Archive for the ‘ CG ’ Category

Modular Panel System & new garage shelving

Overview

I’ve had the idea for sometime to create a new shelving unit in our garage:  When we moved it we tossed some spare Ikea shelves against the wall.  Wasn’t the best use of space.

Rather than go looking for a pre-built solution, I figured this would be a great learning experience:  Make an entire shelving unit from scratch, including all the parts that join it together.  At first I thought I’d use my X-Carve CNC for this, but after much research and though, I instead decided to create a new 3d-printed modular corner bracket system to hold 3/4″ plywood sheets together.  While creating it, more 3d printed items were needed, so I decided to coin the whole operation the “Modular Panel System“, or MPS.  As of this authoring the system includes:

  • MPS – Corner Clamp
  • MPS – Shelf Support
  • MPS – Shim

This blog post describes the process I went through to create the MPS, how you can use them, and the shelving unit I designed to prototype it all with.

Disclamer

This is all common sense, but because lawyers:  I am not responsible in any way for any type of accident, damage, injury, death, or cost incurred from using this system:  By downloading from any source and / or making these files on any printer / fabrication system, you wave me from from any liability now or in the future.  Be smart, use at your own risk, test.

File Download

You can download all the above-mentioned MPS 3d printable files on Thingiverse HERE.

The End Results

Pretty pictures first:

shelf_closeup01_web

Closeup of Corner Clamps in action

final_shelf_web

The final shelving unit installed, using the MPS.

The 3d Printable Parts

All the 3d printable parts I printed on my C-bot.

Corner Clamps

The Corner Clamps are what hold two pieces of plywood together at 90 deg angles.  By using them in different configurations, you can create just about any rectangular-shaped structure.

Prototyping the Corner Clamps

I wanted an adjustable bracket to hold plywood together at 90 deg angles.  Since plywood can have varying width, I needed a solution that allowed for that slop.  I’d seen some interesting brackets at Maker Faire one year that did something similar, so I got to prototyping a system:  An outer L-shaped piece that could have an inner piece cinched against it, taking up any slack.  This was my initial prototype modeled in Autodesk Maya:

first_prototype

The idea is you put a nut in the outer L-shaped piece, and a screw through the end of the inner piece to hold it in place, and both sides press against the plywood.  Prototype was ‘strong like bull’ to humans, and my hope was the dense infill would provide the internal strength it needed, but I quickly broke it when torquing the held plywood.  However, it was still really strong, so I went about a redesign.

Stress testing, & Corner Clamp prototype 2

Based on where the cracks had formed in my prototype I redesigned it to use less material, but put what was there all in the right places.  From there I printed a number of them, assembled a small plywood box out of them, and started bouncing on top if it:

box_prototype box_prototype_closeup

With only one bracket per side (less that in the above shots), four of them could easily hold my bouncing 180lb frame.  I found this encouraging.

Corner Clamp Final Design

At this point, I realized I had purchased 1/2″ plywood for my above tests:  For my final shelving unit I wanted to use 3/4″ ply, to provide more strength.  Because of this I went through one more iteration, requiring me to enlarge the brackets significantly to handle the increased width of the plywood:

shelf_closeup01_web

Corner Clamp Dimensions

The below images show the overall dimensions of the parts in both inch and cm.  When I first started making them they had nice round numbers. But that very quickly went off the rails as design needs were encountered.

dimensions_cm dimensions_inch

And to help with design, when two corner clamps are holding plywood opposite one another, the gap is just about 2″:

shelf_closeup01_width

3d Printing the Corner Clamps

I print mainly in PLA:  I had used a couple different types during prototyping, and around that time I learned about MakerGeeks Raptor Series PLA : It’s supposed to be stronger than ‘normal pla’, and while I have no numbers to back up my findings, it does seem much stronger than ‘normal’ pla.  It’s more pliable, less brittle.  Based on that I bought 8 spools (enough I’d need to print the 100ish brackets, supports, and shims):

filament

And got to printing:

printint_brackets bunch_o_brackets

Corner Clamp 3d Print Settings

These are the settings I used to print them in Simplify 3D, based on the Raptor PLA using a .6mm nozzle.  If you’er using a .4mm nozzle you’ll need to compensate for the layer height and number of roof\floor\shells.

