The PLA I have is 4042D.  What I initially observed was that no matter what I would do, the PLA would eventually get jammed and I would have to tear my extruder apart to get it cleaned up and working again only to have it fail minutes later.

I ruined a PTFE barrier trying to force the PLA through by hand and I broke a heater barrel trying to unscrew a nozzle with solidified PLA in it.  I’ve learned to be very careful now.  Whenever the extruder gets jammed I take it apart piece by piece with the heater on (wearing good gloves) to get the PLA out without damaging its shape.  From this excercise I have learned that the PLA always melts in the PTFE section.  Even using a steel barrel with a heat sink.  I haven’t tried narrowing a section of steel yet, which may give me the short transition zone that nophead recommends.

In hopes of narrowing down the problem, I removed some components from the equation.  First was the extruder motor and drive block.  I simply pushed the filament by hand until it would move.  What I found here was that as long as I continously moved the filament it would not get jammed, but if I stopped for a few seconds I could not get it started again no matter how much I pushed.  I could pull the PLA back out and then force the liquid part out using a steel tool without much effort.

I then removed the nozzle so that all I had left was the PTFE barrier and the heater barrel.  I observed the same behavior.  The pressure I was feeling jam up the extruder was not from the nozzle.

I decided to try something I had read about in the reprap blog.  I coated about a foot of PLA with oil and repeated my simplist experiment.  At this point I knew exactly what to do to cause a jam.  Heat up the PLA, extrude a little be, stop for a few seconds and everything is jammed.  Well, with the oil it didn’t jam, it just kept on going.  I did a few other tests including cooling the PLA after stopping and then reheating it with no problems.  The oil solved everything.

Obviously I wasn’t about to coat every inch of the PLA by hand.  Instead I put a small hole in a piece of fabric (cotton, but I think anything will do), bolted it to the top of my extruder and soaked it in oil.  I ran the PLA through the hole to deposit oil on it as it enters my extruder.

This worked great as long as I kept the fabric wet with oil.  This required my attention every 15 minutes, which was annoying.  It turns out that my MDF extruder block was soaking up most of the oil and so I put a plastic liner between the fabric and the extruder block.  Now it can run for hours without a refill, although it does tend to dry out between uses.

I am using engine oil, 10W-30, I believe.  I bought the wrong stuff for my car once and so I have a quart of it lying around.  I thought about using vegtable oil, but I think it would smoke at my working temperatures and I don’t need my reprap smelling more like waffles than it does just running PLA.

At first I was extruding at 210 C and getting good results.  I found that to print a working whistle I had to reduce this to 180 C.  At 180 C the raft does not stick to my MDF bed, so I have to print the raft at 210 C.

I’ve also discovered that PLA will get into any gaps.  This means that every time you take a part off (nozzle or PTFE) and screw it back on it won’t go on tight with the PLA blocking the thread.  I have to screw it on and then heat it up and then tighten it.

I started by cutting a piece of aluminum bar to get a piece that was 1 1/2 inch x 1/2 inch x 1/8 inch.  I filed the edges and corners down so that they would not cut into the nichrome wire.

Next I drilled and tapped the center so that I could screw it onto my M6 heater barrel.  I tried this in the past, but it was difficult to get a perpendicular thread on such a thin piece, so this time I drilled the hole into two pieces of wood as well, lined them up using the drill bit, clamped them together and then tapped through the first piece of wood and then through the aluminum.  This held the tool perpendicular to the aluminum.

I screwed this piece onto the barrel.  I then put the nozzel on tight and tighted the aluminum block to the nozzle to lock it in place and provide a direct path for heat from the aluminum block to the nozzle.

I attached the thermistor to the aluminum block.  This creates good thermal coupling between the heater and the sensor.  I’m using the old bang-bang control and having good coupling prevents overshoot during warmup and oscillations.  With this setup, I have only 1 degree of overshoot.  The downside is I don’t have an accurate reading of the barrel and nozzle temperature.

