Archive for the ‘MakerBot CupCake’ Category

CupCake Wants the Build Platform Temperature Turned Down After the First Layer

Monday, May 9th, 2011

I had previously noted the shrinking of the first few layers of a build on my CupCake and attributed it to the ABS shrinking too rapidly after extrusion because the room and the build chamber weren’t terribly warm. Although I’d leaned things against all of the CupCake’s windows so the heated build platform warmed the whole chamber, I thought that too much heat was leaking out when I prepped the print and removed the pre-print test extrusion and that it took a number of layers to heat the interior back up to non-shrinking temperature.

Large Kelly forceps with locking mechanism removed

I figured I could retain more heat inside if I didn’t have to move the front “curtain” to remove the test extrusion, so I went to The Yard and picked up a big pair of Kelly forceps. Since I wanted to use them as giant tweezers, I Dremeled off the locking mechanism, leaving myself with a big pair of plain ol’ forceps.

Mounting bracket built on MakerBot CupCake with lower layers warped

I heated the build platform and the now-more-enclosed chamber for half an hour (longer than the time it takes to print past the warped area), then sneaked the forceps in and snaked out the test extrusion. Whaddya know — the build warped in just the same way as before.

Hm.

I don’t yet have my build platform’s thermistor connected, so I’ve been running the heater open-loop using a lab power supply to adjust the temperature via current regulation. I remembered a while back when I had it so hot that the bottom half inch of my objects stayed melty-squishy while being built … and although I no longer run it that hot, I’ve been sloppy lately about turning down the current once the first layer is adhered to the platform.

Mounting bracket built on MakerBot CupCake that popped loose during printing

Maybe, I thinks, maybe the first few layers are too warm and pliable and get compressed as the layers above them cool and shrink. I uncover all the CupCake’s windows, start a print, and dial the heated platform current down from 2.7A to 1.8A after the first layer sticks down. I get perfectly straight walls, so I’m finally on the right track and it’s less heat that I need, not more

Mounting bracket built on MakerBot CupCake that popped loose during printing

but whatever temperature 1.8A delivers isn’t enough to keep the object stuck to the kaptan tape and the bracket I’m building pops loose when it’s almost finished, naturally when I’m in another room, and the last half mile of extrusion doesn’t adhere particularly well to the bracket when the bracket is no longer on the platform.

Mounting bracket built on MakerBot CupCake with minimal warp

2.7A for first-layer adhesion, 2.2A after first layer, slight shrinkage, no popping loose from the platform. Now to the point of tweaking for diminishing returns. I should maybe add a fan pointed at the platform like other folks have done, although that has its own dangers (easy to cool the platform too much).

I’m eager to get the thermistor wired up (heater PCB v1.1 will have less restrictive connector spacing); translate these currents into temperatures; and connect the heater and thermistor to the CupCake for closed-loop, PID control. I will not abide the clickety-clack of relays, so I’ll find some big FETs.

CupCake Wants a Heated Build Chamber

Sunday, April 24th, 2011

I’m doing fairly well printing on my CupCake now that I have (1) my heated build platform (2) levelable with (3) a bearing-supported axle on my filament drive motor. Still need (4) a stepper filament drive and (5) roller-bearing X-Y guides.

My workshop temperature has been pleasantly cool for humans lately (currently about 67°F). The heated build platform keeps the first layer from shrinking and pulling up off the platform; but at 67°F ambient, upper layers shrink also and deform the build.

Uneven shrinkage of ABS plastic object printed on MakerBot CupCake

I’ve been combating upper-layer shrinkage by leaning things against the openings in the CupCake walls while printing; it traps the heat of the build platform and significantly reduces the shrinkage.

Here you can see shrink in early layers from the front of the CupCake being open while I was removing the test extrusion before the print (long recovery time for the build platform to reheat the chamber) and dramatically less shrink in the upper layers (because eventually it recovered after I blocked the front with my laptop screen). It doesn’t take very high temperatures to reduce shrinkage.

(The bottom of the object is shiny from the heated build platform, doodled with a marker for revisions, and holding a screw as an experiment with acetone and mounting boss thread durability.)