  • .6mm E3d-v6 volcano nozzle
  • 300 micron z-height
  • 90mm\sec
  • 230c extruder, 60c bed.
  • 6 floor, 6 roof, 0% infill.
  • Based on my nozzle diameter, 4 shells completely filled all the structures.
  • No raft, nor brim, no supports, did use a offset skirt.
  • Be sure to print them flat, not up on one end.  They’re designed to be printed flat, to provide maximum strength based on those layer lines.

They came to 68g for both pieces, and took about 70 min.  Which means I could print 14 per 1kg spool.  So, I’d do 7 at a time on my c-bot’s 12×12″ bed: One over night and one while I was work (monitored via OctoPrint), allowing me to print 14 (one spools worth) a day.

Other notes:

  • If during assembly you can’t get the washer or nut inserted, it’s likely your printer is over-extruding.  If it’s tuned properly, they should drop right into place with minimal to no pressure.

Corner Clamp Print Cost

I paid around 35$ per spool for the Raptor Series PLA.  For 68g of material, that works out to just about $2.40 per Corner Clamp for the raw materials.

Corner Clamp Initial Assembly

Tools required

You’ll need:

  • A philips head screwdriver.

You may want:

  • An electric drill with 1/4″ bit.

Hardware required

I purchased all of this at my local “Orchard Supply Hardware”.

Per Corner Clamp:

  • 1 Philips flat-head machine screw (or equivalent) :  1/4″-20 x 3″ – K
  • 1 Hex Nut : 1/4″-20 – K
  • 2 Flat Washers : 1/4″ – K

hardware_cornerclamp

Assembly Instructions

  • Insert a 1/4″ washer and 1/4″ hex nut into the L-shaped outer-clamp.  They should drop in easily.
    • If they’re too tight to fit, there’s a good chance your printer is over-extruding.
  • Insert a 3″ long 1/4″ machine screw screw through a 1/4″ washer, and insert that through the smaller inner-clamp.
    • If it’s too tight to easily slide through, you can easily enlarge the hole with a 1/4″ bit on an electric drill.  I used this method often…
    • Optionally you can simply thread the screw through the plastic.  This will give you more holding power (not sure if that is necessary though), but a lot more manual twisting.

assembly

  • Push the machine-screw through the larger bracket, into the nut, and continue to tighten until the tip of the screw just pokes through the nut.  That should give you ample space to later fit the plywood in both sides.

final_assembly

Shelf Supports

The Shelf Supports are used to hold up… shelves.  They are simply triangular supports that are placed under a flat piece of plywood, and screwed into the plywood being held by the Corner Clamps.

shelfsupport_side

3d Printing the Shelf Supports

These are the settings I used to print them in Simplify 3D, based on the Raptor PLA.  If you’er using a .4mm nozzle you’ll need to compensate for the layer height and number of roof\floor\shells.

  • .6mm E3d-v6 volcano nozzle
  • 450 micron z-height
  • 60mm\sec
  • 230c extruder, 60c bed.
  • 4 floor, 4 roof, 0% infill.
  • Based on my nozzle diameter, 4 shells completely filled all the structures.
  • No raft, no brim, did use an offset skirt.
  • Supports are needed:  Since these are printed flat, and not on end (to give them max strength), you’ll most likely need supports to hold one of the sides up, unless your printer is a monster at printing bridges.

Shelf Support Assembly

Tools Required

You’ll need:

  • Philips Screwdriver (magnetic head is handy).

You may want:

  • Electric drill with Philips bit (magnetic head is handy).