I also wrapped the aluminum block in a single layer of kapton tape to provide electrical insulation for the nichrome wire.  I’ve found that this is required even for insulated wire because the insulation tends to break down due to the wire getting much hotter than the working temperature.  Kapton tape stuck directly on aluminum or brass doesn’t get much hotter than the working temperature because it has a good heatsink on one side.

I wrapped the nichrome wire around the aluminum bar.  I already had wire leads attached to the nichrome.  I was careful to keep the amount of nichrome in the air leading to the copper wires short.  This is because the wire can get very hot if it isn’t very close to another metal and tends to burn any insulation material that comes close.  I had to redo one of the leads to get them both to be short.

To wrap the nichrome wire, I taped one end into position.  Then I wrapped about half the nichrome wire around one side and taped it down to hold it in place.  I ran a short bit along the edge of the aluminum block past the heater barrel (on the side opposite the thermistor) and taped it again there so that I could wrap the rest of the coil without the previous bit coming loose.

The connectors are steel butt connectors clamped tightly on each wire and then wrapped with kapton tape to prevent shorts.

After this I wrapped the coil in a few layers of kapton tape to hold it in place.

I also added a few pieces of tape that run along the wire connectors, down around the opposite side of the aluminum block and then back up to the other side of the wire connector.  With another piece of kapton tape wrapped around the outside of the connector it is held in place without putting stress on the nichrome wire.  I also wrapped some tape around the aluminum block on the thermistor side.  This holds the thermistor in place as well as the pieces of tape that hold the connectors.  Finally I put a few more pieces of tape on to make sure there weren’t any loose edges that might come loose.

The last step is an attempt to make the whole thing more durable.  I’ve found that kapton tape that is in direct contact with nichrome wire tends to break down if it isn’t also in contact with a metal surface to cool one side.  I’ve clamped a piece of aluminum sheet around the whole thing.

Unfortunately, I was not able to clamp it very tightly and so it isn’t helping much.  I think if I did it again I would create three pieces of aluminum block that are the same size.  The center one would be tapped as I’ve done here, but the other two would have larger holes in the center.  The two extra pieces would be bolted together clamping tightly to the kapton tape.

Finally I mounted the whole thing on my extruder and tried it out.

At this point I discovered that with all the switching of barrels I have damaged my PTFE insulator .  The only thing I can say about this insulator is that with an 8 Ohm heater and steel barrel it can reach 220 C without insulation and beyond 250 C with insulation.

In addition to that, I had a problem securing the X-axis rods with set screws tapped into MDF.  That wasn’t a very good idea in the first place and I had been hoping that everything held together long enough for me to print replacements.  It all came apart one day when, during a print, one of the X-axis rods slid out of position and dropped the head onto the work piece.  I wasn’t watching at the time.  The combination of the stepper yanking the now unconstrained head around and the hot tip drilled through the part and messed up the work surface.   It wasn’t pretty.  I reassembled everything and I added hose clamps to trap the X-axis rods and prevent a repeat.  This hack wasn’t pretty.  The X-axis rods vibrate a lot and the new metal on metal parts made a lot of noise.

I also had a noise where the plywood base for my extruder contacted the MDF carriage.  It would seem plywood is an excellent sound board.  Anything I can do to dampen the vibrations going into that will be a plus.

So, I decided to print new parts for my X-axis.  They would be more precise and so have less play.  They would have the proper Y-axis 3-point constraint and so I could move faster.  They would be plastic parts that would not resonate with my wood parts.  The set screws would be held in place by trapped nuts.  In addition, this would give me a chance to dogfood my system before printing Mendel parts to give to someone else.  That would turn out to be important.

The printed parts are not all printed in the same orientation that they are mounted.  When I rotated one part to connect to another, I noticed some holes that were mismatched.  In particular, it appeared the Z-axis in the printing orientation was shorter than the X and Y axis.  I reviewed my firmware parameters and recalculated the z steps per mm setting.  It was set to 150, but I calculated it to be 160.  That explained the discrepency.  I also checked the x and y steps per mm settings.  These were set to 10, but I calculated 9.85 as the correct value.  So, x and y were slightly too large and z was significantly too small.  On the small calibration parts I had printed before, the measurement was close enough that I wasn’t sure if what I was seeing was just errors from the raft, perimeter width and loose guides.

