On 2/3/2019 8:08 AM, DerbyDad03 wrote:
On Sunday, February 3, 2019 at 7:59:06 AM UTC-5, dpb wrote:
On 2/2/2019 4:29 PM, DerbyDad03 wrote:
....

Should it be making a planing sound on up to 3 passes even when the head
has not been lowered?

That's a sign of what I've been thinking has to be with the little
planers; even in the big boys like the PM 180 there is _some_ mechanical
play in the various pieces in the planer itself; from the lash in the
height adjusting mechanism to the yield of the bed and head supports
plus what small compression there is in the workpiece itself as it goes
through. All of these effects add up; they're normal and basically
unavoidable no matter what the machine, only how much is dependent on
just how well-built and stiff the machine itself is constructed.

Do you have precise-enough calipers to measure the difference in
material thickness between such passes? For "ordinary" woodworking, it
would be within normal tolerances so it really isn't anything of a deal,
whether with your particular machine and the off-center work it
contributes, I really don't see that effect being the one that would
cause the end effect that you seem to be experiencing.

In short, it's normal to an extent, a second pass on the PM180 is
essentially knife-clearance except for a knot or somesuch. Of course,
it weighs 1670 lb, too...

--dpb

Both of my calipers supposedly measure down to 1/2 a thousandth. Are they truly accurate at
that level? I can't tell because even they don't agree at that level of precision - not that I
actually care. I'm building a bench, not an artificial heart. ;-)
....

For this, you don't care about absolute, only relative with the same set
of calipers...I was just curious about whether you could actually
measure whether there was enough additional material removed that you
could actually measure it. One would sorta' expect the "give" would
mostly be stretched to the limit and things like the adjusting screw
lash wouldn't recover too much between passes if the handle wasn't moved
between and so there would be little "recovery" of whatever slack was
there on initial pass. But, the machine vibrates, the load is removed,
etc., etc., so nothing is completely static.

But, I would expect there simply isn't enough mass in one of these
little guys to prevent at least some movement of the head and bed
relative to each other with a full planing pass so I'm not surprised at
all with your findings.

--