Hardware required

I purchased all of this at my local “Orchard Supply Hardware”.

Per Shelf Support:

  • 2 Philips Flat Head Wood Screw (or equivalent) : 10 x 3/4″ – K
  • 1 Flat Washer : 1/4″ – K

hardware_shelfsupport

Assembly Instructions

  • With the side that has the slot facing down, slide a 1/4″ washer up to the top of the support.
  • With a screw on your driver, thread it through the washer, and into the plastic slot just until it catches.
  • Just start the other screw into the other hold as well.  Note, not all supports need this screw:  I only usually have two per shelf.  They’re just there to keep the shelf from shifting one installed.
  • You can leave it in this state until final shelf assembly.

Here’s how it looks assembled in place.  Note, the screw I have in the top is not what I reference above.

shelfsupport_inside

Shims

Since plywood can have varied thickness, this can have an effect on the overall assembled shelving unit.  For Corner Clamps that hold vertical sections, I noticed they wouldn’t always touch the plwood under them, putting an unnecessary strain on their horizontal bits.  I designed these simple shims to be placed on top, or under a Corner Clamp, to help take up the slack, and help distribute the weight more evenly.

Here, you an see two shims in action, on place on top of a Corner Clamp, and the other underneath one:

shims

3d Printing the Shims

Just print them completely solid.  I made a bunch and used them liberally as needed.  You can make your own by taking what I provided and scaling it by any amount in your slicer software (presuming it has that ability)

Garage Shelf design

This section describes the shelf I designed that made use of all the above Modular Panel System pieces.

Digital Design

At the same time I was designing the Modular Panel System, I was also designing the shelf to prototype it on in my garage.  I used Autodesk Maya for this : Yes, there is probably much better software out there for this sort of thing, but I know Maya best, so it was the software of choice.

After measuring my space, I went about mockup up what I’d think the shelving unit would look like in 3d:

garage_shelving_mockup_02 garage_shelving_mockup_01

All the solid pieces are what will be assembled using the Corner Clamps, and all the gray-outline ones will be held with the Shelf Supports.

Plan Creation

After I (and the Mrs) was happy with the design, I did a manual space-fitting operation in Maya:  I laid all the panels down into shapes that match 4’x8′ pieces of plywood.  This both let me know how much plywood I had to buy, and how to make all my cuts.  Since the Mrs asked that all flat pieces were pained white on top, I also called out that in my plan:

plywood_layout_spacefit

This also led to some design changes:  I had some shelves that were just over 4′ long:  If I could make them fit 4′, then I could maximize my material.  Based on that, I deduced I needed 9 sheets of plywood.

Cutting & painting the plywood

I ended up getting 3/4″ sanded pine plywood.  Has a nice smooth pine veneer on both sides that required no sanding on my part.  9 sheets @ $30 a sheet = $450 in plywood.

Based on my above plans, I’d measure out each cut, and get to it with my circular saw:

cutting_in_progress

4+ hours later, I had this pile:

all_cuts

Which the boy and I spent a couple hours sanding all the cut sides on.  Whew…

From there, all the horizontal parts got laid out on plastic in my yard, and I rolled on the paint:

painting

A few days later the paint had dried, and final assembly could ensue…

Garage Shelf Assembly

It took a whole weekend to just get rid of all the existing stuff on that wall of the garage.  So the next weekend, with the occasional help of my wife and son, the new shelf was assembled.  Guessing it took around 6 hours, which included extra fabrication like cutting holes for electrical plugs, and other gotchas.  But for the most part it wen off without a hitch.  To do something this size, and extra pair of hands is really handy.  BTW, 3/4″ plywood is… heavy.

