Concept model of new 12" Solar Newton

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Concept model of new 12" Solar Newton

Post by [whrudey] » Tue May 31, 2016 6:16 pm

For some time now, I've made reference to my proposed design for a new and larger Solar Newton scope given the success of the current 8" version. Here are two images of a concept model and a description of its design features.
New 12 inch Solar Newton model.jpg
New 12 inch Solar Newton model.jpg (161.17 KiB) Viewed 5927 times
Overall, I've chosen an open truss design for the OTA and a fork mount to keep the footprint small. This design will just fit into the existing Observatory deck when I remove the TS refractor.

Label description:
1. The base frame will be of 1" x 3" x 14 ga steel tube set out in a grid for rigidity. Each end will be fitted with an adjustable jack for leveling. Two inch steel castors will allow for movement prior to setting the jacks.
2. The base will be covered with 3/16" Diamond tread aluminum sheet.
3. The pedestal will be fabricated with welded steel 1.25" x 1/8" angle iron and covered with 1/8" aluminum sheet. Inside the frame will reside the polar axis drive system using a stepper motor driven by a Raspberry Pi and Arduino controller card courtesy of my student intern's electronic genius. A gear train will reduce speed to a belted drive system. A remote control pad will allow for tracking speed and a variety of slewing speeds.
4. The fork arms will be of 1" x 3" x 14 ga steel tube welded to the base of 2" x 3" x 14 ga. steel tube and, the whole structure reinforced with straps and gussets. This item must be perfectly square and parallel so, during fabrication, multiple jigs will be used. The fork will bolted to the 1.75" polar axis shaft which will be centered within the 6.5" aluminum drum to follow.
5. This 6.5" x 3.5" x 1/4" wall drum will roll on a bed of two 1.125" steel rollers, each also supported by ball bearing chases. The face of the drum will be bolted to a matching 1/4" steel disc which has been welded to the base of the fork.
6. The lower end of the polar axis shaft will be held in a 1.75" Timkin tapered thrust bearing set in an adjustable frame to ensure that the drum rides squarely on its rollers.
7. The lower tube of the OTA will be 15.375" in diameter with 5/16 " thick walls. Both edges will be reinforced with slip rolled 1" x 1/8" aluminum rings inside and out. Here also, the 12" mirror cell will be mounted. Rather than machine the mirror cell, I was able to purchase a unit for US$110, which is less than the cost of materials and my time. The supplier is now out of stock - I must have bought the last one which is on its way: http://agenaastro.com/gso-12-primary-mirror-cell.html
8. The centre frame of the OTA will be fabricated of 3/4" good quality birch plywood and its corners reinforced with large internal gussets. The Declination axis will be made of 1" solid steel shafts securely fitted to plates in the frame. They will then rest in 1" ball bearing chases in the ends of the fork arms.
9. The Serrurier truss arms will be 7/8" or 1" aluminum tubing with suitable end fittings for attachment to the centre frame and respective OTA tubing. This truss design is a time trusted method providing rigidity and, was first used in the Mt. Palomar 200" reflector telescope.
10. The top tube of the OTA will support the diagonal secondary mirror, the eyepiece holder/remote focuser/digital camera and Sol Finder.

So, there it is - just needs to be built, not a simple task. However, when completed, it will be one of the largest of its kind and theoretically, be able to resolve as little as 171 miles on the solar surface. Estimated total cost, not including the necessary skilled labour (mine), should be less than US$2,000.

Comments welcomed.

Bill

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Re: Concept model of new 12" Solar Newton

Post by Derek Klepp » Thu Jun 02, 2016 7:23 am

It will be a labour of love Bill.It is a very solid design.

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Re: Concept model of new 12" Solar Newton

Post by zorgdotnl » Sat Jun 04, 2016 7:12 am

Nice project!!! Given your low latitude, why not using an equatorial plateform combined with Dobson mount? It's easy to make from wood, Footprint is less, weight also, no vibration from the fork,....

