After three years, the temple screw on Mary’s oldest and most-battered “reading” glasses worked loose. A dab of low-strength Loctite should hold it in place forever more:
That brass stake pin certainly adds a Steampunk flair to the proceedings …
Category: Machine Shop
Mechanical widgetry
-
Eyeglass Temple Re-re-repair
Reading glasses temple repair -
MPCNC: Z Height Probe vs. Tempered Glass Sheet
Sliding the tempered glass sheet I used for the initial trials and B-size Spirograph plots under the Z height probe eliminated the plywood benchtop’s small-scale irregularities:
MPCNC – Z-probing glass plate The first height map looks like a mountain sproinged right up through the glass:
ProbeArray-Glass-50 More red-ish means increasing height, more blue-ish means increasing depth, although you can only see the negative signs along the left edge.
The Z axis leadscrew produces 400 step/mm for a “resolution” of 0.0025 mm. The bCNC map rounds to three places, which makes perfect sense to me; I doubt the absolute accuracy is any better than 0.1 mm on a good day with fair skies and a tailwind.
The peak of the mountain rises 0.35 mm above the terrain around it, so it barely counts as a minor distortion in the glass sheet. Overall, however, there’s a 0.6 mm difference from peak to valley, which would be enough to mess up a rigidly held pen tip pretty badly if you assumed the glass was perfectly flat and precisely aligned.
Rotating the glass around the X axis shows a matching, albeit shallower, dent on the other side:
ProbeArray-Glass-flip-50-2018-01-05 For all its crudity, the probe seems to be returning reasonable results.
The obvious question: does it return consistent results?
-
MPCNC: Z Height Probe
A little support pillar makes a printable holder for a small tactile pushbutton:
Z Axis Height Probe – solid model A(n) 0-80 brass washer epoxied atop the butt end of a P100-B1 pogo pin keeps the pin from falling out and provides a flat button pusher:
MPCNC – Simple Z probe – push plate With the epoxy mostly cured, ease the pin off the tape, flip the whole affair over, shove the switch into position, realign vertically with point down, then let the epoxy finish curing with the washer held in place against the switch to ensure good alignment:
MPCNC – Simple Z probe – epoxy curing The brass tube ID is a sloppy fit around the pogo pin, but it’s also many pin diameters long and the position error isn’t worth worrying about.
Solder a cable, clamp it in the pen holder, attach to tool holder:
MPCNC – Simple Z probe – installed The pogo pin provides half a dozen millimeters of compliance, letting the initial probe speed be much higher than the tactile pushbutton’s overshoot could survive, after which a low-speed probe produces a consistent result.
Unleashing bCNC’s Autolevel probe cycle:
MPCNC – Z-probing glass plate Although the picture shows the MPCNC probing a glass plate, here’s the first height map taken from the bare workbench top with 100 mm grid spacing:
ProbeArray-100-2018-01-04 The ridge along the right side comes from a visible irregularity in the wood grain, so the numbers actually represent a physical reality.
Doing it with a 50 mm grid after re-probing the Z=0 level:
ProbeArray-50-2018-01-04 Eyeballometrically, the second plot is 0.2 mm higher than the first, but this requires a bit more study.
All in all, not bad for a first pass.
-
MPCNC: Pen Holder Crunch
A few tweaks to the Customizable MPCNC Mount for Round Tools produces a Sakura Micron pen holder:
MPCNC – Sakura Pen Holder – Slic3r preview The pen body seats atop the holder, with its narrower snout inside the clamp, giving positive control of the point position:
MPCNC – Sakura in pen adapter Unfortunately, should one forget to zero the pen tip to the paper surface before starting a plot, Bad Things happen to good tips:
MPCNC – Sakura pen – crushed tip The holder really needs at least a few millimeters of compliance, as a fiber-tip pen makes a fairly delicate tool not intended for applying much force at all to anything.
But the holder might make a Z axis probe …
-
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.
-
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.
-
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.
The Smell of Molten Projects in the Morning 