263 replies to this topic

[Oberon]

The easiest cheapest solution is to start with a larger diameter bearing.

If I decide to tool up for and use CF in my binoscope I'll probably rebuild my UTA and secondary support in CF as well. Between that and substituting the Heim joints I'm reasonably confident I can be rid of all my counterweights.

On that note, I've often wondered what sort of market there is for a well designed stiff lightweight Carbon Fiber UTA that can be used with a variety of spider configurations, what sort of price people would be willing to pay.

[ctcables]

I know this work of art should be light weight, thought you might like this post.  http://www.cloudynig...ch-of-aperture/

[Oberon]

Thank you for that tip, this is interesting. If I slip Merope in this list twice, as she is right now and also as "Merope Lite" we'll see how she stacks up. Merope Lite assumes I can lose 2kg on UTA, all balance weights on LTA (11kg) and shed 5kG from the base and Azimuth (to go from 17kg to 12kg which should be easy). Losing 2kg from the UTA will be hardest, but is required to lose all counterweights; would require use of CF and pretty well everything else we discussed. More realistically you could end up anywhere in between these two figures depending how extreme you tried.

 

Scope--------------------Aperture---Weight---LB/Aperture^2
ctcables 14.5------------14.5-------32-------0.152
ctcables 20--------------20---------69-------0.173
mconnelley 20------------20---------80-------0.200
Hubble Optics UL18-------18---------72-------0.222
Hubble Optics UL16-------16---------60-------0.234
Hubble Optics UL14-------14---------48-------0.245
Tom Clark 16------------16---------68-------0.266

Merope Lite-----------16--------71.6------0.277 (best possible scenario)
Tom Clark 24------------24---------160------0.278
Webster D18--------------18---------92-------0.284
Dobstuff 17.5------------17.5-------89-------0.291
Obsession 20 UC----------20---------124------0.310
StarStructure TL 17.5----17.5-------96-------0.313
Obsession 18 UC----------18---------105------0.324
omahaastro 30-----------30---------300------0.333
Mirzam 14---------------14---------68-------0.347
george golitzin 10------10---------35-------0.350
Obsession 15 UC----------15---------79-------0.351
Jon Isaacs 16 Dobstuff--16---------90-------0.352
Teeters STS 11----------11---------43-------0.355
Dobstuff 14--------------14---------70-------0.357
Obsession 20 Classic-----20---------147------0.368
Obsession 18 Classic-----18---------126------0.389
Starmaster 20------------20---------156------0.390
StarStructure TL 15------15---------88-------0.391
Obsession 15 Classic-----15---------89-------0.396
tezster 10 Dobstuff-----10---------40-------0.400
Orion Optics 12 f/5.3---12---------58-------0.403
Obsession 12.5 Classic---12.5-------65-------0.416
Portaball 12.5-----------12.5-------65-------0.416
Starmaster 18------------18---------138------0.426

Merope----------------16--------111-----0.433 (as is without weight reduction)
1991 Tectron 15----------15---------100------0.444
Starmaster 14.5----------14.5-------96-------0.457
Project Galileo LB16-----16---------120------0.469
Starmaster 16------------16---------121------0.473
Zhumell 16---------------16---------121------0.473
StarStructure TL 12.5----12.5-------78-------0.499
Meade LB 16--------------16---------128------0.500
Starman1 12.5 Teeter----12.5-------81-------0.518
Zhumell 12---------------12---------75-------0.521
Starsplitter 15----------15---------118------0.524
Jason Comet Hunter 480---3----------4.75-----0.528
Orion XT10---------------10---------53-------0.530
Achernar 15-------------15---------120------0.533
FirstSight---------------12---------80-------0.556
Meade LB 12--------------12---------80-------0.556
JimMo 14.5--------------14.5-------120------0.571
isawit 12---------------12---------86.1-----0.598
Zhumell 10---------------10---------60-------0.600
Orion XX12---------------12---------86.5-----0.601
Ed D 6 Strut------------6----------22-------0.611
Starmaster 11------------11---------74-------0.612
Orion XX14i--------------14---------120------0.612
Meade LB 10--------------10---------65-------0.650
Tad S XT8i---------------8----------42-------0.656
Orion XX16G--------------16---------195------0.762
Orion XT8G---------------8----------52.4-----0.819
Ed D 6------------------6----------30-------0.833
Coulter 13.1------------13.1-------150------0.874
Orion XT6i---------------6----------35-------0.972
Azure1961p---------------8----------64-------1.000
Horsetrain Cave----------12.5-------350------2.240 

Edited by Oberon, 11 February 2015 - 01:52 AM.

