The trick is to don't do anything to the table, but only to the right Z axis. First on the left side of the table I put something for example a construction angle in a way showed in the picture. Than I lower the Z axis, that it gets in touch with that angle. Afterward I put the angle to the right side ans unscrew the pulley of the right Z axis. Than I turn the right Z axis until it touches the angle also. When both sides touch the angle equally I fasten the screw of the pulley. Voila!

For better results you should move the table, so that the middle of the table is below the gantry.

Beside that, I tightened the 0.2mm cutter manually, it nevertheless has some eccentric. It's not a new one and maybe the students ruined it a little bit ;-)

I'm also still interested in milling a working TINYPOV. This should be done with a newly generated GCode file with pcb-gcode. Now I know, where to adjust the settings for milling, more important: how to adjust that settings.

It is the blinkie board from instructables realizing the "Design Rules". Each isolation route is milled four times, so the milling time could be recuced do about 3 minutes. This is the very coarse end of MiniCNC, while the TINYPOV seems to be the very fine end.

You can download this file here.

Here is the result in plywood

and here in copper

I also have had a close look to the "waves". I found them only in that region, and maybe this is conditional upon the wooden structure below the black color. I can't truely say, whether this depends on some changings in the color of the wood or in different density of fabrics. The challenge will make it clear.

Today I also did a second milling with that "0.2mm" cutter. It is a 0.2 mm to 0.5mm konical one. If you just touch the board it's diameter is 0.2mm, deeper cuts are 0.5mm broad. Also before I tightened the cutter to strong with a wrench into my dremel. Now I do it manually.

But these kind of cutters are very difficult to handle. They are used with a very high-end mill hci.rwth-aachen.de/mill. I doubt seriously that it is possible to get the precision of that machine with a Contraptor MiniCNC. So I will have a look for different cuters.

Also I will make a new PCB design, because the measurements of the layout in some regions are to sophisticated for DIY hobbyists. I doubt, that I could do it with the toner transfer method I used until today.

Read this article on instructables to gte an idea what I mean.

Also, thanks for the CHDK pointer, I'll check it out, I definitely like the timelapse feature.

The workingspeed for Z direction F100 the other directions are F200.

Some minutes ago I started milling in PCB copper. I haven't seen any difference with milling in wood. But I aborted that run, because I realized, that my 0.2mm cutter is VERY excentric :-(, so that it mills broader than my 0.6mm cutter!

And here is a short impression of milling:

Have a look how much dust is produced. This is an epoxy board. Tomorow maybe I will do an open air milling ;-) and I will test miiling into a card board with 0.6mm cutter. I will generate a new GCode file.

Of course the original board looks different. I just used the eagle files to create the GCode entirely by myself. Because in fablab another software for generating GCode is used, there are some differences.

PS.: Just in the moment I have had a look at your comments at the flickr photo. I used NCPlot to have a quick look to the GCode. In this back tracker also no insulations has been showed at that points you marked. Maybe the reason are some settings in pcb-gcode. Thanks for the hint.

Regarding the accuracy, don't forget that there has been virtually no resistance from the workpiece. We'll see whether mini CNC has enough rigidity to hit 0.01" milling PCB copper, especially in X axis (one with Dremel).

I also found a couple of areas where traces differ from the dorkpov board, but this is how they are in the NC file. I left notes on this flickr photo.

Result of a fully completed milling run :-D

The run took about 1 hour. With ACME leading screws it would be much faster.This has been done with a 0.6 mm cutter. Therefor I doubt that every trace would conduct (in the upper right). These dorkbot people sometimes are doing too strange things (lot of university people ;-). But luckily I have a cutter with 0.2 mm diameter. The next run in a copper board should make a functional board.

Also this shows, that the accuracy must be much higher than the estimated 0.01"

Through-hole milling is definitely doable, because this is a board with 9 (!) through-hole traces ;-)

The weak point in electronics n my opinion are the connectors, specially that ones for the limit switches.

