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Equipment Discussions >> ATM, Optics and DIY Forum

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neo
Carpal Tunnel
*****

Reged: 02/12/08

Loc: Iasi, Romania
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4659200 - 06/26/11 06:59 AM

Beautiful work as always
I like the filter wheel concept, nicely done


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4659201 - 06/26/11 06:59 AM Attachment (23 downloads)

I countersunk the protruding small diamater cogwheel into the Lexan disk at the "front" side of the wheel by means of a 12mm spade bit, with the drill mounted on my portable drill stand.

Here's a view at the side of the wheel that's facing the focuser:


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4659203 - 06/26/11 07:00 AM Attachment (19 downloads)

Here's a view from the side:

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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4659209 - 06/26/11 07:03 AM Attachment (17 downloads)

I placed the filter wheel lid into the recess I routed from the back of the focuser board. Initially I thought about using it in the other direction, but now I realize this way makes more sense.

I still need to find a better way to support the filter wheel at the end facing the diagonal. Probably a thin metal strip mounted along the axis of the secondary cage (vertical in this photo) with an attached bolt or so in the middle supporting the other end of the axis, I'm not sure yet.

Edited by Olivier Biot (06/26/11 07:05 AM)


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4659212 - 06/26/11 07:09 AM Attachment (25 downloads)

I also decided to replace the M3 setscrews in the focuser baseplate with easier to manipulate long brass screws. I'll add a custom brass knob to them next time I'll be in our ATM shop. The knobs are bookshelf holders, I'll have to cut off the screw and drill & tap 2 M3 holes, one for the brass M3 screw (I'll probably have to cut off the head) and one for a setscrew (so the brass screw stays in place).

In this photo you'll see 4 shiny brass screws (without custom knobs as heads), and how the business end looks like, with the focuser currently removed.


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4659224 - 06/26/11 07:23 AM Attachment (22 downloads)

That was the filter wheel.

Now let's see what happened with the ground board

The ground board consists of a welded 3-pronged star made from 20mm x 40mm rectangular steel tube. Circular disks have been welded in the middle as reinforcement.

The rotational axis will be a M6 bolt. To avoid protruding parts I'll use a countersunk bolt pointing up and a blind rivet nut connecting the rocker to the welded "ground board" frame. The rotational axis will run in a M6 threaded insert from which I'll drill out the threads once mounted in the bottom of the rocker.

The friction surfaces are one big PTFE disk and 3 smaller disks made from PTFE or some other more sturdy plastic with similar properties. The central PTFE disk lies on a Formica laminate disk acting as a shim, and an EPDM disk (this is very strong yet very flexible black rubber about 1mm thick used in roofing and natural swimming ponds). The EPDM will allow for some play when tightening the central axis.

The 3 smaller friction disks are mounted on a steel washer and on an EPDM washer.

The 3 feet of the welded frame are 5mm thick aluminum disks, 30mm diameter. Between the aluminum feet and the frame I placed a rubber seal (sanitary equipment, 30mm diameter, 2mm thick, 22mm inner diameter). I attached an EPDM washer to the bottom of each aluminum foot with two-sided high tack tape.

I attached the 3 feet and the 3 friction pads with stainless steel M4 countersunk bolts that are joined via a tall hex nut.

Attached photo shows the assembly of the 3 feet:


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4659226 - 06/26/11 07:25 AM Attachment (24 downloads)

You can see the different "layers" in this design. The stack of washers and spacers should ensure that most of the weight is transferred to the central point, and that the rocker still makes contact with all 3 friction pads.

Here's another view, more from the bottom.


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4659229 - 06/26/11 07:26 AM Attachment (18 downloads)

Here's the "ground board" frame, top view. The countersunk bolt you see is only there to keep the central support hardware in place.

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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4659230 - 06/26/11 07:27 AM Attachment (21 downloads)

And viewed from the bottom:

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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4659238 - 06/26/11 07:33 AM Attachment (20 downloads)

Here's a nifty trick if you need to create rubber washers from thin sheets of rubber if you don't have the proper dedicated (expensive) tools for doing it.

First, use a permanent marker (e.g., a CD pen), and draw the contour of the washer. Cut out the rubber washer's outer contour with sharp scissors.

Next, take a metal washer with a large diameter and a central hole a tad larger than the hole you need in your rubber washer.

Mount a drill bit of the right size (sharp wood bits are excellent, I'd stay away from spade bits) on your power drill, place and align the steel washer on the rubber, the rubber on scrap wood, secure the washer and start drilling in the central hole of the steel washer.

Most holes came out very cleanly.


