Makerbot Upgrades Part 5

After half a year of happily turning out parts, we started having problems with our Makerbot a few weeks ago.  Parts were refusing to stick properly to the print bed.  At first, it was only a few large prints that gave problems, as the corners of the part would curl up after a few hours of printing.  Printing with a raft, or manually designing tie-down pads on the part, helped and most of the parts were still usable.  Then abruptly the problem became much worse, with any attempt to print anything other than a very small part failing as the part broke completely free from the bed.

When watching a print to try and see what was going wrong, I noticed that the printer was struggling to keep the print bed at the proper temperature.  It took a lot longer than I remembered for it to reach working temperature when starting a print, and then the bed would sometimes drift below its target temperature while printing.

On closer inspection, I noticed massive discoloration on one of the pins of the print bed power cable.

The cable to the print bed is one of the first parts to fail on a Makerbot Thing-O-Matic.  The cable support chain I built earlier protected the cable from snagging or getting pinched in moving printer parts, but it didn't protect the cable from overheating.  The connector used on the print bed is not rated for the current that's being put through it.  Over time, the ground pin on the connector heated up hot enough for long enough and became oxidized and discolored.  Oxidization increases the connector resistance, which increases the heat generated at the connector, so it's a problem that only gets worse over time.

The connector and cable assembly carries both power to the bed heater (and print bed conveyor motor, which I never installed) and the signal from the bed temperature sensor.  The temperature sense lines seemed fine, so I initially set out to replace only the high-power pins and leave the sense lines as they were.  I carefully cut the connectors on both the cable and the bed apart, discarding the oxidized power pins, and then installed a 2 pin power connector we had at the office in its place.

This didn't work quite as well as I hoped - the stress on the remaining pins of the original connector cracked the epoxy holding their pads to the print bed.  Not wanting to risk damaging the bed, I desoldered the remaining half of the connector, soldered on a smaller 3 pin terminal strip from the junk bin, and then epoxied both connectors in place securely.

Wired up everything, powered the printer back up, and tested the ability of the head to hold temperature.

Everything looked OK, so I started a simple print.

It still didn't work right.  The first test print failed, peeling right off the print bed.

On closer inspection I noticed that as the bed moved around, the temperature reading on the GUI would occasionally read '1024'.  A temperature reading of 1024 indicates an open connection somewhere in the temperature sense lines.  I spent some time checking over the cable, trying to determine where the loose connection was.

The control electronics for the Makerbot Thingomatic are located inside the base, such that you have to turn the printer onto its side, unscrew and remove the base plate to get at them.  This was enough of a hassle when trying to trouble-shoot an intermittent electrical connection that I spent an afternoon moving all of the electronics onto the outside side and back of the printer where I could perform continuity checks mid-print.  I managed to do this without having to lengthen any of the cables.

After doing this, I managed to pin down the fault in the temperature sense circuit to the cable itself. Flexing back and forth repeatedly during every print had broken one of the wires in such at way that they still made contact most of the time, but during prints would sometimes open and cause the temperature reading of 1024.  The Makerbot software isn't smart enough to stop printing when it sees this obvious error indication, but simply continues attempting to print as the bed cools off and the printed object breaks free from the bed.

We didn't have any sufficiently flexible three-wire shielded cables on hand, so I simply braided together three pieces of fine wire to make up a new temperature cable assembly.

With the new cable assembly, I find that the printer still has trouble with large objects warping during the print, but smaller objects print fine, especially if printed on rafts.  I think that's as good as this printer is going to get for now.

Makerbot Upgrades Part 4

The office Makerbot has been printing nearly constantly for nearly a month now.  It's already more than paid for itself with parts we'd otherwise have to send out for manufacture.  The modifications I've described so far have made it run reliably enough that I can leave it printing unattended in a back room for hours.

