ok i am coming up with how i am going to build my table so i got an idea i like to have my acrylic to be the lintier surface so i came up with this i hope it works tell me what you think if it will or not work

gray acrylic
red IR leds
black just to keep the IR leds from shining everywhere

what is what? why grey acrylic?

Grey Acrylic
Red IR LED’s
Black casing

i am asking if this would work as a multitouch table i do not know if having 2 acrylics touching each other would make a difference or not. so would the internal reflection reflect threw both peaces of acrylic or just the lower one ???

oh and the acrylic is not Gray it is just to represent an acrylic

Red IR LEDs? Red and IR have two different wavelength ranges.

I don’t two acrylic sheets on top of each other would work, and it is more expensive as well.

If the two pieces of acrylic are touching (at the near-molecular level), you should not have a problem.  One thing you need to keep in mind, though, is the thicker you make the acrylic, the less light you can trap.  I have a 3/8” sheet that works fine.

To test, get the seam between them wet and see if it works.  If so, you should get some MC-Bond.  It will dissolve the acrylic, and reform it as it dries. You can literally fuse the two sheets together as if they were one.  It’s how professional acrylic houses fabricate things.

It will also allow you to clean the drill holes for your LEDs (so you have a seamless transition into the acrylic).  It doesn’t dissolve epoxy though, so if you get epoxy-based LEDs, they will be removable.

hmm very interesting i would probly be to afraid to do it but i bet that it could be dun just would need more led’s than normal and would also probly want to put a reflective like a merer on the edge of the acrylic so it never leaves i bet that would boost the ir light a lot

You need to read up on internal reflection.

At a very steep angle, the light can’t “see” the outside world.  The inside of the acrylic acts like a mirror (look in the shallow edge of a polished piece of acrylic).  If you make it too thick, the angle that the light hits the side at changes substantially - the light can see the outside and is no longer reflected back into the pane.  That’s why if you embed LEDs in acrylic the sides of the LEDs are lit up.  The light is at such an angle that it can escape.

For FTIR to work, you need to make sure that the angle of the light rays as they hit the sides of the acrylic is greater than the light’s critical angle.  If you make it too thick, you’re not going to be able to remedy by adding a few more LEDs.  The problem with thick acrylic is not its volume, but the fact that light can escape the pane.

And please, use real words in your posts. =)