Refining a High-Quality Bandsaw

© John A. Swensen 1997. All rights reserved.

Working on my SCMI MiniMax S45 bandsaw was a very rewarding experience because it was a process of making a machine, that was very good to start with, even better. Unlike working on an inexpensive clone, where the object is just to make a machine usable, I only had to correct small quirks in the design or construction as I discovered them. To this day, the saw is the best machine I have; of course, I still plan to make a few more modifications.

After having made the modifications described below, I can saw as accurately with this bandsaw as I can with my contractor-saw-clone table saw, although the cut surface is not quite as smooth as I get with a Forrest blade. When cutting dovetails in maple, for example, I only need to pare off some very slight tooth marks before fitting the pieces together. Having a high-quality, well tuned bandsaw allows me to ignore the machine and concentrate on my sawing.

Many of the adjustments described on this page were learned by reading The Bandsaw Handbook by Mark Duginske, ISBN 0-8069-6398-0, Sterling Publishing Co., Inc., 1989. This is an extremely useful book that I heartily recommend.

Table of Refinements

Description of the Bandsaw

The MiniMax S45 bandsaw is a smaller, lighter version of the 24" and 36" bandsaws built by SCMI, an Italian manufacturer of industrial woodworking machines. The 18" bandsaw is similar to other Italian bandsaws, such as those sold by Felder USA or Laguna Tools, and is a floor-standing machine constructed of heavy-gauge, welded sheet steel. It has removable, hinged doors, a ribbed, cast iron table with cast iron trunnions, and provisions for dust collection.

The fence is constructed of tubular steel, and clamps to a steel angle rail that is, in turn, clamped to the table. This rail has open slots to allow it to be easily swung out of the way to change blades when the clamping knobs are loosened, and also to allow the angle of the fence to be adjusted to compensate for blades that don't want to cut straight. Tightening the knobs holds the split table reasonably flat. The table, fence, and rail are illustrated in the figure below.

Table and Fence

The upper blade guide post is constructed of tubular steel, and is slotted to accept a bolt to lock the height adjustment. The upper blade guide has two side roller bearings that can be adjusted to just clear the blade on either side, and a thrust bearing that is also easily adjustable; no tools are required to adjust the upper blade guide bearings. The lower blade guides are similar to those on the 14" Delta bandsaw, with rectangular plastic side blocks, one perpendicular, the other at 45° , and a small, hardened thrust bearing.

Flattening the Table

Unlike its big brothers, the MiniMax S45 has no provisions for flattening out any warp in the split table surface. Fortunately, it was easy to flatten the table to within .005" by using tapered metal shims between the table and the trunnions.

When I filed my shims to correct for table warp, I also adjusted the angle of the table in the direction of the cut, so that the leading edge of the blade was perpendicular to the table. This squareness is important for making stopped cuts, such as when sawing cheeks for a tenon or when sawing a dovetail.

Adjusting Wheels for Coplanarity

One of the central tenets of Mark Duginske's book is that the bandsaw wheels should be coplanar, so that, with a blade installed and properly tensioned, a straight-edge pressed against the sides of the two wheels would touch them in four places, on the tops and bottoms of the rims of the top and bottom wheels. Coplanar wheels give a blade the best chance of tracking straight. The points of contact, coplanarity, and two forms of non-coplanarity are illustrated in the figure below.

points of contact with straight-edge,
coplanar, parallel but non-coplanar, non-parallel and non-coplanar

In general, varying the blade tension will change the bend of the bandsaw's frame and will affect the coplanarity of the wheels so, theoretically, the coplanarity must be adjusted for each width of bandsaw blade. However, the widest blades with the highest tensions are the most difficult to track, so the wheels are usually adjusted at the highest tension setting. I didn't need to worry about this problem, though, because my bandsaw is stiff enough that I could not measure any appreciable change in coplanarity as I varied the blade tension. In fact, since adjusting my wheels, I have not had to touch the tracking adjustment for any width of blade.

Measuring the Coplanarity with Obstructions

On many bandsaws you can measure the coplanarity using a straight-edge if you, first, remove the table. The design of Italian bandsaws does not allow a direct measurement to be made, however, because the frame extends past the plane of the two wheels. I was able to get around the obstruction by clamping a straight_edge to the edge of the table and measuring the distance between the straight-edge and the four points of the two wheels. Although this method was awkward, I only had to do it once with my bandsaw, so I suffered through the process.