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Re: Concept model of new 12" Solar Newton

Post by Merlin66 » Sat Jun 04, 2016 2:13 pm

Bill,
Looks good....
The Serrurier truss design is very specific; the top section is esigned to deflect exactly the same as the bottom section. This demands some structural calculations to determine the correct sizes of the tubes and the "pin joints" at the ends.
What you have is a good "Truss" design.
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Re: Concept model of new 12" Solar Newton

Post by Brendan » Sat Jun 04, 2016 2:19 pm

I have just completed a 10" solar Newtonian and as I have a 10" dobs I made it to fit on that base, I also have an eq platform to place it on for imaging when I get a Continuum filter (I have a 2" one but the focuser on the Newt is a 1 1/4") will post photos soon.
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Re: Concept model of new 12" Solar Newton

Post by [whrudey] » Sun Jun 05, 2016 2:47 pm

Response to above comments:

Derek - yes , it will be a labour of love - only concern is the evolving solar minimum - may be no spots to image.

Zorgdotnl - interesting thought - a Dob is essentially a fork mount on a vertical axis thus, devoid of any cantilever. I think that the movement I get from air turbulence will outweigh any fork vibration. Although I have a petty complete woodworking shop, I also have a reasonable metal fabrication shop ie: metal lathe, milling head, MIG welder, etc. In this instance, I favour the fork given a solid design and, simply the fun of planning and doing.

Merlin66 - yes, the Serrurier truss concept is a great design - very solid and fun to construct.

Brendon - really pleased that you're building a Solar Newton scope - they are tons of fun and, I think, the best and least expensive way to image granules. Look forward to you images including pics of the scope itself. Hope to encourage more folks to consider Solar Newtons.

Cheers to all,

Bill

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Re: Concept model of new 12" Solar Newton

Post by marktownley » Mon Jun 06, 2016 7:47 pm

Looks good Bill! Keep us updated as it develops :)
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Re: Concept model of new 12" Solar Newton

Post by [whrudey] » Thu Jul 14, 2016 2:45 pm

For what it's worth, here's an iPhone image of the 12" Solar Newton OTA almost completed. Still waiting for the mirror, which will have to be stripped, and the eyepiece focuser. Next, will order the necessary steel and begin fabrication of the mount. Please forgive the chaos in my shop - need a larger one. The standing tube on the left was from an older Meade 12" Dob which lent itself to the new scope. The yellow disc on the OTA centre box will be the DEC scale. The truss struts are 1" aluminum tubing.
SN12OTA.jpg
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Re: Concept model of new 12" Solar Newton

Post by [whrudey] » Thu Jul 14, 2016 9:10 pm

Hi Ghost-fire;

Though I'd have preferred a 2" solid shaft, I just happened to have a 1.75" set of thrust bearings from a previous project. There, it had supported a much heavier scope and worked quite fine. Remember, there will be the 6.5" drum riding on a pair of 1.125" rollers with interior bearings (#5 in images above). As for the fork, I'll fabricate it form lengths of square/rectangular 14 Ga. tubing. The actual 1" DEC bearing cases will be set in machined blocks of aluminum fitted in the 1x3" rectangular tubing.

The OTA with mirror and focuser will weigh 40 lbs. total.

The drive system will use belts driven by a geared down stepper motor. Since the scope will be used solely for the sun, the DEC axis will be managed by a tangent arm as the range need not be great.

Cheers,

Bill

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Re: Concept model of new 12" Solar Newton

Post by Derek Klepp » Thu Jul 14, 2016 11:15 pm

Bill how do you prepare the mirrors ? Do you decoat them so to speak

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Re: Concept model of new 12" Solar Newton

Post by [whrudey] » Thu Jul 14, 2016 11:59 pm

Hi Derek;

The best way is to use Ferric Chloride - used as an etchant in printed circuit boards. Here's a link to Gordon Waite's excellent YouTube video on how to go about it:
https://www.youtube.com/watch?v=PdmwqrdDOMs Times vary but, a few of hours should be enough. Then rinse thoroughly. I only do the primary mirror - not the secondary. The native reflectivity of polished glass is about 4%, essentially the same as what my Baader Herschel wedge does. Then, of course, one needs the Baader Solar Continuum filter, an IR/UV cut filter and a medium ND filter eg: 1.8.

Hope that helps,

Bill

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Re: Concept model of new 12" Solar Newton

Post by Derek Klepp » Fri Jul 15, 2016 2:40 am

Thanks Bill.

