Author: Ed

Running some PETG filament through the M2’s new V4 extruder drive produced nice indentations from the drive gear:

The square-looking indentation at the far left came from having the filament sit unmoving for an hour or so. There’s a smaller indentation to the left of that from a partially engaged gear tooth.

The side view:

That’s with the adjusting screw cranked 1/2 turn inward from what felt like first contact.

It’s an M4 screw with 0.7 mm pitch, so each turn moves the extruder pressure arm 0.35 mm. However, the bearing actually pressing the filament against the drive gear is 1/3 of the distance from the fulcrum to the screw:

Sooooo the bearing should move more-or-less 1/3 as far as the screw, modulo the arm bending, the fulcrum not actually being a pivot, and suchlike: 0.35 mm at the screw should push the gear 0.1 mm into the filament.

Squinting at the filament through a measuring magnifier says the indentations are 0.30 mm deep, which means the screw moved 1.0 mm after the actual “first contact” with the filament. That’s not surprising: PETG filament seems soft and easily indented, the force required to dent the filament doesn’t amount to much, plus there’s plenty of mechanical advantage from my fingers through the screwdriver to the filament.

Turning the screw another half turn certainly won’t mash the drive gear teeth another 0.1 mm into the filament, though, because the force increases dramatically as the dent goes deeper into the filament.

Compare that to PLA filament through the V3 extruder, back in the day:

Looks more or less the same to me, but there’s no way to tell at this late date.

That blue tube anchors the filament guide and keeps the whole affair from thrashing around as the extruder zips back & forth along the X axis.

My M2 dates back to early 2013 and arrived with a 12 V platform power brick and a 19 V brick for everything else. I replaced the platform with a hotrod version, used a DC-DC SSR to control the high-current path, drove it from a 48 V brick dialed back to 40 V, and left the 19 V brick alone.

Recent M2s use a single 24 V brick for everything, including the motors and V4 hot end, so I decided to ditch the 19 V supply when I installed the new hot end. The stock 12 V fans depended on PWM to reduce the 19 V supply to something tolerable, but, with 24 V ball bearing fans being cheap & readily available, I replaced all three.

I bashed a pair of angled brackets from a random heatsink fin to hold the extruder & platform fans together:

All of that hangs from the single screw in the lower left corner of the upper fan, which has worked well enough and never given any trouble, despite my misgivings.

They’re much quieter than the original fans, perhaps as a result of operating at their rated voltage without PWM trickery. In theory, the fan mounted horizontally in the electronics box should survive longer with ball bearings, but the original sintered-bearing fan didn’t complain too much.

The V4 hot end reduced the clearance under the X-axis gantry to the point where a bight of wire from the white LED panels drooped onto the platform during homing. A bit of snipping, drilling, and filing produced a clip from the same steel strap that’s holding the Z-axis switch cable against the gantry:

That was easy…

Mounting the Z-axis platform switch on the X gantry to sense the actual platform position worked perfectly with the original MakerGear V3 hot end, at least after I relocated the switch a bit further from the balance point. It does require moving the nozzle off the platform before homing the Z axis, for the obvious reason:

The smaller MakerGear V4 hot end uses a completely different mount that puts the nozzle higher than the switch lever:

The clearances were close enough to rule out plastic, so I bandsawed some 33 mil (1/32 inch) brass shim stock and drilled holes in the appropriate spots:

After discovering the blindingly obvious fact that you can’t heat brass sheets clamped to a steel vise enough to melt silver solder, I padded the brass with cardboard insulation and tried again:

The cardboard charred and burned and stank up the shop, but held everything in alignment long enough:

A bit of file & sandpaper work shined it up just fine, then I slotted the lower mounting holes enough to accommodate 2-56 nuts between the gantry and the bracket:

Yeah, I could tap 2-56 holes into the brass sheet, but let’s be reasonable: two turns does not a secure fitting make.

Here’s why a plastic bracket wouldn’t work:

That’s with the V4 hot end aligned per instructions, although I may rotate it 1/4 turn clockwise at some point. Note that there’s no filament going in the top, as I did all this before firing that devil up for the first time.

The switch lever had enough free travel that the platform would hit the bottom of the X axis linear slide screws before activating the switch, but lowering the switch would put the lever below the nozzle. I added a 15 mil brass shim to the lever and it’s all good:

Admittedly, the lever rests a bit less than 1.000 mm above the nozzle, but we’ll see how much trouble that causes.

The switch trips 2.0 mm above the nozzle, so the new startup G-Code looks like this:

;-- Slic3r Start G-Code for M2 starts --
;  Ed Nisley KE4NZU - 2015-03-01
;  Makergear V4 hot end
; Z-min switch at platform, must move nozzle to X=135 to clear
M140 S[first_layer_bed_temperature]	; start bed heating
G90				; absolute coordinates
G21				; millimeters
M83				; relative extrusion distance
G92 Z0			; set Z to zero, wherever it might be now
G1 Z10 F1000	; move platform downward to clear nozzle; may crash at bottom
G28 Y0			; home Y to clear plate, origin in middle
G92 Y-127
G28 X0			; home X, origin in middle
G92 X-100
G1 X130 Y0 F30000	; move off platform to right side, center Y
G28 Z0			; home Z to platform switch, with measured offset
G92 Z-2.00
G0 Z2.0			; get air under switch
G0 Y-127 F10000	; set up for priming, zig around corner
G0 X0			;  center X
G0 Y-125.0		; just over platform edge
G0 Z0 F500	; exactly at platform
M109 S[first_layer_temperature]	; set extruder temperature and wait
M190 S[first_layer_bed_temperature]	; wait for bed to finish heating
G1 E20 F300		; prime to get pressure, generate blob on edge
G0 Y-123		; shear off blob
G1 X15 F20000	; jerk away from blob, move over surface
G4 P500			; pause to attach
G1 X45 F500		; slowly smear snot to clear nozzle
G1 Z1.0 F2000	; clear bed for travel
;-- Slic3r Start G-Code ends --

The prime-and-wipe section accommodates gooey PETG, although that will require more attention.