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Author Topic: Need ideas on how to repair Sega hologram parabolic mirror  (Read 5274 times)

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RandyT

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #40 on: December 20, 2005, 11:30:35 am »
I am siding with Avery on this. Here's what I would do. From the appearance of that crack, I wouldn't go messing with any form of heat at all. Glue it back together with a black sandable epoxy. When it glues together, there will be raised portions of epoxy. Get some fine grit sandpaper, and wet sand it slowly back down, being careful not to take material off the surface, but with a fine grit that shouldn't be too much of a problem. Then get yourself some scratch filler, I would think you could use the stuff that fixes scratched CDs, or possibly even some wax, to fill in the small scratches and get the finish back to a high gloss. My $.02 on the matter.

Perhaps something like this - http://www.koalaproducts.net/polish.htm


Optics aren't car bodies.  Hand grinding a curve that is accurate enough for optical use is nearly impossible.

Also, transmissive optics are very different from reflective ones.  You can get away with murder on the transmissive ones, but not reflective or "imaging" optics.

But hey, if someone is really bored it might make a good waste of a weekend  ;)

RandyT
« Last Edit: December 20, 2005, 02:43:34 pm by RandyT »

J-Rod

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #41 on: December 20, 2005, 11:35:29 am »
Yeah maybe, I think it is worth a shot though, as it's already broken. He's not going to make it *worse* by trying to glue and wetsand. And as far as it being optical quality, look at the picture. It's already got a decent amount of scratching, this isn't going into a telescope...

As long as he's careful about sanding into the material too much, there's not going to be crazy distortion from a 1000 grit wetsand. Look at the polish the plexiglass took.


« Last Edit: December 20, 2005, 11:38:03 am by J-Rod »

RandyT

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #42 on: December 20, 2005, 12:57:34 pm »
And as far as it being optical quality, look at the picture. It's already got a decent amount of scratching, this isn't going into a telescope...






I guess you didn't see the part where I wrote:

Also, transmissive optics are very different from reflective ones. You can get away with murder on the transmissive ones, but not reflective or "imaging" optics.

It's not going in a "storm door" either.  And FYI, optics similar to these are used in telescopes.  How do you think they collect the tiny amount of light from stars billions of miles away and focus it on a small receiver?  This application is not as critical, for sure, but the function of the optic is very similar.

RandyT
« Last Edit: December 20, 2005, 01:02:10 pm by RandyT »

ChadTower

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #43 on: December 20, 2005, 02:08:02 pm »

How do you glue something together that is not physically separated?  To get glue in there he would have to find a way to get separation into which he can put the glue... plus, it's not BROKEN, it is a visual reflectivity issue.  You aren't going to be able to be visually rid of a crack by gluing it.

TravistyOJ

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #44 on: December 20, 2005, 02:30:26 pm »
Im sorry I should clarify the problem.  There are 2 cracks, one long one, and one short one that intersects into the other, making a small triangular piece that broke off.   Right now it is all being held together with tape. 

What if used some sort of glue and pressed together to minimize the seam, and then took some novus deep scratch remover on the seams, and then a couple layers of novus polish?
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ChadTower

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #45 on: December 20, 2005, 02:39:37 pm »

Erm, yeah, you just took a small issue and turned it into a giant issue.


nostrebor

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #46 on: December 20, 2005, 02:48:14 pm »
Randy is right on. Your best bet is to tape it together from the backside as best as you can, live with it for now, and look for another one. any polishing /glueing /heating /voodoo you perform on it at this point will just render it completely useless.

I also suggest kicking the guy who moved it for you in the nuts. Perhaps you could contract Chad to do it.

ChadTower

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #47 on: December 20, 2005, 02:53:12 pm »

If it is close enough I will do it for free since he would have robbed me the chance to play a Holosseum.

J-Rod

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #48 on: December 20, 2005, 03:09:08 pm »
Quote
Also, transmissive optics are very different from reflective ones.  You can get away with murder on the transmissive ones, but not reflective or "imaging" optics.

Yes, I must have glossed over that. I guess what I am not understanding is why the relfective properties aren't repaired by a gloss finish compound, that fills the scratches and fixes divergence. I mean you are the expert on optics apparently, Randy so I'll yield if you can help me understand why it is that filling a void with a transparent compound wouldn't help it reflect better.

