PCB Drilling with the MF70 CNC
Posted by retromaster on January 11, 2010
Over the weekend, I worked on getting rid of the backlash in the MF70 CNC. I’ve made new delrin nuts that fit much more tightly in the nut housings and I’ve tightened the stop nuts on each side of the X axis to make sure that there remained no play in the ball bearings. As the first photo shows, this resulted in a huge improvement in the backlash situation, although I had to reduce speed as the X axis became more difficult to move. Also, something I noticed before but I neglected to mention in my previous posts is that the X axis endplates do not seem to sit perfectly flat on the sides of the table. This may be because they are getting bent when the mounting screws are tightened. I think I may have to try rebuilding the endplates using aluminum twice as thick.
In addition to fixing the backlash, I greatly increased vertical speed for drilling and shortened the extension of the drill bit to just a few millimeters below the chuck, eliminating most of the problems due to wandering and flexing of the drill bit. But even these improvements were not enough to get a perfectly drilled PCB. It seems that warpage of the copperclad introduces a significant error as well. So significant in fact, that the holes in the top board in the first photo above did not align properly with the printout of the PCB layout. I also found out that I needed to have the hole locations mirrored since I was drilling from the copper side (this is a single-sided board). So I came up with the drilling setup in the right photo to fix the warpage issues and I had the hole locations mirrored, and I managed to have a drilled copperclad that matches the PCB layout very well.
The PCB I building is for testing the new axis drive circuitry that I mentioned in the previous post. In a few days, I expect to finish making and assembling the PCB. After a little bit of PIC coding, I’ll at least have an idea of the torque increase I’ll get from the new drives. If it turns out to be as worthwhile as I think it’ll be, I’ll build a new board with all drives for all 3 axes and then go back to improving the mechanics of the machine.