Tag: Improvements

Making the world a better place, one piece at a time

Makergear M2: Slic3r Configuration

What you see here represents a stake in the ground, rather than the be-all and end-all configuration. Remember that my intent is to get the M2 working with its more-or-less stock hardware and firmware, make some straightforward improvements, then transition to LinuxCNC for better control and measurement.

While printing a variety of test objects (which I’ll describe shortly), I casually permuted the temperatures, speeds, and timings to gradually improve the results. In nearly all cases, the M2 performs much better than my old and highly modified Thing-O-Matic ever did, so the machinery lives up to its reputation.

Slic3r seems to be nearly as good at slicing as Skeinforge 50 and much faster, although it doesn’t handle very thin walls quite right and produces bizarre speed glitches on (or near?) layers with bridges. I wasn’t taking notes during any of this, which means you should regard it as hearsay evidence at best, but, on the whole, slic3r seems to work just fine for the non-pathological objects I generally build.

This is the Slic3r config.ini file, which (I think) contains all of the configuration information now distributed throughout the smaller files controlled by slic3r.ini:

# generated by Slic3r 0.9.8 on Tue Apr  9 08:43:22 2013
bed_size = 190,250
bed_temperature = 70
bottom_solid_layers = 3
bridge_fan_speed = 100
bridge_flow_ratio = 1
bridge_speed = 100
brim_width = 0
complete_objects = 0
cooling = 1
default_acceleration = 0
disable_fan_first_layers = 3
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 tempeature\nM140 S0        ; drop bed temperature\nM106 S0        ; bed fan off\nG1 Z195    F2500    ; lower bed\nG1 X0 Y0 F30000    ; center nozzle\nM84         ; disable motors\n;-- Slic3r End G-Code ends --
external_perimeter_speed = 75
extra_perimeters = 1
extruder_clearance_height = 20
extruder_clearance_radius = 20
extruder_offset = 0x0
extrusion_axis = E
extrusion_multiplier = 0.9
extrusion_width = 0.40
fan_always_on = 0
fan_below_layer_time = 30
filament_diameter = 1.70
fill_angle = 45
fill_density = 0.10
fill_pattern = honeycomb
first_layer_bed_temperature = 70
first_layer_extrusion_width = 0
first_layer_height = 100%
first_layer_speed = 30
first_layer_temperature = 165
g0 = 0
gap_fill_speed = 100
gcode_arcs = 0
gcode_comments = 0
gcode_flavor = reprap
infill_acceleration = 0
infill_every_layers = 1
infill_extruder = 1
infill_extrusion_width = 0
infill_speed = 200
layer_gcode =
layer_height = 0.25
max_fan_speed = 100
min_fan_speed = 50
min_print_speed = 20
min_skirt_length = 15
notes =
nozzle_diameter = 0.35
only_retract_when_crossing_perimeters =
output_filename_format = [input_filename_base].gcode
perimeter_acceleration = 0
perimeter_extruder = 1
perimeter_extrusion_width = 0
perimeter_speed = 100
perimeters = 1
post_process =
print_center = 0,0
randomize_start = 1
retract_before_travel = 1
retract_length = 1.0
retract_length_toolchange = 5
retract_lift = 0
retract_restart_extra = 0
retract_restart_extra_toolchange = 0
retract_speed = 300
rotate = 0
scale = 1
skirt_distance = 5
skirt_height = 1
skirts = 1
slowdown_below_layer_time = 10
small_perimeter_speed = 25
solid_fill_pattern = concentric
solid_infill_below_area = 70
solid_infill_every_layers = 0
solid_infill_speed = 100
start_gcode = ;-- Slic3r Start G-Code for M2 starts --\n;  Ed Nisley KE4NZU - March 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-125         ; set origin to 0 = center of plate\nG1 Y-122 F30000    ; set up for prime near 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 F2500    ; plug extruder on plate\nG1 E10 F300        ; prime to get pressure\nG1 Z5 F2500        ; rise above blob\nG1 Y-115 F30000    ; move away\nG1 Z0.0 F2500    ; dab nozzle to remove outer snot\nG4 P1            ; pause to clear\nG1 Z0.1            ; clear bed for travel\n;-- Slic3r Start G-Code ends --
support_material = 0
support_material_angle = 0
support_material_extruder = 1
support_material_extrusion_width = 0
support_material_pattern = rectilinear
support_material_spacing = 2.5
support_material_speed = 100
support_material_threshold = 0
temperature = 165
threads = 2
toolchange_gcode =
top_solid_infill_speed = 50
top_solid_layers = 3
travel_speed = 500
use_relative_e_distances = 0
vibration_limit = 0
z_offset = 0

