Double Sided Fixture For PCB Milling. It’ll Flip You. Flip You For Real.

Remember? When the cops got Benicio del Toro and he was saying that Stephen Baldwin was going to flip them? No? Anyway…

Having purchased 100 of the same size copper clad FR4 boards, the extra effort was made to machine a proper aluminum fixture for them. 6061 Al is surprisingly cheap at mcmaster-carr. The purpose of said fixture is to hold the board flat on all 4 sides, force distributed over multiple points per side, with an open center area for drilling. References to locate X and Y are integrated into the fixture, Y along the top edge, and X by protruding ‘nubs’ underneath the side clamps. Enough freedom along the X axis is allowed in order to be able to slide the board to the other sides reference after flipping, so the board is always located on the same side, at the same point. Flatness and squareness are critical.

Highlights includes endmills doing circles around broken taps and the taig covered in aluminum chips like it was snow.

Posted by rmrubin Posted in: CNC Comments Off December 2007

Xylotex Microstepping vs. EMC2 BASE_PERIOD

Microstepping setup notes. Hardware is a Taig 2019cr micromill with a 20TPI leadscrew and 200 steps/revolution motors, driven by a Xylotex 4 Axis stepper driver. The host for EMC2 is an Athlon XP, a 1700+ or 1800+. After calculations, the step mode jumpers on the Xylotex board were configured for eighth-step mode, and BASE_PERIOD=10000 was set in the EMC2 configuration file.

Initial impressions of the setup are quieter and smoother operation. Performance is comparable with the full step configuration: 60 IPM somewhat works, locking up towards the end of the tables travel, 45 IPM seems stable, and maximum working jog speed will remain 30 IPM. Testing the new configuration in the immediate future will likely be done milling circuit boards with a 30deg conical cutter, and .250″ endmilling acrylic. I’m excited already.

60 IPM = 1 inch/sec

200 steps/rev * 20 TPI leadscrew (full step mode)
= 4000 steps/in
= 4KHz step rate @ 60 IPM
= 250us step period / 2
= 125000 min BASE_PERIOD

400 steps/rev * 20 TPI leadscrew (half step mode)
= 8000 steps/in
= 8KHz step rate @ 60 IPM
= 125us step period / 2
= 62500 min BASE_PERIOD

800 steps/rev * 20 TPI leadscrew (quarter step mode)
= 16000 steps/in
= 16KHz step rate @ 60 IPM
= 62.5us step period / 2
= 31250 min BASE_PERIOD

1600 steps/rev * 20 TPI leadscrew (eighth step mode)
= 32000 steps/in
= 32KHz step rate @ 60 IPM
= 31.25us step period / 2
= 15625 min BASE_PERIOD

Xylotex 4 Axis Stepper Controller Datasheet

Posted by rmrubin Posted in: CNC Comments Off September 2007