I have noticed that the printer is getting noticeably noisier over time.  There's a creaking in certain spots of the X stage travel, a horrible screech when the Y axis moves quickly, and the whole machine shudders and rattles when the Z axis moves downwards at the start of a print.  I've also noticed that it takes a lot of force to manually move the X and Y stages, even when the stepper motors are completely unpowered.  I've decided that my next modification will be to redesign the X and Y stage slides, replacing the oil-impregnated bronze bushings with roller bearings.

First to be rebuilt is the X stage. As shipped the X stage rides on two 9.5mm precision steel rods, each passing through two bronze bushings pressed into ribs in the X stage structure.  This design is over constrained.  The print bed heats the entire X stage, which attempts to expand and pushes sideways on the two steel rods, anchored at their ends in the Y stage.  That's probably the cause of the creaking sound and some of the resistance in the X stage movement.

I ordered a few dozen miniature ball bearings, and then designed printable parts to hold them.  I designed two arrangements of three bearings each, to replace the two bushings on one of the rods.  On the other rod I placed only two bearings, so that the stage is physically located by only one of the rods, with the second only providing vertical support, so that the X stage could expand without pressing sideways on the rods.  The support structures for the bearings now took up most of the space under the X stage, so I joined them together, replacing two of the wooden ribs under the stage.

As I did I also replaced the clamping mechanism that clamped the belt to the stage.  On the version of the X stage I built the belt is clamped by two little wooden sticks that are only secured with one bolt each, and easily work loose over time.  I replaced them with a single large piece of plastic, held in place with two screws, to spread the clamping force out and not as easily vibrate loose.

There's really not much room to work with under the X stage.  To get the bearings to fit I had to cut several holes in the X stage mounting plate, and carve a long groove in the Y stage structure to clear the lowermost bearing.  I did manage to get everything to fit, and when I finally reassembled everything and ran the machine there was no creaking as the X stage moved.

The Y stage had been making a terrible screeching sound when moving quickly, so I set about replacing the brass bushings on that next.  Unlike the X stage, the stock ThingOMatic Y stage isn't over constrained.  On one steel rod the Y stage slides on two brass bushings, but on the other it already rides on ball bearings, so the Y stage can float and expand or contract independently.  There's also a lot more space under the Y stage to work with, so I had an easier time designing the bearings in.

I still had to cut holes on the Y stage bottom plate to fit these in.  Here I replaced each of the brass bushings with a single piece of plastic holding three bearings.  Three screws into the face of each anchor them to the Y stage structure.  It's not quite obvious from looking at it from the outside, but I'm also using the bearing blocks to clamp the belt to the Y stage, replacing the two original little wooden clamps.

After I reassembled the machine and ran it, I found that the noise from the Y stage was completely unchanged!  Moving the Y stage rapidly still resulted in terrible screeching sounds.  On closer inspection I traced the sound to the Y stage belt idler pulley.  Both the Y and X belts in the ThingOMatic have idler pulleys on 4mm bolts, without even a brass bushing let alone bearings.  Over time the bare plastic-on-metal contact gets noisy.

I had previously installed Thingiverse item 12528 on the Y stage idler, so the pulley wouldn't be hanging supported only on one side by the plastic baseplate.  Based on that design, I made a new part to support the pulley with ball bearings on each side.

I'm using the same 4mm bolt as an axle, but not instead of the plastic pulley turning on a stationary bolt, the pulley and bolt now spin on two bearings, that are then supported by the plastic bit anchored to the printer structure.  This completely eliminated the Y stage noise.  The Y stage now moves so easily, I have to hold it in place with one hand while trying to remove printed parts from the bed to keep it from sliding around.

For completeness, I've also upgraded the X stage pulley with bearing supports.  This was a much trickier job, again due to the limited space available.  There's barely room in the ends of the Y stage for the pulley as it is.  To get the bearings in there I had to replace the entire upper wooden structural cap on that side with a printed plastic part, and cut a hole in the lower wooden part to fit the support for the lower bearing.

The poor Y stage on this machine has quite a few new holes cut in it now, but both stages are really, really smooth.  The only noise as the machine prints is the singing of the stepper drivers.  It's almost like some kind of music, especially when it prints circles.

