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Unread 01-18-2022, 10:49 AM   #16
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Join Date: Jul 2005
Location: Fairfax, Va
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Hi Rob,

The problem you'll likely find with using shorter screws is that they won't penetrate deeply enough into the plywood to hold. The first 1/8" to 1/4" of the screws are tapered which leaves whatever is left of the full diameter of the shank. With a 1" screw you'd only end up with 1/2" to 5/8" of the full shank into the ply. Not much. The same challenge will exist if you are screwing 3/4" ply directly to the joists; you're gonna want 2" screws for that.

If you orient your 1/4" thick cement backer boards so that the seams do not fall on the on the joists you should be able to avoid all the nail plates.

To get the floor as flat as possible you might consider recessing those nailing plates so that their tops are even with the joist tops.

Correct regarding the drill clutch. Once a certain degree of resistance is met the clutch will slip (actually makes a ratcheting sound. If your dad's old drill has a clutch there will be a collar just below the chuck, with some markings that suggest the lowest to highest setting. Turning that collar one way or another increases/decreases the torque applied to the chuck. A useful feature to have in some circumstances, but only if the material you're screwing into is the same consistency everywhere. If, for instance, you hit a part of a joist that is denser the clutch will slip before the fastener is fully sunk.

For the task of running a lot of screws for a subfloor and tile underlayment (cement board, in your case) I'd reach for an impact driver before a clutched drill. An impact driver resembles a drill but they are typically smaller and, of course, lack a clutch or a chuck. It is also very easy to modulate the fastener depth with an impact driver.

Or, everything cx said.
If I recall correctly my memory is excellent, but my ability to access it is intermittent.
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