Machining Fundamentals 164 Copyright Goodheart-Willcox Co., Inc. Follow the manufacturer’s instructions for adjusting blade tension. Improper blade tension ruins blades and can cause premature failure of bearings in the drive and idler wheels. Cutting problems encountered with the band saw are similar to those of the reciprocating hacksaw. Most problems are caused by poor machine condition. Problems can be kept to a minimum by following a maintenance program on a regu- lar basis. This typically includes checking wheel alignment, guide alignment, feed pressure, and hydraulic systems. 11.4 Troubleshooting Power Hacksaws and Band Saws Most sawing problems can be prevented by careful planning and observing a few rules. These rules apply to both power hacksaws and band saws. 11.4.1 Blades Breaking Blades usually break when they are dropped on the work. A loose blade or excessive feed can also cause the blade to frac- ture. Loose work can cause blade damage, as can making a cut on a corner or sharp edge when the three-tooth rule is not observed. Most causes of broken blades can be avoided by setting up the machine properly. 11.4.2 Crooked Cutting Crooked cutting is usually the result of a worn blade. Remem- ber to reverse the work after replacing a blade, and start a new cut on the opposite side. See Figure 11-16. A loose blade or a blade rubbing on a clamping fixture can also cause crooked cutting. It can also be caused by excessive blade pressure on the work or by worn saw guides. 11.4.3 Blade Pin Holes Breaking Out This reciprocating blade problem can be caused by dirty mounting plates or too much tension on the blade. Worn mounting plates can cause a blade to twist and strain in such a way that the pin hole breaks out. 11.4.4 Premature Blade Tooth Wear When blade teeth wear prematurely, the teeth become rounded and dull quickly. Insufficient feed pressure (indi- cated by light, powdery chips) is one of the major causes of premature blade tooth wear. Insufficient pressure can be corrected by increasing cutting pressure until a full curled chip is produced. Excessive pressure (indicated by burned chips) also causes premature wear. If too much pressure is the culprit, reduce feed pressure until a full curled chip is formed. Lack of coolant or a poorly adjusted machine can also cause rapid wear. Correct by following the manufacturer’s recommendations for coolant and machine adjustments. 11.4.5 Teeth Strip Off A common cause of teeth stripping or snapping off a blade is starting a cut on a sharp corner. A machine setup with a flat starting surface will greatly reduce tooth stripping. Also, be sure the work is clamped securely. Loose work can also cause the teeth to strip, Figure 11-17. Check the manufacturer’s chart to determine the proper blade for the job to be done. A blade with teeth too fine will clog (load) and jam, causing the teeth to shear off. A blade that is too coarse (fewer than three teeth cutting) also cause the teeth to snap off. Make sure the blade is properly mounted and is cutting on the power stroke. Blade guides AMT—The Association for Manufacturing Technology Figure 11-15. Adjust blade guides to provide adequate blade support. Otherwise, the blade will not cut true. Partial cut made by worn blade Rotate work to start new cut with new blade Cut with worn blade Goodheart-Willcox Publisher Figure 11-16. Never attempt to start a new blade in a cut made by a worn blade. Reverse the work and start another cut on the opposite side. Cut through to the old cut.