Fine-Tuning a BandsawVibration and wandering cuts are signsyour bandsaw needs a checkup

by Robert Vaughan

A n improperly adjusted bandsawwill do everything but cut well. Itmay throw, break or dull blades

quickly. Or it may produce cuts thatwander like a drunk failing a roadsidesobriety test.

I've performed surgery on a lot ofbandsaws, and I have discovered there'sno single saw component that causesmost ills. Many jumping and trackingproblems can be traced directly to worn-out tires. But a vibrating bandsaw may justas likely be handicapped by a beaten-updrive belt. A saw that refuses to cutsquarely may be affected by a guidepostthat is out of alignment, or the saw mayhave one of its wheels out of line (see thebox on pp. 78-79).

Solving many of these problems doesn'trequire a lot of fancy equipment. Basictools such as wrenches, try squares, a fileand some washers for shims are often allyou need. A few diagnostics and adjustingtechniques will bring out the bestperformance your saw has to offer. Thebasics include checking your tires forwear, wheel alignment, guidepostalignment and adjusting the guides andblade tension. Begin your tune-up byunplugging your machine.

Tires must be smoothand crownedI begin a tune-up by opening the wheelhousings and blasting the works withcompressed air to clear out the sawdust.Then I look at the wheels and tires. If awheel is broken or badly bent, there's notmuch you can do except replace it.

If your bandsaw tracks poorly or jumpsexcessively, chances are the tires areworn. The majority of bandsaw trackingand jumping problems begin and endhere. Tires should be whole, not missinglarge chunks, and without hairline cracks.

Tires need a crowned surface. Asmooth tire with a slightly crowned sur-face, like this one, will make a bandsawtrack accurately and run smoothly.

Worn-down tires need replacement.The author recommends replacing tiresbefore they get this bad.

The surface should be smooth, clean andslightly crowned (see the top photo). Thecrown defines where the blade tracks.Blades have a tendency to wander backand forth on the surface of uncrownedtires. A crown also keeps the teeth fromcutting grooves in the tire's surface. Agrooved surface will make trackingunpredictable (see the bottom photo).

If you cut a lot of resinous woods, youmay have a gummy buildup on the tires,which can create a false crown. Thatcondition can foul the blade's tracking,allowing it to drift. You can check this byturning on the machine and letting it idle.

see whether a bandsaw needs its wheelscrowned, you don't have to remove thewheel. First remove the wheel guards, andback off the blade-guide components.Install a -in. blade, and set the tensionnormally. Adjust the tracking so the bladestays in the middle of the tire when thewheels are turned by hand. With a scrapof wood, push on the back of the bladeusing the same kind of force you'd use forcutting wood (see the photo at right).Hold the block in place for three or fourrevolutions of the blade, and then releasethe pressure against the blade and turn it afew more times.

If the blade's position on the tire surfacedoesn't change even though the bladedeflects slightly from the pressure of thewood block, then the crown is in goodshape. If the band moves off the centerposition under pressure and returns whenpressure from the wood block is released,the crown is showing signs of wear but isstill functional. If the blade moves anddoesn't return to its original position, thencrowning is needed. You can do thisyourself (see FWW #95, pp. 50-53).

Tires need replacing from time to time.

Check the crown and drive train—To

Most machines that have less than a 16-in.capacity use a rubber-band type of tire.Larger machines may have tires of aspecialized configuration; some have afitting groove in the middle of the wheel'ssurface. When ordering replacements,note your saw's model number; I've seendifferent tires used on similar models.

While you're in the machine's innards,examine the saw's pulleys. Those that are

worn or bent can cause vibration. Wornbelts develop knots at the factory joint,creating a bumping sensation. Replacethese inexpensive items when they showsigns of wear. And check all bolts andsetscrews for tightness.

Align the blade to the guidepostThe guidepost should move up and downin a line parallel to the blade. Otherwise,

Checking for crown wear—Theauthor spins the bottom wheel by hand

block of wood using normal cutting

the blade's position won't change.

the upper guide components must bereadjusted with each change in stockthickness—a nuisance that eventually getsignored until blades start breaking orcutting-precision deteriorates. For mostsmall bandsaws, there are few, if any,adjusting mechanisms for the guidepostitself. But you can reposition the wheelsto compensate for an out-of-lineguidepost. This is a tedious, trial-and-error process, but just think of all the timeyou'll save not having to readjust yourguide components every time you raiseor lower the guidepost.

