Category: Machine Shop

Mechanical widgetry

Makergear M2: Mechanical Setup
That Slic3r configuration presumes a somewhat nonstandard mechanical setup for my M2…

I put the XY coordinate origin in the middle of the platform, so that laying objects out for printing doesn’t require knowing how large the platform will be: as long as the printer is Big Enough, you (well, I) can print without further attention.

The RepRap world puts the XY coordinate origin in the front left corner of the platform, so that the platform size sets the maximum printable coordinates and all printing happens in Quadrant I. This has the (major, to some folks) advantage of using only positive coordinates, while requiring an offset for each different platform.

Yes, depending on which printer software you use, you can (automagically) center objects on your platform; this is often the only way to find objects created with Trimble (formerly Google) Sketchup. I am a huge fan of knowing exactly what’s going to happen before the printing starts, so I position my solid models exactly where I want them, right from the start. For example, this OpenSCAD model of the bike helmet mirror parts laid out for printing:

Helmet mirror mount – 3D model – Show layout

… exactly matches the plastic on the Thing-O-Matic’s platform, with the XY origin right down the middle of the platform:

Helmet mirror mount on build platform – smaller mirror shaft

It’d print exactly the same, albeit with more space around the edges, on the M2’s platform.

Similarly, the Z axis origin sits exactly on the surface of the platform. That way, the Z axis coordinate equals the actual height of the current thread extrusion in a measurable way: when you set the Z axis to, say, 2.0 mm, you can measure that exact distance between the extruder nozzle and the platform:

Taper gauge below nozzle

Now, admittedly, I fine-tune that distance by measuring the height of the skirt thread around the printed object, but the principle remains: a thread printed on the platform with Z=0.25 should be exactly 0.25 mm thick.

The start.gcode file handles all that:
```
;-- Slic3r Start G-Code for M2 starts --
;  Ed Nisley KE4NZU - 15 April 2013
M140 S[first_layer_bed_temperature]	; start bed heating
G90				; absolute coordinates
G21				; millimeters
M83				; relative extrusion distance
M84				; disable stepper current
G4 S3			; allow Z stage to freefall to the floor
G28 X0			; home X
G92 X-95			; set origin to 0 = center of plate
G1 X0 F30000		; origin = clear clamps on Y
G28 Y0			; home Y
G92 Y-127 		; set origin to 0 = center of plate
G1 Y-125 F30000	; set up for prime at front edge
G28 Z0			; home Z
G92 Z1.0			; set origin to measured z offset
M190 S[first_layer_bed_temperature]	; wait for bed to finish heating
M109 S[first_layer_temperature]	; set extruder temperature and wait
G1 Z0.0 F2000		; plug extruder on plate
G1 E10 F300		; prime to get pressure
G1 Z5 F2000		; rise above blob
G1 X5 Y-122 F30000	; move away from blob
G1 Z0.0 F2000		; dab nozzle to remove outer snot
G4 P1			; pause to clear
G1 Z0.5 F2000		; clear bed for travel
;-- Slic3r Start G-Code ends --
```
The wipe sequence, down near the bottom, positions the extruder at the front center edge of the glass plate, waits for it to reach the extrusion temperature, then extrudes 10 mm of filament to build up pressure behind the nozzle. The blob generally hangs over the edge of the platform and usually doesn’t follow the nozzle during the next short move and dab to clear the mess:

M2 – Wipe blobs on glass platform

I’ve also configured Slic3r to extrude at least 25 mm of filament in at least three passes around the object. After that, the extruder pressure has stabilized and the first layer of the object begins properly.

Which brings up another difference: the first layer printed on the platform is exactly like all the others. It’s not smooshed to get better adhesion or overfilled to make the threads stick together:

Robot cookie cutter – printing first layer

I print the first layer at 25 mm/s to give the plastic time to bond to the platform and use hairspray to make PLA stick to glass like it’s glued down.

After that, it’s just ordinary 3D printing…
2013-07-26

Makergear M2: Slic3r config.ini

A stick in the ground…

I think the exported config.ini file corresponds to the currently selected set of sub-configurations; I find it difficult to keep a myriad of selections up-to-date while tweaking things, so mostly I don’t bother with named configurations.