2013-04-13

Makergear M2: Marlin Configuration Tweaks
The slightly customized version of Marlin shipped with the M2 works well enough, but some of the constants required adjustment.

Most of the changes appear in the Configuration.h file…

Start by tweaking the version info so you know what’s in the Flash ROM every time it starts up:
```
#define STRING_VERSION_CONFIG_H "2013-03-27" //Personal revision number for changes to THIS file.
#define STRING_CONFIG_H_AUTHOR "Ed Nisley - KE4ZNU" //Who made the changes.
```
I reduced the maximum temperatures to match the Makergear-defined limits, even though those are far beyond what I expect to use. I’ll probably cut them back even further, but they’ll do for now:
```
// When temperature exceeds max temp, your heater will be switched off.
// This feature exists to protect your hotend from overheating accidentally, but *NOT* from thermistor short/failure!
// You should use MINTEMP for thermistor short/failure protection.
// Ed Nisley KE4ZNU - 26 March 2013 - reduce to M2 limit
#define HEATER_0_MAXTEMP 230
#define HEATER_1_MAXTEMP 230
#define HEATER_2_MAXTEMP 230
#define BED_MAXTEMP 125
```
Long ago, I settled on a much lower extrusion temperature for ABS in the Thing-O-Matic than nearly everyone else and that’s also holding true for PLA in the M2, so I reduced the minimum allowable temperature limit from 170 °C to 120 °C. The firmware seems to use a “less-than-or-equal” test, so it prevents extrusion at exactly 120 °C. Close enough:
```
// M2 - reduce to allow much cooler PLA extrusion
// KE4ZNU - 24 March 2013
//#define EXTRUDE_MINTEMP 170
#define EXTRUDE_MINTEMP 120
```
Before I added the shim around the Z axis leadscrew bearing, the default homing speed excited a howling mechanical resonance. Increasing the homing speed moved the vibration away from the resonance, but the real cure was to reduce the motor current, which eliminated the four dead spots per full step:
```
// KE4ZNU - 24 March 2013 - M2 - Goose Z feedrate to avoid resonance
//#define HOMING_FEEDRATE {50*60, 50*60, 4*60, 0}  // set the homing speeds (mm/min)
#define HOMING_FEEDRATE {50*60, 50*60, 6*60, 0}  // set the homing speeds (mm/min)
```
Dan Newman’s comments to the post about the Z axis performance calculations suggest some rationalization should happen among all the maximum speed and acceleration settings; they appear to be quite inconsistent right now. This will take a bit of measurement, but I think substantive measurements & changes must wait until I get the LinuxCNC controller running.

The block of constants for the motor currents includes some misleading comments. I added the RAMBo design equations, which will become invalid when a board iteration changes either the supply voltage or the sense resistor value, and a bit of explanatory text.

The extruder current seemed slightly low, as it would skip steps while infilling large bottom layers. This happened before I lowered the extruder temperature, so the nominal value may be right on the edge of goodness. The new value of 1.5 A heats the motor to about 120 °C, which is higher than I’d like for something attached to a plastic mount, but I anticipate some changes there in the near future.

