The bandsaw has always been the prima donna machine in my shop. To make it work properly, you need to pay attention to changing blades, tension adjustments and repositioning guides. It was so time consuming that I would use the wrong size blade or a dull blade instead of going to the trouble of changing it. I was unable to reach my head and turn the knop to remove the tension from the blade. That is what finally got me thinking about how to solve that problem.
Simple Modification: Simply replace your saw’s spring tension system with an air-powered piston. No special skills are required.
Parts Off-The-Shelf: All parts of the air system can be found easily and are simple to assemble. The total cost of the system is approximately
Another, and extremely handy, benefit is the ability to control the tension of the blade by connecting a pressure gauge to the regulator. This solves the perennial problem of whether the tension gauge included with the saw actually works. The air pressure applied to an air cylinder and tension on the blade have a direct relationship. This relationship can be mathematically calculated. The only other device needed to make the system work is a needle valve which slows the speed of up and down movement of the upper wheel.
Accurate Tension Control: An air-powered system allows you to turn a knob and adjust the blade tension. Youll need a small air compressor, of course, but it wont run much.
Replace Tensioning System
Photo 1. To create a pattern, trace around the contours of the saw.
Photo 2. Photo 2. These are the riser blocks (A1) and will support the air cylinder.
Two brackets are required to support the air cylinder. Each bracket is composed of two parts: a wood riser block (A1) and a steel stiffening plate (B1)-see Fig. A. The riser blocks must be shaped to fit the back of your saw. Create a pattern ( Photograph 1), then transfer it to the blanks of the riser blocks. Then, cut the blanks as ( Photo 2). To receive the saw’s sliding bracket, cut a recess into each blank (Photo 3; Figure. A)-this part moves up and down as the saw is tensioned.
Photo 3. Photo 3. The bracket will rise into this recess as the blade is tensioned.
Photo 4. Drill three holes for attaching a steel plate (B1) to each riser block. Drill two holes for mounting the plates and riser blocks to the saw.
Two pieces of flat steel should be cut to the same length as your riser blocks in order to make stiffening plates. The steel should be cut or filed to match the profile of each riserblock. Next, drill holes in the plates to attach them to the riserblocks ( Foto 4 ). More holes will be needed to attach the plates and riser block to the saw.
Photo 5. Photo 5.
Fasten the plates to the saw with screws (A2), then mark the location of the holes youll need to make for bolting the assemblies to the saw (Photo 5). Mark the holes with a center punch, then drill 1/20 cm holes about 5/20 cm deep. Enlarge the holes with a #8 bit (a 13/163 cm bit will work OK, too), then tap the holes for 1/4-20 threads (Photo 6). Fasten the riser block/stiffening plate assemblies to the saw with bolts and washers (B2, B3). Note: the tops of the assemblies must be level with each other. You can remove or shorten any assembly that sticks higher than the others.
Photo 6. Photo 6.
Mounting plate C1 is a simple piece of channel iron that allows the air cylinder to rest on. You can order this channel iron precut to the length you need. Mark the center of the plate with a punch, then draw a 3-3/10 cm dia. Circle around the mark. Place the air cylinder over this circle, piston pointing up, and make sure you can see the circle through all four of the cylinders mounting holes. Clamp the cylinder to the plate. Drill holes through the plate for mounting the cylinder (Photo 7). After you drill the first hole, drop a cap screw (D1) through the hole to lock the cylinder in position for drilling the remaining holes.
Photo 7. Center the air cylinder (L1) on a mounting plate (C1) made from channel iron. Drill holes for attaching the cylinder with cap screws (D1).
Photo 8. Photo 8. Fasten the cylinder to the plate.
Remove the cylinder and drill a 1/10 cm hole through the center of the plate. This hole can be used to guide a 1-1/10 cm hole saw equipped with bimetallic teeth. Hold the plate against a fence, or clamp it to your bandsaw table, to make sure it doesnt move as you drill. Drill two pairs of holes on the ends of the plate for mounting the plate on top of the riser blocks with lag screws (C2; see Fig. B). Paint the mounting plate and riser block assemblies to match your saw. Fasten the air cylinder to the plate with lock nuts (D2).
Photo 9. Photo 9. This adapter bolt will connect the piston to a long all-thread rod.
Photo 10. Tap the hole. Use the drill press to keep the tap vertical.
Next, create an adapter bolt E1 to connect the piston of the air cylinders to a 1/4-20 all thread rod F1. Use a 5 cm thick block to hold the bolt for drilling and tapping (Photos 9 and 10). A 5/20 cm hole should be drilled. hole near the end of the block, then use your bandsaw to cut a 1/10 cm wide slot up to the hole. Secure the bolt into the hole. To drill a 1-inch hole, use a #8 bit or a 13/163 cm bits.
Photo 11. Thread the adapter bolt (E1) and all-thread rod (F1) into the air cylinders piston. Add two nuts (F2) to the rod.
Two nuts (F2) should be inserted onto the all-thread rod. The first nut should be about half way down the rod. The second should be about 5 cm away from the rod’s end. This rod’s end should be inserted into the adapter bolt. Secure the second nut to the head of bolt. Thread the adapter bolt into the air cylinders piston (Photo 11).