The start.gcode and end.gcode lines go on forever, with embedded newlines.

# generated by Slic3r 0.9.11-dev on Mon Jul 22 09:28:22 2013
avoid_crossing_perimeters = 
bed_size = 190,250
bed_temperature = 70
bottom_solid_layers = 3
bridge_acceleration = 0
bridge_fan_speed = 100
bridge_flow_ratio = 1
bridge_speed = 150
brim_width = 0
complete_objects = 0
cooling = 1
default_acceleration = 0
disable_fan_first_layers = 0
duplicate = 1
duplicate_distance = 6
duplicate_grid = 1,1
end_gcode = ;-- Slic3r End G-Code for M2 starts --\n;  Ed Nisley KE4NZU - March 2013\nM104 S0		; drop extruder temperature\nM140 S0		; drop bed temperature\nM106 S0		; bed fan off\nG1 Z180 F2000	; lower bed\nG1 X0 Y0 F30000	; center nozzle\nM84     	; disable motors\n;-- Slic3r End G-Code ends --
external_perimeter_speed = 50
external_perimeters_first = 0
extra_perimeters = 1
extruder_clearance_height = 20
extruder_clearance_radius = 20
extruder_offset = 0x0
extrusion_axis = E
extrusion_multiplier = .99
extrusion_width = 0.40
fan_always_on = 0
fan_below_layer_time = 45
filament_diameter = 1.72
fill_angle = 45
fill_density = 0.15
fill_pattern = honeycomb
first_layer_bed_temperature = 70
first_layer_extrusion_width = 0
first_layer_height = 100%
first_layer_speed = 25
first_layer_temperature = 175
g0 = 0
gap_fill_speed = 50
gcode_arcs = 0
gcode_comments = 0
gcode_flavor = reprap
infill_acceleration = 0
infill_every_layers = 1
infill_extruder = 1
infill_extrusion_width = 0
infill_first = 1
infill_only_where_needed = 1
infill_speed = 125
layer_gcode = 
layer_height = 0.25
max_fan_speed = 100
min_fan_speed = 45
min_print_speed = 15
min_skirt_length = 25
notes = 
nozzle_diameter = 0.35
only_retract_when_crossing_perimeters = 1
output_filename_format = [input_filename_base].gcode
overhangs = 1
perimeter_acceleration = 0
perimeter_extruder = 1
perimeter_extrusion_width = 0
perimeter_speed = 100
perimeters = 1
post_process = 
print_center = 0,0
raft_layers = 0
randomize_start = 1
resolution = 0
retract_before_travel = 0.5
retract_layer_change = 0
retract_length = 1
retract_length_toolchange = 5
retract_lift = 0
retract_restart_extra = 0
retract_restart_extra_toolchange = 0
retract_speed = 80
rotate = 0
scale = 1
skirt_distance = 5
skirt_height = 1
skirts = 3
slowdown_below_layer_time = 20
small_perimeter_speed = 25
solid_fill_pattern = rectilinear
solid_infill_below_area = 15
solid_infill_every_layers = 0
solid_infill_extrusion_width = 0
solid_infill_speed = 100
spiral_vase = 0
start_gcode = ;-- Slic3r Start G-Code for M2 starts --\n;  Ed Nisley KE4NZU - 15 April 2013\nM140 S[first_layer_bed_temperature]	; start bed heating\nG90				; absolute coordinates\nG21				; millimeters\nM83				; relative extrusion distance\nM84				; disable stepper current\nG4 S3			; allow Z stage to freefall to the floor\nG28 X0			; home X\nG92 X-95			; set origin to 0 = center of plate\nG1 X0 F30000		; origin = clear clamps on Y\nG28 Y0			; home Y\nG92 Y-127 		; set origin to 0 = center of plate\nG1 Y-125 F30000	; set up for prime at front edge\nG28 Z0			; home Z\nG92 Z1.0			; set origin to measured z offset\nM190 S[first_layer_bed_temperature]	; wait for bed to finish heating\nM109 S[first_layer_temperature]	; set extruder temperature and wait\nG1 Z0.0 F2000		; plug extruder on plate\nG1 E10 F300		; prime to get pressure\nG1 Z5 F2000		; rise above blob\nG1 X5 Y-122 F30000	; move away from blob\nG1 Z0.0 F2000		; dab nozzle to remove outer snot\nG4 P1			; pause to clear\nG1 Z0.5 F2000		; clear bed for travel\n;-- Slic3r Start G-Code ends --
start_perimeters_at_concave_points = 1
start_perimeters_at_non_overhang = 1
support_material = 0
support_material_angle = 0
support_material_enforce_layers = 0
support_material_extruder = 1
support_material_extrusion_width = 0
support_material_interface_layers = 0
support_material_interface_spacing = 0
support_material_pattern = rectilinear
support_material_spacing = 2.5
support_material_speed = 125
support_material_threshold = 0
temperature = 175
thin_walls = 1
threads = 2
toolchange_gcode = 
top_infill_extrusion_width = 0
top_solid_infill_speed = 50
top_solid_layers = 3
travel_speed = 250
use_relative_e_distances = 0
vibration_limit = 0
wipe = 0
z_offset = 0

