The cutter-location points are calculated by bringing the cutter into contact with the vertices of the triangle (green cl-points), the edges (red cl-points), and the facet (blue cl-points). Then the cl-point with the highest Z-value is selected as the final cutter location. At the white points we did not make contact with the triangle at all.

If you look closely enough, all surfaces in the world are made of triangles, even Tux:

Due to compression, the video might not show enough detail, so here’s a screenshot:

I wonder if anyone is still interested in this stuff? Given enough time I would like to develop waterline-paths and an octree-based cutting simulator also. It would help if these algorithms were incorporated in a CAD-program, or someone would develop a GUI.

1: Motor power U
2: Motor power V
3: Motor power W
4: Hall sensor +5V
5: Hall sensor U
6: Hall sensor V
7: Hall sensor W
8: Hall sensor GND
9: Encoder +5V
10: Encoder A
11: Encoder B
12: Encoder Z
13: Encoder GND
14: +Limit switch Common
15: +Limit switch N.O.
16: +Limit switch N.C.
17: -Limit/Home switch Common
18: -Limit/Home switch N.O.
19: -Limit/Home switch N.C.

The motor currents go through the AMP-connecor, everything else through the 25-pin D-connector.

I’m glad the lathe only has two servos (and a spindle), I would go mad with a 5-axis machine…

We’ve done the CAD design, CAM-toolpaths, and CNC-machining for a set of RG65 model yacht (looks roughly like this) fin and rudder moulds. They will be shipped to the customer on Monday.

From time to time I get enquiries about making moulds like this, for fins, rudders, bulbs, etc., from people around the world. Usually by people who’ve gone to a professional mould-shop or cnc-workshop with their drawings, and suffered a bit of sticker-shock when they’ve seen the quote. For this set of moulds we asked 500 euros, which is not a lot I claim. Production and delivery in one week or less after the final CAD-drawings were available.

If you’re interested in CNC-cut moulds in aluminium or steel, please send your ideas, preferably a CAD drawing, and I’ll send you a rough quote. Keep in mind that our machine has a working XY envelope of ca 500×200 mm, so no single parts can be bigger than this. There are lots of examples of what we do in this blog, you might like: bumper mould (2010 Jan), Rudder mould (2009 Dec), IOM MDF plug (2009 Feb), Microscope part (2009 Sep), IOM Fin moulds (2008 Jun), Telescope rings (2008 May).

Drilled four holes for AMP-connectors and used a hole-punch to make cut-outs for eight 25-pin D-connectors. The four motor-connectors will provide 3-phase power to the spindle-servo, the X- and Z-servos, and a high-speed live-tool spindle. The servos have three Hall-signals and three(single-ended) or six(differential) encoder signals which will enter the cabinet through the D-connectors. I’m using these since I’ll use 25-pin printer-cables for the Hall/Encoder signals. There are eight D-connectors just to provide some room for expansion. Three will be in immediate use for the three servos, one for limit/home switches, and one or two will be used for a jog-pendant.  That still leaves three 25-pin connectors unused (tool-changer? tool-length probe? etc.)

Also mounted the breakout-boards inside:

In 2006 I made optoisolator cards for the cnc-mill project, but now with the lathe I am using servo-drives and a VFD which mostly already have optoisolated inputs, so I will use these very simple breakout boards instead. There are two pitch-standards for the screw-terminals, an imperial one with a pitch of 5.08 mm (i.e. 0.2 inches), and a metric one with 5.0 mm pitch. These boards are for 5.0 mm.

Pads logic and layout files: 2010_01_16_m5i20_breakout_board

Etch-mask (PDF): etch-mask

I put together this small computer which will be used to control the lathe. The components for this kind of box are quite inexpensive:
D945GCLF2 motherboard including 1.6 GHz Atom330 CPU, 76 eur
Codegen MX31 case including 420W PSU, 46 eur
2Gb DDR2 memory stick, 46eur
Samsung 320Gb HDD, 44eur
Labtec keyaboard + mouse, 17eur

Total:  229 eur (no display) parts from jimms-pc and verkkokauppa.com

The motherboard has one PCI-slot for a Mesa 5I20 FPGA-card which provides 72 digital I/O pins for real-time control.

Here is the D945GCLF2 motherboard. The CPU doesn’t need a fan, but there is a small fan for the PCI-controller(?).

Realtime performace should be OK, I was getting about 10 us of jitter for a 1 ms thread.

Most of the electronics I’ve ordered for the lathe has arrived by now. Still waiting for the servo-drive for the main spindle.

Bottom left are three switched-mode power supplies: 5V 3.5A (logic etc), 12V 3.3A (brushless amps, E-stop chain, etc), 24V 1.3A (spindle brake)

Bottom right are two Chinese 350W 48VDC 7.3A power supplies for the X- and Z- servos. Bought on e-bay from one of the Chinese sellers that has free worldwide shipping, and these were not caught by the local customs, so I paid around 28 euros/supply!

Mid row: on the left a Siemens Micromaster 420 0.37 kW VFD which will be used for a future live-tool spindle, and on the right two pico-systems brushless servo-amps.

Top: limit switches, Mesa 5I20 PCI-card, 180W Brushless servos for X and Z, CUI encoders, Amphenol connectors.

$199 from Mesa electronics