Obviously it likely won't work anyways if the crack is so bad that it cannot be fashioned/glued back into a perfect shape. It also might  be a long shot hand sanding, since you wouldn't be able to bend sandpaper to smoothly sand the inside of a concave shape. You'd have to find some abrasive cloth or somesuch. My main point is, he's going to have to find a replacement anyways, so why not give it a try?

DrewKaree

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #49 on: December 20, 2005, 03:12:01 pm »

I also suggest kicking the guy who moved it for you in the nuts. Perhaps you could contract Chad to do it.


You're such a jag.  Didn't you read before where I SAID he's gonna have to start learning how to do stuff himself?  Farming out a kicking is NOT helping him at all.  No soup for you, bad post-fu ;D
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TravistyOJ

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #50 on: December 20, 2005, 03:17:55 pm »
I will give it a try MYSELF, and maybe Ill get lucky and score another one which i will move MYSELF.  :) Thanks for all the suggestions and time.  One last idea, what if I recoated everything is some sort of reflective sheeting like this...
http://www.growell.co.uk/p/0309/Mylar_Reflective_Sheeting.html
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nostrebor

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #51 on: December 20, 2005, 03:19:57 pm »

I also suggest kicking the guy who moved it for you in the nuts. Perhaps you could contract Chad to do it.


You're such a jag.  Didn't you read before where I SAID he's gonna have to start learning how to do stuff himself?  Farming out a kicking is NOT helping him at all.  No soup for you, bad post-fu ;D

I am following the BossX posting methodology... read the last 3 posts and respond. He also allows for simply disregarding all posts by Drew Karee. I'm just learning by example :)

DrewKaree

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #52 on: December 20, 2005, 03:29:46 pm »

I am following the BossX posting methodology... read the last 3 posts and respond. He also allows for simply disregarding all posts by Drew Karee. I'm just learning by example :)


Shows what you know.  He hangs on my every.......werd. ;)

Oh, and Travisty, that'll never work.  Take it from someone who's never done it before ;)
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Avery

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #53 on: December 20, 2005, 05:28:07 pm »
For gluing the pieces together, what about one of those liquid solvent based glues used for models.  You're going to have to be REAL careful not to let it mess up the front.  I'd set it on a pair of saw horses and glue from underneath - let capillary action pull the glue into the crack (and I'd test the glue first on the back, away from the crack, where there's no way it's going to effect the front).

The amateur astronomy crowd grinds their own telescope mirrors (and some damn big ones too), but they have special equipment that I don't think you're going to be able to find for something the size your dealing with.  I think in this case you just want to polish out the little scractches you can.  Reshaping that thing, to any serious extent, is going to be impossible.

Avery

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #54 on: December 20, 2005, 11:42:03 pm »
I was thinking along the lines of Avery But I would consider using liquid methylene chloride (available at most glass Shops) instead of the model glue. Its what they use to glue sheet acrylic together and it wicks into the cracks.

If you do it use tape to hold the pieces together in the exact position once you apply the solvent you wont be able to move the pieces. Whatever you do don't put the tape on the front the solvent will wick under it and make a  big mess.

RandyT

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #55 on: December 21, 2005, 08:36:02 am »
Quote
Also, transmissive optics are very different from reflective ones.  You can get away with murder on the transmissive ones, but not reflective or "imaging" optics.

Yes, I must have glossed over that. I guess what I am not understanding is why the relfective properties aren't repaired by a gloss finish compound, that fills the scratches and fixes divergence. I mean you are the expert on optics apparently, Randy so I'll yield if you can help me understand why it is that filling a void with a transparent compound wouldn't help it reflect better.


The answer is simple.  I'm assuming you have seen a typical "funhouse" mirror.  These are usually made out of polished metal, but could be made out of plastic and coated just as well.

In any case. imagine a funhouse mirror and the distorted effects it creates  This is accomplished by bending the mirror in one direction or another to achieve the distortion required.  If that mirror had its mirror coating stripped away, you could see perfectly through it (not counting refraction) with virtually none of the distortion seen in the reflected image. 