PS.: I have seen that you are using a Canon camera, might be the Canon Hack Development Kit is interesting for you ;-)

PPS.: You are not disqualified because of ACME leadscrews (tuning is allowed), but we both didn't start from scratch. And beside that, you have done a drawing not milling into a solid material. ;-)

I tried lowering the FAST_Z_FEEDRATE and still got the problem with Z (try #3), which most likely indicates vibration-induced problem with electronics. On the next try I reseated all connections on Z driver board, removed Arduino from the mini CNC frame and attempt #4 was completed successfully - see below. Unfortunately I had little space left on SD card so I don't have the video. I will try again with Arduino off the frame but FAST_Z_FEEDRATE at previous value, to validate the result.

The accuracy seems to be not bad. I doubt it can mill SMT PCBs, but through-hole should be doable (once we work out all the bugs).

Regarding the vibrations, I'm hoping that microstepping drivers will mostly take care of them. But it seems clear that electronics need to be away from the frame.

On YouTube you can see a low quality video with 16x speed of the milling process

So I decided to evoke a challenge! That one (me excluded) who is able to mill the dorkpov (tinypov) completely into stiff material will get a dorkpov set milled on the PCB mill from fablab Aachen from me. Here is the TINIPOV GCode file. It is made for a cutter diameter 0.2 mm / 0.00787402". Instead you can do it with a cutter 0.5 mm / 0.019685", but I guess this one will not work (electronic rule check).

Here you can see how the result should look like:

(The GCode file will engrave TINYPOV instead of "dorkpov V1.0"

Just the backside is needed

The set includes all parts which are needed to build a nice POV device for your bycicle.

You are right, according to DIN 66217 my X axis goes from left(-) to right(+), my Y axis from ahead(-) to back(+) and the Z axis from bottom(-) to top(+).

Now I have put some oil to all axis, reduced the fast feedrate (10 IPM (~250 mm/min) and I'm looking forward to mill the very first PCB with MiniCNC worldwide ;-D

First, I'm having a problem with Z axis - sometimes it loses its position. The Z axis connection at Arduino end is not very solid and I think what's happening is vibration might be making some contacts loose every now and then, probably closing limit switches (they're +5V in open position). When that happens, Z doesn't move in response to commands, loses its position, and ruins the entire job. This can be seen towards the end of the video when "TINYPOV" is being plotted:

Might be the reason is stalling. At the moment I can't install a flywheel on the X axis, because I shortened it too much and can't get imperial threaded-rod here, maybe I will look around in the net. So I will try a slower feedrate. I emailed the file.

Since it doesn't seem to happen on Y axis (where you have a flywheel), one version is that without the flywheel, X axis stalls on some moves, which results in offsets like this. It shouldn't happen at low speeds though, but as far as I remember, the stalls tend to happen on shallow angle G0 XY interpolations - when the feedrate on dominant axis is close to maximum and there are nasty vibrations. I've had it happen at 15 IPM (380 mm/min) without flywheels and had to drop the feedrate to 10 IPM (~250 mm/min).

According to your _init.pde above, your fast (G0) feedrate is 360 mm/min. The remedy would be to either install the flywheel or to not exceed 250 mm/min feedrate. This is one potential reason, but there may be others, such as something in GCode that causes this. If you email me the file, I'll try it out and see if I can reproduce this.

For myself I prefer using KiCad. One but not the only reason is, that it is Open Source. The tool chain would be exporting a dxf file and import it into CamBam. I have done this before and it works. But my target is to use a complete Open Source tool chain.

So no of these alternatives are perfect in my sense. But this is just a question of time.

Meanwhile I will use both alternatives. KiCad / CamBam for my own boards and eagle / pcb-gcode for boards I derive from others, who use eagle.

I will produce my first board with eagle / pcb-gcode. It will be the dorkpov (eagle files) from our dorkbot group in Aachen. There I presented Contraptor and so the board should have some connection to that group. ;-)

Don't expect a result tomorrow, because I have to get more experiences how to convert a board layout to gcode. ;-)

Regarding PCB milling - might I suggest making the table flat first. From what I read it's critical to have the flat table for accurate PCB milling. I think this could be achieved by resurfacing a sacrificial piece of plywood attached to the table.

Additionally: It's a good idea to put some drops of oil to the axis!