Special note : Before assembly, I used my stud-finder to figure out where on the wall the studs were:  On the large, back-pieces of plywood facing your, I used 3″ wood-screws to anchor them directly into the studs post-assembly.  I’m in California, earthquake territory.

final_shelf_web

Installing Corner Clamps

This was the method I used:

  • It will vary based on what section of the shelf you’re assembling,but the general process goes:
  • Make sure the machine-screw is loose enough so you can get plywood on either side of the clamp.  Or, if you’re attaching a clamp to an already assembled section, you can completely unscrew it, put the pieces on either side of the corner, and then re-thread the screw.
  • I use a screwdriver to tighten it up:  I watch the plywood on either side “suck” up into position.  While tightening, I make sure the plywood is pressed up flush against the middle of the bracket, so there’s no gaps exposed.
  • On a large section with many Corner Clamps, I’ll leave them all slightly loose until all are in place, square up the section, then tighten each one.
  • Don’t forget to add shims in where needed, before you tighten everything up, and before you put a load on the shelf.

How many Corner Clamps to use per section?

For the above shelving unit, I used two Corner Clamps to hold each side of each section.  For example, for the middle desk table by the chair, it had two clamps on the left, two on the right, but based on it’s length, three on the back.  It’s all based on the sizeof the shelf, an the load it will be holding.  If in doubt, add more.  You can always safely add more.

How tight should I make the Corner Clamp?

Tight enough, but not too tight? :)  I never actually broke one from tightening, but very quickly I got a feel for how tight I thought it should be.  If you hear it start to crack either you’ve tightened way to much, or you have a bad print.

Installing Shelf Supports

This was the method I used:

  • I first marked where the top of each Shelf Support should be.
  • With the screw just barely poking out the back, I held the Shelf Support in-place on the wall, and used my screwgun to tighten it up.

How many Shelf Supports should I use per shelf?

For the above shelving unit, I used two on either side of each shelf, and 2-3 on the back based on their length.  Again, it’s entirely based on what they’ll be holding.  If you’re going to fill them with books I may place one ever 6″.

How tight should I make the Shelf Support?

For the screw that goes into the wall, through the washer, I cinch it up with my drill until I can no longer twist the bracket back and forth.  For the screw that goes up into the piece of wood above it, this can be left nearly loose:  I tighten until the screw head his the plastic and I stop.  If you over-tighten that one, you can split the bracket.  And it doesn’t need to be tight to do its job.

Total Shelf Cost

Rough figures:

  • 9 Sheets of plywood at $30 a sheet: $270.
  • 8 rolls of filament at $35 a roll: $280.  Used nearly all of it, but that’s also counting print failures that happened as well.
  • Various nuts, bolts, washers: $30 (estimate)
  • Can of paint: $15.

Total:  Just under $600.

Final Thoughts

Was a great experience.  Was a lot of work.  Was hopefully cheaper than buying Ikea shelving :)

As of this blog post the shelving has been installed for three weeks, fully loaded with stuff, and nothing yet has broken.  It’s my hope you can uses these files, tools, and ideas to aid in your own creativity.  And  always, be safe!

New 3D Print: Maui

I’ve 3d printed a few other maps, and got a lot of enjoyment out of it:

I recently spent a week in Maui:  This gave me inspiration to do a (painted) 3d print of it on my C-Bot:

maui_painted_main

The below post is an overview of how I designed, printed, and painted it.


Getting the Mesh Data

I first headed to the web app Terrain2STL : This is the great little program that lets you download 3d-printable terrain data.

However, no matter what you set the capture-box size to, it captures the same resolution of data.  If you make the box the size of the whole island of Maui, you end up with a pretty low-resolution capture mesh, based on the detail I want to 3d print.  So the only way to get a ‘high-res’ Maui mesh is to download many small chunks, that will later be seamed together to build a high-res island.

In Terrain2STL, I set the box size (ARC seconds) to 360.  Based on that size, I can adjust the latitude & longitude values by .1 values, to offset the box by one length in either direction.  So stating at the NW corner of Maui, I started capturing squares of it’s mesh.  In total, I made 30 captures.

