Spoil board height vs working height

Troubleshooting
1

I have successfully calibrated my Maslow 4.1 machine. When I ran the calibration, the Maslow was riding on the spoil board. When I go to cut, the Maslow will be riding on the work surface which will likely be between 1/2"-3/4". I would think that the taller the work surface that is being cut, the more inaccurate the belt length will become towards the edges. However, I would also think that the math on compensating for this should be relatively straight forward.

Should the calibration have an entry for the spoil board height? Should the Maslow controls also have an entry for cutting thickness? Would this help make for more accurate cuts on taller work surfaces?

2

Dan Strassberg wrote:

Should the calibration have an entry for the spoil board height? Should the
Maslow controls also have an entry for cutting thickness? Would this help
make for more accurate cuts on taller work surfaces?

in theory, yes. In practice, it depends on how large the z offset values are,
the smaller they are, they less a small difference matters.

in theory, you want the z offset values to match whatever you are riding on
(spoilboard only or spoilboard with workpiece). We have talked about adding a
workpiece thickness setting so that you don’t have to manually edit the 4 z
offset values, but most people sucessfully using their maslow don’t bother
changing for different workpiece sizes.

in an ideal world, you set the Z offsets and calibrate on your common workpiece
thickness.

not accounting for thicker material would tend to make the belt a little shorter
than the machine thinks it is as the belt angle gets steeper, which would tend
to cause errors towards the corners (especially the top arm’s anchor). Current
measurements are showing that errors tend to be affected more by the long belts
stretching.

If you use tall (stiff) anchors that come close to maching your arm height, the
error in belt length due to the same Z height difference gets much smaller.

let’s say the belt is extended 600mm (near a corner) with the Z offset 120mm.
The horizontal distance would be sqrt(600^2 - 120^2)= 587.8775mm

now let’s say that you add a 20mm workpiece, increasing the z offset to 140mm,
the result is 583.4381mm and error of ~4.4mm

if you add a 2x board on it’s side (~40mm) you would become 578.2733mm an error
of 9.6mmm

but if the Z offset started at 5mm you would be at 599.9791mm and adding the
20mm workpiece changes it to 599.4789mm (and error of 0.5mm), adding a 40mm
workpiece would be 598.3101mm (an error of 1.6mm)

there is additional error introduced by the arms flexing when the angle gets
steeper

This is why I advocate for the belts to be as flat as practical when doing the
calibration. But you do need to make sure that the anchors do not flex or they
can introduce more error.

David Lang

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3

I never bother to adjust anything, but there has been some talk of putting in a “material thickness” setting which would adjust the math to compensate for the wood thickness

4

It’s not just material thickness. It would also depend on length of bit and where the zero is based on bit length.

Running my first cut now and I notice that when cutting at the surface, my z axis is raised about 1.5" plus the 3/4 for material. This raises the arms 2.25" above the calibrated position.

I am also noticing on small cuts where the machine is changing direction a lot, the sled keeps lifting off the board (maybe 1/8") on the side opposite the direction it’s moving

5

Dan Strassberg wrote:

It’s not just material thickness. It would also depend on length of bit and where the zero is based on bit length.

The height of the router is taken into account, but the higher the Z offset + z
height, the more any error in z offset will show up in the triangles

Running my first cut now and I notice that when cutting at the surface, my z
axis is raised about 1.5" plus the 3/4 for material. This raises the arms
2.25" above the calibrated position.

but only 3/4" above where it thinks it is.

I am also noticing on small cuts where the machine is changing direction a
lot, the sled keeps lifting off the board (maybe 1/8") on the side opposite
the direction it’s moving

horizontal or vertical (sorry, can’t keep track with all the threads)?
see if you can do anything to make the sled slipprier (wax it, put teflon tape
on the bottom, etc)

David Lang

6

Thanks. I have some paste wax that I keep in my shop for jigs and tool surfaces. I’ll put a coat of that on the sled.

FYI, I have a horizontal setup.

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7

I ran my first test cut where I used the entire piece of plywood. I was cutting a 27"x30"x23" cabinet with 6 parts. I noticed in the final cuts that all of the long cuts seemed straight. I probably should have used a string to double check how straight they were, because something was definitely off when I measured the final pieces.

The cut was essentially 6 pieces. All pieces were 23 wide, which allowed for 2 pieces to the left side of the plywood, 2 pieces at the center and 2 pieces to the right. If you looked at the plywood from the long edge, there were 3 columns of parts.

The two pieces that were in the center of the plywood were close to accurate in dimensions. The pieces toward the edges dimensionally off. The far edges were 23-3/32". I am wondering if this is related to the belt stretch that is currently being discussed in the forum.

I am also wondering if this is due to the z-axis calculations. My frame is horizontal with the belts ends connected by bolts to drop in anchors. There is almost no flex in this setup, but the setup keeps the belt ends near the concrete. I calibrated with the sled on top of a 7/16" OSB sheet that is my spoil board. My cut was on a 3/4" plywood sheet. I am still not sure if I should be adjusting the z-offsets in the yaml file based on my workpiece thickness, or if I should calibrate from the workpiece height. It seems like if this calculation would be most important when cutting near the edges of the workpiece, since the angles will be the greatest then.