On 2/1/2019 10:26 AM, DerbyDad03 wrote:
On Friday, February 1, 2019 at 10:31:32 AM UTC-5, Leon wrote:
On 1/31/2019 3:10 PM, DerbyDad03 wrote:
On Thursday, January 31, 2019 at 3:38:18 PM UTC-5, Michael wrote:
On Thursday, January 31, 2019 at 2:19:30 PM UTC-6, Jerry Osage wrote:
On Thu, 31 Jan 2019 07:23:56 -0600, dpb wrote:

How long is the workpiece and how are you supporting it coming out the
backside of the planner? That sounds like it may be that the whole
workpiece, sled and all is causing the rear table to droop and raising
the back end up into the cutter head owing to the moment arm off the
rear table...these little guys aren't all that beefy, the table may well
flex, too, without additional support.

Even if the out feed table does not flex the board will try to pivot the
tail end up with the fulcrum at the outer edge of the out feed table.

Although the in feed and out feed rollers in my planer are not spring loaded
they will flex and deform slightly causing what may be a similar problem if
my out feed support is slightly lower than the planer bed. Somewhere in the
last third of the board it will develop a very slight taper as the weight of
the board starts pressing up on the feed rollers - and a bad snipe when the
end of the board passes the in feed rollers...
--
Jerry O.

Maybe an extended feed table or standing feed rollers will minimize the problem.

How about an extended feed table supported by roller stand on the in and out
feed side? That's what I've been using.


If your board has a twist or bow, as mentioned in another part of this
thread, a 100' long in feed and out feed will be of no help to
straighten/flatten the work. The work has to be supported where the
board bows up or twists up. I use small wedges between the
twisted/bowed work and a sled longer than the work.

Yes, I know that. I was simply responding to Micheal's comment about an
extended table by noting that I am already using one. While it, by itself,
does nothing to flatten the board, it does provide support for the sled.
When using a 6' sled and 8/4 boards like I am, it's nice to have a few feet
of solid support before and after the planer instead of relying on the
relatively short planer infeed and outfeed tables.

OK, ;~) Actually I have a 15" stationary planer with fold up/down in
feed and out feed rollers/tables that are about 2' long. They work just
fine and I do not worry with them being on the exact same plane as the
planer bed/table.

FWIW the sled you have and the one I am talking about are completely
different. My sled travels through the planer at the same rate as the
work. I use the wedges to keep the work from moving up or down, because
of bow or twist, between the sled and the work.





As shown below, I am using an extended table for support and a sled for the
actually flattening process. The only thing not shown in the image is the
shims/wedges. Rest assured that I am shimming the boards solid to prevent
rocking and flexing. The image is just an example of the set-up in response
to dpb's request to see it.

https://i.imgur.com/fSSwztH.jpg


The in feed and out feed rollers are not intended to flatten a board
into submission nor are they in any way instrumental in flattening a
warped/twisted, or bowed board. They simply push or pull the work
through the planer.

Agreed. But is it possible that they could *screw up* the flattening if they
were misaligned or applying uneven pressure?

No, as long as they are in constant contact with the work, preventing
the work from lifting.
You have a constant indexing point, the bed/table of the planer. As
long as the cutter and bed are parallel to each other there should be no
issue with screwing up a cut. Think of ripping a board on your table
saw. You have the constant indexing point, the fence, that keeps the
distance between the blade and the fence constant. Your hands, that
work like in feed rollers, contentiously apply "different" pressure as
you feed the work. This done properly does not affect the width of the
cut.

IF the in feed and or out feed rollers are high or low on one end the
cut will remain the same as long as the cutter and the bed of the planer
are parallel. A high or low, on one end, in feed or out feed might
cause the work to not go straight through the planer as it feeds but
that does not normally affect the thickness of the cut either. It is
seldom that boards go straight through a planer.




That is basically been the question that I have been trying to get an
answer to.

On 2/2/2019 11:18 AM, Leon wrote:
On 2/1/2019 10:26 AM, DerbyDad03 wrote:
....

Yes, I know that. I was simply responding to Micheal's comment about an
extended table by noting that I am already using one. While it, by
itself,
does nothing to flatten the board, it does provide support for the sled.
When using a 6' sled and 8/4 boards like I am, it's nice to have a few
feet
of solid support before and after the planer instead of relying on the
relatively short planer infeed and outfeed tables.

OK, ;~)Â* Actually I have a 15" stationary planer with fold up/down in
feed and out feed rollers/tables that are about 2' long.Â* They work just
fine and I do not worry with them being on the exact same plane as the
planer bed/table.

