DIY Screen: Mitered or un-mitered joints

[mpompey]

Do mitered corners give better performance/bracing versus un-mitered joints?

I'm going to be building another projector screen over the weekend. My last one I mitered the joints and then covered the frame with felt. It was a pain after covering with felt to get the cut pieces to line up correctly. Part of my learning pains was making sure the felt didn't get bunched in the join.

But someone was asking me why I was mitering them versus cutting the ends flat then securing them together. I didn't know the answer.

 

[highfigh]

Do mitered corners give better performance/bracing versus un-mitered joints?

I'm going to be building another projector screen over the weekend. My last one I mitered the joints and then covered the frame with felt. It was a pain after covering with felt to get the cut pieces to line up correctly. Part of my learning pains was making sure the felt didn't get bunched in the join.

But someone was asking me why I was mitering them versus cutting the ends flat then securing them together. I didn't know the answer.

If you miter the joints, you have more gluing surface than a butt joint, but a half-lap joint has even more. Not knowing what you have for tools/machinery, it's hard to make a recommendation. If you paint the wood flat black before covering with felt, you don't need to be quite as perfect but not leaving any gaps is still best. With miters, you can either use dowels or screws and glue to secure the corners. With a butt joint, it's harder to screw them together unless you have long drill bits and then, you need to make sure the joint lies flat. You could also use biscuit joints, glued.

 

[jostenmeat]

No on felt. Yes on velvet. BMX has said repeatedly that the one glaring error of DIYers is the omission of velveted borders. Even the flattest black paint in the world is mega reflective compared to a mid grade velvet. You will need this absorption for any intended overscan.

Whether felt or velvet, do it last.

You cut the rough lengths (go too long), and glue the most of it, leaving some space away from corners. You cut with a razor, then apply glue to the ends/corners.

When you have these corners cut, the two meeting flaps should "fall perfectly in place".

The reason I instruct you to still glue the most of it before final cuts is because I found that 3M Super 77 somehow shrunk my velvet, which made it stressful. This was not foreseen, and so far as I know with just about any other fabric it would have been fine.

Go with whatever build technique gives you the most shear strength, just for peace of mind.

 

[highfigh]

No on felt. Yes on velvet. BMX has said repeatedly that the one glaring error of DIYers is the omission of velveted borders. Even the flattest black paint in the world is mega reflective compared to a mid grade velvet. You will need this absorption for any intended overscan.

Whether felt or velvet, do it last.

You cut the rough lengths (go too long), and glue the most of it, leaving some space away from corners. You cut with a razor, then apply glue to the ends/corners.

When you have these corners cut, the two meeting flaps should "fall perfectly in place".

The reason I instruct you to still glue the most of it before final cuts is because I found that 3M Super 77 somehow shrunk my velvet, which made it stressful. This was not foreseen, and so far as I know with just about any other fabric it would have been fine.

Go with whatever build technique gives you the most shear strength, just for peace of mind.

When I posted that flat black should be used, it's on the wood behind the fabric. That way, any gaps won't show up as light-colored bare wood.

Also, to keep from having to worry about glue spots and shrinkage due to the solvents, miter joints with a slight groove cut at the edge of the miter face can be used to staple the cloth in place and then the corners can be butted together, using L brackets with threaded holes and a backing plate, like the metal-framed screens. As long as the screws aren't tightened too much, the wood won't split. This is one advantage to metal frames- they can be tightened enough that they won't come apart without worrying about the wood.

Another way to secure the fabric is with a vinyl spline, like what's used on a screen door. Cut a groove into the backside of the frame pieces (near the inner and outer edges) and only use contact cement near the spline, so it never gets around to the front.

 

[jostenmeat]

When I posted that flat black should be used, it's on the wood behind the fabric. That way, any gaps won't show up as light-colored bare wood.

Yes, I know, your post was perfectly clear. I still wouldn't change any part of my post, assuming that it is wood we are talking about. Your advice seems to be good advice, and in fact he can probably just paint the immediate area of the corners only.

For gluing of velvet in particular, I am not worried at all about glue spots except in the case of overkill with liquid glue (not worried about spray). [strike]The splining at miter faces is interesting, but it doesn't sound easy for someone like me, in fact, I'm not sure if it's really worth the effort for my own point of view.[/strike] Nevermind, you meant stapling into grooves. Splining screen material didn't work out for me, on the back of the frame. Oh, that was a PITA!!! lol. That ended up all stapled. The velvet was glued.

Lastly, whether flat black paint, screws, if one was to use a very good velvet, there is always the risk that it still stands out, as they are comparatively reflective compared to black hole velvet.

edit: if splining with vinyl, best to have both the spline and material on hand, so that you can test them before going too wide with the dado.

 

[lsiberian]

If you have a miter saw I'd do it that way. If you are like me and don't have one then butt joints would be fine.

 

[mpompey]

Thanks for all the advice. This is some really good info. I was planning to paint the corner areas flat black then use spray adhesive for the black felt/velvet after I joined. So it's good to hear I was already on the right track. I have a decent miter saw, but no table saw yet. So dadoes and splines are out for now, but maybe if I knock off a couple of items of the proverbial Honey Do list, the Anniversary fairy will get me one. Thanks guys, I'll post results and pics when I'm finished with the project.

 

[highfigh]

Thanks for all the advice. This is some really good info. I was planning to paint the corner areas flat black then use spray adhesive for the black felt/velvet after I joined. So it's good to hear I was already on the right track. I have a decent miter saw, but no table saw yet. So dadoes and splines are out for now, but maybe if I knock off a couple of items of the proverbial Honey Do list, the Anniversary fairy will get me one. Thanks guys, I'll post results and pics when I'm finished with the project.

You can do splines with a router, too.

If you have a good hand saw, you could do a mortice & tenon joint, too. One end has the cafes removed at a depth of 1/3 of the thickness and the material toward the end is removed (this can be done with a router, too). This constitutes the tenon. The other end has the middle 1/3 removed so it can fit over the tenon. As long as the corners fit well and are clamped square while the wood glue dries, it will be far stronger than any other type of joint.