Now consider a spherical (or parabolic) surface that has been meticulously calculated to collect light from an object a certan distance (and angle) from the mirror and then to bring the light generated by that object to focus at a very specific point in space.  Any deviation in angle/curvature is going to move portions of that light disproportionately to the rest of the image, creating severe distortion.  If the deviation is enough (and it doesn't take much) the reflected light will be somehwere else in space entirely and appear as a void, or a very out of focus blob in the image.

This doesn't even take into account whether or not one can polish the plastic to a point approaching the reflectivity of the original.

As for why not?  I guess that's a personal choice TravistyOJ is going to have to make for himself.  But if he has limited funds for purchasing experimental materials for futile "fix attempts" or values his time in the slightest, I was just trying to save him some heartache.

RandyT
« Last Edit: December 21, 2005, 08:41:56 am by RandyT »

TravistyOJ

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #56 on: December 21, 2005, 09:30:40 am »
Yeah, I will try to make the current one i have as best as possible while still looking for a replacement.  The only really way I know to improve it without possibly making it worse is to tape it up as close as possible, and apply some novus.  From what I've gathered, any solvents, glues, etc will probably make it worse.  Please PM if anyone comes across one of these or even a destroyed holo-cabinet with one in it.
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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #57 on: December 21, 2005, 09:33:48 am »
I wasn't grasping what RandyT was saying before, I thought like anyone else that just a high polish woud do it, but the funhouse theory explains it pretty well

Tim

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #58 on: December 21, 2005, 09:50:19 am »
I understand the funhouse effect. From my experience, when plastic breaks, it's usually not a totally clean fault. So you can put the pieces back together and they almost lock, something like a jigsaw. If that's the case, then the geometry should be almost identical. He could test by putting them back together with the tape like he wanted, and testing it out. If the image coalesces into the right spot, then it has a chance. I am bothered by the smallish triangle piece he says broke off though, instead of just one break there's several. His main hope is to look for a replacement in a busted machine, would be much cheaper than trying to have one made. Sucks in any case, good luck with your endeavor. -JC

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #59 on: December 21, 2005, 03:59:55 pm »
For gluing the pieces together, what about one of those liquid solvent based glues used for models.



I don't know what kind of plastic this is made of, but I use those types of solvent 'glues' pretty often. The two main brands that I use are Tenax & Plastruct. Both work great on styrene (which is what most scale model kits are made of) but won't touch acrylic, which seems to be what most here are assuming this dish is made of.

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #60 on: December 21, 2005, 04:52:25 pm »
Both work great on styrene (which is what most scale model kits are made of) but won't touch acrylic, which seems to be what most here are assuming this dish is made of.

Good to know.  Maybe just getting the geometry close and smearing JB weld all over the back of the crack is the right answer then. 

Meanwhile, back at the ranch - is this disk just reflecting a flat screen image that has been distorted to allow for the curvature?  Is it really parabolic or just a spherical section?  Is there a fresnel lense in this setup anywhere?
Avery

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #61 on: December 21, 2005, 05:05:15 pm »
Quote
Meanwhile, back at the ranch - is this disk just reflecting a flat screen image that has been distorted to allow for the curvature?

Yes, basically if you run "mame holo -flipy" that is the output of the JAMMA board.

Quote
Is it really parabolic or just a spherical section? 
I think both, are these terms mutually exlcusive?  Please excuse me on this, since I dont use these words very often. :)

Quote
Is there a fresnel lense in this setup anywhere?
I dont know what that is, but my guess is no.  Its just a TV and the plastic mirror.
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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #62 on: December 21, 2005, 08:05:02 pm »

Quote
Is it really parabolic or just a spherical section? 
I think both, are these terms mutually exlcusive?  Please excuse me on this, since I dont use these words very often. :)


A parabola has a constantly changing curve, whereas a sphere has a constant one.    Based on how this was probably manufactured (blow molding), I'm going to guess that it is a sphere.  Parabolas are more difficult to make, thus much more expensive.

Not to mention that fact that a parabolic segment won't work in that configuration.

RandyT

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Re: Need ideas on how to repair Sega hologram parabolic mirror
« Reply #63 on: December 21, 2005, 10:35:08 pm »
Quote
Is there a fresnel lense in this setup anywhere?
I dont know what that is, but my guess is no.  Its just a TV and the plastic mirror.


Hey Travis, The lensing on the top of that thing is fresnel. It is how they give the illusion of bending the image to stand up on the table.
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