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Re: Concept model of new 12" Solar Newton

Post by marktownley » Fri Jul 15, 2016 5:10 am

Progressing very well there Bill. Impressive!
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Re: Concept model of new 12" Solar Newton

Post by [whrudey] » Tue Sep 13, 2016 4:13 pm

Earlier this year, I'd posted details on my design for a fork mounted 12" Solar Newton. Despite the lack of further posts, work has been proceeding and I can now submit some iPhone images of progress to date. Those interested in the DIY aspect of this project may find them to be of interest. Those not interested, may be at least impressed with the amount of effort involved. For convenience, I've provided legends for each image below. More to come as things progress.
SCSN12 Const A.jpg
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SCSN12 Const B.jpg
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Legend:
1. Aluminum (1/8” x ¾”) flats were “slip rolled” in my DIY rolling device to fit and reinforce the tube ends – both outside and inside at the outer ends and, just inside for the inner ends.
2. Here the rolled straps have been fitted and flat head screws through tapped holes used to hold them in place. The screws are countersunk and their heads covered with autobody Glazing Putty – the red stuff. Since the tubing was salvaged from an old 12” Dob. Some patching was required prior to painting.
3. Tubes are now positioned for painting – an oil based semi-gloss paint which is rolled on.
4. Turning to the spider, here 3 slots are made in the spider base to receive the wings.
5. Holes are positioned perpendicular to the slots for fastening screws.
6. Some 32 angled pieces were needed for the strut ends – here one is being drilled. All had to be exactly the same – often a challenge unless one uses jigs.
7. Here are the 32 angled ends ready for painting.
8. For the struts, hardwood plugs (about 2” long) were made from a carefully turned dowel – store bought dowels were either too large or too small.
9. The ends of each dowel plug are centre drilled for accurate assembly.
10. With the plugs epoxied in place, locking screws will fit into these holes.
11. Now the finished 1” aluminum tubes with their plugs.
12. The angle ends are painted with an oil based semi-gloss spray paint.
13. The struts both long and short were also sprayed with an oil based semi-gloss paint and hung out to dry.
14. Now, all the strut parts can be assembled. Believe it or not, making the struts is quite a tedious task but, worth it in the end as the Surrurier truss design is a winner.
15. Assembling the top tube and centre box with struts.
16. A peak at the installed spider.
17. Here’s the completed OTA. Note the Declination scale in yellow.
18. Work now begins on the base. Here the plate to receive the thrust bearing at the RA lower end is being bored out on the lathe. The smaller hole at the back will allow passage of the 1.75” precision ground steel shaft (+/- 0.0005”) – U$60 for a 24” length.
19. The main RA bearing drum was turned from as 6.5” aluminum tube with .25” walls. Here a shoulder is being bored to receive a .5” aluminum disc in the next image. Once assembled, it will be fitted on a mandrel and turned true.
20. The 6.5” disc is being centered in a four jaw chuck so as to bore out a perfect 1.75” passage for the main shaft.
21. Work now begins on the belt drive arrangement – bearing flanges are being fitted for tapped FH screws – this will make more sense in later images.
22. One of two drums for the belt drivee has been turned true and is now being drilled for a setscrew.
23. The belt drive “pulley” has now been fabricated and is being trued upon the lathe.
24. The base pedestal is of welded 1.25” x 1/8” steel angle and, is positioned on an appropriately shaped jig for welding. Two will be made – mirror images of each other.
25. Here the two side frames are fitted in a jig for final welding. Perfect sizing and square is essential.
26. The RA axis and its two end bearings are positioned on the pedestal frame and, using a dial indicator, checked for run-out. This turned out to be +/- 0.002” - not bad.
27. Now, since they are expensive and hard to get on a Caribbean Island, one resorts to making their own worm wheel using an ordinary tap between lathe centres and a positioning jig.
28. In a mock up frame, the elements of the belt drive system are fitted. A NEMA 17 stepper motor will drive the worm gear from its position on the lower left of the frame and will be controlled by Raspberry Pi and Arduino.
29. Here’s a view of the pedestal with the RA axis and bearings fitted.
30. This image shows the lower (rear) RA thrust bearing.
31. The drive and driven pulley have now been installed with temporary vacuum cleaner belts – the final belt will be an 1/8” x 1.25” Urethane belt.
32. The drive rollers are spring mounted for even pressure on the drum. A release lever (not shown) drops the assembly for free slewing.

