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Is ATM too expensive? Lets scavenge around!

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#1 Giorgos

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Posted 17 March 2019 - 05:37 AM

I wonder whether mirror making kits are very expensive. More than a ready made mirror especially considering the cost of aluminizing (plus shipping). An 8" kit can cost 50$. The abrasives cost is 2€ / kg (lets say 1$/lb), pitch approx 10 euros/kg and CeO 10 euros for 100 gr. The prices asked for mirror making kits are totally unjustified. Probably the kit sellers buy the abrasives by the 25 kg bag split it into 200gr "portions" and get 1000% profit by selling it in kits. I consider scavenging around for abrasives. Perhaps sandblasters will even give away for free a little of them as they consume it by the ton. Pitch can be made by mixing rosin with refined wax and rouge or titanium oxide are very cheap too and easy to find (cerium oxide is expensive).


Edited by Giorgos, 17 March 2019 - 08:33 AM.

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#2 Starman47

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Posted 17 March 2019 - 06:58 AM

waytogo.gif



#3 Ian Robinson

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Posted 17 March 2019 - 07:11 AM

Try Newport Glassworks , they sell kits and blanks and abrasives and pitch.

http://www.newportglass.com/polish.htm

Edited by Ian Robinson, 17 March 2019 - 07:22 AM.

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#4 sg6

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Posted 17 March 2019 - 09:06 AM

Have never done any mirror making but I suppose that the idea is that you buy a kit and make say 6 mirrors, not a single mirror.

 

Another aspect is that the idea is the handmade by you mirror is significantly better then say one by GSO. So maybe the cost comparison needs to be made more towards Zambuto specification not GSO.



#5 stargazer193857

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Posted 17 March 2019 - 01:32 PM

Grit for telescopes is much smaller than for sand blasting.

If you want to save money, go at least 10". That is the tipping point.

A lot of your cost is one time tool making, whereas professionals reuse them. They also get bulk pickup on many aspects.

The main reason to make you own mirror is custom focal ratio and glass thickness, if you don't like the standard ones. Or just the fun of learning and making.


If aluminizing is expensive, you can silver it yourself much cheaper, but it does not last as long.

I watched people in India make a 6". The only reason to make a 6" is so you see changes happen faster and can do more trial and error while the instructor is there. Once the class is over, 10" is better. Though there is a saying that you can make a 6" and a 12" faster than you can make just a 12".
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#6 Cameron_C

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Posted 17 March 2019 - 04:21 PM

I can only speak for myself, but I made my mirrors simply because I wanted to.

The experience has been incredibly frustrating at times, and still somehow so very satisfying when things finally go right.

 

I expect that the mirrors I have made would have been much cheaper to simply buy outright.

Maybe a GBF (great big fat?) mirror is cheaper to make than buying, but I am not there yet.

 

I spent a lot of time trying to find bits and pieces, and tools.

And I found this community where everyone shares information freely.

 

Anyway, just my two cents worth.

In my case the cost of a mirror was not why I decided to make one.

I enjoyed the build journey and the satisfaction at the end, knowing I had made something.


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#7 Pierre Lemay

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Posted 17 March 2019 - 04:39 PM

If you want to save money, go at least 10". That is the tipping point.

Actually it’s closer to 13 inch. See this study published six years ago by Gary Seronik. 


Edited by Pierre Lemay, 17 March 2019 - 04:55 PM.

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#8 mark cowan

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Posted 17 March 2019 - 04:45 PM

I wonder whether mirror making kits are very expensive. More than a ready made mirror especially considering the cost of aluminizing (plus shipping). An 8" kit can cost 50$. The abrasives cost is 2€ / kg (lets say 1$/lb), pitch approx 10 euros/kg and CeO 10 euros for 100 gr. The prices asked for mirror making kits are totally unjustified. Probably the kit sellers buy the abrasives by the 25 kg bag split it into 200gr "portions" and get 1000% profit by selling it in kits. I consider scavenging around for abrasives. Perhaps sandblasters will even give away for free a little of them as they consume it by the ton. Pitch can be made by mixing rosin with refined wax and rouge or titanium oxide are very cheap too and easy to find (cerium oxide is expensive).

Many unwarranted assumptions in your OP but otherwise decent. 

 

Take the John Dobson approach and get your grit from ocean sand that you titrate for finer grades in buckets, or get grit from places that sell lapidary supplies.  Steal tar from pothole patches on the street to make your pitch laps (be sure to strain the rocks out).  Salvage glass portholes for mirror blanks (not so easy anymore).  Make your tubes from cement forms, your spider supports from shingles, use recycled mirrors from copy machines for the secondaries (just score them with a glass scribe to cut to size).  Scrap plywood from building sites to build the rocker box.  Get an inexpensive silvering kit (Angel Gilding I think) to save from aluminizing (might be hard to import though).  Use Teflon cut from scrapped semi-trailer hitch plates for the altitude bearings, old records for the azimuth plates.  Make EPs from surplus lenses (check our SurplusShed.com for this stuff).  You don't need hardly any cerium oxide to polish a mirror (less than a 35mm film can's worth) so don't cheap out on the $1 or so that costs.

