Precision Band Saw
By David Charlesworth
I wonder how many of us are friends with our band saw and consider it one of the most useful and versatile machines in the workshop? My 43-year-old Robinson Cadet is not only my favorite machine, but it is also capable of incredible precision. This may come as a surprise to those who consider that a band saw is a machine for coarse work only.
While considering the content of this article, I came to the conclusion that a good band saw is capable of coarse, medium and fine work, and this ties in nicely with our esteemed editor’s views on handplanes.
Coarse: Break Down Rough Stock
A good-size band saw can rip huge waney-edge planks, quickly disposing of the sapwood and bark. Wide boards often contain the pith at the center of the tree and many exhibit heart shakes. Cutting these planks up the center, into two manageable widths, is not a job for a table saw. The band saw is much friendlier and safer, as the flexibility of its blade will usually cope with the absence of a machined surface to ride on the machine’s table.
My machine has 20″-diameter wheels, so it should not be confused with small hobby benchtop models. I note that the band saw that is featured extensively in James Krenov’s book “The Fine Art Of Cabinetmaking” had 18″ wheels. He states that it was capable of ripping 8″-thick hardwood, provided that a sharp, suitable blade was used.
Medium: Cut Then Refine
I do a lot of freehand cutting on my band saw, sawing perhaps 1⁄64” to a 1⁄16” away from a pencil line, depending on the circumstances. The small amount of remaining timber can be handplaned or machined quite quickly to achieve the desired result. For example: When using the band saw to make the long shallow triangular jigs that I use for dovetail cutting, the remaining stuff can be edge planed on the jointer with a few light passes.
Fine: Joinery, Veneer, Resawing
I have to confess that my handsawing skills are rather poor because I have not practiced as much as I have with planes and chisels. This is one reason I cut my dovetails on the band saw. The other reason is that my band saw cuts perfectly square every time.
Remarkably, the finish left by the .022″-thick, 3tpi, 5⁄8” “meat & fish” blade that I use for fine work and veneer cutting is just as good as that left by my best dovetail saw, even in 3⁄8“-thick hardwood. So from my point of view it is win-win – all the way to a good fit.
If you do small Krenov-style work, band sawing is almost the only way to do the female half of the signature bridle joints. These are so useful at the corners of delicate frames, for paneled backs and small doors.
Similarly, the face cheek of a tenon can be cut in exactly the right place after a few test cuts are made. Tenons are usually cut in multiples, and each and every cut will be in exactly the same place. As the work gets bigger, I tend to cut the opposite cheek a little thick and adjust it with a low-angle rabbeting block plane or router table. In small work, one can probably cut both cheeks straight from the saw.
There can be a considerable advantage in leaving a project’s components slightly wide for as long as possible. We can then complete all the machine and handplaning on two faces and one edge. If you need to shoot or handplane the end grain, this extra width allows room to first create a small bevel to protect against spelch (the splitting out of the far corner).
Once your final width has been gauged on your work, a band saw with a correctly set fence, or even a point fence, is capable of cutting to within .004″ to .008″ of this line. Very few handplane shavings are then needed to arrive at your finished width, and little thought will be needed as the resulting cut surface is extremely accurate and parallel to the face edge. I simply set the band saw’s fence (or a point fence) with the aid of a steel engineer’s rule, measuring to the tip of an inward set tooth. See the photos below.
This is always much safer than using the table saw as there is no possibility of kickback on a band saw.
The ability to cut solid veneers, say 1⁄16“, 3⁄32” or 1⁄8“, from the same stock you are using in the rest of your project allows for continuity of color and figure. For more on this topic see James Krenov’s first two books, “The Fine Art of Cabinetmaking” and “A Cabinetmaker’s Notebook.”
Old air-dried stock works best. Veneers from kiln-dried stock tend to curl worse due to the internal stresses caused by kiln drying. If the finished veneer thickness is gauged on the edges before cutting, it is easy to plane them to uniform thickness and remove the sawn finish after cutting. A simple way to hold the veneers is to mount them on a thick piece of MDF. I like to use a few spots of Super Glue Gel at the starting end, as shown in the drawing below. The veneer will be in tension when it is planed, and the majority of the veneer can be lifted to check its thickness with calipers if you have difficulty seeing the gauge lines.
Band-sawn veneer is much more robust than knife-cut veneer and can be used to create panels, box tops or shelves that have virtually no seasonal movement. Alternatively, a nicely figured board can be sliced up and used on the show face of a whole chest of drawers. Please do not forget to apply some plainer stuff to the back of your drawer fronts etc., to keep them flat and in balance. Water-based glues will always curl a panel if veneer is applied to one side only.
