Band Saw Feed Rate and Feed System.
Feed Rate and Feed Systems in band saw operation are important cutting variables that impact production rate and machine-ability.
So, what is Feed Rate and the various types of Feed Systems that exist?
The Feed Rate is defined as the amount of material (in square inches) that a band saw can cut per minute. This number or amount is often referred to as S.I.P.M. (Square Inches Per Minute).
Critical to the proper operation of a band saw is the smooth steadiness of the head of the saw as it drops onto the material being cut. The feed should always be smooth and steady, not erratic or choppy.
Hydraulic fluids are used in larger, more industrial-sized band saws while on smaller machines, springs may be more commonly used to adjust the feed rate.
For proper feed to occur on larger machines that use hydraulic fluids, it is important that all of the hydraulics tanks be full. Air in the hydraulics line can contaminate the fluid. Also, if there is an inadequate volume of fluid, that fluid can over-heat and affect feed consistency.
Larger band saw machines will have either a gauge or digital read-out indicating the pressure, and most machines’ Operator Manuals will provide information on the proper pressure settings to assure the proper feed rate.
Another thing to be aware of with hydraulics is that the feed compensate valve connected to the workings of a saw has a top blade guide. This valve must be working properly, and any chips not properly cleared from the saw blade gullets will cause the valve to function incorrectly.
Similarly, but certainly more manual in nature, are the springs used on smaller machines that eventually weaken or stretch, allowing the saw to over-feed. It is important to check the feed pressure to assure the proper fall of the head. This should be part of the operator’s due diligence each time a new task on the same saw is undertaken.
The types of Feed System found on various band saws include:
• Gravity – the feed uses the weight of the saw’s head to lower itself onto the material being cut.
• Gravity/Spring – same as above, but springs are used to balance the head weight of the saw for adjusting the pressure.
• Cylinder Bleed Off — same as a Gravity Feed but the downward movement is regulated by a valve that can be set to slowly bleed oil out of the cylinder, slowing the head fall.
• Air Over Hydraulic – the weight of the saw’s head plus assistance from air pressure pushing the head down onto the material. Down movement is regulated by a valve that can be set, which will bleed oil out of the cylinder.
• Hydraulic Feed — same as above, except that oil pressure versus air pressure is used to bleed the valve.
• Constant Feed – in this system, the feed is much the same as a Hydraulic Feed, however the cutting rate is set and remains constant regardless of what shape is being cut.