More on flat making

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Күн бұрын

More information on flats; grinding a flat and and how you can use (in some cases) the water test without using a collimating lens. A large collimating lens may be hard to find.

Пікірлер: 29

@paulvalleli2744 10 жыл бұрын

The optical spherometer-comparator was introduced to amateur telescope makers by Robert E. Cox, editor of the Sky & Telescope "Gleanings" column in the late 1950's. It allowed amateur telescope makers to make the difficult optics for Maksutov telescope designs. Ed Jones has shown us an even simpler approach using a triangular plate of baltic birch, a material that was not available then. The advantage is that it is a laminated material for rigidity. It should be shellacked so that it does not expand and contract with humidity changes and should be more stable under temperature changes. Previously, plywood has been used for lap forms for polishing pitch and works pretty well. Adding a thin sheet of plate glass to a Baltic Birch disk should make a viable alternative to dental plaster forms that take time to dry. Ceramic tiles can be epoxied to the glass disk to make up a grinding tool. They can easily be removed by heating the squares slightly with a propane torch. The threaded rod is a neat change from a micrometer head or dial indicator that would be much more expensive. Great care must be taken to not drop the comparator on the flat under test. Even aluminum nails can cause a bullseye fracture defect much like a BB strike. Great care should be taken when tapping the plate for the screw rod. If the screw is not tight in the threaded hole, it will rock back and forth, leading to erroneous readings. The aluminum nails avoid the use of steel balls that need a complex calculation to correct for their radius. Great contribution to the craft Ed ! Starman Paul

@jeffwells641 Жыл бұрын

While it's true that the Birch plywood is an excellent material for this, it's absolutely not necessary. The key to this tool is the three aluminum standoffs and the adjustable center brass post. Any material holder - plywood, solid wood, acrylic, steel - will do the job just fine, and the flatness of the substrate doesn't matter as long as it does not touch the glass to be evaluated. The key insight is that even a micron level difference in flatness will allow the tool to spin on the convex plate if the distance is set on the concave plate. To refine this further, you'll want to be sure the aluminum posts and the brass post have spherical ends or come to a dull point. An imperfectly flat post could cause some irregularities in the readings you get with the tool - best to eliminate that possibility.

@captianmorgan7627 13 күн бұрын

The hardest thing about this set up in 2024? Getting the brass threaded rod. Most places have stopped carrying it. Online or in hobby shops are the only places I can find it. And it is a little hit or miss in hobby shops.

@klebics 7 жыл бұрын

HOLY $^%^ half-micron detectability with just screws and wood!?!? Forget thermal/moisture expansion of wood blah blah blah it CLEARLY works, thanks for great vid!

@sofjanmustopoh7232 Жыл бұрын

This is awesome

@honoriosergio5454 10 жыл бұрын

Hi Ed Jones great job!

@yinvirak4891 10 жыл бұрын

Hello Mr i work in korea i want to buy such mirror but i don't know what kind of store i shoud go tell me please

@dest101101 7 жыл бұрын

Fantastic

@spook_dad 6 жыл бұрын

I would like a packet of them straight drill bits please oh and while ye there I'll take an uncalibrated gauge I've been sent here for a long wait, and 2 sky hooks and this this how you grind the optics to project the sun? where can i get blocks of glass like that please?

@sacriptex5870 10 жыл бұрын

hey Ed great videos!!!! can you post some videos on refractor telescope lenses...?? crown and flint ??? there´s nothing on internet about it!! Greetings from brazil!!!

@billshiff2060 Жыл бұрын

6:50 I think that;s wrong. The second part has to be convex if it spins easily. If it were concave then the outer pins would touch and the center would be free so it could not spin.

@perspectivex 4 жыл бұрын

Thanks for the interesting video. I am having a hard time finding anyone grinding flats for their telescope star diagonals....do you happen to know why? (not sure how you would grind an optical flat for a piece of glass that is only 4-5mm thick...maybe have to back it with a thicker optical flat as support). It seems like you could grind a couple ~20cm flats and water jet cut out a bunch of star diagonals (again, not sure how you'd grind thin flats).

@Opticsed 4 жыл бұрын

Commercially flats are made using a planetary polishing machine, something I'll bet you rarely find in a shop making telescope optics. Glass 200 mm by 4 or 5 mm thick is not much stiffer than a piece of rubber (some exag.). You could back it with wax or blocking pitch but unblocking will invariably relieve any mounting stress if you aren't experienced at it.

@perspectivex 4 жыл бұрын

@@Opticsed Interesting. Seems like a big hole in the d.i.y. telescope efforts, that is, nobody's making their own flat mirrors for star diagonal or ellipticals (e.g. for Newtonians). It seems kind of weird that that part of the d.i.y. effort has never really been attacked and people cave in and just buy the flat mirrors. Or they're just way harder to make than a large parabolic mirror.

@edjonessongs5308 4 жыл бұрын

@@perspectivex Secondary mirrors are a lot thicker than your thin star diagonal and is a bit easier for ATMs to do. Texereau in his book describes how to make a secondary mirror. One method is to block it up with pieces of glass all around it to make a circular part, (probably the best way). (Secondary mirrors are done in large blocks commercially). The other method is to mount a larger circular flat imbedded in plaster at 45 degrees and to core it on a drill press. The resulting thin edge however will often turn up due to the Twyman effect. Making a flat is still not easy compared to making a primary mirror and if you can do it you can call yourself an optician.

@perspectivex 4 жыл бұрын

@@edjonessongs5308 I have to admit I'm only interested in star diagonals at the moment. It looks like nobody diy's those or so few that they're not to be discovered. On a similar note....do you think the Whitworth three plate method work to make three round optical flats? Just keep using smaller grits, no pitch lap or anything like that.

@Opticsed 4 жыл бұрын

@@perspectivex If I were to try making your star diagonal 4 or 5 mm thick I would cut it to size first (2 X 3 inches?) then wax it to a backing plate surrounded by other pieces to make it 6 inches in diam. (I wouldn't use the 3 flat method unless I actually needed 3 flats.) I might expect some stress relief when unblocked.

@JasperJanssen 4 жыл бұрын

Is the difference in cost of three blanks versus two blanks really significant enough to do it this way?

@Opticsed 4 жыл бұрын

You can also make it with one blank and a tool but cost and having to polish 3 optics instead of one is your decision.

@jeffwells641 Жыл бұрын

I don't think you can ensure flatness by the process alone with 2 blanks or 1 blank and a tool. You'll have to read when one piece has flipped from convex to concave so you can switch the pieces, and I don't see how you do that without a tool like this.

@glenking3337 3 жыл бұрын

I was thinking this could be done with a fidget spinner.

@yinvirak4891 10 жыл бұрын

About 20cm how much does it cost. Thank you

@yinvirak4891 10 жыл бұрын

About 20cm does it cost. Thank you

@Chuchumm Жыл бұрын

In space year 2023, the tool might be cheaper than the plywood.

@BobChaz 4 жыл бұрын

5 year old video, but what the heck. Problem with the 3 flat method. You have a process shown with steps like "Grind B on C then grind C on B" as if they are different steps. The process is A --> B, B --> C, C --> A, rinse and repeat.