Thursday, 11 February 2010

PLA on a vacuum bed

Having successfully made one Mendel z-leadscrew-base_2off as an experiment to try ABS on a vacuum bed, I decided to make the second from PLA to see how well that works on a vacuum.

Three of the corners lifted very slightly during the build (about 0.2mm) but not enough to matter except to a perfectionist.



When the object cooled it did not break the vacuum, unlike ABS. The part was still easy to remove though.

The base is flat apart from the corners and a few shallow dimples.



The quality was very good with no clean-up at all. I recently discovered a simple bug in all my builds after I moved away from 0.5mm filament. With 0.3mm and 0.4mm filament my layer height was 0.24mm and 0.32mm respectively. The problem is my z-axis only has 0.05mm resolution, so layers alternated in height, none of them being spot on. That caused the sides of my objects to not be as flat as they should be as the filament width varied from layer to layer. I now use 0.375mm filament giving a 0.3mm layer.
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13 comments:

  1. Casainho12 February 2010 at 01:33

    Heated bed is not a perfect solution :-)

    Today I printed an PLA relative big piece (about 10x10cm) with heated bed at ~70ºC and I got warp on corners...

    http://lyre.sourceforge.net/?q=content/my-first-3d-print-mini2440-enclosure

    Anyway, I am very happy with the results :-)

    Would heated room help avoiding this corner warps?

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  2. Murray12 February 2010 at 06:18

    Some commercial machines do just that. They encase the entire build environment, and heat the air, giving you a total heated environment.

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  3. nophead12 February 2010 at 09:26

    Yes a heated build chamber would allow larger objects to be made, but all the parts of the machine inside would need to be high temperature (so not self replicating) and the machine would need to be a moving head design.

    One could imaging taking the roasting bag idea a bit further on Darwin by having a bellows to form the walls of the chamber and a very elastic membrane to form the roof with the extruder nozzle going through it.

    The bellows could be frames cut from thick plastic sheet with Kapton tape making the hinges. The roof would have to very elastic, perhaps a thin sheet of latex rubber if it will handle the temperature.

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  4. Unknown12 February 2010 at 23:07

    Very nice looking print..

    Is your layer size determined by the speed you move the print head (Extrude)?

    Is this calculated in your software?

    Are you micro-stepping the XY&Z axises?

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  5. nophead12 February 2010 at 23:26

    X & Y are x10 microstepped giving 0.006mm resolution. Z is half stepped giving 0.05mm.

    The notional filament diameter is determined by the extruder flow rate expressed in volume per second divided by the head travel speed and is currently 0.375mm.

    The layer height is set by the z-axis position. I always use 0.8 times the diameter, so that is 0.3mm. The width of the filament is calculated using the area of an ellipse and is always 1.2 times the diameter when the height is 0.8, i.e. 0.45mm.

    Yes it all calculated by my software and I set Skeinforge to the same diameter and aspect ratio so it slices it to match. Nothing about the geometry is trial and error. When I started out I found that 0.8 was a good height by trial and error and never changed it since. If you make it bigger the layers bond less well. If it is smaller the minimum feature size suffers as the width increases.

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  6. aylr12 February 2010 at 23:28

    Nophead,

    After catching up on your (amazing) progress, a question occurred to me. What do you do with all the practice mendel parts you're printing? As someone running his makerbot full speed ahead printing a mendel (progress at http://bit.ly/mendelparts ), I'd be willing to buy some of the larger pieces from you.

    Thoughts?

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  7. nophead12 February 2010 at 23:34

    I am building a Mendel with them so I don't want to sell them. I haven't printed any more than the required quantity of each part.

    When the Mendel is running I will be in a position to make parts for people.

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  8. aylr12 February 2010 at 23:54

    Cool, I'm thrilled to hear they're not just for research!

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  9. nophead12 February 2010 at 23:57

    No I am killing two birds with one stone. I am making a Mendel and trying out new ideas at the same time. Fortunately nearly all the experiment results are usable apart from two big failures.

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  10. Unknown13 February 2010 at 18:18

    Thank you.. I remember maybe 2 years or more ago reading the Neat table Spec looking for a cheap one eventualy giving up.

    I need to calculate my Mendel resolution next as Im using the 0.080" belt with 0.5" pulleys.

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  11. nophead13 February 2010 at 18:30

    Belt pitch * no. teeth on pulley / steps on motor

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  12. Unknown13 February 2010 at 19:41

    LOL.. yep I was trying to avoid counting the the teeth ~ calculation with Pi.D gave 19.xxx teeth. So ended up counting them using my SMT 5 x magnifying head set and marker.

    Surprisingly nice result for imperial to metric using half stepping gives 0.1016 mm a step.

    Will this be an adequate resolution to print with or will I need to add Microstepping?

    I think it means the resolution will be:-

    0.1mm + 1.6% accumulative error.?

    requested size 0.3mm = 0.3mm * 1.016 Actual size = 0.3048mm

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  13. nophead14 February 2010 at 11:44

    I think 0.1mm resolution is fine for FFF. The main advantage of microstepping in this application is less vibration and resonance.

    There shouldn't be any cumulative error as I think the firmware handles fractional steps / mm.

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