Machine Shop – Page 193 – The Smell of Molten Projects in the Morning

MPCNC: Pen Wobble

GCMC includes cycloids.gcmc, a test program producing a fixed set of hypotrochoids and epitrochoids, more commonly known as Spirograph patterns:

I’m using them to get familiar with bCNC’s Workspace Coordinate System settings and to exercise the MPCNC hardware; ya gotta plot before you can cut.

Most came out fine, but some showed distinct wobbles:

MPCNC - Cycloid wobble - star — MPCNC – Cycloid wobble – star

Tight curves and higher speeds produce more wobbles:

MPCNC - Cycloid wobble - loops — MPCNC – Cycloid wobble – loops

You’d probably never feed a wood router over 6000 mm/min = 240 inch/min, so this isn’t as much of a problem as it might appear. Also, I expect a few pounds of router will have fewer wobbulations than a weightless pen hung on a thin plastic mount:

MPCNC - Pen Holder Detail — MPCNC – Pen Holder Detail

Just one more thing to keep in mind.

2017-12-17

MPCNC: Tool Length Probe, Reshaped for Plotter Pens

It turns out old-school plotter pen nibs skid right off the rounded top of the switch lever:

MPCNC Tool Length Probe - plotter pen — MPCNC Tool Length Probe – plotter pen

You can’t see the nib inside the cap, but you get the idea.

Flattening the top and adding a snippet of masking tape produces a better outcome:

MPCNC - Reshaped Tool Probe switch — MPCNC – Reshaped Tool Probe switch

I aligned the flat section so it’s parallel to the platform when the switch activates.

Stipulated: plotter pens aren’t a good test for tool length probing, because they have a locating flange to ensure a consistent position in the pen holder and a rigidly controlled flange-to-tip length:

HP 7475A Plotter Pen Body - in holder — HP 7475A Plotter Pen Body – in holder

What’s going on here involves configuring and testing bCNC’s overall tool change process: not using cutting tools preserves both sanity and hardware!

2017-12-16

MPCNC: GCMC Configuration

The default GCMC prolog(ue) spits out some G-Codes that GRBL doesn’t accept, requiring tweaks to the incantation.

A first pass at a useful prolog, minus the offending codes:

cat ~/.config/gcmc/prolog.gcmc 
(prolog begins)
G17 (XY plane)
G21 (mm)
G40 (no cutter comp)
G49 (no tool length comp)
G80 (no motion mode)
G90 (abs distance)
G94 (units per minute)
(prolog ends)

Including any of the usual “end of program” M-Codes in the epilog(ue) causes GRBL to pause before exiting the program, so leave only a placeholder:

cat ~/.config/gcmc/epilog.gcmc 
(epilog begins)
(M2) (allow program to continue)
(epilog ends)

Having done a git clone into /opt/gcmc before building the program, the GCMC library routines live in:
/opt/gcmc/library

Limiting numeric values to two decimal places makes sense:
-P 2

With all that in hand, unleashing the compiler on an unsuspecting source file requires this jawbreaker:

gcmc -P 2 -I /opt/gcmc/library \
-G ~/.config/gcmc/prolog.gcmc \
-g ~/.config/gcmc/epilog.gcmc \
-o cycloids.ngc \
cycloids.gcmc

One might, of course, tuck all that into a little script, rather than depend on extracting it from the bash history as needed.

The resulting G-Code file looks about right:

head cycloids.ngc
(prolog begins)
G17 (XY plane)
G21 (mm)
G40 (no cutter comp)
G49 (no tool length comp)
G80 (no motion mode)
G90 (abs distance)
G94 (units per minute)
(prolog ends)
F2500.00
[pi@MPCNC tmp]$ head -25 cycloids.ngc
(prolog begins)
G17 (XY plane)
G21 (mm)
G40 (no cutter comp)
G49 (no tool length comp)
G80 (no motion mode)
G90 (abs distance)
G94 (units per minute)
(prolog ends)
F2500.00
G0 Z1.00
(-- tracepath at Z=-1.00mm --)
G0 X-145.50 Y-30.00
G1 Z-1.00
G1 X-145.51 Y-29.93

... vast snippage ...

G1 X175.50 Y30.00
G1 Z1.00
G0 Z25.00
(epilog begins)
(M2)
(epilog ends)

Then it’s just a matter of tweaking cycloids.gcmc to make interesting things happen:

2017-12-14

MPCNC: Tool Length Probe Station

Having a tool length probe station on the Sherline, I had to build one for the MPCNC:

It’s little more than a flange atop a wide base:

MPCNC Tool Length Probe - Slic3r preview — MPCNC Tool Length Probe – Slic3r preview

The flange offset puts the switch actuator on the midline of the base, not that that matters, and the base features rounded corners and a suitable legend, because I can.

I clipped the PCB’s through-hold leads nearly flush and stuck it to the flange with 3M permanent foam tape, which seems to work much better than screws & inserts for simple things that need never come apart.