The default printing speed set in the ReplicatorG software is 30mm/second.  I had trouble getting the machine to print complex shapes accurately early on, so I dropped the speed to 20mm/second for a while.  Since upgrading the X and Y stages with bearings I've increased the speed back to 30mm/second without noticing any drop in quality.  I even printed a few parts experimentally at 50mm/second.  Some of the surfaces were a little wavy and there were a few small gaps, so I don't think I'll be printing many parts at that speed, but it's nice to see the machine still works fairly well even at that speed.

The next step would be to replace the Z stage bearings, but as the Z stage moves slowly and infrequently, I'm not sure it's worth replacing the bushings there with bearings.

Makerbot Upgrades Part 3

When building our Makerbot ThingOMatic, I was surprised by how little thought was given to cable management.  After carefully detailing the mechanical assembly, the instructions for wiring the machine are little more than a hookup diagram and some vague advice on taping the wires together to keep them neat.  There seems to have been little to no thought given to how to run the wires to the moving parts of the machine.  Most of the wires can be run along the inside corners of the machine and merely given enough slack to let the moving parts move freely.  The real problem is the build platform cable.

The build platform moves along two different axis, and is in near-constant motion when the machine is printing.  The connector on the front of the platform is completely unsupported, and the cable tends to drape down onto the rails and belt and get pinched against the frame when the platform is near the front of the machine.

It's unsurprising that the HBP connector is one of the most common parts to fail on these machines, and the Thingiverse has countless files for strain reliefs and cable clips and management systems.

My first attempt to keep this cable out of trouble was to simply zip-tie it to the mounting for the Y axis endstop switch, and then try to encourage it to coil in loops off to the side of the platform, as shown above.  This really wasn't satisfactory, the cable was still scraping on the Y axis belt, and tended to get caught when the platform was all the way at the front of its travel.  Getting pinched didn't just risk damaging the cable, it interfered with the movement of the platform, which was a problem as some of the parts I needed to print nearly filled the entire print volume.

A cable guide downloaded from the Thingiverse helped to some degree.

While not a complete solution, this at least kept some strain off the HBP connector.  I also began experimenting with designing a piece to anchor the build platform cable to the side of the Y axis.  My first few attempts didn't work very well - while they were keeping the cable bundle mostly out of the way, I was still losing some travel on the build surface due to the cable getting in the way of the platform's movement near the edges of the print envelope.  This solution worked well enough for printing small parts, but I needed to come up with something better to get the full use out of the machine.

We use industrial pick and place machines for circuit board assembly at the office.  While helping to maintain them, I had noticed that they used a cable chain system to manage the wire bundles to the moving gantries.  I decided to try and build something similar, as much to see if the ThingOMatic could print well enough to make that kind of complex moving part as to try and fix the HBP cable issues.

The result is this.

Admittedly, it's a bit of overkill for what it needs to do.  It's also not at all how cable chain is normally used - the chain should really be lying flat in a channel and bending with a constant radius when the gantry moves across it, not hanging free in space like this.  This works well enough for what I needed here anyway.  The chain constrains the cable to a single plane of movement, keeping the cable in front of the build platform from rubbing against the stationary parts below, and keeping the cable off to the side from getting pinched between the corner of the build platform and the frame of the machine.

Since I installed this modification (and those mentioned in the previous posts) the machine is working well enough to sit in a back room printing objects unattended for hours.  The cable chain has held up remarkably well, considering that the moving parts are just irregular plastic surfaces rubbing against each other.  I have yet to see any sign of the HBP connector failing, but I expect it will eventually, as even with the strain relief the connector is being operated beyond its rated maximum current and temperature.