 

As John used to say in his class, "To make a telescope mirror, first thing is you need to get the Navy to scuttle a battleship."  Scrap yards are your best friend for this stuff.  You absolutely can do it on the cheap if you really know how to scrounge and repurpose.


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#9 stargazer193857

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Posted 17 March 2019 - 05:45 PM

I think there are even cheaper mirror glass sources. I'll post later after I know it works.

A good reason to make a scope is what else would you spend your free time doing. Although, the once used pitch adds up when you only make one.

I really want to make secondary mirrors. People don't agree though on the best way to cut at 45 degrees. Certainly cheap if you are ok with 90 degrees.

#10 Stephen Kennedy

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Posted 17 March 2019 - 08:55 PM

Have never done any mirror making but I suppose that the idea is that you buy a kit and make say 6 mirrors, not a single mirror.
 
Another aspect is that the idea is the handmade by you mirror is significantly better then say one by GSO. So maybe the cost comparison needs to be made more towards Zambuto specification not GSO.


Mirror making is not nearly as easy as you think it is. With no prior mirror making experience, you would be lucky if you could make six good mirrors in a year. Also, with no mirror making experience I doubt you could make a mirror as good as a GSO. In fact, you would have to be lucky to make one anywhere near as good as the mirrors GSO is producing now. As far as trying to match Zambuto specifications, he has been making mirrors for decades and is among a very small group of exceptionally talented mirror makers.

I buy mirror making kits from Newport Glass and hope to end up with a mirror as good as I could buy from GSO. I know I could buy a mirror from GSO that would be as good as the mirror I am likely to make and I will not save a penny. I do it because I enjoy it.
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#11 stargazer193857

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Posted 17 March 2019 - 10:30 PM

Mirror making is not nearly as easy as you think it is. With no prior mirror making experience, you would be lucky if you could make six good mirrors in a year. Also, with no mirror making experience I doubt you could make a mirror as good as a GSO. In fact, you would have to be lucky to make one anywhere near as good as the mirrors GSO is producing now. As far as trying to match Zambuto specifications, he has been making mirrors for decades and is among a very small group of exceptionally talented mirror makers.

I buy mirror making kits from Newport Glass and hope to end up with a mirror as good as I could buy from GSO. I know I could buy a mirror from GSO that would be as good as the mirror I am likely to make and I will not save a penny. I do it because I enjoy it.

Well now you scared me into starting with 8" f6.25 0.83" instead of 10" f5 0.78".

I was even going to buy a 6" 1" f8 blank, but none were available cheaply. There are borofloat ones, but I am not going to hog out borofloat.



I will not make money making an 8" scope. But I'll build it anyway just for practice. I've built more than one minidob, and I've noticed they get better with each experiment.

Edited by stargazer193857, 17 March 2019 - 10:42 PM.


#12 Ian Robinson

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Posted 17 March 2019 - 11:23 PM

save youself some time and get a glass blank that's already got a curve generated by the seller , see http://www.newportgl...com/angwcat.htm

Edited by Ian Robinson, 17 March 2019 - 11:29 PM.


#13 mark cowan

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Posted 17 March 2019 - 11:47 PM

Well now you scared me into starting with 8" f6.25 0.83" instead of 10" f5 0.78".

I was even going to buy a 6" 1" f8 blank, but none were available cheaply. There are borofloat ones, but I am not going to hog out borofloat.



I will not make money making an 8" scope. But I'll build it anyway just for practice. I've built more than one minidob, and I've noticed they get better with each experiment.

That's not sensible.  A 10" is perfectly fine size to start with, moreover an f/5 is not going to destroy your children's inheritance even if you end up having to do it over a few times before you figure out how to do it right.  But the same goes for an 8".  You just want to pick SOMETHING and DO IT.


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#14 Giorgos

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Posted 18 March 2019 - 01:36 AM

Try Newport Glassworks , they sell kits and blanks and abrasives and pitch.

http://www.newportglass.com/polish.htm

Ian I am living in Greece and ordering heavy packets from overseas is unfortunatelly out of the question. I can't find under 220 abrasives from sandblasting supplies locally so I may order only 400, 800 and 1000-1200 from some european supplier, 80, 120 220 is easy to find locally. I also find attractive the HCF lap as describeed in ATM 1 book! Beekeeping is very popular here and a sheet of HCF costs less than 1€. You can even make yourself HCF sheets with a homemade press! HCF seems easy to make, clean and fuss free, totally unlike the nasty messy pitch. For initial polishing seems HCF is the definite way to go! BTW what is the coarser abrasive to use before polishing?



#15 stargazer193857

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Posted 18 March 2019 - 02:28 AM

Ian I am living in Greece and ordering heavy packets from overseas is unfortunatelly out of the question. I can't find under 220 abrasives from sandblasting supplies locally so I may order only 400, 800 and 1000-1200 from some european supplier, 80, 120 220 is easy to find locally. I also find attractive the HCF lap as describeed in ATM 1 book! Beekeeping is very popular here and a sheet of HCF costs less than 1€. You can even make yourself HCF sheets with a homemade press! HCF seems easy to make, clean and fuss free, totally unlike the nasty messy pitch. For initial polishing seems HCF is the definite way to go! BTW what is the coarser abrasive to use before polishing?




