Tuesday, July 21, 2015

3D: Torturing the Folger 2020 i3.

There are a few "torture tests" for 3D printers out there on the web: objects that are hard to print and expose the qualities and limitations of your printer. Benchy is one, and Makezine published another set of them. Here is what happened when I tried the Makezine set (and you can read about Benchy at the end). They make the STLs available for seven tests and also publish a scoring scheme. It is supposedly objective, although I am less confident of this than they are, and certainly looking at results from other people, there are examples where one looks better than another but the authors used the same score. The comments on the Makezine article include a link to a spreadsheet comparing 23 printers. I have some doubts about the quality of the data. The columns don't correspond exactly to the tests. There is some information that simply cannot be true, in that the Z resonance test requires printing an object 150mm tall, and printers with a maximum height of less than this are recorded as passing the test.

Regardless of these issues, here are my test results. In each case I've given a picture or two, my best guess at the right score, and how many of the printers in the Makezine result did better, equal and worse than this.

All prints are with PLA at 0.2mm layers, 30% infill, using my standard (moderately slow) speed. I've given the time estimates reported by Slic3r. I didn't note the actual times. My printer is a Folger 2020 i3 with a few minor modifications, none of them affecting the mechanical operation.

Unrelated side note: over the weekend, I partially disassembled the Y bed. It's always made a lot of noise, and I was going to take it all the way back to the bearings and put it back together. In the event, I didn't do this. I just saw some of the bolts holding the bearing mounts could be retightened. In some cases, I had never screwed the nylock nuts flush down into the mounts. It's now much quieter. Now it's the X movement that is getting noisy.

1. Dimensional accuracy

The metric here is the diameter of the second largest disc. It should be 20mm in both X and Y. Mine was 19.9mm in X and 19.8mm in Y, giving it a rating of 3. Makezine has 5 better, 8 equal and 10 worse. 43 minutes.

2. Bridging
I'm surprised how well this and the next test worked. Even the longest bridge, 65mm, shows only slight sagging, and it is (I think) in the perimeters. I rate this as either 3 or 4. Assuming 3, which is worse, there are 9 printers better, 3 the same, and 11 worse in the survey. 59 minutes.

3. Overhang
This one is the really amazing test. It prints overhangs at angles ranges from 30 degrees to the vertical to 70 degrees to the vertical.

The Allen key is to hold the piece up, as it doesn't support its own weight. This seems like a 3, as there are some hanging loops on the 70 degree tile, though it isn't far off a 4. 10 better, 4 the same, 9 worse. Better cooling airflow would probably help this and the previous test. 1 hour 28 minutes.

4. Dimensional accuracy
Here you print a block with pegs in it and see which ones can be removed, to see the finest tolerance in the space between the pegs and the block. My first try failed as a peg came loose while the print was still in progress. This is the second try.

I was only able to get the 0.5 and 0.6 pegs out, with a score of 2. 15 printers are better than this, 4 the same, and 4 worse. The print took 42 minutes. The result is consistent with what I've seen on prints with interior holes - they are always too tight. It can be fixed by a lower extrusion multiplier. Maybe less infill would help too.

5. Fine positive space features
Also known as the pointy print.

The thing to look for in this is the fine strands between the points, which gives it a 3. The spires are well formed and quite regular. The strands are an issue I have with my extruder. According to calibration measurements, it does not over extrude, but it does ooze a little before starting the print, and I often get these strands on fast travel moves. One possibility is that the retraction isn't very good. Replacing the extruder is an improvement I'm likely to make one day.

6. Mechanical resonance in XY

This is a pass fail test. I think this is a pass, like 10 of the 23 printers in the test. It took 37 minutes to print.

7. Mechanical resonance in Z
The test object for this is 150mm tall, and that's beyond the capabilities of my printer (though this awesome mod might make it possible). I get nervous when the Z position is above 110mm: I start to hear clunking noises during Z movement. It's probably due to misalignment of the threaded rods, as this would become more apparent closer to the end of the travel when it becomes more mechanically constrained. I decided to do the test with the object scaled down to 100mm. It passes the test conditions in showing no layer registration or ridging problems. In the reported test, 18 printers passed and 5 failed. The print time was 1 hour 9 minutes.

Bonus: Benchy Boat
Benchy is another well known torture test. I did print this once before with fairly good results, but afterwards realized that I was not using the recommended settings, i.e. 0.2mm layers and 10% infill. Here are some pictures from another go with these settings.

I'm really happy with this. There's not even much sagging on the cabin roof, which I did get last time. I won't go through all the analysis listed at http://www.3dbenchy.com/dimensions/. They were all very close except the interior dimensions of some of the round hole. The word 3DBenchy on the stern isn't legible, though you can tell there is something there.

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