There are a couple of things to keep in mind.
The blade has a kerf wider than the body of the blade. This is a little easier
to allow for with a carbide tipped blade you can easily feel how the teeth are
thicker than the main body of the blade. It is important to allow for that when
measuring.
It helps a lot if the blade is properly aligned with the fence, sometimes the
trunions shift so the blade isn't square to the fence or more importantly for
most operations parallel to the miter slots.
The fence too can be off parallel to the blade, again it is best if the blade
and the fence are both parallel to the miter slot.
Many people deliberately set the fence off just a little out of parallel to the
rear to reduce any binding. This will effect the width of cut at the blade
particularly if you are measuring from the blade and not the fence cursor where
most optically enabled sawyers measure.
Finally, your measuring device must be at right angles to the blade and/or the
fence. The correct distance should be from the fence to the tooth side of the
front tooth of the blade. The Rotomatic works well, remember though to keep the
shaft up so it too is parallel to the table top, the small angle may not seem
like much but it is amplified as it tilts the nut from perpendicular.
If absolute accuracy is needed then run a sample scrap and double check.
In practice I have to admit that I tend to include a fudge factor of a slight
extra, maybe the thickness of a card. I don't know exactly why but both my
miter saw and my table saw seem to cut just a tad closer to the fence than I
measure for. It may be that not all teeth are created equal or maybe there is a
little more wobble or what they call run-out than I can appreciate.
Hope this helps.
----- Original Message -----
From: Agent086b
To: Handyman
Sent: Friday, December 04, 2009 7:53 PM
Subject: [BlindHandyMan] Alining a saw blade when ripping
Hi all,
the earlier question and answers got me thinking. When ripping I find it
hard to measure from the fence to the saw blade accurately.
What wonderful answers can we get to this one.
Thanks as always for the help.
Max.
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