After I replaced the X-axis I tested the X and Y motion without the extruder mounted to make sure everything was working fine.  I was surprised that it wasn’t much quieter than before.  I was relieved later when I put the extruder on and the X and Y motion became much quieter.  It seems that a little mass is required to make the steppers run smoothly.

The biggest play issue I observed with the old X axis was that the carriage would rotate around the X axis, lifting the head up off from the bed.  There was a lot of play in the carriage guides.  The new X axis does not have that play, but unfortunately it still rotates around the X axis.  This appears to be because the 8 mm steel rods that hold it bend a little bit.

I printed a Mendel part after I changed the X axis and adjusted the step distances.  The texture on the sides looks a little better than previous things I’ve printed.  I discovered while printing this part that the layer thickness was now too high leading to a lower density infill than expected.  That is because I setup all the Skeinforge properties using the incorrect z step size.  Now I have to adjust it for the corrected values.  I’m printing a second part now with different Skeinforge settings and it is looking very good so far.

The first few things I printed were Opto Endstop mounts, which I’ve been using ever since.  There are three of them on my machine.

After that I printed 20 diagonal tie brackets.  I had made a few of them out of MDF, but they didn’t work well and I wanted to replace them.  The Darwin designs call for 20 of them, so I had to print these out to complete the build and make the frame rigid.  There are two of them in the image below, one white and one black.  I printed several of these parts during the Ann Arbor maker faire.

After that I printed three y-axis brackets.  In the above image, it is the part on the top.  All three of them are in use on my machine.

I printed two parts that are connected to create a fan mount.  Unfortunately, I don’t have a convenient spot on my carriage to mount a fan, so I’m not using these parts right now.

I attempted to print a Y motor coupling several times, but this part was unable to handle the stress of the job and every part eventually cracked.  I’ve given up on this part and have instead made a coupling out of a steel spacer.

The Darwin design was updated between the time I started on my MDF version and the time I finished it.  One of the more interesting changes was the Z flag mount, which is now easier to adjust.  I decided to print it out.  I haven’t put it on my machine yet.  I’m still trying to figure out how to add it without taking the whole machine apart.

I began to print extruder drive blocks for members of the RepRap-Michigan group.  The first two I gave away.  The third one I still have.  Each one has slight changes and improvements.  This is a part I designed.  It is loosely based on the NEMA-17 extruder drive blocks used by the Mendel design.  I modified it to use a NEMA-23 motor and a larger idler bearing.

In hopes of improving my print quality, I started using Skeinforge instead of the RepRap Host software to generate the tool paths.  I printed many bed clamps while I calibrated the new software and I ended up with four nice pieces that I put on my machine.

I still had problems printing fine details, so I picked a part from the Mendel design that was a big challenge and tried to print it.  I had to change to the 5D firmware to get this to print out well.  I now have 9 of the 10 y bar clamps required for to build a Mendel.  I will likely give these parts to someone in the RepRap-Michigan group.

After that was settled, It was time to start printing some useful parts.  I want to rebuild my X-axis since it has a lot of play and loose parts.  Yesterday, I printed the first part toward that goal.  This is the x-carriage and is the largest object I have printed so far.

That record didn’t last long.  This morning, I printed the x-motor-mount, which is a little larger.

I’ve printed a couple smaller X-axis parts today.  It has been a very productive weekend.  I expect to have all the parts for the X-axis printed today.  Most of the remaining parts are small.

Here is a video of my RepRap printing a new part.   Click the image to download the video.  You will need the DivX codec to play this.  The video runs at 10x speed and I’ve removed the audio.  My memory card filled up before the part finished printing.