The ability to resaw thick timber has many applications. I now follow a tip from Robert Ingham to create thin quartersawn stock that’s useful for drawer and box making. I start with the widest available 3″-thick planks of timbers, such as black cherry or maple. These are invariably plain-sawn, so if resawn into 3⁄8” strips, the resulting material is almost perfectly quartersawn, as shown in the drawing at right. Once a face side and edge have been machined, the sequence is to rip off a strip, then re-plane the edge before cutting the next strip.
Laminations for curved work that are cut from solid wood are very similar to veneers. It is extremely wasteful and potentially dangerous to cut these on a table saw with its wide kerf. We are turning more wood to dust than we are keeping.
Meat & Fish Blades
I am fond of using stainless “meat & fish” blades for all my precision cutting. These are manufactured primarily for the food industry. They are thinner and have less set than standard wood-cutting blades. The consequences of this strategy are:
1. The kerf is only about 1.1 mm wide, which creates less waste.
2. The surface finish is much smoother than from a blade with regular set. I feel the surface is quite good enough for gluing, but if one wishes to plane it totally smooth, only a few shavings are necessary.
3. The blades are absolutely useless for anything other than very gentle curves or straight cutting!
An ex-student tipped me off about these blades years ago. We use regular blades for heavy cutting and rough work, but change over for fine work. My current favorite comes from Atlanta SharpTech (sharptech.com or 800-462-7297; the blades are sold as “general all-purpose” blades for the food industry). These are beautifully wrapped and prepared. The back edge has been smoothed and rounded over, a job one usually has to do for oneself with a slipstone. I have to order 10 blades at a time, as they are an industrial supplier. The cost is slightly higher than a wood-cutting blade, but I think these blades are worth it.
Unfortunately, to perform all these wonderful precision operations, you need a robust machine that is capable of good blade tension and is correctly set up with a suitable blade.
There is not room here to delve into all the details of setup, and there are excellent encyclopedic books on band saws, such as “The New Complete Guide to the Band Saw” (Fox Chapel) by Mark Duginske.
In brief, the frame must be rigid enough to sustain considerable blade tension without twisting. The wheels must be in the same plane, with true, slightly cambered tires. Out-of-true or unbalanced wheels create vibration. It is not possible to get the blade to track in the center of the tires unless there is a camber present across the width of the tire surface. A sharp suitable blade, well-set guides and correct feed angle are the other prerequisites for successful cutting.
My Robinson Cadet
I was extremely lucky to find the Robinson, which was being sold by a very crude, cheap pine kitchen outfit in Bideford, my local port and market town. The band saw was in a rather battered state but fundamentally sound.
We “turned” the surface of the tires, in the machine, with a large wood turning scraping tool (no blade on the wheels, of course). The surface of the vulcanized rubber was trued and the vital 1⁄16” camber across the width reinstated. Having taken the blade off, the bottom wheel was turned under power, with a jerry-rigged tool rest, and the top wheel was done with my students supplying human power. I am certain that these operations aren’t recommended on safety grounds; fortunately, most band saw tires already have this camber.
The machine had no fence and initially I thought it would be expensive to get a metal fabricator to make one up. Just to get going, we used a nicely planed up bit of oak about 5′ long and 43⁄4” x 3″ in section. It is still in use to this day, and we learned one of the most important things about band saws by using it. The feed angle is paramount, and it is rarely at right angles to the front of the table! So any band saw that does not have an adjustable fence is made by scoundrels or nincompoops.
(Some authors suggest that feed direction can be corrected by the position of the blade on the crowned wheel, and this may be true in some cases. However if the guides are not aligned with the table this may not work.)
What’s more, feed direction can change in the twinkling of an eye if the blade’s set on one side of the blade should be blunted by mineral inclusions in the wood. This is one of the reasons why the point fence is so useful. The operator is in control of feed direction and can adjust it as necessary. (You may have noticed that badly set handsaws that have more set on one side than the other cut a curved line).
Determining Correct Feed Angle & Fence Orientation
We take a parallel piece of scrap about 2′ long and 4″ to 6″ wide. A face side and two parallel edges are needed. MDF is ideal but plywood or solid wood will do as long as it does not spring when cut. Use a pencil gauge to draw a line parallel to one edge, perhaps 2″ in from the left side of the board. Now saw this line freehand while using a point fence (or place a stationary finger on the table to act as a point fence).
Saw slowly and experiment with the feed angle as the cut proceeds. I watch the back of the sawblade in the kerf. You have found the correct feed angle when the back of the blade is touching neither side of the kerf. Ideally the back is exactly centered in the kerf, though serious trouble begins only when one side is pressing hard against either side.
It should be possible to establish the correct feed angle when one is about halfway through the length of the setting board. When satisfied, stop the machine without disturbing the angle of the board.
Set up a straightedge parallel to the edge of the test piece, near the right-hand edge of the saw’s machine table. Then make three marks with a fine permanent marker.
