Raftless Printing with PLA

I’m no expert at 3D printing, but through a lot of trial and error I’ve discovered a few nuggets of information that I wish I’d known a few months ago.

A few weeks ago I said I was chasing a raftless print. I’ve finally got it, at least with PLA and ABS, printing Seej bloxen.

This comparison isn’t entirely fair, since the bloxen are sourced from different models, but the difference between a hot, rafted print on the left and a cool, raftless print on the right should be pretty clear. Both of these are printed from the same roll of 1.75mm PLA.


Here’s what I’ve learned.

PLA likes a cool build platform, somewhere around 45° C: My MakerBot Replicator ships with a heated build platform, and ABS plastic seems to stick nicely around 115°.

When I first started printing with PLA I just assumed it was more or less like ABS. When prints started shifting off the platform I kept cranking up the temperature on the HBP, eventually resorting to elaborate raft structures with painters’ tape.

It never occurred to me that lowering the HBP platform temperature was the solution.

Changing the build temperature in gCode is easy: just find a line that looks like:

M109 S100 T0 (set HBP temperature)

And change S100 to S45. This assumes that you’re using ReplicatorG to generate your gCode.

There’s one other change that seems to be helping: print a nice, gooey first layer of PLA, and then back off the printing temperature to maintain the model’s integrity through the rest of the print. The gCode for this isn’t much more complicated, but you have to get it in the right place. First, set the extruder temperature at the beginning of the print, close to the top of the gCode:

M104 S240 T0 (set extruder temperature)

Change 240 (or whatever it is in your gCode) to 210.

The last step is to find the point in the gCode where the first layer stops and the second layer begins, and back off the temperature a bit.

In the other two instances there are existing M codes that tell the machine to wait for the extruder or bed to reach the specified temperature before proceeding. You’ll have to put those codes in yourself for this line.

Find the first example of:

M73 P1 (display progress)

and add these lines after the next <layer> tag:

(*custom gCode here*)
M104 S190 T1 (set extruder temperature)
M6 T1 (wait for toolhead, and HBP to reach temperature)
(*end custom gCode*)

That should drop the extruder temperature down to 190° and then resume printing. The delay can be a little unexpected the first time your Replicator just seems to stop printing abruptly, but then your forebrain will kick in and you’ll realize it’s just doing what you told it to do.

The usual warnings about bricking your Replicator or burning down your apartment building apply. Use this code at your own risk, and you should probably own couple of fire extinguishers anyways.

5 thoughts on “Raftless Printing with PLA

  1. brucethehoon

    I’m sorry if I’m dim, but I can’t determine what surface you ended up printing on. I print on my replicator with PLA at 205 regularly on blue painters tape. Are you getting it to stick to polyimide?

    Reply
  2. willstone3

    thanks for posting this. i used to get phenomenal prints on regular masking tape and on blue painter’s tape (it would adhere very well with no warping) – but for some reason I’ve been having a lot of trouble.

    I’m wondering if in fact it’s due to the new shipment of PLA having excess moisture. I was told by a mat. sci. eng. that it often happens to him and is the culprit for warping etc. how can I rule this out? any thoughts?

    Reply
    1. zheng3

      No idea about moisture, but that’s a promising lead. Try putting a PLA sample in a bag of dessicant for a week (white rice) and compare it to a control group with the same print, maybe?

      I’ve been having stellar results lately at HBP 45° and a print temp of 220°. But I’m also printing really small stuff. I’m printing on really beat-up Kapton, but I’m also printing relatively small things.

      Reply
      1. willstone3

        rubbing alcohol on the tape seems to have fixed the slipping issue. now to solve the 10 other issues that all appeared over night… (mostly that it’s not extruding enough material?)

        i plan to post a lot of details for skeinforge settings // other tests // etc on my blog uselesspuzzles.blogspot.com

        i’d love to share notes re: 1.75mm pla skeinforge 50 settings, there are so few resources online (that I can find). see some ideas on my post here:
        https://groups.google.com/d/msg/makerbot/w5-ENtVne2s/U1U9a7KcBk0J

        Reply

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