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who started the myth that glass is flat?
- Thread starter broken003
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- Joined
- Sep 16, 2003
- Location
- Knoxville, TN
Its not, but its alot better than a countertop
- Joined
- Aug 30, 2004
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- Santa Barbara, CA
broken003 said:
If the alternative is a $500 Granite flat top (the kind found in machine shops), I'd stick with glass.
A good read on the flat glass manufacturing process:-
http://www.saint-gobain.com/en/html/groupe/verre_plat.asp
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- Aug 30, 2004
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- Santa Barbara, CA
broken003 said:
Mate,
How can you hold it in your hand and lap it ? Very difficult
It sits on a table. However, all that is desired is relative flatness between the top of the glass and the HS surface.
- Joined
- Jul 12, 2002
It's a whole lot flatter than you can hold the heatsink parallel to. Industrial-grade glass is fairly flat, not perfect, but it's simply not the limiting factor. You always remove more from the outside edges than the center due to the unavoidable rock of the heatskink as you move it, and this factor dwarfs the effect of glass's imperfect flatness.
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- Joined
- Nov 18, 2003
why? do you have info that would prove otherwise? it seems like you're looking for a debate. it might be better to present your opinions / data and then people can mull it over. there are a few people around than can probably provide data that glass is flatter than any other readily available product, but most of us don't get into it that much. do you have some knowledge as to why glass isnt flat? or know of something around the house that could be found that is flatter?
- Joined
- May 6, 2004
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- I live by a Delta
There are many variables to consider when looking at glass flatness.
If we are talking about a piece of glass at least 1/4" thick that is sitting on a fairly flat surface depending on the quality of the glass and how it was rolled yeah it should be damn near flat, within a few thousanths on average.
If we are talking about tempered glass that is a whole different story the thinner the glass the harder it is to hold the flatness since you heat it up in an oven to several hundred C and then air quench cool it quickly. On a thicker sheet you will get better flatness then on a thinner sheet since it will warp if not heated and rolled (not through a press it just oscillates back and forth on ceramic rollers in the oven to ensure even heating) properly in the oven. Which brings up another point if the oven that heated it had a few heating elements burnt out or missing or the recipe was off when it was run through the machine this can also cause problems with the glass as well.
How do I know all this? I have set up and programmed several glass cutting, tempering, as well as glass laminating automated lines over the years in relation to my job.
I will say that all glass has quality control checks in place and each batch is tested for flatness and clarity. Tempered is tested using a mechanical center punch to study shatter pattern and size of the glass chips to determine if proper heating occured through the test pane.
So while it is a bit of a crap shoot in regards to flatness. It is still the most readily available, and most accurate for the money material that you can use to gauge flatness.
and for what we are doing with it. It will more then suit your needs.
If we are talking about a piece of glass at least 1/4" thick that is sitting on a fairly flat surface depending on the quality of the glass and how it was rolled yeah it should be damn near flat, within a few thousanths on average.
If we are talking about tempered glass that is a whole different story the thinner the glass the harder it is to hold the flatness since you heat it up in an oven to several hundred C and then air quench cool it quickly. On a thicker sheet you will get better flatness then on a thinner sheet since it will warp if not heated and rolled (not through a press it just oscillates back and forth on ceramic rollers in the oven to ensure even heating) properly in the oven. Which brings up another point if the oven that heated it had a few heating elements burnt out or missing or the recipe was off when it was run through the machine this can also cause problems with the glass as well.
How do I know all this? I have set up and programmed several glass cutting, tempering, as well as glass laminating automated lines over the years in relation to my job.
I will say that all glass has quality control checks in place and each batch is tested for flatness and clarity. Tempered is tested using a mechanical center punch to study shatter pattern and size of the glass chips to determine if proper heating occured through the test pane.
So while it is a bit of a crap shoot in regards to flatness. It is still the most readily available, and most accurate for the money material that you can use to gauge flatness.
and for what we are doing with it. It will more then suit your needs.