Assembling the Mesh Data

In Autodesk Maya, I created a new scene, and started importing in each STL that Terrain2STL generated.  Starting in the NW corner, I’d import in the next stl, line it up with the last, and repeat that process.  Which gave me something that looked like this upon completion:

maui_maya_chunks_raw

I then went through the process of deleting all the mesh that wasn’t part of the island, stretching all the edges down to make a cliff-like effect, making a base for it, and creating the text.  I also did a lot of mesh cleanup since the Terrain2STL tool isn’t perfect.  Final Maya result:

maui_maya_final

tried to boolean all the mesh together, but Maya just wouldn’t do it.  This left me frustrated, but I realized that Simplify3D (the slicer I use) allows you to import in multiple mesh:  In Maya, I made sure the pivots of all the mesh were at the origin (so they’d all show up in Simplify3D in the correct location), the transformations frozen, and I exported every individual piece as a new STL.

Slicing The Data

I imported all the stl’s into Simplify3D:  They appeared to all line up correctly.  I wanted the island to be scaled 2x on the Z axis, so I grouped all that mesh, and applied the scale transformation.

But when I sliced it, I noticed lots of little gaps between the mesh chunks:

maui_sliced

Come to find out, even though all the mesh was lined up correctly, in some cases… it just wasn’t enough for Simplify3D : This spawned a painful process of me moving pieces, re-slicing, checking gaps, etc.  But eventually I got rid of them all.  The general prints stats were:

  • 200 micron, .4mm E3D-v6 Volcano nozzle
  • Maker Geeks Gray’matter Gray PLA @ @210 deg.  Bed @ 50 deg.
  • 90 mm\sec print speed.
  • 2 shells, 4 roof\floor. 10% ‘fast hexagonal’ infill.

Took around 13 hours to complete.  Based on my 12″x12″ build platform, printed diagonally it came out to 14″ across:

maui_noPaint

Painting the model

I wanted to try a new (for me) dry-brush technique to show off the mountains.

To start, I shot the whole model in a pleasing Rust-Oleum ‘Meadow Green’ color:

maui_midPaint

After that dried, I sprayed “Maui Blue” (can’t believe I found a color that matches the medium I’m painting) onto a foam brush, and painted up the ocean.  Finally, I sprayed a light-brown onto a paper towel, and then brushed it across the mountain peaks for the final result.

maui_painted_NW maui_painted_SW

Was really pleased with the results!

New X-Carve project: Soap Dish

Working with the X-Carve has been a lot of fun.  A while back I 3d printed the “Soap Holder by piuLAB“, and figured something similar would be great to route.

Took some time in Maya generating a pleasing voronoi pattern for the top of my soap dish, which I cut out of alder, and the bottom out of some red oak:

soap_wip

Generated the gcode in MeshCAM, and use Chilipeppr to send it to the X-Carve.  Still a lot of learning:

  • For the top:
    • Used a 1/8″ 1-flute upcut endmill at 120″/min, 1/16″doc, 1/16″ stepover, Dewalt611 at 1.5, based on chipload calculators.  It seemed to cut just fine. but as you can see (if you zoom in) there is vertical banding on the Z.  After posting to the forums, the consensus is I’m cutting too fast.  So… I’ll slow it down next time 😉
    • It didn’t cut all the way though, so I had to use an x-acto to cut out the rest of the pockets.  Either I need to trick it into thinking my material is thicker, or do more tuning on my Z-steps.
  • For the bottom:
    • Used a 1/4″ 1-flute upcut endmill at 120″/min, 1/8″doc, 1/8″ stepover, Dewalt611 at about 2, based on chipload calculators.  It seemed to cut just find as well using a conventional climb cut on the rough pass, but on certain sections I got a lot of chugging.  Again, too fast.  Slower next time.

When it was done I applied some stain to the top, and sealant to both, and came up with this:

soap_final

Not too bad all things considered :)

You can download the STL’s from Thingiverse here for routing, or 3d printing.