Here is a video of the milling:

In process_string.pde, find the following fragment:

 // Must reverse if dominant sign is negative and clockwise, or positive and counterclockwise (which is the same as dominantSign != direction) if (dominantSignTbl[startOctant] != arcDirection) stepOffset = -stepOffset;

and replace it with the following:

 // Must reverse if dominant sign is negative and clockwise, or positive and counterclockwise (which is the same as dominantSign != direction) // Must count backwards in sign table for counterclockwise if (dominantSignTbl[(arcDirection == ARC_CLOCKWISE) ? startOctant : 7 - startOctant] != arcDirection) stepOffset = -stepOffset;

It fixed the problem with "e" in my tests and I think should also fix the other problems with arcs. I'll upload the updated code to Sourceforge.

"Frohe
Ostern
liebe Vesna"

The letters which went wrong are marked bold. The root cause seems to be, that there are failures in the Arduino firmware, which misinterpret circles and parts of circles.

I will do some testings in it.

G1 X2.8045 Y1.4874 G3 X2.8894 Y1.2057 I0.8737 J0.1096

My guess is that the inaccuracies in other letters ("o","k","b") and extra circles in your engraving have the same root cause.

Here you can see the beginning of the engraving.

Today I made my first engraving :-). It's a "Happy Easter" wish. the hight of one letter is about 1.5 cm which is about 0.6". What I realized is, that the working piece isn't in an exact right angle to the Z axis and there seems to be some failures in circle drawings like for the "e". Also there are three unmotivated circles in the lower right, which didn't apear in CncSimulator. But nevertheless I'm happy to get the machine working :-D

The photo shows something what is hard to read as "Hello World" because the pen bended. But now it's working.

All the time I wondered, whether Arduino firmware has a storage or routine which waits for the 'ok'. My fault, maybe I have been to narrow minded.

just at the moment I'm uploading several videos which are showing all strange results. I did the uploads of the GCode files with cutecom, which of course doesn't wait for the 'ok' responses. This should be the explanation for the strange results. I will test the python script and will post the outcome.

Thanks for that hint.

I forgot to ask one question - what are you using to send GCode file to the interpreter? The thing here is that the host software should wait for the "ok" response from the interpreter before sending next command, otherwise the commands get lost etc.

Sorry, I should have documented this. I added a Python script which can be used to send GCode file to the interpreter in this manner: http://www.contraptor.org/motion-control

So, what happens if you update the feedrate in your file, replace "G21 G90 G64 G40" line with the following:

G21 (mm) G90 (absolute) G92 X0 Y0 Z0 (zero to current position)

and send the file to interpreter? Can you take a video?

Here is my complete init.pde:

