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Old 4th February 2005, 11:10 PM   #1
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Default Ellipsoidal reflector-building one

I'm thinking of building myself an ellipsodial reflector to my upcoming 7" project. It will use the familar ellipse (in cartesian coordinates x^2/a^2+y^2/b^2=1 where a,b is the half axles) that is rotated and then cut by two planes(perpendicular) to achive something like this image.
So it's basically a ellipsoidal reflector cut in half but with a shade around it so it can be assembled together with bolts or dot welded together. The idea is that this will be done in practice with the use of a english wheel Click the image to open in full size.
I'm not really sure if will be able to do it, and if it actually will be impossible to make to similar shapes. The material I was thinking of is either aluminum or polished stainless steel. I have seen some great results with this wheel that is used to make car chassie details. The question is if it's even worth the job, but then on the other side could it be fun to see how it would turn out. This is btw my first post, been reading some but i can't really find if there is any good MH lamp/ballast distributers in europe?

/Gilgamesh
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Old 5th February 2005, 08:22 AM   #2
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And the upload did ofcourse not work properly.
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File Type: jpg reflector.jpg (24.0 KB, 697 views)
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Old 5th February 2005, 05:49 PM   #3
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Most excellent.

I'm playing with something similar but in 1/3s. This would avoid any dark line from the joint. It is easier for the eye to notice if is simetric - left/right or up/down. going at an angle through the lcd would be harder to spot.

Is that you with the rolling press? Then you have access to a shop. You can also consider spinning one piece steel with spreading press wheels from inside. Must have supports outside so it wont buckle/deform.

fun stuff
...........
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Old 5th February 2005, 09:36 PM   #4
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Oh my no it's not me, just a pic from internet I'm quite a bit younger than that To make it in one piece will probaly be very hard, i'm considering mayby to make it like you said out of more bits, but it depends on how hard it will be to make them look about the same!
I got access to a metal sheet workshop due to my father, the only problem is that i'm at uni now ---- 1300km from him but i'll be going home at easter so i hope it will be time to assemble my projector then, if i got all the parts that is. I'm thinking of building the chassie it of polished stainless steel, it will look just like it is chromed then, and put in some red LEDs for fan holes etc.
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Old 5th February 2005, 10:07 PM   #5
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Default reflectivity

Even the very best stainless steel is only 65% reflective. Polished aluminum can get up over 90%. I think that dictates your choice of materials, unless you want to pay for silver plating the stainless!

I was thinking of trying this with at least four pieces. I would make a stamping mold, so I could make many identical pieces. Then just bolt them together.

BTW: You don't need to plot the equation to draw an ellipse. Just mark the two focal points on your template material. Put a little nail or pin at each point. Cut a piece of string or wire that is larger than two times the distance between the two focal points, and tie it in a loop. Put the loop of string over the pins, and then use it to guide a pencil as you draw the maximum-sized shape all the way around. That is a perfect ellipse. You can vary the width of the ellipse to match a condensor fresnel by making the loop longer or shorter.
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Old 6th February 2005, 12:17 AM   #6
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Yes, aluminum or coated steel works. Not being a machinist i would find aluminum harder - requires more skill i think to keep an acurate shape with soft material. Steel is more resilient and puts up with my level of machining skill.

One note on the lip- I dont have a lip all the way around. When joined they leave a small gap (radius of bend) unless you weld and grind. Consider grinding the edge like a knife chamfer and overlap. The joint will be smaller i think.
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Old 6th February 2005, 03:01 AM   #7
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Quote:
BTW: You don't need to plot the equation to draw an ellipse. Just mark the two focal points on your template material. Put a little nail or pin at each point. Cut a piece of string or wire that is larger than two times the distance between the two focal points, and tie it in a loop. Put the loop of string over the pins, and then use it to guide a pencil as you draw the maximum-sized shape all the way around. That is a perfect ellipse. You can vary the width of the ellipse to match a condensor fresnel by making the loop longer or shorter.
Why not just use Cad or Light Tools

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Old 6th February 2005, 08:32 AM   #8
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True but just so everyone knew what I was talking about
I'll focus on using aluminium as a material then! But because I do not know which lamp I will be using is it hard to design anything right now
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Old 6th February 2005, 10:09 AM   #9
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Default MH light distributor

Quote:
This is btw my first post, been reading some but i can't really find if there is any good MH lamp/ballast distributers in europe?
I'm looking for a light distributor myself. I know of one in germany http://www.gadaffy.ch.vu/ and I think I'll order from there. It is a DIY projector store, so it has optics and other stuff too but it would be good to compare with other sources.
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Old 7th February 2005, 09:54 PM   #10
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That seems like a decent place. I got some extra costs when i ordered from hongkong from ups, so right now was it almost as expensive as ordering it from a store in sweden. So my project will be a tad more expensive than i thought it would. I'm probaly going to use the 150W setup with the ballast. Does anyone know anywhere else to order ballasts in europe? I saw 150W ballasts @ebay with ignitor for around 36€+shipping.
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