FWIW the sled you have and the one I am talking about are completely
different.Â* My sled travels through the planer at the same rate as the
work.Â* I use the wedges to keep the work from moving up or down, because
of bow or twist, between the sled and the work.

....

His "sled" does, too, Leon. He's just done basically like I described
with also making a false table but the sled is the 2x under the
workpiece and it progresses thru the planer carrying the work...you just
dispense with the lower false table.

What isn't shown in the picture is just how he did actually do any
shimming when planing "in anger"; he just has the two pieces laying on
top of each other as all the picture illustrates is that the two don't
lay flat face-to-face after he did make one or more passes to try to
flatten.

What we've not been able to see is an actual working pass.

--

On 2/1/2019 12:32 PM, dpb wrote:
....

I did it by either applying a laminate or taking another piece of
melamine-faced ply to the sled and then just used a thinner sled to hold
the work and let the planer do the work to pull it thru on the base
rather than having a mobile sled as the whole arrangement.Â* Then I
didn't have to worry about propping up the outfeed other than just
support the base boards as it was fixed in place--a replacement table
entirely, iow.

That's why I said that in general I didn't find it worth the trouble!Â*

Actually, I had forgotten at the time I wrote the above that that's the
basic idea you used -- mine was just a lot "beefier" because I was doing
much heavier stock at the time.

I've never tried to do smallish pieces that way; when doing a lot of
work that would have needed to I had access to a 12" Crescent jointer so
it was never an issue excepting for that one set of 16/4 x 15-16" walnut
slabs a customer wanted to use for mantle-pieces. They had come from
his grandfather's place and been sitting in the barn for nearly 50 years
and he couldn't bring himself to cut them down...

--

On Saturday, February 2, 2019 at 12:18:51 PM UTC-5, Leon wrote:


FWIW the sled you have and the one I am talking about are completely
different. My sled travels through the planer at the same rate as the
work.

Not true.

Start at the top of the pile.

1 - Poplar board that I want to flatten
2 - 2" thick sled, with the stop at the front end so the poplar board pushes
it along at the same rate
3 - 1.5" thick particle board/melamine bed, used as an extension table

https://i.imgur.com/fSSwztH.jpg

I use the wedges to keep the work from moving up or down, because
of bow or twist, between the sled and the work.

As do I and as I've mentioned numerous times. The shims/wedges are just not
shown in the picture because I was just trying to show the table, sled, etc.

I can set it all up again, shim the board and post another picture or you
guys can trust me when I say it's shimmed correctly so that all movement
is prevented. As I mentioned to dpb, every board needs to be shimmed
differently, so even if I posted a picture of *that* shimmed board, you'd
have no way of knowing of I shimmed *every* board correctly. You're just
going to have to trust me...or not.

On 2/2/2019 1:44 PM, DerbyDad03 wrote:
....

I can set it all up again, shim the board and post another picture or you
guys can trust me when I say it's shimmed correctly so that all movement
is prevented. As I mentioned to dpb, every board needs to be shimmed
differently, so even if I posted a picture of *that* shimmed board, you'd
have no way of knowing of I shimmed *every* board correctly. You're just
going to have to trust me...or not.

Other way 'round ... not that we don't "trust"; you came asking for help
and from afar, _seeeing_ pictures of how you had the set up when you
actually tried to make a trial run is the only way we can see if
something shows up to us that didn't to you.

Your choice of how far to try to push the long-distance diagnostics but
the clearly obvious seems to have mostly been eliminated (other than the
very first basic test I suggested to prove the planer itself is doing
what it's supposed to).

Remember, too, you're looking for minute details...a few thou here and a
few thou there can add up to real...

--

On 2/2/2019 3:31 PM, dpb wrote:
....

Remember, too, you're looking for minute details...a few thou here and a
few thou there can add up to real...

Actually, another thought came to me after posting.

Are there bed rollers on this little guy? How much above the table are
they sitting if so?

Possibly the last few inches compresses your bed board from being about
in line with them to the table when there's not a long run of the sled
but only the last few inches. That _might_ explain why most of the
problem appears in the last few inches of the cut...

--

On Saturday, February 2, 2019 at 4:31:15 PM UTC-5, dpb wrote:
On 2/2/2019 1:44 PM, DerbyDad03 wrote:
...