Checking the guidepost's alignmentstarts with the table. Remove the upperguide bracket, and raise the guidepost allthe way up. Turn the wheels by hand for afew revolutions to make sure the blade'stracking is properly adjusted. Using twotry squares, check to see if the table isperpendicular to the blade (see the photoon p. 78). Adjusting the table side to sideis done through the trunnion stops. Toadjust it front to back, install flat washersbetween the trunnion bolts and thebottom of the table to raise a section thatsuffers from a dip (see the top photo onp. 79). If so equipped, be sure that thetaper pin or locking bar is installed in thesplit of your tabletop. Tabletop flatness inthis region is controlled by tapping thepin in or out. Perfection may be elusivehere; get it as close as you can.

Lower the guidepost, and check it withthe try squares (see the bottom photo onp. 79). The guidepost should also beperpendicular to the table. If it's off by

in. or more over 6 in. of height, you'llneed to make adjustments.

Some professional-duty bandsaws haveseparate adjustments for the guideposttravel path. Light-duty machines, such as14-in. bandsaws, usually have no suchprovisions. To adjust them, you'll need tobe creative and use shims or file downcertain components to shift the upperwheel alignment. You are trying to get theblade to run parallel to the guidepost (seethe drawings and photos on p. 80).

If your guidepost tilts to the left or right,filing down the tilt adjustment hinge,

pressure. If the crown is in good shape,

while pushing against the blade with a

Adjust the table's tilt mechanism asneeded for side-to-side alignment. Thencheck front-to-back alignment.

located behind the upper wheel, on oneside and shimming the other will get theblade more in line with the guidepost.

If the guidepost tilts fore or aft, you'llneed to shim one of the wheels with awasher. Be careful about what kind ofwasher you use here. If the wheel has abearing pressed into its hub, standard flatwashers will work because the wheel iskept square to the shaft by the bearing. Ifthe wheel doesn't have a bearing, you'llneed to use precision machined washersto avoid introducing a wobble, which canbe caused by hardware store varietywashers that aren't very flat. You canorder a machined washer from Delta (partno. 904-061-4982) to fit the 20mm lowershaft of a 14-in. bandsaw.

After shimming a wheel, you will haveto square up the blade to the table again.Then check the guidepost alignment.There's a bit of trial and error involved infinding the right amount of shim.

The true test of just how well you'vealigned the guidepost will make itselfevident when you adjust your guides andthen raise or lower the guidepost. If youneed little or no adjustment to the guidesover the travel of the guidepost, you'vedone a good job.

All this work will be an exercise infutility if your handsaw's guidepost isflimsy and deflects under normal cuttingpressure. To see whether you have thiscondition, raise the upper guide about

Troubleshooting guide for bandsaws

Problem

Causes

Blade comes offwheels whenmachine is running.

Tires need crowning;wheel bearings areloose or worn;wheels are out ofline; top wheelcarriage is loose.

Blade comes offwheels whenbacking out of a cut.

Wood is pinching bladeand dragging it out;blade tooth set hasbeen worn out; tiresneed crowning; wheelbearings are loose;top wheel carriage isloose; wheels are outof alignment.

Machine jumpswhen running.

Tires need truing;wheels are out ofbalance; blade haskink in it; drive beltis worn; drive trainpulleys are bent;machine is notsitting squarelyon floor.

Blade seemsto dull veryquickly.

Back guidebearing hasmoved awayfrom blade;wrong bladefor the wood.

Machine cutstruncated conesinstead of cylinders.

Guidepost is out ofalignment; blade isnot perpendicular totable; upper wheel isout of alignment.

Using try squares, determine whetherGuidepost alignment procedure-

the blade is perpendicular to the table.

Blade moves inand out whenmachine is idling.

Wheels are bent orwarped; blade isnot weldedstraight; blade haskink in it; pitchbuildup on tires.

Ticking blade soundwhen machine isrunning.

Blade weld joint isnot ground smoothat sides or back;blade has kink in it;blade is cracked andready to break.

Blade doesn't cutstraight whenresawing.

Incorrect blade isbeing used; wrongtension on blade (tooloose); feed rate istoo fast; guidepost ismisaligned.

Guides don'tclose in tightlyenough on blade.

Blade guidechannels needcleaning; bladeguides aregrooved or worn.

Blade drifts andwon't follow line.

Not enough setin blade; upperguide is settoo high; sideguides are settoo wide; feedrate is too fast.

Scraping noisewhen upperguide is raised.

Top of guard ismisaligned andrubbing wheel.

er inserted between the table and either

square the table to the blade.

additional adjustments.

in. off the table, and push against theguidepost. When the guide starts todeflect, you have determined how hardyou can push your stock before knockingthe blade out of alignment.

Wheels in a twist will causetracking problemsThe wheels of a bandsaw must be inparallel planes. Having them in the sameplane (coplanar) is preferable, but it'snot necessary. And it's impossible if youhave moved a wheel to correct amisaligned guidepost.

