Thursday, 31 March 2011

My repstrap tuning, and Prusa Mendel parts printing

The first thing I had to do is setup a machine profile. This defines how many steps are required to move 1mm in each of the 3 axis. In This case 320 steps moved things 1mm and was the same on all axis.
  
The next thing to work out is the extrusion rates. I calculated the speed the machine moves at 3.33 mm/sec.

NB this is incredibly slow! This is because it takes 320 steps per mm, the final machine the axis are driven by belts and one step move approximately 1mm

So I moved the Z axis to it a high point and set it to extrude for 10 seconds. The aim being to get as close as I can to extruding 33.3mm of filament.

The following is a picture of some of the extrusion speed testing. Pick a extrusion rate, extrude for 10 seconds, measure the length, to long and shorten the rate and try again and if its to short increase the extrude rate and try again. 


Once your happy set this rate into Skeinforge speed settings.

You also need to set your temperature settings, these are different for ABS and PLA. The temperature information can be found on the pages I have linked to.


NB ABS sticks like mad to acrylic, I was using a chisel to remove parts from it.


I started with ABS as it was all I could get in a hurry.  I have since switched to PLA, why? mostly because the fumes given off by ABS are not fun, and it is a oil based plastic.  PLA is much nicer and is corn starch based and is biodegradable.


The next step in tuning is to try and get a test cube to come out like a cube.
this can be found here,


My test cube came out brilliant! But did take over an hour... So I skipped the rest of the tests as I wanted to try something else more fun.

I had a look on thingiverse.com and found the Stanford Bunny

He was huge, so I scaled him down a lot and hit print.
To my surprise I got the following (after a little bit of clean up)


I did a little more tweaking and learning to use the software and began to print Prusa medel parts

The large piece took 6 hours to print! This was followed in time by the following parts

Here I ran into a problem, dispute the ABS sicking like mad to the acrylic, it still started to lift up in the corners badly on large prints.

After lots of trial and error, I switched to PLA which doesnt curl up anything like as much.
I also switched to a new build surface, 3M Blue masking tape. This enabled me to print the larger parts (a heated build platform will also get around this issue)


This is one of the last medal pieces, it took 16 hours to print!!

I now have a full set to Prusa Mendel printed parts, though some of them are in ABS and some are in PLA.

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