Makerbot Upgrades Part 2

As I mentioned in my previous post, one early print on the machine was ruined when I touched the Z-motor while it was running, giving the machine a static zap that locked up the Z motor control board.  No permanent damage was done to the machine, but the part being printed was ruined.  The Makerbot ThingOMatic does not incorporate any static protection in its design.  It is made from a mix of wood, plastic, and metal, with several large metal pieces (including the motor housings) that are ungrounded and electrically floating.  As I found out, it can be easily crashed by static electricity.  In theory, it may even be generating its own static, as there are a lot of places in the machine where conductive and non-conductive materials are rubbing against each other.

This page has a guide to installing static drain lines.  The instructions are meant for the MK5 extruder, rather than the MK7 we are using, but what needs to be done is essentially the same.

There are five points that really need to be grounded on the printer.  The three motors, the extruder, and the print bed.  I started by preparing five lengths of wire with crimped ring terminals on the ends.  Green with yellow stripe is traditional for grounding wires, and we had plenty of it on hand anyway.  First was the Z axis motor, which I had already learned the hard way needed a static drain line.

The Y axis motor doesn't really need grounding as badly, since it's buried down in the base of the machine, but for completeness I connected it while connecting the others.

The X axis motor is tricky, since there's very little space where the wire can be attached and run without interfering with the X axis travel. I think I've managed to install it without reducing the X axis travel, but to be really sure I may go back and drill a hole to pass the wire through.

Grounding the print head is easy, as there are multiple unused holes on the mounting plate and no clearance issues with the wires.  There is some controversy as to whether this part should be grounded.  Some people have had their extruder temperature readings go off when they connected this wire, possibly as a result of shorts between the nozzle thermocouple and the frame.  I was careful to make sure that the thermocouple was electrically well-insulated from the nozzle when I built the printer, and I haven't seen any problems with the temperature reading after installing this ground lead.

The last grounding wire connects to the heated build platform.  We have installed the aluminum heat spreader, which makes connecting a ground wire easier as I don't have to figure out how to connect a wire to metal foil.  I have rearranged these wires a few times since this photo, as part of the ongoing challenge of dealing with the HBP cable.  I'll get into that more in the next post.

The five grounding wires are run down to the power supply in the base of the printer, connecting individually to mounting holes on the metal frame.  These are static drain lines, not power grounds, so even though they are theoretically electrically connected to the ground lines in the power connectors they need to be run separate from the power ground lines and from each other back to the chassis ground.

With these in place, the sensitive control electronics should be protected from static zaps to the motors, extruder, or heated bed.  I haven't had any prints fail due to static lockup since making this modification.  I have found a persistent issue where the Z axis sometimes randomly reverses direction while homing after a print, but I suspect that's a software rather than hardware issue.

While I was making this modification, I also made the modification described here to all four stepper motor controllers.  The power supply provides 12V and 5V on each connector.  The stepped drivers only use the 12V, generating 5V locally through a linear regulator.  I cut the regulator off each board, and then added a jumper to draw local 5V from the power connector instead.  In theory this should make the stepper controllers more reliable.  I haven't noticed any obvious difference, but it seemed like a good precaution to take.

Makerbot Upgrades Part 1

The company I work for has, over the last few years, ordered many parts from rapid prototyping shops. We frequently have need for one-of-a-kid jugs and fixtures, custom trays to hold parts for automated assembly, and prototypes for enclosures and other mechanical parts. This year we purchased a Makerbot ThingOMatic printer kit, as the cost of parts we've ordered in the last year alone exceeded the cost of the ThingOMatic. Since we've bought it, after the initial setup and tuning time, we've had it running nearly non-stop, as we've been constantly finding new uses for it. It's amazing how after you buy a 3D printer, you start to realize how many uses it has beyond what you originally bought it for. It's been a very worthwhile investment.

As useful as the Makerbot has been at the office, it took a lot of tweaking and adjustment to get it to work. As initially delivered, the ThingOMatic has a lot of mechanical and electrical deficiencies that needed to be corrected for it to print accurately and reliably.

