Choosing a bandsaw for structural sections
- Peter Dawber
There are a multitude of different bandsaws on the market, designed to perform a variety of tasks. It would be easy to assume that capacity is the main deciding factor when selecting a saw, however with applications varying from mitre cutting small box sections and angles to cutting solid bar stock in exotic materials, it is essential that the other features of a bandsaw are also assessed. So what should be looked for when cutting structural sections and beams?
Mitring head or double mitring head
Unlike older models, most bandsaws now mitre by moving the head, otherwise known as the bow or saw frame, rather than turning the clamps and rotating the material. Smaller saws are often single mitre, as it is quicker to turn the material over, than to reset the saw frame to make a mitre cut in the other direction. However, when working with larger beams, e.g. 610mm wide beams in 12 metre lengths, it is difficult to turn or otherwise manoeuvre the material around a workshop to perform a mitre. In these cases it is essential to be able to angle the saw frame in both directions to perform opposite mitres.
Hydraulic clamping is desirable when cutting larger and heavier beams as it requires a lot of force to pull a beam back in line with the machine, should it be placed into the machine at a slight angle. For double mitre machines it is also common for the vice to move sideways from one side of the machine to the other as the saw performs mitres in each direction. With many models this is a manual operation although with some machines, this is powered by hydraulics.
Saw frame or bow design
While saws designed for cutting solid bar may have a generous capacity when processing round or square material, the height capacity tends to drop off significantly the wider the cut becomes. Machines designed specifically for structural applications will often have a longer bow to allow a full width cut at a suitable height for standard beam sizes, while still allowing the cutting of larger box sections.
Counterbalance method on pivot saws
Except for very large structural sections the majority are cut on pivot bandsaws. When cutting with a pivot saw the centre of gravity of the bow shifts as it descends, causing it to speed up or slow down at different stages of the cut. To counter this one or more springs are fitted at the back of the bow although models such as the Sterling SRA440 DGSA feature a hydraulic counterbalance system which is synchronised with the main downfeed cylinder; this gives a more consistent down feed rate resulting in better blade life.
Mitre angle scales - manual or digital
Saw for a mitre cut, it is important that the angle is easily read from a scale or digital display. Small inaccuracies on a scale close to the pivot point will be exaggerated over the full width of a beam. A digital mitre display, accurate to 0.1 of a degree, will ensure an accurate angled cut every time. Some models feature hydraulic mitre lock allowing the saw frame to be quickly and easily set at any angle.
Feed pressure adjustment
Feed rate is about controlling the descent of the saw frame during cutting, in order to optimise performance. Some machines work purely on gravity with a damper cylinder controlling the descent via an adjustable valve. Full hydraulic systems actually control both the speed and pressure of descent; this allows the saw to cut through material more quickly when there is less resistance but ensures it slows down when more material is encountered, for example when cutting changes from the flanges to the web of a beam.
Other factors to consider
For higher production environments, numerically controlled models are available with powered operation of the mitre position and vice movement. Feeding and measuring systems can be used alongside saws for increased productivity and measuring accuracy. The choice of bandsaw blade and tooth pitch can heavily influence cutting results - you can read more about blades for structural steel in our article here.
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