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#376 Datapanic

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Posted 26 July 2014 - 01:45 PM

The 2" Crawmach focuser is installed on the focus backplate that Bob Burns made.

Today I will install the secondary holder and then install the OTA onto the mount.

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#377 Bomber Bob

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Posted 26 July 2014 - 01:46 PM

It's hard to believe that it's been 4 1/2 years going.

To quote the late great Roy Orbison: Mercy!!

But it is a work of art, and well worth preserving.

#378 Datapanic

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Posted 26 July 2014 - 11:02 PM

Here's what makes up the Secondary Holder. There is an inner and outer machined housing, the shaft that slides and rotates to infinite precision on the Spider Vane, a soft gasket that goes on the outer end of the holder and the mirror itself. Two machine screws hold it together. There is no cotton material stuffed into the back of the housing, it was designed to be just snug enough as it is!

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#379 Datapanic

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Posted 26 July 2014 - 11:04 PM

(Lots of Dust!) Here it is assembled. You can see in the previous picture where the coating on the edges has failed, but the lip covers it up for the most part. The optics will be recoated eventually.

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#380 Datapanic

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Posted 26 July 2014 - 11:08 PM

With the Secondary Installed, I then used my peep-eye colimation tool to position it just right and then my HoTech Crosshair Laser colimation tool to adjust it.

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#381 Datapanic

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Posted 26 July 2014 - 11:11 PM

Collimation was surprisingly easy and only took about 3 minutes. The adjustments for both the Secondary and Primary were very precise and smooth.

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#382 Datapanic

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Posted 26 July 2014 - 11:16 PM

And here it is as of tonight! Just a sneak peek because there's still a bit more to do - The inside of the tube needs to be touched up, the RA and Dec friction needs to be adjusted, it needs a finder, and I want to balance the OTA with Tube weights. But it's now ready for first light!

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#383 Datapanic

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Posted 26 July 2014 - 11:22 PM

...of course, first light might be a while! It's the rainy season in the southwest. The weather is like this every year, I don't attribute it to the "curse". Tomorrow, I'll move it back into the garage and continue on.

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#384 herrointment

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Posted 27 July 2014 - 05:16 AM

Bravo! :bow:

#385 Datapanic

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Posted 28 July 2014 - 10:50 PM

Yesterday, I brought the telescope back into the garage and tinkered with it. First up was to find where focus was for infinity, which for this test, the Santa Rita mountains on the other side of Tucson. This pic just shows where the 1.25" Focuser is at that position.

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#386 Datapanic

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Posted 28 July 2014 - 10:51 PM

The telescope is top-heavy, so I didn't work with the 2" Focus Base. Tube weights are going to be added, once I do the math.

#387 Datapanic

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Posted 28 July 2014 - 10:56 PM

Next up was to adjust the friction on the RA and Dec. This picture is of the underside of the Dec Drive Back Plate, where an allen wrench is used to adjust the friction by turning the 6 bolts to just the right amount of torque. The telescope needs to be really torqued down on the Dec side to hold it in position, but after Tube Weights are installed, it can be loosened up a little.

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#388 Datapanic

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Posted 28 July 2014 - 11:02 PM

The RA friction is adjusted with 6 allen socket bolts and there is a problem here, even with the bolts totally loose, there is too much friction. So, I will have to take the mount apart and see what's going on with that. These things happen, and I'm sure it can be easily fixed. If not, the amount of friction is tolerable and there is a knob on the RA Motor Drive Assembly for fine motion control.

It's not too much of a big deal to investigate, the lower RA Shaft Retaining Ring is removed, along with two bolts that hold the RA Motor Drive Assembly to free up the RA Shaft and slide it on out. I think anyway - it's been a few years since I put this thing together and don't exactly remember! :bigshock:

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#389 Datapanic

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Posted 28 July 2014 - 11:06 PM

I also tested motion control on both the RA and Dec axis by placing a torpedo level on the tube, leveling the tube and then running the motors one axis and direction at a time for a few minutes. If the level's bubble moves, then it's good. The Slip Clutches of both drives work fine!

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#390 Datapanic

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Posted 28 July 2014 - 11:10 PM

Shown here is the 1.25" Motorized Focuser Control Box I put together with a 70's era aluminum project box and 2 micro switches for in and out focus. This will be good to use with imaging because it's always been difficult, at least for me, to set focus with a webcam or camera by turning the focus knob - whatever object I'm trying to focus on would bounce all over the place. Hands off focusing is probably a good thing, right!?

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#391 Datapanic

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Posted 28 July 2014 - 11:21 PM

So here's my list of things to do before it's ready:

1. Install a Finder Scope - I have one as well as a pair of Cave 50mm Finder Scope Rings. I was going to polish them but I think it would look better painted Satin Black like some of the other parts.

2. Do the math and install Novak Tube Weights. I have the brackets and rods for this, but only have a limited set of weights, so I have been playing musical tube weights to balance out the OTA's of the Cave 8" f/7 or the Horsetrail Cave for whatever role I use them for. Need to have some more weights made!

Sub dilemma on the Tube Weight Math - the weight and position of the Tube Weights are contingent on the weight and position of the Finder that I have yet to pick out and install. I am trying to find a 7/8 x 50mm Towa 50mm Straight Through Finder, but no luck. I could just swap around finders with what I have, but eventually want a permanent finder for it and it is critical for weight and balance to have a static value to use when solving the formula to balance the tube. Different finders have different weights and center of balance. I'll get more into balancing tubes later :)

3. Disassemble the mount enough find and correct the RA Shaft friction problem I mentioned earlier. There may be no solution to this and could be just by design. I'll take the OTA and Dec Shaft Counterweight off the mount and if rotation in RA is loose, then the problem has to do with weight force and probably cannot be fixed!