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: neo]
      #4659241 - 06/26/11 07:36 AM

Quote:

Beautiful work as always
I like the filter wheel concept, nicely done




Thanks Alex

I hope others will find inspiration in what I learned and did. I also learned a lot reading so it's my turn of giving

The filter wheel is not entirely done yet, there's some friction where I don't want it, and I need to find a working solution for supporting the filter wheel at the end facing the diagonal.


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4659332 - 06/26/11 09:11 AM Attachment (21 downloads)

I had still some time now so I prepared the brass knobs for attaching to the 4 brass focuser screws.

First I mounted the brass bookshelf holders in my power drill, and then I took a metal saw to cut through the brass as follows:


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4659334 - 06/26/11 09:12 AM Attachment (17 downloads)

You need to securely hold everything. The drill is battery operated, runs at various speeds and stops immediately when I release the power button.

Here I'm almost through the first cut:


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4659336 - 06/26/11 09:13 AM Attachment (17 downloads)

Ten minutes later all 4 were done:

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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4664398 - 06/29/11 07:14 AM Attachment (22 downloads)

Just before yesterday's evening's thunderstorm outbreak I decided to benefit from the warm weather to have the welded base spray painted with black Hammerite paint (it's a spray canister, the same I used for spray painting the welded mirror cell frame).

First I sanded the frame, then I washed the sanded frame with hot water (so it would evaporate more quickly), then I wiped the frame with acetone.

To enable coating both sides of the frame at the same time I added "legs" with long screws mounted in nylon plugs in the 3 drilled holes at the extremities of the welded frame. This way I could apply one coat, wait 15 minutes, turn over the frame and apply the next coat. In total I did about 10 spray sessions or so, meaning that each side received at least 5 thin coats of spray-on paint.

Actually the thunderstorm interrupted the process, half of the coats were sprayed two hours later. This is okay, since you should wait no more than 8 hours between coats or you have to wait 2 weeks (!).

I should have used a tiny little less paint on one coat, but overall the result is great. Now the paint is curing. Whenever the sun shines I set the frame outside in direct sunlight so the curing process accelerates.

Here's a shot of the frame in the sun:


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nictorax
member


Reged: 05/11/10

Loc: a hop skip and a jump away
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4664416 - 06/29/11 07:47 AM

Hi Olivier,

First off, that's a beautifully constructed scope you're building!

Do you know if the distance between the filter and the first eyepiece element has any consequences on the final image?

regards,
kevin


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: nictorax]
      #4664491 - 06/29/11 08:40 AM

Quote:

Hi Olivier,

First off, that's a beautifully constructed scope you're building!

Do you know if the distance between the filter and the first eyepiece element has any consequences on the final image?

regards,
kevin




Thanks Kevin!

As far as I know the only thing that could happen if the eyepiece is too far from the filter is vignetting. Indeed, the clear opening of a filter is 48mm. With "slow" optics (f/8 and longer) this is not really a big deal, but with faster optics (f/5 and shorter) the light cone originating from the primary converges (or diverges as seen from the eyepiece) more significantly (blunter angle), so you'll be vignetting faster.

That's the reason why I mount my filter wheel as close as possible to the eyepiece. In my case I even foresee the use of a ParaCorr. The clearance between the bottom of the ParaCorr and the filter wheel is only a couple mm.

Edited by Olivier Biot (06/29/11 08:41 AM)


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4665309 - 06/29/11 04:54 PM Attachment (16 downloads)

Tonight I decided to build an eyepiece holder for the scope, as I did for the AT Voyager the same evening.

The eyepiece holder will have room for 4 2-inch eyepieces and 5 1.25-inch eyepieces. The small barrel eyepieces will be in front of the large barrel eyepieces.

I already drilled the 2" holes with my hole saw and using the hole drilling template trick, now I need to drill the remaining 1.25" holes. I know there's a 1.25" hole saw at our ATM place so those holes will be done Friday (hopefully). As usual I'll apply marine varnish.


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4670629 - 07/02/11 07:37 PM Attachment (17 downloads)

Last Friday night was very productive. First I drilled the 1.25" holes in the eyepiece board by means of my drilling template trick (yet again )

The first holes were done on a drill press, the remainder with a handheld cordless power drill. Eventually I should have done all holes with a handheld power drill.


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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4670635 - 07/02/11 07:41 PM Attachment (14 downloads)

After drilling the many 1.25" holes I worked on the filter wheel: I filed the head of a protruding screw (the one that will act as the axis of the filter wheel knob) so it wouldn't anymore bump into the filters when rotating.

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