Enjoy,

Bill

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Re: Concept model of new 12" Solar Newton

Post by marktownley » Tue Sep 13, 2016 5:12 pm

Really impressive stuff Bill. I do like a good build story! I like all the engineering detail, much appreciated thanks :)
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Re: Concept model of new 12" Solar Newton

Post by [whrudey] » Tue Sep 13, 2016 9:29 pm

Thanks Mark - pleased that you enjoyed the post. So much of the fun comes from the designing and construction process. Yet in today's world, so few of the folks ever get to enjoy this aspect. A while ago, I taught an ATM course where we built a number of 6" Dobsonians. Since the most tools anyone had-might have been a hammer or screw driver, I wound up spending hours machining all the parts to the level of kits for simple assembly and painting. This made the course totally impractical and had to be scrapped. Though missing two students, the following mage shows some of the resulting scopes.
ATM2.jpg
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Re: Concept model of new 12" Solar Newton

Post by kohamher1 » Wed Sep 14, 2016 12:57 am

Great job!!!

A few years ago I read David Groski's article and followed his instructions to desilver both the primary and secondary mirror on my 8" Newt.

I've never been able to bring it to focus. I think I'm getting a ghost image from the back side of one or both the mirrors.

Question. Anyone else have this problem?
Does the configuration you use have any special baffles or shielding or anything behind the primary to eliminate reflections?

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Re: Concept model of new 12" Solar Newton

Post by [whrudey] » Wed Sep 14, 2016 2:23 am

Hi kohamher1;

Not familiar with the Groski method but, it is likely the same as my reference from Gordon Waite: https://www.youtube.com/watch?v=PdmwqrdDOMs which worked very well for me.

The focusing issue is interesting and, there are arguments for and against grinding vs. polishing the rear mirror surface as well as painting it flat black vs. leaving it clear. Christian Viladrich has written on this subject - his writings are well worth looking up: http://www.astrosurf.com/viladrich/astr ... /N300.html for starters.

This prepossesses that there is not an issue with focal point - had everything been fine prior to the stripping ? Was the mirror of good quality - was it polished out completely - this can be determined with a laser pointer: https://stellafane.org/tm/atm/polish/polish.html

Finally, I think it is unnecessary to strip the secondary. Stripping the primary reduces reflectivity of incident light to about 4%. This is comparable to the reduction obtained with an Herschel wedge which is 4.6%. All that remains is the addition of a Baader Solar Continuum filter, an IR/UV cut filter and a ND2 filter. It might be worthwhile trying your setup with an aluminized secondary. With the latter, you should also be able to image the moon as an alternative target.

Another reference is the following thread outlining some of my initial trials and tribulations with an 8" solar Newton: https://www.solarchatforum.com/viewtopi ... =9&t=18204

Hope the above thoughts are helpful. Pleased to see that more folks are giving solar Newtons a try - I think a very practical way for w/l solar imaging without breaking the bank. Also the larger optics improve resolution (Dawe's limit) if you're into granules.

Cheers,

Bill

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Re: Concept model of new 12" Solar Newton

Post by [whrudey] » Wed Oct 26, 2016 2:11 am

Now that our STEM Carib 2016 Conference is over, attention can be directed to my 12" Solar Newton. Last week I was able to cut and weld pieces for the base using 14 ga. 1" x 3" rectangular steel tube. Ignore the green cardboard strips under the pedestal which is being centred on the base prior to being bolted in place. Note the four steel castors and the adjacent screw jacks awaiting their foot pads. All steel surfaces have been coated with red oxide primer given the propensity for rust in the tropics. 3/32" aluminum panels will cover the pedestal sides but, will be easily removed for servicing. 1/2" plywood covered with plastic laminate will cover most of the base.

Yet to be done are the fork made of 1" x 3" steel tube (see concept model for design); fitting the Raspberry Pi/Arduino controller for the stepper motor RA drive; constructing the DEC tangent arm drive with a smaller stepper motor; stripping the 12" mirror; fitting the secondary mirror and focuser; etc.

The urethane belt is a little problematic in that the welds come apart. I'll likely make my own reinforced continuous belts using vacuum cleaner belts as a starting point.

Overall the base length is 48" and the base front width 32". The RA shaft as it exits the front of the drum, is 24" above ground. When the OTA is installed and in its home position, the total height will be 49" above the floor.
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Enjoy,

Bill

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Re: Concept model of new 12" Solar Newton

Post by marktownley » Thu Oct 27, 2016 8:52 pm

Seriously impressive Bill! Much respect Sir!
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Re: Concept model of new 12" Solar Newton

Post by [whrudey] » Thu Oct 27, 2016 9:25 pm

Thank you Mark - do hope it works when completed.