I increased the XY motor currents to 1.5 A in anticipation of using higher speeds, although that wasn’t based on any evidence. The motors now run at about 120 °C, which is OK because they’re attached to solid metal parts (albeit without heatsink compound).

As described earlier, reducing the Z motor current to 0.6 A from 1.1 A didn’t materially affect the maximum torque, dramatically smoothed the motion, and slightly reduced the temperature. It still runs at nearly 130 °C, despite heatsinking to the chassis, and is in line for replacement.
```
// Motor Current setting (Only functional when motor current pins are connected to digipot)
// Values 0-255
// RAMBO 135 = ~0.75A, 185 = ~1A
// Ed Nisley KE4ZNU - 25 March 2013 - increase XY current to 1.5 A (185 was 135)
//		decrease Z current to nominal 600 mA (75 was 135) based on 19 V / 28 ohm winding
//		value = 255 * (0.8 * Imax) / 1.66 V
// Ed Nisley KE4ZNU - 27 March 2013 - increase E current to 1.5 A (185 was 165)
//		to support 300 mm/s XY extrusion speed
#define DIGIPOT_MOTOR_CURRENT
#define X_CURRENT 185
#define Y_CURRENT 185
#define Z_CURRENT 75
#define E0_CURRENT 185 //For MakerGear M2, 165 is a good starting point
#define E1_CURRENT 125
```
The only change to Configuration_adv.h increases the stepper timeout to allow the build platform to reach operating temperature; the default value shut off the motors just before printing started. The value obviously depends on the start and end temperatures, so more testing is in order:
```
//default stepper release if idle
// Ed Nisley KE4ZNU - 25 March 2013 - make deactivate timeout exceed plate heating time
#define DEFAULT_STEPPER_DEACTIVE_TIME 400
```
2013-04-12
Makergear M2: Filament Drive

The M2 filament drive works surprisingly well. The OD of the curved section around the drive gear could easily be another few millimeters larger, which would put the mounting screw holes completely within the plastic perimeter:

M2 extruder – filament embossing

I haven’t changed the position of the filament compression screw and the default setting produces a really aggressive grip on the filament; the picture shows the deep track from the drive gear in the natural-color PLA filament along the bottom of the opening. That may be entirely too much of a good thing, but I’ll leave well enough alone for now.

Makergear had scraped out the recess that accepts the end of the motor gearbox housing, but it still didn’t quite fit the motor’s snout, so I continued the scraping job until the drive sat square on the end of the gearbox. It mounts to the gearbox with three screws: the gearbox has four threaded holes, but the fourth screw would pass through an inconvenient spot above the bearing / below the compression screw / beside the filament / inside the clamp arm.

Perhaps rotating the motor slightly would reposition the mounting holes a bit better? Disadvantage: hard to make the extruder sit vertically with a crooked motor. Maybe integrate the extruder with the motor mount, so the vertical reference comes from the X stage linear slide platform and the mount forces the proper motor and extruder alignment?

The filament compression screw is offset rearward from the filament, so the upper part of the clamp must apply serious torque through its plastic body to the bearing pressing the filament against the drive gear:

M2 extruder – added filament guide

I think a spring-loaded bearing would work better, with force applied through a pair of springs bracketing the bearing to reduce the single-point load and torque, with a hinge pin below the bearing. The Wade-ScribbleJ bearing clamp on the Thing-O-Matic has worked perfectly since I installed it, but there are now simpler designs out there that should be adaptable.

The twist of paper embedded in a blob of hot-melt glue encourages the filament guide tube to stand up straight and not flop over during reversals. That should be somewhat longer and fit neatly around the guide; it should be part of the filament drive body. This end of the guide tube should not be anchored, so it can pop upward when the filament reverses; there’s no need to push the filament backwards through a fixed guide tube at full reversal speed.

