TM 9-4910-638-14&P
LAPPING THE OFFSET BORING TOOL
#1, #2 and #3 faces on the tool bit are lapped with the large swivel lapping jig that is used for lapping standard boring
tools. Set the number one position the same for both roughing and finishing.
The #3F position is set for lapping the finishing tool on the same line indicated on the swivel head jig, but in lapping
the roughing tool, you will find it is not possible to go back as far as the #3R position without removing a good bit of
the soft metal. Move the swivel head jig around about half way between the 3F and 3R position and then check the
tool on the disc so you can maintain the original angle that was ground on the tool. This position normally will come
about half between the 3F and 3R position. The #2 position is then lapped on the line indicated on the swivel head
jig and the width of the #2 on a roughing tool should be held to a fine line, approximately .005 to .008 while the width
of the #2 on the finishing tool can be increased to .030 to .040 in width.
Since the purpose of using the offset boring tool is to bore to the very bottom of a closed cylinder, it is important that
you no more than just touch the end of the tool to the disc when you are lapping the #1 face. should this #1 face
become too wide, it will leave a fillet in the bottom of the counterbore. If you want to narrow the #1 face or want the
tool so it will cut a counterbore with sharp corners, move the swivel head jig around until the tool holder is parallel
with the top of the jig, check the tool on the disc to see it is flat, then lap this face until the #1 position has been
removed or narrowed down satisfactorily for your particular boring operation.
The #4 face on the roughing tool is lapped with the special jig for offset boring tools. When using this jig, it is
important to check to see that you have a positive relief on this face of the offset boring tool so that as the roughing
tool, it will peel the metal off rather than scrape or plow it off. The #4 face on the finishing tool can be lapped in the
#4F position on the large swivel head lapping jig.
When ordering offset boring tools for this machine specify:
062-1258-02
Offset Tool Bit
The offset boring tool does require special tool holders and when ordering specify:
062-1030-00
Offset Tool Holder - Short
Or
062-1031-08
Offset Tool Holder - Long
When ordering lapping jig for offset tools specify:
051-0455-13
Lapping Jig Assembly - Offset
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