I will be at the Ann Arbor Maker Fair on Saturday 29th August with this machine if anyone wants to check it out and see it running.

There are a few quality issues I have to address still.  The bottom few layers don’t lie down right and so the bottom of the part has all sorts of strange loops.  In the video, I attempted to print 10 foundation layers instead of the normal 4.  This didn’t help at all.  I also have a lot of play in the carriage, which means the the nozzel sometimes rocks back and forth.  Finally, I think there might be some backlash in the x axis, but it is hard to get to the pulley that is loose.

I spent a lot of time trying to get an extruder kit I got from Bits-From-Bytes working, but it never worked for more than an hour or two.  The biggest problem was that one of the gears was off-center.  This meant the amount of force seen by the motor was highly variable and I was never able to get it to run in the sweet spot.

While I was working on that, the good people at reprap.org developed a new pinchwheel extruder.  This thing is much simpler and I was able to build one using MDF, like everything else.  The new extruder runs off a stepper motor, and the shaft runs right against the plastic rod, no gears to mess with.

I’ve also had a lot of trouble with the stepper controllers overheating.  I decided to over-solve this problem so that I don’t have to worry about it any more.  I connected the 4 heatsinks with a piece of aluminum and mounted an old graphics card cooler to it.

I used thermal compound to make a good connection and I used the old heatsinks to provide a rigid clamp and prevent the thin aluminum from warping.  The first time I did this, the heatsink was parallel to the plywood.  This made it difficult to get to the connectors and the potentiometer.  I also spent a lot of time filing the edges so they were not so sharp.

The second time I did it, I orientated the heatsink perpendicular to the plywood and the accessibility has improved.  To avoid sharp edges I just folded the metal over and clamped it tight.  This was faster and ended up with a less sharp edge.  I also orientated the factory edge away from the board, where my hands are more likely to be.

I’ve finished the cartesian robot and setup the electronics.  I put all the electronics on a single piece of plywood.  The wires that run between the various boards are tied down with wire ties so they don’t move around and come loose.  The wires that are connected to the cartesian robot are tied down to the frame.  I used an ATX motherboard extension cable to connect to the power supply.  This allowed me to put a power switch on the board and make a few power connections off a single plug.  The stepper drivers are all powered directly off the power supply, while the rest of the boards run through the large ATX connector.

I don’t have an extruder yet, but I decided to test the cartesian robot out.  I connected an LED to the extruder signal from the microcontroller.  I used a 520 Ohm resistor in series with the LED.  After shutting the lights off, I took a video of the LED “printing” a corner bracket.  My camera would only record for an hour continuously, so I just got the bottom quarter of the part.

The top edge isn’t parallel with the bottom edge.  I believe this is because there is slack in my y-axis belts.

Since I have now discovered that it will take a long time to print a part, I’ve decided to set up a dedicated computer to run the RepRap.  I’m using my old MythTV system, which has a 500 MHz P3.  I’ve also built a table to hold the computer and the RepRap so that they are out of the way of my workspace.

I’m going to order pre-made parts for the extruder to save time.  Those should arrive within a few weeks.

I made the four bed clamps out of some 1/4 inch plywood.  Each one is cut out of a 41 x 41 piece.  I cut a 45 degree diagonal 18 mm from one corner.  I drilled three 5.4 mm holes at (9, 9), (9, 31.5) and (31.5, 9).

For the z-motor-coupling I drilled an 8.4 mm hole through the center of a 5/8 inch dowel.  I used a hack saw to cut a slot along the side.  I put two small pipe clamps on it so I can tighten it down.

I also made the diagonal-tie-brackets.  There are 20 of these.  I started with a 35 x 35 block that was 3/4 inch thick.  The first hole is through the side.  It is 21 mm from the front and 10 mm from the top.  This hole was drilled with a 8.4 mm bit all the way through.

The next hole is through the top and is 13 mm from the front and 17 mm from the side.  This one is 8.4 mm and goes all the way through to the bottom.

