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  1. #1
    Super Moderator curious aardvark's Avatar
    Join Date
    Jul 2014

    can you cure/ anneal pla in a food dehydrator ?

    I'll let you know tomorrow.

    I did some reading on curing pla recently.

    And while you can do it in an oven - most ovens aren't that precise at low temperatures.

    But it did say the lower the temp the longer the cure.
    Also that you could actually cure at 70c if you left it long enough.

    My excalibur food dehydrator will hit 68c - is that going to be hot enough ? No idea :-)

    So i printed a box from transparent pla, and I'm going to 'cure' it overnight and see if it:

    a) becomes any more transparent. it's got 2mm thick walls printed at a slant. But you can see your fingers through it - which is already fairly impressive.

    b) shrinks significantly in size. I do have a black pla box that is identical, that I can use as a control. So I can use if for flextual texts as well as size comparison.

    If it does work and has apositive efect on the pla - it means there's an idiot proof way to easily and cheaply cure standard pla.

    I'll also do ma temperature comparison in the future if this first test does anything noticeable.

    It's not like I'm making much jerky or snackstix at the moment, so it's about time the excalibur did some work :-)

    see you tomorrow.

  2. #2
    Super Moderator curious aardvark's Avatar
    Join Date
    Jul 2014
    well I never made it back in here saturday so the part had about 40 hours or so of curing at 68c.

    So has it changed.
    well yes it has.
    This is the box on fridey - for the record it's printed with transparent pla (I finally found an ebay supplier who had it for a sensible price) the box walls are 2mm thick and it was printer on Saffy at 150mm/s and 0.3mm layer height. Even before curing it feels really solid and just looks like something made by conventional methods.
    Considering that's a 2mm wall - it's surprisingly transparent.

    This is the same box after - approx - 40 hours at 68c.

    There has definitely been significant changes in the crystalline structure of the pla.
    It's actually MORE opaque - the opposite to what I was expecting.
    Other than that it feels the same.

    There was some shape deflection. I haven't measured it with calipers against the original model yet. But I did compare it to the original black one that's now in my mates car. And visibly there was no obvious size discrepancy.
    But the cooked one has bowed at the ends - I fettled with the colour so you can see the curvature:

    so there is obviously some size change somehwhere.
    It is a peculiar shape as it fits the hole/pocket between front seats in my mates car. So whether you'd get the same thing with a cube and straight sides - I don't know - yet :-)

    Now i should have checked this before cooking it - but I have checked it now. It is 100% water proof.
    If you've ever tried printing a 2mm shell at 150mm/s and 0.3 layer height - the last thing you would expect from 3d printing is for it to be completely impermeable to water.

    Given how good my sapphire pro2 is - I wouldn't be surprised to find that it was watertight before I cooked it. But I will testing this.

    The other thing I need to check is whether or not the glass point has changed. So I figure, fill it with boiling water from a kettle and then poke it to see if it gets soft.

    More experimentation is necessary. So I'm going to print a couple other boxes/containers out and check them for water tightness and heat resistance before and after 'dehydrating'.

    There is definitely some kind if structural change going on. I just need to p9in down exactly what and if it's of any actual use.

    Stay tuned :-)
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  3. #3
    Super Moderator curious aardvark's Avatar
    Join Date
    Jul 2014
    If you'd like to play along at home.
    This is the box set I'll be printing and curing next.

    It's a square box and a cylindrical box.

    // square and cyclindrical box


    bh=50; // box height
    bd=30; // box diameter - length of side
    wt=2; // wall thickness

    cylinder(d=bd, h=bh);
    translate([0,0,wt])cylinder(d=bd-2*wt, h=bh);
    } // end diff

    cube([bd,bd,bh], center=true);
    } // end diff
    paste that into openscad and hit f6 on your keyboard.

    I'm going with 30x30x50 and a 2mm wall thickness.
    The script generates one of each.

    You need to print 2 of each.

    I'm going with bq black pla at 205c, 150mm/s speed, 0.4mm nozzle and 0.3mm layer height.
    4 base layers and 3 top layers with 3 shells. That gives me a completely solid print with no infill.
    I'm really curious to see if the uncured parts are watertight. I mean, technically they should be. But totally watertight 2mm printed walls are fairly rare.
    I'll be printing all four boxes at the same time.

    That will actually make the likelyhood of the uncured print being watertight pretty unlikely and also really test the precision of the printer.

    This is why you never need to print a benchy. Just about every relevant print quality setting can be seen in any multi object print.

    I've gone with a cylinder and cube here to see if there's any uneven shrinkage of the material during curing.
    The cylinders particularly will show that.

    Also curious to see how accurate the sizes of each model will be.

    okay that's the setup.

    watch this space .... :-)

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