// define the parameters of our machine. // belt drive //#define X_STEPS_PER_INCH 200.0 //#define X_STEPS_PER_MM 7.874 // all thread leadscrew #define X_STEPS_PER_INCH 8000.0 #define X_STEPS_PER_MM 314.961 // ACME leadscrew //#define X_STEPS_PER_INCH 6400.0 //#define X_STEPS_PER_MM 251.968 #define Y_STEPS_PER_INCH 8000.0 #define Y_STEPS_PER_MM 314.961 #define Z_STEPS_PER_INCH 8000.0 #define Z_STEPS_PER_MM 314.961 //our maximum feedrates in units/minute #define FAST_XY_FEEDRATE_INCH 15 //300 #define FAST_Z_FEEDRATE_INCH 15 #define FAST_XY_FEEDRATE_MM 360 #define FAST_Z_FEEDRATE_MM 360 // Maximum acceleration in units/minute/second // E.g. for 300.0 machine would accelerate to 150units/minute in 0.5sec etc. #define MAX_ACCEL_INCH 50.0 //500.0 #define MAX_ACCEL_MM 1200.0 // Maximum change in velocity per axis - if the change in velocity at the start // of the next move is greater than this for at least one axis, we will decelerate // to a stop before commencing the move, otherwise we will keep going // value is units/minute #define MAX_DELTA_V_INCH 5.0 #define MAX_DELTA_V_MM 100.0 // Set to one if endstop outputs are inverting (ie: 1 means open, 0 means closed) // RepRap opto endstops are *not* inverting. #define ENDSTOPS_INVERTING 1 // Optionally disable max endstops to save pins or wiring #define ENDSTOPS_MIN_ENABLED 1 #define ENDSTOPS_MAX_ENABLED 1 // How many temperature samples to take. each sample takes about 100 usecs. #define TEMPERATURE_SAMPLES 5 // The *_ENABLE_PIN signals are active high as default. Define this // to one if they should be active low instead (e.g. if you're using different // stepper boards). // RepRap stepper boards are *not* inverting. #define INVERT_ENABLE_PINS 0 // If you use this firmware on a cartesian platform where the // stepper direction pins are inverted, set these defines to 1 // for the axes which should be inverted. // RepRap stepper boards are *not* inverting. #define INVERT_DIR 1 // CHANGED CM - ONLY ONE FOR ALL AXES #define STEPPERS_ALWAYS_ON 0 /**************************************************************************************** * digital i/o pin assignment * * this uses the undocumented feature of Arduino - pins 14-19 correspond to analog 0-5 ****************************************************************************************/ //cartesian bot pins #define X_STEP_PIN 3 #define X_DIR_PIN 4 #define X_ENABLE_PIN 5 #define X_MIN_PIN 6 #define X_MAX_PIN 7 #define Y_STEP_PIN 8 #define Y_DIR_PIN 9 #define Y_ENABLE_PIN 10 #define Y_MIN_PIN 11 #define Y_MAX_PIN 12 #define Z_STEP_PIN 14 #define Z_DIR_PIN 15 #define Z_ENABLE_PIN 16 #define Z_MIN_PIN 17 #define Z_MAX_PIN 18 //extruder pins // NOTE - USING Timer1 FOR STEPPER TIMER SO CAN'T USER PINS 9 OR 10 FOR PWM // OUTPUT (EXTRUDER_MOTOR_SPEED_PIN, EXTRUDER_HEATER_PIN, OR EXTRUDER_FAN_PIN) #define EXTRUDER_MOTOR_SPEED_PIN 19 #define EXTRUDER_MOTOR_DIR_PIN 19 #define EXTRUDER_HEATER_PIN 19 #define EXTRUDER_FAN_PIN 19 #define EXTRUDER_THERMISTOR_PIN -1 //a -1 disables thermistor readings #define EXTRUDER_THERMOCOUPLE_PIN -1 //a -1 disables thermocouple readings

I actually ran your file as it is (only search/replacing the feedrate value in F commands). Prior to running, via serial terminal, i set the interpreter to metric (G20G21), then absolute mode (G91G90) and then zeroed the origin (G92 X0 Y0 Z0), then ran the file.

What is your acceleration settings from _init.pde?

Regarding the "Huh? <cmd>" response, I noticed that sometimes it seems to be out of order, but I haven't looked at the problem closely.

P.S. Sorry for the confusion above, I mixed up G20 with G21 and G90 with G91.

I'm getting complete unpredictable results. This should be a hint to interferences. Have a look at my wiring:
The cables from arduino to the stepper boards are shorter than showed in the picture above. The distance to the cable of the stepper motors are as far as possible also to the cables of the PC power supply. Also I separated the perf bord for the PC power supply from the Mini CNC frame. The next step would be to make a complete EMF isolation.

Beside that I will post step by step what I have done.

• I changed my firmware settings in init.pde to

//our maximum feedrates in units/minute #define FAST_XY_FEEDRATE_INCH 15 //300 #define FAST_Z_FEEDRATE_INCH 15 #define FAST_XY_FEEDRATE_MM 360 #define FAST_Z_FEEDRATE_MM 360

• I changed all the speed settings for the F commands to 180.0

• I changed the beginning of my GCode file to

G21 (metric units) G91 (incremental mode) G92 X0 Y0 Z0 (set zero)

• I removed all commands from the GCode file, which gives something like "Huh? M3" (G17, G64, T0 M6 etc.), but not at the very end M5 M30, which should also give a "Huh?" response. (Being in incremental distance mode has no effect on the action of G92. see http://www.linuxcnc.org/handbook/RS274NGC_3/RS274NGC_33a.html#1015878

• I made a reset several times. After that I powered the PC power supply and send via serial the GCode file.

My environment is a Arduino Duemilla and Arduiono 0018.

Conspicuous is, that I don't get any "Huh?" responses from the last both commands, also the Z axis is moving up only in the beginning, afterwards there are no more movements. It looks like some (most) commands are not executed by the Arduino firmware.

Please post your GCode (maybe just for the letter "H") and all your step by step instructions, how you got it run!

