Selecting the correct speeds for a gear shaper is another necessary step in the gear shaping process. Selecting the correct speed for the gear shaper will ensure that the gear shaping process run without interruptions. If the selected speed for the gear shaper is too fast, the cutters will overheat and the edge of the cutter will break down.
If the edge of the cutter breaks, the formed gear will have inaccuracies in the tooth profile. If the selected speed is too slow, the cutter will lose time rubbing against the material instead of cut it. The chart provide will help to avoid these problems by allowing the operator to set the correct speed for each material without having to guess.
How to Choose the Right Speed for Gear Shaping
The shaper cutter will move back and forth over the gear blank to remove the material. The teeth of the cutter are a hardened gear so they will need to stay sharp throughout the shaping process. The speed at which the cutter teeth travels over the material will create heat at the teeth of the cutter.
The value of the surface feet per minute are important for the gear shaping process. This value is calculate based off the diameter of the cutter and the RPM of the gear shaper. Different metals will react to the heat generate by the cutter at different rates.
For example, the speed that can be used with mild steel will be different than the speed used with stainless steel. Stainless steel will work harden very quick with gear shaping so using the recommended speed for mild steel for stainless steel will cause the cutter to glaze. Aluminum and plastic will allow for more higher speeds because these materials will conduct the heat generate by the cutter.
For metals that are harder than stainless steel, the speeds will be slower. For softer metals, the speeds can be higher to create a betterer finish. The diameter of the cutter will impact the speed of the cutter.
For instance, a small cutter will have a lower speed of travel of the cutter teeth over the metal then a large cutter that is spinning at the same RPM as the small cutter. Because the small cutter will reach a lower speed with the teeth of the cutter, the small cutter can reach more higher RPM for the same metal. The chart shows the different RPM speeds for cutters within a specified diameter.
The stroke rate of the gear shaper will have an impact on the speed at which the cutter remove the material from the gear blank. High speeds is used during the roughing passes for gear shaping to remove large amounts of material from the gear blank. However, during the finishing passes, the speed per stroke will be slower but the number of stroke per minute will increase to create a more even finish of the teeth of the gear.
The chart illustrate the different speeds that can be used during the various passes of gear shaping. Another factor to consider during gear shaping is the use of coolant for the gear blank. For metals such as steel, flood coolant can be used so that the chips will move away from the steel and excess heat will be remove.
For cast iron metal part, air or a light mist of coolant is used because excess coolant will turn the graphite in the cast iron to a smear in the metal. For stainless steel parts, heavy sulfurized oil coolants is used because the sulfurized oil can penetrate the layer of hardened steel in the stainless steel part. To ensure that the gear shaping process runs at the correct speeds, there are maintenance task that need to be performed.
The diameter of the cutter needs to be measured to accurately calculate the speed at which the cutter should run. When setting up a new cutter, it will need to be start at a reduced speed to begin the first few minutes of operation. This allows the cutter to seat properly and for any runout of the cutter to be spot.
The rake face of the cutter should also be inspected after each job to spot any micro-chipping of the cutter, which, if not corrected, will result in a broken tooth. Maintaining the correct speed range for each gear shaping task will ensure consistency in the gear shaping process. By ensuring that the cutter remains sharp and cool, the gear will have accurate tooth spacing and an accurate involute profile of its teeth.
If the specifications of the gear are met, the gears that will be mated to this gear will not require any further fitting or scraping to mate with this gear. Maintaining the correct speed range for gear shaping will save the company time during the production run of the gears.
