CNC with Sanguinololu/GRBL? Advice needed

Hi CNC'ers!

I am building a microCNC, and I have all axis hardware complete; I just need to add a dremel. In my test setup, I am currently using a Sanguinololu and Sprinter, and I seem to be able to control the axis hardware OK

I have a plan for software/firmware, and I just want to see if its the optimum system, with advice from the forum.
I plan to change to GRBL, as it is designed for CNC specifically. For design work I was planning on using Inkscape and Sketchup for 2D and 3D respectively, with the plugin for inkscape and PyCAM for Sketchup for toolpath generation. This should let me use either my mac or PC with the CNC.

Does this plan seem sound? is there a better firmware/software combination for use with an arduino-based CNC? I'm not sure how GRBL handles endstops and home positions, and I see the version 0.8 Edge supports Coordinate System Select, but I have no idea if this is relevant for my setup.

Thanks in advance for the help!

PS. Is there a simple way to wire in a Dremel/clone with the arduino so as to use the GRBL Spindle Control (M3,M4,M5)?

Edited 1 time(s). Last edit at 08/29/2012 04:19AM by dnhkng.

I have been running a CNC mill (built using this MF70 CNC Conversion Kit) with Sanguinololu and Gen6 reprap electronics and both electronics work just fine in CNC use.

I have been using the Marlin firmware. I have heard that GRBL and Teacup firmwares would work better in CNC use, but I haven't had any problems with Marlin either, so I haven't bothered to try anything else yet.

For the CAM program, I got better results from HeeksCAD with the CNC add-on than from PyCAM. The Profile, Pocket and ZigZag operations give very nice results.

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I have heard that GRBL and Teacup firmwares would work better in CNC use

It's mostly a matter of the supported G-code command set. There were times when Marlin didn't even support G0.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Another thing I noticed is that with both electronics (Sanguinololu with 16x microstepping, Gen6 with 8x) the maximum speed is 300 mm/min, when using the standard M6x1 lead screws. Anything over that causes the motors to just start stuttering. I wonder if this is a firmware limitation in Marlin? (Maximum step rate being hit?) I might try Teacup since I'd like the mill to move at 600 mm/min for milling easy stuff like POM.

Edit: Hmm, I guess I won't be trying it, since it doesn't support G2/G3...

Edited 1 time(s). Last edit at 08/30/2012 09:20AM by ttsalo.

I had a look at the ShapeOKO video tutorials, and there they use GRBL.

When they start up the milling process in the tutorial, they first move the router head to the 0,0,0 position by hand. They can do that, as they use timing bests and pulleys. Is there a way to do homing and a reset of the coordinate system with GRBL? As I use a lead-screw system to move the axis's, I can't position them by hand so easily. Also, can soft distance limits be set, so as to prevent the CNC from being driven past the mechanical limits of the machine? I didnt see that kind of settings in the configure.h file, but I would have thought is pretty important stuff!

Lastly, I am using old micromanipulators for my CNC, so I only have a travel distance in all three directions of ~25mm, but a step size of about 0.5 microns. Does anyone have any recommendation for a good spindle for this accuracy? I have been considering using a dental drill. Of course, I had to edit the arc parameters "#define MM_PER_ARC_SEGMENT 1" to be a bit smaller

... my first choice would be dental drills too, as most other small drills don't have bearings with the needed circular accuracy.

If you can make your own spindle housing with precise micro-bearings, then the next suggestion would be a brushless DC motor with >80000 rpms ...

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Viktor
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Maximum step rate being hit?

M6 requires 200 * 16 = 3200 steps/mm, so 300 mm/min require 960'000 steps/min or 16'000 steps/second or 16 kHz, which is, yes, about the maximum an ATmega doing acceleration calculations can achieve.

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my first choice would be dental drills too

I've searched a lot for suitable ones, but european manufactured stuff is prohibitively expensive ( EUR 500.- and up ), while chinese ebay sellers can barely provide more than a symbol photo of their spindles. Also, everything above 20'000 RPM apparently runs with pressured air, only. I'm not so keen on buying a dozen of these things, just to find out they have play on the axis.

