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As promised, the video of the roughing + finish operation on the finderscope-ring drilling jig.

Jari shot some videos during the milling of the beaver-tail bulb. They now appear on YouTube.

For a mostly home-built cnc minimill of this size, this is pretty ‘hard core’ stuff…

As a first serious test-run for our now servo-controlled cnc mill we decided to make an IOM bulb out of steel. It ends up a bit bigger in volume when made out of steel compared to lead, but the difference isn’t huge. Making it with a cnc mill allows designing almost any reasonable 3D shape you can imagine.

The mill worked fine during the whole run, about 3 hours of rough-cutting and 1.5 hours of finish cutting, but there was a slight operator error in the setup which means this bulb will likely not sail. The following error stayed low throughout the run, and the servos weren’t even hot to the touch after the workout.

We used adaptive roughing paths and then a simple parallel finish path. Both operations are cut with an 8 mm flat cutter. The adaptive paths did seem to work, and on this size machine they are really handy since a slight over-cut will likely stall the spindle motor (1.5 kW and 5000 rpm, small by big-iron cnc-standards).

0:00 rough cutting begins. The stock is a 45 mm diameter steel bar, face-milled down on the sides so it can be clamped to the machine vises. Note the cutting feedrate which is 500mm/min and ‘high-feed’ in the (x,y)-plane when the tool is positioned for the next cut. When the tool lifts up to the clearance plane it does normal G0 (rapid) moves.
1:34 more rough cutting on the other end of the bulb.
1:58 still pics of the rough-pass almost ready
2:15 view of emc2 while cutting. Note pyVCP bar widgets showing commanded PWM to servo motors.
4:29 beginning of parallel finish cut. programmed feed 1500 mm/min which is attained briefly in the middle of the move.
5:00 more finish cutting, about 2/3 done.
5:50 another view of emc2 and the pyVCP panel. Note Y and Z motors working to position the tool. The following error for each axis is also shown.
6:15 still pictures of the finished bulb (well, one half of it anyway). Note at the front of the bulb we tried to run the program at 150% of programmed feedrate, but that didn’t work at all and resulted in a poor surface finish. We did try to slow down also from 100% but that didn’t improve the surface much.

Google video doesn’t really do justice to the nice 640×480 video and 5 Mpix still-photos that come out of the N95, so if you’ve bothered to read this far, here’s the original 100 Mb mp4 (I hope I don’t exceed my bandwidth limit).

A fast but unstable way of radio-sailing.

Some promising results yesterday with trying to stretch DNA molecules. The molecule is attached between two microspheres, and we are actively moving the smaller sphere while the force acting on the bigger sphere is being measured. The image and video shows the view through a 100x microscope objective on the optical tweezers instrument I am building. Towards the end you can see the construct breaking in two stages, so that probably means there were two molecules of DNA between the beads and not one as intended. This is a control experiment and will hopefully set the stage for bigger and better things to come…

Jari upgraded the spindle motor to 1.5 kW and shot a few more milling videos.

movie 1:

movie 2:
movie 3:
movie 4:
Finished parts:

Jari has made an enclosure around our cnc-mill, and that allows us to use a liberal amount of flood coolant. Here’s a short video with some tests in aluminium.

Before you run to the shop and get an Opti-BF20 of your own please remember that our machine is seriously modified. We put a new table on it with linear guides, we’re using ballscrews, and the stock spindle and spindle motor are replaced.

Most conventional CAM algorithms are geometry-based. They create toolpaths that are usually parallel to either the coordinate axes (’zigzag’-paths) or to the part contour (contour-parallel, or spiral paths). One problem with this geometry-based stuff is that you don’t take into account the cutting forces. The algorithm has no idea about how much material is removed while the tool is moving. A quick patch is to run a cutting simulation after the path is created and adapt the feedrate for constant material removal rate (MRR).

Another option is to base the toolpath algorithm on a stock model. Then you know the shape of the stock at all times and you can control the MRR or cutter engagement angle. To quickly test how this could work I made a small test in matlab.

The cutter (green circle) is moved around by some rules, and cut’s the red pixels as it travels over them. Cut pixels are drawn in blue. The cutter is moved around in discrete steps in some direction, and you’re only allowed to cut a certain number of pixels per move. The tricky part is coming up with the rules for our ‘lawn-mower’ robot. Now I’m using a simple idea: If the past move was made at an angle alfa, try to take the next step in the same direction, but if that’s not possible increase alfa until the MRR goes down to some preset value.

This idea will need refinement so that the robot can cope with walls, can do cutting in only one direction (climb vs. conventional) etc. etc., but this seems like a promising and fun start!

I’ve worked on steering our Optical Tweezers instrument using Acousto Optical Deflectors. Here’s an example of what it can do. We’re trapping four 1 um silica microspheres in water using a single 1064nm laser that is time shared between the beads (it hops between them at a fast rate). Then we can program the AODs to steer the beads around in whatever patterns we want.

Last day at model-expo, my first try at using google video!

First the new Futaba 2.4GHz radios. There are two wheel-model radios already on the market, and I was told two stick-radios (a 3-channel and a 6-channel model) will be in stores very shortly. Priced close to the Spektrum offerings at around 200 eur. Then to the pool for some scale-models. A fast electric racing boat after that, followed by some aerobatics, and some car-racing at the end.

(the noise from the fans was not as bad as it sounds in this video…)Then MicroMagic sailing! We had a lot of fun and a fair bit of spectators for each of our sailing shows, about 15-20 minutes every hour. You can see that the two fans we brought with us don’t cover all of the pool, and that the wind speed is quite fast near the fans and lighter downwind. More boats and more fans for next year!

When someone interested came to talk to us it was so easy just to point to the many MicroMagic vendors and say ‘there, that’s where you get it and it costs around 250eur with everything (boat, radio) included.’ This relates to what I wrote earlier, I believe the success of the micromagic largely depends on it being cheap and easily available.

So, for the IOM class to experience continued growth I think it would be a great help if a competitive boat would be mass-produced (in ABS or similar). I know Graham B in the UK and John E in the USA have had some plans… but nothing seems to have materialized yet. Newcomers to our sport don’t want to send 1000 or more euros overseas and then wait 3-6 months for a (hand made) boat, they want their new boat now, cheaply, and from the local hobby store.

Thanks to Jari for lending me his MiniDV camera.