Making The OneHundred

I always found it, humorous, when some Instagrammer got ‘X number’ of people and made some crazy post about it:  “LOVE you all, hugs and kisses”, etc.  I recently hit 100, and figured this would give me a good excuse to combine both my 3d-printing and newfound CNC-routing skills:

I’ve been wanting to do a piece that combined both 3d printing and CNC routing, some came up with idea of a routed background, with 3d printed text.  “The OneHundred” was thus created:

beautyShot

Info on the techniques used to make it:

3D Modeling

The model was created in Autodesk Maya:  I wrote a super simple tool to randomize the rotation and position of simple poly cubes that made up the background.  A 3d model of the text was generated, and Booleaned out of the background.  An stl was generated for both the background, and the text.  The piece is 12″ square, by 3/4″ deep.

3D Printing

The text model was sliced using Simplify3D, and printed on my C-Bot directly off the SD card (I recently was printing something via Octoprint, bumped the RaspberryPi, and it lost USB connection half way through a multi-hour print… don’t like that at all).  Settings:

  • Filament: Makergeeks Orange PLA
  • Extruded @ 230deg (hot for PLA, but per manufacturer recommendation), bed @ 60 deg
  • 1.2mm E3D-v6 Volcano nozzle
  • 600 micron layer heights, 1 shell, 20% fast hexagon infill.
  • Print speed is 45 mm/sec : Sounds slow, but that’s a volume of 32.4 mm3/sec extruded.  For those keeping score, a the volume extruded of a .4mm nozzle with 200 micron layer heights at 90mm/sec is 7.2 mm3/sec:  Volcano is printing 4.5x as fast, crazy.
  • Took about 1.5 hours.  (so, based on the above specs, it would have taken 6.75 hours on a ‘normal’ printer).

CNC-Routing

MeshCAM was used to generate the toolpath cut from the MDF background.  The gcode was sent via the Chilipeppr GRBL workspace.  MeshCAM settings:

  • Roughcut:
    • 1/4″ 2 flute upcut endmill
    • DOC: .0625″
    • Stepover: .125″
    • Feedrate: 60″/minute
    • Took about 1.25 hrs
  • Finish Pass:
    • 1/8″ 2 flute upcut ballnose
    • DOC: .0312″
    • Stepover: .025″
    • Feedrate 60″/minute
    • Took about 3.25 hours

The above settings are completely based on previous trial and error, and could be improved no doubt.  Things I noticed while cutting:

  • Got some chatter on the roughcut, even when I turned up my DeWalt 611 speed all the way.  Guess I was cutting to aggressive.
  • The final piece has more scalloping than I’d like:  Think I need to lessen the stepover next time.
  • Having to babysit the machine for 4.5 hours was… not fun.  But I got to read some magazines I needed to catch up on.

Final Thoughts:

Great learning experience, I’m really getting the two-cut process down using my touchplate.  Can’t wait to do more!

Exporting usable CAD data from Maya

It’s that time of year again:  Time to help my father build a new aluminum boat.  It was an enjoyable process last year:  Based on a napkin sketch with some dimensions and angles he gave me, I modeled a boat out of NURBS in Maya, and through a lot of hoop-jumping, got him some useable data:

The biggest hurdle was getting him ‘the usable data’. The process of making the boat in Maya is discussed above.  But these were the export steps:

  • Export the mesh from Maya as obj.
  • Use online converter to go from obj -> pdf.
  • Then, my father gave the pdf to a buddy who traced it in CAD, gave it dimensions, then provided that to the plasma-cutter (as a DWG).
  • Ugh.

That process was super clunky.  I’ve been using Maya since… 1998(?) and never once needed to export anything CAD related, so this was all new territory.  To make this work I need a way to generate the CAD data myself, add dimensions to it, and export out as a DWG.  There must be a better way!

