Most of the time, once you’ve installed a new bandsaw blade and set it up correctly on the wheels, the bandsaw will just keep running trouble-free with little or no adjustment until the blade wears to dullness and needs replacing again. Unless something happens, it will generally keep running smoothly but the occasional need for a tweak will arise and you, the machine operator, should be sensitive to hear and see the need for a small change by adjustment of tracking or tension. The more you use a bandsaw the more you recognise changes in sound that affect the machine’s performance and thereby the quality of the cut. For most bandsaw work, the tension on the blade, that stretch between the top and bottom wheel, is the one most likely to throw you off. Too much tension puts much strain on all things and over-tightening can cause the blade to take the path of least resistance. If the top wheel tilts even slightly too far back or forward at the top, the blade will move off-centre towards one edge of the wheel or another. Whereas we do want a strong tension, too much puts undue pressure on the wheels and the bearings that allow its fast revolving and then too the blade itself which will usually snap at the often weaker point of the weld. When this happens there is an almighty bang as the top spring-tensioned wheel shoots up and bangs somewhere against the steel housing enclosure.
Go back 50 and more years and roller bearing guides on domestic bandsaws didn’t exist though they did have them as industrial guides for commercial milling bandsaws. Most domestic bandsaws were under 18″ and your machine came with 1/2″ square steel blocks for guides that sat barely touching either side of the blade and aligned just behind the kerf of the blade teeth. To stop the blade from deflecting under beam press, that’s front to back, and so keep the blade perpendicular under thrusting pressure, a further 1/2″ square block sat directly centres against the back edge of the blade so that the blade always presented perpendicularly to the wood. Below the table was an identical set-up. Aligning both sets top and bottom guaranteed square cuts. The downside of the square blocks in contact with the blade at any point for prolonged cutting is of course that the blocks are fixed and not moving, so with any friction, we also get a build-up of heat. Heat to the blade makes it longer and this can affect the tension by making it slacker on the two wheels. Because of this, we generally allow a breather-gap a paper thick between the guide blocks and the blade for safety as well as the tension issue.
Any flex in the beam front to back results in the blade bending to one side at the leading edge where the teeth are. When this happens, even for the smallest amount, the blade will usually creep more and more into a barrel cambering and such gain will ultimately increase in pressure to even bind the wheels and stop the bandsaw altogether. The cut itself will result in a cambered cut to one side of the cut on one piece and a convex shape on the adjacent piece. On my first two bandsaws in the USA in the mid-1980s, a 14″ American-made Delta and an 18″ Taiwanese-made Grizzly, the blocks lasted a long time and because they could be rotated to a new corner as needed and then too flipped end for end; thus they lasted through the 20 or so years that I owned them before selling them on for near what I paid for them. The steel blocks were just mild steel so refining them square-ended to remove worn areas or remaking new ones cost little time and only pennies to replace. The beam flex of a blade is somewhat constrained by both the block guides and the roller bearings depending on which are fitted to the machine. The greatest control against beam flex though is the alignment of the blade to the two wheels and the tension of the blade. The guide blocks only help, they are not the key components or the answer by any means.
Creating some book-matched panels for my doors, seeing the smoothness of the cuts and the accuracy in the thickness of my finished board at dead on 17/32 (13.5mm), I was suddenly aware that not everyone enjoyed such results from their bandsaw. It made me think about encouraging others in their bandsaw working. The width of my boards were 8″ (20cm) across. I first hand planed true the initial registration faces of eight panels ready for glue-up. In using my bandsaw mostly for work such as this, resawing larger stock sizes for project components through five decades or so, I take my working knowledge of bandsaws for granted. In the midst of several longish long-grain cuts through various wood types this week, oak, beech, sycamore, walnut and then too some hard mesquite, I subconsciously fine-tuned the bandsaw mid-cut without hesitation and the adjustment was instant. It also struck me that there are in general only two key aspects to obtaining optimal performance from your bandsaw and no, it’s not much at all to do with the side cylindrical roller bearings or the square blocks I spoke of and neither is it the rear thrust bearings bumping up against the back of the blade top and bottom. The two important elements are blade alignment on the wheels and the tension applied to the blade. You can adjust these two at a macro level and then fine-tune them in the zone and even mid-cut as and if needed. Get these right and the guides will have very little or even nothing to do.