[GShaffer]

Well that is interesting.......my 20" f/5 falls very close to the middle of the pack at .445  (178/20^2)  That includes a set of rather heavy steel wheel barrow handles that probably push 20 lbs for the pair with steel wheels and aired tires.....refigured without them at 158 gives .395......Not bad considering it is a rather conventional build albeit I did figure it with weight savings considered as I pulled the glass out of my 20" Obsession and wanted it to be considerably lighter than the overbuilt thing it was...... No doubt the panelized rocker box contributed to the savings by quite a bit along with a UTA that is close to half the height of the Obsession

 

Edited by GShaffer, 11 February 2015 - 02:47 AM.

[Oberon]

Note I wasn't trying to make Merope lightweight because I never planned to pick her up in one piece - I care far more about the structure being stiff and rigid, about minimizing flexure - but would have preferred she was balanced. The only thing that needs to be lightweight is the UTA, and even that could be avoided with a bigger altitude wheel.

[Oberon]

Minor Mass items

 

Spider

Guitar Machine Head:-    36g x 8 = 288g

Mounting Blocks:-           14g x 8 = 112g

Screws M5 x 30mm:-        4g x 16 = 64g

Wires:-                               2g x 8 = 16g

Aluminum Plate 5mm:-     50g x 1 = 50g

 

Total weight of wire spider (excl. secondary or secondary support) = 530g

 

 

Heim Joints

M8 male, steel (as used on UTA):-  35g x 6 = 210g

M6 female with 75mm LH threaded rod and locknut, steel (potential alternate):- 23+13+2 x 6 = 228g

M8 female with 100mm RH threaded rod and locknut, steel (used at LTA):- 45+32+4 x 6 = 486g

M8* 60mm threaded rod cross bolt with nuts:- 30g x 3 = 90g

Moonlite truss inserts:- 15g x 6 = 90g plus rivets say 10g = 100g

 

Total weight of Heim joints and truss inserts arrangement in use at UTA end of truss:- 210+90+100 = 400g 

 

Total weight of Heim Joints and truss inserts in use at LTA:- 486+90+100 = 676g

 

 

Misc Optical additives

 

31mm Nagler:- 933g

Paracorr:- 423g

TV Big Barlow:- 233g

Delos 10mm (with dioptrix) + adaptor + Big Barlow:- 413+110+233 = 756g

Orion 50mm Finder:- 590g

Laser Finder:- 122g

[Oberon]

Cutting Plans

 

most of the timber in Merope can be cut out of two sheets of cheap construction grade ply as most exposed surfaces are edges only. You may prefer a better quality ply for the UTA. Below are the cutting plans I used.

 

1 x full sheet of 25mm ply for azimuth ring, mirror cell, altitude bearings and the leveling screw supports. The clearance between the rings is sized for a 1/2" router with 3mm spare for trimming. None of these dimensions are critical, but later as the pieces are cut to inter-react with each other you will want to measure and work from actual dimensions.

And this is what comes out of it...

 

 

minus the mirror cover...

 

[Oberon]

Cutting Plan #2

Upper Telescope Assembly, Ground Plate and Mirror Cover

 

 

IMPORTANT! Excuse typo, sheet size is 7' long x 4' not 5' x 4' metric sizes are correct

 

Note that if you size the mirror cover right the UTA will drop over it and be held in place, ie, it won't slide around in your car when cornering etc, and generally makes storage more manageable as below.

[MitchAlsup]

My 20 f/4 comes in at 111 pounds for 0.2775 on the lb/in**2 scale.

 

also note the primary is 2" thick.

Edited by MitchAlsup, 12 February 2015 - 02:59 PM.

[Alex Parker]

Oberon,

 

I just wanted to add that the degree scales on the bearing wheels are a fantastic visual addition - how did you make them so nice looking?

[Oberon]

Hi Alex, I created the artwork in Adobe Illustrator and sent an *.ai file that looked like this to a commercial online sign maker (a pdf would also do) scaled to the correct size and selecting black acrylic as the base with print on surface. An alternative would have been to reverse print on clear but without seeing samples I wasn't sure whether it would be as black, or whether it would adhere to the timber as well. I mention this because the print side is covered with a fine plastic protective film, which is very soft and scratches very easily; mine has several scratches especially where it rubs on the side of the altitude bearing. I'm sure I could find a perfect solution if I was willing to pay for it, but as you say, its a fantastic visual addition as it is, not to mention very practical for finding faint fuzzies. Who needs digital setting circles and encoders?

