Tolerances for PLA Printing on Makerbot Replicator 2

[Jon McCoy]

Hi,

I started building my first InMoov last month - so far I'm up to the bicep... I started with the left arm, so as to work glitches out before printing the right as well. I want to complete a whole arm/shoulder first, as even at this stage there are a few parts I plan to replace/adapt/improve.

I will add at this stage that Gael's work is amazing, so that fact there are a handful of issues just shows how good his work is!

I noticed a few issues printing with 3 shells on the wrist/lower arm assembly, but with a rasp, wet/dry paper and some patience, I've been getting things to fit. Similarly, I've had really bad luck with the bicep parts not fitting at all. Some really heavy work needed, which with PLA is difficult (it's not the nicest material to work with) - I've been relying upon the glue to work it's magic with those bits. I've been printing 3 shells, at 0.3mm resolution and 30% fill. I knew there were going to be issues with the bicep, but I shrugged it off, thinking the additional shell will add strength.

I've just finished re-printing the piston (PistonanticlockV1) and piston-base (PistonbaseantiV1) at 0.2mm resolution and 2 shells, and found them lock together - the piston snapped badly when trying to separate. I'm printing at 30% still, whether this is having an effect? The other problem I've having with the piston-base is the support material being joined to the spigots and ripping material off the spigot when I can manage to break it away...

With the bicep and I suspect the torso too, I'm able to build bigger parts than those supplied - so I think I might have to adapt a few models and combine the parts for single piece printing to avoid some of the difficult joints. I'm getting some strange warping in places, but I'm, thinking that's the 3 shells causing that. A few mouse ears on parts should help I hope!

So, a few questions:

1) what resolution, shell-count and fill are others printing at?

2) has anybody with a Rep 2 tried Replicator G or the O/S firmware?

3) I've seen a number of threads and comments regarding scaling - what scaling is working for people?

4) any suggestions for the piston?!

I've abandoned the piston for now, and printing the servo top/bottom. I've got a box full of servos, so I'm really keen to get these bits done!!

Best regards

Jon

PS One of my big pet peeves with MakerBot slicer, is it completely ignoring material widths for the outer shells. A 10mm square would be 10.3mm for 0.3mm printing, 10.2 for 0.2mm and so on. It appears to lay the plastic on the actual border line, so that 50% of the width of the materials extends outward. Whilst you can achieve higher tolerances when printing at lower resolutions, it does seem to make lower resolutions unnecessarily oversized.

[Kevin Watters]

Hi Jon,

  I've been printing an InMoov in PLA on a makerbot rep 2 since late November 2013.  I have pretty much everything printed out and assembled.  I am on my second print, the first one was really just to learn how to assemble the thing, the second one I hope will be better all around now that I've put one together already.  I have noticed a bunch of things in that process.  First to answer your question..  I've printed a lot of it with 2 shells, some of it with 3 shells.  I've printed some items with 10%, 25% and 50% infills.  

  As you noted, there is some swelling on the prints.  It seems to be worse as you increase the number of shells.  For example,  I've printed things out with 2 shells and they are a tight fit, then with 3 shells they're almost too difficult to put together.  That being said,  the Dremel and some grinding bits have become my best friend in getting the peices to fit properly.

  There are some particular issues that I faced, as you mentioned, the robot parts for the forearm are a very difficult fit, i'm not sure if people have the same issues with ABS prints.  I've been using PVC all purpose cement to glue the PLA together and that seems to hold very nicely.  (Same stuff you use on the PVC drain pipes under your sink.)  

  It sounds like you havent' gotten to it yet, but the gear boxes for the shoulder really need a lot of work when you print them out.  

I've found that you can scale objects when you print them a bit to help them fit together so you don't have that much sanding to do...  

  In particular the worst fitting part that I've found is the  PivWormV2.stl  This is a very important part, but it needs a ton of sanding to start fitting into the gear box properly.  If you need a lot of sanding on a part, I print them out with a larger number of shells, so that I don't break through the surface when I'm sanding them down.  

  I found that if you scale the PivWormV2.stl to 95% of it's original size in the X and Y plane only (retain the height of the part at 100%) that the printed version doesn't require so much sanding.  I think it's important to keep the height of the part so that the gears still line up in the gear box.

  anyway,  I hope this helps! 

-Kevin