Retromaster’s Electronics Projects

…related to old computers and other assorted stuff…

Archive for December, 2009

MF70 CNC New Y Axis

Posted by retromaster on December 28, 2009

Here are a couple of photos showing the new parts for the new Y axis installed. The speed has been improved by a factor of at least 3. This is with the existing stepper control board drives based on the ULN2003. With the planned new bipolar stepper drives,  the speed should increase even more. This said, however, the new Y axis is far from perfect. The motor swings up and down while the axis is in motion.  I am guessing that this is due to the imperfect motor-screw coupling, and perhaps also because of the extension standoffs that I’ve milled for extending the travel of the Y axis. While the Y travel has been extended successfully, it seems that the standoffs do not sit very well on the face of the Y axis slide, therefore the endplates are not at a perfect right angle.

It seems that the speed increase may have resulted partly from the motor mount screws (only 2 as opposed to previously 4) acting as a flexible coupling, compensating for the rigidity of the actual couplings. Although these problems prevent the machine from reaching its true potential, it still performs acceptably, and for this reason I’ve gone on to build parts for the X axis. Once the new X axis is complete, I’ll be able to mill parts much more quickly and build the new parts (such as new couplings or standoffs) needed for fixing the imperfections in the machine.

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Improved MF70 CNC Underway

Posted by retromaster on December 24, 2009

Here are a couple of aluminum plates, some of the very first milled by my CNC-converted MF70. These are intended for the Y axis of the new, improved version of my MF70 CNC. A standard type 606 ball bearing fits in the circular recess in the middle, just like the bottom one in the photo. The outer holes are for mounting the axis stepper motor, and the inner holes are for attachment to the table. At the moment I am about to start the process of milling a couple of standoffs that will go in between the table and these plates. This will hopefully extend the woefully limited Y axis travel of the MF70.

Milling new parts is going rather slowly at the moment. The current mechanics of the machine are not very precise and rather inefficient. To ensure that the motors do not miss any steps, they need to be driven at a rather low speed. This is in contrast to the built-in spindle of the MF70, which seems to do best with relatively light cuts with a high feed rate, due to the rather high RPM (5k to 20k). The new parts should help alleviate this problem.

One other thing that does not help the situation is that the torque obtainable with the current stepper drivers is quite beneath the potential of the motors I use. To overcome this, I’ve started to work on a new controller board that implements bipolar chopper drive instead of the unipolar L/R drive of the current board. In addition, the new board will increase max current per coil from 0.5A to 0.6A. For the new board, I am also seriously considering to switch to the LPT port instead of USB, as this will enable me to use readily existing software such as EMC2 without a lot of work.

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MF70 CNC Working!

Posted by retromaster on December 1, 2009

I’ve finally managed to complete all the axes and get the CNC-converted Proxxon MF70 to work. The photo above shows the whole machine, and here is a video:

Vodpod videos no longer available.

 

The USB control board is able to do linear and circular interpolation on board. I’ve made the host-side into a Python module, and coded a few scripts that enable me to move the axes using the keyboard or interpret Gerber or NC drill codes. It’s all in quite early stages, though. Shortly after I recorded the video above, the controller got stuck in one of the line segments and ruined the workpiece, so it seems I’ve still got some debugging to do. Nevertheless, it all seems to be on track, and I am already planning improvements to the machine, with parts to be manufactured using the machine itself.

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