Civil Engineering Reference
In-Depth Information
12
Boring Holes and Repetition Work
BORING TOOLS
Boring tools are used to clean up a previously drilled hole, possibly to make it
run true but more likely to ensure the hole is to the correct size. Boring tools
are normally longer than ordinary tools and tend to stick out further from the
tool holder. HSS tools are available and are suitable for most uses.
Different styles of boring bars
The two most useful types of boring bars will be the high-speed steel ones
(HSS) and the carbide-tipped ones, either brazed-on tips or inserted tips.
Carbide inserted tip-boring bars are the best bet for boring cast iron in the
small workshop.
Youcanalsogetboringbarswithmildsteelshanksandinsertedhighspeed
steel tool bits, usually in the form of short round bars held captive with a grub
screw.
For the really small holes, solid HSS and carbide boring bars are readily
available. Although they are not cheap, they will be found very useful and
quick to use. They go down very small - holes and 2 or 3mm diameter bores
are possible. I often buy these little tools in second-hand tool shops or on
eBay for a fraction of their new price.
Another method of boring a hole is to use a long series slot drill as a boring
tool. In use, clamp the shank in the boring head, making sure the rest of the
slot drill is clear of the side of the bore. You can then run it through the bore
similar to a standard boring bar.
If you just need to true up a hole, where the size is not important, you can
just run the slot drill straight through the hole while holding it in a collet. If
you have a hole that needs reaming, a boring bar or slot drill will be the ideal
method of bringing the hole nearly to size while also truing it up. An old slot
drill could be backed off and the remaining tip stoned or lapped down slightly
undersize on the nominal diameter, leaving just a few thou for finish reaming.
