On 1/31/2015 10:24 AM, Leon wrote:
On 1/31/2015 9:49 AM, Leon wrote:
On 1/30/2015 5:40 PM, whit3rd wrote:
On Friday, January 30, 2015 at 1:43:01 PM UTC-8, Leon wrote:
On 1/29/2015 5:05 PM, whit3rd wrote:
On Wednesday, January 28, 2015 at 7:16:37 AM UTC-8, dadiOH wrote:
"DerbyDad03" wrote in message



I took the shot from
above to show the shoulders left by the wobble dado.

In another reply, you said you were going to reduce the width of
the dado.
Good idea. If you had it set to way beyond the 1/4" you need,
reducing it
to a hair over 1/4" will markedly reduce the curve.

This may be misguided; wobble-dado blades are sharpened at the
factory in
a manner that will be a bad match for either extreme (wide or narrow)
of the width setting. There IS likely a setting at which the
wobble-blade cuts
a flat bottom.

For my (Sears Craftsman 720.3261) blade, the instruction sheet
indicates
that width is 3/4" (0.750 inches).


Regardless of how a wobble blade is sharpened at the factory or where
ever, if it wobbles/cuts wider than the width of the teeth on the
blade,
it will not produce a flat bottom.

Not true. The sharpening of a wobble blade is NOT RIGHT ANGLE at
all the tooth faces. That analysis holds only for straight-blade
sharpened
blades used with wobble washers, not for wobble-dado assemblies.
Standard blades are sharpened in the zero-wobble-angle state, of course.

The only setting that the wobble blade will create a flat bottom is
when
it is adjusted to not wobble at all.

That depends on the manufacturer's wobble-setting when the blade was
put into the tooth-grinder. For my blade, flat cuts occur at 3/4".

Think of it this way: to cut a flat bottom dado with a 24T blade
tilted at 10 degrees,
the leftmost edge has to be cut by tooth #1 whose crest is 80 degrees
to the
left sawblade face, and 100 degrees to the right blade face. The
rightmost
edge has to be cut by tooth #13 whose crest is 100 degrees from the left
face, 80 degrees to the right blade face. And the middle of the cut
is made by tooth #6 which is 90/90 degrees, regular square-cut, but
at a slightly smaller distance from the axis of the blade rotation.
Dado blade teeth for wobble-dado assemblies are sharpened exactly
as required to make a flat-bottom cut, but ONLY AT ONE SETTING.

OK then...........
I think you have read some hocus pocus info promoting wobble blades.

But to be clear, I am not talking about a smooth bottom, I am talking
about a bottom that is the same measurement in the middle of the cut as
the outer edges of the cut.

In order for a wobble blade to not cut a round bottom, when adjusted to
wobble, the blade would have to elongate where the outer cutting teeth
come in contact with the outside of the cut and shorten where they come
in contact with the center of the cut. The wider the blade setting, the
longer the part of the blade with the teeth cutting the outer sections
of the dado will have to be. If the wobble blade was manufactured to be
non adjustable it could be made to cut a flat bottom but it would not be
perfectly round. The outer teeth would be farther from the center of
the blade than the teeth in the center of the cut.

Think of a ladder standing straight up in the air. It stands 10' up in
the air. Now lean the ladder over 12", how high up in the air is it
now. This is how a wobble blade works the farther away the teeth are
from dead center the shallower they cut. Those teeth that are still
located near the center of the blade will cut deeper.


OK, I'll step back and retract the hocus pocus comment. ;~)
I can see how a wobble blade can produce a flat bottom but only at one
particular width setting. It does in one way as I indicated have
properties that the cutting surface of the outer teeth are farther from
the center of the blade as those that are closer to the center.

But with that in mind, is a blade that only cuts one width well worth
having? While a 3/4" setting seems like a common size to cut, in the
real world it only works well for cutting dado's to receive 4/4 S4S
lumber and possibly MDF but not for receiving the common 3/4" piece of
plywood.


That is why I got a stack up blade set - in metric. Plywood is mostly
if not all metric. The stack up does imperial as well. My very old
wobble is in the case - for the job just made for it.

Martin