A STAND FOR A PORTA-BAND BANDSAW
Bob Engelhardt

PortaStand.jpg is a composite of 9 pictures.

My design objectives for the stand: small, mounting and dismounting the saw
should be fast & easy, it must be structurally stiff, and built from on-hand
parts.  Without having used it to any extent, I am pretty pleased with the
results: the size is 24 x 13 with the saw mounted, the stand weighs 20 lbs,
the saw another 18 (with adapter), and it was built from common stuff.
Material: 1 1/2" x 1/4" angle; 1", 1 1/4", & 1 1/2" sq tube for arm; 7/8"
pillow blocks (probably overkill, but it was what I had); 7/8" shaft for
pivot.  It cuts quite smoothly with hands off.  It mounts and dismounts
using 2 knobs.  The only big tools required were a welder & drill press.

I did not make it a "miter" stand for a couple of reasons.  Primarily, it
would require too much structure to support and keep stiff.  The vast
majority of my cuts are 90 deg.  Anyhow, angle the saw or angle the stock,
what's the difference.  I.e., I'll just turn the stand and clamp the stock
at the angle I want.

Also I did not build in a vise.  I thought I would, but I concluded that a
fence that I could clamp to would be just as good.  My general approach is
try what seems reasonable and change it if needed.

ALIGNMENT
---------
The most critical part of the build was getting the pivot axis perpendicular 
to the plane of the blade.  If the axis (i.e., the center of the shaft
through the pillow blocks) is horizontal and running East-West, then the
blade must be vertical and run North-South.  

If the blade is off the N-S orientation, then when it rotates, it will cut
at an angle.  Worse, the blade will actually trace the surface of a cone as
it rotates.  Without doing the math, I suspect that the deviation due to the
curved path would be insignificant, given that the deviation from N-S is
likely to be pretty small.  So, just adjusting the pillow blocks to remove
the angle should be OK.

However, if the blade is oriented N-S, but not vertical, it is much worse.
In this case, the blade will be tilted relative to the direction of the cut
(by definition, the direction of the cut is perpendicular to the axis, i.e,
vertical for a horizontal axis) and will cause the cut to veer off.  This
cannot be corrected by shimming the pillow blocks because that would just
change the direction of the cut, but not the angle of the blade relative to
that direction.

I had this problem and I solved it by shimming the blade guides to bring the
blade into alignment.  It only took .007 under one side.

As a practical matter, it is very difficult to get the axis-blade alignment
just right during the build.  I clamped the saw/adapter/arm upside down
and used a straight edge and square.  I got pretty close.  The best way, I
suppose, would be to clamp the assembly upside down on a mill table.
Indicate on the blade using table feed and table up-down to get the blade
straight and vertical.  Then indicate on the pivot shaft (top and side)
while cross feeding.  Then weld it and hope that it doesn't heat-distort.
Or, build in some kind of fine adjustment (I didn't want to get into that).

The other aspect of alignment: the blade to the stand & stock is trivial by
comparison.  Just tweek the pillow blocks back & forth for horizontal
adjustment.  And shim under one block for vertical adjustment (I had to use
a small washer).