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.

Author: Ed

Eyebrow Lights

A high energy collision / accident / mishap in front of Adams Fairacre Farms (a.k.a., the grocery store) demolished 20 feet of their dry laid stone wall along Rt 44, flattened several bushes, gouged trenches in the grass, and scattered plastic debris into the parking lot. The remains of a headlight eyebrow running light emerged from a snow pile:

Eyebrow light – front

From the back:

Eyebrow light – back

Contrary to what I expected, it has one white LED at each end of the chromed reflecting channel, topped with a shaped plastic lens collecting the light:

Eyebrow light – Lens mount

The LED PCBs are in series, which produced a backwards wire color code on one end:

Eyebrow light – LED PCB 1

The other end looked more reasonable:

Eyebrow light – LED PCB 2

The white SMD LEDs draw 300+ mA at 3.6 V, so they’re obviously depending on external current limiting provided by the regulator PCB, sporting a TLE4242 linear current regulator and a handful of passives:

Eyebrow light – Regulator PCB

AFAICT, they didn’t use the chip’s PWM control input or its LED failure status output.

Extracting the various PCBs from the wreckage and reconnecting the wires produced a satisfactory result:

Eyebrow light – resurrection

The regulator limits the LED current to 120 mA at any input from a bit over 7 V to well past 12 V, with each LED dropping 3.0 V.

Dunno what I’ll use this junk for, but at least I know a bit more about eyebrow lights. The chip date codes suggest 2010 and 2012; perhaps linear regulators have become passe by now.

2018-01-09
MPCNC: Sakura Micron Pens

After shimming the corner posts, a plot with Sakura Micron pens came out nicely:

Spirograph pattern – Sakura Micron – Z-0.25

They’re all 01 size pens, with a nominal 0.25 mm line.

Just for fun, a plot done with four sizes of black Sakura pens at Z=-1.0 before the Great Leveling:

MPCNC – Sakura Micron black pen widths

The 005 pen made a nearly rectangular single-pass tour around the perimeter of the plot, so you’ll see it passing through every legend.

The chunky-by-comparison 08 pen = 0.50 mm:

MPCNC – Sakura Micron 08 Black – detail

The 05 pen = 0.45 mm looks much crisper:

MPCNC – Sakura Micron 05 Black – detail

The 01 pen = 0.25 mm:

MPCNC – Sakura Micron 01 Black – detail

The almost-can’t-see-it 005 pen = 0.20 mm:

MPCNC – Sakura Micron 005 Black – detail

If you were doing this for a living, you’d probably use 05 pens, because plotter pens are hard to find.

Original HP plotter pens produced a 0.3 mm trace (with a hard to find un-worn tip) roughly equal to Sakura 03 pens, but I haven’t seen anything other than black at Amazon. There’s apparently a 003 pen with a 0.15 mm line; that’s just crazy talk.

Jamming Sakura pens into a plotter pen adapter for the MPCNC makes little sense, so I should gimmick up a specialized holder with some thumbscrew action to keep them from crawling upward out of the holder.

2018-01-08
Lathe-Turned Almond Butter

Pure almond butter comes with the somewhat stilted admonition “Must stir product. Oil separation occurs naturally.” I’d just opened a new jar and was busily (and laboriously) stirring when I realized we have the technology:

Lathe-turned Almond Butter

I installed the chuck’s outside jaws to grab the jar lid.

About three hours at 50 rpm, the lathe’s slowest speed, did the trick. We now have the smoothest, creamiest, best-mixed almond butter ever.

In a month or so, I’ll chuck up an unopened jar to see how well it works without any manual intervention.

2018-01-07
Doing Biz On eBay

I’ve always wondered what the Chinese-script company names on eBay meant, so I fed some into Google Translate (clicky for more dots):

Chinese eBay Company Names

Huh.

As the saying goes, ol’ Deng must be living “… modestly, if the kind of money he was getting out of me meant anything to him.”

2018-01-06
MPCNC: Corner Post Shims

The rail height measurements suggested three shims could level the MPCNC rails:

MPCNC Rail Height – 2017-12-23

The numbers inside the lower square give the additional height required to sorta-kinda level the result, keeping in mind we’re not dealing with a particularly stable mechanical setup.

The figures in the lower right translate sensible metric values into mils. I plucked those sheets from my brass shimstock selection, taped them together into a 42 mil stack, and introduced them to Mr Bandsaw:

Sawing MPCNC Corner Post Shims

The sacrificial sheet underneath the stack prevents bending. Using the saw (with a 24 tpi blade), rather than tin snips or scissors, produces a nice clean flat cut without any curling or bending.

A brief conversation with Mr Drill Press created screw clearance holes:

Drilling MPCNC Corner Post Shims

N.B.: Brass is fiercely grabby, so don’t use an ordinary twist drill. Blunt ’em if you have a spare set of drills, but a step drill works for my simple needs, shallow holes, and infrequent drilling. In any event, don’t hand-hold the sheets, because they can turn into whirling knives without the formality of warning you first.

I bandsawed the holes into slots, so I could slide the shims under the corner posts without completely removing the screws, in the hope the posts would stay more-or-less in the same place. Probably doesn’t make any difference:

MPCNC Corner Post Shim

Looks like I overtightened the post clamp screw a bit, doesn’t it? So it goes with 3D printed parts.

