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Winter 2013-2014

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Tune Your Bandsaw

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Tune Your Bandsaw

6 adjustments deliver professional results.

By Mark Duginske

I love bandsaws, even though they have a reputation as troublesome tools. I suppose that’s why I like them, because I enjoy investigating woodworking machinery. I’ve tinkered with dozens of 14-in. bandsaws, trying to understand how they work and how they should be set up. Here’s what I’ve concluded: most bandsaws benefit from a tune-up. 

In the next pages, I’ll show you six procedures to improve your saw’s performance. I’ll demonstrate these steps on a standard cast-iron 14-in. saw, but they apply to just about any type of bandsaw. Once you complete your inspection of your own saw and correct any problems (or learn to live with your saw’s limitations), I’ll show you how to adjust it for a typical blade. 

The alignment procedures we’ll perform are a one-shot deal. You shouldn’t have to re-check your saw again. The tensioning, tracking, and guide-adjustment procedures must be followed every time you change blades, however. 

Before we begin, let’s review the major parts of the saw and what they do.

A visual guide to your bandsaw

Two wheels and a blade. Those are the essential parts of a bandsaw, but of course there are many more. Here’s a guide to the parts you’ll be handling or adjusting when you tune up your saw.

Wheel. Both top and bottom wheels are covered with a piece of rubber or other material called a tire. The tires on most 14-in. saws have a slightly convex surface, or crown. The crown forces the blade to the center of the wheel.  

Tension knob. Turning this knob raises or lowers the upper wheel. Raising the wheel tightens the blade, increasing the blade’s tension. Lowering the wheel allows you to remove the blade.

Tension scale. This indicator gives you a rough idea of the blade’s tension. It doesn’t actually measure tension, though. It shows you the amount of compression in the spring located behind the scale, which acts as a shock absorber for the wheels. Numbers on the scale correspond to a blade’s width. Wide blades require more tension than narrow blades. Minor variations in the length of a blade don’t affect the scale’s reading.

Tracking knob. Turning this knob tilts the upper wheel. This moves the blade forward or backward on the wheel, as you face the saw. 

Thrust bearing. There are two thrust bearings: one above and one below the table. When you’re cutting, thrust bearings stop the blade’s rearward deflection. They rotate to reduce friction.

 



Guide. There’s a pair of guides above and below the table. They prevent the blade from deflecting sideways or twisting as you cut. Some guides are fixed blocks; others are bearings, which rotate.

Guide post. This bar adjusts up and down in order to position the guide assembly close to the workpiece. 

Throat plate. Remove this part to see the position of the lower guides. 

Column. Cast-iron bandsaws have a joint in the middle of the column. The joint allows you to extend the column’s height by inserting a riser block, which increases the saw’s height capacity by 6 in.

Trunnion. Two trunnion assemblies, one in front and one in back, allow the table to tilt. Each assembly has two mating halves: a convex part attached to the table and a concave part attached to the saw’s frame. A knob under each trunnion assembly tightens the table in position.



Align the wheels

If you look at the upper wheel on your 14-in. bandsaw, you’ll notice that it has a crown: the center is higher than the edges. The crown exerts a pulling force, moving the blade to the top of the wheel. In a well-tuned saw, both wheels and their crowns are coplanar (in line with each other). This allows the blade to run as straight as possible. If the wheels aren’t in alignment, they compete with each other for control of the blade. This isn’t a problem for narrow blades, but aligned wheels improve the performance of wide blades, such as those you’d use for resawing. 

1. Unplug your saw. Remove the blade, then unbolt and lift off the table (Photo 1).

2. Install a 1/2-in. wide blade and tension it according to the saw’s scale. Some authorities skip this step and align the wheels without a blade. That isn’t correct, because the saw has to be under tension when the wheels are aligned, to simulate real running conditions. A wider blade requires more tension than a narrow blade, and it’s best to align your wheels under the most tension they’re likely to receive. On most 14-in. saws, the largest blade you’ll use is one that’s 1/2 in. wide. Back off the upper and lower guides and thrust bearings so they’re at least 1/8-in. away from the blade.

3. Open both wheel covers and place a long straightedge across the wheels (Photo 2). If the wheels aren’t parallel, turn the tracking knob behind the saw to tilt the upper wheel forward or backward. Once the wheels are parallel, you can determine whether or not they’re coplanar (Figure 3).

4. If the wheels are not coplanar, determine how far one wheel must be brought forward. Measure the gap between the straightedge and the wheel. If the gap is less than 1/32 in., your wheels are sufficiently coplanar and you can skip ahead to step 6. If the gap is greater than 1/32 in., one wheel should be adjusted. 

