More upgrades to the table

To address the bend in the table, I added another 75 by 25 mm truss that runs lengthwise under the middle of the table, and two more legs so that the X-axis doesn't span as far. The dip is gone, and the table is stiffer.

I've also added a jig for holding the wood in place while dovetailing it.

The two auto-adjust clamps don't need to be adjusted for different thickness of wood, and do an excellent job of keeping the wood in place. The clamp on the right is attached to the new truss that runs lengthwise under the middle of the table. It's also a lot easier to line up the vertical piece with the horizontal piece with the jig, because locking in in place is just a matter of closing the clamp.

The one unexpected surprise was that clamps will push the extrusion that the wood is centered on. I fixed this by attaching it to the new truss.

Z-Probe dovetail results

Today I used the Z-probe to zero the spindle for all three axes. The results were not as good as I'd hoped. The biggest problem was that thanks to an accurate depth of cut, I was cutting more deeply than before and there was a lot of tear out from the dovetail bit.
There were also problems with how far the cut went along the X-axis --- it needed to go about another 4mm than it did. I'm not sure how that went wrong.

Z-Probe works!

One of the wonderful items that came with the X-Controller was the Z-probe.

Tonight, I tested it. It worked fine --- and there were only two surprises.

The first was that the default units for the probing seem to be English units.

The second is that the probe's mount for the carriage is not thick enough to make it all the way through my 1/4 aluminum plates. I've updated my model so that the next time I mill a plate there will be a larger, 13mm 6.25mm deep hole for it. For now I can get along without it, because the plug is snug enough for zeroing the Z-axis.

Latest GRBL settings

These are the GRBL settings The x steps are different than the Y because the X has a GT-3 belt, and a different microstep, than the Y axis. The Y axis has GT-2 belts.

X microstepping is set at 1/4 (on, off, off), Y microstepping is set at 1/8 (on, off, on) and Z microstepping is set at 1/2 (off, on, off).

$0 = 10    (step pulse, usec)
$1 = 255    (step idle delay, msec)
$2 = 0    (step port invert mask:00000000)
$3 = 6    (dir port invert mask:00000110)
$4 = 0    (step enable invert, bool)
$5 = 0    (limit pins invert, bool)
$6 = 0    (probe pin invert, bool)
$10 = 3    (status report mask:00000011)
$11 = 0.020    (junction deviation, mm)
$12 = 0.002    (arc tolerance, mm)
$13 = 0    (report inches, bool)
$20 = 0    (soft limits, bool)
$21 = 0    (hard limits, bool)
$22 = 0    (homing cycle, bool)
$23 = 3    (homing dir invert mask:00000011)
$24 = 25.000    (homing feed, mm/min)
$25 = 750.000    (homing seek, mm/min)
$26 = 250    (homing debounce, msec)
$27 = 1.000    (homing pull-off, mm)
$30 = 12000.    (rpm max)
$31 = 0.    (rpm min)
$100 = 11.111    (x, step/mm)
$101 = 40.000    (y, step/mm)
$102 = 320.000    (z, step/mm)
$110 = 8000.000    (x max rate, mm/min)
$111 = 8000.000    (y max rate, mm/min)
$112 = 500.000    (z max rate, mm/min)
$120 = 500.000    (x accel, mm/sec^2)
$121 = 500.000    (y accel, mm/sec^2)
$122 = 50.000    (z accel, mm/sec^2)
$130 = 740.000    (x max travel, mm)
$131 = 790.000    (y max travel, mm)
$132 = 100.000    (z max travel, mm)

Dovetail math

I want to get the math down for cutting half blind dovetails down in one place, so here we go.

First, the variables from the diagram

• h --- the height of our cut
• bw --- the width of our dovetail bit, at the bottom
• p --- how far apart we cut dovetails
• a --- the angle of our dovetail bit
• top width --- how much wood is left at the top 

We need a few intermediate values, the first of which is the amount of wood the dovetail cuts.

d(h) = h * tan(a)
One quick sanity checks for the math is to see what happens with a straight bit: tan(a) = tan(0) = 0, which is what you'd expect. Another check is for a mythical 45 degree dovetail bit: tan(45) = 1, also as expected.
Now we need to figure out the top width, which is a function of h and p.

top width(h, p) = p - bw + (2 * d(h))
top width(h, p) = p - bw + (2 * (h * tan(a)))

Substituting for a straight bit we get the sensible value of p - bw.
Setting the top width to be equal to the bit width we get:

bw = p - bw + (2*h*tan(a))
2bw - (2*h*tan(a)) = p
p = 2(bw - (h*tan(a)))

Now we have to figure out how we want to round out the pins.

In this case it is just a matter of making two arcs of the same radius as the bit to get nicely rounded pins.

Upgrades, mostly complete

Over the last weekend I've managed to install several new upgrades, centered around a new X-axis. The goal was to be able to run a dovetail bit through oak, and I'm happy to say it can.

X-Axis, front

X-Axis, back

The two 1800mm lengths of MakerSlide for the X-axis have been replaced with a single 80/20 25-5010 extrusion that is 100mm tall and 50mm wide (you can get an idea of big it is by looking at the X-Axis pictures). The V-Wheels for the X-axis ride on black OpenRails that are attached to the 25-5010 extrusion.
To mount the new 25-5010 X-axis I've milled new plates for the X-axis and the Y-axis. The plates are made out of 1/4" aluminum, and are considerably larger than the steel Shapeoko 2 plates I started with. The Y-axis plates sprout three V-Wheels on top instead of two. Since I knew exactly where all of my screws were going to be before I started, I replaced all of the slots in the original Shapeoko 2 plates with simple holes so I wouldn't have to make any adjustments. The holes were also faster to mill than slots.

Y-Axis

I've replaced the 1.8Nm NEMA 23 motor on the X-axis with a 13Nm NEMA 34 motor from omc-stepper online. The new motor required a new, larger pulley, and I upgraded the X-axis belt to a 15mm wide GT-3 belt. The new belt required custom clips milled out of acrylic to hold the belt. The new belt also needed custom 15mm wide idler wheels, which I ordered from Pulley-N-Wheel.

The X-Controller is driving the 13Nm NEMA 34 motor just fine, although the X-Controller can only put out 4 amps and the motor wants 5 amps. I'd rather have motors that can take down more current than the controller can put out than the other way around.
The design works pretty well, but the drag chain mounts remain a work in progress. I'd add a fourth wheel to the X-axis plates if I got a chance to mill them again. The X-Axis plates have holes to mount NEMA-34 motors, but I'll probably need the 4th wheels if I add the weight I'd get from two more NEMA-34 motors. My first attempt at mounting the X-axis ran into a collision between the screws holding the terminal block and the screws holding the OpenRails in place.
The only problem I've ran into so far was that I forgot to fully tighten the set screws for the X-axis, and debugging the backlash caused by the screw moving along the flat portion of the axel took a while.

X-Axis acrylic tabs

New milling strategy

Tonight I tried a new milling strategy for the final contour cut of my aluminum plate.
Instead of cutting the entire plate with .2mm depth cuts, I cut first 2mm at .2mm depth cuts, and then switched the depth cuts to .25mm

The cutting feed speed was set to 330mm/minute, but I suspect that GRBL is gating the feed speed.