On the more common, two-wheeled bandsaw (three-wheelers are rare) the top and bottom wheels must be as coplanar as possible. The bottom wheel is the actual drive wheel driven by the electric motor. The top wheel is then driven by the bandsaw blade itself connecting the two wheels as a sort of steel driver belt. Aligning one wheel to the other is simplified if the bottom wheel is correctly aligned as then you need only line the top one to the bottom. Unfortunately, this can only really be done when the correct amount of pressure is applied to the wheels when the wheel adjustment is applied to the top wheel. And how much pressure is the right pressure? In the beginning, this is mostly guesswork as there is almost no way to convey the felt pressure to another user without the other user being there to feel what you set. I will try to help with that shortly.
On rare occasions, altering the fixed bottom wheel to tilt the bottom wheel into near alignment is a rare thing. Tilting it vertically forward or backwards at the top of the wheel in turn moves the bottom of the wheel in the opposite direction. This is usually quite a time-consuming adjustment to do but thankfully the set-up at the factory in this day and age is mostly done well at the factory of manufacture before it goes out. I have only adjusted one bandsaw this way and the only reason to do it is if the installation of a bandsaw blade resulted in the position of the blade being too far forwards or backwards on both the top and bottom wheels to where the blade is near to or even riding on the rim of one wheel and on the opposite side of the other wheel. This should be the rarity and hopefully, you don’t have this problem.
Each time you install the blade in a bandsaw the blade tension is relaxed and will need resetting. Reinstalling a new blade generally does not mean that you can simply use the same setting as before. Most modern bandsaws come with a quick-release lever that takes off or applies tension with the single sweep of a cammed mechanism via a lever arm somewhere on the back of or beneath the top bandsaw wheel.
If it doesn’t have one of these, say on an older or less sophisticated machine, then there is a simple wheel somewhere that can be turned to apply tension to the blade. Though quick and effective, the lever generally does not reset the tension at all accurately. Various things affect the tension not the least of which is any difference in the length of the blade, the width of the blade and so on when manufactured to custom-fit your machine. With the best will, any maker can add or subtract a millimetre.
With the new blade installed, and most of the tension applied, rotate the top wheel by hand to establish the blade to its natural tracking position on both wheels by these initial rotations. In most cases, the blade should find its tracking on the same path as previous blades installed unless you have changed the width of the blade itself or if it is a different length. I rarely ever need to adjust the tracking of a newly installed blade simply because I don’t generally change the blade width. A half-inch beam width is good for a variety of tasks including all of my resawing. The weld holds well on this size whereas narrower blades have a higher tendency to break.
It’s now that we apply the right tension. The tighter the tensioning between the two wheels the less allowance there is for any lateral deflection side to side or beam-bend front to back in the blade between the top and bottom bearings. That said and as I mentioned earlier, it is not a question of applying as much pressure as possible as this will cause additional problems. On bandsaws, as with no other machine, it is critical to find the balance between tension and blade alignment in accord with the alignment of both the top and bottom wheels. It sounds complicated but with sensitive listening and continuous searching for perfect cutting, you will own the skills of setting up and listening to your bandsaw.
I recommend a heightened distance between the top bearings and the table of about 6-8″. Now stand a square or a block of wood directly against the blade and push on the blade midway between the top and bottom bearing with firm pressure as shown. With the blade tight there will be a little flex. Release the blade and let it spring back. The gap should be no more than say an eighth of an inch from the square or the block of wood.
If the blade does need further tightening, adjust the tension wheel by turning it. You can feel for the tension on the blade as you turn the adjustment wheel. Check again with the square or the block of wood for spring-back from the blade.
Shut the bandsaw doors and blade covers, switch the machine on and let it run for half a minute just to ‘seat‘ the blade and centre it on its tracking path.
Now check the side-to-side squareness and adjust the table for squareness.
The front-to-back squareness, though stopped by the rear thrust bearings top and bottom, really relies on the alignment of the blade to the top and bottom wheels. By tweaking the adjuster at the back of the machine you can tilt the top wheel to send the blade forwards or backwards on the wheel and by this we optimise the performance of our bandsaw.
Turn the top bandsaw wheel by hand and the blade will move on the first and subsequent revolutions. The blade will also probably be hitting the two rear thrust bearings if the top of the wheel is tilted too much one way. It’s best to release the thrust bearings and let them float until you have aligned the track of the blade on the wheels and they register square by your adjusting the tilt of the top wheel. Don’t panic. It’s not rocket science and it becomes completely intuitive. By watching the alignment of the blade you will identify which direction to turn the adjuster. If the blade is already centred or biased towards the back then adjust the tilt to change the tilt of the wheel which will then move the blade forward until the blade is free of the thrust bearings and the square shows the blade is square to the table front to back.
Now, with the blade tracking and plumb square to the table in both directions, bring the rear thrust bearings up lightly against the back of the blade and cinch them tight. They should just kiss the back of the blade top and bottom.