5. To re-align a wheel, remove it from its axle and add or subtract bushings (Photo 4). On most saws, you can only remove one wheel, not both, without using specialized tools. On Delta saws, the upper wheel comes off easily; on most other brands, the lower wheel comes off. The bolt that secures the wheel has a left-hand thread. Turn it clockwise to loosen it. If your wheel must be moved in, and there are some bushings behind it, simply remove one or two, corresponding to the gap you measured above. Replace the wheel and you’re ready to move on. If your wheel must be moved out, measure the axle’s diameter and purchase a few machine bushings at the hardware store. Standard washers work OK, but are about 1/16 in. thick. Machine bushings are thinner (about 1/32 in. thick). Once you’ve put the wheel back on, replace the saw’s table and re-install the blade.

1. Begin aligning your saw by removing the table. It’s easy to do. Take off the blade, then unscrew and remove the knobs under the trunnions. The table just lifts off.


2. The first alignment check is to see if the saw’s wheels are coplanar (lying in the same plane). Tension the blade, then place a long straightedge across both wheels. Tilt the top wheel so that it’s parallel with the bottom wheel.


3. Here’s what you may find using the straightedge test. In A, the straightedge touches at four points. The wheels are coplanar, and you’re all set. In B, the wheels are parallel, but don’t lie in the same plane. Measure the gap behind the straightedge. In C, the top wheel must be tilted before you can determine whether the wheels are coplanar. 


4. The fix for wheels that are out of alignment isn’t hard. You simply pull off one wheel and remove or install a machine bushing or washer to act as a shim. Some wheels can’t easily be removed, however, so you may have to live with a misalignment problem.



Track & tension

Before moving on to the next step, your blade must be adjusted to run in the center of the wheels. This is called tracking, and it’s a procedure you follow each time you change blades. The correct method is to steadily increase tension while you track your blade, so you’ll make both the tracking and tensioning adjustments at the same time.

6. Unplug the saw. To begin, the blade should be under very little or no tension. Rotate the upper wheel by hand and slowly increase tension (Photo 5). After a few revolutions, note where the blade sits on the upper wheel. Adjust the tracking knob to move the blade in or out (Figure 6) as you continue to rotate the wheel. Keep rotating the wheel and adjusting the tracking knob until the blade is under full tension and tracking in the middle of the wheel.

7. Check the blade’s tracking under power. Close the wheel covers and plug in the saw. Turn the saw on for a second and then turn it off again. Open the top door and see if the blade still tracks in the wheel’s center. If it does not, make a minor change in the tracking knob’s position, and check again.

 

5. To prepare for the next step you have to re-install the blade and track it in the center of the wheel. Slowly bring the blade up to tension as you rotate the upper wheel by hand.


6. Adjust the tracking knob to center the blade (A). Turning the knob counterclockwise (B) tilts the upper wheel and moves the blade forward. Turning the knob clockwise (C) tilts the wheel in the opposite direction and moves the blade backward.



Square the table

It’s easy to understand why your bandsaw table should be set at 90 degrees to the side of the blade, but did you ever check whether it was also square to the back of the blade? This is important for advanced joinery techniques such as cutting tenons or dovetails. It will also help in the next alignment check, squaring the guidepost.

8. Raise the guidepost as high as it will go. Remove the throatplate if it sits proud of the table (it should be exactly even, or, better yet, a little low in front and high in back). Loosen the trunnion bolts and tilt the table side to side until it rests solidly on its 90-degree stop (the stop is usually a bolt located under the table’s left side). Tighten the trunnion bolts.

9. Place an accurate square alongside the blade. If the table isn’t square, adjust the stop.

10. Place the square behind the blade (Photo 7).  If the table isn’t square in this axis, shim the front or back trunnion (Photo 8). You can use any hard material for shims, including a cut-up soda can. This can be tedious, but it’s not difficult. The screws that fasten the trunnion to the table may be hard to access. If so, remove the table from the saw. You will lose the trunnion’s position when you loosen all of its screws (it must align properly with the lower trunnion), but the correct position isn’t hard to regain. After inserting the shims, loosely tighten the screws and return the table to the saw. Tighten the trunnion bolt, which will pull the upper trunnion into position, then tighten the trunnion screws.

7. After centering the blade on the upper wheel, place a 6-in. square behind the blade. If there’s a gap at the top or bottom, the table isn’t square to the blade. Measure the gap with shim stock.


8. Shim one of the trunnions to adjust the table. Remove the table to access the trunnion’s mounting screws. To start, insert shims that are the same thickness as the gap you measured above, in Photo 7. 



Adjust the guide post

On a well-tuned saw, the guide post runs parallel to the blade.  When you raise or lower the guidepost to accommodate material of different thickness, the blade guides and thrust bearing are always in the correct position relative to the blade. If the guide post doesn’t run parallel to the blade, you’ll have to readjust the positions of the side guides and thrust bearing each time you move the guidepost up or down to saw wood of different thickness. That’s a situation you can live with, but you don’t have to. 

11. To check your guide post, the blade must be tracked and tensioned, and the table must be square to the blade. There are two ways to proceed. The easiest method is to lower the guidepost as far as it will go and plane a short stick, of minimum thickness, to fit between the post and a 12-in. square (Photo 9). Or you can remove the lower guide assembly from the guide post and place the square directly against the guidepost.

12. To re-align the guide post, you must tilt the entire upper casting of the saw. First, remove the blade. Next, loosen the bolt that connects the saw’s upper and lower sections. Place brass shim material in the joint to tilt the guide post front-to-back or side-to-side (Photo 10). It takes trial and error to find shims of the correct thickness. Tighten the joint before checking the guide post. Once the guide post is square, go back to the start of the alignment checks (Step 1) and check that the wheels are still sufficiently coplanar.

9. The third alignment check is to see if the guide post is square to the table, front-to-back and side-to-side. Place a wood spacer between your square and the guidepost to get an accurate reading.


10. Align your guide post by shimming the saw’s column. Loosen the bolt between the saw’s upper and lower sections. Place shims in the joint to tilt the column and guide post.



Round the blade

This is an optional step, but it increases the life of your blade and thrust bearings. The rounder the back, the less likely the blade will crack. The stone also smoothes over the welded portion of the blade, so it can’t scar the thrust bearings.

13. Round the back with a stone (Photo 11 and Source, below). It will take about five minutes. Begin with the corners, then round the rest of the blade’s back.

11. Now that your saw is aligned, turn your attention to the blade. It’s a good idea to round the back of a new blade with a dry oilstone. Removing the back’s sharp corners will extend the blade’s life.

Caution:  This operation causes sparks. Disconnect your dust collection system from the bandsaw.



Adjust the guides

Many of the procedures above are one-time only adjustments, but every time you put a new blade in your saw you’ll have to reset the guides and thrust bearings. Here’s how to do it right.

14. Back off the thrust bearings above and below the table. Adjust the side guides, above and below the table, so they don’t touch the blade. Track the blade in the center of the upper wheel. 

15. Position the guide assembly about 1/4 -in. above your workpiece. Adjust both thrust bearings so they’re about .015-in. behind the blade (Photo 12). That’s equivalent to four thicknesses of a dollar bill, or four pieces of standard weight (20 lb.) printer paper. Whatever system of measurement you use, it’s important that both bearings sit an equal distance behind the blade. 

16. Adjust the side guides forward or backward until their leading edge is about .015-in. behind the blade’s gullet (Photo 13). Be sure to adjust the guides below the table, too. When you cut, the blade will bend backwards and ride against the thrust bearings, but the blade’s teeth shouldn’t contact the side guides. The narrower the blade, the more care you should invest in getting this setup just right.

17. Adjust each set of side guides close to the blade (Photo 14). The gap should be very small, but not so close that the blade contacts the guides when it’s not cutting wood. If you have bearing guides, rather than blocks, make sure that the guides are rotated in such a way that their high points are directly opposite one another. The lower guides on some saws are hard to access. You may find that tilting the table makes them easier to get to through the throatplate opening.

12. Adjust the upper and lower thrust bearings about .015 in. behind the blade. That’s equivalent to the thickness of a dollar bill folded twice, making four layers. Remove the guard to make this measurement easier to see.


13. Adjust the forward position of the upper and lower guides. The front edge of the guides should be slightly behind the bottom of the blade’s gullet.


14. Adjust the clearance between each guide and the blade. The gap should be about .004-in., which is the same as the thickness of a dollar bill. You’re all set to saw.



The tension squabble

I wouldn’t be a bit surprised if you’re confused about blade tension. A lot of misleading information has been published about it, and I’d like to set the record straight.

Some folks claim that the tension gauge on your 14-in. saw is erroneous and that using its indicated settings doesn’t deliver enough tension. They would have you replace an old spring with a new one, replace a standard spring with a more powerful one, or purchase an aftermarket tension gauge to substitute for the one on the saw. None of this is necessary.

First, old springs don’t wear out, and don’t need to be replaced. Second, most springs provide adequate tension. The exception would be a spring that is fully compressed at its highest tension setting. This spring should be replaced with a more powerful one. Third, the scale on your saw may not be perfect, but as a rough indicator, it’s adequate for the purpose. According to my measurements using the best aftermarket tension gauge available, these scales are accurate enough. 

For most work, you’ll get good results with the tension gauge set at the mark corresponding to the blade’s thickness. But if the blade isn’t sharp, or the workpiece is especially thick, increase the tension one mark. In any case, no saw will perform well unless it’s tuned up first.



Source

(Note: Product availability and costs are subject to change since original publication date.)

Highland Hardware, highlandhardware.com, 888-500-4466,  Blade Rounding Stone, 086031.


This story originally appeared in American Woodworker January 2008, issue #133.

January 2008, issue #133

Purchase this back issue.


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Comments

mikekelly wrote re: Tune Your Bandsaw
on 04-13-2010 2:07 PM

Good article. Clear and easy to understand. I am on my way to my shop for the tune-up