Sunday, August 31, 2014

Project CNC making parts for Project 3D Printer

Successfully installed new lead screws, new bed and new spindle mount on my CNC. Did a rough calibration of the x and y axis, manually leveled the bed and then fine tuned the calibration for all 3 axis.

My top speeds for x and y axis are fairly high but z axis is still the limiting axis. Any faster than about 14in/min and the z-axis stepper squeals and stutters – resulting in a lot of missed steps. After a bit of research I found a few issues that may be causing this:
  1. stepper motor resonance
  2. lead screw (likely to be less of a problem when I change to acme screw on z-axis)
  3. GRBL
Some good links on this issue:

It looks like I won't be able to get faster moves until I finish my rebuild of the frame and spindle mount/carriage (including swapping the z-axis lead screw with an Acme screw). I have tried tweaking the acceleration and max speeds but when I push it a bit for better performance the Z-axis seems to loose steps when retracting resulting in a number of pocket cuts being to deep.

Finally done with both sides of the Z-axis on the 3D Printer and will be cutting out the X-axis shuttle

Cutting X-axis shuttle tonight, tried this afternoon and GRBL stalled (first time ever).  Already re-cut acrylic for mount for extruder out of acrylic.  Lining up printer bed on Y-axis and designing cuts for securing drive belts on X and Y axii.

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.

Wednesday, August 20, 2014

Project CNC and Project 3D Printer - challenge using CNC to make parts for 3D Printwer

I am trying to produce some 3D (or at least 2.5D) cuts on my home-built desktop CNC router with the goal of producing better (tighter tolerances) machined parts for my 3D printer.

So far I have primarily used Inkscape (for drawing out parts), Makercam (for generating tool-paths), OpenSCAM  (for previewing cuts) and MS Notepad (to edit the Gcode).

Currently my main issue is that I cannot produce contoured cuts into material using Makercam. I am comfortable designing this type of object in Sketchup but have not been successful in generating gcode and toolpaths from my resulting diagrams.

I've worked through a good number of tutorials for Autodesk's 123D-Design and TinkerCAD, as well as FreeCAD and FreeMill but have not quite found what I want.

My main issues:
  • difficulty or inability to position parts/shapes with precision
  • learning curve too steep and/or online instruction to sparse
  • unclear how to generate gcode for router tool-paths from files generated (can do this with Autodesks 123D CNC Utility but not for other CAD programs)

My current approach:
  1. design parts in OpenSCAD export rendered files as “.stl” and save on computer (be sure to save the openSCAD file for future editing).
  2. In browser open Autodesk 123D CNCUtility
  3. Click on “Start New Project”
  4. Sign in (free to create account)
  5. Select Browse Computer
  6. Open STL file
  7. (opening an STL from your own computer seems to be more reliable and faster than opening file in 123D-Design, saving to “My Projects” in Autodesk's native format and then opening in the CNC Utility or importing directly to the CNC Utility from 123D-Design).
  8. set units to mm (bottom right corner of screen)
  9. In Bottom Menu set:
    1. Under the crossed wrench/screwdriver symbol
      1. Machine to “Shopbot Desktop”
      2. Stock (change this to what you are actually using – may need to use the “add” portion of pull down menu) – change Operation to “Cutout” (instead of “Carve”), add Margin (I change units to mm and make a 5mm margin) -  correction use "Carve" since "Cutout" will not do pockets (only outlines them).
      3. Add “Tabs” to secure part
    2. Under the Drill symbol
      1. choose tool size/type you are using and then choose “add” under “Feeds”
      2. in feeds you need to adjust feed and plunge rates – the utility states the rates in in/sec but is actually in in/min
  10. position part – snap to bottom of stock material (“underlined down arrow” in icons in upper left of screen)
  11. In the last tab on the bottom you can preview cuts
  12. Once you are satisfied with how it all looks click the far upper left file tool and select export tool paths and select folder to save them in (file will be saved with a “.g” extension). - using the "Carve" operation use the rough.g file that is generated.
  13. Preview in OpenSCAM, you will have to open folder and set to view all files (not just gcode files) and select the “.g” file. Examine result carefully – all of my files seem to begin with a 3D diagonal to the deepest point and then back up. To eliminate this open the “.g” file in a text editor and delete the “Z” portion of the first X Y Z move.
 Below is a the start of a ".g" file created from Autodesk 123D CNC Utility Online.  The highlighted area is what you need to delete to correct the file.

;Toolpaths generated with Autodesk 123D CNC Utility Online(Version 1.3.0)
;Rough Pass Settings:
; Tool parameters :
; Type : End Mill
; Name : 1/8 in Straight (13728)
; Diameter : 0.125 in
; Pass Parameters :
; StepOVer : 70
; Pass Depth : 0.05 in
; Jog Height : 0.25 in
; Feed Rate : 14 in/sec
; Plunge Rate : 14 in/sec
; Jog Rate : 14 in/sec
; Spindle Speed : 20000 rpm
G04 P1
G00X30.34Y31.6929Z-6.35 (DELETE THIS PORTION)

Un-Corrected G-Code

Corrected G-Code
Over the weekend I was able to calibrate my Desktop CNC Mill and tighten up parts of the frame and gantry to make everything stiffer and more accurate/consistent.

Saturday, August 16, 2014

The Countdown to Mokena Mini Maker Faire Begins!!!

3D-Printer Build at Present
After finding out that the Mokena MiniMaker Faire is on for September 13, 2014 I decided that I really needed to attend as an exhibitor.  So... I thought it would be great idea to exhibit the 2 things that I have been working on for most of this year: my desktop CNC machine and my 3D-printer. Both of these machines are home built home fabrication machines which is why I thought my exhibit should be called “Making Machines that Make”.

I figure that signing up for this will provide the extra motivation for me to finish up the 3D Printer and add improvements/fixes to my CNC machine – since there is a definite deadline and people will be expecting to see what I've done. In addition, it should help push me to document my progress, pitfalls, solutions etc. to help others who want to attempt these type of projects.

Wish me luck!