Suddenly the two hardware stores near me have all sorts of varieties of spade bit sets from multiple manufacturers displayed in prominent aisles, which makes me wonder whether that's the reason I am tempted to use a spade bit for this job, or else spade bits have always been there and it's only now I'm noticing.
Anyhow, I'd like to confirm.
A quick summary of the project:
I am hanging a chin-up bar on drywall, as shown in the picture below. From two previous questions on this site I know that:
- Several pieces of two-by lumber, along with 3/8″ - 5″ lag screws, are needed to take the load from the metal frame to the studs, and
- A lag bolt, a fender washer, a regular washer, and a lock washer are needed to attach the metal frame to the two sheets of 3/4″ plywood.
What is the right tool for burying a 3/8″ bolt, along with washer and fender washer, in plywood? The lag bolt appears in the bottom half of the image. Also, my hunch is that I do not need to glue the two sheets of 3/4″ plywood together; would you care to comment?
Regardless of whether I would use a spade bit or something else (a sawtooth bit? a hand chisel?), it's difficult to measure this sort of thing at the outset (at least using an amateur's handheld drill). Is my guess correct that I need to do this by trial and error: shave a bit, put the bolt and two washers; shave some more; until the head of the bolt no longer protrudes?
If you are following the previous two questions and the present one very closely, you will notice that I am no longer discussing the need for three kinds of attachments (A, B, and C in the previous two questions), but only two, as the picture above shows. I asked based on the posted dimensions from customers' reviews and expected that the manufacturer had cleverly separated the holes by exactly 16″, the common dimension separating studs. Since then the chin-up bar arrived in the mail, and the separation is actually 52 cm (~20.5″). As a product meant for worldwide consumption, this makes sense, and, ironically, it simplifies the job on my side.
I didn't know this when I asked the question, but it turns out that in this project I don't have the luxury of choosing whether to bury the bolt and washers in the plywood. That decision is forced by the available bolt lengths. The 3/8″ bolts at the largest chain of stores are available in only 2″, 2 1/4″, 2 1/2″, and 3″ length. Since I'm going with acorn nuts to avoid getting cut from the exposed bolt, I need to use 2 1/2″ bolt and to bury them. At the unavailable 2 3/4″ size (as luck would have it) I could have drilled a hole in the drywall for the bolt head and kept the plywood intact.