My table is well waxed, so I remove the wax locally with acetone and apply three strips of tape where the marks are to be made. Then I set up my oak fence parallel to these marks.
I know this sounds rather cumbersome but it is worth the effort. If you have an adjustable fence, you can simply make ripping cuts in scrap and observe the position of the back edge of the blade in the kerf. It should be centered without touching either edge.
Exciting and undesirable things happen if the fence and feed angle are not correct. You can easily show this by deliberately holding (or clamping) a temporary fence crooked. In one direction the work drifts away from the fence and is ruined; in the other the blade starts to be alarmingly deflected toward the fence and you can see that breakage will follow shortly.
The Point Fence
If you practice and become familiar with a point fence you will rarely use anything else. It is a little intimidating for beginners, as some lateral twist must be applied to the workpiece at the start, and for the majority of the cut. The vital requirement is that the work does not drift away from the point (which is in fact a small flat) during the cut. The flat is essential for the start of a cut and must be positioned correctly relative to the cutting edge of the blade. Point fences can be made at differing heights, and setting one is a breeze as only one ruler measurement need be made. (A single quick-acting clamp secures the fence).
If my guides are in good condition, I reckon to be able to set the cut width to plus or minus about .004″. If test cuts are made and calipers used to measure the result, it is possible to get even closer. This is fantastic for precision jig making. The component can be gauged, cut from a board and cleaned up with no more than five or six fine shavings.
Lignum Vitae Guide Blocks
When it arrived, the Robinson had some rather unusual bent sheet metal guides. These were difficult to prepare (by filing) and even more difficult to set up.
So I decided to use Lignum Vitae sticks and contrived a holder to fix them with a simple screw clamp. Two holders were needed, as good machines have a set of guides below and above the table. True Lignum is now an endangered species, but you can use any dense, oily exotic wood.
Metallic guides are always set with one sheet of newspaper clearance away from the blade. Lignum is well lubricated by its natural oils, wears relatively fast and can be set with zero clearance, though I always turn the wheels over by hand to check that they are not too tight or stick on a bumpy weld. The condition of your guide blocks is vital as they prevent the blade from twisting in the horizontal plane. After heavy use the surfaces become convex, allowing more and more twist and slop. The ends of mine are trued regularly on a disc sander equipped with a simple wooden fence.
Guide setting is a delicate operation, as the blade must not deflect at all for precision work. My blocks slide easily in their holders. I bring the first one up to the blade with gentle finger pressure. The blade tension is sufficient to slide the block out again if I have pressed too hard. This guide is now secured with the brass knob. The second guide is then pressed gently against the opposite side of the blade. If any deflection is seen, I allow the blade to push it back, then secure its clamping knob. By alternating several times from side to side, it is quite easy to arrive at zero clearance with no deflection.
When running free, the blade should just clear the saw’s thrust bearing, which is the support behind the blade. I like to check that the thrust bearings on both the upper and lower sets of guides fire up and start rotating when sawing commences.
After many hours of thought and experiment, I managed to build the “wrap around” dust extraction unit, which you can see at left. This allows the table to tilt to 45° and collects dust as near to the source as possible. It makes the machine more pleasant to use. Most extraction points are too far from the throat. Wind generated by the wheels and blade carry dust around inside the case, over the top and eventually blowing it in your face. With my setup, I find virtually no dust at all on the ledges of the door and casting when the blade is changed.
I learned this cunning technique from a magazine. Some years ago, I was asked to “make up” a set of Edward Barnsley dining chairs. Having made an accurate template from melamine-faced hardboard, I was able to saw the gentle curves with total repeatability. The resulting shape was so good that a few shavings from a plane or spokeshave completed the profile of the back legs. This saves a great deal of time if the shape you want is amenable to this technique.
The template is secured to the top surface of a rough blank with double-stick tape or small screws in the end waste. The blank has been thicknessed and sawn about 1⁄8” oversize. The guide or follower is supported on a stick, which is a fraction thicker than the work.
It is quite impossible to cover all aspects of this fabulous machine in one article. I have not mentioned circle cutting or the benefits of a tilting table. My machine table tilts all the way to 45°, and I find it much safer to make bevel cuts here than on the table saw. Unfortunately I have heard that some modern machines are now limited to a fairly useless 30°, for “health and safety reasons.”
The “meat & fish” blade is a wonderful thing, with its fine kerf and excellent surface finish. Who would have thought that a massive, ancient band saw could do work of such finesse? With a little tender loving care, a heavy old cast machine will outperform many lightweight modern ones. A sharp blade, true tires, good tension and accurate guides are capable of the finest work. PW
David is the author of three books and five DVDs, including the new “Chisel Techniques for Precision Joinery.” He teaches woodworking classes in his shop in Devon, England. More information is on his web site at davidcharlesworth.co.uk.