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- Joined
- Dec 5, 2003
- Location
- Huntington, WV
I think that everone knows that it isn't flat. But it is the most logical, easily acceptable, closest thing. The key here is that the glass surface is flatter that a lot of (or maybe just some) heatsink bases. Glass is a liquid that has been poured into a sheet and cooled. And the surface of a pool of water is about the only true flat surface in nature. But keep at it broken003, and maybe you can change some peoples minds. Remember, everyone used to know the world was flat too.broken003 said:
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- Sep 9, 2003
- Location
- New Jersey
Glass flat? My glass is round and cy...cy...cylindrical with a drink in the bottom of it. Cheers!
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- Mar 11, 2001
- Location
- Auburn California
i use a 6" by 3" piece of of glass for lapping by hand no probs here.
yes glass is not flat by any means but with skill and practice it works the best for what we have too work with and does the job in the rite hands
yes glass is not flat by any means but with skill and practice it works the best for what we have too work with and does the job in the rite hands
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- Aug 30, 2004
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- Santa Barbara, CA
Now mate,
I work with glass that is "Optically flat" everyday (not used for lapping, but in Optical Physics). I mean flat to lambda/4 of 1/4th the wavelength of a particular color of light (for eg. 1/4 *852 nanometers). You can almost get glasss as flat as you want. As larva precisely pointed out, the hand motion negates any benefit of having a super flat surface.
The general rule of thumb I would recommend is that see if two pieces of glass stick together if pushed against each other (this is really extreme though). This happens when air is expelled out between the contact surfaces, and the atmospheric pressure acting on the outer surfaces holds down the two panes with a measure of rigidity.
Hope this answers your Q
S-N
I work with glass that is "Optically flat" everyday (not used for lapping, but in Optical Physics). I mean flat to lambda/4 of 1/4th the wavelength of a particular color of light (for eg. 1/4 *852 nanometers). You can almost get glasss as flat as you want. As larva precisely pointed out, the hand motion negates any benefit of having a super flat surface.
The general rule of thumb I would recommend is that see if two pieces of glass stick together if pushed against each other (this is really extreme though). This happens when air is expelled out between the contact surfaces, and the atmospheric pressure acting on the outer surfaces holds down the two panes with a measure of rigidity.
Hope this answers your Q
S-N
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- Apr 22, 2005
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- A Labyrinth
I love it when discussions gets this technical. You see this on discussion boards about telescopes when trying to grind the primary mirror. There you are going for the perfect parabola else you end up with an expensive dinner plate or punch bowl. If we have to start figuring our glass for heat sink grinding, we might as well go to the PMEL lab and have them machine off a piece or hardened metal that when two pieces make contact you have a problem pulling them apart. I you would swear the things bonded. This is why we polish the sinks, I think rseven just though up in one.
"It's pass 2am and my right brain is saying WTF is a parra-bola?"
"Is that edible"
."It's pass 2am and my right brain is saying WTF is a parra-bola?"
"Is that edible"
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How did you know?AlabamaCajun said:I think rseven just though up in one
"It's pass 2am and my right brain is saying WTF is a parra-bola?"
"Is that edible"
Hey, a Parabola? I believe Sally Bowles had a parabola in Cabaret.
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- New Hampshire
good points and info in this thread! it's all relative because nothing can be manufactured that is absolutely flat.
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- Apr 22, 2005
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- A Labyrinth
Thats good :LOLrseven said:How did you know?
Hey, a Parabola? I believe Sally Bowles had a parabola in Cabaret.
Answer: Found the glass next to sink, and the glass was half full,
Jalousie glass may work. Its the kind seen mostly in the south where you turn a crank and the glass slats open. One side might be pitted, but the other should be smooth and some slats are thick up to a 1/4.
Sally Bowles may have been a little Jalousie or the other women's parabolas in Cabaret. (français)
