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NStiesi's Official C8N Reconfiguration Thread

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#26 nstiesi

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Posted 12 June 2019 - 09:55 PM

Flush trimmed the mirror box tonight, then set to work test fitting the mirror cell.

I turned some spring cups on the lathe from some salvaged 17-4 stainless. Ground flats on the end of the springs with a bench grinder.

Next I have to make some knurled nuts for collimation. I could buy, but I don't know if 8-32 thumb nuts off the shelf will be big enough diameter for comfortable adjustment. I may buy a few and try them out before I start turning.5f5688c2ead34473abbf8072d29e2240.jpg1bbcfdb3f9827270532ac4f55c5764ad.jpgf44d30ff8c76b9b48d9474a4f3bfb818.jpg083b3673d0d071c92c846ab57c5481d8.jpg

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#27 nstiesi

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Posted 26 June 2019 - 10:01 PM

I accomplished a tedious task that needed done; locating holes in mirror box for threaded inserts, and making the likewise mounting blocks for the UTA. Only problem I had is that Lowe's only had 6 inserts when I needed 16!

Next up: finish mirror cell (delrin pads and edge supports), install mirror, install secondary, truss poles, then star test!0264f4488e5dd7fc1ce459e3008fe354.jpgc8f39dfc051d1e270bc092bd2ba0c8f8.jpg8c57770aeb5795d2dd5e2f5abc49f508.jpg

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#28 nstiesi

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Posted 28 June 2019 - 06:48 AM

I dont know if anyone is actually reading this, but I would like to reach out for some opinions.

 

I am struggling with edge supports....a fact that is complicated by the issue of installing the mirror cell wrong by 90 degrees.  My edge supports will be 120 degrees apart.  I didnt think I needed to do anything fancy since this is a full thickness commercial mirror.  (1" thick at 8" diameter)

 

With the cell off by 90 degrees, the mirror will not have two supports spaced 60 deg from altitude plane when scope is tilted.

 

I was considering some sort of bearing arrangement, but now I am thinking of simply a piece of round stock with a flat on one side (the side facing the upright of the mirror cell.)  The "set screws" in the upright will push the round stock into contact with the mirror at all three points (gently, so as not to pinch...but snug enough to prevent movement).

 

The top of the round stock will be drilled and tapped for a plastic clip to act as a safety so the mirror cant fall out.

 

Does this make any sense?  Anyone see an issue with this plan?  (edited for sketch attached)

 

Note drawing is NOT to scale.  There is about half inch of clearance between the cell uprights and mirror.  I would use 1/2' stock and mill the flat down to .4" or .45".

Capture.JPG

 

Thank you!


Edited by nstiesi, 28 June 2019 - 07:09 AM.


#29 nstiesi

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Posted 29 June 2019 - 10:21 PM

Here's what I came up with. It seems to work ok, after some trial and error. I didn't originally have the scallop cut in the post, but it was needed so that the post resists rotating. The screw pushing on the back of the post is such a shallow and loose fit with the hole on the post that it will not itself resist such rotation.

I still need to get some nice thumb screws and jam nuts, and ditch the black oxide screws for stainless. A shim may be needed here or there, but in all it seems to hold the mirror securely, and hopefully without pinching.

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Edited by nstiesi, 29 June 2019 - 10:22 PM.

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#30 nstiesi

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Posted 01 July 2019 - 08:38 AM

Two poles done, 6 to go. It's really starting to look like something! Shown next to the old beat up C8N tube.

I can't wait to actually be able to look through it again!bc15e74609f571b7f7918a7e1c3d4f24.jpg

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#31 nstiesi

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Posted 01 July 2019 - 08:15 PM

Couldn't resist finishing the trusses. Despite a small mishap and messy rework of the truss attachment points on the UTA, I think it turned out nice!

This week I will mount mirrors and pray that I nailed the calculations on length.

Then it's on to altitude bearings.8a7ab3ab36fed8de99c3ceecea44a902.jpg4c1a1843787ae6d2fd06e64ce2acd6a1.jpgb873ea68a5bbdd7f88352ef3a4ec1a0d.jpg

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#32 drneilmb

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Posted 02 July 2019 - 11:21 AM

Altitude bearings are completely un-necessary for first light in my experience!

 

Once you have the mirrors in, make sure to lean it up against something (I use a lawn chair) and see what you can see. Polaris is a classic target, but I like to just point it up into the sky and see what's in the FOV.

 

I like to see another truss 8" f/6, that's what my first truss scope was, not one of these stubby little f/3 things that people keep coming up with. Great work!



#33 nstiesi

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Posted 02 July 2019 - 11:27 AM

Altitude bearings are completely un-necessary for first light in my experience!

 

Once you have the mirrors in, make sure to lean it up against something (I use a lawn chair) and see what you can see. Polaris is a classic target, but I like to just point it up into the sky and see what's in the FOV.

 

I like to see another truss 8" f/6, that's what my first truss scope was, not one of these stubby little f/3 things that people keep coming up with. Great work!

Thanks!  

 

I agree with you completely, and that is the plan.  I am going to put the mirrors in, rough collimate, lean it on something and test it out to make sure I got the truss lengths correct.  That is my biggest worry right now. I considered making a test sled, but clearly decided to plow forward....



