The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Tag: Improvements

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

Tour Easy: Yet Another Shifter Pulley

Somehow, I think I’m never going to get around to doing a CNC version of this thing, but at least now I have more pictures…

The overall problem comes from the fact that the Tour Easy frame geometry doesn’t match the expectations of the front shifter: the cable bends over a small finger that, on a diamond frame bike, should simply hold it in position. Here’s the finger, with a very early version of the pulley that just holds the cable slightly higher than the normal position, complete with one snapped wire showing that the pulley wasn’t getting the job done:

Front derailleur cable with broken strand

The obvious solution involves running the cable over a nice, rounded surface that prevents abrupt bending. The most recent version looks like this:

Shifter pulley installed – left view

Yes, the end of the cable sticks out over the chain; I haven’t tucked it in yet.

A bit of lathe work produces a 0.42 inch diameter thin brass disk with a 50 mil half-circle trench around it; in retrospect, the diameter of the trench bottom should be 0.42 inch and the OD should be about 0.45 inch. If you have really good parting-off-fu, you can produce a disk with a finished backside right on the lathe, but I had to drill an off-center hole anyway, so I thinned it on the Sherline:

Shifter pulley – thinning

It looks like this after all the thinning:

Shifter pulley – thinned

One flange is wider than the other: the thin flange faces front and gets a bunch of cutouts, the wide flange faces rearward and must support the bitter end of the cable.

I lined it up in the shifter, filed a notch to fit around the shifter finger, scribed the hole location, clamped it down, and drilled the hole:

Shifter pulley – center drilling

I think the hole could be on-center with the larger disk; now that I’m keeping better notes, I’ll try that next time. If so, then I can drill it on the lathe, part it off to the correct width, and hand-file the backside flat. The general idea is to have the cable pass over the finger, which almost happens with the smaller diameter.

Some tedious hand-filing produces notches that index over the finger and clear some protuberances on the shifter arm. This is the front face of the pulley that sits against the shifter arm, with a 5 mm socket head cap screw for scale:

Shifter pulley with bolt – front face

The rear face has one side of the trench filed away to get the cable out of the trench and around the bolt:

Shifter pulley with bolt – rear face

Then it looks like this from the right side of the bike:

Shifter pulley installed – right view

A pleasant morning with some Quality Shop Time…

2013-07-14
Makergear M2: Platform Lighting

Adding a strip of white LEDs under the X stage helps shed some light on events atop the M2’s build platform; this was very nearly the first improvement after getting the printer, but somehow I’ve never written down where that nice white glow comes from.

This view shows the strip from below, looking up from the -Y direction in front of the stage:

White LED strip under X axis frame

I originally screwed the wires into the terminals from the hulking 12 V Dell laptop brick for the platform heater, but then I had to unscrew the wires whenever I moved the M2 and I didn’t like sharing the connectors with those huge conductors. Now the LEDs are in parallel with the extruder fan (which runs continuously), sharing the FAN1 screw terminals inside the electronics case.

The M2 firmware uses PWM to cut the 19.5 V supply from a much smaller laptop brick down to roughly 12 V RMS for the fans, but that isn’t such a Good Thing for LEDs. The strip has 120 Ω resistors that drop about 2.4 V at 20 mA from a 12 V supply, leaving 9.6 V for the LEDs (at about 3.2 V each). Running from 19.5 V means the resistors will see about 9.5 V and pass nearly 80 mA, four times the nominal rating, during each PWM pulse.

Based on those measurements, the light output doesn’t go up by nearly a factor of four during each pulse.

I plan to add a 12 V supply to the LinuxCNC box, probably by recycling the 12 V brick from the M2, which will get the LED current back down to a reasonable level. With any luck, they’ll survive this mistreatment and not carry a grudge.

You could, of course, just power the LEDs from a separate 12 V wall wart, but that adds Yet Another Thing when I carry the M2 to demos.

2013-07-12
Makergear M2: Heated Build Platform Insulation

Although I don’t have any data to support the idea, it seems that there’s far too much heat loss from the bottom of the HBP. Admittedly, air is a great insulator, so most of the energy should go into the aluminum plate, but having air blow over the bottom can’t be a Good Thing. There’s a very thin space between the bottom of the silicone heater element and the black aluminum spider supporting the corners, so I added a thin cardboard sheet:

HBP insulation – cardboard base

The curiously shaped cutout clears the heater power wires, the thermistor in its lug, and the thermistor wires.

Atop that goes a pair of very thin cotton cloth sheets (again, not much to focus on, so it’s a bit blurry):

HBP insulation – cotton sheet

And then the plate fits atop the corner support pads as usual. I suppose the heater duty cycle should be lower at any given temperature, but I don’t have any records to compare against.

2013-07-08
Makergear M2: HBP Connector Stabilization

Given my experience with the TOM’s platform heater connector, I was bothered by having the M2’s heated build platform connection flex as the Y stage travels back and forth. After replacing the Z axis motor, I added a strut to the Y axis stage to stabilize the HBP connector.

