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6" F3 Mirror and Scope Build

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#126 DAVIDG

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Posted 30 December 2019 - 11:22 AM

I like the respirator.  Small particles do go airborne and they aren't good for the lungs.

Harm might not be felt until years later.

 Be safe,  if wearing a respirator with the correct  filter cartridges is what you want to do, go for.  On a  side note you need to have the correct cartridges for what you need to protect yourself from, if not it does no good and  it is just gives you a false sense of security.  The same goes for  the material in the gloves one uses since many chemicals will easily passes through certain materials.

   In reality thou you get much more silicon particles in your lungs from a day at the beach then you do in the process, of grinding a mirror by hand when the surfaces are kept wet.  When you grind by hand and keep things wet it would be difficult to generating enough force to make particles go airborne. 

   The key is to really understand the the process and understand the true dangers and then have the proper personal protection if needed to correctly protect oneself. 

   Those that have developed lung problems from optical glass fabrication are from the fact that  high speed machine grinding with a oil/water mixture is used and that creates a mist of silicon particles in the air.  Bob Cox the former editor of Gleanings For ATMs column died from silicon related lung problem but has he stated in his story it was from the high speed grinding  and oil/water mist created that he breathed for years that led to his  health issues. 

    Be safe.

 

                    - Dave 


Edited by DAVIDG, 30 December 2019 - 04:54 PM.

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#127 Aaron_tragle

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Posted 31 December 2019 - 04:04 PM

I have taken the advice of many and am building a 6" F5 scope, however, I am building the 6" F5 and 6" F3 at the same time since I have two blanks. I've always wanted a nice scope for galaxy imaging and think a 6" F5 would be a perfect fit. I will be doing all steps on the F5 first to get a feel of how it will work and etc then go onto working with the F3. I think this approach is a good combo of learning easier and getting the scopes that I would like. I think this will also be very beneficial when I get to figuring.


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#128 Garyth64

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Posted 31 December 2019 - 04:48 PM

Question:  If you are going to be using an f/5 for galaxy imaging (and DSOs), what are you going to be doing with the f/3?

 

IMO, they are both very close in f-ratios.

 

Again, IMO, make the one f/3, and the other f/8.  You'll be able to use the one for DSOs, and the other for looking at the planets, where the longer fl will help.  Figuring the f/8, will give you a "feel" of how things will work.



#129 PrestonE

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Posted 31 December 2019 - 05:15 PM

He is building the F3 to observe INF Integrated Flux Nebulae 

like Mel Bartels...

 

Happy New Years,

 

Preston


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#130 Pinbout

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Posted 31 December 2019 - 11:13 PM

Question:  If you are going to be using an f/5 for galaxy imaging (and DSOs), what are you going to be doing with the f/3?

 

IMO, they are both very close in f-ratios.

 

Again, IMO, make the one f/3, and the other f/8.  You'll be able to use the one for DSOs, and the other for looking at the planets, where the longer fl will help.  Figuring the f/8, will give you a "feel" of how things will work.

Plenty of people figure f5’s like an f8 and f8’s like f3... lol.gif


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#131 dogbiscuit

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Posted 01 January 2020 - 12:58 AM

Have you reached the target sagitta on the f:3?



#132 Aaron_tragle

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Posted 01 January 2020 - 02:48 AM

Have you reached the target sagitta on the f:3?

I’ve gotten to the target sagitta for 60 grit, I am considering doing the 80 tomorrow but will have to wait on anything past that until my plaster arrives.

#133 dogbiscuit

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Posted 01 January 2020 - 12:17 PM

Already having the sagitta,  I would do 80 grit with full size tile tool. 



#134 dogbiscuit

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Posted 01 January 2020 - 06:47 PM

Probably should cast 2 plaster tools, one for tiles for fine grinding, another for the pitch lap for polishing and figuring.

Make the one for the pitch lap fully equal to the diameter of the mirror.  If the lap is slightly smaller in diameter you will likely have (more) trouble with turn down edge.


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#135 Aaron_tragle

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Posted 02 January 2020 - 06:16 PM

Probably should cast 2 plaster tools, one for tiles for fine grinding, another for the pitch lap for polishing and figuring.

