I've had a few questions about this build asked in my theater build thread. I thought the information would be helpful here also:Question: is MDF ok for screen frame and can I explain the frame to steel chassis mounting better:
No problem with the screen frame being MDF. My horizontal pieces are exactly that. The vertical sections where made from some 2" finger jointed pine I had around the shop, but the horizontals are made from two strips of skirting board (baseboard for the Americans ;-) laminated together with wood glue AFTER being partially routed. The reason why I performed most of the routing prior to glue up was because the frame is curved. I glued the two strips using the frame as a curve profile to make the pre-bent piece. Routing the curve section would have been unwieldy. In retrospect I might have been able to make a straight frame and then bend as it was clamped into place, but I think the pre-bent approach made for a much cleaner and risk free fit.
I'll see if I can put together a sketch of the frame profile (horizontal sides) and the frame mounting a little bit later but I'll try and describe the build process:
1. the aluminium (British spelling just for you) flat was clamped onto the bend steel frame so that is was flush to the inside edge and overhung the outside edge by about 3/4" (this is important). Holes were drilled and regular intervals (6" I think) sized for future tapping.
2. The aluminum was removed and the holes in the steel were tapped. The aluminum was drilled oversize and countersunk so that it could be later fixed with countersunk head machine screws for a flush surface.
3. In a clean
workshop the screen material was layed on the frame and the rubber O-rings were fitted (obviously I has screwed in self tapping screws with a nylon sleeve on the back side to match where I had fitted grommets around the edge of the screen) so that it was wrinkle free. The location of the tapped holes were marked in the screen material.
4. The screen cloth was removed and the marked holes were punched with a home made punch to about 5/8" or so. The reason for this will aid understanding of how it all then fits together...
5. After painting of the frame, the screen fabric was fitted for the final time. I let it sit overnight so it was correctly stretched and tensioned. Then the aluminum flats were re-attached to the steel frame with countersunk machine screws. These screws passed through the holes in the screen material and essentially clamped the screen material in place. I did think of adding small washers so the aluminum stood above the steel and would allow the screen material to retain tensioning from the O-rings. This probably would be an improvement, but my clamped approach has worked perfectly so I don't think it is necessary. I also believe the aluminum flat stiffened the steel so I did not get any additional sag once the screen was hoisted vertically.
6. Ok, so now the frame is placed on the aluminum and squared up and set so that the masking edge rods run free (equal separation across length of . It is attached through some holes drilled in the part of the aluminum flat that overhangs the steel ... you can screw through the overlap and into the wood frame.
7. Note that I did find that the 1/8" aluminum flat was not sufficient to prevent the masking from binding. Either shim out with washers as described in step 5 or do what I did which was to stick a strip of approx. 1/8" think plastic tape on top of the aluminum before the frame thus lifting it an additional 1/8". Edit: Or use 1/4" aluminum flats instead
Here is the hastily drawn visual:Question: follow up on size of washers to separate aluminum strip and steel to allow screen material to move :
The spacing washer is just an idea. The washers would have to be small enough to sit in the punched holes in the screen fabric. The idea is that you would want the fabric to be able to move a little and not be trapped. Penny washers would be too big even if you enlarged the punched holes. BTW I'm not advocating this approach since I have not found it necessary after living with my screen for two years -- perhaps a good idea with a different, more stretchy, fabric though...
1/4" aluminum strips would be perfectly fine, just a little more expensive. The extra tape spacer was an afterthought because although the edge of the masking moved perfectly well initially, it became tight when wrapped in velvet.
Here are the pics of the profile as promised:
Couple of notes:
- Frame dimensions are approximately 4 1/2" wide and 1 3/4" deep.
- The inside routing profile is, from left to right: (i) cutout for bungee cord (aluminum strip just covers this to prevent cord from jumping out), (ii) track cutout (depth so track is flush with surface), (iii) little slot I used to staple the velvet so that the staples could not snag on the masking as it moved (possibly not required)
- The center section, where the inside of the track ends had a pocket routed out so that the bungee cords could cross over.
- The vertical parts of the frame obviously are different on the inside to (i) create a pocket for the roll of masking fabric and (ii) allow the insertion of a tube for smooth edge for the masking to rub against -- I think my thread has enough pictures of this but let me know if you have questions.