This last Thursday, I went ahead and got a second hand HP DC7700 (with KB and mouse, but without a monitor) for about $100, along with a cheap and suitable external video card (since LinuxCNC is supposed to fail with on-board video cards) with VGA, DVI, and HDMI outputs.
I installed LinuxCNC from a flash drive (the other one was too old to boot from USB!), and tested the on-board and the external video cards for latency. They were pretty similar, around 15000ns. But since my LCD monitor only has VGA, and I don’t want to take no chances, I use the external one. I use soft OpenGL drivers, and all is well. Good to use a 2GHz Core II Duo with 2GB RAM. No more flickering AXIS and late opening windows! I did a test cut, and all was fine.
The next day Pamir came, and we worked on some cuts, and a dust collector system from noon ’til night. I also gave up on the rig for the lighting and the dust collector hose, and resorted to Redneck methods (for now). The light fit nicely in one of the spare holes of the Y-axis stepper motor. I also changed the Z-axis motor for it was heating up extremely (full coil bipolar driving a unipolar motor is not worth it), and I was losing steps. Luckily I found the exact same motor I used for the x and y-axes at my friend’s shop.
Pamir’s CAD/CAM work was well done. Yet, as the program was about to cut around the part, (I dunno what caused it, I remember accidentally hitting the keyboard with my elbow) it started from a wrong spot and hit the clamps, breaking the bit. This was red acrylic, clear acrylic I got melts like a candle, and I still don’t know what makes them different. Our second cut was a failure, because the bit was not a perfect cylinder, but a slightly tapered one. So the holes were ok (6 mm) at one side, but not ok on the other (about 5.5 mm). Our final cut was on red acrylic again. This time all was good until the program started cutting the frame, the final line went through the holes, and the last three rows were offset irregularly, due to some reason still unknown to us.
And here’s a video of the failing cuts on acrylic. 6 x 1 mm + 1 x 0.5mm scalar feeds on 2 x 3 mm red acrylic stacked together.
As the cuts took about an hour each, we worked on a dust collector system in the mean time. We had to improvise as always. I had some 1.5 mm PVC hose, and managed to make an adapter from a garlic crusher (easy screw on lid for portability) and a syringe. All fit snuggly, and I sealed them with black hot glue. An old vacuum cleaner was also laying around to be utilized for this purpose. We mounted the hose around the spindle with cable ties and sticky cable tie holders.
The dust collector works nicely, yet I still need to build a good jig for it, and add a mouth part for better and wider angle dust collection.
Today, I worked on the sound absorbing part of the box I was planning for. Since most of the sound was coming from the hole (for the spindle) on the top of the box, I decided to cover it with a sound absorbing box. I made the box out of 4 mm plywood, using PVA glue and small nails. Later on, I covered the inside with sound absorbing sponge (foam?). Finally I covered the side walls and the ceiling of the box with more sponge. The result is much better than before, but not as good as I expected it to be. I know nothing about this subject anyway. The distance is probably too short.
I still need to install some sort of clamp to hold the acrylic door closed (worst sound barrier). I’ll probably work on that tomorrow. Here’s what the setup looks like right now.