I’m (still) thinking of cutting acrylic pieces to cover the CupCake’s windows. The challenges are

  • How best to attach the acrylic for easy removal for service? Hinges? Magnets?
  • How to route the heated build platform cables out the back window so they don’t snag? Maybe I should rotate it 90° CW and bundle them with the Y drive and X-Y endstop cables?
  • How to remove the test extrusion before printing? An auto-scrubber would be lovely, but in the short term I might get a loooong tweezer and leave an access hole in the front window, biohazard gloves sandblaster style.

Why Does It Do That?

The ABS all cools to room temperature eventually (okay, we could talk asymptotes, but I’d rather not), but it appears that only rapid cooling makes it shrinkalot. Interesting, n’est-ce pas?

Also

Devil bunny needs a ham.

MakerBot CupCake: Print from the SD Card

Sunday, March 27th, 2011

The CupCake plastic-extruding 3D printer can have its printing instructions sent to it live from the controlling computer or stored onboard on a mini-SD card and printed from there. We’ve all seen suggestions to print from the card for improved print quality, but it didn’t make sense to me that USB communications were slow enough (bandwidth) or unpredictable enough (jitter) to make a difference. How wrong, how wrong I was.

Wade idler block printed on MakerBot CupCake with default settings

I’m intending to print several different versions of the Wade filament drive to test and upgrade my Plastruder MK3, starting with Wade’s original. In the model of the idler block, each corner has a mounting bolt hole all the way through; but the CupCake slows down so much while circling the holes (without the filament drive slowing down at all, thereby depositing extra plastic) that halfway through the holes were closed over and by the end they were blobbed up above the deposition plane. Besides making an unusable object, this snags the extruder nozzle every time the mound comes by.

The bearing is supposed to spin freely in the slot and I couldn’t press it all the way in.

Wade idler block printed on MakerBot CupCake with Unpause

I’ve had tremendous luck with Skeinforge’s Unpause module before, which is supposed to mitigate the time the CupCake’s relatively slow Arduino CPU needs to calculate the toolpath for every segment of a curve, but here it didn’t help a bit. Circling the holes seemed just as slow and the result was almost identical.

I was able to press the bearing all the way in, but it was a tight fit.

Wade idler block printed on MakerBot CupCake with Stretch

The Stretch module widens curves and corners to take into account the inner edge of the filament following a smaller-radius path than the center. It looked promising on the first couple of layers, but soon I had so much blobbing that the Y-axis stepper lost steps.

The bearing fit easily into the intact underside of the slot.

Wade idler block printed on MakerBot CupCake with default settings from an SD card

Scrounged up an SD card, copied the code to it, and printed from the card. No Unpause, no Stretch, no tricks. More than an order of magnitude better than any holes I’ve printed before.

The bearing fits perfectly except where I impatiently squeezed the block too hard with pliers trying to pop it loose from the build platform too soon.

“Printing” the code from the MacBook to the card took 15 minutes. Printing from the card took 18 minutes. The similarity of those two times demonstrates that USB-serial transmission speed to the CupCake (and reception thereat) is much slower than I realized. It’s easy to see how the transmission becomes the bottleneck when sending many small steps around tight circles.

Given the widespread knowledge in the larger RepRap community about the advantages of designing (particularly) small holes as low-edge-count polygons instead of circles, I am genuinely surprised that Skeinforge doesn’t have a module to reduce tight curves, with specifications for things like maximum number of segments, minimum degrees of arc per segment, and minimum segment length.

Yes, I’ve had a couple of significant breakthroughs in my CupCake usability this weekend. I’ll cover them when I have a few moments.

Huge Blob

ABS blob created on MakerBot CupCake when laptop battery died

And a word to the wise: If you’re still printing directly from your computer, don’t walk away when your laptop battery is about to die.

PCB Milling with the MakerBot CupCake: Aluminum Leveling Platform

Saturday, March 19th, 2011

Last weekend I got my Dremel rigidly mounted in my CupCake for PCB milling, but the platform holding the PCB was attached with double-stick foam and was being deflected by the milling bit cutting the copper, causing considerable deviation from the intended milling path.

