DB Astro - Club Reflector - Refurb Pics

Discuss practical questions about using equipment,
finding celestial objects etc.
justanotherpete
Posts: 171
Joined: 07 Sep 2007, 20:24
Location: Rosyth

Re: DB Astro - Club Reflector - Refurb Pics

Postby justanotherpete » 26 Jun 2014, 18:09

And a quick trial fit of the adjusted spider in the newly matt blacked tube...

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justanotherpete
Posts: 171
Joined: 07 Sep 2007, 20:24
Location: Rosyth

Re: DB Astro - Club Reflector - Refurb Pics

Postby justanotherpete » 26 Jun 2014, 18:31

A very reasonable 25mm eyepiece (also Astro Buy Sell) for use with the scope when it's finished...

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justanotherpete
Posts: 171
Joined: 07 Sep 2007, 20:24
Location: Rosyth

Re: DB Astro - Club Reflector - Refurb Pics

Postby justanotherpete » 26 Jun 2014, 18:42

By the way if anyone has any telescope parts that might help complete this project and that they want to donate please respond below or contact our chairman, Paul.
Currently we are particularly looking for either plywood or MDF to build a dobsonian base or an unwanted telescope tripod i.e. a sectional aluminium such as was supplied with the AZ2, EQ3, EQ5, CG5 mounts that could be used to build an Alt-Az mount.

Thanks
Pete

Opel star
Posts: 104
Joined: 29 Feb 2012, 00:25
Location: Rosyth

Re: DB Astro - Club Reflector - Refurb Pics

Postby Opel star » 29 Jun 2014, 23:57

Good old astrobuysell :D looking good and I like your telescope workshop.Looks very professional.The only plywood I have is 9mm so it would have to be screwed and glued together but I have lots of it.

justanotherpete
Posts: 171
Joined: 07 Sep 2007, 20:24
Location: Rosyth

Re: DB Astro - Club Reflector - Refurb Pics

Postby justanotherpete » 30 Jun 2014, 19:18

Thanks Chris, I'll get something drawn up, hopefully during the week, then we can go from there with building the base.
Pete

justanotherpete
Posts: 171
Joined: 07 Sep 2007, 20:24
Location: Rosyth

Re: DB Astro - Club Reflector - Refurb Pics

Postby justanotherpete » 30 Jun 2014, 20:07

Once you have all the bits you intend to use, draw everything out to scale, the drawing below is half scale.
Don't cut, drill, file or sand, metal, plastic, wood, fingers (joking) until you've done that.
Always keep a sketch pad handy, you never know when a good idea is going to come along.
Draw your new ideas out, that way you can see if things will work and what has to change.
Don't be dismayed or surprised if things have to change during the build.

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This shows the light cone, the diameter of the mirror on the left (150mm in this case) forms the open end of the triangle, the apex (focal point) is positioned using the focal length we measured.
The minor diameter of our secondary mirror is 36mm, you can measure the width of the cone and find out where it is 36mm across.
Everything between the eyepiece and the point where the surface of the secondary mirror crosses the centre-line of the tube has to be accounted for, i.e...
The height of the focuser at mid travel
The thickness of any mounting plates between the focuser and the tube
The thickness of the tube,
The distance from the inside of the tube to it's centre-line.
Add all of these dimensions up, be careful when converting them to the drawing scale, the total of all these dimensions is measured back down the tube centre-line and will show you the point where surface of the secondary mirror should cross the tube centreline.
Ideally this should be close to the line denoting the 36mm width of the cone, our position is slightly higher in the tube where the light cone is about 34mm across which isn't a problem. Larger differences might require some adjustment or compromise.
Last edited by justanotherpete on 30 Jun 2014, 20:28, edited 1 time in total.

justanotherpete
Posts: 171
Joined: 07 Sep 2007, 20:24
Location: Rosyth

Re: DB Astro - Club Reflector - Refurb Pics

Postby justanotherpete » 30 Jun 2014, 20:22

For things like the focuser and the central spindle of the spider both of which have travel i.e. the focuser moves in or out, the spindle can be moved up or down the tube, always position these so that they are in the mid position, that way you will have adjustment in either direction.

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Always check your dimensions - spot the deliberate error :oops:

The dimension that should be 95mm is measured back up the tube from the point where the surface of the secondary mirror, it shows the position where the spider should be mounted in the tube.

PS: Having spotted that error I went back to check and correct the main drawing.

justanotherpete
Posts: 171
Joined: 07 Sep 2007, 20:24
Location: Rosyth

Re: DB Astro - Club Reflector - Refurb Pics

Postby justanotherpete » 02 Jul 2014, 19:31

The mounting plates for the new focuser...

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New focuser attached for a trial fit...

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Nearly always a bit of fitting or adjustment is needed, in this case with a Dremel to make sure the securing bolts have space to clear the tube wall...

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justanotherpete
Posts: 171
Joined: 07 Sep 2007, 20:24
Location: Rosyth

Re: DB Astro - Club Reflector - Refurb Pics

Postby justanotherpete » 04 Jul 2014, 00:00

OK so this might look just like two bits of 12mm ply glued together but it is in fact a dummy mirror...

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This is the mirror cell with our dummy mirror fitted...

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And now fitted in the telescope tube...

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justanotherpete
Posts: 171
Joined: 07 Sep 2007, 20:24
Location: Rosyth

Re: DB Astro - Club Reflector - Refurb Pics

Postby justanotherpete » 04 Jul 2014, 00:19

The dummy mirror helps position the spider.

First position the mirror cell so that it is at the midpoint of it's adjustment screws. Measure, on your scale drawing, the distance from the mirror surface to the line denoting the mid point of the spider, in our case 976mm. Find a piece of tube the same diameter as the secondary mirror spindle, make sure it is reasonably straight and long enough to accommodate our measured distance (B&Q sell 1m lengths). Insert the tube into the spider making the distance from one end of the tube to the mid point of the spider the same as we just measured; 976mm...

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Push a screw in to the central hole in the dummy mirror...

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and put the tube over the screw head...

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The axis of the spider is now pointing at the centre of the mirror (located by the tube and the screw head) and the spider is positioned the correct distance (976mm) from where the mirror will be. Now we can mark and drill the securing holes for the spider.


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