#34 nstiesi

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Posted 02 July 2019 - 11:23 PM

Short!!!!! Of course, the trusses are bleeping short! I did the math many times, but still ended up blowing it!

Got it all set up and collimated, and I couldn't bring ANY of my eyepieces to focus. I estimate I was off by 1.313"! I was right, too, because I spent the next 2 hours making 4 new trusses from the VERY last of my material, and moving the attachment points up for the remaining 4 short trusses.

I moved everything up 1.5" to give me some breathing room. Now all my eps focused close to fully racked in. I am going to make my final adjustment by setting the mirror up higher in the box with longer springs or standoffs.

So much time and energy wasted though.....ugh!!!!!

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#35 nstiesi

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Posted 10 July 2019 - 10:42 PM

I've made more progress this week. The rocker box is mostly done. I used melamine covered shelf for the base. The rest is 3/4" birch. I cross pinned the bottom in with twelve 1/4" dowels. The sides are box jointed with my hacked together table router jig. It was crude, and I had to basically hammer the joints together, but it got the job done. I either need to put serious effort into making a good jig next time, or break down and buy one....

I also made the altitude bearings and spacers, although I need to mill or sand the spacers down a bit for a perfect fit width-wise with the rocker box. I also need to set their orientation with a dowel pin. I also still need teflon pads on the rocker box.

Plenty more to go. Next up is the ground board and all that goes with it. I also need to think about height. It needs hardware upgrades here and there....some screws were used at random, but that's the easy stuff. And sanding.....so much sanding.b53e81b8855003853d84df6465f850b9.jpgc781643cedb9190b839c1ebb67556b85.jpg97fbb856f7d5ad3dea6e59df95cfbc38.jpg

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#36 nstiesi

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Posted 17 July 2019 - 06:50 AM

First light!  

 

Now that all the bearing surfaces are installed, I put the mirror back in to test focus again.  When I first performed this test and discovered the poles were too short, I didnt have bearings, I was just tilting and holding the scope, which was a PAIN to try and find anything.  This also gave me a chance to evaluate the movement and balance.

 

1) I was very happy with the movement in both directions.  Didnt take too much force to break static friction.  No overshoot.  I dont have grounds for comparison, but this should work fine for a push too.

 

2) Balance is good, although I didnt test it to the extreme of low altitudes.  The small plywood circles I installed to restrict lateral movement of the altitude bearings adds a nice extra pit of friction, but not too much.  I do wonder how they will hold up to wear.  In the future I may need to replace them with delrin or malamine.

 

3) I am going to need a small, stable platform.  The eyepiece is a little low for me, but only a few inches.  I MIGHT be able to get away with just a couple feet on the ground board.  I need to do more testing.

 

4) Views were good!  I wasnt even collimated.  The moon was the moon.  Jupiter was about as crisp as these optics have ever shown it.  I pushed mag to 250x with decent result. (again, not collimated)

 

5) I will need 1/4"-1/2" inch spacer under mirror cell.  When I re-cut the poles I left them a tad longer than perfect.  My zoom EP focuses with absolutely zero spare in-travel.  I'd like some cushion.  At least spacers are removable.

 

6) The biggest problem: part of the reason I took on this project is that my old mount shook terribly when focusing.  I was very disappointed to see this one does as well.  I cant perform a side by side, but touching the focuser induced shakes such that it was hard to tell when I was in focus at high power.  One thing to note is that the temporary 2x4s under my ground board were warped and introduced some rocking, so I will be interested to see improvement when I get proper legs on the ground board.  Any other tips here for mitigating the shakes?  I assume it is from flex in the thin walled aluminum poles.  Should I attempt to fill the poles with foam?  Anything else I could do here?

 

Any help with #6 is greatly appreciated!


Edited by nstiesi, 17 July 2019 - 06:52 AM.


#37 nstiesi

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Posted 01 October 2019 - 06:51 AM

I'm FINALLY back to work on this. Took some time to work on the house, and with the new school year starting it's been an adjustment.

This week I made some simple plywood feet for the ground board, spacers for the mirror cell, and started on custom collimation knobs

I'm getting to the nitty gritty on this, save for adapting my digital dsc and motorizing g. What's still needed are a uta shroud, truss light shroud, and alot of sanding and Tung oil.61f6fdfdbdf4ed9be43d64a983d5c2ab.jpg

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#38 nstiesi

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Posted 10 October 2019 - 06:36 AM

3 coats of Watco Tung Oil Finish, and reassembled.

Plan for this weekend is UTA liner and truss light shroud. I'm also working on re-incorporating my digital dsc system, and the control motors. I am switching from 2 rpm gear motors (the old mount was 1:144 reduction), to NEMA 17 steppers.

With microstepping, I should be able to run these slower than 2 rpm, but also much faster when I need to. I'm only planning a 1/12 reduction, but I think I can step these slowly enough to compensate at high magnification.097c9e51ee9ae41d1c7bb3498872d6c1.jpg

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#39 nstiesi

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Posted 15 October 2019 - 07:52 PM

Uta lined. I ended up with a poster board type material from fabric store, but it's thick and stiff. It was hard to bend, creased a little, and was too short to cover the whole cage, but I was able to place the break behind the focuser, so you can't see it from the outside.

It is held in with super glue. I hope it holds up to humidity is all.29771991c23eb57a2b227b66dc066146.jpg65a5158306c43d49cec89ebaa28a07b1.jpg

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