Saturday, March 15, 2014

Reducing Warped Prints With The Printrbot Simple

Update: I eliminated the warping issue by installing a heated bed. Details here.

I was recently pondering extending the X axis on my Simple, using the extensible X axis brackets. I decided to try printing a small, simple project enclosure first, since I had really only printed fairly tall things with small bases. The only previous print I had tried that was fairly wide was an 808 camera mount for a friend's drone and it had warped badly. I had been able to straighten it by softening it under some really hot water, but I wanted to understand how big a problem it was.

I printed a box, and it came out looking like this. Ouch. Off to do some research.

Warping is caused by uneven cooling of the part. Objects longer in one direction than the other tend to do it more, and it's worse as you add layers. ABS apparently does it a whole lot more than the PLA my Simple uses, but I wanted to figure out how to fix it. A very good Makerbot blog post describes some common solutions, and variations of them worked for me.

I print in my unheated basement, which runs a pretty constant 58 degrees F. I think this contributes greatly to the problem.

The Printrbot Simple is a very cool piece of machinery, but you do sacrifice some features to have a lower cost. One of the biggest ones is a heated print bed, which most people indicate solve the problem completely in PLA and is necessary in ABS. There is not yet a kit for the Printrbot Simple to add one.

Here's what worked well for me:

1) Clean your blue tape on the bed with rubbing alcohol after you apply it, and then don't touch it. This removes wax and oils that your skin leaves behind that prevent sticking.

2) Turn on "Brim" in Slic3r, maybe 5mm around. This increases the surface area adhering your part to the bed, reducing the odds it will curl off the bed.

These two things alone helped a lot, but I still had a small amount of curling.

3) Want it to really stick? Tell Slic3r to print a "raft" of perhaps 5-8 layers. This works very well but requires you to cut or sand the raft off your part. The raft is sacrificial support material that warps instead of your part. This worked, but would be a hassle, so I kept tinkering. Here's what the raft material looked like:

But hey, it's a lot flatter. I'll keep it in mind for parts I can't print flat any other way. A lot of guys on the forums sneer at rafts, saying the are obsolete, no one uses them, they are old school. Those guys have printed heat beds. My Simple does not. So if I need to print a raft occasionally, so be it.

4) Make a "slow" saved settings for Slic3r that you use when you want to minimize warps. I set it to print at 10 mm/sec, 1/3 the speed the Printrbot usually prints at. Sure, it takes a while. I value print quality over speed.

5) If your printer is in a chilly environment, you might consider enclosing it. I found that simply parking a large cardboard box over the printer, with a hole cut for the filament to enter, caused the air in the box to rise 20 degrees F to 80F. With that, my warping went away entirely with no raft. I did use a 5mm brim.

It stuck to the bed so well I had to use a putty knife to pry it off. Victory. I think that the box causes the print to stay at a more even temperature, reduces the temperature delta from the bottom of the print to the top layers, and causes the whole thing to cool more evenly.

Please consider the risk of fire if you choose to enclose your printer. I used the cardboard as an experiment only, and will be replacing it with something more fire resistant. Your safety is your own responsibility.