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How to cut curves with bandsaws


Kamille - March 16, 2019 - 0 comments

No other woodworking machine can cut curves as quickly, easily and accurately as the bandsaw. When compared to other machines designed for cutting curves, such as scroll saw or the jigsaw, the bandsaw has greater power and cutting depth. In many situations, the bandsaw cuts more smoothly. That is because a bandsaw blade continuously cuts downward but a scroll saw blade or jigsaw blade has an erratic reciprocating movement. When equipped with the right blade, a bandsaw is much more versatile, since it can cut broad, shallow curves or tight, ornate scrolls.

Laying out curves

A good pattern is the key to bandsawing a great looking curve. I never sketch a curve or design directly on the stock and begin sawing. Instead, I draw my design on thin plywood and cut it out for use as a pattern. This method has three distinct advantages.

Firstly, it enables me to get a better concept of the design once it is cut out on plywood. If I’m not satisfied with the outline of the curve, its scale or its proportion, I can easily and inexpensively modify the pattern or make a new one.

Secondly, it makes it easy to duplicate the curve, as when making four identical legs for a table or chair. Third, if the design is a complex series of twists and turns, I can get a more accurate result if I simply make a pattern for one-half of the design. By flipping the pattern over when tracing it on the work piece, I get a perfectly symmetrical layout.

I sketch the curve on the plywood, checking, erasing, and redrawing until I’m satisfied with the design. Next, I carefully bandsaw the pattern and smooth the edges with a spindle sander and various sizes of files until they are free of lumps and dead, or flat, spots. Once I’m satisfied with the pattern, I trace it onto the stock.

My plywood patterns are valuable data storage centres because I write construction notes for future reference on the face of my patterns. Information such as the location of a mortise in the leg, the finished diameter of the ankle after sawing and shaping, and the required stock dimensions will be invaluable data when I want to build same piece of furniture sometime in the future.

When laying out a complex pattern, keep your eye out contours that are portions of true circles (see the drawing above). One way you can save a lot of time when sawing contours is to drill any true circles. Besides being faster than bandsawing, it is also more precise because it yields a true circle or part of a circle.

Choosing a blade for cutting curves

With so many combinations of material, width, pitch, and tooth form available, choosing a blade for cutting curves can seem like a formidable task. The right blade for sawing a particular curve takes into account a number of factors, such as the radius of the curve, the size of the bandsaw, and the thickness of the stock. Let’s look at some of the things you need to consider when selecting a blade for cutting curves.

source: instructables.com

Blade width

The minimum radius that you can cut your bandsaw is determined by the blade width (see the drawing above). As you follow the layout line while cutting, you must rotate the work piece around the blade. The narrower the blade, the tighter the radius you can cut. If you attempt to cut a curve that is too tight for the width of the blade, the blade may break or pull off the wheels.

So why not just mount a narrow blade and cut all curves with that? The difficulty is that cuts tend to wander more with narrow blades. When you are scrolling around tight curves, it’s not a problem, but if you’re cutting the broad curves of a chair rocker, your line will distinctly wavy unless you are very skilled. For that reason, geting the best bandsaw is depending on the types of projects you are going to work on.

When you’re first learning to cut curves, you’ll most likely find a blade-radius chart to be helpful. It will show you the minimum radius that you can cut with the various blade widths available.

Tooth form                     

More than any other factor, tooth form determines how a blade will cut. When smoothness is concern, the best choice is a regular-tooth blade. Because of their 0˚ rake angles, regular tooth blades cut with a smooth, scraping action. In addition, they have the greatest number of teeth, which also contributes to their smooth cutting.

When the curve to be cut is broad and the stock is thick, I’ll reach for a hook-tooth blade. Hook blades have positive rake angles and little feed resistance, features that make them well suited for sawing curves in thick stock. I cut all curves with either a hook-tooth blade or a regular-tooth blade.

Pitch

It’s best to have 6 to 12 teeth in contact with the stock at any given time. A blade on the finer end of that range will produce a smooth surface on the stock. If you go too fine and have more than 12 teeth in the stock, the gullets may become packed with sawdust and the teeth will overheat. The stock may burn, and the heat will severely shorten the life of the blade.

The best pattern material

I like to use ¼-in. birch plywood for pattern because it is stiff and its light colour enables to see my sketch. Also, the edges of plywood won’t curl or become frayed as paper or cardboard will.

Drill first, then saw

A technique you can use to save time when sawing contours is use a drill to contour any parts of true circles. It is faster and more precise than sawing. Always do the drilling first, then the bandsawing. Otherwise, the drill bit may wander off centre and miscut the stock. You can stack several pieces and drill them together to save time. For safety reason, check this article.

Source: https://www.instructables.com/id/6-Tips-for-cutting-complex-curves-on-a-bandsaw/

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