronomer

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johninderby

johninderby

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Carton 100mm f/13 Refractor Project

I had been looking at the Skylight Telescopes 100mm f/13, which got me interested in building something similar, and when the chance to get hold of a Carton 100mm f13 achromat objective and cell came up recently I decided to go ahead with it and have been gathering the other various bits and pieces together. Finally I have everything I need to go ahead with the project.

Surprisingly the hardest thing to get was the brass tube for the dew shield. Apparently it's not imported in sizes over 4" any more. Ian Poyser was able to put me onto someone that had a piece of 5 1/2" brass tube left, and although it had a lot of dents in it, I was able to get an undamaged length cut out of it sufficient to make to dew shield. Fortunately the 4" 16 swg aluminium tube for the OTA is readily available from just about any metal stockist.

I decided to use a Baader Steeltrack focuser as I've used them before and know how well they work. The finder is a Lumicon 50mm finder, a bit on the heavy side as it's all CNC machined, but very solid and has the very useful feature of using a drawtube for focusing which also means the diagonal can be removed and the drawtube extended allowing straight through viewing. Such a simple solution allowing the finder to be used as an RA or straight though. For the diagonal I'm using an Omegon 90 degree erect prism. The finder bracket is a combination of a Baader shoe, Ascension RDF type base and WO rings. I'm using Astro Professional CNC rings, an ADM dovetail and a TS carry handle.

Richard at Skylight Telescopes is machining the countercell for me at the moment, so that should be ready by next week, and then I'll be able to assemble everything and weather permitting a first light should follow soon afterwards.

Now I've just got to decide on the colour. While I could have the OTA powder coated in traditional white I've always liked the translucent anodised red as used on the WO 80FD Anniversary Edition scope (see photo).

Hmm........ anodised red tube with black fittings and a brass dew shield. :)

John

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JamesM

JamesM

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John, how do you propose to attach the dewshield? Will it be fixed or are you going to show boat this project with a sexy sliding number! I take it your choice of tube size for the scope was mostly determined by the diameter of the focuser to make its attachment as simple as possible? Lastly are you going to insert any baffling?

James

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johninderby

johninderby

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The dew shield will fit onto the countercell that's being machined up now. Similar to the scope in this photo. 4" tube is the correct size for this objective and since 4" tube is so widely used there is a standard focuser flange sized to fit so that works out nicely. The tube lining and baffling will be made from Protostar Flockboard.

John

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johninderby

johninderby

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that will be a superb scope John! I am not into refractors really but can see why some people are. I'd be interested where you get your anodising done as I may need some doing for some dob parts in the future.

There should be some good firms doing anodising in your area. Fortunately this place is about five minutes drive away from where I live.:D

http://www.electroplaters.uk.com/about.htm

John

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johninderby

johninderby

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This company is pretty good, but as with most metal suppliers getting just a short length can be a headache, but worth a try.

http://www.smithmetal.com/locations.htm

Of course there's always eBay. For an f/12 I think you should get awy with a one metre length of the 4" 16 swg ali tube. About £20.00 delivered. I've bought from this seller several times. Great service.

http://www.ebay.co.uk/itm/Aluminium-Round-Tube-4-Diam-x-16SWG-x-1000mm-Long-/150337210747?pt=UK_BOI_Metalworking_Milling_Welding_Metalworking_Supplies_ET&hash=item2300cbc97b

John

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AndyH

AndyH

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Mmmm. Red anodising. That'll look purty.

Merlin - As for alluminium stockist, see if you have a stockholder nearby, although they may have a minimum cash order policy. Mine does, last time I used them.

For small amounts, I've found these guys very helpful. Can get you anything in that's not listed.

aluminium sheet, round bar items in aluminium store on eBay!

Andy.

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philj

philj

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Looking good John. You will enjoy this scope I know. My 102 F15 is still a firm planetary and double favourite, they just have that certain something and yours certainly will with that red tube:)

Looking forward to hearing how your 1st light goes.

Philj

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Leo.A

Leo.A

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The scope looks beautiful!

You have just given me a great idea.

I'm having trouble getting an adaptor machined to fit my William optics crayford focuser to my old 80mm Tasco with, an 80mm tube. The problem is there's only one engineer in town with the machine (other than the government weapons factory and I can't get it done there) and the engineer has been too busy. I could probably rig a new tube with the Vixen cell and focuser quicker.

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johninderby

johninderby

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Almost there now. :) Received this photo from Richard at Skylight Telescopes this aft.

I'll have the countercell in a couple of days and then it'll be time to do the finish assembly and testing before the tube etc. are sent off for anodising. The off-cuts of aluminium OTA tube and brass dew-shield also visible in photo.

John

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johninderby

johninderby

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The project isn't far off being finished now. I was going to have the tube anodised in red but having been let down by a local company who have now decided they can't do it I've decided to paint it myself in translucent candy red. I've ordered the special paint which is due here on Monday.

I've never painted anything in this type of paint before but I'm going to give it a go. It's a bit more involved than just using normal paint. First there's a couple of coats of an acid etch primer to bond into the surface of the aluminium, then a couple more coats of regular primer. Then a few coats of a silver base paint and then 3 to 5 coats of the translucent red candy paint. Finally a couple of coats of a clear 2 pack lacquer and rub it out when it's hardened. Whew !

I'm replacing all the chrome thumbscrews with nice brass ones made by Rob at Epsilon Telescopes. When I'd fitted the brass thumbscrews to the finder and also used them for fastening the brass dew shield in place they made the chrome ones on the focuser look out of place. I waiting to see if Rob can make me up some brass replacements for the silver thumbknobs on the tube rings.

Why is that with so many projects it's the last few things that seem to take forever. :)

John

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MjrTom

MjrTom

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This is really impressive looking, cant wait to see it in all its glory with the red paintwork :)

Just out of interest where did you source your CNC tube rings from? I could do with some for my 102mm refractor (114mm O.D.)

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johninderby

johninderby

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Just out of interest where did you source your CNC tube rings from? I could do with some for my 102mm refractor (114mm O.D.)

I got them from Telescope Service. The closest ones they do to the size you need are these. They're 116mm ID but you'd just need to add a layer of felt to the inside of them to fit your OTA.

http://www.teleskop-express.de/shop/product_info.php/info/p3283_Astro-Professional-CNC-clampshells---Set-OTA-diameter-116mm.html

I bought the 105 ID rings and added some self adhesive felt to the inside as they were a couple of mm too big. WO did rings just the perfect size but at nearly twice the price. :)

John

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