Saturday, December 3, 2011
The Hammer Beam Low Table . . . Flattening a Table Top with a Hybrid Approach
I often wonder whether my procedure for a given task is the "right" way to go about things. I suspect that I'm not alone in this feeling. Woodworking magazines make it seem very arbitrary - creating a linear approach that gives consistently good results. And that works well, up to a point. On the other end of the spectrum is an approach that says "I'll let the wood be my teacher." You experiment with a number of known techniques until the wood yields the outcome you desire -- and those techniques may vary given the wood species, your mood, the weather, and the application.
As a hybrid hand tool/machine woodworker, I'm comfortable moving forward with my preferred method (generally hand tools) but jumping ship the minute the going gets rough. This is how I approach the all-important flattening of a table top.
It starts with two things: a Number 12 Scraping Plane and an open mind.
That's not quite fair, it actually begins with a sense of what's possible and important during glue up. I always orient my boards with the grain in one direction in order to keep the option of hand planing to completion in play. This limits my design choices a bit, but I've not found that to be too onerous. Depending on the species, whether I'm re-sawing, and my deadline, I machine-surface my stock over a series of days. Hopefully I can keep any post-planing movement to a minimum. I try to bring the machined thickness to somewhere around 1/16" above my goal, but I've not been in a situation where (within reason) final thickness was visually critical.
This is a five board glue-up, and I do it in two steps. Perfection is the goal, but I've found that it is nearly impossible to fully correct any bend down the long dimension. You must keep checking the joints to see that they are even and use a straightedge across the boards ensure that they are not cupping. I use bog standard pipe clamps since I find them easier to adjust than Jorgenson clamps. My experience is that in spite of your best efforts, the wood will want to move to its own stasis point. Forcing joints closed with too much pressure can result in instability down the road. If things really start to go pear-shaped, I stop, scrape off the glue, and think about resurfacing/rejointing the boards.
My finished glue up (I'm doing two tables at once) looks like this. It is not perfect, but it is within my own personal tolerances for quarter-sawn white oak. For the record, I find QSWO to be prone to movement after cutting and surfacing, and sometimes balky to finish with a hand plane.
Once out of the clamps, I have a go at all the glue lines with a card scraper -- doing this while in the clamps and the glue is gelatinous is even better.
It has taken me a long time to understand fully the real difference between Flattening and Surfacing. The first, Flattening, has much more to do with geometry (is it level, across all the boards, with no variations between each board.) It is a prerequisite for Surfacing which has to do with the texture of the flat surface. In this case there are ridges on the boards, and in some places the variation is around 1/64" of an inch. I began flattening with my Number 12 scraper, equipped with a Hock blade. The blade is honed to a 45 degree angle (with no hook), and I lean it well forward. Moving diagonally, but with the grain, I come from two directions -- creating a crosshatch pattern and removing stock at a pretty good rate.
I prefer scraping to planing with a jack plane. In my experience a scraper will only dig as deep as the blade is set (in this case, the thickness of a paper towel) without any real risk of tear-out. I'm sure that there could be a long discussion here about "type 1" or type 2" chips, toothing planes, and scrub planes -- I'd I'd like to explore that -- but this is what I know and it works for me. I'm looking to create a uniform cross hatch pattern that touches all surfaces of the wood.
I also look at the quality of the scraping to make sure that it is fluffy and long (not chunky or just dust) and adjust the scraper accordingly.
. . . And right away tear-out begins to appear on one board. I quickly switch to my high angle 4 1/2, and though it is better, tear-out continues. I even give my low-angle jack a try, but it is no better. For the record, I have found that this light-colored, slightly stringy oak can be difficult to work. Using a card scraper, I surface the wood to a depth below the tear-out. I suspect that with ultra light cuts I could get the rest of the surface down to this level, but I'm not up for the task.
Breaking out the RO sander, I begin with 120 grit paper and in about 15 minutes have the surface completely finished to 220. It could have been done more quickly if I could have found any 80 or 100 grit paper in my mare's nest of a sanding cabinet. Was this my first choice? No. Would I have preferred to finish this with my 4 1/2 plane? Absolutely. But I'm long past the idea of pursuing a course of action simply because I want to prove to myself (or the hand tool orthodoxy gods) that I can complete the task with style points intact. I'm interested in making furniture, not making a point. Now all that is left to complete are the breadboard ends.
I'm curious to hear about your procedure for table tops and results and style points. Cheers!