Following the 'Signs'
This morning, while edge planing a piece of Cherry I decided it would be a good time to demonstrate a trick I frequently do to determine the 'flatness' of the surface being worked. In the next photograph I've just taken a few through shavings down the reference edge. Please note that the stock is simply sitting on my bench top; it isn't 'dogged-down' or clamped in any way. This will insure I'm not pinching the work, creating a bump or hollow over it's length. I do have it resting up against a thin, scrap piece of plywood secured across the width of my work bench as well as having my bench dogs raised slightly along the front edge to keep the piece from moving about. With this method there's no danger of transforming the profile of this important, reference edge in any way while I'm working it.
This is important and should be noted.
I arrived at this point after the larger 'work' or 'reference' surface was first determined and flattened. This first face surface being the most important, it will be our 'reference' surface to which all of our other lay-out will be referenced from. Some woodworkers when using the term 'face side' are usually referring to the outside 'show surface' which can get a bit confusing...so to be clear-the work surface is actually my inside 'reference face' while dimensioning and laying out.
Now the trick I mentioned is a simple visual solution that clearly determines what your surface edge really looks like. Winding sticks and straight edges are great tools and visual aids showing you how straight and square you're work really is; even a light rub with your finger tips can assist the eyes in determining this narrow, 'surface flattening'. But to be absolutely sure the reference edge is flat you'll need some hard evidence...these are the shavings lying before you.If you look closely at the photos you'll see the shavings I'm taking-these are only possible with a depth of cut in the neighborhood of one thousandth of an inch and taking a full, through shaving you'll begin to see the signs. This type of shaving can only be obtained after you've flattened and tuned the sole of your bench plane as well as working with a plane iron that is razor sharp!
Lying there before me is a kind of road map...this clearly shows where there are still dips or hollows in the surface. In the next photo you'll see how I'm getting closer to a truly flat edge. Again, the 'map' in the edge grain is unequaled in its ability to clearly demonstrate the progress. Simply take a fresh shaving and carefully unroll it. I've laid it on my steel flat edge to make it easier for you to see. With each pass these small 'holes' in the shavings get smaller. Another shaving and I'm almost there. The small 'holes' or 'tears' in the edge grain shaving mark any low or hollow spots in the surface. I can plane 'around' these valleys and bring things closer together. In the bottom photo you can see the three passes it took: from right, my first pass with two big sections that are obviously low. The middle shaving in the photo represents the next pass bringing the surfaces closer together; and finally the left shaving being my third pass is almost complete. I'll follow with one or two stopped shavings to uniformly 'hollow' the length of the edge slightly and finish off with one or two more through shavings calling this side done.
My steel straight edge, winding sticks and engineers square together will tell the story of square and straight but for these tiny surface hollows, in the thousandth of an inch range, this road-map trick is something you should try. It can be difficult to see with the naked eye any slight valleys and a finger tip touch can only get you so far...this method of watching these signs will give you the confidence to move on with the dimensioning process of the lumber being worked. I should also mention the technique of 'hollowing' the edge along it's length is a technique best demonstrated by David Charlesworth. His DVD on hand planing techniques available through Lie Nilesen Toolworks is extremely imformative and should be viewed by all using hand planes in the workshop.