Tooth Modification on Chains for Carving Bars
The carving bars currently available have two tip sizes,
the Dime and the Quarter. They are so called because the radius approximates
that of the two USA coins of the same name. The Quarter tip has a radius
of approx. 12.5mm. The Dime, a radius of approx. 8.5mm. Both of these
guide bar tips offer an extremely tight curve for the chain to follow,
as well as cut. All of the chains available, that are recommended for
these types of guide bars, fail to cut efficiently at the nose of the
bar. The reason for this is that the chains in question have been designed
for bars with a far bigger radius at the tip as compared with carving
bars. The top plates of the cutting teeth on all of these chains are
too long for the radius of curve/cut dictated by the carving bars.
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Shown here is an actual scaled up picture profile of a
new quarter inch pitch cutter from a saw chain as it would sit on the carving
bar while travelling round the tip of the bar. The path the cutting edge
takes is marked in green; the path the heel takes is marked in red. The
tooth is shown as it would be on the Dime Tip. The dimensions and the paths
taken by the same tooth on a Quarter Tip are also indicated. |
| It can be seen that the path the cutting edge takes is
within that of the path of the tooth heel. This would result in the failure
of the tooth to bite into the wood. It would therefore be incapable of achieving
a plunge (boring) cut. In order to rectify this problem the shape of the
tooth must be modified. |
| By removing the rear portion of the tooth (heel), the cutting
edge is able to actually contact the timber. This enables it to cut far
more efficiently and with considerably less friction. The figure of 35%
of tooth to be removed is a minimum. It might also be beneficial to reduce
the depth gauges of the chain slightly more than that recommended by the
manufacturer (DO NOT REMOVE THE DEPTH GAUGES). |
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These modifications relate only to the use of chains on carving
bars and should not be made to any chain used on standard chainsaw guide
bars.
Bumper drive links do not seem to adversly effect the "bite"
of teeth on a carving bar . However, bumper tie straps (as can be found
on chain supplied to the consumer market) do interfere. Consumer type
chain should not be used on carving bars.
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