So far, my preferred spindle is a Micromot 50 (not the 50E variant). Can be modified to be play-free by just opening and readjusting the internals. Allows RPM to be set by PWM, just like an extruder heater. Not exactly precise, though, effectively milled diameter varies on the spindle's daily mood by some 0.2 mm. Reasons so far unknown.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

I'm using Marlin with Sanguinololu: [vimeo.com]

Spindle is a KERS 1050 (around $180) max tool diameter 8mm. It is noisy but cheap. Our newer version is a Teknomotor spindle with ER20 that costs around $260 and then you need a VFD that will cost another $150 or so.

I'm building a ShapeOko for which I've bought this DC motor with ER16: [www.ebay.com] for which you can use this holder [www.thingiverse.com] I have created.

Edited 1 time(s). Last edit at 09/11/2012 11:34AM by misan.

Dnhkng,

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dnhkng
When they start up the milling process in the tutorial, they first move the router head to the 0,0,0 position by hand. They can do that, as they use timing bests and pulleys. Is there a way to do homing and a reset of the coordinate system with GRBL?

I use a Gen7 with Teacup and I know that litteraly pressing the Reset button resets the position to 0,0,0. It's not pretty and the com link is lost in the process but Pronterface seems to reestablish the link all the time. Teacup's programmable limits are working good also, but 300mm/min is the max speed I have chosen too for the lead screws, and I switched to ramping acceleration with an acceleration of 10.

As for the software suit, I was planning on using pyCAM, which seemed to offer a lot, but I will investigate more on GCAM and visolate. For last resort, I keep HeeksCAD/CNC and Inkscape's plugin in mind, but I give it to you bro, it is a large world of possibilities.

MikE

When I started to build my CNC mill, I specifically wanted it to be running on RepRap hardware. Initially I tried to use Marlin, but it just did not support quite significant features of G-code (e.g. pyCam, pcb2gcode, dxf2gcode output was not usable with Marlin).

There was a fork of grbl by lincomatic, but it was outdated, so I forked latest stable version of grbl and made it run on Sanguinololu: [github.com]

Hi Guys

I also posted this on the Laser Cutter Working Group forum but then found this thread

I wonder if any of you can help me. I have designed and built a CNC platform that I intend to put a laser on. It's using a Sanguinololu 1.3 with the ATMega 1284p chip on it. I'm trying to upload a grbl.hex file that I have compiled that is configured for the Sanguinololu. The issue I am having is uploading the .hex file. The board has a boot loader installed and I have already got a Marlin version up and running in order that I could test motors, endstops, etc. All work fine via Pronterface. The error I am getting from avrdude is below along with the command line string I'm using. It seems so close (I've spent days even getting this far smiling smiley.

C:\Arduino\hardware\tools\avr\bin>avrdude -CC:\arduino\hardware/tools/avr/etc/av
rdude.conf -v -v -v -v -patmega1284p -carduino -PCOM5 -b115200 -D -Uflash:w:"C:\
Users\Andy\Google Drive\Laser Cutter\grbl-sanguinololu-master\grbl.hex":i

avrdude: Version 5.11, compiled on Sep 2 2011 at 19:38:36
Copyright (c) 2000-2005 Brian Dean, [www.bdmicro.com]
Copyright (c) 2007-2009 Joerg Wunsch

System wide configuration file is "C:\arduino\hardware/tools/avr/etc/avrdude.conf"

Using Port : COM5
Using Programmer : arduino
Overriding Baud Rate : 115200
avrdude: Send: 0 [30] [20]
avrdude: Send: 0 [30] [20]
avrdude: Send: 0 [30] [20]
avrdude: Recv:
avrdude: stk500_getsync(): not in sync: resp=0x00

avrdude done. Thank you.

Hope someone can help

Regards

Andy

I would try a different baud rate.

XLoader seems to be the recommended way to download GRBL, would that help?

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Hi Bobc

The baud rate I'm using works fine for uploading Marlin to the Sanguinololu via the Arduino IDE. I assume I would have to alter the baud rate in my Marlin configuration.h in order to connect to the board with a different speed now? I downloaded Xloader but it doesn't cater for the ATMega 1284P that I have on the board. It would have been so easy if it did. I may have to give up trying to upload a hex file without a programmer but surely it should be possible ???

Andy

Managed to get it sorted. Please PM me if you have similar issues