Calculating Feed Rates And Rpms With Chip Load - ShopBot PRSalpha Quick Start Manual

Quick-Start Guide for PRSalpha and PRSstandard tools
Number of flutes: The number of flutes on a bit is essential to calculating proper feed and speed
rates. For most applications, a bit with 1, 2, or 3 flutes can be used, but feed rates and RPMs must be
adjusted to maintain proper chip load (see below).
End shape: Straight and up-spiral bits come in a variety of end shapes. Square ends are most common,
and are a good choice for creating pockets and grooves, cutting profiles, simple lettering, and drilling
operations. Ball (or rounded) ends are best for 3D carving. VCarve bits are often used to create com-
plex letters for sign making. They can also be used to chamfer edges and create countersinks for screw
holes.

Calculating Feed Rates and RPMs with Chip Load:

Chip load refers to the actual thickness of the chip cut by each revolution of the cutter. It is the meas-
urement that all feed rates and speed calculations are based on.
A spinning bit generates friction and heat as it moves through the material. Part of this heat is pulled
away by the flying chips. A larger chip load pulls away more heat, but also puts more stress on the
cutter. Each material has its own ideal chip load range that balances heat dissipation with cutter stress.
A basic chart (in .pdf format) for common materials can be found in the SB3 software by clicking on "[T]
ools", "Chip [L]oad Calculator", and "Chip Load Help". Use this chart along with the Chip Load Calcula-
tor to determine a good starting speed for each toolpath.
Do not rely on the tool database default settings when calculating feeds and speeds for a toolpath.
Those values are only placeholders and are not intended for any particular material.
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