The drive came pre-assembled to and aligned with the hot end, here seen without the paper / glue guide after the first-pass assembly:

M2 extruder wiring

I want to insert strain gauges between the mount and the extruder barrel in order to measure the force applied to the hot end during extrusion, but it’s not clear how to do that with this design. I think I must build a bench model that extrudes a plastic tangle into air before I understand the problems. Again, an integrated motor + extruder mount might work better.

The PTFE (?) filament guide tube had both ends slightly crimped from the pliers that cut it off the reel, which isn’t unexpected. I reshaped / reamed the ends of the tube to pass the filament without undue friction. There’s still a bit too much friction, methinks, but it doesn’t pose a problem yet.

The spool holder and filament guide don’t match the drawings at all; some discussions in the Google Group indicate this design works much better than the original, fiercely complex, design.

The end of the filament guide tube over the spool also tends to flop over and bend the filament, so I blobbed enough hot melt glue around it on the guide bracket to both anchor it and enforce good alignment. The red cable tie holds the blob in place, as there’s no mechanical interlock on the bracket for the glue to grab:

M2 spool filament guide anchor

Another design for a much longer bracket positions the guide tube over the spool’s midline, which should reduce the snap when the filament slips over a bunching on one side or the other. I think I’ll gimmick up something with an integral alignment doodad for the filament tube.

The guide tube reorients the filament to be tangential to the spool, with the bracket providing the reaction force required to hold the guide tube in place while the filament transmits force from the extruder motor that unrolls the filament. Given that we know exactly how much filament travels into the extruder, we could add a motor drive to unroll exactly that amount from the spool and maintain the length of the filament loop without a guide tube. At higher feed rates, that would allow the extruder drive to feed filament into the hot end without any drag, thus eliminating any effects not related to the actual extrusion process. I like that sound…

2013-04-09
Makergear M2: Extruder Motor Mount

The general idea is that the extruder motor mount will clamp the exceedingly smooth and totally featureless circumference of the motor gearbox:

M2 extruder – motor and mount

The as-built interior of the circumferential clamp has enough ripples and ridges and imperfections that it can’t get a solid grip on the metal gearbox:

M2 extruder – motor mount clamp – plastic ripples

That allows the motor to rotate slightly in the mount, with what seemed like very little torque, and misalign the extruder nozzle with respect to the platform. There’s about 80 mm between the motor shaft and the nozzle, so a mere 4° tilt raises the nozzle an additional 0.1 mm, entirely enough to throw off the Z axis height setting.

I smoothed the worst of the bumps with a file and applied a generous dose of rosin for a better grip. Two Nylock nuts sunk into the motor mount anchor a pair of M4 screws that compress the circumferential clamp around the motor, but there’s not enough plastic around them for proper support and the mount promptly cracked in exactly the places you’d expect. I reamed out the holes to pass overly long 10-32 pan-head screws, scraped out the nut traps to accept 10-32 nuts, then added two small nuts and a large jam nut to each one:

M2 – Extruder motor clamp – 10-32 screws

That’s a temporary expedient until I rebuild the entire mount, as the plastic remains split and the clamp isn’t applying uniform pressure to the gearbox.

The extruder motor mount on my M2 doesn’t match the drawings: it seems Makergear changed from a one-piece extruder motor mount (which required slipping the extruder cable loom and connectors through a tunnel above the motor) to a two-piece design (which clamps the cable between two U-shaped strips). Unfortunately, there’s simply not enough plastic to provide sufficient strength in several vital sections; the nuts just described being one.

More conspicuously, the lower U-shaped cable clamp strip cracked just behind the motor clamp body, because the plastic filaments run across the mount, perpendicular to the direction of maximum stress and have very little cross-sectional area. I applied extra cable ties on both sides of the fracture, so that the top strip serves as splint for the lower:

M2 – cracked extruder cable guide

That photo shows the M4 Nylock nuts splitting the mount prior to the 10-32 screw fix.

