On 3 Aug 2004 14:02:31 -0700, (Dominic Ostrowski) wrote:

I'm doing some rebating on the tablesaw (in the UK, so equipped with a
riving knife rather than a splitter) 2.4m long, 75 by 100mm (3 by 4"),
cutting a 12 by 40mm (0.5 by 1.5") rebate. Currently removing the
riving knife (it would extend above the blade crown and usually has
the crown guard attached), using a full length fence and a homemade
crown guard (shaw guard like cover bolted to t slots on the fence).
Safest config I could readily come up with.

My question is, would it be worthwhile/safer to buy a spare riving
knife, shorten it to below the blade crown (would always be correct as
it follows the blade height) ? Is this a common modification?

First, the disclaimer - I don't have the foggiest idea what I'm talking about as
I have zero experience with riving knives. With that in mind, here goes:

As I understand it, a riving knife and a splitter have similar functions. They
guide the work downstream of the blade and prevent the kerf from closing with
the intent of preventing/reducing any tendency for the rear of the blade to
catch the workpiece and throw it back in your face..

Fixed splitters are usually recommended for shop made zero clearance inserts,
are effectively fixed height riving knives, and I've heard no reports that they
are ineffective or dangerous. Since they are fixed height, they will sometimes
be higher than the blade, sometimes lower.

Putting these observations together, I would theorize that a riving knife that
was cut down to the same height or slightly shorter than the blade extension
would be better than a fixed height splitter on a zero clearance insert.
Especially true when the blade is extended higher than the height of the fixed
splitter.

Therefore, unless there is someone who can assert otherwise from hard
experience, if I were in your position, I would get out the file (or hacksaw, or
whatever), shorten a spare riving knife to the point of having a small clearance
between the knife and the bottom of a blind (non-through) kerf, and be damned
cautious until I was reasonably certain there were no unanticipated effects.

That's what _I_ would do. I'm not recommending that you or anyone else do it.
And if you do, I'm not interested in hearing from your lawyer in the event there
are unanticipated effects.

Tom Veatch
Wichita, KS USA