Mechanical horizontal masking system for 1.78 fixed frame screen

[mjg100]

I posted this in my screen thread, but I noticed in another thread a poster asking about building a mechanical masking system so I decided to make a new thread for any posters that might be interested.

I have now added an adjustable horizontal masking system to my 106" fixed frame screen.

My masking system consists of the following items:
1. 7 ply fiberglass faced plywood. (Had this at the shop so I used it)
2. Two pieces of flat stock sheet metal. (Had this at the shop. I think it is 24gauge.)
3. Flat stock of sheet metal. (Had this at the shop. I think it is 28 gauge.)
4. 12' of 1/16" air craft cable. TSC
5. Triple black velvet. SY Fabrics
6. Two small turnbuckles for cable length adjustment. TSC
7. Four 1/16" cable clamps. TSC
8. Two oval chain links to connect turnbuckles to masking system. TSC
9. Two screw hooks to hang pulleys. TSC
10. Four heavy duty draw slides. Lowes
11. Two pieces of 12" long 1/2"x1/2" aluminum angle. (Had this at the shop.)
12. Sheet metal screws, wood screws, wood glue and 3M Super 77 spray adhesive. (Had these materials at the shop.)

I made four sheet metal angles (24 gauge) 3/4"x2"x8" long for brackets. These were fastened vertically to the back of the screen frame, about 1-1/4" in from the outside edge of the screen frame. I attached the draw slides to these brackets. I made four sheet metal (28 gauge) U-brackets to wrap around the end of the screen frame. These brackets have a 3/4" leg coming off of the "U" so that I could connect the other half of the draw slide the the "U" bracket. The "U"-brackets are 6" long and the legs are 3" (face) 2-3/8" (side) 1-1/4" (return at back) and 3/4" leg to attach to draw slide. With the brackets and draw slides in place I now have four pieces of flat sheet metal (face of "U"-bracket 6" high x 3" wide) in front of my screen frame to attach the masking panels. These brackets are free to move (18" total) up and down the vertical face of my screen frame.

For the masking panels I cut three 8" wide strips from the plywood. The third strip is need so that I can make two panels 98-3/8" long. I beveled the top edge so that when the panels are in place there is a slope on the edge towards the screen. I used wood glue and biscuit joints to make the panels the length I needed. Next I simply covered the panels with Triple Black Velvet.

Since the distance from the back of the masking panel to my screen is about 1-1/4" I needed a way to extend the masking back to the screen. For this I made two sheet metal angles (24 gauge) 91-1/2" long with 1-1/8" leg and a 2" leg. inside to inside of my screen frame is 91-3/4" so I have 1/8" clearance on each side. These sheet metal angles serve two purposes. One is to extend the masking to the screen and the other is to keep the masking panels from ever bowing. Angle is attached to the masking panel every 10" with wood screws. The angle sticks up above the masking panel 1/8".

To cover the angles I cut two strips of velvet 4" wide and 94" long. I sandwiched the velvet between the masking panel and the sheet metal angle. The ends of the velvet were folded back and tucked under the ends of the angle. This created an edge that extended about 3/16" past the end of the angle. This was done to fill the 1/8" gap between the masking and the inside edge of my frame. I then sprayed the inside of the angle with Super 77 and wrapped the velvet around the angle.

I removed the sheet metal "U"-brackets from the screen. They slide off when you press a release button on the draw slide. I then screwed the brackets to the back (end) of the masking panels. Then I simply slid the brackets back onto the draw slides. With the masking panels fully open (1.78) the 91-1/2" long sheet metal angle rests against the inside edge of my screen.

The cable system is very simple and used by others. I attached the 12" long x 1/2" x 1/2" aluminum angles to the back of the "U"-brackets on the top mask so that I would have a cable attachment point six inches below the masking panel. This allowed me to mount the two pulleys lower so that they are behind the screen rather than above the screen. I installed the two pulleys so that the top of the pulley is about 1-1/2" below the top of the screen. I connected a turnbuckle to the bottom mask and ran the cable up to the pulley and then down to the bottom of the 1/2" x 1/2" aluminum angle connected to the "U"-bracket. I did the same on the other side. I adjusted the turnbuckles so that the masking when fully open has the 91-1/2" sheet metal angle resting against the inside edge of my screen. Now when one panel is moved the other panel moves the same amount in the opposite direction.

I did not take pictures during the install, but here are pictures of the masking panels in place.

1.78 screen aspect ratio
http://i243.photobucket.com/albums/f...m/IMGP0576.jpg


2.40 aspect ratio
http://i243.photobucket.com/albums/f...m/IMGP0580.jpg


2.40 aspect ratio (the above picture over exposed to show masking system)
http://i243.photobucket.com/albums/f...IMGP0598-1.jpg


Close up of lower left corner. (over exposed so that you can see the masking)
http://i243.photobucket.com/albums/f...m/IMGP0599.jpg


Cable system. This photo was taken before I painted the "U"-bracket black.
http://i243.photobucket.com/albums/f...m/IMGP0585.jpg

The key to this whole thing is the 91-1/2" velvet wrapped sheet metal angle. Since the mask panels are in front of my screen frame I needed a way to get the mask edge to the screen and yet when fully opened would not block off much of the screen when watching 1.78 material. The only problem with my masking, you can't just reach up with one hand a pull it into place. You have to adjust each side of the top masking panel to get a perfect alignment. You only have to do this with one mask since the masked are connected with cables. Not a big deal because I can slide the masking into the correct position in about 5 seconds.

I have a solution for the above problem and it will be cheap to implement, just have not had time to do anything with it yet. I am going to get two or three 1/2" stamped steel pillow block bearings and a 98-1/4" long, 1/2" steel pipe. That and a little bit of wood blocking is all I will need. The pipe with pillow blocks will be placed horizontally behind my screen so that the edge of the pipe lines up with the 1/16" cable. Then I will just need to wrap the cable around the pipe (2 wraps). This way when you pull down on the masking the pipe will rotate and move both ends of the masking the same.

Added
I added the pillow block bearings and a piece of 1/2" EMT to my horizontal masking system as I talked about in the last paragraph of my post above. With the cables wrapped two turns around the EMT, both side are now tied together. Now when I pull down on the top mask to slide the masks into place the top mask moves down level and the lower mask moves up level. I think my masking is complete.

Picture showing the 1/2" pillow block bearings and 1/2" EMT.
http://i243.photobucket.com/albums/f...m/IMGP0601.jpg

I used these pillow block bearings.
www.thebigbearingstore.com/servlet/the-63/1-fdsh-2"-Pressed-Steel-Pillow/Detail

The cables, clips and drawer slides are concealed behind my screen in fact it is contained in the 3.25" width of my screen frame. The only parts that are directly behind my screen are the 1/2" EMT and the 1/2" pillow block bearings. I painted these items flat black. The blocking was already in place to space my AT screen out from the wall.

[umr]

What do you think this cost you?
Posted via Mobile Device

[mjg100]

umr wrote:

What do you think this cost you?
Posted via Mobile Device

It cost me $112. I already had the lumber, sheet metal, screws and glue. I had to buy:

Approximate costs
Velvet $29 (I have some left over)
Cable, pulleys, hooks, clamps, oval link and small turnbuckles $25
Drawer slides $24
Pillow block bearings $32
Emt $2

Since I added the pillow block bearings I am real happy with the system. I can reach up anywhere on the top mask and pull it down into position or move it up and both masks move together and stay level. I would have had to spend thousands to buy a masking screen that performs as well as this does.