Saturday, November 13, 2010

An Aid to Lamination

With the price of material what it is, I'm inclined to use lamination and biscuit joinery whenever and wherever possible to build up scraps and salvage into usable stock.

A difficulty that often arises when gluing up a lamination is that the wet glued interface(s) want(s) to slip-slide away as you clamp the thing up -- you can't keep things aligned as they're meant to be. A way to eliminate that problem is to install dowels clear through the assembly to act as alignment pins. Here's a photo of an assembly that I've readied for gluing.

One dowel is shown partially inserted. There's another hole for a dowel at the other end of this two-foot long assembly. The dowels are located in what will end up being waste. (This is going to be the central spire for an angular, four-legged garden trellis.)

Make the dowels just a bit shorter than the total thickness of the lamination, so they can be set to just below flush at both ends, and won't interfere with any sawing operations to come.

Before I take this out of the vise to apply the glue, I'll mark the edges of the three pieces so I can't lose their present relationship. There's no way I got those two holes drilled perfectly symmetrically and perpendicularly; this will have to go back together exactly as it is now.

Undersize Dowel

This technique works best with snug-fitting dowels, but a lot of dowel stock that's sold is slightly undersize. I find it rare to ever obtain true-sized lengths of dowel. (Fluted dowel pins intended specifically for dowel joinery don't share that defect. I find them to be reliably true-sized.) I used 1/4" diameter dowel here and sure enough, the dowel stock I had on hand was a bit undersize.

Twist drills have a characteristic you can exploit to improve the fit of undersize dowel. A twist drill is not a reamer. When a twist drill's centre tip (the 'web') is unsupported by solid material, as is the case when enlarging a pre-existing hole, the resulting hole will be ever-so-slightly undersize. The effect is very slight, but it's enough to be helpful when fitting undersize dowel stock.

When I drilled those two holes, I first used a 15/64" drill, then followed up with a 1/4" drill. It gave me quite a good, snug fit for the dowels.

Here's the glued up, clamped up assembly back in the vise with its alignment dowels fully in place, just below flush.

I wasn't concerned here with protecting the material from jaw marks; this lamination is going to get a lot of resawing done to it before it's finished.

The job went quite smoothly. With the dowels maintaining alignment, I was able to just go through the requisite motions with nothing drifting out of place on me. This time tomorrow, I'll have the piece I need for that trellis' spire.

# # #


# # #

No comments:

Post a Comment