2013-07-25

Makergear M2: The End of Torture Test Objects

While pulling together a talk on OpenSCAD modeling (more on this later), I ran off a batch of calibration and “torture test” objects, with the intent of seeing how my somewhat modified M2 performs. The short answer is that you (well, I) can’t ask for anything better…

Using my OpenSCAD module based on nophead’s polyholes to adjust low-vertex polygons by a constant +0.2 mm produces results that are within ±0.1 mm of the nominal value for holes larger than 3.0 mm:

M2 – Small Hole Calibration Test

That level of as-printed cleanliness is typical: no stringing, no hair, no misplaced globs, no retraction problems. Basically, the plastic shape on the platform matches the mathematical shape on screen.

Goaran’s Calibration Block came out fine, except for the intended-to-be-impossible overhangs:

M2 – Calibration Block – overview

All of the linear features are with ±0.1 mm of nominal; both the 0.5 and 0.25 mm walls came out at 0.40 mm, because that’s the thread width. Slic3r doggedly puts a thread down the middle of hair-fine walls, which I think is a Good Thing.

The holes came out less than 0.3 mm undersize, which is about what you’d expect because they’re not pre-distorted and have far too many sides. The 1.0 and 0.5 mm diameter holes are present, but just barely visible; those simply aren’t reasonable sizes for this technology.

The bottom view shows a few strings in the bridge test area and more detail of the overhang:

M2 – Calibration Block – bottom

Grouping the overhangs like that produced a flat surface that tended to curl upward, so the final slopes don’t match the design. In round numbers, the M2 can handle something like a 60° overhang reasonably well.

Cymon’s 3DHacker demo object came out OK, even the severe overhangs in the legs of the digit 3:

M2 – 3DHacker object – front

The top view shows the shape in the box looks fine, but with some curls in the main structure. The arch closed over a few random strands, so it’s rougher than I’d like:

M2 – 3DHacker object – top

The spires are lumpy and there’s more striation than I’d like, but this lies well outside the realm of stuff that I build. If I were doing it for real, I’d add some support structures here & there.

A new Tux Cookie Cutter is perfect:

Tux cutter – M2 single-wall blade – overview

The wall stacks up neatly to the single-thread blade on the top, with none of the retraction glitches found in the Thing-O-Matic version:

Tux cutter – M2 single-wall blade – side view

So, all in all, I’d say there’s not much room for improvement.

Now, to coerce LinuxCNC into producing similar results on the same hardware, then proceed onward from there…

2013-07-24
Vexta C6925-9212K Stepper Motors
A box of surplus Vexta NEMA 23 stepper motors arrived:

Vexta C6925-9212K stepper motors

The data plate sayeth:
- Model C6925-9212K
- 2 phase
- 1.8°/step
- 2.3 V
- 3 A
According to Dan, who happened into the deal, that Vexta model number applies to their custom motors, which accounts for the fact that there’s no further data available anywhere.

[Update: A National Instruments description of the motor wiring.]

Dividing 2.3 V by 3 A = 0.77 Ω windings. Multiplying 2.3 V by 2 A suggests a 7 W maximum dissipation.

