Monday, August 25, 2014

Project 3D Printer - Challenges with 3D Printer Continue

Challenges continue with cutting out z-axis pieces for 3D Printer Build.

Autodesk's CNC Utility issues:
  • Step Over is opposite in rough cut and finishing
    • 25% Step Over in rough cut = 25% of width of present cut overlaps last cut
    • 25% Step Over in finish cut = 75% of width present cut overlaps last cut
  • Feed rates
    • in inch/sec but actually inch/minute
  • Initial positioning includes cutting diagonal swath through material
    • manually edit out
Current cuts – contoured portions are not cut down to depth or the width that they need to be (about 1mm short for each dimension), even after x-axis finishing cuts (the finishing cut did increase dimensions somewhat but still not to design dimensions).

14.11 after x-finish 13.54mm before (design goal was 15mm, so still a bit small)
7.25 after x-axis finish cut, 6.19 prior to cut (still short of design of 7.5mm)

Profile cuts (all the way through) and “Cut Out” instead of “Carve” cuts (for straight right angle z-axis cuts) seem to be right on.  I really do not know what the problem is but time is short.

Well...its back to MakerCAM for now and I'll have to stick to square pockets instead of contoured ones (I could do nested pockets but I expect that I'd run into others issues if I tried that).

My main issue with Inkscape to MakerCAM is that shape dimensions in Inkscape end up slightly smaller when imported to MakerCAM (and I don't mean the settings for SVG import resolution – I already encountered and found the simple solution to that issue – change to 90px/inch). When I go the alternate route of OpenSCAD to Autodesk's CNC utility – a cut out 9mm square is actually 9mm. The result is that I have to run test cut dimensions to find correct dimensions for what I design in Inkscape. Does anyone else have this problem??? For me, at least, this seems to be an issue with the SVG file since the cut depths that I enter into MakerCAM do measure out as what I entered in.

On the bright side, at least I already have the Inkscape files for the parts I'm cutting out (since I made and used them to cut the same parts from wood). I still need to re-do all the tool paths in MakerCAM.

It's taken me awhile to get the tool paths correct - first issue was that I had forgotten to include pockets for the  X-axis guide rods, then I did not comprehensively preview an operation in OpenSCAM and missed the drill holes being set to 0.75" instead of 0.5" (extra stress on the Z-axis stepper and burned off half the collar on my endmill).

Test Cuts Autodesk CNC Utility

Test Concave Cut Autodesk CNC Utility

Test Cut Size Check With Inkscape/MakerCAM

This is what I'm aiming for

First Test from Autodesk CNC Utility
A few of my trials from Inkscape/MakerCAM
 After all this work it seems the bed of my CNC is not level, like it used to be - depth of cuts is not consistent across pieces.  Since I need to put a new sacrificial bed on the CNC and add some additional anchor points to hold it down better - I figured that I'd also finally change out my Lead Screw's.  I've had new Acme Thread (single start) 1/4" lead screws for well over a month but put off installing them. 
Old Lead Screws with Anti-Backlash

New Lead Screw- gluing Anti-Backlash
 I decided to change out my lead screws so that I can speed up my cutting procedures - currently the top speed that my CNC travels is 14"/min.  This is because the threaded rods I was using for lead screws had 24 turns per inch - my new acme screws are 14 turns per inch.  My GBRL settings for the threaded rods were about 200 steps per mm - potentially very high precision (current configuration not stiff enough though) but this meant that I could max out stepper speed fairly quickly.  In the future - if I can come across some reasonably priced multi - start acme screws I will have to pick them up.

After I get these screws in tonight, along with a new bed - I'll get the machine re-calibrated for the X and Y axis then route the bed to make it level.