 

You'll notice that while I'm paying for circular Merope artwork I may as well print anything else I could think of that might be useful in the unused areas. I even managed to print a second altitude circle for another telescope. And of course it is essential to mark out any drill holes such as the circle center-points. The compass points I printed out as an attachment for photography; I like photographing ISS solar crossings and wanted something better than pencil scribbled on the tube to work out orientation.

 

Basically all you need to do is drill out the center (in my case I use a 48mm post on my router table), glue the circle to the bearing and then trim with the router. Alternatively first route it out roughly to correct size, glue and trim later. Then follow through on the inside using a 1/4" trimming router cutter for the curves and fiddle about with some guides for the corners to end up with this...

 

Ditto for altitude.

Incidentally, while I had the degree circle floating about prior to gluing I found it coming in very handy for measuring, marking out and setting up all sorts of things. Next time I'll print another one, or perhaps a set of of degree circles for permanent use in my workshop. Below I am using the setting circle to position my UTA for marking out and drilling, protected from scratching by masking tape.

Edited by Oberon, 12 February 2015 - 10:25 PM.

[starman345]

In the third picture down in post #36 you show the ring with the teflon strips mounted in their positions, how did you cut those angles to get the strips located properly? router-template? Also, your cell ring is inset into your altitude bearings, how did you accomplish those inset cuts?

I agree with Alex, those setting circles are beautiful.

[Oberon]

Azimuth Section #1

The azimuth section is a simple ring manufactured from 3 layers of 25mm ply laminated together provides all the support necessary for the OTA. Essentially it is a 70x75mm (3"x3") solid circular beam with a Laminpanel plate on the bottom (which in theory should make it stiffer, but not really necessary). Originally my design was just a ring with no center pin, but as it came together there was really no reason not to put a thin plate on the bottom, so I did, mainly because the plate adds another barrier to creepy crawlies.

 

 

The most difficult bit to do was cutting the altitude bearing recesses. Several reasons. First there was no straight edges to work from, and at the time no bottom plate with a center point either. Second I didn't have a tool that could make the cut in a single set up. And third I didn't take enough care building a jig and relied too much on measuring, clamping, unclamping, marking and realigning everything to marks. Consequently the cuts didn't align as well as I expected and needed some rework.

 

Mounted in jig from behind

 

Jig from front showing angle grinder with 4" saw blade mounted in jig

 

 

This is about as dodgy and vicious as it looks. I had to take the guard off to use it and was terrified it would bite and grab and do something really evil. In practice it was as smooth and easy to use, gave no hint of grabbing, and I just shaved the job a few millimeters at a time. This involved lifting the entire cutting assembly to slide up its defining point and then slowly let gravity work its way down slice after slice. Unfortunately with only a 4" cutting blade it soon interfered, hence the step cut to clear space. This meant I had to locate the job 4 times and the saw 4 times, which is not a recipe for repeatability and precision.

So the lessons learned for next time were:-

1. take the trouble to make a very good jig - much better than the photos show

 

2. buy a 6" angle grinder and saw blade

 

3. build a better safer jig for the saw

[Oberon]

Azimuth Section #2

Because I was fitting setting circles I needed a pointer for the altitude. It pays to make a pointer adjustable, and in my case it had to fold flat so that the altitude bearings could stack flat on top when packed away for traveling. This required making a double hinge arrangement and was one of the more fiddly detailed jobs; although the end result works really well it was a lot of work for something that looks as though it should be simpler.

 

 

 

 

 

Just to play safe I installed some threaded inserts into the timber in case I wanted to fit stuff later, like an eyepiece holder or an iPad table or handles - whatever. I didn't have plans but I like to be prepared.

 

 

Setting circle bonded with polyurethane glue and clamped overnight...

 

 

0.25" thick Teflon pads fitted. Forgetting the cost of teflon I also used slabs of 10mm teflon on the sides because it was just the right thickness and it gave the bearings a slippery surface to work against. And I liked the colour. But they aren't important.

 

 

Note my original plan when this photo was taken was for the teflon pads on the feet to run against the side of the azimuth bearing and constrain it, so no need for a center pin. But something didn't work as intended so I went to plan B and fitted a bottom plate, and those feet with their lovely slabs of 10mm teflon were shelved.

[NickK-UK]

I'd be tempted to get a set of sharp chisels on it then finish with a sander.

 

Edit: you've just added the next post with images

Edited by NickK-UK, 14 February 2015 - 05:22 AM.

[MikeMcCaskey]

Oberon,

 

Fantastic engineering and craftsmanship! Several (well, more than several!!!) interesting ideas in your build. I'll be using them when we get back to the EE.UU in a couple of years.