Leveling platform in MakerBot CupCake

Last night Steve cut some more aluminum plate for me and today I assembled a rigidly-mounted leveling platform to replace the stock build platform. The lower plate has holes matching the machine screws attaching the top of the Y stage, and I used slightly longer screws to bolt through both the aluminum plate and the original wood top into the Y carriage.

Leveling screw with nylock nut, upper view

I drilled holes in the corners, tapped the upper plate, and enlarged the holes in the lower plate. The socket-head cap screws spin freely in the lower plate while adjusting the upper plate’s height (I used a continuity meter to check when the milling bit was just barely touching the plate in each corner); then the nylon-insert nuts lock the screws in position. The whole assembly is quite rigid once tightened.

A number of designs for leveling build platforms use only springs between the two plates. I was concerned that without a nut, the machine screws might back out under vibration. Also, when extruding, having a platform with some give reduces the damage if you miscalculate the Z position and gouge the platform; but for milling, the whole point of this replacement is to remove any play in the platform.

PCB milled in MakerBot CupCake

The results were not tremendously better than before (left board, top row of pads; right board from commercial mill for comparison), so I slowed the feed rate to .1″ per minute and let the mill finish the rest of the board for five hours, just to see whether I could produce usable traces. The traces cut at an outrageously slow feed rate are much better than previous results, but still a bit, shall we say, interpretive for my taste.

Having watched the Dremel bit trying to cut the copper and having tested it handheld out of the machine, I do recognize that it’s not the right bit for this job. I have some carbide engraving bits recommended by Pierre (exuinoxefr) on the way from Hong Kong, and I think they’ll make a significant difference. In April.

Meanwhile, note the three pads in the center of the board. Even at only one stepper motor step per second, the board took a very consistently incorrect path under the toolhead. Also note that the diagonal lines look like they were drawn with a left-handed quill pen — NE/SW lines are thicker than NW/SE.

I believe this is caused by the considerable play between the original CupCake bushings and the guide rods. Tighter bushings would cause more friction, so they were chosen for a bit of a loose fit. Even though the platform is now rigidly mounted on the Y carriage, the Y carriage wiggles on the Y guide rods and the X-Y carriage wiggles on the X guide rods.

I’m extremely interested in the Mendel-inspired replacement X-Y assembly by Thingiverse contributor “twotimes.” It replaces the bushings with sets of roller bearings spaced around the guide rods; the bearings can be tightened against the rods and still roll smoothly. I intend to get in touch and ask whether it successfully removes the play from the carriages.

Leveling platform in MakerBot CupCake, closeup

Although my immediate interest is whether I can use the CupCake that I already own as a PCB milling machine, the enhancements I’m making will improve it as a filament deposition machine as well. The lack of leveling in my heated build platform prevented me from printing larger models; I’ve already drilled my heated platform to fit interchangeably into this new system. Smoother X-Y action from a replacement carriage can only help, too.

PCB Milling with the MakerBot CupCake: Aluminum Z-Stage Supplement for Rigid Dremel Mounting

Sunday, March 13th, 2011

In my previous attempt to trace-isolation-mill a PCB with my MakerBot CupCake, the CupCake’s entire acrylic Z platform (intended to support the light weight of the filament heater and extruder) was flexing under the torque of the Dremel bit dragging through the copper layer of the PCB.

MakerBot CupCake with aluminum Z-stage reinforcement and Dremel mount

This week I picked up 1/4″ aluminum plate at the yard to reinforce the Z stage and support a more rigid Dremel mount. Steve Atwood printed the DXF of the MakerBot Z stage mechanical drawing for me, which I used as a template to drill and tap holes matching those in the acrylic (forgetting, unfortunately, to double-check the accuracy of the feed rate on Steve’s inkjet printer — but I compensated for the resulting aspect ratio problem with a file).

MakerBot CupCake with aluminum Z-stage reinforcement and Dremel mounted

I put together a good-enough Dremel mount with plastic from the visual arts scrap bin. Initially I lined the mounting hole with foam weatherstripping, but the Dremel was wiggling just a bit even with the clamp tightened down. It’s less wiggly without the foam.

