It is with great trepidation and mixed feelings that I’m launching into my screen building. The reason for the emotions is that I am so desperate to watch some movies in my HT since I’ve hardly seen any since I started my build and the movie-catch up is going to take weeks.
Anyway, I haven’t come this far to give up on my screen plan, so here is the first installment.
130” wide curved AT screen with integrated (within the frame border) horizontal masking with full independent left/right masking control. The goals I’ve set are that I want to create a professional job that is less than 4” thick so that it disappears into the screen wall frame, the mechanism needs to be simple to reduce build and setup time and the budget should be around $1600. Possible….??? We shall see.
After numerous design scribbles I realized that building a curved screen complicated what really should be a fairly simple process for a flat screen. Some of the problems include attachment to the screen fabric along the arc whilst allowing a very close fitting mask, bending of any linear slide mechanism for the mask, keeping a simple drive mechanism that can stay within the 4” thickness goal.
The basic construction approach is shown here:
The goal is to leverage the precise repeatability of the new Somfy ILT motors and to use a constant spring to provide closing tension. I.e. no pulleys, no wires, just the KISS approach. Of course the devil is in the details and I’m under no illusions that a cheap, curved and smooth linear motion track that doesn’t get stuck is the key. The plan is to have the mask ride right next to the screen fabric (to prevent shadows) and to have a minimal gap at top and bottom for the leading edge of the mask.
Step 1. I wanted to be sure that the size was going to work, particularly the location of the leading edge of the mask at the prime aspect ratios. The leading edge of the mask will be solid and I didn’t want this to fall in the direct path of the tweeters.
Step 2 was to get the horizontal frame members bent to my calculated 42’ radius. My preference was to use an extruded aluminum frame with various t-slot cutouts for convenient attachment but I completely failed to find somebody to bend these or to purchase them pre-bent. The problem with bending aluminum is that it is difficult to keep the extrusion profile intact without the correct bending die or by bending as the extrusion is made.
My fallback was to opt for a steel frame. Aluminum would have been nice and lighter but one advantage of steel is that it is much easier to bend and weld. So off to my local steel yard to purchase the steel and to get them to run a couple of pieces through their Eagle rolling machine. Cha-ching: $320 including bending.
Once home I cut the pieces to size and welded up the frame, taking care to ensure it stayed square. The primitive rolling machine the metal yard used did get the radius curve correct but gave me a slight warp which I needed to work out during the welding process. You can see a laser level in the second photo keeping me honest.
Once welded it was outside to do a bit of cleanup of the welds on the inside edge (the side that I plan on using a cunning plan to mount the screen fabric). In fact the screen attachment plan is so secretive that I don’t know it myself yet…
Then a coat of primer. You can see the cleaned up weld to create a perfectly smooth surface.
It was precisely at this point that I panicked and questioned what the heck I was doing and call up Jason Turk at AVS to see if I could get a 130” non-masking SMX screen cheap. No luck. A few beers later I calmed down and got my wife to lift this monster back into the garage. Then I panicked again… what if this wouldn’t fit through the theater doorway? Luckily, I think it will simply due to my fortunate door arrangement (alignment).
I then spent the rest of the day on-line ordering parts:
2x Somfy Sonesse LT50 ILT motors: $740 (yikes!)
RS485 interface: $60
2” tubes and roller blind mounting h/w: $100
Grommets + tools, rubber rings: $32
USB to RS485 interface: $40
6061 aluminum bar, t-tracks, etc: $70
SeymorAV CenterStage XD fabric: $280
Plus steel, total to date: $1,622. Well, that’s blown the budget already so I might as well give up... Seriously, other than some miscellaneous fabric, misc hardware, some scraps of steel plate and some MDF (most of which I have lying around) I think I have all the raw materials I need.
I should probably explain my choice of the expensive Somfy motors a little. There is no way to get around the fact that these are expensive, but I know from experience how much time a motor control system takes to build when I converted my home mill/lathe to CNC. The neatness of the Somfy system, the quietness of their Sonesse motor (44 dbA), the ability to program 16 intermediate stopping positions, repeatable encoder based positioning and the fact that the RS485 control bus can easily interface to IR/RF/Z-wave, etc makes this an obvious cost/time trade-off to me. If anybody is curious I’d suggest you read up on the ILT line of motors and their “SDN” control bus. I briefly looked at the SMX masking system functionality and this motor and controllers can do everything that can do…
To be continued…