Sunday, 23 October 2011

Preparing the Machine – Pre-Flight Checks

This post is just a quick summary of the checks that I try to remember to carry out before each group of print runs – say at the beginning of an evening of printing.

Print Bed Medium

Firstly - if you are printing with PLA onto a non-heated acrylic bed, put down a layer of “Scotch 3M Blue Tape 2090". I can’t over-emphasize what a difference it makes having a good substrate that the build will adhere to, but will separate from the printed object at the end of the job. The surface of the blue tape tends to get a bit damaged with repeated use – be prepared to replace it periodically when the marks and scores from your earlier prints become very apparent. The frustration of having a long print job de-bond and separate part-way through is MUCH greater than the cost of a  metre or so of blue tape it needs to “refresh” the print bed surface (as I found out – the hard way!) Do yourself a favour – just do it!
Level Print Bed

Check the gap between the extruder nozzle and the print bed. I am using a feeler gauge, and aiming for about 0.3 – 0.4 mm. I’m not perfect at getting an even gap over the whole print bed, but I seem to be doing OK. My print bed levelling screws are installed screw-head-down / thread-up, and have the following components (from bottom to top):
1.       Screw Head
2.       Washer
3.       Lower Bed Plate
4.       Washer
5.       Spring
6.       Washer
7.       Levelling Nut
8.       Washer
9.       Upper Bed Plate
10.   Washer
11.   Locking Nut

I am sure there are many permutations on this theme, but this works for me.

My levelling procedure is as follows:
a)      Slacken the 4 top Locking Nuts.
b)      “Home” the machine, and adjust the Levelling Nut nearest the (0,0) corner to get the gap right at the “Home” point.
c)       Move the X-axis to near its upper limit (about 170 mm in my case), and adjust the gap at that corner.
d)      Move the Y-axis to its upper limit (again, about 170 mm in my case) and adjust the third Levelling Nut.
e)      “Home” the X-Axis, and adjust the 4th Levelling Nut.
f)       Tighten all 4 Locking Nuts
g)      Cycle through the four adjustment locations again, to make sure all is well; adjust if necessary.
h)      Move to somewhere near the middle of the print range - about (100,100) in my case - just to check the gap in the middle.

Free Movement

Check free movement of all axes – should all be quiet and free of audible “chatter”. If any of the movements is showing a bit of “stickiness” or noise, I put a couple of drops of light machine oil on the smooth rods, and move the axes through their full range a couple of times. I’m not sure how much this improves print quality – but it can’t hurt!
When the pre-flight checks are complete – you’re ready to print!

And the results:

I’m pretty pleased with what I am getting out of my machine now. Having got the machine working to my basic satisfaction, I am now concentrating on printing useful objects; that is not to say I am done with fine-tuning and calibration, but I figure I built this thing to MAKE stuff, not just for its own inherent magnificence (which is substantial!) and perfection.

In particular, I decided I need a Filament Spool so that longer prints can run continuously without me having to continuously check and untangle the filament coal lying next to my printer.

I looked at a few options on Thingiverse  before deciding on this stand  (which clips onto the top bars of a Prusa Mendel), together with this printable spool  , both by a contributor who calls himself 4ndy. Undertaking a substantial bunch of print jobs like this is a good test of whether my machine is basically up to the task. I'm still printing all the bits, but so far, I'm pretty happy with quality and progress: