Yea, I know. Really, really cheezy title. Tough.
Last week I went to make a print for my underwater video light – a quick disconnect ball mount so I can leave the ball mount permanently attached to the video light no matter what housing I use. It looked pretty straightforward, and I started to print…
… only to find it was pooping it’s thread from about 5mm instead of onto the bed. I checked and confirmed the height was off, so corrected it. It did it again! I tested the x-axis extruder height, and it was also off level. This was very strange as nothing had changed, but as I was checking I discovered the z axis was moving when I touched it. It is NOT supposed to do that.
More checking confirmed the bad news – one of the nuts that is part of the z axis was totally stripped. You could take the threaded rod and zip it back and forth holding the nut. The other nut was OK, but for now the printer was down.
A detailed analysis plus a bit of an “aha” moment involving the same threaded rod and the video light made me realize the so-called 5mm threaded rod was actually a 10-32 imperial thread. It was not metric at all. I have 10-32 nuts, bought as part of the video light project, and they fit perfectly on the threaded rod. More interestingly, the 5mm nuts showed significant “lash” on the rod while the 10-32 nuts showed almost none.
The only problem was the 10-32 nuts were too large to mount on the printer. I tried epoxy, but it just peeled off the PLA mount once cured. All the fancy stores were closed Saturday, including one that was supposed to be open but could not bother to post that on the website or make an answering machine message, so I was out of luck until today.
This morning I went to Fastenal in Nanaimo, looking for “threaded rivets” a.k.a. rivet nuts. These are marvelous threaded tubes about .5 in long by whatever thread you want. They would solve the problem perfectly. Unfortunately, they were out of stock and it would be a week for more. However, they did have true 5mm stainless threaded rod and stainless 5mm nuts. I bought both, came home and cut the rod to length and installed it. With the new nuts, it was back to a working printer in a matter of about an hour.
Once rebuild, I had to level the x axis again. The height is controlled by the two z axis threaded rods, and though you can get really close by evening the nuts before you assemble it, it’s best to fine tune with a strip of paper and the extruder.
The first print was again the 20mm cube, as that’s a really good test of the printer and allows me to verify all dimensions. It turned out the z face was high – 20.05mm and not 20mm, so I grabbed the internet and checked thread pitches. It turns out they are most certainly NOT the same. 10-32 is 32 tpi (thread per inch), or 0.03125 / inch. Metric 5mm is usually 0.8mm pitch, which is 0.03150. It seems so close, but when dealing with 0.1 mm it’s not close enough. The 0.8mm pitch is just a tad coarser – equivalent to 31.75tpi. I adjusted the firmware print constant to account for the difference, and the second 20mm cube was exactly 20mm as it should be.
Now I’m printing a new z-endstop for the printer. The current z endstop is just zip tied in place, and it would move while I was leveling the x axis. This is not good, so I found some printable ones and will see what I can devise.
At least the printer is again functional, which is a great relief to me.