Tony dropped off his 4×6 metal cutting bandsaw. It needs some TLC and improvements, but holds great potential.
This same basic saw is widely available from a number of different importers like Harbor Freight and Grizzly. Many people have devised improvements and modifications to make the saw more versatile. Like many inexpensive imported power tools, it is usually considered to be a bit of a “kit” that requires some modification and improvements to turn it into a truly useful tool.
A band saw like this is intended mainly for use as a chop saw to cut metal stock to length. It serves a very similar purpose to the abrasive chop saw, but will make a much cleaner cut without heating up the metal nearly so much, and can handle much larger material. The saw can be left (only somewhat!) unattended while you continue work on other things nearby. When the cut is complete, a limit switch automatically shuts the power off.
- 1786 RPM motor (no-load speed)
- 1/2” wide ~22.5” long fractional-horsepower V-belt (replace stiff belt with Fenner link belt? McM p/n 6173K37)
- 3-speed cone pulley transmission (ratios: 0.55, 0.83, and 1.32)
- worm gear drive in oil bath (23:1 ratio)
- 7.3” diameter drive wheel (22.92” or 1.91' circumference)
|Drive wheel RPM||42.7||64.4||102.4|
- Steel: around 100 FPM
- Aluminum: up to 1000 FPM (this saw is obviously not capable of such high speeds)
- Brass: a bit over 100 FPM
Further reading: http://web.mit.edu/machineshop/Bandsaw/speeds.html
Cutting hard metals like steel at too high of a speed creates too much heat. This can damage the blade, and it can also cause hardening of the surface of the steel the teeth are touching, making cutting harder and dulling the blade. If in doubt, stick with slower speeds.
The saw uses a 1/2” x 64-1/2” x .025” blade. (64.5” = 5' 4-1/2”) Cheap blades are cheap, but they cut poorly and will wear out quickly. A good bi-metal blade will cut faster and last for many months if used properly. Bi-metal blades cost easily twice what a plain steel blade costs.
Blades are available in a variety of tooth counts (teeth per inch or TPI) and two main tooth profiles. Variable set or anti–vibration blades have a varying toothcount that changes from coarser to finer every inch or so. This allows the blade to cut a wider range of thicknesses of material and can reduce vibration. Tooth count is listed as a range such as 14-18 TPI. Raker set or standard blades have a constant tooth count and shape. They are less expensive to manufacture, but typically lack some of the desirable characteristics of anti-vibration blades.
The appropriate TPI blade to use depends on the task at hand. For cutting metal, a very general rule of thumb is to always have at least three teeth in the work. This means that a thinner piece of metal should be cut with a blade of a higher TPI. Using too coarse of a TPI blade causes rough cutting and exerts high loads on one or two teeth at a time, causing blade damage and poor cutting performance. Conversely, using too fine of a blade for the task at hand can also be bad. Each tooth only has a limited amount of space to store the shaving of metal that it removes. The finer TPI, the smaller these spaces are. When cutting a thick slab of steel with a fine-toothed blade, these pockets can become jammed with material before the tooth has passed all the way through the workpiece, resulting in poor cutting performance, excess heat, and probably blade damage.
Here is a guide to help select an appropriate blade TPI based on the thickness of metal the blade will be passing through:
Here is a list of blades that fit this saw with McMaster-Carr part numbers and prices. (remember that TPI listed as a range is an anti-vibration blade, and TPI listed as a single number is a standard blade)
|Material||Teeth Per Inch||McM p/n||Each|
|Blades for Hard Metals|
|Blades for Thin Metals|
|General Purpose Blades|
|Blades for Thin Metals|
The gearbox containing the worm gear drive is full of sticky viscous black goo where I was hoping to find honey-like gear oil. This should be cleaned out and replaced with proper oil before the saw is used appreciably. Does anyone have some heavy gear oil in their garage? This will take all of two cups, if that. Just about anything intended for use in a gearbox should be fine, but I figure thicker is better because there is no need to worry about low temperature viscosity issues.
Somewhere online I saw mentioned that there is sometimes sand in the gearbox on these saws from the factory for some reason. WTF? All the more reason to clean it out.
The plastic blade tension knob is broken and gone. It should be pretty easy to make a replacement from something on hand. A knob with multiple set screws should clamp onto the .384” diameter shaft quite nicely. A hole about one diameter deep (or less) would be a good match for the particulars of the tension mechanism. An angled thrust washer epoxied in place to level the top of the casting would be a swell addition, too. Karl's rough measurements of an ideal knob: about 2” overall height, about 3” diameter of knob end, about 1/2” height of knob end, about 3/4” to 1” diameter of smaller shaft beneath knob end. Three set screws (Karl has M5x.8 set screws and an M5 tap). A blank of aluminum round stock about 2” long by 3” diameter would be perfect. Sounds like a lathe project!
The upper wheel is probably not tracking very well. Proper alignment needs to be done, and there are probably opportunities to improve the adjustment capabilities. The main tracking adjustment is a set screw that tilts the upper wheel's axle. Crude, but apparently effective.
Karl's initial measurements show that the lower wheel sits significantly further out than the upper wheel. Hold a yardstick on the surface of the wheel to see what I mean. The proposed fix: The spacer behind the lower wheel should be removed and replaced with a snap ring on the shaft (there is a groove for it) and a counterbore cut into the back of the wheel to get the wheel as far onto the shaft as possible without scraping on the bearing cap. Spacers can be made on the lathe as needed, but our (6”) lathe is not large enough to counterbore the back of the wheel. The wheel's largest outside diameter is about 7.48”, so this sounds like a job for an 8” lathe (or a milling machine).
Make better guides for the upper wheel guide: The thickness is important (and is what will make them better). Steel bar/plate .175” to .180” thick would be perfect. The stock guide plates are .95” wide, 3.8” tall, and .155” thick with rounded (thinner) edges from being stamped by a punch press. We can do better! The centers of the two ~8mm (.325”) holes in each plate are 2.575” apart vertically and .525” from the critical edge. See ghetto mspaint sketch:
measure and adjust saw to make it cut at as perfect of a right angle as possible both horizontally and vertically. Vice jaws can be angled easily, but there is no built-in way to change the angle of the main pivot. If that's off significantly, we've got a problem. Some people have cut off the stock pivots on the lower casting and replaced them with pillow block bearings to align the saw. Sounds like a lot of work…
A new and somewhat taller base would be much sturdier and put the saw at a more useful height. Incorporate casters like on the big tablesaws? Storage for blades/attachments in the bottom?
Build a coolant recirculating system?
Build a hydraulic downfeed speed regulator?
Better power switch with a proper shutoff limit switch? Incorporate a thermal override on the motor to shut off the power in case of unattended overheating? (see the mini-lathe.com page for overheating info)