Day 9
The Table Top
The frame was going well; it was now just a matter of mounting the equipment and arranging the table top. Having taken measurements of the frame I extrapolated a couple of different size table tops that I would potentially buy. The original idea was to have a 10cm border all around the frame however this proved to be a little extreme with the overall width calculating at about 2 meters. I eventually settled on a 7cm overhang on the sides with this being reduced vertically to only 3cm as to decrease the distance between the user and the projected screen on the table top.
The local glazier only had one frosted glass available in 10mm thickness called Matlex. I took a sample home with me to test out with the projector to see how well it caught the projected image; the result was not good. Below on the left is the drafting film which was used on the test screen, the middle is the Matlex and on the right the Matlex from an angle. The image was quite appalling.
Due to the poor image on the Matlex I decided to purchase the glass as clear 10mm toughened glass, once shaped and with polished edges the whole top cost $1280 delivered and weighed in at a hefty 60kg. I tested a frosted laminate from a local window tinting company and found it comparable to my existing test screen.
Whilst testing these new materials I noticed a strong correlation to the opacity of the materials and how well good they looked at lower angles. Since I was building a coffee table and it wasn't intended that you would stand above it while using it a wide viewing angle was more important than top down clarity. I came across a more opaque drafting film (whiter to the naked eye, seemingly thicker too) that from above looked washed out however when viewed from a seated position was a lot brighter than the previous film and using two layers of the existing film gave a similar effect. In both of the below photos the left half is the original film and the right half is the more opaque film.
At this stage the intention was to use one or two layers of the frosted laminate available through my local window tinting company to provide the projection screen however I also came across specialised materials available from a few companies to provide for this situation; Rear Projection Films (RPF) that can be applied to existing glass and projected onto to create a rear projection screen for things like displays in shop windows. Having decided to go with the clear glass and laminate later however also provided me with the opportunity to decide later, I could initially tape my drafting film onto the glass when it arrived to use in testing and calibration while I further investigated other surfaces.
Mounting the Equipment
After a few attempts I finally managed to come up with a stable enough mount for the projector that was adjustable in both pitch and roll that allowed me to square the projection up with the screen. I also then made a mounting bracket for the camera using a similar approach. I reused some of the slotted angle iron to make a support for the bottom of the mirror and to hold the computer tower in place. The only thing then preventing me from moving the frame easily was the test screen, so I did away with the support underneath and made a support that would allow me to sit it on from above the table and easily remove it. I put some plastic chair leg 'tips' on the bottom of the frame legs to allow it to slide and used rubber ones on top which would be used to support the glass table top. The white rubber-foam pads that I had previously used on the top of the table legs were relocated to the tops of other items that the glass may or may not touch such as the cross support for the projector and the top of the computer tower.
As you can see from the below profile shot the glass would have ~5mm clearance from the top of the mirror and the computer tower however it was definitely cutting it fine given that the rubber feet would compress under the weight of the glass top.
All that was left to go at the end of the Saturday of the 5th weekend was to mount the speakers and once the glass arrived put it in place and test out the screen. Below is one last shot with the test projection screen in place taken the following morning.
With everything cable tied up, all that was left was to await the arrival of the table top.