I can set it all up again, shim the board and post another picture or you
guys can trust me when I say it's shimmed correctly so that all movement
is prevented. As I mentioned to dpb, every board needs to be shimmed
differently, so even if I posted a picture of *that* shimmed board, you'd
have no way of knowing of I shimmed *every* board correctly. You're just
going to have to trust me...or not.

Other way 'round ... not that we don't "trust"; you came asking for help
and from afar, _seeeing_ pictures of how you had the set up when you
actually tried to make a trial run is the only way we can see if
something shows up to us that didn't to you.

Your choice of how far to try to push the long-distance diagnostics but
the clearly obvious seems to have mostly been eliminated (other than the
very first basic test I suggested to prove the planer itself is doing
what it's supposed to).

Remember, too, you're looking for minute details...a few thou here and a
few thou there can add up to real...


All true, no argument.

As far as "the planer doing what it is supposed to do" I have another 'test'
question, as in "should it be doing this".

I was doing some basic thickness planing today. Assume a board that was
already flat. 8/4 x 3.5" x 26", S2S.

I need to get it down to 1.5" thickness. I sneak up on the cut, half a
handle turn at a time (should be 1/32") Eventually the rollers grab the
board and pull it through without actually cutting anything. Another half
turn and I hear a full length planing sound. So far so good.

The question: If I pass the board through again, *without turning the handle*,
should I hear a full length planing sound? If I then pass it through again,
*without turning the handle*, should I once again hear a full length planing
sound?

I have found that I can pass the board through at least 3 times and still
hear it cutting. The sound is a little quieter each time, but there's no
doubt that it's more than just the rollers pulling it through.

Since it's a narrow board, I tried passing it through the middle, the left
and the right to see if it made any difference, but as far as I can tell, it
doesn't.

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

On Saturday, February 2, 2019 at 5:03:04 PM UTC-5, dpb wrote:
On 2/2/2019 3:31 PM, dpb wrote:
...

Remember, too, you're looking for minute details...a few thou here and a
few thou there can add up to real...

Actually, another thought came to me after posting.

Are there bed rollers on this little guy? How much above the table are
they sitting if so?

Possibly the last few inches compresses your bed board from being about
in line with them to the table when there's not a long run of the sled
but only the last few inches. That _might_ explain why most of the
problem appears in the last few inches of the cut...


No bed rollers.

On 2/2/2019 4:29 PM, DerbyDad03 wrote:
On Saturday, February 2, 2019 at 4:31:15 PM UTC-5, dpb wrote:
On 2/2/2019 1:44 PM, DerbyDad03 wrote:
...

I can set it all up again, shim the board and post another picture or you
guys can trust me when I say it's shimmed correctly so that all movement
is prevented. As I mentioned to dpb, every board needs to be shimmed
differently, so even if I posted a picture of *that* shimmed board, you'd
have no way of knowing of I shimmed *every* board correctly. You're just
going to have to trust me...or not.

Other way 'round ... not that we don't "trust"; you came asking for help
and from afar, _seeeing_ pictures of how you had the set up when you
actually tried to make a trial run is the only way we can see if
something shows up to us that didn't to you.

Your choice of how far to try to push the long-distance diagnostics but
the clearly obvious seems to have mostly been eliminated (other than the
very first basic test I suggested to prove the planer itself is doing
what it's supposed to).

Remember, too, you're looking for minute details...a few thou here and a
few thou there can add up to real...


All true, no argument.

As far as "the planer doing what it is supposed to do" I have another 'test'
question, as in "should it be doing this".

I was doing some basic thickness planing today. Assume a board that was
already flat. 8/4 x 3.5" x 26", S2S.

I need to get it down to 1.5" thickness. I sneak up on the cut, half a
handle turn at a time (should be 1/32") Eventually the rollers grab the
board and pull it through without actually cutting anything. Another half
turn and I hear a full length planing sound. So far so good.

The question: If I pass the board through again, *without turning the handle*,
should I hear a full length planing sound? If I then pass it through again,
*without turning the handle*, should I once again hear a full length planing
sound?

I have found that I can pass the board through at least 3 times and still
hear it cutting. The sound is a little quieter each time, but there's no
doubt that it's more than just the rollers pulling it through.

Since it's a narrow board, I tried passing it through the middle, the left
and the right to see if it made any difference, but as far as I can tell, it
doesn't.

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

On Sunday, February 3, 2019 at 7:59:06 AM UTC-5, dpb wrote:
On 2/2/2019 4:29 PM, DerbyDad03 wrote:
On Saturday, February 2, 2019 at 4:31:15 PM UTC-5, dpb wrote:
On 2/2/2019 1:44 PM, DerbyDad03 wrote:
...

