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Slicing up the 3D object

by Ivan Sentch 1. October 2013 14:55

I've had a couple ask about this so here's what I've found (I don't do this professionally so this is just what I've discovered by playing around)

First off the object needs some depth, 3DS Max has a shell tool that you can specify a inner or outer shell depth (I think this tool effectively clones the object, scales it out or in then applies edges or sides) anyway it's pretty easy so long as you have a clean object with all the polygon normals facing the same way (normals:

3DS Max has a slice tool which is a plane you can move and/or rotate then create a slice, I usually slice from the middle out in one direction (top/bottom, left/right or front/back) in 105mm jumps as below 

Then once I've done all the slices along an axis they need to be detached and capped (use the element selection tool to select and detach a section and use the border selection tool to select and the cap tool to cap the open faces)

Sometimes this can get confused, this is usually because there is more than one angle in the open faces (i.e. if you've sliced multiple separate elements at once or if you slice more than one axis without capping it) but what it tries to do is cap both angles at once but it is never right (see below) 

This cannot be printed like this so you will need to fix it, to do this use the polygon selection tool to select the incorrect face and delete.

Then using the edge selection tool select the 2x end most edges on one angle then use the bridge tool to make a polygon from the 2x edges

Now using the border selection tool again select the edge (which now will be constrained by the polygon you created) and cap

So using this theory do another axis (remember to cap all the sections before moving onto the last axis or you'll have the issue I raised above)

Then the last axis

Now you've got all the sections which you need to rotate (to an appropriate angle that can be printed), align as many as you can into single print jobs, export, re-align (I use ReplicatorG to "center" and "put on platform" - this is so it's centered for the printer otherwise it'll try to go 2km to the left and break), convert it to GCode (I use skeinforge, takes about 2 hours but that's ok) and it's ready to print

(You may have noticed I've done the dash, I'll start printing that soon)


3D Printing | Design

Creating the framework

by Ivan Sentch 9. February 2013 13:50

The 3D design tool I'm using is Autodesk 3DS Max 2011, this has the standard feature of creating cross sections of your object which is how I make the framework the panels sit on.

I first give the object depth so the printed sections will sit flush on the framework, then create the sections, no real science with this just as many as I feel are needed to keep it true but i do offset their positions so they do not line up with where my extruded edges will be (otherwise I'll need to manually take more off the outline in order for the sections to sit flush)

I then export the shapes to another program (I can't seem to find a print to scale option in 3DS max so I use another very simple CAD program called AllyCad) and print them out to scale (normal printer that is). With these I transfer the shape to MDF and cut it out (you could use a 2 axis CNC machine for this but a jigsaw works just fine)

These are then glued / screwed together using square blocks to keep it square.

There's a good youtube video about this here:


Body | Design

3D Printing, what I've found so far

by Ivan Sentch 5. February 2013 08:55

I've got a Solidoodle 2 3D printer which has a build envelope of 150 x 150 x 150mm so the first thing I did is cut up the bonnet into to 150mm cubes (I should point out I didn't have the printer at this point so I couldn't test any of this), gave it some extruded sides for rigidity, first mistake. The printer can't print on thin air so I would have to build up the top extruded side at 45° or beter yet cut the squares at 45°. so I cut all the squares diagonally and then gave them 1.75mm depth, second mistake. 3DS Max 2011 (which is the design tool I'm using) gives depth along each segment's normal (imaginary line perpendicular to the average face direction) instead of uniformly in one direction (x, y or z axis). So start again, give the bonnet depth first, then cut, then make the extruded sides (and give them depth as well).

Once all this was done (just the bonnet so far) I had to rotate each segment for printing, export and convert into gcode, given the trouble I had creating the segment I only did one and waited for my printer to arrive. When it did it was pretty straight forward, plug the USB key in, use the software provided to turn the exported .stl file into gcode and print!

The first print worked fine except the printer didn't handle the 45° angle very well, it printed it but it had trouble and it wasn't true (was actually a bit saggy). I need all sides to be true or when I attach them all together it will be misshapen. So start again!! This time I gave it 5mm depth, cut it into 150mm squares and only extruded the sides by another 5mm (as being 5mm thick it's sturdy enough, the sides are only to enhance the accuracy when I stick them together, also it's much much much easier and faster doing it this way as well).

Another problem, converting it to gcode creates rails the print sits on (used to keep it stuck to the print bed as as it cools it wants to distort) and as I've used the full build envelope it looses the sides, also the bed is heated from the middle so the outsides are cooler and the edges curl up too much, but the last straw was the printer got to 109mm, threw errors and wouldn't go any higher. I'm sure there was just some adjustment required to fix this but with the rail and the warping I decided to start yet again, this time I did the boot as I had had enough of the bonnet by now.

Something I found out along the way was you can spray hairspray onto the bed to help keep the print stuck to the bed, also (which I have yet to try) use a pane of glass (sprayed with hairspray) on top of the bed (kept in place by paper binder clips).

The final solution that worked:

1) Give the object (boot) 5mm depth

2) Cut it into 105mm squares

3) Extrude the sides by 5mm

4) Export to .STL, convert to gcode (using the rail settings)

5) Heat the bed up to 95°

6) Spray the bed with hairspray

This works pretty well, occasionally the edges still peel of the bed but most of the bottom is still straight so there's enough to stick them together accurately.


Body | 3D Printing | Design

First blog

by Ivan Sentch 1. February 2013 11:51

This will be a scratch built replica of a 1961 series II Aston Martin DB4, fiberglass body, space frame chassis using a donor car's bits (engine, drive train, suspension, etc).

The fiberglass body I will make by first making a plug, taking a mold from that plug and casting the body from that mold.

The donor car will be (at this stage at least, I may change my mind closer to the time of needing it) a Nissan Skyline GTS25T which is pretty cheap (about $4000 NZD if you're looking hard enough), fast (250Hp at 7psi and intercooled standard, no internal changes required to run 12psi), it's wheel track will fit the body (which is important as it's not easy to certify suspension modifications in New Zealand), and I'm already using this engine in my 250 GTO replica I built a while ago so I've got spare parts when I change that to a BMW V12 (much much later)

Once I've got the above I'll build the space frame chassis (can't design this until I can measure the suspension), I'll be tacking this together myself and then handing it off to a professional welder to complete.

Then attach the body, paint, interior, etc.


Body | Chassis | Design | Donor Bits | Interior | Miscellaneous