Am I Breaking Bits?
There a likely
hundreds of potential reasons for this problem.
Some are not diagnosable, but several are. When working with our
customers, here are some of the more popular areas we have uncovered.
Improperly mounted equipment
use of bits require little or no movement in the overall structure of the CNC
platform. If the equipment moves,
it is hard to maintain straight edge cutting.
Please make sure that your equipment is properly mounted in a manner that
provides a stable platform for the equipment to complete its work.
feeds and speeds
There is a
tendency to run routers at feed rates that are too low and spindle speeds (RPM)
that are too high. PreciseBits bits were designed to run at high feed rates with
spindle speeds of 20k RPMs or greater.
Low feed rates do not allow the efficient removal of swarfe (cutting
debris). At best this will make the bit run hotter, at worst, the debris
packs the flutes and causes the bit to break. For every material,
there is an optimum combination of cutting depth, spindle speed and feedrate
that yields the best cut and the longest bit life. The process of finding
that "magic" combination can be quite straightforward if
approached in a logical, methodical manner. For more information, see
the tutorial on "Finding
the Sweet Spot in Microtool Woodworking"
Wrong Type of Bit for the Material Being Cut
optimum performance, we have designed and tested bits for specific uses.
Bits designed for soft media (hardwoods, softwoods, polymers, ivory,
horn and resin impregnated wood)
should be used for cutting soft media. Likewise
for bits designed for composites (paper phenolic, fiberglass, carbon fiber,
turquoise, malachite and Micarta)
and bits for non-ferrous metals (aluminum, brass, copper, gold, silver, sterling,
Wood bits should not be used for cutting metal and metal bits should not
be used for cutting wood.
rates that exceed the tip cutting capacity of a tool can cause the bit to
deflect and break.
With most PreciseBit microtools a plunge rate of 60 - 80 IPM is acceptable.
"Runout" is defined as the deviation of the axis of a
cutting tool from the rotational axis of the spindle. It most often
shows up as a side-to-side displacement of the entire bit or as an angular
"wobble" of the cutting tip. Sources of runout in a high speed
spindle can include asymmetric flute grinding, a worn / damaged collet, dirty
/ corroded collet, dirty / corroded spindle bore, poor collet seating
during tool loading, bad spindle bearings, and/or loose spindle
Generally speaking, with carbide microtools, runout (designated TIR for
Total Indicated Runout)
greater than 5 - 10% of the bit's cutting diameter can cause premature bit
breakage in most hardwoods.
- Variable Wood Thickness
bits work better in different material thickness. Please see Plunge Rate description
(hysteresis) in the X/Y drive