Wheels in a twisted configuration willcause the most problems. However, I'veseen bandsaws where a good tire crownoffset minor wheel misalignment. If yourbandsaw has good, crowned tires yet stillsuffers from tracking problems, check thewheel alignment. Unfortunately, on themost common 14-in. bandsaws, there areno easy adjustments that you can make tocorrect twisted wheels. You'll need theservices of a machinist to modify theupper axle housing. Industrial qualitymachines have adjustment provisionsbuilt into them.

To check alignment, turn the wheelsforward by hand for a few turns, andwatch where the blade tracks. Next turnthe wheels in reverse. If the blade'sposition on the crown changes, thewheels are in a twist. A pronounced twistwill allow the blade to fly off the wheels.

You may find that your wheels areslightly misaligned, but there's noproblem directly attributed to thatcondition. So leave things alone.

Adjusting blade guidesBlade-guide components, like tires, arewear surfaces meant to be replaced or

renewed. There are many varieties ofguides, from simple solid-steel bladeguides to costly bearing-type guides. Alldo the same thing: They keep the bladefrom moving side to side and front to rearwhen under a load.

Solid-steel guides should be regroundflat and filed smooth from time to time.The bearings should be checked for freerotation, and the screws and guidechannels should be cleaned regularlyto allow quick and easy adjustments.The bottom guides should be checkedmore frequently than the top guidesbecause they are constantly being floodedwith sawdust.

Guide components should never beadjusted so tightly that they constrictblade movement. They should be justclose enough to restrict blade deflectionunder cutting pressure.

I don't find that it's necessary to usemeasuring devices to check the clearancebetween the blade and guide blocks orthrust bearings. I make these adjustmentsby sight and sound.

Here's a foolproof way to do this. Firstloosen all the guide components, andmove them back from the blade. Adjustthe blade tension. No two experts seemto agree on how to make this adjustment,so suit yourself. I get on my tiptoes andsight down the front edge of the bladefrom the top wheel and tighten theadjusting knob. As the blade tensionincreases, the blade straightens out.When it stops straightening, I give theadjusting knob a half revolution or so,and I'm there.

Begin adjusting the guides by spinningthe top wheel by hand and gentlypressing one guide block until it justkisses (but does not deflect) the blade. At

Front-to-back adjustment—A flat wash-

the front or back trunnion will help

perpendicular to the table. If it's out byNow check the guidepost. It should be

saw's performance can be improved byin. or more over 6 in. of its height, the

Correcting bandsaw guidepost alignment

You can't adjust a misaligned guidepost on most small bandsaws. The solution is to repositionthe wheels so the blade runs parallel to the guidepost. After repositioning the blade, you mustagain align the table to the blade at 90° by adjusting and/or shimming the trunnions.

the same time, make sure that the guideblock is aligned just behind the gullet ofthe blade's teeth.

Once those components are in position,tighten the lock screws. Then press theopposing guide block until it just touchesthe blade, and tighten it. Spin the bladeby hand some more, and observe thecontact against the guide blocks. If theblade rubs constantly, back off the guideblocks just a hair so that the blade runsfreely. Adjust the other pair of guideblocks the same way.

To adjust the thrust bearings, I bring oneup gently against the blade, spin theblade, back the adjusting screw off untilthe bearing only ticks against the bladeonce or twice over the course of acomplete revolution. Then I do the otherone the same way. All these guidecomponents need to be readjusted eachtime a new blade is installed.

I don't bother using plastic guide blocks.I think they create friction, don't last andmay even smell up the shop when theyget overheated.

A few other detailsBecause machines aren't perfect, I'malways looking for ways to improvethem. Simple modifications sometimesmake all the difference in the world. Forexample, I replace adjusting screws onbandsaws with matching socket-headscrews and adjusting nuts with wing nuts.The fewer tools you have to hunt down,the faster it is to adjust the machine andchange the blades.

If the saw's power switch is located onthe stand, then consider relocating it tothe arm. That way, you won't have to putyour face near the blade to turn themachine on or off. A flexible work lightaimed at the blade also comes in handy.

Beef up a flimsy sheet-metal stand withplywood panels screwed and glued onwith construction adhesive.

Consider modifying the stand forconvenient dust deflection or collection.When positioning a bandsaw in yourshop, find a level spot on the floor, orlevel the saw's legs with shims or someother kind of leveling device. Moving abandsaw around the shop can distort theframe and create slight misalignments.

Robert Vaughan is a contributing editorto Fine Woodworking magazine, and herepairs and restores woodworkingmachinery in Roanoke, Va.