Make the one for the pitch lap fully equal to the diameter of the mirror.  If the lap is slightly smaller in diameter you will likely have (more) trouble with turn down edge.

Plaster arrives monday, I went to home depot to pick up tiles but the cheapest tiles I could get were a pack of 100 for 25 bucks so I am going to do a penny tool.



#136 Pinbout

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Posted 02 January 2020 - 06:20 PM

Yummy

Seal the plaster with acrylic matte spray. It helps adhesion of epoxy and whatever

 

D32D2A80-4D58-44A4-8911-CF86060391B9.jpeg

 

i also glue my nuts for rough grinding 

 

541B93F4-7327-4889-BDE6-E0D6F6F63006.jpeg

 

 


Edited by Pinbout, 02 January 2020 - 08:09 PM.

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#137 Aaron_tragle

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Posted 07 January 2020 - 09:25 PM

Sorry for the lack of updates, but I have been hard at work getting back into school and working on these mirrors. I have gotten both mirrors done through 80 grit and have started 120 on the F5 first. Making the tools out of dental plaster was frankly easier than expected. Focuser, Spider and Secondary acquired for the F3. One thing I am starting to look for metal tubing for the scopes, Hasting tubing would be nearly 200 dollars for the two scopes. Is there a good alternative source for metal tubing?


Edited by Aaron_tragle, 07 January 2020 - 09:45 PM.

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#138 Pinbout

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Posted 07 January 2020 - 11:14 PM

I just tubes from HD 

 

this weighs 8lbs 14oz - rings and all

 

8F48A563-3A56-42E1-B4A2-1BAD5DAA517D.jpeg



#139 Aaron_tragle

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Posted 08 January 2020 - 10:34 AM

I just tubes from HD 

 

this weighs 8lbs 14oz - rings and all

 

attachicon.gif8F48A563-3A56-42E1-B4A2-1BAD5DAA517D.jpeg

Smallest tube ID I can get at my local stores is 7.5", would this work? I've heard there could be issues with a tube substantially larger than the mirror itself.


Edited by Aaron_tragle, 08 January 2020 - 10:35 AM.

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#140 Venator

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Posted 08 January 2020 - 11:54 AM

7.5” or more would be fine. Remember the light entering the mirror is going to be a cone. For an F/5 with let’s say a 30” tube, if you had an eyepiece with a 3° field of view you would need to add 0.78” either side of you mirror at a minimum. So you would want a tube at least 7.56” ID to not crop any incoming light. Might as well bump it up to 8” for this example. You need to find out what your lowest power eyepiece is going to be and then calculate your true field of view, and then take your proposed tube length and do some trig to figure out how big of an opening you really need for the cone of light coming in. Then give it a little bit of bonus diameter to be safe.
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#141 Garyth64

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Posted 08 January 2020 - 04:09 PM

"I've heard there could be issues with a tube substantially larger than the mirror itself."

 

Actually I believe the opposite is true, having a tube too small in diameter, could cause thermal issues that enter the light path.  When I've made my scopes, I've tried to keep the tube diameter 2" larger than the mirror.  I have had no issues with them at all.


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#142 Aaron_tragle

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Posted 08 January 2020 - 09:15 PM

Moonlite focuser on the way, planning on moving it back and forth between scopes as I will never have both at the same time after I go off to school.



#143 Aaron_tragle

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Posted 19 January 2020 - 11:18 AM

I've been slowly going along working on the mirror, I can only work ~30 minutes/day during the week due to my college classes. Mirrors are both to the 240 stage of grinding and I plan to get them to 25u today. Tube has been cut and primer applied, carbon fiber arrives tomorrow. I got the dovetail on the way and have the materials for anodization at the ready. One problem I noticed is that my tube isn't a standard size and won't fit in off-the-shelf tube rings. The tube OD is 193mm and I either need to get 235mm rings or 180mm rings. I have entertained the idea of making them out of wood, I am electroplating them aluminum anyways so that'd add structural support.


Edited by Aaron_tragle, 19 January 2020 - 11:19 AM.

