Let's get some vocabulary straight first so we are both on the same page as to what we are talking about when we use the word 'jigsaw.' It's a bit confusing but traditional 'jigsaw' puzzles were originally cut out on a 'scroll saw' which used to be called a 'jigsaw.' Today, the term 'jigsaw' refers to a hand-held portable woodworking power tool while the word 'scroll saw' refers to a stationary woodworking machine. Another way to look at it that in the case of a jigsaw, the tool is brought to the work piece and in the case of the scroll saw the work piece is brought to the machine. Another name for a jigsaw is 'sabre saw.'
I've been using jigsaws longer than I'd like to admit. I found the first one lying around my dad's woodworking shop in the basement of my childhood home. A few years after that, I purchased a cheap one from Sears. That machine gave me the quick convenience that all jigsaws provide but there were ever-present and annoying problems without clear solutions: First, The blades had no guides so they would habitually deviate away from the cut line, especially when I was trying to track curved pencil lines. Second, when cutting curves in thick material, the jigsaw blade would bend toward the outside of curves. Third, early jigsaws did not have orbital pendulum action and so they would load up and burn in thick materials. Switching out blades required a screwdriver and you had to be cautious not to lose the set screw.
Today's top-quality jigsaws have eliminated all of those problems and are, by comparison to the earlier models, a vast improvement. I will confine my remarks to good quality jigsaws because there are still cut rate models out there with the problems I just talked about. Having said that, here are the foremost things that should come along within your next jigsaw:
At the top of my list are the subjects of blade tracking and blade guides. Take a close look at how each jigsaw manufacturer has approached these challenges because you are not likely to get a chance to try out your next jigsaw before buying it. Look for details: Some manufacturers simply say something like 'exceptional blade tracking' without saying how this is accomplished. Others are persuasively descriptive.
Another concern with all jigsaws is lumber splintering. Most, but not all, jigsaw blades are made to cut on the upward stroke which means that the splintering often occurs on the good side of the board or plywood. Splintering can be lessened in two ways: (1) fine-cut blades and (2) anti-splinter inserts mounted in the saw foot immediately next to each side of the blade. Fine-cut blades cut slowly and so if speed is a requirement and you are using a more aggressively-toothed jigsaw blade, a splinter insert is an absolute essential unless you mean to sand and/or rout away the splintered area later.
Recurrent blade changes are a fact of life with all jigsaws. In support of production efficiency, this process should be as fast and easy as possible. Gone are the days of screwdrivers, Allen wrenches and set screws. You want a jigsaw that lets you change blades fast..
If you are health conscious and want to minimize airborne dust in your work area, you may want to gather dust right where it's made by attaching a vacuum hose to the jigsaw. In that case, check for a dust port and make sure that it is compatible with your vacuum hose. Personally, I usually wear a good dust mask and thus avert the annoyance of hauling a vacuum hose along with the saw when I am trying to turn the machine along curves.
I mentioned orbital pendulum action above and I would not even consider buying a jigsaw that did not include it. My first orbital machine was a Bosch barrel grip model. I was allowed to try one out in a woodworking store while I was on a business trip and it went home to Hawaii in my suitcase. Here's why: The salesman had a slab of eight-quarter White Oak and encouraged me to cut some curves in it. There were four orbital settings on that machine with the first being 'no orbital action' and each one after that being more aggressive than the one before. With the orbit in the 'off' position, I began a cut. As I expected, the machine slowly pushed through the cut and I realized that if I pushed it with more effort, the jigsaw blade would either burn or break. Then, at the suggestion of the salesman, I put the orbit lever in position '4', the most aggressive, and made another cut. The blade flew through the thick oak as if it were butter. There was a bit more splintering than before but not really that much. Sold, American!
A side plus of an oscillating jigsaw is greater blade life. When a blade is wedged inside a cut, it has nowhere to go to dissipate the heat. The pendulum action oscillates the blade in and out of the cutting face, letting cool air in while the blade is momentarily positioned away from the cut. In the same moment, the accumulated sawdust is allowed to drop out of the cut so the blade is always cutting new wood, not old sawdust. That's why it can go faster and cooler.
Most good jigsaws, but not all, have Electronic Speed Control (ESC) which is an important nicety. ESC is like the cruise control on your car: It maintains a constant speed with changing load conditions. The harder you push the jigsaw, the more electrical power is delivered automatically to the motor so that the saw blade will not slow down. The analogy is your car on cruise control going up a hill.
Many jigsaws today are obtainable in two different body styles: Barrel grip and top-handle (sometimes called D-handle). I have owned both and I have a personal preference for the barrel grip style because it is easier to control when making fine cuts. Just like when using a router or any hand power tool, a low center of gravity and a solid grip equate to better control. With a top-handle jigsaw, your hand is at the top of a taller machine and the tendency to tip over is greater. With a barrel grip jigsaw, the center of gravity is as low as it can be. There is a knob on top, right over the jigsaw blade, for your other hand for better control. The big, round barrel is easier to hang onto than the thinner D-Handle.
