Wednesday, January 30, 2008

DIY MPG for Mach3 (Part 1)

After failed attempts using stepper motors as encoder for the Mach3 MPG (details), I decided to find alternative encoder to use and I am still unwilling to spend USD75 for an industrial encoder. While attending a CAD/CAM training, which heavily relied on mouse center scroll function, it hit upon me that cheap optical mouse may offer me a solution. True enough, after a quick scope check, the center encoder do provides quadrature output needed for MPG operations. Resolution is roughly about 20ppr and the circuit is physical contact rather than optical.

The encoder is only 3 pins, i.e., Ground-OutputA-OutputB. Two 10k pullup resistors to the USB +5V are needed to provide suitable signal to the PC parallel port. Quick config update and MPG calibration in Mach3 and I was in business... yahoo....
The photo below show the actual encoder after removal from the PCB. I'm in the process of designing and building a suitable pendant to house the encoder and relevant switches for practical use... next installment though... going vacation this weekend...

Monday, January 21, 2008

Got time to kill so...

I design and cut the various pieces to fabricate the peltier-based heat exchanger below. The black box came from a CPU cooler (water-based). It has an internal water pump and copper heatfins. Coupled to it is an aluminum heatfin with a small fan designed for a pentium CPU. The stand was cut from 4mm acrylic. The contraption works but the fan may be too small to efficiently remove the heat from the aluminum heatfin. Suitable for low power cooling... Yet to hook it up to the high speed spindle for heat removal testing...
I received a complete ER11 collet for the high speed spindle a while back. They came in individual box as shown in picture below. I decided to make a simple holder for it and engraved the lettering for easy identification and storing.
The holder in a plastic 'drawer' ready for slotting into the wall mounted chest. The 6.0mm hole is empty since the collet is in the spindle...

Friday, January 11, 2008

Switching Panel...

Don't you love CNC :-)

Modified the power switch panel of the PC casing to house multiple switches and LEDs.
Main Power Switch with LEDs for 12V, 5V supplies & Stepper Supply
Next switches: Reserved, Reserved, Spindle Power, 5V output, 12V output


Tuesday, January 8, 2008

PWM to Analog Update

After getting tired of trying to 'fine-tune' Mach3 to get it to control my spindle speed correctly, I gave up. I had some scrap populated boards on hand and I saw nice optocouplers on them (CNX82A). A quick check on the 'net shows that it should be fast enough for my use. I modified the original schematic to drive the output with 2 gates and reduced the RC resistor to half of the original value giving me a longer time constant. I guess, with original values, the VFD was draining my RC tank faster than it was charged.

Hooked it up to the parallel port and VFD and, guess what, it worked. With additional 20 minutes of fine tuning values in the VFD (max operating frequency & min output frequency), it worked flawlessly now. The VFD is now perfectly tracking Mach3 speed request (accuracy to about 0.1Hz!). The PWM frequency in Mach3 could be reduced from 200Hz previously to only 50Hz now. With current setting, my spindle speed control has a resolution of about 50rpm...

The new schematic below...

Wednesday, January 2, 2008

On the 1st Day of 2008...

The new year is here... so what... it's just another normal day...

I managed to complete the new mount for the high speed spindle... both the horizontal and vertical plate were cut using the high speed spindle with 6mm endmills. Couldn't find the needed M4 & M5 cap screws so I used what's available in my tool box... The whole thing is purrfect...

Having some spare time after doing the above, I quickly made a simple ZIF-based adaptor for the PICKIT2 unit below. With the adaptor, I could program PIC of various pins with ease...

BTW, I also replaced a few capacitors on the stepper driver... They were flacky long ago but I couldn't be bothered to replace them... now with 3A/phase, they are causing headache... occasionally my motor would whine and current consumption easily doubled... so far no noise or overcurrent after the replacements...