I can set it all up again, shim the board and post another picture or you
guys can trust me when I say it's shimmed correctly so that all movement
is prevented. As I mentioned to dpb, every board needs to be shimmed
differently, so even if I posted a picture of *that* shimmed board, you'd
have no way of knowing of I shimmed *every* board correctly. You're just
going to have to trust me...or not.

Other way 'round ... not that we don't "trust"; you came asking for help
and from afar, _seeeing_ pictures of how you had the set up when you
actually tried to make a trial run is the only way we can see if
something shows up to us that didn't to you.

Your choice of how far to try to push the long-distance diagnostics but
the clearly obvious seems to have mostly been eliminated (other than the
very first basic test I suggested to prove the planer itself is doing
what it's supposed to).

Remember, too, you're looking for minute details...a few thou here and a
few thou there can add up to real...


All true, no argument.

As far as "the planer doing what it is supposed to do" I have another 'test'
question, as in "should it be doing this".

I was doing some basic thickness planing today. Assume a board that was
already flat. 8/4 x 3.5" x 26", S2S.

I need to get it down to 1.5" thickness. I sneak up on the cut, half a
handle turn at a time (should be 1/32") Eventually the rollers grab the
board and pull it through without actually cutting anything. Another half
turn and I hear a full length planing sound. So far so good.

The question: If I pass the board through again, *without turning the handle*,
should I hear a full length planing sound? If I then pass it through again,
*without turning the handle*, should I once again hear a full length planing
sound?

I have found that I can pass the board through at least 3 times and still
hear it cutting. The sound is a little quieter each time, but there's no
doubt that it's more than just the rollers pulling it through.

Since it's a narrow board, I tried passing it through the middle, the left
and the right to see if it made any difference, but as far as I can tell, it
doesn't.

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. ;-)

At the 1/64 setting, it does not appear that any measurable amount is being removed although,
honestly, I haven't checked every time at every location of the bed. Maybe when the bench is
done I'll play some more.

I agree that that behavior is unrelated to the flattening issue. There was no intent to connect
the two situations.

Thanks again.

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.

--

On 2/2/2019 1:44 PM, DerbyDad03 wrote:
On Saturday, February 2, 2019 at 12:18:51 PM UTC-5, Leon wrote:


FWIW the sled you have and the one I am talking about are completely
different. My sled travels through the planer at the same rate as the
work.

Not true.

Start at the top of the pile.


My mistake, sorry. I did not want to go through tall of the redundancy
from the beginning.

I thought the sled was the melamine part and that you simply had lumber
sitting on top. I now see that the large piece has the stop on the far
end. ;~)






1 - Poplar board that I want to flatten
2 - 2" thick sled, with the stop at the front end so the poplar board pushes
it along at the same rate
3 - 1.5" thick particle board/melamine bed, used as an extension table

https://i.imgur.com/fSSwztH.jpg

I use the wedges to keep the work from moving up or down, because
of bow or twist, between the sled and the work.

As do I and as I've mentioned numerous times. The shims/wedges are just not
shown in the picture because I was just trying to show the table, sled, etc.

I can set it all up again, shim the board and post another picture or you
guys can trust me when I say it's shimmed correctly so that all movement
is prevented. As I mentioned to dpb, every board needs to be shimmed
differently, so even if I posted a picture of *that* shimmed board, you'd
have no way of knowing of I shimmed *every* board correctly. You're just
going to have to trust me...or not.



Got it! LOL sorry you had to repeat yourself to me, again.

If you are continuing to have issues it is probably a situation where
you are going to be wasting time trying to get more out of a bench top
planer. I never expected my bench top planer to do anything besides
change the thickness of a "flat" board.

AND FWIW flattening a board on my 15" stationary planer is not a
pleasurable thing either. Technically that is the job of a jointer but
that is another story.

Moving the sled and work with out disturbing the shims takes
considerably more time and effort than it is worth, for me.

"Leon" wrote in message
...

On 2/2/2019 1:44 PM, DerbyDad03 wrote:
On Saturday, February 2, 2019 at 12:18:51 PM UTC-5, Leon wrote:


FWIW the sled you have and the one I am talking about are completely
different. My sled travels through the planer at the same rate as the
work.

Not true.

Start at the top of the pile.


My mistake, sorry. I did not want to go through tall of the redundancy
from the beginning.

