Tuesday, 8 May 2007

Successful milling

The new metalwork did the trick. It completely solved the snatching problem I had previously. I managed to mill this test shape out of 2.5mm polystyrene, at least that is what I thought it was. I found a site: www.tempatron.co.uk/weld_rods.htm which describes how to identify plastic by setting fire to it and the closest match is ABS, so it may in fact be ABS.

As you can see it has nice clean edges and it measures 34.07mm by 60.02mm by my cheap electronic calipers so is pretty accurate.

Getting the feed rate and cut depth right took a few attempts. The problem was that the plastic kept melting as you can see here :-

I found that with a cut depth of 0.5mm I could only feed at about 0.2mm per second to prevent melting. Reducing the cut depth to 0.1mm allowed me to increase the feed to 10mm per second which is ten times more productive. I probably could have pushed it further but I am not particularly interested in making anything from this material. Here is a video of the test :-

I now have a small but highly accurate CNC milling machine. A few improvements are definitely needed :-
  1. Dust extraction!
  2. Tool height detector
  3. Spindle motor control and stall detect


  1. very nice! i see you're making great progress.

  2. Yes thanks, yourself as well. From little acorns ...

  3. I see you've gone down the same path that I am heading down (I have an X-Y table that I got second from Ebay on the way and enough other bits and pieces). One thought - what kind of bit are you using for the plastic? I believe plastic does much better with steeper cut angles at the bit head than other materials.

  4. Hi Bozz,
    The bit I am using is a 1/8 inch end mill that came as part of a set for doing PCBs. You can see a picture of it at the end of a previous article: http://hydraraptor.blogspot.com/2007/04/trouble-at-mill.html on the far right. I think it is quite coarse for its size. The drill is only 12V so it is a bit lacking in power for anything bigger. I have upped the feed rate to 20mm/s and it sill works fine.

  5. Using cutting fluid would certainly help to reduce the problem with melting; it would also aid in keeping dust from getting airborne. That said, it's also quite messy, so I wouldn't use it if you have anything you want to keep clean nearby!