Had I needed to check and adjust the coplanarity often, I would have made a special, interrupted straight-edge for this purpose, as illustrated below.

Straight-edge with gap in center

Adjusting for Coplanarity

The top wheel of most bandsaws can be varied in tilt to adjust the tracking, and this tilt adjustment can be used to get the top wheel parallel to the bottom wheel. However, in order to adjust for coplanarity, either the tilt of the lower wheel must be adjusted or the top and/or bottom wheel must be shifted in or out, parallel to the axis of rotation. The figure below shows two alternative methods of adjusting for coplanarity.

Adjust by altering tilt of lower wheel
or by displacing upper or lower wheel

In the case of the MiniMax, the bottom wheel can be tilted vertically as well as horizontally by adjusting four bolts that locate the lower wheel shaft. The bottom wheel is tilted via the adjustment bolts while the upper wheel is tilted using the tracking control until the two wheels are coplanar.

Even though I had to struggle with my non-interrupted straight-edge, the adjusting process only took about an hour to complete, and that included time to adjust the drive belt tension. Unless I make some drastic changes to my bandsaw, I won't need to do this again.

Now, when I change bandsaw blades, I only need to set the blade tension and adjust the guides; I don't need to touch the tracking control.

Correcting Blade Guide Post Alignment

The rectangular, tubular steel, upper blade guide post on the MiniMax bandsaw is housed in the steel frame of the bandsaw, traveling up and down (more or less) parallel to the blade. The bandsaw with the guide post is illustrated below.

Guide Post
Ideally, to change the height of the upper blade guide one only needs to loosen the clamping knob, move the guide up or down, and re-tighten the knob, without having to adjust the blade guides before continuing to saw. Unfortunately, my post did not run parallel to the blade, and moving it from the lowest to the highest position required me to adjust the upper guides and thrust bearing. Even though these adjustments can be made quickly and without tools, I found them to be tedious and I would sometimes fail to make the adjustments, resulting in slight changes in the blade angles. To avoid these adjustments I needed to correct for alignment parallel to the side of the blade and parallel to the teeth.

Alignment Parallel to Side of Blade

My post (actually, my frame) was not parallel to the side of the blade, tilting slightly away from the blade as the post was raised. To correct this problem, I made a tapered shim that fit between the post and the frame. I measured the difference in offset of the guides from the blade in the top and bottom position and ripped a small piece of wood to this thickness. To do this safely, I used a hook-type push block, cut from a piece of tempered hardboard, as shown in the figure below. This push block allows me to hold the small piece of wood down and next to the fence, while keeping my fingers well above the saw blade. I hook my fingers over the edge of my fence so that if the push block slips, my fingers will not slip onto the blade.

Push Block
I next attached a piece of tempered hardboard to a scrap of plywood using double-stick cloth tape, and then I ripped and crosscut the hardboard and its plywood carrier so that the hardboard would fit between the guide post and the inside of the frame. Using the thin wood piece to determine the taper, I then ripped the hardboard side of the assembly until the thin end of the hardboard tapered to almost nothing, as shown below. I used the hooked push block to keep my fingers clear of the blade.
Taper Jig
I next drilled a hole in the tapered hardboard for the bolt of the clamping knob, reassembled the blade guide, and tested the alignment. Despite my attempts to carefully measure the error and calculate the correct taper, I over-compensated and had to cut a new taper. The second taper corrected the misalignment, so I toughened the hardboard by saturating it with thin cyanoacrylate glue. After the glue cured I fastened the hardboard to the inside of the frame using some double-stick cloth tape.

Alignment Parallel to Teeth

The guide post is held in place against the back side of the frame by a spring-loaded, adjustable angle plate inside the frame. This plate also keeps the post from dropping when the locking knob is loosened.

The alignment parallel to the teeth of the blade was almost perfect, only requiring that a brass shim be glued to the bottom edge of the back side of the frame, using epoxy cement. Although shimming at a single point (rather than with a wedge) causes the end of the post to follow a curve, rather than a straight line, the size of the correction was so small that the difference in the path was negligible. With such a small change in angle and with the angle plate exerting its pressure at a single point, no changes to the angle plate were necessary. The installed hardboard and brass shims are shown in the figure below.

