Having two kids really means that you get almost Zero time to tinker, I can ponder many ideas, but often can’t carry them out in a reasonable time
Referring back to my post here – https://bleughbleugh.wordpress.com/2015/06/22/where-to-put-the-mill/
I’ve just googled someone that’s done just that!….
Off to watch Mach 3 tutorial videos, mayaswell get some theory practice in!
It’s been a few weeks now, still haven’t actually cut anything proper like,
however, a BIG occasion, I can now JOG all 4 axis quite happily in Mach3!
for those looking everywhere (and I did), no-where really quite states obviously or easily the pins on the connector needed to control the 4th Axis, it’s pins 8 & 9
|Axis||Step Pin#||Dir Pin#|
And Also – another setting needed,
Under CONFIG – Homing / Limits.
Set Soft MAX and Soft MIN on A axis to ZERO, that’ll allow it to rotate forever.
Now, one plus side of getting the A axis to work, it uses the same stepper motors as the X,Y,Z. it should help me to be able to accuratley calibrate the system now as many websites suggest that the 400 steps per rotation is ‘off a bit’….
Here goes. Need to figure out ‘homing’ and how exactly the G-Code relates to the position on the table. most ‘dry runs’ so far have pushed the CNC past its limits…..which is annoying as i don’t have limit switches yet!
Noting some of the ‘stuff’ on the board, we can see that it’s quite simple really, it’s a small microprocessor controlled, dual sided PCB Two voltages – 18V AC and 36V AC from the secondaries of the transformers, 18V dropped down to 5V to feed the processor electrics….. 36V rectified to DC, then passed to the spindle somehow the micro takes in the variable resistance from the POT at the front of the box and converts it to DC, PWM at whatever voltage the 36V AC is converted down to. Not sure what the extra plugs do yet though, i’ll keep adding to this board STC 15W408AS –
- SOP16 – Single Chip Micro – 8051 based – 8-12 times faster than standard 8051
- 8K RAM,
- 512 Bytes SRAM,
- 3 Channel PWM,
- 10 Bit ADC,
- 5K EEPROM
- 5 external interrupts
- 2 timers
- internal clock
- RS485 Control
Page 68 onwards of the english PDF datasheet covers this IC, LNK 306DN – AC TO DC CONVERTOR – DATASHEET HERE – 8 PIN IC WITH PIN 3 MISSING IRF 640N – IOR P447D – 5TH Generation power Hexfet MOSFET – DATASHEET HERE KBJ 1510 – Bridge Rectifiers – DATA SHEET HERE 78M05 – 5V Voltage regulator – DATASHEET HERE EL817 X 4 4 PIN DIP PHOTOCOUPLER – AKA OPTOISOLATOR – DATASHEETS HERE ES1J X 3 – 1A Ultra fast recovery rectidier – DATASHEET HERE
There is a few versions of this board around, one older one seems similarly laid out but based upon a 555 timer! Theres a fellow Aussie doing much more digging than I at this time, ill pinch some wording from his page on how my board works. The spindle speed control works by passing the PWM through a low pass filter, then reading the DC voltage produced on an analog pin of a PIC micro. The micro then reads the value (most significant 7-bit’s of 10 bits), and sends it to a digital pot. The digital pot contains an 8-bit data register (16-bit really with command byte) and is 10K and we need 5K, so that’s why we are grabbing 7 bits (need 8 bits and grabbing 7-bits divides the value in half). The last log explains why I need to convert PWM to a resistive value (voltage divider). I’ve also added a feature for the Z auto level probe on the board. The issue there is, my system has been configured to work with Normally Closed limit switches and the act of probing, is a Normally Open operation. Have look at his projects on Hackaday.io Here
Have been reading up on control methods for the CNC (yep, too much reading, not enough actual do-ing),
Stumbled across something called GRBL, which to summise,is, “an arduino CNC controller”
There’s a shedload of websites regarding GRBL…..so……
I actually own various quantities of each of the following microcontroller boads that i’ve acquired over the years, a few more modern ones include
- Arduino Duemanelivove
- Teensy V3.0
- Intel Galileo
- ST Stellaris Launchpad
- Raspberry Pi (too many of these, one of the first 1000, one B 256 Mb, two B 512Mb, two A+ and one 2!
And, given my recent discovery of GRBL,and a penchant for hoarding un-used demo boards,
I’ve purchased one of these………
It’s a blatant clone of a couple of other shields out there, at under eight AUD though, it was worth a punt
I picked up five of them also….for just under $14 AUD, three for now, a fourth if I ever figure out 4 axis machining and a fifth as i’ll probably blow something up
so, for a grand sum of $13.81 Plus $7.63 = $21.44 delivered, I have a nice CNC Shield for my Arduino
Specifications for the CNC suggest that the maximum working area is
- Max.workpiece dimension：200mm*300mm＜65mm
Z axis dimensions are <65mm
Measuring the total Z axis travel, there’s only 56mm of travel available….
it does look like I can slacken off the screws on the spindle a little to move it upwards to gain some workspace back,
great for using a sacrifical piece of wood orsomething on th ebase and maintain the full movement
I’ve discovered now that CNC devices are fundementally, quite rudimentary.
During my five minutes of ‘wow’, giggling like a small schoolgirl whilst repeatedly jabbing the arrow keys (mixed in with some heavy page up / down banging too) whilst proudly exclaiming vociferously to a somewhat bemused missus at half ten at night “it’s moving”. I’ve, somewhat soberly come to the conclusion that ‘it’s all a bit naff, really.
CNC should be quite easy in theory – just draw ‘this’, tell motors to go ‘there’, done…
it’s not quite like that
Some immediate observations.
- Co-Ordinates….That X,Y,Z stuff. I, at this time have no idea how what’s on the screen relates to what’s on the CNC bed.
- Limit switches….There aren’t any on my machine, I need some to stop me wrecking the thing whilst learning
- Speed (or lack of)….CNC’ing is going to be a looooooong process. Also, it’s a tad slower than anticipated
- Software…..Mach3 is going to be ‘fun’, CAD is going to be ‘funner’, and not quite sure about the levels of amusedness involved in linking those two yet.
- PC specifications. My ‘procured from hard rubbish Toshiba NB255 2010 1 Gig memory mini 10.1″ laptop really doesn’t cut the mustard. The CNC was making all sorts of odd grinding noises whilst running the GCode demo. This caused a little worry until my previous interweb searching memory kicked in and i’d remembered that someone had reported similar issues with a crappy PC. Swapped it for my normal laptop Asus G51Jx and it all went quite well.
- USBCNC software from that ebay bloke works quite well, out of the box for my 3020T, your mileage may vary but I suspect it’ll help me get some of the basics downpat in a hurry
In the vein of useless information and googling waaaay too much, i’ve figured it’s probably a good thing to purchase some measuring thingy
Picked up a stainless Steel digital vernier calipers from ebay for eight bux!…will see how well it goes,
probably only marginally more accurate than my previous ‘eyeballing’ and scaling against an A4 sheet of paper attempts