On Tue, 10 Aug 2010 11:17:46 -0500, -MIKE-
wrote:

On 8/10/10 11:10 AM, Kevin wrote:
On Sun, 08 Aug 2010 08:47:58 -0500,
wrote:

If you are needing downward pressure on a jig or stock, enough to bend a
1/2" MDF ZCI, there is either something very wrong with your saw or you
are doing something very wrong.

Okay I dare you or anyone else that's said I'm doing something unsafe
to cut a piece of 1/2" MDF that is 14" long and 2.5" wide (The width
of my insert on the right side of the blade), support it at the ends
and then try to flex it with ONE FINGER.

Then try the same thing with 1/2" Baltic Birch ply. You can use your
whole hand this time.

Then come back here and tell me I'm doing something wrong by using the
one that doesn't flex.



-Kevin

I didn't say you were doing anything wrong by using the one that didn't
flex, but nice attempt at trying to change the subject without anyone
noticing. :-p

I'm staying focused on the original point, that 1/2" MDF is a little
flimsy for this application, rather than the example I used where it
became evident to me that was the case. You may find yourself in a
different situation where it comes into play. How much do you save
using MDF instead of baltic birch ply? 10 cents? The OEM insert is
steel and they ribbed the hell out of it. They could have made it out
of plastic and saved some money, and you know that'd make the
accountants happy. But they didn't. For some reason they thought it
was important that it be very rigid and I've never seen a saw that
came with one that wasn't.

What we're saying is that any operation (and specifically your tenoning
technique) which causes you to push the stock downward to the table and
subsequently, the blade, is not only bad woodworking technique, but very
dangerous technique.

I happen to have shot some video of a project and I have me in action
using the jig. So here is a still frame of the horrible accident
waiting to happen. Please cover the eyes of any small children or
shop dogs so they don't have to live with the shock.

http://www.krtwood.com/tenonjig.jpg

Does it look like I'm pushing down hard? Cause I'm not. But if that
had been an MDF insert the cut depths would have been inconsistent.

Some amount of down pressure is a normal part of most operations at
the table saw, you just don't think about it. Don't try running some
1/8" plywood through the saw without pushing down on it. It'll bounce
like crazy and then almost certainly kick back. Whatever force you
apply is NOTHING compared to the force the blade can generate into the
table. It's just common sense to make the insert as rigid as you can
practically make it. MDF is a poor choice.

-Kevin