The wire loom evidently corresponds to the previous mount design, as there’s not enough slack in the thermistor and heater cables to mate the connectors. I trimmed off some loom and rerouted the wires appropriately:

M2 extruder wiring

With all that in hand, a tiny machinist’s square aligned the motor with the X axis slide and set the extruder perpendicular to the platform:

M2 extruder – vertical alignment

I’m unhappy with how that worked out, but it’s good enough for now. I think rebuilding the mount in aluminum will work better for what I have in mind; this seems to be one of the places where 3D printed plastic isn’t quite appropriate.

2013-04-08
Makergear M2: Heated Build Platform Cable

The power + thermistor cable for the M2 Heated Build Platform attaches to the Z axis stage at the Y axis motor, with the conductors encased in a fairly stiff braided loom. The cable flexes from fully retracted to fully extended as the HBP moves along the Y axis. Here’s a view at about mid-travel:

M2 HBP cables – wire loom

Unfortunately, there’s no provision for strain relief at the HBP or around the connectors. The silicone heating pad firmly anchors the two pairs of power wires to the aluminum plate, but that simply means they flex sharply at the edge of the pad:

M2 HBP connections

I removed the loom between the motor mount and the connectors, but that still doesn’t provide nearly enough flexibility:

M2 HBP cables – loom removed

The wires still flex sharply at the outboard side of the connector and at the HBP pad; this can’t possibly survive more than a few thousand long cycles before something expensive breaks. The Thing-O-Matic HBP connector debacle suggests that I may need to attach a strut to the Y axis stage that rigidly supports the connectors, with a much longer loop of wire soaking up the strain to the fixed end.

The 18 AWG wires carrying the 10+ A of HBP current get unpleasantly warm, suggesting that new loop will require heavier wire. In round numbers from that table, 18 AWG stranded wire runs 6.5 mΩ/ft, so the (roughly) four feet of wire pair between the electronics case and the HBP will drop 250+ mV and dissipate 2.5 W. I suspect it’s worse than that, but haven’t made any measurements to back up that suspicion.

2013-04-07
Makergear M2: Z Axis Bumpers and Upper Bearing Bushing

The M2’s Z axis will descend under its own weight with the stepper motor disabled, landing with an emphatic thud when the Nylock nuts holding the leadscrew nut in place hit the top of the motor case. I stuck a pair of rubber feet atop the motor to cushion the impact:

M2 Z axis motor – added thermal compound

Yes, that’s thermal compound peeking out from between the motor and the chassis. More about that later, but it derives from those measurements.

The top end of the leadscrew passes through a ball bearing, but the bearing OD is about 15 mils smaller than the top plate recess ID. I slid a strip of 6 mil brass shimstock around the bearing to soak up the difference and reduce a nasty mechanical resonance:

M2 Z axis bearing – shimstock bushing

The leadscrew is also a loose fit in the bearing ID, which I’ll correct with a dab of low-strength threadlock when the time comes.

Note, however, that there’s no other mechanical compliance in the Z axis assembly, so a slightly misaligned leadscrew may actually need that slop when the stage approaches the top of its travel. That wasn’t the case in my printer, but don’t take it for granted; if the leadscrew doesn’t turn easily by hand, remove the shimstock.

2013-04-06
Reflectorized USB Flash Drives

It turns out that dropping a dark-gray USB flash drive on a dark carpet under a table in a dimly lit room doesn’t produce a net increase in happiness. The next time that happens, we’ll be able to find the thing:

Centon 4 GB USB Flash Drives – reflectorized

Each side has a snippet of retroreflective orange tape; the tenth drive lives with the Token Windows Laptop. Done!

In related news, the Dremel Wrench went missing despite its high-viz tape. I vaguely recalled tucking it into a tool bag for a remote house-call repair jog, but a week later it turned up in the breast pocket of my demin jacket. Maybe it needs a bulky lanyard?

2013-03-20