Assuming that the interference is ruled out, I think the problem is most likely that the bot was running in relative mode - i.e. every supplied XY coordinate is treated as offset from current position, as opposed to absolute target coordinate. This is the default mode and the switch to absolute never takes place because the absolute mode command (G91) is on the same line with metric mode command (G21, first line in your file).

Also, the feedrate used (4 and 8 mm/min) seems to be too slow, which probably adds to the impression that the bot is doing something strange. You might want to regenerate the file (or search/replace) with faster feedrate (say, 250 mm/min).

I also looked at the interpreter code yesterday and I think I tracked down the problem with switching between metric and imperial modes. I'm going to try some modifications and see if they fix it.

I ran the same code on my mini CNC. Before it worked, I had to manually (via serial terminal) ensure that:

• metric units are selected (G20G21)
• absolute mode selected (G91G90)
• zero is set (G92 X0 Y0 Z0)

Another difference is that my mini CNC currently has ACME leadscrews on X and Y which move the stages 0.25" per revolution, but I don't think this should affect anything as long as the feedrates are within the range of all-thread screws.

I also have to add that once I upgraded to Arduino Duemilanove from Diecimila, I could not reproduce the problem that I posted above.

The pen was bending a bit, so some lines are not quite straight. An interesting thing is that "e" is rendered with an extra circle around the letter (see the large inch version). I'm not sure whether this is in the GCode or if it's interpreted that way.

Some observations:

• GCode Interpreter can't process several G commands on one line. There is a line in the beginning of the file, switching to metric and absolute mode on one line. That command probably has no effect on the interpreter.
• I saw problems with feedrate and units after switching between metric and imperial. As if the next command after switch is still executed in previous mode. Sometimes it looks like feedrate value is taken from another system (too slow in metric mode and too fast in imperial mode). To add to the complexity, there are 2 values of the feedrate - current (supplied via F code) and fast (used with G0 moves). All of this looks like a problem in the interpreter and needs more research.
• The feedrate should not exceed bot capabilities, otherwise the motors will stall and lose the position. Depending on your friction, flywheels, alignment, the upper limit should be about 15 IPM for all-thread leadscrew. 20 IPM was unreliable in my tests. Sometimes a stall might happen in the normal speed envelope (probably due to vibrations/noise) but it's rare from my experience.
• Default setting for fast feedrate (G0) in the firmware may be too fast. It was in my case and the motors stalled on a couple of G0 moves. This can be fixed by restricting the fast XY feedrate in the firmware.
• After the gcode file is completed and if units are changed (G20 or 21), the bot often responds to the next command unpredictably. For example the command would be "G1 X1", but all 3 axes would start moving in unexpected direction. I wrecked a Shapie fine point that way :( I'm not sure why this happens, but again, I think it's something in the interpreter/arduino as everything works fine after reset.