Turns out there is (and probably even a super-moar-better way than what I’m about to describe, if you know CAD better than I do, which wouldn’t be much of a stretch).  In the back of my head I remembered that Maya has a DXF exporter.  I don’t think I’ve ever once used it…

Part 1: Get CAD Software & Configure

Since this process is (currently) a once-a-year thing, I didn’t want to drop a bunch of cash (any really) to get some newfangled CAD software.  I’d read a lot about FreeCAD on the interwebs, it was available for Mac, so I installed it.

Fumbling around however, I realized it neither could import DXF, or export DWG, by default.

To get the DXF importer\exporter working, I followed the instructions here.

I never could actually get the DWG export working from the software, even following the instructions here.  However, that links to a standalone “Teigha File Converter” that will batch convert a directory of DXF files to DWG.  Good enough.

Also, this data needed to be in inches, so I changed the FreeCAD prefs as such.

Part 2: Export usable CAD data from Maya

I started by exporting the unrolled mesh as DXF from Maya:  There are zero options available.  But FreeCAD happily imported it.  Immediately, problems:  Missing triangles (you must exported triangulated mesh, can’t have quads\n-gons).  As a check, I exported this same data out as DXF, and reimported it:  Empty.  I don’t think FreeCAD likes to deal with polygonal mesh.

Next, I tried exporting the unrolled NURBS surfaces as DXF:  Those came in as empty groups in FreeCAD…

Finally, I converted the trimmed NURBS to their perimeter curves, and exported the curves:  Success!  This is what is important to know:

Export NURBS Curves from Maya as usable CAD data.

Polygonal Mesh = highly questionable.  NURBS Surfaces = no go.  Note I also tested locators & ‘distanceDimShape’ nodes:  They don’t export at all.

Once I had the boat’s unrolled\flattened curves in FreeCAD, I started adding draft dimensions.  Where I encountered my next problems:

  1. The scale was off by a factor of 10:  Even though Maya was set to inches, and FreeCAD was set to inches, everything was 10x as small in FreeCAD.  I noticed this is the same issue when I 3d print in cm:  Even though I have Maya in cm, and my slicer (Simplify3D) is in cm, they come in 10x smaller.  The fix?  Scale everything up in Maya 10x before export.
  2. From the top view in FreeCAD, all the curves looked just like Maya.  But when I went into a perspective view, the curves were actually going shooting up & down in space quite a bit:  Not on a flat plane.  But they are in a flat plane in Maya.  What’s going on?  Long story short:  In Maya after you do the 10x scale up, be sure to ‘freeze transformations’ on all the curves.  In addition to the scale, I had many other translate and rotate values on the curves to get them flat on the ground plate.  It appears that FreeCAD hates this.  But once everything was frozen, the curves showed up a-ok, from all angles.

Note:  Maya uses the Autodesk ‘DirectConnect’ file translators to export (and import) DXF data.  See the docs on the 2016 version in this pdf.

Part 3 : Add Draft Dimensions

Since I was told that this needed to be provided to the plasma cutter in inches, in FreeCAD’s ‘General -> Units’ prefs, I’d set them to “US customary (in/lb)”.  Next, via FreeCAD’s ‘Draft’ toolbox, I used the ‘Dimension’ tool to provide width & height values for all the curves.  This is where I ran into the next (and as of this authoring, unresolved) issue:  FreeCAD seems to auto-change the what unit is displayed in the dimension based on the length of the part being measured.  For example, I want all the dimensions to be in inches.  But they’d report inches, feet, and yards, depending on the length of the part.  After posting this issue to the forums, I learned that if you switch the units to “Imperial decimal (in\lb)” the dimensions will always be in inch.  Problem solved.  Thanks forum peoples!

Part 4 : Export

From FreeCAD, I export all the curves and dimensions as DXF, then using the Teigha File Converter, convert that to DWG.

And…. done?  Still need confirm from the plasma cutter the DWG is valid (I have no way of testing myself), but overall, a far less clunky data-export-pipeline than last time :)