The final hole is through the front.  It is 10 mm from the top and 17 mm from the side.  This is a 4.2 mm hole and only goes through to the vertical hole.  I will put threads in this last hole.

Update:  The diagonals has to be 15 mm longer than listed in the BOM to accommodate these.  I had already cut them, so I just half threaded the nuts on the end.  I think I’ll leave them like that until I can print plastic parts that are the right size.

I started with 7 blocks that were 56 x 56 and 1.5 inches thick.  I marked one of them ‘Top’ and two each of ‘Left’, ‘Back’ and ‘Right’.

In each block drilled a hole for the x rods at (y, z) of (28, 26).  This was drilled with an 8.4 mm bit all the way through the block.  I drilled another similar hole for the y rods at (x, z) of (28, 12).

I drilled a hole through the center for the set screws.  This is at (x, y) of (28, 28).  I drilled this with a 4.2 mm bit all the way through the block.  I used the tap set to thread this hole from the surface to the first hole it intersects.  I threaded from both the top and bottom.

In the ‘Left’ and ‘Right’ blocks I drilled holes at (x, y) of (15, 15) and (41, 41).  These were drilled with an 8.4 mm bit all the way through.  In the ‘Back’ and ‘Top’ holes I drilled similar holes at (15, 41) and (41, 15).

Update:  I had to drill a third hole from top to bottom for three of the corner brackets for the y-post-rod.  Fortunately I marked all four holes so I just had to figure out the right one and drill it.  Unfortunately, I had to disassemble the top frame to drill the holes.  I also had to drill and thread a hole for a set screw, similar to the directions below.

Next I drilled set screws for the z-posts.  In the image above I have drawn arrows parallel to where I drilled these holes.  Each hole is at a z position of 19 and is 15 mm from the nearest corner.  These were drilled with the 4.2 mm bit just until I intersected the z-post hole.  I then used the tap tool to make threads in these holes.

The z-posts will protrude 39 mm below the corner brackets instead of the 42mm called for in the assembly instructions.

Update: Because these blocks are larger than the plastic parts would be the 8 x and y rods must be 512 mm instead of 500 mm.  I tried putting everything together with the short rods and the bed just wouldn’t fit.

Through the top I made three 5.4 mm holes.  These are at (x, y) of (23, 4), (7, 19) and (39, 19).  Each hole goes all the way through the block.  These holes will be used to secure the bed.

There is also a hole for the studding.  This is an 8.4 mm hole all the way trough at (x, y) of (23, 40).

Next, I created the space where the nuts will fit.  I put a nut about 50 mm down the studding and then slipped the block on it.  Then, I put another nut on the end of the studding and turned it until it was close to the block and one edge of the nut was parallel to the nearby edge (on the short blocks.)  On the long blocks, I didn’t have to worry about making it parallel.  Once close, I held the block tight to the nut and tightened the nut underneath the block with my fingers so the the nut on top is held in position.

Once in position, I used a pencil to trace the nut.  Then, I cleared this area 6 mm deep using my side cutting bit.  To get close I frequently stopped and checked to see how well a nut fit in the hole.  I repeated this on the other side.

From the bottom side of the block, I used a 10 mm bit to create clearance for each of the 4 holes.  These stop 12 mm before reaching the top of the block.

With one of the long pieces I drilled an 8.4 mm hole at (x, y) of (23, 76.75).  This goes all the way though.  This block will be used on the datum corner.

With the other long piece I drilled two 8.4 mm holes at (x, y) of (23, 75.5) and (23, 78).  I then flattened the space between these holes.  This block will be used opposite the datum corner.

Finally, I used the side cutting bit to clear the area from the 3 10 mm clearance holes to the side of the block so that I can get a nut in there.

Next, I cleared two rectangular holes through top and bottom.  The location of the first is (x, y) is (10, 8 ) – (32, 16).  The location of the second is (42, 8 ) -(64, 16).

I put a small screw through one end to hold a nut in place, then a longer screw and nut to make the adjustable end.