Another round of measurements with the shims in place:

MPCNC Rail Height – 2017-12-25

The numbers on the outside of the bottom set give the difference from the lowest rail in each direction, the inner numbers are the average of the two differences in each corner.

All of which seems to indicate the pen height now varies by a smidge over 0.1 mm across the span of those 16.5×14 inch plots.

A plot with all the legends and traces at Z=-0.25 came out OK:

MPCNC – Leveled plot at Z -0.1

The legend in the upper left looked slightly faint:

MPCNC – Leveled plot at Z -0.1 – legend detail

The upper right legend looks about the same, suggesting my average of differences probably isn’t meaningful.

Lowering the pen to Z=-0.25 should darken the traces a bit and reduce the effect of any inconsistencies in the tool length probe switch.

Not, of course, that this will make much difference in actual use; a router will probably shake the whole thing out of alignment in a matter of seconds.

2018-01-05
MPCNC: Rail Height Measurements and Plot Effects
After once again figuring out how to read a vernier height gage, I measured the height of each end of the MPCNC rails:

Brown and Sharpe 585 Height Gage

The process:
- Position the gage near the end of the gantry’s travel
- Twiddle the knurled ring to lower the probe (a.k.a. lathe bit) until …
- It firmly captures the paper slip, then …
- Twiddle the ring the other way until …
- The paper barely moves
- Read the vernier and take a picture
So the numbers come out one paper thickness higher than the actual rail height; subtract 0.1 mm = 4 mil to get the true height:

MPCNC Rail Height – 2017-12-23

In round numbers, the difference is under 0.3 mm along each rail.

The outer numbers on the lower sketch show the difference between each reading and the lowest value along that axis: the left rear corner is (roughly) 0.5 mm higher than the right front. The numbers inside the square give the additional height, rounded to sensible values, required to raise the low corners.

Which means you can’t plot at, say, Z=-0.2 mm to reduce the pen loading, because the pen doesn’t uniformly touch the paper across the entire plot:

MPCNC – Unlevel Z -0.2 plot

These images have been perspective & aspect ratio corrected, then ruthlessly contrast-stretched to make the traces visible; the lighting isn’t that awful in person!

With the plot at Z=-0.2, the legends toward the front came out OK, but they’re missing along the far edge. The Spirograph traces go completely missing toward the left rear as the pen rises away from the paper, although I think we’re also seeing some ripples in the paper sheet.

Although such a small error probably makes no difference to a wood router, let’s see what we can do.

Manually editing the G-Code to put successive traces at 0.1 mm increments from Z=-0.3 to Z=-0.6 mm, then replotting on the same piece of paper, shows the problem a bit better:

MPCNC – Unlevel plot – multiple Z

All of the legends remain at Z=-0.2, because I wasn’t up for editing every pen-down command.

Even at Z=-0.6 mm, the pen doesn’t quite touch in the left rear corner. Previously, I’d been plotting at a nice, round Z=-1.0 mm, which worked fine. I didn’t run any tests below Z=-0.6, but I think Z=-0.8 would draw a complete plot.

That agrees reasonably well with the height gage measurements.

It’s obviously impossible to re-level the rails by dinking around with the corner post lengths, because I can’t move the EMT in precise increments and it’d never stay in that position anyway. Instead, I should slide shims under the three lowest corner feet to raise them enough to match the left rear corner.
2018-01-04
MPCNC: Emergency Stop / Feed Hold / Resume Pendant

The Protoneer CNC Shield has pin headers for GRBL’s Feed Hold and Resume inputs, so it seemed appropriate to put big buttons on the far end of the cable:

MPCNC – E-stop Hold Resume switch box

The Emergency Stop Push Button Switch Station arrived for ten bucks delivered halfway around the planet.

There’s not much to the wiring inside the box:

MPCNC – E-Stop switch box – interior

I drilled a hole to fit the 6 pin Aviation Wire Connectors I got for this very purpose:

MPCNC – E-stop switch box – drilling

You could CNC machine a precise D-hole, but let’s stay realistic about the application. Applying a deburring tool enlarged the 9/16 inch hole enough to force the 16 mm threads into it, with the drill press holding the connector perpendicular to the box while I hand-turned the chuck to screw it in.

Although I like the Protoneer CNC Shield, I really really dislike using header pins as connectors:

MPCNC – Protoneer Wiring – SSR

Those pins are much too delicate.

The DC-DC solid state relay input connects to the Arduino’s +5 V power supply through the red mushroom disconnect switch. The mushroom is normally closed to turn on the SSR and connect the power brick’s +24 V supply to the motors; it opens when slapped. GRBL will continue about its business, but without any power to the steppers the MPCNC will stop dead in its tracks. Turn the mushroom cap clockwise to unlatch and reset.

The disconnect switch should also kill AC power to the router, when I get around to adding one to the mix, probably through a DC-AC SSR.

AFAICT, the cable should come out of the box on the end with the mushroom switch, putting the “normal” pushbuttons closer to me. I did it the other way around, because I want the panic button to be the most easily reached thing on the benchtop. If I have time to think about it, I can reach around the mushroom to the Hold switch.

2018-01-03