Need to attach 66 inch piano hinge to ply and pine. I found the right size sheet metal screws at Lowe's. Can I use them? Otherwise I need to order on line.
The screws should be the correct length, appropriate head to fit flush, and a compatible finish to go with the hinge. Installed properly, they should work OK. Here is some info that may help you.
There are a few ways to align the leaves of hinges. But getting the hardware straight and fitted properly is only part of the success for a good fit. When installing screws, if done improperly, can throw off the hinge alignment. What's important is that once the leaves are set and marked, that the screw goes in absolutely dead center of the holes and seats flush, or slightly below the leaf surface (into the countersink).
What would happen if done otherwise, is if the screw is slightly off center, or skewed as its being inserted, it can move the leaf as it gets tightened down. If the screw goes in at a slight angle, it may not seat, and stand proud of the leaf affecting the closing of the two leaves. A suggestion would be that once the hinge is placed and marked for mortise, use a very sharp scratch awl and eyeball the center of the screw hole and tap a starting hole holding the awl perpendicular to the box edge. I wouldn't use a vix bit or one of the spring loaded hole punches, as they are not as predictable as using an awl.
I would drill a pilot hole appropriate for the screw size, and again, that has to be @ 90į to the box edge. Once that is done, make a small countersink at the hole opening. This allows the "V" shape of the underside of the head to seat in the wood without restriction.
It may help to install one screw in each leaf, and check the alignment, before installing the rest of the screws. For a continuous pin hinge like a piano hinge, I would set only a couple of screws on each leaf, to check the fit of the hinge before punching and drilling all the holes. When installing screws, use a cordless drill on slow speed. Don't spin them in fast, as they can strip out very easy by over spinning. When the screw gets close to tight, bump the trigger to tighten, or do it by hand. You don't want to skip out of the head, or mar the hinge.