( Made using CamBam - http://www.cambam.co.uk ) ( HelloWorld 3/27/2010 9:13:40 PM ) ( T0 : 0.0 ) G21 G90 G64 G40 G0 Z1.5 ( T0 : 0.0 ) T0 M6 ( Engrave1 ) G17 M3 S0 G0 X1.744 Y1.7862 G1 F4.0 Z0.0 G1 F8.0 X0.6561 G1 Y0.8448 G1 X0.8768 G2 X0.9608 Y0.8214 I0.0099 J-0.1267 G2 X0.9862 Y0.7628 I-0.0474 J-0.0553 G2 X0.9608 Y0.7042 I-0.0764 J-0.0017 G2 X0.8768 Y0.6807 I-0.0741 J0.1033 G1 X0.3065 G2 X0.2225 Y0.7042 I-0.0099 J0.1267 G2 X0.1971 Y0.7628 I0.051 J0.0569 G2 X0.2225 Y0.8214 I0.0728 J0.0033 G2 X0.3065 Y0.8448 I0.0741 J-0.1033 G1 X0.492 G1 Y2.8018 G1 X0.3905 G2 X0.3045 Y2.8233 I-0.0106 J0.1402 G2 X0.2792 Y2.8839 I0.0533 J0.0579 G2 X0.3045 Y2.9424 I0.0728 J0.0033 G2 X0.3905 Y2.9659 I0.0755 J-0.1075 G1 X0.8768 G2 X0.9608 Y2.9424 I0.0099 J-0.1267 G2 X0.9862 Y2.8839 I-0.0474 J-0.0553 G2 X0.9608 Y2.8233 I-0.0787 J-0.0026 G2 X0.8768 Y2.8018 I-0.0739 J0.1141 G1 X0.6561 G1 Y1.9503 G1 X1.744 G1 Y2.8018 G1 X1.5253 G2 X1.4413 Y2.8233 I-0.0101 J0.1356 G2 X1.4159 Y2.8839 I0.0533 J0.0579 G2 X1.4393 Y2.9424 I0.0757 J0.0037 G2 X1.5253 Y2.9659 I0.0755 J-0.1075 G1 X2.0116 G2 X2.0566 Y2.9617 I0.0026 J-0.2152 G2 X2.0975 Y2.9424 I-0.0154 J-0.0859 G2 X2.1229 Y2.8839 I-0.0474 J-0.0553 G2 X2.0975 Y2.8233 I-0.0787 J-0.0026 G2 X2.0116 Y2.8018 I-0.0753 J0.1187 G1 X1.91 G1 Y0.8448 G1 X2.0956 G2 X2.1795 Y0.8214 I0.0099 J-0.1267 G2 X2.2049 Y0.7628 I-0.0474 J-0.0553 G2 X2.1795 Y0.7042 I-0.0764 J-0.0017 G2 X2.0956 Y0.6807 I-0.0741 J0.1033 G1 X1.5253 G2 X1.4413 Y0.7042 I-0.0099 J0.1267 G2 X1.4159 Y0.7628 I0.051 J0.0569 G2 X1.4393 Y0.8214 I0.0757 J0.0037 G2 X1.5253 Y0.8448 I0.0755 J-0.1075 G1 X1.744 G1 Y1.7862 G0 Z1.5 G0 X4.3104 Y1.6534 G1 F4.0 Z0.0 G3 F8.0 X4.0526 Y2.0948 I-0.7038 J-0.1151 G3 X3.5585 Y2.2647 I-0.4773 J-0.5846 G3 X3.2965 Y2.2245 I-0.0068 J-0.8279 G3 X3.0643 Y2.0967 I0.2306 J-0.6943 G3 X2.8065 Y1.6534 I0.4521 J-0.5595 G1 X4.3104 G0 Z1.5 G0 X4.4764 Y1.4874 G1 F4.0 Z0.0 G1 F8.0 X2.8045 G3 X2.8894 Y1.2057 I0.8737 J0.1096 G3 X3.0702 Y0.9737 I0.6847 J0.347 G3 X3.3297 Y0.8258 I0.504 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Y0.7628 I0.051 J0.0569 G2 X5.1795 Y0.8214 I0.0728 J0.0033 G2 X5.2635 Y0.8448 I0.0741 J-0.1033 G1 X5.9081 G1 Y2.9659 G1 X5.4354 G2 X5.3495 Y2.9893 I-0.0095 J0.1344 G2 X5.3241 Y3.0499 I0.0533 J0.0579 G2 X5.3495 Y3.1085 I0.0764 J0.0017 G2 X5.4354 Y3.1319 I0.0755 J-0.1075 G1 X6.0721 G0 Z1.5 G0 X8.4725 G1 F4.0 Z0.0 G1 F8.0 Y0.8448 G1 X9.117 G2 X9.1621 Y0.8406 I0.0026 J-0.2152 G2 X9.203 Y0.8214 I-0.0154 J-0.0859 G2 X9.2284 Y0.7628 I-0.0474 J-0.0553 G2 X9.203 Y0.7042 I-0.0764 J-0.0017 G2 X9.117 Y0.6807 I-0.0755 J0.1075 G1 X7.6639 G2 X7.5799 Y0.7042 I-0.0099 J0.1267 G2 X7.5545 Y0.7628 I0.051 J0.0569 G2 X7.5799 Y0.8214 I0.0728 J0.0033 G2 X7.6639 Y0.8448 I0.0741 J-0.1033 G1 X8.3085 G1 Y2.9659 G1 X7.8358 G2 X7.7499 Y2.9893 I-0.0095 J0.1344 G2 X7.7245 Y3.0499 I0.0533 J0.0579 G2 X7.7499 Y3.1085 I0.0764 J0.0017 G2 X7.8358 Y3.1319 I0.0755 J-0.1075 G1 X8.4725 G0 Z1.5 G0 X11.5409 Y1.5225 G1 F4.0 Z0.0 G3 F8.0 X11.3202 Y2.0479 I-0.7091 J0.0112 G3 X10.7889 Y2.2647 I-0.5179 J-0.5097 G3 X10.2557 Y2.046 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I CncSimultor it looked perfectly:

Maybe the Arduino firmware is not capable to control such small movements. I consider to use a 3 Axis Parallel Interface with EMC

I also reproduced the problem when trying to engrave a small text in the acrylic piece above - see unfinished "Hello W". The text height is about 0.1", or about 2.5 mm. The V bit I used is really sharp, I think the groove should be finer with a larger angle. Nevertheless, the text seems to be fairly accurate.

I'm using older (and buggier) Arduino software (0012) because it's the latest software with which GCode Interpreter actually fits into Arduino (Diecimila) on Ubuntu. Apparently newer software has larger libraries. The interpreter comes with Reprap related extruder code, I guess I will try removing this code to see if the interpreter will fit on a later version.

The good thing is that the problem appears to be easily reproducible.

This is the cutting process video. The noise is very manageable, but the mess isn't. I need some kind of vacuum to get the swarf out as it forms, otherwise it'll get on the leadscrews, bearings and cause trouble.

Areas for improvement?
1. Speed - I'd like to go 60 IPM +. 15-20 IPM is probably as good as it gets with all-thread leadscrews. Also not sure how will Dremel take faster feedrates and whether pass depth needs to be decreased proportionally.
2. It's pretty inconvenient to attach workpiece to the table. Ideally it should have tapped holes.
3. Vacuum

We're currently using Reprap v1.2 Stepper Driver Boards to drive stepper motors and Arduino as controller. We have not tested Reprap v2.3 stepper board with Contraptor steppers - so I can't really say that they work, but unless overheating of the board is an issue, they should.

The motor you linked has higher torque than Reprap recommended one, but also higher resistance/rated voltage (8V) which makes me wonder whether the stepper board (either v1.x or v2.x) will have enough power to drive this stepper. Usually steppers are driven at significant overvoltage - for example Contraptor steppers are rated for 2.3V while PC power supply puts out 12V.

If you're looking at the above 80/20 sketch, my wild guess is that torque rating around 150-200 oz*in would be needed to move the gantry with more or less decent speed. This would require more powerful stepper board. Please don't hold me to this number though :)
Y and Z motors on the contrary would not need to be as powerful, so if you needed to upgrade, it would likely be for one motor/board set.

My preference in an unknown situation is to start with something cheaper and upgrade as needed, but that's me.
Alternatively, you could estimate the power you'd need based on the estimated weight of the gantry and your desired speeds and accelerations.

On the reprap page (http://reprap.org/bin/view/Main/Generation3Electronics) I saw that they have a new mainboard (V1.2) and new stepper drivers (2.3).
Do you actually use the original reprap board or is your arduino board something else?

The reprap site says, the new stepper driver can control motors up to 2A.
I'd select the following NEMA 23 motor:
http://uk.farnell.com/jsp/displayProduct.jsp?sku=4743167&CMP=e-3e6f
Do you think this particular motor may be powerful enough?

Since buying multiple sets of hardware will become very costly, I'd be happy to choose appropriate hardeware from the beginning.
Please let me know, if you have better motor/stepper driver proposals…

As soon as I have a shopping list, I'll sort out the total costs and go on…

Thanks for all your input!

I'm simply trying different designs, T-slot is useful with larger sizes and it is also faster to build with. On the other hand it's more expensive than angle so there isn't as much flexibility in trying different designs. One of the goals for this particular design above was to build a mini CNC router for cutting 12"x24" size of plywood/MDF/acrylic with Dremel/Proxxon.

Regarding workpiece clamping - with the mini-router, I milled the material in shallow passes - about 1/32" - so the cuts were gradually made deeper without disconnecting the milled part. Deeper passes are difficult for Dremel anyway, and this allows the workpiece to be clamped at the corners. The table can have the grid of holes drilled and tapped for clamping screws.

