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

  • Thing-O-Matic: Lazy Susan Filament Spool

    All of those thermal tests on the MK5 head gave me plenty of time to ponder the problem of what to do with the filament bundle. Thingiverse has many plans for spools that fit over, under, or beside the printer, but they all seemed complex and fiddly. Besides, I didn’t have the printer running yet, so I couldn’t print up the parts… much less laser-cut anything.

    The Parts Heap disgorged a 4-inch Lazy Susan bearing, some double-layer corrugated cardboard, and odd bits of wood. The end result fits neatly atop the Thing-O-Matic printer:

    Filament spool - front view
    Filament spool – front view

    The base is 2 x 3-inch (actually measuring 1.5 x 2.5 inch) lumber, cut to exactly fit between the front and back plates of the printer box. The boards also butt against the socket-head cap screws securing the printer’s side plates, so they’re not moving. A scrap of 1/4-inch plywood bridges the two; it’s held in place with hot-melt glue atop the lumber. The weight of all that wood holds the assembly in place; making it lighter might not be productive.

    Filament spool - left side
    Filament spool – left side

    The filament coil rests on a hexagon of double-thick corrugated cardboard, cut about 12 inches across the flats and 13 inches across the points; you could glue two single-thickness sheets together. I laid it out with compass-and-ruler techniques, but do what you like.

    The pegs are 7/16-inch wood about 2 inches tall; the outer ones are on the hexagon points and the inner pegs are on a circle 1.5 inches inside the outer pegs. The rectangular caps on the inner pegs prevent the filament from creeping upward while feeding and are angled to let it slide off into the conduit. They’re held in place with hot-melt glue, of course, and a bit more glue stiffens the hexagon points.

    The only store-bought part is the 90-degree PVC elbow originally intended for electrical work: it’s a “1/2-inch Schedule 40 Rigid Nonmetallic Conduit” elbow. I slipped a spring inside the bore to prevent collapse, applied a hot-air gun until it was flexy, bent the second right angle to align the end bell with the incoming filament, and introduced it to Mr Belt Sander to angle the entrance bell more-or-less at right angles to the incoming filament.

    The Lazy Susan bearing must be centered on the top of the printer, but the hole for the conduit must be forward of center to align with the MK5 Extruder head’s filament entry. As it turned out, butting the conduit against the forward rim of the bearing (the non-rotating base part) worked perfectly. More hot-melt glue holds it in place.

    Filament spool - front detail
    Filament spool – front detail

    This front view shows an out-of-focus peg and filament pile at the top, the Lazy Susan bearing between the plywood and cardboard, and the filament dropping straight into the MK5 head.

    The spool easily rotates backwards when the extruder motor reverses. You can lift the spool off, put it down next to the printer, fiddle with the extruder machinery, then replace the spool without cutting the filament. Trust me on this, I’ve done it a lot.

    If I hadn’t dropped the filament bundle, it would probably have slipped right into the spool without any fiddling; the coils are about a foot in diameter as shipped. I devoted a few minutes to feeding the greatly enlarged and somewhat tangled mess neatly into the spool, after securing the bitter end to the cardboard with (wait for it) a dab of hot-melt glue.

    If I ever build another spool, I’ll replace the cardboard with either 1/4-inch plywood or acrylic, then print up some better-looking peg-like objects. A shot coat of paint couldn’t possibly hurt its appearance in the least, either…

  • Adobe Reader Print Colors

    While printing up handouts for my talk at Cabin Fever, I finally tracked down why Adobe Reader was producing such crappy colors.

    The left is before and the right is after the fix, scanned at the same time with the same image adjustments:

    Oversaturated vs normal printing
    Oversaturated vs normal printing

    All of the print settings appeared correct (plain paper, 720 dpi, normal contrast, etc, etc), but Adobe Reader (and only Adobe Reader) looked like it was trying to print on vastly higher quality paper than I was using. Too much ink, too much contrast, generally useless results.

    The solution was, as always, trivial, after far too much fiddling around.

    In Reader’s Print dialog, there’s a button in the lower-left corner labeled Advanced. Clicky, then put a checkmark in the box that says Let printer determine colors.

    And then It Just Works.

    Equally puzzling: ask for 25 copies of a two-page document, check the Collate box, and you get 25 page 1, 25 page 2, then more page 1 starts coming out. I bet I’d get 25 x 25 sheets of paper by the time it gave up.

    I have no idea what’s going on, either.

    Memo to Self: verify that the box stays checked after updates.

  • X10 Appliance Module Local Control: Disablement Thereof

    After we rearranged the living room, we had a few floor lights in different locations that called for more X10 Appliance Controllers. I’m not a big fan of automated housing, because X10 communication is unreliable with a bullet, but it’s convenient to turn off all the lamps from the bedroom.

