reprap

A few improvements

I spent the afternoon fertilizing plants and trees, then cleaning the garage and disposing of a lot of boxes that I decided I don't need anymore, then moving the outdoor furniture into the garage and actually getting the van in the garage for the winter

Then I decided to have a poke about at the new printer and fine tune a bit.

I was being completely unable to make the Z axis move reliably; one motor or the other would simply stop moving every few seconds After two rewirings (trying series and parallel) and a bunch of fiddling with the drive current, I finally thought "I should start at square one and make sure there's not a mechanical problem." I couldn't imagine that there was since it's just a smooth rod with linear bearings, and 4 nuts on threaded rod. However, I loosened the motor couplings and found that the threaded rod was actually quite bound up. Huh. I added a drop of oil on one nut and found it made a huge difference. So I tightened the couplings back up again and ran the Z axis through an full cycle, adding a drop of oil every few seconds as it moved up then back down again, then wiping off the excess with a paper towel. It moves very smoothly now and the motors no longer miss steps.

I printed out a Z axis fine tuning addition, and while printing noticed that it sure seemed like the plastic was deforming a lot. When it finished I started cleaning up a bit around the shop and 5 minutes later poked at it. It still didn't want to let go so I checked the temp, and it said zero degrees. Uh oh. I thought the print bed seemed to be giving off a lot of heat. I wiggled the connector to the thermistor and checked again, and it said 168 degrees. It's supposed to be 110. 168 after sitting for 6 to 8 minutes is pretty crazy.

I think it's a bad design idea for the thermistor on the RAMPS board to go to 0 degrees when the connection is broken. It should go to 1023 as the MakerBot does, so that you won't wind up with the print bed or hotend going crazy and overheating. Alternatively the firmware should recognize a zero degree reading as an error condition and shut down the heater.

So anyway, I rewired both the thermistor connector and the entire Z axis endstop wiring. Both have been flaky. The connectors that I used are a bit finicky about assembly, so this time I was quite careful and I think I now have a reliable connection on both.

The Z axis fine tuning gimmick works very well also, despite being slightly deformed by being printed on a stupidly hot print bed.

I did another print after all that was in place and it seems to be working pretty well now. The extruder hasn't given me any guff at all, which is great since I was extremely frustrated with it for the last 2 weeks. It seems like a complete winner right now. It's such a relief to have something that was causing so much frustration to just start working perfectly.

On another note, these Chinese linear bearings are absolutely horrid. Not only do they make horrible noises, but they're not even very accurate. They are not tight on the shaft, they wobble noticeably. The PLA printed LM8UU lookalikes from Triffid_Hunter will be an improvement. I'm going to order up some PLA and print some of those out and replace all the bearings with them. I think some of the slight wobbliness of the edges of my prints is down to the horrible bearings.
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