Stayed Z-axis

The structural part of the Z-axis in my RepStrap 3D printer is a pair of 8 mm rods which were fixed only at the base of the printer. When printing a higher speeds, both X and Y-axes are causing the Z-axis to wobble a bit. This has not been a problem so far, but especially when printing tall objects, there where some unwanted artifacts. I decided to make the Z-axis stronger in a weekend when all the shops where closed and I had to use the materials I had at hand. The top of the Z-axis was connected to the corners of the base of the printer using steel wire which was once used to hold up a curtain.

I printed 2 plastic pieces  with an 8 mm hole in the bottom to fit at the top of the vertical rods. I used 123d to design the part.

The steel cable was fastened using the metal pieces I removed from a terminal block like this:

The pieces from the terminal block where used both a the top of the printer and below the base of the printer.

Adjusting the tension of the wires is not very easy in this setup, it requires 4 hands. But once set up, I expect this to last for a long time. This printer is stronger now and the printing quality improved again a bit.

Printer upgrades

Finally a bit of time to update this blog with the current state of the printer. Very little was done on the printer the last year, but during the last few weeks I had some time to do some upgrades. The printer looks like this now:

Upgrades done include:

• Ramps 1.4 electronics
• Sprinter & Slic3r software
• Heated print bed
• Stays to support the top of the printer
• Y-axis extension

I will try to write something about each upgrade later, for now just a picture displaying  the quality of the prints at this moment:

The design is from thingiverse: 3Dknot.

Greg's Hinged Accessible Extruder

No posts for for half a year... a new job was getting in the way of my hobby.
I decided to build a spare extruder using the old hot-end of my makerbot MK4 extruder that broke a while back. I printed the parts of Greg's hinged accesible extruder, which is variant of the wade extruder which I am currently using. As my printer is not standard, I used a sheet of 3 mm plastic between the extruder and the aluminium frame. I printed the parts in PLA which is not the best option as I found out. The old makerbot MK4 hotend has a metal ring that transfers a lot of heat to the bolts which keep it in place. The bolts are getting so hot that the PLA deforms. I noticed this early enough so no serious damage was done.  I guess I could order a new hotend later which has proper (peek) insulation, but I wanted to get this to work now, so I improvised. A special aluminum bracket was created with 2 glued-on m3 nuts to which the hot-end can be connected. The aluminium strip and the hot-end is further cooled by a small fan which I took from an old modem. This setup seems to work fine.

The back of the extruder looks like this:

The bolts which get too hot are the two long m3 bolts (one visible) in the middle:

The bracket:

And the bracket and the fan installed:

The extruder works fine. Of course it needed some serious calibration:

I printed some knurled bolts from thingiverse:

Quality seems to be OK. I am waiting for the delivery of the parts for a heated bed which will allow larger ABS objects to be printed. I also ordered a new stepper motor controller which will allow me to use a more standard software configuration and which will increase the accuracy of starting and stopping extrusion.

Improved quality

No major new developments with the printer. I received white PLA from mendel-parts.com and have been using that after the green color all over my apartement started to hurt my eyes.

Green and white seem to behave pretty similar (which is not guaranteed!) but lately I had issues with the printquality being lower than with the previous extruder. For some reason the plastic was not always sticking to the layers below it, but tended to curl up a bit, leave a small void, and than deposit a blob a bit further instead of making a nice line. I tried cleaning the extruder hot-end, varying the temperature, varying the extrusion speed, but nothing gave major improvements. Last weekend I changed for the first time ever the layer thickness from 0.34 to 0.25 mm. This was a major change! Of course you get better details because of the layer thickness, but the plastic does not get the chance to escape anymore to curl up and it will always stick to the layer below.

Some pretty nice quality in the pictures below:

There is a drawback: both running skeinforge and printing takes much more time than before, but for now I can live with that. The remaining unwanted jitter in the surfaces which should be flat is due to many different small factors like: z-axis wobble, belt tension, x and y stepper gear train play etc.

Extruder rebuilt

The extruder worked fine for a long time, but started to become unreliable. Sometimes for no apparent reason the stepper motor missed a few steps; the force needed to drive the filament through was increasing. I increased the temperature a bit, but this did help only for a while. I did not want to risk damaging the rest of the extruder, so a rebuilt was needed.

Though the old extruder worked fine there were some parts which needed improving.

• An aluminum bar was keeping the hot end in place; this leads to loss of energy causing long warm-up times and heating of the extruder's plastic part in the places where the bolts are attached (see here).
• The hot end was very short making the placement of the thermistor difficult. basically the thermistor was taped with kapton on the nichrome wire which is not the best place.

I already bought a new hot end v4  form mendel-parts last month and now was time to take it into use. The new hot end has a machined piece of PEEK to keep it into place which solves the slow heating-up problem and it is longer to help in placing the thermistor in a better place. In addition the PTFE part is screwed into the metal tube and not the other way around which make the chance of leaking plastic much smaller (though I never had that problem, others seem to suffer from that).

Because the old hot end was kept in place with a aluminum bar with m3 bolts and the new PEEK bar has m4 holes in different positions, an adapter piece (copper) was made to make it fit.

 The old thermistor and new nichrome wire attached again (old nichrome wire had turned white and the insulation was falling off when taking it off the old hot end).

 Since the new hot end is a bit longer I decided to insulate the it, just like the original makerbot extruder (see here). The insulation tape was bought locally in Finland from www.robomaa.com.

The temperature of the extruder seems to be much more constant. It seems the actual temperature is always about + or - 1degree of the set temperature. The old hot end had + or - 5 degrees.

The extruder with the rebuilt hot end has been printing all day and seems to be OK again. There are some small issues with precision of placement of plastic (belts?) but that is a worry for later.

3D print from start to finish

Though similar videos exist on the internet, I wanted to document the full printing cycle of my repstrap printer. A 40 minute print condensed into 4 minutes:

The final object is here:

From the video a few issues with printing can be seen which I hope to work on improving in the future:

• Speed. The printer is not very fast. Increasing the speed is certainly possible, but I need to make sure I have enough spare parts to repair the printer if I break it before I attempt to do that.
• PLA dripping out after the extruder motor stops. It can be observed that after the test extrusion, when I have removed the extruded plastic hanging from the nozzle, that melted PLA drips out. This results in blobs on printed objects which should not be necessary.
• The first few centimeters of printing did not work. This could be related to the previous issue: plastic has been dripping out and pressure has to be build up before there is a constant flow of plastic.

This object can be found at thingiverse here and is my favorite test object which has been printed quite a few times in different materials and different sizes.

What is this?

I printed this thing:

Documented on thingiverse: here.