[Noisebridge-discuss] Moar Laser Cutter Infos

Danukeru danukasan+nb at gmail.com
Thu Nov 12 08:53:41 UTC 2015


Reading the manual for the laser cutter reveals that we could already drive
the laser cutter now with a copy of EMC2.

We have a custom toolchain built around EMC2 for our hobby CNC at foulab,
so I can tell you pretty certainly that your standard LPT-USB board/cable
will not work due to buffering of the pin state that their controller board
most certainly does.

EMC2 is a GCODE interpreter that drives an analog controller over LPT
directly.

EMC2 takes advantage of the LPT port to make sure that the timing is as
accurate as possible because there is very little feedback from the
steppers themselves. You generally need a real-time linux kernel for the
best results for this reason. Our CNC runs on an old ubuntu with such a
kernel.

Due to USB being much faster, packetizatioin, driving voltage levels, no
guarantee on command order, etc, there is no assurances on timing on the
LPT pins with a cheap adapter.  You'll most likely have cumulative
errors/jumps/ etc on actual long runs .

The LPT board in the cutter itself is very dumb and relies entirely on what
is driving it. It's literally a bunch of shift registers bitbanged over the
LPT by either EMC2 or the USB controller in this case.

As such this is where the buffering comes in on that small board. Proper
timing and command queuing.

ie. Why Henner's BUMPS cape for the BBB uses the A8s specific programmeable
PRU for real time control of the pins.



On Wed, Nov 11, 2015 at 9:00 PM, Zachary Morriss <zmorriss at gmail.com> wrote:

> I don't want to distract this perfectly excellent hack in progress, but
> being that the laser is EOL, it might be time to invest in some new jank:
>
> http://www.amazon.com/Engraving-Cutting-Engraver-Parallel-Winsealxp/dp/B00C9UZCOS/ref=sr_1_1?ie=UTF8&qid=1447304268&sr=8-1&keywords=40+watt+laser
>
> Price goes up and down and can be had cheaper on ebay.
>
> Or even better, something with a DSP controller, z adjust, air assist, and
> a little moar power:
>
> http://www.aliexpress.com/item/Free-ship-Best-price-rayjet-laser-engraver-3040-co2-laser-cutting-machine-50W-with-rotary/32247621015.html?spm=2114.01010108.3.48.cC334H&ws_ab_test=searchweb201556_1_71_72_73_74_75,searchweb0_0,searchweb201560_9
>
> Just stirring the pot,
> Zach
>
>
> On Wed, Nov 11, 2015 at 8:22 PM, Brian Klug <brian.klug at gmail.com> wrote:
>
>> > USB to DB25 Adapter Uses GRBL For Parallel Port CNC ...
>>
>> The following USB <-> GRBL interface might help..?
>>
>> http://www.esreality.com/files/placeimages/2013/93363-gerbil.gif
>>
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