Circuit board milled on MakerBot CupCake

The multi-pass milling looks like someone applied a GIMP randomizing filter to the original pattern, but at least the bit is consistently cutting the copper. The Dremel mount isn’t flexing any more — the irregularity is from the double-stick foam I used to attach the milling platform to the XY stage; the platform and board were swaying significantly under the bit.

PCB Milling with the MakerBot CupCake and a Dremel (Almost)

Monday, March 7th, 2011

Dremel mounted in MakerBot CupCake (lower view)

My Dremel’s spindle had much more solid bearings than the Handy Grinder, so I mounted it in the CupCake tonight to try milling with it.

Dremel mounted in MakerBot CupCake (upper view)

It fit even worse through the Z stage than the Handy Grinder, but I remember having said something about the drill not even needing to be vertical as long as the bit’s tip made contact with the workpiece.

Dremel milling PCB in MakerBot CupCake

The XY platform wasn’t quite level (deeper cutting on the right than the left); but the real problem was that the Z stage was flexing. Not lifting off the Z stage guides — I could feel the acrylic bending as the tool direction changed. This demanded backing off the Z axis to an extremely shallow, ineffective cut to keep the milling tip from tracking the cutting direction as it did with the Handy Grinder.

Increasing the rigidity of the Z stage by bolting a large plate to it while mounting the Dremel is my top priority for getting closer to usable performance.

PCB after milling attempts

Straight off the mill after a variety of different attempts on the same workpiece. Parts of it almost look usable …

PCB after milling attempts, sanded

But sanded, it’s clear that in most places the bit barely scratched the copper and wasn’t even close to scoring through, because of the obligatory shallow cut.

PCB Milling with the MakerBot CupCake (Almost)

Sunday, March 6th, 2011

I crave a CNC mill for trace-isolation milling prototype PC boards and I haven’t managed to get my CupCake filament deposition machine calibrated so I can use it. (Build platform leveling and filament feed are my current showstoppers. I’ll get back to it.)

I knew that someone had proposed mounting a Dremel in place of the CupCake’s extruder and that MaskedRetriever had modeled a mounting bracket; but curiously, I haven’t heard any more about using the CupCake for milling. Surely someone has done it; I just haven’t run across it.

Last night while I was asleep, the facts and the immediacy of the situation came together: EAGLE can output trace-isolation g-code and ReplicatorG reads g-code and drives the CupCake. Really??? PCB trace-isolation milling is that simple???

Yes. Yes it is.

Circuit board layout drawn with pen in MakerBot CupCake

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MakerBot CupCake Aluminum Idler Wheel and Printing in Plaid Due to Motor Shaft Deflection

Tuesday, May 25th, 2010

Aluminum idler wheels for MakerBot CupCake

At the end of March, I broke my MakerBot CupCake idler wheel while trying out my new filament drive worm-pulley. In April, my friends Scott Smith and Ben Wynne in San Diego machined me some aluminum replacement wheels, which are totally awesome.

Broken acrylic and replacement aluminum MakerBot CupCake Plastruder idler wheels

Old and busted; new hotness. Yeah, baby!

This wheel press-fits perfectly onto the bearing, starting by hand and then leaning heavily on it on a countertop. It’s thicker than the original wheel, making precise alignment with the drive pulley less important. It even has a knurled edge — showoffs!

Plaid print from MakerBot CupCake

I’d been experiencing “plaid” printing, in which the filament feed rate dropped at very regular intervals, and attributed it to the (tangible) irregularities of the acrylic idler wheel. But I’m still getting plaid prints, and I don’t think my aluminum wheel (hot off the lathe) is irregular, so the problem must be elsewhere.

MakerBot CupCake filament feed

Hm, look at the deflection of my filament feed motor shaft, all the way to the left of the hole in the enclosure.

MakerBot CupCake filament feed

Hm, look at the deflection of the shaft now, when the flat hits the edge. That would explain why the weak feed is so regular — recovery doesn’t rely on the drive pulley maybe grabbing the filament and maybe being able to spin the idler wheel to a different spot before it gets going again.