I thought the sled was the melamine part and that you simply had lumber
sitting on top. I now see that the large piece has the stop on the far
end. ;~)






1 - Poplar board that I want to flatten
2 - 2" thick sled, with the stop at the front end so the poplar board
pushes
it along at the same rate
3 - 1.5" thick particle board/melamine bed, used as an extension table

https://i.imgur.com/fSSwztH.jpg

I use the wedges to keep the work from moving up or down, because
of bow or twist, between the sled and the work.

As do I and as I've mentioned numerous times. The shims/wedges are just
not
shown in the picture because I was just trying to show the table, sled,
etc.

I can set it all up again, shim the board and post another picture or you
guys can trust me when I say it's shimmed correctly so that all movement
is prevented. As I mentioned to dpb, every board needs to be shimmed
differently, so even if I posted a picture of *that* shimmed board, you'd
have no way of knowing of I shimmed *every* board correctly. You're just
going to have to trust me...or not.



Got it! LOL sorry you had to repeat yourself to me, again.

If you are continuing to have issues it is probably a situation where
you are going to be wasting time trying to get more out of a bench top
planer. I never expected my bench top planer to do anything besides
change the thickness of a "flat" board.

AND FWIW flattening a board on my 15" stationary planer is not a
pleasurable thing either. Technically that is the job of a jointer but
that is another story.

Moving the sled and work with out disturbing the shims takes
considerably more time and effort than it is worth, for me.

===============================================
Two thoughts
Does your planer have a head lock for the height? If not, this could be why
you can make 3 passes at one setting. Each pass takes off less material and
thus can deflect the head less.

In regard to the sled. Could you try planing a twisted board that is
significantly shorter than the sled. If the sled is tilting this would then
happen after the board has gone completely through.
John

On Sunday, February 3, 2019 at 3:49:46 PM UTC-5, John S wrote:
"Leon" wrote in message
...

On 2/2/2019 1:44 PM, DerbyDad03 wrote:
On Saturday, February 2, 2019 at 12:18:51 PM UTC-5, Leon wrote:


FWIW the sled you have and the one I am talking about are completely
different. My sled travels through the planer at the same rate as the
work.

Not true.

Start at the top of the pile.


My mistake, sorry. I did not want to go through tall of the redundancy
from the beginning.

I thought the sled was the melamine part and that you simply had lumber
sitting on top. I now see that the large piece has the stop on the far
end. ;~)






1 - Poplar board that I want to flatten
2 - 2" thick sled, with the stop at the front end so the poplar board
pushes
it along at the same rate
3 - 1.5" thick particle board/melamine bed, used as an extension table

https://i.imgur.com/fSSwztH.jpg

I use the wedges to keep the work from moving up or down, because
of bow or twist, between the sled and the work.

As do I and as I've mentioned numerous times. The shims/wedges are just
not
shown in the picture because I was just trying to show the table, sled,
etc.

I can set it all up again, shim the board and post another picture or you
guys can trust me when I say it's shimmed correctly so that all movement
is prevented. As I mentioned to dpb, every board needs to be shimmed
differently, so even if I posted a picture of *that* shimmed board, you'd
have no way of knowing of I shimmed *every* board correctly. You're just
going to have to trust me...or not.



Got it! LOL sorry you had to repeat yourself to me, again.

If you are continuing to have issues it is probably a situation where
you are going to be wasting time trying to get more out of a bench top
planer. I never expected my bench top planer to do anything besides
change the thickness of a "flat" board.

AND FWIW flattening a board on my 15" stationary planer is not a
pleasurable thing either. Technically that is the job of a jointer but
that is another story.

Moving the sled and work with out disturbing the shims takes
considerably more time and effort than it is worth, for me.

===============================================
Two thoughts
Does your planer have a head lock for the height? If not, this could be why
you can make 3 passes at one setting. Each pass takes off less material and
thus can deflect the head less.

No head lock.


In regard to the sled. Could you try planing a twisted board that is
significantly shorter than the sled.


Please define "significantly shorter". My sled is 6'.

If the sled is tilting this would then
happen after the board has gone completely through.

I assume you mean tilting on the way out, thus pushing the tail end
of the board up. (If not, please explain) I have considered that as
possible cause from the very beginning, therefore...

I have been extremely diligent in preventing that from happening. The
extended table gives me lots of time to walk to the other side of the
planer to be ready to support the sled long before the tail end of
the board is even under the head. In fact, I've been *lifting* the
front of the sled even though there is no indication that the melamine
extended bed is sagging.