The Protoneer CNC Shield includes a Probe input on the GRBL-compliant A5, although it took me a while to find the legend on the SCL pin in the I2C header. I moved the endstop power jumper to another header, then conjured a quick-and-dirty connector:

Protoneer CNC Shield - Tool Probe Wiring — Protoneer CNC Shield – Tool Probe Wiring

When I embed the endstop switch PCB in epoxy, I’ll add a drop to the connector while engaging in Magical Thinking. The whole Arduino + CNC Shield must go into an enclosure after I finish measuring the motor currents.

To forestall discussions about switch repeatability and accuracy, suffice it to say the MPCNC doesn’t claim to be much more than a woodworking router, so those switches seem Good Enough.

The OpenSCAD source code as a GitHub Gist:

	// MPCNC Tool Length Probe Station
	// Ed Nisley KE4ZNU – 2017-12-08

	/* [Extrusion] */

	ThreadThick = 0.25; // [0.20, 0.25]
	ThreadWidth = 0.40; // [0.40]

	function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

	/* [Hidden] */

	Protrusion = 0.1; // [0.01, 0.1]

	HoleWindage = 0.2;

	/* [Sizes] */

	EndstopPCB = [40.0,16.5,1.6]; // endstop PCB
	ComponentHeight = 6.0; // max component height above PCB

	SwitchOffset = [35.0,21.0,4.75]; // touch point center from lower left PCB corner
	SwitchTravel = 2.5; // first touch to switch actuation

	TapeThick = 1.0; // foam mounting tape

	WallThick = 4.0; // basic wall & floor thickness

	BaseRadius = 5.0;

	Base = [IntegerMultiple(EndstopPCB[0] + 2*BaseRadius,20),
	IntegerMultiple(EndstopPCB[2] + TapeThick + WallThick + 2BaseRadius,225),
	2.0];

	NumSides = 8*4;

	TextDepth = 2*ThreadThick;

	//- Build it

	union() {
	difference() {
	hull()
	for (i=[-1,1], j=[-1,1])
	translate([i(Base[0]/2 – BaseRadius),j(Base[1]/2 – BaseRadius),0])
	resize([0,0,Base[2]])
	intersection() {
	cylinder(r=BaseRadius,h=BaseRadius,$fn=NumSides);
	sphere(r=BaseRadius,$fn=NumSides);
	}
	translate([0,0,Base[2] – TextDepth])
	linear_extrude(height=TextDepth + Protrusion) {
	translate([0,-10,0])
	text(text="MPCNC",size=8,spacing=1.05,font="Arial:style=Bold",halign="center");
	translate([0,-18,0])
	text(text="Tool Probe",size=6,spacing=1.05,font="Arial:style=Regular",halign="center");
	}

	}
	translate([0,
	WallThick/2 + TapeThick + SwitchOffset[2],
	(EndstopPCB[1] – Protrusion)/2 + Base[2]])
	cube([EndstopPCB[0],WallThick,EndstopPCB[1] + Protrusion],center=true);

	}

view raw Tool Length Probe Station.scad hosted with ❤ by GitHub

The original doodles show a severely over-complexicated solution desperately searching for an actual problem:

MPCNC Tool Length Probe - doodles — MPCNC Tool Length Probe – doodles

Putting a large flat pan at the end of a relatively long lever arm, with the pivot arranged to put the pan level at the switch actuation point, made sense at the time. Give the relatively small tools I expect to use, directly ramming them into the switch lever should work just as well.

Putting all that complexity in harm’s way seemed like a Bad Idea when I sat down and looked at it in cold blood.

2017-12-13

Finger Wrench

A friend recommended a Finger Wrench and it looks useful, indeed:

That’s a 10-32 socket head cap screw, on the large end of the screws I normally use.

The orange PETG required a bit of smoothing around the overhangs, but should work well enough. The dark tinge near the bottom comes from the black filament I used for the MPCNC’s Z Axis sensor and won’t affect its operation in the least.

Done with one perimeter thread and a 3 mm brim to glue down the bottom:

Finger Wrench - Slic3r preview — Finger Wrench – Slic3r preview

That was easy …

2017-12-12

Epson R380 Continuous Ink Supply Tubes

After fixing the yellow ink tube, the Epson R380 printer occasionally gave off a horrible clunk as the tubes slapped around inside the frame. This routing seems much quieter and, as you can see from the marks on the tubes, leaves much less free to flop around:

Epson R380 Printer - CISS tube routing — Epson R380 Printer – CISS tube routing

I cut a small collar (to the left of the white block with the red cable tie) to guide the tubing up over the edge of the ink cartridge holder, with a ramp from the upper edge and raised edges to hold the tubes in place, from a block of black closed-cell foam. It seems perfectly happy to do its job without anything other than the tubes holding it in place atop the cartridges.

There’s also a block of foam filling a gap under the printer’s top frame member (along the far left edge of the picture) to cushion the tubes as they whack against the edge.

So far, so good.

I’ve dumped a few more tanks of waste ink down the drain. When this printer eventually gives up, I’ll get a color laser and move on.

2017-12-10

Salty Spider

An unusual ingredient in the water softener salt reservoir:

They’re everywhere!

I figured it found a way in and can find its own way out, so I just closed the lid and backed carefully away …

2017-12-09