Photo 12. Photo 12. These pieces can be unscrewed and taken apart.
Remove the old tensioning system from your saw (Photo 12). Unscrew the adjusting bolt (the rod with a knob at the top). The sliding bracket will now be free from the square nut, red washer, and spring. You won’t use these parts for the new system.
Photo 13. Photo 13.
Lower the all-thread rod into the sliding bracket (Photo 13). Place the mounting plate for the air cylinders on top of the riser block. Adjust the plates position so the rod is plumb and centered in the sliding bracket. Mark the positions of the plates mounting holes at the tops on the riser block, and then drill holes in the riser block for the lag screws. Install and tighten the lag screws ( Photo 14).
Photo 14. Fasten the mounting plate to the riser assemblies with lag screws (C2). Add a washer and nut to the end of the rod, then tighten the nut against the sliding bracket.
Grab onto the rod and pull the piston from the cylinder. Push it back half-way. The rod’s nut should be turned in the middle until it touches the top of the sliding bracket. Place a flat washer (F3) over the bottom of the rod and thread on a nut. Tighten the nut against the bottom of the sliding bracket.
Put a F4 spring under the rod’s bottom. When you loosen the tension on your blade, the spring will stop the sliding bracket sliding down too much. This completes the tensioning mechanism.
Pneumatic Parts
Fig. A. Bandsaw Hardware 1
Fig. B. Bandsaw Hardware 2
Fig. C. Pneumatic Parts Inside Control Box
Fig. D, The Control Box
Bandsaw Hardware
Install The Pneumatics
Photo 15. Build a box to hold the components that will regulate the flow of air to the cylinder. Mount the components on a plywood panel.
Build a wooden box to hold the pneumatic controls. My box measures 20 cm in width, 20 cm high and 15 cm deep. The top can be removed and the front panel slides in from above. This allows for easy access to all components. Drill one 15/163 cm dia. For air in, drill one hole in the bottom and two in the top for air out. Make a bracket to secure the box to the saw. My bracket is made of flat steel stock bent at an angle, and bolted to my saw. Attach the bracket to the box.
Photo 16. Add a needle valve, then connect the components with tubing. All you have to do is push the tubing into each fitting.
Drill holes in the panel for an air regulator (G1), air gauge (H1) and air valve (K1). Gather the fittings youll need, then wrap Teflon tape around their threads and screw them into the components (Fig. C). C. Connect a needle valve to the air regulator, then cut short lengths of nylon tubing (M1) to connect the components (Photo 16). The ends of the tubing must be cut square, but all you have to do to install them is to push them into the fittings.
Photo 17. Slide the panel into the box, which is fastened to the bandsaw. The lid can be added to the top of your box.
Cut two pieces of tubing to go from the box to the air cylinder. Connect them to the air valve (Fig. C). To connect the air compressor to the box, cut another piece of tubing. This tubing should be connected to the regulator. Run the tubing through the holes in the box, then slide the front panel and top of the box into place, but dont fasten the top yet (Photo 17).
Photo 18. Photo 18. The piston is pushed up by the lower line for tensioning. The piston is lowered by the upper line for relaxation.
After fittings are installed in the aircylinder, connect the tubing ( Foto 18 ). Attach a fitting to the compressor’s hose, and then thread it into another larger fitting that will fit your specific compressor. Turn the air regulator knob counterclockwise, all the way, to deliver the least amount of air to the cylinder. Push in the airflow direction switch at the front of control box (Fig. D).
Photo 19. Attach a line to the compressor. A small compressor will work fine-this system doesnt require a large volume of air.
Connect the tubing to your compressor and turn it ON ( Foto 19). The compressor should be set to 100 psi. Turn the air regulator knob to gradually increase the amount of air flowing to the cylinder. The piston, rod and sliding bracket should move up; if they move down, reduce the air pressure to zero and switch the hoses that run to the air cylinder. Adjust the rate at which the piston moves (slow is better than fast) by turning the needle valve (Photo 20). Assemble the control box.
Photo 20. Adjust the needle valve by turning on the compressor. This valve controls how fast the piston moves.
To fine-tune the air mechanism, increase the air pressure to the amount appropriate for your blade (Photo 21). The piston of the air cylinder should be about halfway out. Reduce the pressure to zero, adjust the nuts and tighten the bolts on the all-thread rod if it isn’t.
Photo 21. Photo 21. Adjust the tension of the blade by changing the air pressure. The system is quiet and precise, making it easy to use.
To change the blades, remove the airflow direction switch. The piston will be pushed down by air pressure, which will remove all tension from the blade.
Tensioning By The Numbers
The knob adjusts air pressure. The gauge shows you the actual level. Using a conversion chart taped to the top of the box, you can easily tell how much pressure is necessary for a particular blade.
The thickness and width of the blades will determine how much pressure you need. However, it will also depend on the alloy the blade is made from. These numbers are only guidelines. Your favorite blade may require more pressure than you think.
After you have found the right tension for your blade’s edge, keep track of the air pressure required. You’ll be able quickly to adjust the tension every time you replace or install a blade.
Product Recommendations
Here are some supplies and tools we find essential in our everyday work around the shop. Although we may be compensated for sales made through our links, these products have been carefully chosen for their utility and quality.
