|Depth setting rings
are plastic collars that are securely pressed onto the 1/8 in. shank of a
drill bit, end-mill, router bit, or similar rotary cutter. They
are 0.20 in. (5.1 mm) thick by 0.25 in. (6.35 mm) dia.. The shank side
of the ring (top side in the picture to the right) is accurately
positioned (d ±0.004
in.) relative to the tip of the tool. If the shank-side of the
ring is pressed against the collet when the tool is loaded, the tip of
the bit will be a known distance (d) from
the face of the collet. Knowing this distance, the programmer can
plunge the tool, confident that the depth of cut will be as expected
and will remain the same no matter how many times the tool is changed.
If all of the tools in the programmer's magazine have been fitted with
depth setting rings, an automatic tool changer can load and unload
tools with the tip of each one the same distance from the face of the
This is especially helpful with micro-tools
where "touching-off" on some reference surface to calibrate
the tool height can damage or break the tip of the tool. Rings also
find widespread use in inlay pocket cutting where relatively large
diameter cutters are used to "hog out" basic shapes,
followed by much smaller diameter finishing bits that clean up the
edges, sharpen the corners and add fine detail to the finished part.
Most PreciseBits 1/8 in. shank bits are
available with or without depth setting rings. There is no
charge to add the rings, but the user is cautioned to make sure that
their equipment is compatible with their use.
The most common values
for d are 0.570 in. (small diameter
micro-tools) and 0.800 in. (industry standard). However, with the advent of mechanically etching printed circuit boards in the mid 1970s, a new standard was implemented for the special purpose tools developed for this application. To wit:
- drill bits/ router bits - d = 20.32mm (actually 0.800 in.)
- V-tip engravers / tapered-stub mills / stub end mills - d = 18mm (approx. 0.720 in..)
Today, only machines made by LPKF and T-Tech adhere to this special standard. Systems from AccurateCNC, MITS, Sun and EverPrecision are compatible with the original industry standard depth of 0.800 in.
Note: LPKF and T-Tech users must specify the make and model number of their CNC routers to insure that the rings are properly positioned!