    Anyhow, the old RCA HC25 X10 Appliance Modules I pulled out of the Big Box o’ X10 Stuff suffered from the usual conflict between compact fluorescent lamps and the “local control” misfeature that’s supposed to let you turn the appliance on by simply flipping the switch. The problem is that a CFL ballast draws a nonlinear trickle of current that the module misinterprets as a switch flip, thus occasionally turning the lamp on shortly after you turn it off.

    This has been true since the first compact fluorescent bulbs appeared. The circuitry inside X10 modules hasn’t changed much, at least up until I bought the last round of switches quite some time ago. That’s either a Bad Thing (still a problem) or a Good Thing (everybody knows about it).

    The solution (everybody knows about it, just use the obvious keywords) is to cut a jumper on the module’s circuit board that’s obviously placed there for this very reason. In this view, it’s just below the lower-right corner of the fat blue capacitor. If you need confirmation, it’s connected to pin 7 of the only IC on the board.

    Snip the wire, move the cut end a little bit, and button the module up again.

    Local control jumper cut
    Local control jumper cut

    Oh, yeah. No user serviceable parts inside is a challenge around here…

  • Thing-O-Matic: Arduino Mega Heatsinking

    The Thing-O-Matic Motherboard rides atop an Arduino Mega (with the auto-reset option disabled), drawing most of its power from the hulking ATX connector at one end. The Mega draws power from the ATX +12 V supply and produces +5 V through its on-board regulator.

    As I noted there, that regulator runs surprisingly hot when fed from +12 V, even without any additional current flowing to the Mega’s pins. The solution here required another search through the parts heap, which eventually disgorged a small heatsink that was, I think, intended for a 16-pin DIP, although I obviously added the hole for some other, long-forgotten purpose.

    Motherboard regulator heatsink
    Motherboard regulator heatsink

    A bit of fin-bending to clear the (unused) power entry jack, a dab of JB Kwik epoxy, and a clamp to keep it in place while the epoxy cures:

    Clamping the Motherboard regulator heatsink
    Clamping the Motherboard regulator heatsink

    You won’t have such a heatsink, but any similarly shaped chunk of metal, even without fins, should suffice. Nothing critical about it, as long as it clears the Motherboard that will be plugged atop the Mega; you’re just increasing the surface area for heat dissipation.

    The Motherboard and Mega sit in the large opening across the Thing-O-Matic’s baseplate from the ATX supply’s fan intake, where they get plenty of cooling air. Do a before-and-after test with a fingertip on the regulator to feel the improvement for yourself.

    This is, admittedly, just a feel-good tweak, but a cool regulator is a happy regulator. Spread the joy…

  • Thing-O-Matic / MK5 Extruder: Cartridge Heater Doodles

    During the conversation following my original post on the MakerBot support forum, CodeRage suggested using cartridge heaters. I asked Eks about that and he said something along the lines of “Damn straight! We used ’em all over the place! Just do it!”

    CodeRage plans to retrofit his MK5 head with a pair of 230 V 150 W heaters running at 120 V to get a total of 75 W. I have qualms about running line voltage around the extruder head, but it’s certainly a better solution than toasting power resistors.

    The trouble with 1/2-inch models is that they don’t fit conveniently on the Thermal Core. I’d make an adapter block with a hole for the heater and two holes for the existing cap screws, but the screws don’t quite pass around a half-inch cartridge heater.

    He suggested 1/8-inch heaters from Sun Electric Heater Company, which look like just the ticket except that they’re nigh onto 40 bucks a pop. Ouch.

    High Temp Industries [Edit: new link 2013-12-27] has 1/4-inch heaters for under $20 that will fit in the space available. If I understand the configuration options, you can even get 12 V 30 W heaters (the same power as the existing resistors) with a 1000 °F (call it 500 °C) temperature rating.

    So I think what’s needed is to get some of those heaters, machine blocks to hold them on each side of the Core, and see how that works. The heaters will fit between the resistor screw holes and the Core is just about exactly 1 inch long. What’s not to like?

    This might work… except for the fact that HTI has a $150 minimum order, which is somewhat off-putting even for me. Anybody up for a group buy of ten cartridge heaters?

    Note that if you swap in some cartridge heaters, you really should do the separate +12 V supply Extruder Controller hack described there.

    [Update: Zach @ MBI has ordered a stack of cartridge heaters for their internal testing (he promises to send me some), plans a retrofit kit, and may become a retail source for the heaters. He reports the lead time to get heaters in bulk is something over two weeks, which is a lot longer than I expected.

    In light of that, I will hold the “group order” until I have a better handle on what’s needed to retrofit cartridge heaters into the existing MK5 head, how they’ll actually work, and what PID loop retuning may be required. Once I know more about all that, we can proceed.

    Having MBI handle the ordering & shipping makes sense to me!]