Aligned Post

Replacing Guide Blocks with Cool Blocks®

The lower guide blocks on my bandsaw were originally a slippery black plastic material that worked reasonably well, but which had a tendency to melt if set too close to the blade. Also, the soft plastic was marred by the steel set screws, which made them hard to adjust precisely. I wanted to try using Cool Blocks® , but I could not find any that were the right size.

My solution was to buy a set of larger Cool Blocks® , which I cut down to size on my table saw. With a zero-clearance insert and a hooked push block, it only took about a minute to rip the Cool Blocks® to a sliding fit in the lower guide assembly.

Replacing Thrust Bearings

The lower thrust bearing on my bandsaw appeared to have arrived in a damaged condition (my saw was a floor model), as it seemed to make a lot of noise during use. My local dealer had no replacement bearings in stock, so I went to a local bearing supply house. They had a bearing with an 8mm hole that would fit, but they had no 8mm shafts to use as the post, so I needed to press out the old post and fit it in the new bearing.

To do this without damaging the old bearing I drilled a piece of angle iron with hole that just cleared the post. After clamping the angle in a vice, I removed the circlip from the post, dropped the post in the hole so that the inner shoulder of the thrust bearing rested on the angle, and then drove the post out with a punch. The drilled angle and the thrust bearing assembly are illustrated below.

Driving Out the Post
I then placed the new thrust bearing, front-side down, on the angle, replaced the circlip on the post, and drove the old post into the thrust bearing.

Although I was pleased with the ease of changing the thrust bearing, I was disappointed to discover that the substitution did nothing to solve the noise problem. The problem was the upper thrust bearing.

Quieting a Noisy Thrust Bearing

The upper thrust bearing of the MiniMax bandsaw is a relatively large bearing with a hardened face. Unlike the lower thrust bearing, this bearing would not be easy to find at a bearing supply house. When correctly set, the thrust bearing does not contact the back of the blade when the blade is not cutting. The force of the cut pushes the blade back a few thousandths of an inch, contacting the thrust bearing and causing it to rotate. At this point, my saw begins making a terrible noise, kind of like the sound of a screwdriver held against the flatted shaft of a running motor.

I tried lubricating the bearing shaft, which helped a tiny bit, but lubricating the hardened face of the bearing helped quite a bit more. Upon closer examination, I discovered that the hardened surface of the thrust bearing was slightly damaged. The noise was caused by the back of the blade catching on the roughness and vibrating. Lubricating the thrust bearing shaft with high-viscosity oil damped out some of the vibration, and lubricating the face of the thrust bearing reduced the amount of catching of the blade and, hence, the vibration. Unfortunately, in the dusty environment of a bandsaw thrust bearing, the lubrication on the face only lasted a few minutes.

The obvious solution was to grind the face of the thrust bearing smooth, followed by a polishing. To to this, I held a fine diamond honing stick, lubricated with oil, in contact with the face as the blade drove it around. This improved the noise some more, but it still did not solve the problem.

I may break down and buy a new upper thrust bearing from SCMI unless I can figure out how to improve it further.

An Improved Tire Brush

My bandsaw came with a brush to help keep the lower wheel clean, but the supplied brush was no more than a soft-bristled, disposable, paint brush with the handle cut off. The bristles were far too long and soft to remove any chips at all. Plastic chips were particularly troublesome, becoming embedded in the rubber tire and resisting attempts to remove them.

I bought a stiff, nylon-bristled, wooden-handled cleaning brush (kind of like an oversized toothbrush), cut off the handle, and glued pieces of plywood to either side and on top of the brush so that I could bolt it in place with the stiff bristles in contact with the tire. The new wheel brush is shown in the figure below.

Stiff Wheel Brush
With the new brush in place, the lower wheel stays clean, even when I cut plastics. The plastic bristles are stiff enough to remove chips, yet do not seem to damage the rubber tire. This type of brush could be adapted to other bandsaws by drilling a hole in the lower case or frame and installing a bolt parallel to the wheel shaft.

Tuning Bandsaw Blades

Most bandsaw blades come from the supplier in usable, but untuned shape, but a few minutes of work can greatly improve their performance. The parts of the blade that can be improved are the sides at the weld, the teeth at the weld, and the back edge.

