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.

Category: Machine Shop

Mechanical widgetry

  • Aligning to a Hole With a Defocused Laser Spot

    Defocused Laser Spot on Hole
    Defocused Laser Spot on Hole

    When you’re aligning to an edge or scribe mark, you want the laser spot as small as it can possibly be, so you tune for best focus.

    To locate the center of a hole, you first find the edge, then move toward the center by one radius… so you must know the diameter, too. It’s tricky to find an edge exactly on the X or Y axis, which means you generally resort to successive approximation. I did something like that there with good results.

    If you defocus your laser aligner to produce a spot slightly larger than the hole, you can simply position the hole under the beam to produce a nice bright ring. Adjust the focus to make the spot barely larger than the hole and you can get pretty close to the center without any messy arithmetic.

    Now, should you happen to own a real laser aligner, you might actually have a nice-looking defocused spot. My homebrew Orc Engineering aligner, as shown there, starts with the beam from a chip laser in a hacked carpenter’s level, so the defocused spot is rather, mmm, ragged, even after passing through the not-very-restrictive aperture behind the lens.

    With the lens in the spindle, though, I can spin it at a few hundred RPM and persistence of vision blurs the beam into a nice, symmetrical disk. Jog to center the disk around the hole, twiddle the Z-axis position to adjust the focus / size / blobbiness, jog more slowly, tune for best picture, and it’s all good.

    This obviously doesn’t produce jig-boring quality alignment, but, then, I’m not doing that sort of work. In the picture, I’m enlarging a 4-40 hole molded in a Pactec case to fit a 6-32 screw. Normally I’d do that by hand on the drill press, but this time I also had to enlarge the counterbore at the top and figured I’d use a quick G2 with an end mill after I had it aligned for the drill.

    Maybe everybody else knows this trick, but I was delighted to find that it actually works pretty well…

  • Electronic Ballast Shoplights: So Much For Efficiency

    Just picked up a batch of electronic-ballast shoplights from Lowe’s, motivated by a 10% off card they sent a while ago. Not a killer deal, but it evidently got plenty of folks into the store on a Sunday morning.

    The new lights don’t claim much about their abilities, other than “Electronic Cold Weather Start (0° F)” and that the reflector sizing requires T8 (1″ dia) fluorescent tubes. One would expect an electronic ballast to have a decent power factor and improved efficiency.

    Because I’m that sort of bear, I opened one up to see what was inside. Here’s the ballast:

    Electronic Ballast Dataplate
    Electronic Ballast Dataplate

    Although the fixture is sized for T8 tubes, the ballast would be perfectly happy with T12s. Similarly, the box insists on F32 tubes, but the ballast is OK with F40s.

    I thought a comparison with one of my old magnetic-ballast fixtures would be of interest, so I hitched up the Kill-A-Watt meter and ran some comparisons.

    The results…

    Amp Watt VoltAmp PF
    Old magnetic ballast
    F40T12 0.64 60 76 0.79
    F32T8 1.11 80 126 0.62
    New electronic ballast
    F40T12 0.75 47 89 0.53
    F32T8 0.77 49 91 0.54

    The electronic ballast has a much lower power factor and thus much higher current. The box & ballast don’t say anything about power factor correction and, wow, there sure isn’t any. The power company hates gadgets like this…

    I cannot compare the brightness because the F40 tubes are several years old, but it’s interesting that the electronic ballast runs both tube sizes at essentially the same power (just as the dataplate indicates, sorta-kinda). The magnetic ballast really cooks the piss out of the smaller tubes, though… or it’s dumping a lot of energy into the ballast. Hard to say.

    The T12 tubes are rated for 3000 lumens & 20 k hours. The new box of T8 tubes I got a while back are 2800 lumens and 24 k hours. Frankly, I don’t believe any of those numbers, particularly given the actual power consumption: it looks like either ballast runs them at just 75% of their rated power.

    Anyhow, these were the cheapest shoplights in stock; I bought eight of ’em, because I’ve been replacing one dead fixture every month or two for the last year. I’d like to think I’d get a better ballast if I spent twice as much, but to a good first approximation the additional cost seems to have gone into black plastic trim and a burnished-chrome exterior finish; not what I need in the Basement Laboratory.

    I wish the boxes were more forthcoming so you didn’t need to perform exploratory surgery.

  • Rattle-free Sherline Handwheels

    Knobless Sherline handwheel
    Knobless Sherline handwheel

    The standard Sherline mill comes with tapered plastic knobs on the handwheels, which is exactly what you want for a manual mill and what you don’t want on a CNC machine: they rattle like crazy during computer-controlled moves.

    Some folks contend the knob unbalances the handwheel, but I’m not convinced that’s a real problem. Their advice is to remove the entire knob assembly, leaving a bare shaft sticking out of the motor. Seems a bit extreme to me.

    In any event, shortly after I got the mill, I unscrewed the little retaining screw from the end of each knob, put all the parts in a ziplock bag, tucked it in my tool box, and have been rattle-free ever since.

    The metal shaft is entirely adequate for those rare occasions when I turn the knob manually, the graduated settings let me detect when if I’ve screwed up the acceleration (on a new installation) to the point where the motor is losing steps, and all is right with the world.

    Oh, that orange-barred white tape in front of the motor? That’s a reminder to keep the usual pile of crap away from the spinning knob. That little shaft can fling small objects a fair distance and makes a nasty tangle out of a misplaced red rag…

  • Digital Caliper Roller Repair

    Broken caliper thumb roller mount
    Broken caliper thumb roller mount

    The thumb roller fell off my digital caliper in the heat of a project, forcing me to deploy a hot backup from the upstairs desk.

