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Tips for making accurate angle cuts in bandsaw operations |
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 There are a number of issues that must be considered to ensure making accurate angle cuts in bandsaw operations.
Most users making angle cuts are sawing mild steel tubing and structurals. Typically, problems encountered when sawing angles can be divided into four categories: the stock being cut, machine setup, the blade and cutting fluid, and the saw being used.
Initially, when an end user is experiencing problems achieving an angle cut that isn’t true, the first issue to be considered is the stock being cut. If it doesn’t meet mill specifications for straightness, there’s never going to be consistent angle cuts. Another problem that can cause inaccurate cutting is the conveyor that moves the stock into the saw. Make certain that it is securely fastened and is level with the saw table. Use one of the new laser beam tools or a minimum of a 6 ft. straight edge to insure alignment. The end user will always have problems making accurate angle cuts if the sawing machine and conveyor aren’t anchored to the floor and level.
Additionally, check to see that the stock is lying flat on the saw’s table and across the blade path. A loose machine vise has a tendency to lift the stock off the table; and worn pads on the gripping edge of the machine vise can prevent the stock from being held true.
The saw blade and cutting fluid are both critical components of any sawing operation. Initially, always inspect the blade prior to cutting. A damaged blade can cause many problems.
For instance, a blade with a broken tooth or one that is bent out of line from the tooth set can cause a jagged or out-of-square cut.
For making precise angle cuts, the widest blade a machine can handle should be used. Wide blades have fewer tendencies to wander, and they have greater beam strength so they won’t bend or deflect upwards when they cut. If the blade curves, the circumference is greater on the back of the blade than it is on the tooth side. The tooth side becomes wavy and doesn’t make straight cuts. Too heavy of a feed rate can also cause this problem.
When cutting tubing or other structurals, you are making an “interrupted cut”. That is the blade teeth start out cutting a solid then move to cutting “air”, then return to cutting a solid. This type of cut can be hard on teeth and it is important to select the proper blade pitch for these applications. It is tempting to specify a coarse pitch blade for making the solid portion of the cut; but too often, this leads to broken saw blade teeth and ragged cuts.
For the best results, have no less than three teeth in the cut at all times to distribute the load. Determining the proper blade pitch is based on the length of contact. For solids, this length is determined by measuring the diameter of a round or the side of a rectangle. For tubing, use two to three times the wall thickness. For structurals, use the contact length through most of the cut.
When cutting structurals and tubing use a blade with a wide set (the amount of offset the teeth have from the centerline is called set). A wide set cuts a bigger slot or kerf as the blade passes through the cut. Structurals and large tubing with thick wall cross sections have a tendency to close down or pinch as the blade passes through them. A wide set prevents the blade from being pinched and damaged. Cutting fluid dispersion is another area that can cause problems. If the fluid is blocked from being applied to one side of the cut or is significantly less on one side of the cut, the blade will have a tendency to dull prematurely. In other words, it will “walk” toward the sharp edge of the blade resulting in an uneven or out-of-square cut.
The end user should apply flood coolant through the saw blade guides when making angle cuts, particularly when cutting structurals or tubing. In this scenario, the interrupted nature of the cut can misdirect the fluid, leaving an insufficient amount of fluid in the cut. Flood coolant application assures the right amount of fluid reaches the cutting area. A lack of fluid can also cause chip welding where packed chips created by sawing can be heat welded to the blade gullets. Direct fluid application can also be used but it is usually only suitable for cutting one or two pieces at a time.
In some cases, angle cutting problems can be traced to bandsaw maintenance. Even though saw guides feature solid carbide inserts, the inserts eventually wear, break, or are improperly positioned so the blade rides too high and the tooth set is flattened. Roller bearings on the saw guides can also wear away; and sometimes the guides are positioned too far away from the cut so that the blade isn’t running true through the cut. The guide arms should be placed as close to the work piece as possible.
If the machine is properly anchored to the floor and conveyor, the stock meets mill specifications, and you are using the right saw blade and cutting fluid, there is little else to stop today’s bandsaw machines from making accurate angle cuts in all types of stock. However, the right saw must be used.
Bandsawing machines can be divided into three types. There are vertical or contour machines, which are suitable for making single cuts and are most often used for maintenance operations where accuracy isn’t critical. Angle cutting on these machines is accomplished by tilting the table of the saw or by using an angle cutting attachment
Tilt frame saws are vertical machines with a counter-balanced saw head that tilts to make angle cuts from 0° up to 60°. Some models have such features as a programmable head angle tilt with a digital read-out and automatic indexing with kerf compensation. They are used for production and general purpose sawing of large stock.
The most common bandsaws are scissor type models where the blade moves horizontally and the saw head is hinged on the saw base. Another type is supported between two columns and cuts like a guillotine. Both styles have models that are capable of angle cutting.
For smaller quantities, there are swivel head saws whose desired angle is manually adjusted and also NC controlled models that can be programmed for the number of cuts and lengths and are capable of multiple indexing. Some models have a head that can be rotated up to 45° in one direction and other more advanced machines have a double swivel head that can be rotated up to 45° in one direction and 60° in the other. Heavy-duty dual column saws with a guillotine type action are notable for their high accuracies and fast cutting rates for making angle cuts at production rates. Some operate by rotating the saw base and head around a fixed platform and can make angle cuts on work pieces up to 26-in. high by 22-in.
This article was written by Al Terronez, sawing and applications manager, DoALL Sawing Products, Elk Grove Village, IL.
doallsawing.com
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