Poking around with a meter identifies the windings:
- Blue – White – Red
- Green – Yellow – Black
Given those colors, the Y G B W R K color sequence on the connector doesn’t make any sense to me. Most likely, there’s a standard I’m unaware of.

The resistance from the center taps outward measures 1.0 Ω, which is close enough to 0.8 Ω for me. Measuring across the whole winding gives 1.8 Ω.

The inductance is 1.0 mH from the center tap and 4.0 mH across the whole winding. Remember that inductance varies as the square of the number of turns.

The time constant for a complete winding = 2.5 ms = 4 mH / 1.6 Ω.

That’s all I know…
2013-07-23
Water Heater Anode Rod Access Done Right

For reasons I won’t go into, I just installed another water heater. This one, nominally a GE that’s made by Rheem, has a perfectly aligned anode rod access port. This view shows the insulation filling the port, after removing the plastic cap:

GE Water Heater Anode Rod – as shipped

A bit of excavation reveals the top of the rod:

GE Water Heater Anode Rod – excavated

And the 1-1/16 six-point socket fits exactly through the port and mates perfectly with the rod:

GE Water Heater Anode Rod – socket in place

Unlike the never-sufficiently-to-be-damned Whirlpool, no metalwork is required.

Oh, and they have a very nice drain valve at the bottom, with wide opening that shouldn’t clog with the slightest trace of sediment:

GE Water Heater Anode Rod – drain valve

Overall, it looks like a definite win.

2013-07-22
Repairing Yet Another Garden Sprayer

Evidently, it’s impossible to make a spring both good and noncorrosive:

Garden sprayer – corroded spring

I found a suitable (i.e., good, but rust-prone) spring in the Big Box o’ Medium Springs:

Garden sprayer – spring replaced

Unlike the repair for that sprayer, this spring turned out to be long enough to work perfectly. I have no idea how long I can keep this up, but … at least I’m now keeping pace with the failures.

2013-07-21
CNC Platform Corner Clip Fixture
This is a classic case of investing more time and effort creating the fixture than machining the parts.

Start by squaring up the block, which came from the end of a random chunk of smoke gray polycarbonate, with two 10-32 holes matching the tooling plate hole spacing:

Corner Clip Fixture – squaring

Then drill-and-tap four holes:

Corner Clip Fixture – tapping

The left station will be for drilling the blanks clamped under a sacrificial sheet, so those screw holes aren’t used for anything other than clearance; the top millimeter will get chewed up pretty quickly. The screws in the right station will clamp a stack of drilled blanks under a cover plate. If I went into production, I could see using both stations for both functions, but …

There’s a locating pip in the front left corner that works perfectly with laser alignment:

Corner Clip Fixture – aligning

The blank sheets show where they’d be located for drilling, minus the sacrificial sheet and its clamps that you’ll see below.

The G54 coordinate system origin sits at the locating pip. The G-Code then slaps a G55 origin at each of the two stations in turn to simplify their coordinates, with offsets from M54:
- Drilling = (+5,+5)
- Milling = (+40,+5)
With all that in hand: stack, clamp, and drill some blanks:

Corner Clip Fixture – drilling

I tried milling a single drilled blank with a sacrificial plastic top plate:

Corner Clip Fixture – first milling setup

But that didn’t work well. I don’t know if this was due to an inept combination of climb milling, using the wrong speed / feed / material / cutter, and just poor style, but the edges of the blank mashed against the clamp plate and curled, instead of cutting cleanly:

Corner Clip Fixture – rounded-over milled edges

So I made a pair of aluminum plates to clamp both sides of the blanks, then milled another stack:

M2 platform clips – milling edgesM2 platform clips – milling edges

That worked quite well, although the top and bottom clips needed some slight attention from a riffler file and I did break the edges on all the clips. This shows four new clips along with a hand-cut prototype:

Corner Clip Fixture – end result

So I made a dozen more clips, picked the best eight for two sets, sent one set to Dan, installed the other, and … now I have a bunch of spares.

I suppose I should sell clip sets on Etsy / eBay to all the other M2 owners, but I have no idea how to price ’em. If you want some fancy corner clips, send whatever you think they’re worth … [grin]
2013-07-19