  • Thing-O-Matic / MK5 Extruder: Resistor Wrapup

    Extruder resistor wiring
    Extruder resistor wiring

    As nearly as I can tell, using a pair of 10 W power resistors as 30 W heating elements in the Thing-O-Matic’s MK5 Extruder Thermal Core isn’t going to work, at least if you want even minimal reliability.

    The fundamental problem is that the resistor specification limits the dissipation to a few watts, tops, near 250 °C, where they must run in order to melt any of the plastic filaments.

    The Thermal Core requires 20-30 W to maintain 225 °C, so each resistor must dissipate an average of 10-15 W at that temperature. That’s half of the MK5 extruder’s original design point and still nearly a factor of 10 beyond the resistor rating.

    The original design runs at less than 50% duty cycle to maintain 225 °C, which agrees with my measurements:

    • 50% of 60 W = 30 W
    • 33% of 60 W = 20 W

    If you want to run at lower power, it’s a drop-in replacement. Change the original 5 Ω resistors to 2.5 Ω resistors (from Digikey / Mouser / wherever), change the wiring to put them in series (not parallel!), and see how long they last. They’ll certainly fare better than at 30 W, but I wouldn’t expect more than a few hours of lifetime. The specs give them 1000 hours at rated power, which this certainly is not.

    A series connection means that when one resistor fails, the heat goes off. The original parallel connection left one resistor carrying the load and, at 30 W, it can actually get the Core up to operating temperature and keep it there. Many folks have been baffled by that, but the diagnosis is simple. Measure the resistance of the parallel resistors at the Extruder Controller end of the wires:

    • 5 Ω → one resistor has failed
    • An open circuit (infinite resistance) → both are dead

    The problem with the lower power dissipation, whether from a failed resistor in the original design or my suggested change, is that the extruder head has a thermal time constant of 10-11 minutes. Lower power means a longer cold-start time; 30 W should get it up to 225 °C in about 20-30 minutes depending on the insulation. That’s not really a problem if you’re printing a series of objects, but might be objectionable for quick printing sessions.

    However, when a resistor fails, the heat goes off, the plastic stiffens up, the DC extruder motor stalls, and the essentially unlimited motor current kills the A3977 driver on the extruder board. My incandescent lamp workaround may alleviate that problem: when the light goes on, check for a failed resistor.

    I picked up a stock of 2-to-3 Ω power resistors and will do some further experimenting with power levels, insulation, and suchlike. This is a short-term fix to get my Thing-O-Matic running, but there’s a better long-term way to go: cartridge heaters on a modified Thermal Core, which I’ll discuss shortly.

    If you arrived by search engine, jump there for my earliest guesstimates, go there to the beginning of the Thing-O-Matic hardware hackage posts, then read until you get back here. The story will, perforce, continue…

  • Thing-O-Matic / MK5 Extruder: DC Motor Safety Lamp

    The DC motor used on the MK5 Extruder head seems unusually prone to sudden death, either by mechanical failure or something electrical. A stalled or shorted DC motor becomes a low resistance that destroys the A3977 H-bridge driver chip on the Extruder Controller board.

    Makerbot recommends inserting a 10 Ω power resistor in series with the motor, so as to limit the maximum current. Other folks have build a diode decoded relay driver that’s certainly more durable than the A3977.

    Downsides:

    The power resistor reduces the voltage available to the motor, which draw something like 40 mA when unloaded and up to maybe 250 mA at full load. I don’t know what load the extruder puts on it, but at 100 mA the resistor drops 1 V, which seems excessive.

    The relays seem like a nice solution, but they go clickety-clack and require actually building something, of which I’ve had quite enough lately, thank you very much.

    While I was mooching those lugs, my buddy Eks suggested simply putting a low-wattage 12 V incandescent lamp in series with the motor. The cold filament has a very low resistance, but limits the current when if the motor shorts out.

    Extruder motor with series #89 bulb
    Extruder motor with series #89 bulb

    A bit of rummaging in the Lamp Box produced an old automotive #89 lamp that allows 560 mA into a dead short, which works out to 7 W.

    If the motor draws 100 mA, it drop only 100 mV: good enough!

    Not finding a suitable socket in the heap, I wired it in by soldering the wires directly to the brass shell and central solder tip and taping up the mess. Next time I get near the local AutoZone I’ll pick up a socket.

    The Anderson Powerpoles may look like overkill, but they make life a lot easier when you’re fiddling with the machinery all the time.

    Now, the lamp won’t prevent inductive transients from blowing away those puny signal-level Zener diodes that should protect the A3977 chip, but it’s exactly what you need for long-term overload prevention.

    [Update: An experiment that shows why a lamp works better than a fuse.]

    As an added benefit, when the bulb lights up you know the Extruder Motor has died!