Makerbot Upgrades Part 1

Axis tensioning

The Makerbot ThingOMatic uses two belts for positioning the build platform. Both X and Y carriage movement use a continuous belt stretched between the drive and idler pulleys, with the movable platform clamped to the middle of the belt. You adjust the belt by loosening the motor mount screws and shifting the motor along oval mounting slots till the tension is right. This does not work very well. It's tricky to get the tension right while simultaneously pushing the motor sideways and tightening the screws to clamp it down. The plastic base plate of the Y axis flexes enough to make it hard to tell how much tension the belt will have when you let it go. The belt tension is only held by the friction of the mounting screws and motor face plate. Inevitably the motor slips out of position. If you clamp the motor down enough to make sure it never slips, the screw heads dig into the wood or plastic structure, making permanent indentations that will make it hard to properly adjust the tension in the future.

Slack in the belt shows immediately as uneven lines, circles with flat sides, and gaps in the finished printed parts. A way to properly set and hold the belt tension is the most important improvement to make to the machine. There are a lot of items on Thingiverse designed to fix this flaw, typically by capturing the motor bolts and anchoring them to a nearby structural element with a bolt that can be turned to precisely set the belt tension. Thingiverse item 14098 was the one I chose to fix my printer. First up was the X axis tensioner. This was the first functional part I made on the machine, and it was pretty ugly.

Gaps in the print, irregular lines, non-round holes that I couldn't fit screws through without lots of trimming. It was still good enough to correct the X belt tension, improving the print quality for the next belt tensioner. This one was still crude, but better than the first one. This one went on the Y axis.

Another cause of poor belt tension is the lack of support for the X axis idler pulley. As supplied the pulley is supported on a bolt screwed through the plastic base plate. It's really not very rigid – the base plate can flex under the belt tension Thingiverse item 12528 fixes this by securing the top of the bolt to the printer frame. This also helps to prevent the loose cable from the heated build platform from getting caught on the protruding bolt.

With the X and Y belts holding proper tension, the quality of the build is much improved: the machine can print solid surfaces without gaps and can make reasonably round circles.

The Z axis has its own tension problems. The Z axis is driven by a screw rather than by a belt, s there are no problems with belt tension. The problem with the Z axis is that the print head is mounted quite far out from the screw, on a not very rigid wooden platform. Tension on the plastic filament being pulled into the print head lifts the entire print head, as the filament drive motor has more than enough torque to bend the Z platform upwards. If the filament feed snags and pulls irregularly, the up and down movement of the print head leaves irregular-width layers on the printed objects. In the worst case, a sudden upwards bending of the print head – caused by a snag in the filament feed – results in the layer being printed detaching from the object being printed, ruining the part.

At first, I just looped the filament on the desk next to the machine and periodically unwound more filament from the loose coils. Later, I propped up a metal pole behind the machine and placed the spool on that. This still required me to check the filament every few minutes as the machine printed. As my goal was to have this machine run mostly unattended in a back room eventually, this wasn't acceptable. I needed the filament to feed into the machine by itself.

Thing number 12974 was one solution for this.

This was the largest thing I'd printed on the machine so far, taking several days for all the parts. It didn't print perfectly, with one part failed due to layer detachment after the filament snagged and I didn't catch it in time, and other failed due to static electricity induced lockup of a stepper motor driver.

The spool holder helped with the filament feed issues. It still wasn't perfect – the plastic-on-plastic rolling of the spool on the holder had enough friction to pull the print head up, leaving uneven layers in the printed objects. It was still good enough at this point for us to start using the machine for production use at the office.

I later found some ball bearings in my junk box, and printed inserts that allowed me to mount the filament spool on some metal rod also from my junkbox. Now the spool rolls with very little friction, and the filament unwinds freely. It spins almost too easily at this point – the slightest tug from the extrusion motor starts the spool turning for a while, resulting in loose loops of filament around the spool. Not a big problem yet, but I do worry about the loose filament getting caught in the Z axis movement.

The next step would be to make a tension sensor for the filament and attach a motor drive to the filament spool, unwinding it so that the print head never feels any significant upward pull while printing. I probably won't be bothering with that – there are still a lot of other things I can do to improve this machine.