How to smooth a rough glass edges into a sparkling smooth surface.

Lots of variables here.

How big are the pieces? How thick is the glass? Just POG (plain old glass)? No patterns or textures? Clear in color?

This glass has to sit edge to edge in a vertical position and the top piece has to slide on the bottom pieces' top edge?

If you are talking about pieces of glass that is the size of your hand, there are several people on this glass forum who do beveling and could do it for you. Any bigger, and I think you'd better be looking for someone who bevels mirrors or table tops.

It is possible to grind the edges of glass perfectly straight..well, within reasonable tolerances, (a few .001"), and to polish those edges as smooth as the face of the glass.

However, it seems to me that the edges would have to have some small radius to them, otherwise you'd be succeptible to chipping the edges and/or cutting yourself. And that small radius might be visible, even if it were polished, too.

Any chance you could post a link to a photo of this prop?

The 2 pieces will have to fit together so well that there will be no gap, and therefore no air in the gap to cause reflection and refraction. For a sliding surface, that level of straightness will have to be maintained for the length of the seam.

Perhaps you can lap the 2 pieces against each other?

D

wrote: The 2 pieces will have to fit together so well that there will be no gap, and therefore no air in the gap to cause reflection and refraction. (clip) ^^^^^^^^^^^^^^^^^ How about introducing a drop of liquid with the same index of refraction as the glass?

Sam

Not sure I understand what you are doing but the usual method that optics people use to hide interfaces is oil/glue of the same refractive index as the glass. Doesn't take much if you are using float glass, since it's already nearly perfectly flat. Mineralogists use oil to measure refractive indexes so you might ask around in that part of the web.

Water works pretty well for a lot of applications, like the old disappearing quarter illusion where the glass circle sticks to the bottom of the glass by surface tension and is virtually invisible. I'd try it first, since it's cheap and readily available. If you're not doing close up work, you can be a lot less picky. A couple feet of distance will hide a lot of mismatches.

A few distracting parallels will help hid things too. The eye tends to ignore repeating patterns (probably part of our rodent ancestors filtering out the leaves to see the predators), so you can hide a join in plain sight if it's part of a pattern.

Sounds like an interesting project.

Jim

Take it from a guy that does optical glass work that you'll never get a fit good enough that you won't see the gap except at a very narrow angle. However, you can put some oil, cooking oil or such, on the joint and it will go away on you real easy. You don't need much oil to do the job if your glass is good and flat but you can't touch that surface with anything else or you will wick up some of the oil and thus have a problem You do need to grind and polish the edges flat to at least 1/4 wave of flat and parallel to each other or the effect may not happen. You also need to keep the corners of the edges as square as you can which means that you're going to have to handle those edges very carefully as any chips will happen with a mild touch with something hard and the chips will show badly if not destroy the glass. Don't even plan on hand edging the glass but rather do it on a machine so that the long length will be flat. I'll note that large diameter flats (6" and larger) tend to be rather expensive as they are flat over the whole area and you're going to be even more expensive because the work won't be common work that is done by the shop. You might want to specify that they do a dozen of them at a time which will bring the cost of each piece down by that amount. Also note that an optical shop will normally chamfer an edge so you will have to specify that the edges be fully sharp and this will be helped by doing a bunch of the surfaces together.

-- Why do penguins walk so far to get to their nesting grounds?

Ahh this is a much bigger trick than the trick you'll be using this for is my guess.

I'm thinking I know somebody who is just itching to sell this guy a wet belt sander. Wouldn't that do the trick? :

One trick from woodworking (or somewhere... I can't recall where it is that I used this) is to grind the two pieces against each other. No need for a reference "straight" piece -- the two will self-correct for any non-straightness.

But it sounds like that would be awfully hard to do with glass by hand.

No guarantee they'll be straight, that way. They can have an equal curve, and still fit each other. Afair, the early toolmakers used to lap *three* straight-edges against each other (in all possible pairings). That way, they have to come out flat.

"Moonraker" wrote

Thanks for creative responses from the posters. To get an idea, here's a miniature image I'd just drew.

The real one willbe 2 x 1.5-feet total. I'll be using the thinnest POG for a table top.> This glass has to sit edge to edge in a vertical position and the top piece> has to slide on the bottom pieces' top edge?> If you are talking about pieces of glass that is the size of your hand,> there are several people on this glass forum who do beveling and could do it> for you. Any bigger, and I think you'd better be looking for someone who> bevels mirrors or table tops.> It is possible to grind the edges of glass perfectly straight..well, within> reasonable tolerances, (a few .001"), and to polish those edges as smooth> as the face of the glass. I didn't believe it was possible to polish the glass as smooth as the surface of the glass itself. If lapping by hand is difficult, what polishing tool might work on a milling machine head?

The sharp edges are an acceptable risk but the design will put safety into account.

I was in Japan and saw the amazing magic trick performed. I knew who ever made this prop must have use a fairly expensive equipment to get the glass polished so smooth. The good part was that the magic prop can be operated safely.

Not the right approach. Polishing glass is a 4-5 step process. You can't do it with a milling machine. Glass has to be water cooled while polishing. Find a commercial glazier that has a beveling/polishing machine. The kind of place that makes glass table tops. They can edge polish the glass. You can't polish glass by sliding it up against another piece of glass. The final polishing step is a SLOW speed felt wheel and a slurry of Cerium Oxide.

Excuse this newbie for poking her nose in (a pokey nose?), but after reading this posting for a time, I was wondering if what you really want isn't acrylic? First, it is about half the weight of glass, which I suspect would be a consideration for a performer. Secondly, it would make the safety issue a lesser issue. And third, I understand that it is frequently used in magic props in place of glass, making the one you saw in Japan possibly acrylic. Oh, yeah..fourthly (?) it is used in aquariums alot...specifically because it can be made colorless (as opposed to thicker POG which tends to appear greenish) and the seams can be made to appear "invisible", both through polishing and chemically. Hey, it looks like glass 'cuz it's magic!

Just a thought.

alot...specifically

Very interesting...and the edge of the plastic can be "flame polished".

"Moonraker" wrote

Sound like a good idea but I have a few questions...

Any scratches or finger prints can foul the trick. Can that be practically removed easily?

Will it work with the drop of liquid/oil/glue with the same index of refraction as the glass?

Should I use Cerium Oxide for polishing acrylic?

When tapping the acrylic with a silver ring, will it sound like glass?

Thanks

alot...specifically

removed easily?

refraction as the glass?

Plastic will scratch.

Dunno about the oil for the refraction.

No. don't try cerium on plastic. Plastic edges are flame polished.

It won't sound like glass....

I repeat....go to a commercial glass shop and have them make this. You might have them make some polished chamfer edge bevels and "flip" one so the two chamfers were the mating faces? Might be less apt to chip and have sharp edges. Blood is a dead giveaway that you were tricking somebody....

Glass can be had in waterwhite if needed but I'd rather use the plain green glass for this trick as it will tend to hinder the viewing of the oil on the glass surface as the viewer would tend to understand green glass a lot better and when the edge disappears due to the oil, he'll be more believing of the trick. A flame polished edge of an acrylic sheet won't be flat enough to do the oiling trick on the edges either so you need to polish them with the abrasive techniques and make sure that the edge is good and square - you will still have the location of the edge marked with a V if you don't get that edge square.

-- Why do penguins walk so far to get to their nesting grounds?

No, it's a literal description of running over the cut edge of a piece of acrylic with a propane torch. It takes some finesse, but does work, though not in this case where a very flat surface is required.

Ned Simmons