This overview shows the aluminum strut sticking out to the rear (Y+) end of the platform support spider:

HBP connector support strut – overview

A closeup shows a quartet of 4-40 holes drilled and tapped along the strut’s midline:

HBP connector support strut – mounting detail

Admittedly, that’s a bit of a kludge, but I didn’t want to drill holes in that nice steel bracket… particularly since I’d have to dismantle the whole stage to get to it. The four screws wedge the strut firmly in position and have jam nuts on the bottom so they don’t loosen.

I extracted more wire from the braided sheath and moved the cable a bit further out at the cable tie holding it to the Y axis stage, then cable-tied the HBP connector to the strut.

With the stage all the way to the rear:

HBP connector support strut – at Y min

And to the front:

HBP connector support strut – at Y max

The wires may break, but now the HBP connector and heating pad joints should survive!

2013-07-05
Makergear M2: Grippier Z-min Switch Mount

The printed bracket for the M2’s Z axis home switch doesn’t get a good grip on the oiled steel rod, so it can slide around just a little bit when nudged. That doesn’t happen often, but when it does, all your careful alignment Goes Away.

A single wrap of silicone tape solves that problem:

Z min switch on silicone tape

While I was in there, I replaced the socket-head cap screw I’d been using with a longer hex bolt and swapped the nylock nut for a plain nut that’s easier to adjust. I should file the raised markings off the top of the bolt head so it presents a smooth surface to the switch.

That was easy…

2013-07-04
Makergear M2: Z Axis Stepper Motor Transplant
Dan sent me a Kysan 17HD-B8X300-A, a leadscrew-equipped stepper motor with much higher torque than the Makergear Z axis motor. According to the Kysan description, which is all we have to go on: 4.2 V @ 1.5 A means 2.8 Ω, at which current it produces 5.5 kg·cm = 540 mN·m of torque. I measure 3.2 Ω and 3.5 mH, not that that makes much difference.

I worked out some of the numbers in that post and, if they’re close, then the new motor has twice the torque of the OEM one. What’s more important is that the new motor will work correctly with a microstepping drive and won’t bake while doing so.

The new motor has more metal to it than the old one:

M2 Z Axis motors – OEM vs replacement

The leadscrew follower nut has unthreaded holes, but, mercifully, has the same OD, fits nicely into the Z stage, and those four holes line up perfectly.

I chopped off most of the wires and spliced a JST plug onto the end; of course, the motor ran backwards. Having foreseen that eventuality, I had not shrunk the tubing over the wires: swap a pair, shrink the tubing, and it’s done:

M2 Z Axis motor replacement

Some notes from the operation:
- Disconnect all the cables
- Remove HBP + glass plate
- Lay printer on +X side of the chassis
- Remove screws holding Z motor to chassis
- Remove nylock nuts and screws from leadscrew follower nut
- Remove Z axis home switch
- Run Z stage to top of rods
- The leadscrew bearing will probably have fallen out by now
- Loosen Z rod clamp nuts & bolts (top & bottom of rods)
- Push Z rods out using a nut driver, pull with a rag for traction
- Be ready to catch the Z stage when you remove the rods!
- Angle motor & leadscrew out of the chassis
- Angle new motor & leadscrew into the chassis
- Reinstall everything in reverse order
- Recalibrate everything…
The Z rod sliders have little balls inside, but they didn’t fall out during this adventure. I don’t know if that’s reliable information or not.

Now, to see what a better motor can do…
2013-06-28
Poughkeepsie Waterfront Reclamation

Back in the day, long before the environmental movement got any traction, the Poughkeepsie waterfront along the Hudson River used to be an industrial hotbed. That tapered off and, after a while, only the Dutton Lumber treatment facility remained; they manufactured classic CCA pressure-treated lumber. Quite some years after (IIRC) they went bankrupt and abandoned the facility, various buildings burned and the site seems to be slated for redvelopment into condos and suchlike.

The wisdom of siting condominiums along a tidal estuary, just a few meters above the current waterline and well below the future projected flood stage, seems dubious to me, but, then, I’m not a developer.

Anyhow, a recent ride across the Walkway showed that they’re sealing off the contaminated soil under what was once the lumberyard:

Poughkeepsie waterfront brownfield reclamation – overview

An excavator moves gravel from the barge, which probably came a few miles upriver (or downriver, depending on the aforementioned tidal flow) from the Tilcon quarry at Clinton (no relation) Point, into the dump trucks:

Poughkeepsie waterfront brownfield reclamation – gravel barge

The scale of the operation snaps into focus when you notice the guy standing on the quay:

Poughkeepsie waterfront brownfield reclamation – truck detail

An old joke defines the difference between electrical and civil engineers: electrical engineers build weapon systems, civil engineers build targets…

2013-06-22