Looks like I need a bearing on that motor shaft. I printed a shoulder washer/bushing for it and it helped for a while, but not enough. I think a real, metal bearing is in my future. And perhaps a different drive geometry. A lot of good filament feed designs are being uploaded to Thingiverse.

Glastherm HT Insulation with Glass Standoffs for Hotplates

Monday, May 3rd, 2010

As I discovered a couple of weeks ago, Glastherm HT is not a good enough insulator to protect the acrylic mounting plate under my MakerBot CupCake heated build platform. Last night I tried it with glass standoffs between the hotplate and the Glastherm.

Glass feet taped to underside of MakerBot CupCake heated build platform

I had some leftover glass from having a window cut recently. I bought a glass cutter and cut a half-inch strip off the end of one of the pieces, then cut that into smaller tiles. I smoothed the sharp edges on a diamond file, then pried apart the hotplate sandwich and stuck the glass tiles onto the leftover kapton tape.

Checking insulating value of Glastherm plate on glass standoffs under MakerBot CupCake heated build platform

I repeated my earlier test, standing the sandwich on edge on another piece of insulating material and running the heated build platform up to (and past) operating temperature. (Sorry no laser dot in the picture — I’m not quite coordinated enough to hold the thermometer’s capture button, point it the right direction, hold my hand still, and take a picture all at the same time.)

Plate Temp Back Max Temp Back Min Temp
120°F 85°F
145°F 95°F
175°F 120°F 105°F
Approximate CupCake target temperature
220°F 155°F 135°F
310°F 200°F

The air gap did a considerably better job of insulating than the Glastherm alone. Also when I remembered to measure the temperature separately under the glass feet, the spots were 15-20°F hotter than the rest of the Glastherm, suggesting that smaller glass dots could provide a significant further reduction in heat transfer.

Testing Glastherm insulation on glass standoffs under MakerBot CupCake heated build platform

135°F on the back side is pretty manageable; 200°F is a bit warm to be in contact with plastic. However, as Leon pointed out last time, it’s not just about how hot the back side gets, but about how rapidly the heat is transferred into the backing material.

I set the heated platform onto a spare piece of plexiglass and also dropped some scrap filament onto the top of the platform. Already above operating temperatures, the filament softened nicely and the plexiglass stayed cool to the touch and didn’t warp. Leaving the setup unattended for a while and letting the platform drift up to 340°F, the plexi got a little soft.

I think this is usable for the CupCake, but I’ll need to exercise a little care managing the plate temperature (and I’m overdue hooking up the thermistor for closed-loop temperature control). I think this may not yet be enough insulation to tape my SMT hotplate directly on top of a plastic enclosure and run 290°C (~550°F) soldering temperatures.

Glastherm HT: Not So Good for Insulating Hotplates

Monday, April 19th, 2010

Two pieces of Glastherm HT for aluminum hotplates

I got a care package this week from my friend Scott in San Diego. Half of it was two pieces of Glastherm HT that he cut to fit my soldering hotplate and my MakerBot CupCake heated build platform. Scott and his buddy Ben Wynne are building hotplates and were also planning to use Glastherm to insulate them.

Last night I pried the warped acrylic off the underside of my platform, cleaned the surfaces with alcohol to ensure a good stick, and affixed the Glastherm to the heater PCB with kapton tape. I then set the assembly on edge on another piece of Glastherm and ran it up to operating temperature.

Testing Glastherm HT insulation on MakerBot CupCake heated build platform

The Glastherm was not nearly as good an insulator as I expected. The “cold” side of the sandwich lagged only 25°F behind the hot side as I was heating it from room temperature and once it stabilized at 250°F, (at which point the “cold” side reach equilibrium around 225°F).

I’m surprised that the Glastherm provided so little insulation. Perhaps it’s not intended to be used in direct thermally-conductive contact with a hot surface — although the diagram on their web site certainly suggests that it is.

At any rate, the “cold” side of my sandwich is still far too hot to be in contact with my acrylic mounting plate. And since Glastherm is supposed to be pretty good stuff, I think I’m resigned to finding a way to assemble my sandwich that leaves an air gap between the heater and the mounting plate, which I hadn’t wanted to do.