Aluminum oxide is used between silicon carbide and polishing.

Think of silicon carbide as hammering a sharp spike in to crack and quickly remove chunks of glass during hogging. It leaves lots of subsurface damage that can be seen in the sun. You use finer sizes as you reach your curve so that you can remove the deepest shattered areas faster and leave less of them. Once you are close, 320 or 500, you can switch to 25 micrometer aluminum oxide. It kind of shaves the class, removing most of the remaining glass, and making the glass look clear but not that shiny.
Aluminum oxide removes subsurface cracks but still leaves a jagged surface. Polishing rounds the points like water making river rocks.

I don't know what would happen if you give to 800-1200 silicon carbide. Start with finer aluminum oxide, single size?

I know someone who does 320, 500, then 12 micron, then polish. He does not use anything coarser than 320 and says it cuts great. I'm planning 320, 25, 9.





Please tell us more about the bee's wax. I'd love to work with something that does not stink.
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#16 Giorgos

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Posted 18 March 2019 - 03:35 AM

stargazer,

I didn't make myself clear. I mean alundum for abrasives finer than 220 not carborundum. Regarding the HCF (honeycomb foundation) lap it is described in ATM 1 book that you can find and download legally from here (pages 149-153).
If in your part of the world beekeeping is a common practice then you can find and try HCF but only for an initial fast polish.Ask for pure wax HCF as there are variants containing paraffin. For critical work polishing has to be completed with pitch. In any case a little experimentation does not do any harm! I am not aware of any modern examples of it. IMHO it definitely deserves a try!  


Edited by Giorgos, 18 March 2019 - 03:35 AM.


#17 Oberon

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Posted 18 March 2019 - 04:03 AM

That's not sensible.  A 10" is perfectly fine size to start with, moreover an f/5 is not going to destroy your children's inheritance even if you end up having to do it over a few times before you figure out how to do it right.  But the same goes for an 8".  You just want to pick SOMETHING and DO IT.

hush. The future of universe is at a crossroad.


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#18 mark cowan

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Posted 18 March 2019 - 04:30 PM

Be nice.



#19 gregj888

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Posted 18 March 2019 - 08:44 PM

The best non-optics source for grits here are the lapidary (rock polishing) outlets.  I don't know how fine they go, but it's worth a look.


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#20 gordtulloch

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Posted 18 March 2019 - 09:28 PM

Grinding smaller mirrors for me is building skill to make very large ones. So I'm making an investment in myself, which will pay dividends once I start getting into the 16" + mirror range. Plus it's fun, bonus :)


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#21 Giorgos

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Posted 19 March 2019 - 05:29 AM

The best non-optics source for grits here are the lapidary (rock polishing) outlets.  I don't know how fine they go, but it's worth a look.

Greg you are right I guess. Have a look here. They sell fine abrasives for rock tumblers. The five stage rock tumbling process is similar to mirror making stages:

 

          Stage 1: Rough Grind (Shaping) with 80-Mesh Silicon Carbide
          Stage 2: Medium Grind (Sanding) with 220-Mesh Silicon Carbide
          Stage 3: Fine Grind with 600-Mesh Silicon Carbide
          Stage 4: Extra Fine Grind (Pre-Polish) with 1000-Mesh Silicon Carbide
          Stage 5: The Polishing Stage

 

I also found a European seller of rock tumbling supplies in Germany.


Edited by Giorgos, 19 March 2019 - 09:55 AM.

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#22 stargazer193857

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Posted 19 March 2019 - 11:42 AM

I read that machines can jump by factors of 3 because it is easier to let it run than to do all the clean up to change sizes. When bringing by hand, you will save time if you do factors of 2 or maybe less.



Also, though glass dust is the smallest and thus most dangerous, I would be careful with any fine powder. I've not yet used any, but since 25 micron aluminum oxide is applied already in a water bottle, maybe the reason is for safety. 80 grit is so coarse I doubt water could apply it. So it is sprinkled on and then sprayed. I don't know what the switch size is where it is kept in water, but 600 and 1000 look like candidates.

Edited by stargazer193857, 19 March 2019 - 04:52 PM.


#23 gregj888

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Posted 19 March 2019 - 02:50 PM

I use water on all the Aluminum Oxide lapping compounds.  It's really just to keep the contamination down so less apt to get some 25um grains showing up in my 10um or heaven forbid 3um wet... :-)

 

Just cleaner and easier...  at least for the number of mirrors (just a few) I make.


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#24 Giorgos

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Posted 20 March 2019 - 01:23 AM

Another question (don't want to start a new thread): Is it ok to grind in the open? (plate glass blank). Of course polishing and figuring has to be made indoors in a steady temperature environment.



#25 mark cowan

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Posted 20 March 2019 - 01:32 AM

Yes.


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