Warning On Humidity And Temperature

In the midst of my build, I took a weekend off. (I’m from Minnesota, so with Prince passing away, many of us dropped everything and flocked to different gatherings in Minneapolis to the celebrate his life and talents.) Two weekends ago, I pretty much had all of the hardware put together and all I had left was to put on the belts and hook up the electronics and everything was cool. This evening when I went out to the garage to resume my build, I noticed that my X and Y axis were cracked.

The bolts were not tight. Some were snug, but some bolts had 1/8 inch of wiggle room yet. My conduit is a bit thicker because of the heavy galvanization, which made a snug fit by itself. Then the temperature dipped into the low to mid 30’s (Fahrenheit) and we had a bit of rain, and yes, sometimes it snows in April (sometimes even May). Anyway…I believe the temp and humidity changes likely caused the plastic to swell a bit and with the weight of the Middle Z, it was a bit too much and caused a split.

I’m not sure what type of advice to give here. Maybe sand the parts and conduit a bit more so it’s not so tight, and maybe expose your parts to a bit of moisture before your build. Does anybody else have any advice on this topic?

Sure do, don’t use PLA or Nylon. Both are unstable and subject to deformation in heat, and pull in moisture from ambient humidity.

Parts that are used for structural purposes should always be printed out of ABS, or even better, PETG.

Neither of those are susceptible to heat or moisture. ABS isn’t as “dimensionally accurate” as PLA, but that’s where PETG comes in. As accurate as PLA, but has the heat and moisture resistance of ABS.

Happy Printing!

I prefer PET as well but it is not as rigid as PLA.

My machine, PLA, was built more than a year ago in humid San Diego, very near the ocean, and now I am even closer to the San Fransisco bay. It ran almost continually since the day it was built. I wholeheartedly do not believe such a young machine had issues with humidity. Many mornings this winter I had my machines with an under temp warning which means they experienced temps under 5C. I would warm up the bed and extruder with a heat gun to over 5C and get them started again. I have been intentionally beating up these machines looking for obvious issues.

I am not sure what could have caused your issues. What is your conduit measuring?

I live in Wisconsin, but my MPCNC has been indoors in relatively constant temperatures and humidity. I do have some 3D printed parts in PLA on a snowmobile that has been out in the elements over the past year and I haven’t noticed any effects from cold, heat or humidity.

I did a lot of sanding on my MPCNC parts and conduit to make them all fit snug but not over tight. I also didn’t tighten anything up very tight, like the parts holding the conducts or bearings. I sanded all my conduits quite a bit so they were smooth. I even chucked the conduit in a drill to spin it, first sanding then finishing it off with steel wool.


Dave you recommend sanding the conduit then? Did you do it just enough to get the galvanized coating off? What grit did you need to start out with?

I have to agree with vicious1 on this. I designed a PLA part for my job last summer and it’s held up remarkably well despite constant exposure to water and mechanical wear for extended periods of time, this includes being hand washed at least once a day. It still looks and has the dimensional tolerances as the day I printed it.

My battery died on my caliper, so I don’t have the diameter offhand. Humidity and temperature was the only thing I could think of. The bolt heads were flush on some holes, but the nuts were loose enough to fall off on a few when moving the axis around. Everything sat fine for several days, but when I got back to work on it, there were nice big splits. I attempted to use some plastic weld, but after one popped back open,i continued to print. The ones I printed were slightly more loose, but still needed to do a little sanding. I did sand the conduit on the ends, but there is still a bit of galvanized coating. The conduit at Home Depot is a lot more smooth, but I try to buy what I can from the local hardware store.

I just took the rough galvanizing off. I used some fine grit, maybe like 120 and finished off with 00 steel wool.

Don’t forget, the steel and the plastic will change size depending on the temperature, and at different rates. I don’t think the water absorption is the issue, it’s the temp swings. I had several of my pla parts split on me as well, and my router lives in an unheated barn in Ohio, where if you don’t like the weather, wait 5 minutes and it will be a different season! It was in the mid 80’s a week ago, and we almost had frost this morning. So far my pet-g parts haven’t broken.