 

At some time in the future is there any chance we could see the complete build in a PDF? I've been cutting and pasting in a word document when I remember to check the article.

 

Thanks!!!

 

Miguelito

[Pierre Lemay]

Fantastic engineering and craftsmanship! Several (well, more than several!!!) interesting ideas in your build. I'll be using them when we get back to the EE.UU in a couple of years.

 

At some time in the future is there any chance we could see the complete build in a PDF? I've been cutting and pasting in a word document when I remember to check the article.

Jonathan, you are to be congratulated not only for a well designed and well built telescope but also for the thorough description of the design and fabrication steps. Your use of photos and sketches, added to well written descriptions, make things very clear. You obviously made it a point to well document every step since you have so many pictures.  Although it is easy for us to remember to type in "Merope" in the CN search engine to locate the descriptions of your scope, I agree with Mike that a regrouping of your articles in one location would be a great idea. Maybe a website?

[GShaffer]

So the lessons learned for next time were:-

1. take the trouble to make a very good jig - much better than the photos show
 
2. buy a 6" angle grinder and saw blade
 
3. build a better safer jig for the saw

We have two terms around here that come to mind regarding that jig and method you used to make those cuts....

1. Redneck engineering

2. Hold my beer and watch this!

 

But then necessity IS the mother of invention lol

 

     
 

Edited by GShaffer, 14 February 2015 - 10:04 AM.

[Pinbout]

Oberon,

 

do you have a plan view of your mirror box and truss layout to show how much clearance there is - mirror edge to tubes?

Edited by Pinbout, 14 February 2015 - 03:39 PM.

[GShaffer]

Oberon,

 

do you have a plan view of your mirror box and truss layout to show how much clearance there is - mirror edge to tubes?

 

There are several pics that show that clearance earlier in the thread......

 

But here is one I stole from another thread   Looks to be approx. an inch

 

Edited by GShaffer, 14 February 2015 - 04:48 PM.

[Starman1]

I hope you have that much clearance at the UTA end, too.  The general rule of thumb is to make the ID of the UTA the diameter of the mirror plus the width of the field stop on your lowest-power eyepiece, i.e. 17.65" for a 31 Nagler for example.

Edited by Starman1, 14 February 2015 - 06:14 PM.

[starman345]

Clearances are on the cut plans in post #32 and #33

[Oberon]

I hope you have that much clearance at the UTA end, too.  The general rule of thumb is to make the ID of the UTA the diameter of the mirror plus the width of the field stop on your lowest-power eyepiece, i.e. 17.65" for a 31 Nagler for example.

 

Ok thanks for the note. I wasn't aware of that rule of thumb, I had only heard "about an inch larger than the primary" or as Newt for web puts it "Allow ½ to 1 inch around primary mirror". Consequently my cut out size is 450mm but it would be trivial to adjust. Newt advises that were I to make it just 3mm larger at 453 then even the 75% ray would be unvignetted by the tube (but would remain vignetted by the focuser). As the 75% illumination diameter is 54mm (larger than the focuser) and the Nagler 31 is only 42mm I figured I was quite safe using a 450mm aperture for UTA.
 

 

Edited by Oberon, 14 February 2015 - 07:30 PM.

[Oberon]

Oberon,

 

do you have a plan view of your mirror box and truss layout to show how much clearance there is - mirror edge to tubes?

 

Just for you Danny....

 

[Oberon]

 

Fantastic engineering and craftsmanship! Several (well, more than several!!!) interesting ideas in your build. I'll be using them when we get back to the EE.UU in a couple of years.

 

At some time in the future is there any chance we could see the complete build in a PDF? I've been cutting and pasting in a word document when I remember to check the article.

Jonathan, you are to be congratulated not only for a well designed and well built telescope but also for the thorough description of the design and fabrication steps. Your use of photos and sketches, added to well written descriptions, make things very clear. You obviously made it a point to well document every step since you have so many pictures.  Although it is easy for us to remember to type in "Merope" in the CN search engine to locate the descriptions of your scope, I agree with Mike that a regrouping of your articles in one location would be a great idea. Maybe a website?

 

 

Maybe. I have a website reserved. But its easier to do it bit by bit here and respond to RFI's. When this is complete I'll probably tidy it up and export a lot of it. So the more questions asked the more likely you end up with something comprehensive.

 

So far as documentation, I did go through a few stages of leaving my camera in the workshop and taking lots of photos. But there are lots of gaps too.

Edited by Oberon, 14 February 2015 - 08:43 PM.