I can't speak for everyone here but Riley and I are American night owls, correct :)

thanks - I'll need the luck! ;-)

I've already had a look at the other contraptions - including your mini router.
Why did you change the design for your cnc so radically? - Stability?

Besides that, I'm struggling with ideas how to fix the workpiece to the cnc table, while routing.
Large CNCs kind of suck the workpiece and therefore don't require additional clamps, etc..
However, when using clamps the workpiece might start moving around on the cnc table (once the part of wood where the clamp is fixed is cut off).
Neither is it feasible to attach a clamp somewhere at the center of the workpiece or attach it from beyond (using screws or whatever means).

How to you fix your work pieces on the mini cnc?

Before starting some actual work, I think I'll need to clarify a few more issues, such as this.

Another thing: given your response times, I assume you guys are either American night owls or europeans, right?
I'm asking because it appears that you support each other with building your contraptions…
BTW, I'm in Austria

To go from DXF to G-Code, you need CAM software. I've been using CamBam recently and there are other free/open source alternatives out there too. Once I have functional mini CNC, I hope to get to documenting the software chain. Arduino G-code interpreter supports very basic subset of G-Code - straight lines, circles, pauses. No advanced stuff like tool changing (you'd need a tool changer for that too:).

As far as Blender - we'd love to see Contraptor components converted to other 3D formats since not everyone prefers Sketchup. Blender, being open source, would be a great start.

Thanks for kind words, after nearly 2 years tinkering with Contraptor assembling contraptions comes easy :) It's the adjustment and tuning to decent performance that's pretty time consuming. In short, yes - it is possible to build larger CNC using Contraptor components. There are several factors though that need to be taken in consideration:

1. Power of the rotary tool - the best match for Contraptor is probably Dremel/Proxxon cutting wood/plastic in shallow passes. To get benefits of more powerful routers you'd need stronger frame, linear bearings and motors. Probably something to take care of the noise, too.
2. Rigidity of longer beams - this is mostly taken care of by using 80/20 T-slot, which Contraptor is compatible with (80/20 is fairly inexpensive on Ebay)
3. Weight of 80/20 and longer beams - this means either slower acceleration/speed or more powerful motors => more powerful driver boards => bigger power supply. Basically, more $$$.
4. Wear/long term reliability - because the set is mostly intended for prototyping and bootstrapping, long term reliability was not a design goal. With prototyping you would assemble and disassemble things all the time. With bootstrapping, you would assemble a small CNC machine or Repstrap which would mill or print parts for another CNC machine/Reprap.
Now, this doesn't mean that contraptions will fall apart after first use :) it just means that some design solutions will work in the long term for particular applications and others won't. One way to see what works and what doesn't is to try.

The Cubespawn projects goals are to:
Provide a starting point for a bootstrapped manufacturing facility, with open source versions of the main (existing) manufacturing techniques to be added over time. (flexibility is desired over capacity) Like Vacuum Forming, pick and place, CNC routing/milling - and perhaps someday: Aluminum re-melt (induction/arc furnace) plastic re-grind - plastic or aluminum extrusion, on and on…

To keep part counts as low as possible - if it has to make its own parts, then re-useing components and short BOMs are important.

To add a library of parts to make whatever is needed over time and share that as open source designs.

To do it at a reasonable cost - there is more to it than that, but…

There are two main (percieved) benefits to the cube approach…
Mechanical:
Structural ridgidity from a relativly lightweight frame, also modularity - its not clear on the site yet, but it incorporates a pallet handler at the base, power, network, motion control in a small package - I have started with the 1/2 meter version to control costs while prototyping - but most designs will scale up well.

Form Factor:
If designers have a standard to build to, and the completed designs are modular, everybody wins for usability - anything I design, you can use - and if you contribute your designs, I (or anyone else) can then use them, but more important, if you design a Vacuum former, it'll bolt up to my router so you can form and trim-out parts in one process.
This is an open ended system, no constraints except working envelope - but, at the same time, it retains the benefits of standardization.

One thing to note - the cube form makes it harder to access the workpiece, but a second (open) frame for loading/unloading the pallet solves this, and, really, the goal here is automated handling - so its not intended to work like an open CNC table….

I hope this answers your questions, if you have any more, I'll do my best to answer them ;-)

James