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#144 Aaron_tragle

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Posted 19 January 2020 - 05:26 PM

Ok I think I know what I am going to do now, I am going to make wooden rings. The original plan was to buy standard GSO rings and do modifications from there, however, making them from wood is actually cheaper and allows me more customization (which I am planning extensive amounts of). I was going to electroplate 500g grams of aluminum nitrate to the GSO rings to create a better surface for anodization, but going the wood route I am able to form them to the shape I want to while cutting them making electroplating much easier. This leaves one problem however, electroplating needs a metal surface to plate onto since you need to be pumping voltage into the surface you want plated and we all know wood is a very good insulator. This is where I had a revelation today

 

I can make a electrolytic paint

 

I found a very cheap way to make an electrolytic paste/glue using graphite and elmers glue, but that left me with another problem, where the heck was I going to get nearly 1lb of graphite for as cheaply as possible? I originally was going to spend 40 dollars on graphite until my Chemistry teacher helping me with the anodization and electrolytic plating process brought up that pencils have graphite. Kids at my school commonly throw away/leave pencils on the floor. I am going to collect pencils for a few weeks for the graphite making that cost nearly zero except maybe 20 minutes work over the next month or so. I can now cover my wooden rings in this paste and plate aluminum on them. I know this process sounds extremely convoluted and it may all not make sense but I just felt that a breakthrough this huge was worth a CN post no matter what.


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#145 Aaron_tragle

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Posted 19 January 2020 - 05:27 PM

If you can make the tube rings out of wood, you can make them out of aluminum.  (of course depending on tools available, like a bandsaw.)

Sheet aluminum is quite pricey in my area.



#146 Aaron_tragle

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Posted 20 January 2020 - 03:23 PM

Moving back to the topic of grinding the mirrors, I have come across an oddity. I am doing MOT normal stroke grinding on the mirror with 120 grit, but the sag isn't going down. I have done nearly 2 hours of MOT on the F3 mirror and the sag didn't change more than 1 thou, any ideas as to what could be happening? I think I may try out some chordal just so I can get it back down.


Edited by Aaron_tragle, 20 January 2020 - 03:28 PM.

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#147 perfessor

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Posted 20 January 2020 - 03:59 PM

You should probably wait until the experts chime in, but my comments would be:

 

1) I would stay with 80 grit until I've reached the desired ROC.  How close to your target were you when you switched to 120?  

 

2) If you are staying with 120, then certainly try offsetting the mirror for a chordal stroke.  Once you reach the desired ROC, switch back to center-over-center for a few wets, the better to spherize the surfaces, before progressing to 220.

 

Just my two cents,

 

Cheers!


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#148 dogbiscuit

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Posted 20 January 2020 - 04:27 PM

By "coming down" do you mean more or less sagitta, shorter or longer ROC?

 

There are many normal strokes.

 

One normal stroke for making the ROC shorter is a stroke that is more to left or right of center.  MOT  chordal stroke or a wide W can do that.

Normal stroke for making the ROC longer would be the same chordal or wide W TOT.

 

Chordal stroke far offset from center works faster but makes less spherical shape.

Wide W stroke makes the curve more spherical.

Decreasing the width of the W makes better sphere.

 

Chordal to get close to sagitta,  Wide W to get right on and make more spherical, decreasing W size to finish to sphere.



#149 Aaron_tragle

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Posted 20 January 2020 - 04:40 PM

By "coming down" do you mean more or less sagitta, shorter or longer ROC?

 

There are many normal strokes.

 

One normal stroke for making the ROC shorter is a stroke that is more to left or right of center.  MOT  chordal stroke or a wide W can do that.

Normal stroke for making the ROC longer would be the same chordal or wide W TOT.

 

Chordal stroke far offset from center works faster but makes less spherical shape.

Wide W stroke makes the curve more spherical.

Decreasing the width of the W makes better sphere.

 

Chordal to get close to sagitta,  Wide W to get right on and make more spherical, decreasing W size to finish to sphere.

Sorry, I should be using correct terminology. I mean the sagitta is becoming a smaller number and ROC is getting longer. I have been doing the 1/3 normal stroke as shown on the stellafane strokes page MOT. 



#150 Aaron_tragle

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Posted 20 January 2020 - 04:53 PM

What does a wide-W stroke look like exactly, is it the W stroke on the stellafane site?




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