No Star Test yet, patience :)
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#392 droid

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Posted 08 August 2014 - 04:08 AM

Just a thought, ever consider taking ti , back, to Stellafane?



#393 turk123

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Posted 08 August 2014 - 05:04 AM

Very nice job Dan.   Great dedication to bringing back a one of a kind  classic.  



#394 Datapanic

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Posted 16 August 2014 - 10:11 PM

Just a thought, ever consider taking ti , back, to Stellafane?

 

That's a long drive from here!  But, if I'm ever close to Stellafane I definitely would do that.  This year, I'm all set to bring it to the Julian Starfest next week. http://www.julianstarfest.com

I am 99.9% finished with it, will post the latest things done in a few minutes :)



#395 Datapanic

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Posted 16 August 2014 - 10:54 PM

There were a couple things missing from the scope that I felt neccessary to have in order to use it properly.  First, was the missing finder scope.  In the two old photos that I have of it, there was a finder mounted on some sort of bracket on the upper rotating ring.  I thought about reproducing something like that, but on the other hand, Newtonians on a G.E.M. normally have Guide Scopes mounted on the rotating rings, not finders, and the distance between the finder eyepiece at that location and the main eyepiece was too far apart and not "normal".  So, I decided on using a 7x50mm Circle-T classic finder (borrowed from my 8" f/7 Cave Lightweight Deluxe) properly located near the main eyepiece.  This finder scope is from about 1975, so it matches, but until I find a second finder scope just like it, I will have to play musical finders between those two scopes.  I had a set of Cave Finder Rings that I originally intended to polish, but the cast aluminum was too rough, so instead, they were sanded down a little and then painted a nice satin black to match the other parts painted that color.

Attached File  Finder Mounted.JPG   108.62KB   0 downloads



#396 Datapanic

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Posted 16 August 2014 - 11:12 PM

There was one problem with installing anything on the tube that was not originally there - the extra weight on the tube would throw off the main balance and there was not enough Dec Shaft length to counter that.  So, the other missing part, I think, was a Dec Shaft Extension.  There is evidence that something like that was made for it and lost along its time, so I made a mechanical drawing for it and brought the mount over to Jon at Western Drawn Machine Shop in Tucson.  Jon was extremely helpful in the early disassembly of this scope for parts that were rusted together, and he's also a very busy guy.  Today (he came in on Saturday just to finish it), Jon finished this critical part needed if a finder and tube weights were to be installed. It is basically an 8" extension to the Dec Shaft with a 7" section that slides up into the original hollow Dec Shaft.  The reason I think something like this was part of the design is that there are two thread holes in the original Dec Shaft that I now use to hold the new extension in place. 

 

This picture shows the Dec Counter weight above the junction of the extension to the main Dec Shaft - a later picture will show where the counter weight balances, keep in mind that the extension also adds to the total Dec Shaft counterweight amount - I did the math and knew it would balance out in the end :)

 

I don't have enought time now to make the extension shiny now, but it's on the list of things to do.

 

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#397 Datapanic

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Posted 16 August 2014 - 11:29 PM

A couple nights ago, I did the dirty work that involved Algebra, Trigonometry and Physics to figure out where to mount the Tube Weights.  I know I've harped enough about balancing tubes, and all I can say is it's worth the brain-hurt math to do it.  The forumlas are found in the November, 1958 Sky & Telescope Gleanings for ATM's.  One of these days, I PROMISE, I will write up a modern How To on this since nobody seems to have done so over the past 5 decades. 

 

Anyway, the math works, I originally mounted a set of Novak Tube Weights on my Cave 8" Lightweight Deluxe in the early late 70's for AP.  Tube Weights are the difference between Night and Day.  Without them, you have to clamp down on the Dec Shaft Lock and mess with moving the Dec Shaft Counterweight one way or the other depending on which direction the scope is pointed at the sky.  With Tube Weights, it's like Set it and Forget it, no matter where you point the scope, it's balanced and stays on target and (the big part) - you're not putting extra work on the RA and Dec Motors to track an object. 

 

I ran the formulas for 3 different configurations:  Visual with 1.25" Eyepieces, Visual with 2" Eyepieces and Prime Focus with a Canon T3i body at Prime Focus.  The 1.25" and Canon solutions were nearly identical, but the 2" Eyepiece configuration added a lot of weight.  So, I averaged it based on the 1.25" and Canon weights.  There is a 10-degree and additional 4 pounds difference between balance of the average and the 2" eyepiece solution!  The good thing is that with a little friction on the RA and Dec shafts, the extra weight and where it balances is not going to matter that much, as long as the offset in weight is close to the ideal location.

 

Attached File  Tube Weight Math.JPG   85.63KB   0 downloads



#398 Datapanic

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Posted 16 August 2014 - 11:33 PM

And here's how it looks tonight!

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#399 Datapanic

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Posted 16 August 2014 - 11:36 PM

First Light?  Are you wondering?  I have a feeling it wont happen until we're at Julian Starfest!  Hope to see you there!

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#400 fjs

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Posted 16 August 2014 - 11:54 PM

Nice work on that math, as well as the drawing, Dan! Three cheers for Jon. :applause: :applause: :applause:

 

Cloudy here too :lol: .

 

'Frank








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