Slotted screw holes and table tops

[Jan Bianchi]

What tool do I use to drill slotted screw holes in cleats to hold my madrone table top to its base? Drill press, router? Will a small spiral upcut bit work? The bits I see advertized under this name seem to be for cutting slots in aprons for buttons, and aren't reall long enough for cleats.

Second, my plan is to use round head screws that ride on washers in a groove cut along the top of slot. Is 1/4 inch long slot long enough, or do I need to do a shrinkage calculation using one of those on line calculators.

Finally, about movement. The author of an earlier post on a beautiful bubinga table said he didn't expect his table top to expand any more than it had at the time he was working on it, so he placed his screws to the inside of the slotted screw holes. I assume he was working in an environment that was warmer and or more humid than where he expected the table to live. Since my working environment is similar to the environment where the table will be, how would I know if it will still expand or only contract? The wood for the table top has been in my shop for about two months, and the finished table top, about two weeks. Should I just aim for the middle?

[glenn bradley]

They make router bits for this. I have just used two different diameter spiral bits to accomplish the same profile.

[Jamie Buxton]

To widen screw holes/slots, I often use a 1/8" router bit in a laminate trimmer. The biggest challenge is to get the thing to plunge. An alternative is the bit from a Rotozip, chucked in a drill. And the lowest-tech version is a needle file.

Lee Valley even makes oval washers, so the sliding action happens between the screw head and the washer (metal to metal) rather than between the round washer and the wood. http://www.leevalley.com/US/hardware...=3,41306,41309

[steven c newman]

I just use the same drill and bit that was used to make the first hole. I drill all the way through, and then simply lean the drill (and bit ) over. A little lean in each direction does the trick. I raise and lower the bit as I lean it. Usually front to back, since that is how my tops are set-up. Since this hole is a bit larger the the screw's shank, I can use a biiger drill bit, and not risk breaking the drill bill. This trick came from Norm Abram, one several of his shows.

[Jamie Buxton]

I just use the same drill and bit that was used to make the first hole. I drill all the way through, and then simply lean the drill (and bit ) over. A little lean in each direction does the trick. I raise and lower the bit as I lean it. Usually front to back, since that is how my tops are set-up. Since this hole is a bit larger the the screw's shank, I can use a biiger drill bit, and not risk breaking the drill bill. This trick came from Norm Abram, one several of his shows.

I find this trick widens the hole at the top and the bottom, but not in the middle. And the usual drill bit doesn't cut very well going sideways, so it is difficult to widen the hole in the middle. That's why the bit from a rotozip is a good alternative; it is sharpened in such a way that it cuts going sideways.

[Jan Bianchi]

How wide should the slot be?

[steven c newman]

By doing that way, the screw will lean in the hole. I use a bit a size or two larger than the shank of the screw. Just a regular twist bit, I also run the bit in and out while leaning it. I do have a few Oak tables sitting around the house I made, that uses this system. One is over 20 years old, no problems yet, and I live in Ohio. By leaning the bit like I do, it places the screw in the middle of the slot, allowing either expansion, or contraction as the top moves around. Since I also use drywall screws for this, the "bugle head can lean over better than a flat head screw.

[Kent A Bathurst]

How wide should the slot be?

check one of the on-line calculators. You can be too big, but you don't want to be too small. the length depends on the total dimension you have to accomodate, and the anticipated max movement over that dimension, so not possible to answer your question. Is each screw required to handle the movement for 10" of wood? 30" of wood? - you see the point, I'm sure.

And - you'd have to be fairly sure you aren't ever moving to a different [more extreme] climate if you pegged the screws to one side or the other, and that you know the current m/c of the top, so you know there won't be any more shrinkage [unless the wood has been sitting in your shop for a good while]. I wouldn't do that, but that's not an argument - just me.

I make my elongated holes by drawing a short, straight line, and use a hand-held drill to stick a few holes in there, then chisel, rasp, etc. - drill-drill-drill-whack-whack-whack. I don't worry about a perfect slot - not like I'm ever going to see it again - and I don't put the washer/screw head in a recess [some designs would give you no choice, tho] - there's nothing wrong with that, of course - I just never wanted to put that much time into that detail.

For elongated holes, I use round-head brass screws w/ washers. But, I also use Z-clips, and figure-8 clips [usually for no reason other than I pick one I haven't used in a while - nothing like actual "logic" to it - and sometimes I use whatever works when I get down to the final strokes, because I haven't thought about it before-hand].