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Re: Concept model of new 12" Solar Newton

Post by [whrudey] » Sun Nov 20, 2016 2:06 am

Notwithstanding the lengthy period since my last update, progress has continued on my 12" Solar Newton. The pedestal frame has been painted (black), the base frame painted (Hammerlite silver), the 12 V regulated power supply is in place, the screw jacks now have feet and, the base panels (1/2" plywood covered with plastic laminate) have been installed as shown below:
Image5.jpg
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The more daunting task was the fabrication of the fork. Given that both arms had to be parallel in two planes and, perpendicular to the base plate such that everything lined up in a coaxial manner with the RA axis shaft, the challenge was clear. For those who have had any experience with welding (MIG or otherwise), appreciation will be had for the effects of heat distortion/warping despite the best laid plans of jigs, clamps and careful tack welds. The fork was fabricated from 14 ga. steel tubing with dimensions of 1"x3", 2"x3" and 1" square. These were carefully cut to size and positioned on a flat layout pattern prior to welding as shown below:
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A 6 3/4" diameter disc of 1/4" steel plate was machined and bored to fit the 1 3/4" RA shaft. Here the shaft opening is being bored out and, eventually this plate will be welded to the base of the fork frame. Holes are positioned such that the plate/fork assembly can be bolted to the face of the drum bearing (1/2" aluminum plate) and the shaft itself. Here the disc being machined on my Myford 7 lathe.
Image6.jpg
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The following images show the completed fork in its primer coat yet to meet the Hammerlite Silver final finish. Autobody filler was used to fillet all inside corners for cosmetic purposes. In total, the fork weighs 18 lbs. (8 kg.) and is incredibly stiff/rigid.
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When the fork assembly is fitted to the RA shaft, concentricity is essential. Although distortion/warping of the welded fork was fortunately minimal, allowance has been made for shims to be placed between the drum face and the steel base disk during assembly using a laser alignment setup to be described later.

So, that's where we are at present - more to come including fitting 0.09" aluminum panels over the pedestal, slip rolling an aluminum arch over the pedestal, machining of the aluminum bearing blocks for the fork arms and, installing the stepper motor system and remote control. Lots yet to do.

Enjoy,

Bill

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Re: Concept model of new 12" Solar Newton

Post by marktownley » Sun Nov 20, 2016 8:52 am

A superb project! This is exactly the sort of thing I like to do myself, but don't have the time with work. Love the updates Bill :)
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Re: Concept model of new 12" Solar Newton

Post by [whrudey] » Sun Dec 04, 2016 1:14 am

Given poor viewing conditions, more time has been spent in the shop working the new scope. In the first image, one can see that the pedestal and base frame have been painted and, a 1/2" plywood/plastic laminate deck fitted.
Image5.jpg
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Next, 0.09" aluminum sheet was fitted to the pedestal sides and eventually painted. One image shows the almost completed fork whilst others show the removable West panel exposing the electronics within. The last image in this series shows the South end of the pedestal with a 4" fan, neon On/Off switch and power socket. Eventually, a DB25 F/F gender changer will be fitted between the two to accept the remote cable. Using a gender changer avoids the tedious soldering to small pins. Rather, a 15 foot DB25 M/M cable can be purchased and 12-15" removed from one end. The raw end of the longer section goes to the remote control box. The shorter length plugs into the gender changer on the inside of the pedestal with sufficient wires to the Arduino board.
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Finally, I had a sheet metal shop slip-roll the arched hood over the pedestal. It wasn't inexpensive but, I don't have a large slip-roller in my shop (yet). This was fitted with guides and trim then painted. Four knobs secure it in place but, also allow for removal to service the inside of the pedestal. The last image shows a red knob on a lever - no, it does not lower the landing gear but, rather disengages the RA drive belt. Also, one can see the holes in the North surface of the bearing drum to which the base plate of the fork will be bolted. Meanwhile, the 1.75" RA shaft is being centre bored/tapped to accept a stainless steel 1/2" bolt - also in a local machine shop since the piece was too large for my lathe.
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Still a ton of stuff yet to do but it's getting closer to completion - perhaps early spring 2017. Constructing the OTA was the easy part - constructing a suitable base is another story.

Final words of advice. Years ago when I was building my sailboats, a wise old shipwright/joiner told me that the most important tool in one's shop is the following:
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He advised spending a lot of time sitting on it and thinking before cutting a piece or, making an irreversible step. I've had that very stool since 1974 and it has served me well. The match sticks are from my pipe.

Enjoy,

Bill

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