Jigsaw manufacturers usually express motor power in terms of amperage, rather than horsepower. This is fine because amperage is a more reliable indicator of actual power than horsepower. The more amperage, the more power and power is important when cutting thick or dense materials.
The rapidity of the jigsaw blade is expressed in 'strokes per minute' or 'SPM.' The more, the better.
Cutting depth is something you will want to consider when dealing with very thick or dense materials. In soft wood, cutting depth refers to the maximum distance between the bottom tooth on the blade and the foot plate of the jigsaw when the blade is fully extended. In metal, plastic or other materials, cutting depth is based on the ability of the saw and blade to cut through dense or resistant materials.
Jigsaws are often used to cut expensive and delicate materials such as veneered plywood panels and a typical, steel foot plate may leave scrapes as it drags along behind the blade. Some manufacturers offer coated foot plates, some provide an 'overshoe' for the foot plate and some completely fail to focus on this issue. If you cut delicate materials that can be easily marred, pay careful attention to this feature (or lack of it.)
Machine weight is the next consideration. My knee-jerk reaction is to look for the lightest machine so that I won't tire so easily during a long day of cutting. On second thought, the light weight is nowhere near the advantage as it would be in, say, an impact driver or electric drill because the jigsaw's weight is almost always resting on the material being cut. Further, light weight could mean that the builder skimped on construction materials, possibly substituting plastic parts for metal as a cost savings.
Stroke length is the distance the saw teeth travel up and down while cutting. This is almost universally one-inch and so it is not a useful number when comparing designs from different makers. Generally speaking, the longer the stroke, the faster the cut and the shorter the stroke, the smoother the cut.
Jigsaws can make bevel cuts, usually up to 45 degrees from vertical, both left and right. The more bevel, the thinner the material that can be cut. Adjusting the bevel can be tricky or straightforward. Some jigsaws require you to use a screwdriver, hex wrench or Allen wrench to loosen or tighten a set screw that holds the foot at a certain angle. Other jigsaws are designed with the adjusting mechanism built-in and, thus, requiring no tools. Opt for the latter when possible, everything else considered.
All jigsaws vibrate and make noise. Obviously the less vibration and noise the better. Vibration is transmitted to the point of cutting and affects your ability to control the cut. More importantly, vibration is tiring when it goes into the operator's hand and arm. Various jigsaw manufacturers have dealt with this problem in different ways but the most common anti-vibration technique is to 'counterbalance' the motor. The other way is to put vibration-absorbing material on the outside surfaces of the machine that come into direct contact with the hand(s) of the operator. Padding will not, of course, minimize the vibration transmitted to the jigsaw blade at the point of cutting. Noise reduction varies by machine design and the only way to make this comparison requires running the jigsaws you are considering for purchase.
Some jigsaws come equipped with a variable speed wheel to set the maximum speed of the tool for better cutting results in different materials. This is different than the speed control of the variable speed trigger. Full speed on the trigger will always be limited by the setting of the variable speed wheel. Most jigsaw triggers have a lock-on feature because holding the trigger on all day long can actually make your hand go numb. Barrel grip jigsaws do not have a trigger but use a lock-on type thumb switch instead. If you have the variable speed set at half-speed and you lock the trigger or thumb switch, you will get half-speed at full trigger deflection until you move the setting on the wheel.
Most jigsaws come equipped with some sort of air blower to keep chips away from the cut line. The air blower on the earlier machines was located half-way between the operator's chin and nose. Some manufacturers mount the blower nozzle near the point of cutting, others on the top of the machine. Some have adjustable nozzles. The important thing is effective chip and dust removal so you can see where you are supposed to cut.
Another aid to clear vision of the cut line is a built-in light. LED lights are best because they are bright white and last virtually forever. Just in case they don't, see if they are replaceable and available.
There are several types of jigsaw blades sold and you will have to use the kind that your jigsaw is designed to accept. There is a difference in blade types. The T-shank is my preference because it stays locked in the saw plunger. Other types include tang shank and U-shank. Once you know what type of blades your jigsaw requires, be sure to check for the availability of blade designs appropriate to the work you will be doing. Rough cut blades power through thick and coarse materials but leave a lot of splinters.
Fine-cut blades have many more teeth, leave fewer and smaller splinters but cut slower and are generally shorter in length. They also may be thinner (front to back) to allow for tighter turns around sharp curves. They will break more easily than a coarse blade. Metal cutting blades are also to be had. Use these only for metal because they will not cut wood very easily and they will load up and burn in wood. On the other hand, a wood-cutting blade will not be able to cut metal effectively. Depending on the maker, there are many other specialized types of jigsaw blades available. Make sure you always have plenty of extra blades on hand to avoid unexpected trips to the store right in the middle of a job.