Q & A from Woodworkers Journal eZine 257

Woodworkers Journal eZine 257 Q & A

Formula for Plywood Thickness?

I'm building some furniture for my son -- bed, headboard, bookshelves. We're going to use plywood. Is there a formula for determining what thickness of plywood I should use? I can guesstimate it by looking at the thickness and how much I can get the large sheet to bend, but is there a rule that determines what thickness is needed for given dimensions and expected load?- Chip McDaniel

Tim Inman: From your question, it sounds as though you are wanting to make curved or bent surfaces. Without knowing more, it is very difficult to give good advice. However, if you are wanting to make pieces with significant curves, I'd suggest using a product called “bending ply” for your lay-ups. For serious work, I'd laminate multiple pieces of 1/4 inch bending ply to get the curve, and the thickness, you'll need for your structure.

Causes for Floppy Biscuits

I have a Ryobi biscuit jointer that cuts slots for 0, 10, and #20 biscuits. I upgraded to the newer unit because I had a smaller unit that cut slots where the biscuit would literally flop around in the slot, making a good joint impossible (unless I did something wrong). Anyway, with this new jointer, the biscuits still flop around, only not as much. But a tight fit there isn't. When possible, I watch The New Yankee Workshop with Norm Abram. I noticed when he uses a biscuit jointer, the biscuits fit tightly, with no flop. So my question is this: Are there consistency standards in the biscuit manufacturing industry, or are the machines that cut the slots using different size cutters? I am annoyed when I purchase a unit like this and can't get a good outcome. Or am I doing something wrong? Please help. - Tom M.

Tim Inman: Have you tried a different batch of biscuits? This sounds too simple, but it may not be the tool, but rather the insert biscuits that are undersized If you get a sloppy fit from more than one source of biscuits, then the tool - or the tool user - need to be questioned. My biscuit joiner leaves me with a nice, snug fit -- with multiple sources of biscuits. If I need a looser fit, I can manipulate the tool and make the groove sloppy. So from that, I can say the operator does have control over the fit. Maybe you're making multiple cuts on the same groove? Be sure the guide surfaces on the cutter are flat and seated before you plunge the cut.

Preventing Tearout

I just got a Box Joint sled from Rockler and started to make small drawers from Baltic birch plywood. Is there a trick to prevent the tearout from the spiral router blade on the plywood? I was thinking of either rolling glue onto the edge or sandwiching the plywood between two sacrificial pieces of wood. Any suggestions? - Abbott Fleur


Tim Inman: Perfection is always more difficult. If the little tearout is too much, then some sort of "sacrificial" surface is probably your best answer. Sometimes a little tape can do the trick. Adhere masking tape along the edge before you make your cuts. That jig makes it easy to lay another piece over the "real" one. I'd suggest something like 1/8-inch Masonite or hardboard to protect the finish wood, and let the bit cut clean. You may need to sandwich the workpiece between two sacrificial ones so both the front and theback cut clean.

FEEDBACK:

We received a little feedback on my answer to a questioner wanting to know how to get a hole through a lamp stand he had already turned.  The wood was 15-inches long.  My sage advice was to drill from both ends to meet in the middle, then use a piece of 1/8-inch threaded pipe to join the fittings together. 

It seems one of our readers felt I was 'more furniture maker than turner' and thought we had missed the mark by not telling the fellow to turn the piece in his lathe and drill it there.  Of course, that would be my first choice!  But, I was answering the question put before me - by an obviously inexperienced crafter.  Our reader suggested buying a lamp drill, which is always good.  (Never pass a chance to add to your tool room!) 

For me, using a time-honored 'D' drill would be the best.  D drills are always shop made.  They are made with high speed steel or high carbon/vanadium chrome drill rod.  The cutting end, when ground properly, resembles a 'D' exactly.  These are the drills used by the ancients to bore straight holes in important things like gun barrels and ivory cigarette holders and pipe stems, etc.  They will not 'lead' off to the side, but instead find the center and follow it straight and true every time.


Let me know if you have an interest in learning more about 'D' drills - or anything else I might be able to share with you about.  Just leave a comment with the tool at the bottom of this blog.

Until then, Good luck!

Tim Inman