    This looks like a clear-cut case of underdesign, because it broke exactly where you’d expect: at the midpoint of the arch. Having my thumb right over the spot marked X, though, meant that I had all the pieces and could, at least in principle, glue everything back together.

    Glued and clamped
    Glued and clamped

    As with all repairs involving adhesives, the real problem is clamping the parts together while the glue cures. I clamped a stack of random plastic sheets to the back of the case to establish a plane surface behind the mount, with a small steel shim to prevent the top sheet from becoming one with the repair.

    The roller shaft was about the same size as a #33 drill and the opening was about 110 mils. Some 3/32″ (actually about 96 mils) rectangular telescoping brass tubing was about the right size & shape to hold the opening in alignment. Another length of tubing kept the broken part from sliding to the left.

    A dab of solvent glue (I still use Plastruct, but it’s not like it used to be before it became less toxic) on both pieces, line ’em up, apply a clamp to hold it in place, and let it cure overnight.

    I have no confidence that this will stay together for very long, so I’ll probably be forced to mill a little replacement mounting doodad.

    Ought to be good for a few hours of quality shop time…

    Memo to Self: Don’t run the slide off the end of the body, because that rubber boot is an absolute mumble to put back in place.

  • There’s No Undo Key in CNC

    The Axis user interface for EMC2 has a manual command entry mode, wherein you can type G-Code statements and EMC2 will do exactly what you say. That’s handy for positioning to exact coordinates, but I rarely use it for actual machining, as it’s just too easy to mis-type a command and plow a trench through the clamps.

    OK, on a Sherline mini-mill, you’d maybe just snap off a carbide end mill, but you get the general idea.

    I was making a simple front panel from some ancient nubbly coated aluminum sheet. The LCD and power switch rectangles went swimmingly.

    Then I tried to mill an oval for the test prod wires using G42.1 cutter diameter compensation. I did a trial run 1 mm above the surface, figured out how to make it do what I wanted, then punched the cutter through the sheet at the center of the oval and entered (what I thought were) the same commands by picking them from the history list.

    EMC2 now handles concave corners by automagically inserting fillets, so it must run one command behind your typing. I drove the cutter to the upper-right end of the oval (no motion) so it could engage cutter comp mode, entered the G2 right endcap arc to the lower edge (cuts straight to upper right), and then did something wrong with the next command.

    Epoxy-patched front panel hole
    Epoxy-patched front panel hole

    The cutter carved the endcap properly, then neatly pirouetted around the end and started chewing out an arc in the other direction. Even looking at the command trace I can’t figure out what I mistyped, but as it turns out it doesn’t matter… I was using the wrong dimensions for the hole anyway.

    So it’s now patched with epoxy backed up by a small square of aluminum. When it’s done curing, I’ll manually drill a pair of holes at the right coordinates, manually file out the oval, shoot a couple of coats of paint, and it’ll be OK.

    Nobody will ever know!

    If I recall correctly, Joe Martin of Sherline was the first person to observe that, unlike word processing programs, CNC machines lack an Undo key…

    Update: Like this…

    Patched panel - rear view
    Patched panel – rear view

    The shoot-a-couple-of-coats thing did not go well: a maple seed landed on the front panel. Ah, well, it’s close enough. Here’s a trial fit; the bellyband height extenders on the sides need a dab of epoxy and a shot of paint, too, but I may never get a round ‘tuit for that.

    Front panel trial fit
    Front panel trial fit

    It’s the long-awaited Equivalent Series Resistance meter…

  • Recommended Pliers

    Having just finished tweaking the nosepieces on my new sunglasses into shape, it’s worth mentioning a few pliers you should have.

    This set of pliers (PN HH02075SET) from Circuit Specialists is absolutely invaluable. Mine were about twice the current price; the picture looks the same.

    You’ll use these four metal-forming pliers (PN 60398) from Micro-Mark somewhat less often, but when you need ’em (like for adjusting your glasses), you need ’em bad. Mine were about half the current price, but I’m sure they cost the same in constant dollars.

    I picked up a bunch of surplus Plato 170 flush cutters a long time ago, but even their current price isn’t too forbidding. Great for circuit board work.

    Invest in tools: put your money in metal!

  • Sherline Collet Pusher Tweakage

    Better-fitting pin & redrilled hole
    Better-fitting pin & redrilled hole

    My simple collet pusher has been working OK, but the locking pin was a few mils too small for the hole in the spindle and eventually put a burr on the edge. The fix is straightforward, although I’ve been putting it off for far too long; I warned you about this in the original post.

    Shoemaker’s child, anyone?

    The locking hole in the spindle starts life at 0.094 inch. I grabbed a #40 drill in a pin vise and drilled it out to 0.098 by hand, which wasn’t nearly as difficult as you’d think, took out all the deformed metal, and didn’t even leave any burrs. Ditto for the hole in the collet pusher.

    My heap yielded a defunct #40 drill, from which I cut 15 mm of shank with a Dremel abrasive wheel. Chucked the shank stub in the drill press, spun it up, and applied a Dremel grindstone to put a very short taper and a nice smooth end on it.

    Pulled the old pin from the handle I built a while ago, added a dot of urethane glue to the new pin, and squished them together (tapered end out!) in a vise until cured. Done!

    No, that’s not a burr on the hole in the pusher…