Two useful tools to have are a fine diamond hone, such as an EZ-LAP Diamond Hone and Stone, which I bought for about US$5.00, and a die grinder, such as a Dremel grinder. The die grinder with a mounted stone point is an aggressive tool for removing metal, while the diamond hone smoothes rough corners and ridges.

Bandsaw blades are welded or brazed to size, and the joint is often far from smooth. The back of the blade may have a step at the weld, the sides of the blade at the weld may be rough or may stick out, and the teeth at the weld may stick out. I like to grind the back of the weld straight with a die grinder, and then I grind off any roughness from the sides of the blade. I usually do this with the blade mounted on the saw, moving the side guide blocks closer and closer until I am sure that the welds do not catch on them.

After this I run the saw with the thrust bearings backed out, away from the blade. I lubricate the diamond hone with a drop or two of oil and hold it against the side of the blade, being careful to avoid the set teeth. This operation further smoothes the weld.

I next round the back of the blade with the diamond hone, first smoothing the back of the blade, then cutting off the corners, then swinging the hone around to form a smooth, rounded edge. A rounded blade is less likely to damage the thrust bearings and will cut a smoother curve, the back catching less on the tooth marks in the kerf.

Finally, I adjust the guides and thrust bearings and try a test cut. A periodic ticking sound when cutting, but which goes away when pressure is removed, suggests that one or more teeth at the weld stick out slightly more than the rest (usually it is a piece of brazing material or weld splatter). To correct this problem I use a 1" cutoff disk in my die grinder to cut back the offending tooth or teeth.

The entire process takes less than 5 minutes, and only needs to be done once for each blade. The reward is a blade that cuts smoothly and quietly and guide blocks and thrust bearings that last longer.

Other Refinements to Try

Even though my bandsaw runs very smoothly and cuts well, I still have a few more optimizations that I would like to try sometime. I plan to update this page with my experiences as I get around to making more changes.

Wheel Brake

The Laguna Tools version of this bandsaw design features a wheel brake attached to a foot pedal. This brake bears on the lower wheel and stops it more quickly when changing blades or when stopping the saw to back out of a difficult cut. I would need to cut into the front of my case to add a brake, but there is room to install a lever and a pad that would bear against the lower wheel.

Quick Door Latches

The Felder versions of this bandsaw have quick door latches that mount on the front of the frame and engage a pin on the door with a helical slot in the knob. A half turn is all that is required to open a door (the current thumb screws seem to require about 20 turns to open the door; actually, I counted nine and a half turns). SCMI supplies these quick latches on their bigger bandsaws, so I may try to order them and adapt them to my saw. Alternatively, I may just install some magnets on the frame and let them hold the doors closed.

Magnetic Lamp

I can always use more light where I am cutting, so I may try to adapt a small goose-neck lamp by gluing a strong magnet to its base. I haven't yet figured out how to power the lamp, as the saw runs on 220V and most lamps take 110V bulbs.

Improve Trunnions

The cast iron trunnions that support the table are not quite uniform in thickness, so the trunnion clamps must be loosened far more than should be necessary. This makes fine adjustments of the table angle difficult and frustrating. I plan to either fly-cut the trunnions to uniform thickness, using a friend's milling machine, or to file the trunnions parallel myself.

Redesign Lower Blade Guides

The lower blade guide is buried under the table with very tight clearances, so that adjusting these guides requires several minutes of frustrating work with an open-end wrench and long hex-key wrenches. One of these days I may make a new lower blade guide housing with knobs to adjust each of the guides and bearings.

Miter Gauge

The miter slot for this bandsaw, at 12mm by 7mm, is not a standard U.S. size, nor does its close distance from the blade allow a standard, table-saw-type miter head to be used. I actually filed a bar of steel to fit the slot and cut a miter head out of some heavy aluminum angle stock, but I haven't figured out how to rule the angle gradations, nor have I found someone who will anodize the head for a reasonable price in the San Francisco Bay area, so that project awaits my finding more time and inspiration.

If you have any suggestions, corrections, or experiences that you would like to share with me, I would love to hear from you.

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Refining a High-Quality Bandsaw / / revised 1997 June 26