Tuesday, April 30, 2013

0.25mm Nozzle, Cartridge Bearings, and Pluto.

I purchased a new nozzle for the printer in an attempt to get higher resolution parts. My original nozzle was a Lulzbot Budaschnozzle 1.3, 0.5mm diameter, which I don't know if they even sell as a stand-alone part anymore. It worked fine, but seemed to make a mess of smaller parts and liked to ooze a lot. I thought I'd go the other direction and went to the smallest nozzle Lulzbot.com sold- a 0.25mm.

While I was on the lulzbot site I noticed they really upgraded their hot end- their new 2.0 version looks really nice- a machined stainless steel backer plate and aluminum heatsink. Much more industrial looking than the older version I purchased only a few months ago.

Since the new 0.25mm diameter nozzle only puts out 1/4 as much plastic per pass as my original 0.5mm nozzle, build times are longer, but the smaller output filament produces a much finer quality part. It also seems to ooze much less when heating and traversing than the original 0.5mm nozzle. I've heard clogs can be an issue with smaller nozzles but I haven't seen that yet. The new nozzle was a snap to install. I was worried about all of the solidified plastic on the inside of the old nozzle making it impossible to remove, but it came off without any trouble.

As long as I was trying to further improve print quality, I thought I'd further reduce free play in the Z-axis 3/8" ACME threaded rods. The bottom is relatively fixed by the stepper motors and the flex couplers. The X-ends attach to the rod via two large brass ACME nuts, but those nuts have some side-to-side free play. During Z traverses the top of the rods can and do trace out an orbit. This must have some effect on Z-axis precision. It's probably very minor, but why not try to reduce it as much as possible. I was able to find some nice cartridge bearings with the correct ID at D&S Machined Products for $2.50 each. NTN R6ZZ/LO14QC. These fit very nicely over the 3/8" threaded rod.

I was planning on designing and printing a slick bearing retainer, but then my father-in-law suggested I simply hot glue them in place. How can you argue with that? Quick, easy, and it'll supply a tiny amount of flex to prevent binding.

Right Side upper Z-axis bearing hot glued in place

For a test of these two improvements, I printed a few copies of the "Pluto" dog off thingiverse. It's a nice size, has smooth compound curves, and some really tough overhangs for the ears and mouth. In short, a good test for trying to improve print quality.

The 4 Dogs, numbered left to right
Dog #1, far left, is 0.2mm layer height with a 1mm Z-lift. I've been using a 1mm lift since the beginning since I was having all kinds of problems with the nozzle hitting ooze piles, jamming the stepper motors, then ruining a print.  In this dog you can see some variability in layers, some gaps visible, etc. Lots of stringies from the bottom of the mouth and ears also.

Dog #2: Since the new nozzle doesn't ooze nearly as much, I thought I'd take a chance and get rid of the Z-lift entirely. That made a huge difference- note how uniform and clean each layer is. No issues with skipping steps either. I also reduced the Bridge Flow Ratio (BFR) from 1.0 to 0.95 to try and improve the mouth and nose details. That didn't seem to help much, this dog still had bridging challenges on the mouth and ears.

Dog#3: The final two dogs were meant to fix the bridging entirely- #3 has a BFR of 0.85

Dog#4: BFR of 0.75. Minimal effect.

A fan might be required to get this dog to print nicely. Otherwise a nail file and wire clipper will clean it up nicely.

How about trying a vapor polish? Just don't leave it in there too long like I did. It's also a smart idea to let the vapor chamber fill first, before inserting your part. Otherwise the bottom of the part gets over-polished and the top gets under-polished. Here is what it looked like after 45 minutes:

Melted Dog!
 The bottom of the dog was very, very soft and had partially collapsed and the top still looked good.

Next, now that small part performance is starting to look pretty good, I thought I'd actually do something useful with the printer. I installed some under cabinet LED lights from amazon.com. These were very nice- decently warm color, and easy to install. However, I needed a better solution to fasten the wires in place to the bottom and inside of the cabinets. Neither Home Depot or Lowes had appropriate wire clips or staples, so I thought I'd design and print my own. All of the commonly available clips are made for coax cables, CAT5, romex, etc.

These custom clips securely clamp the wire in place and attaches using a #6 flat head screw. The .STL file, part model, and dimensions are available now on thingiverse.

tags: mendelmax 1.5, rep rap

Tuesday, April 2, 2013

More MendelMax 1.5 reprap improvements....

The original vinyl tubing Z-axis connector was showing it's age- starting to crack and slip. The version of MendelMax 1.5 I built uses a 3/8 inch ACME thread Z-axis threaded rod- so it's not easy to find a drop-in replacement My first try at an improved Z-axis connector was to design and print one. This connector can be found on thingiverse.

Printed 3/8" ACME to 5mm Stepper connector, installed

Printing parts with the new connector
The new connectors didn't work quite as well as the vinyl tubing- and seemed to introduce a good wobble to the Z-axis threaded rods, and thus made the parts print with irregularities in the layer thickness.

Unfortunately nice machined aluminum couplers are not available to join 5mm shafts to 3/8" ACME rod. I was able to find some very inexpensive 5mm to 8mm aluminum flex couplings on e-bay. Then, a friend helped me turn down 0.5" of the shaft end to 8mm to fit the couplings.

3/8 ACME rod with end turned to 8mm
Coupler Installed
I've also been fighting part warping. I thought one way to combat this would be to control airflow, and to keep the air around the printed part still and fairly warm. I found some thin acrylic sheet at the local Lowe's hardware store. It cut very nicely by scoring it with a knife and also with a bandsaw.

Cutting Acrylic Sheet
Material Detail

Draft Guards installed