As many fabricators know, workpiece shape can affect cutting performance. Likewise, cutting performance can ultimately affect the quality of the cut, which can affect the quality of the weld. It is, therefore, important to handle downstream operations in the best way possible to ensure that upstream operations can be executed properly.
Structural configurations, such as I-beams and tubing, tend to put more stress on a bandsaw blade compared to standard shapes and solids because as the blade goes through the varying sections of the work, the teeth are not all in contact with the material, which increases stress. That stress can in turn, affect the quality of the cut. To reduce the challenges surrounding the fabrication of structurals – and achieve optimal results – it’s key to understand and follow some basic guidelines.
When cutting I-beams or square or round tubing, making straight cuts is crucial to prepare parts for welding. A crooked cut makes a part difficult to weld. In the case of a misshapen cut, welders might consider using a filler metal or additional welding wire to fill the gap that the crooked part created. In some cases, however, filler metal may not be sufficient and the part may have to be recut or scrapped altogether.
Clearly, the better solution is to ensure that the initial cut is straight, which can be facilitated by getting the sawing parameters right before the cut is ever made. To do so, set the bandsaw to the correct blade speed and cut rate for the material being cut. As a general rule, slow down the blade when processing tough material and speed up the blade for softer material.
It’s also critical for straight cutting to check the conveyor rollers that hold the workpiece for alignment. Rollers that are out of alignment can also be the culprit behind crooked cutting.
To avoid excessive tension, which can also have an effect on the quality of the cut, use a gauge to measure and set the tension on the blade in the bandsaw. Most bandsaws work best with blade tension set to a minimum of 25,000 psi or a maximum of 32,000 psi. Anything less than 25,000 psi leads to poor beam strength, band fatigue or crooked cuts. Setting the tension at more than 32,000 psi, however, can break the band, crack the gullets or wear out the machine bearings.
For cutting through a weld seam on tubing, it is easier and more efficient for the blade to enter from the back of the weld seam. Contrastingly, having the blade cut directly into the weld seam is a shock point to the teeth on the blade, often resulting in shortening the blade life or causing the teeth to strip.
When sawing bundles of material, it is best to strap the entire bundle together or tack weld the ends of the bundle to prevent any piece from moving. If the individual pieces vibrate or move during the cutting process, the teeth may strip.
Beyond the Cut
In addition to the cutting portion of the process, there are several tips to further ensure long blade life, which leads to quality cuts that meet the standards required for welding.
Lubrication is just as important in the process as setting up and executing the cut. Using proper lubrication prevents a premature shortening of blade life. As an example, bandsaws that use a flood coolant or a mist system to lubricate the blade maximize blade life and help minimize the buildup of chips.
Ideally, coolant should wash over the blade as it enters and exits the cut. And although coolant is re-circulated and used continuously throughout the cutting process, be sure to replace water that evaporates from the mixed coolant solution.
Breaking in new blades is also a key consideration for achieving quality cuts. In doing so, operators can “hone” the teeth and, therefore, extend blade life.
The best way to break in new bimetal blades, for example, is to reduce the normal feed rate by half during the initial period. However, be aware that band speed isn’t what breaks teeth during blade break in; pressure from excessive feed rate is typically the most damaging cause.
To make sure that operators are breaking in bimetal blades in the proper manner, they should use the following formulas:
Break in rate = 50 percent of recommended blade feed rate
Break in formula = Multiply the recommended blade speed by 25 percent and cut that number of square inches. As an example, if the recommended blade feed rate is
200 ft. per min., the operator should cut 50 sq. in.
Once the break in period is completed, the bandsaw feed rate can be gradually brought back to normal.
Overall, routine maintenance on the bandsaw is also important. If a saw has problems with its feed system or its variable speed system, the life of the blade can be negatively impacted.