and in one step generate the gcodes required to do this:

All credit for cad.py goes to the original creator Neil Gershenfeld of  MIT Center for Bits and Atoms and David Carr of Make Your Bot who optimised the code that is in use here.

By attaching a pen to a 3D printer it is easy to turn it into a basic pen plotter. However producing the G-codes require to drive your 3D printer as a pen plotter can be anything but easy. This short guide seeks to change that. There are currently a number of ways of producing plotting paths from images. A selection includes:

• The five step Unicorn Tutorial
• The Scribbles Method
• Using the Reprap host software
• Using cad.py (A python script with GUI)

Program Installation

Download the following software for your respective OS. Note that python 2.6 must be used for cad.py to work. Either un-install newer versions or dirct cad.py to work with python2.6 only.

• 1. python-2.6.5.msi (Python 2.6 Website)
• 2. numpy-1.6.1-win32-superpack-python2.6.exe  (Numerical Python)
• 3. PIL-1.1.7.win32-py2.6.exe (Python Imaging Library)
• 4. scipy-0.10.1-win32-superpack-python2.6.exe (Scientific Library for Python)
• 5. Cad.py and some test images (SourcForge)

Generating the gcodes.

Run the Cad.py that suits your hardware. I have included three types all with the same interface but each outputs slightly different gcodes.

• (Cad.py) Plotting with Z axis movement.py -> For use with a three axis Cartesian bot such as a reprap, Makerbot etc. where the pen is lifted off the page due to the movement of the Z (vertical) axis.
• (Cad.py) Plotting with solenoid or laser.py ->For use with a 2 axis bot where the pen is lifted of the page by an action such as a solenoid or a cutting action like a laser is required. (Use fan port for solenoid as it is switched on off with gcode M106 and M107. Commands need to be switched for use with a laser, see “Optimisation” below.)
• (Cad.py) Plotting with Makerbot Unicorn.py -> For use with Makerbot Unicorn system which uses a servo to lift the pen off the page.

When the program begins do the following to test your setup:

1. Select the test image.png file by clicking the “Input File” button and navigating to the “Test Images” folder.
2. Set “in. per unit”: 25.4
3. Click “Cam” button
4. Click “Output Format” and select file type: “.gcodes”
5. Set the following values:
   1. maximum vector: 0.75
   2. tool diameter: 0.03
   3. tool overlap: 0.1
   4. contours: 1
6. Click “contour” and wait for the paths to be generated. They appear as red lines over the image at its edges.
7. Click the save butting and the file will be output to the input directory.

Thats it, your done. Now load up your desired host, run the gcode and watch your bot draw. Here is a timelaps of my plotter at work.

Optimisation

Now that you hopefully have the basics out of the way you may want to know a little more detail. It appears that cad.py takes a black and white image, performs edge detection on the black areas and then calculates tool paths based on that. When choosing your image I recommend you keep its size under 1000pixels or else the rendering time will be come very long (hours+). For best effect use images with clear distinctions between white and black. Although other image formats such as .jpg do work they dont appear to give the same results as png images. Therefore I recommend you convert .jpg to .png and make sure the image is in black and white with high saturation using your desired image software such as irfanview. When the plotting is started the image will be plotted in the positive dictions from where ever the pen is when printing begins. Therefore you can print many images on the same page by moving the pen to a new position between prints.

Furthermore you can copy and past past multiple gcode files into one as long as you add the new starting position at the end of each file. As mentioned above you have a number of variables to play with in Cad.py. To the best of my knowledge this is their functions:

• Window sizes – Changes the size of the display window of cad.py. A larger window can make it easier to see when you have the settings right.
• X Width and Y Width - The size of the image when printed. Roughly equates to the size of the image printed in cm when a .png file is used. Best to do a ‘dry run’ with out a pen first to check the size of your image then adjust accordingly.
• Zmin and Zmax – The distance the pen is lifted using the z axis (Works for (Cad.py) Plotting with Z axis movement.py  only)
• Intensity min/max – Change these to change the level of darkness that cad.py interpreted as an edge in an image. Often a low “Intensity Max” value will help the edge detection pickup less distinct areas.
• Inches per unit – At 24.5 roughly 1cmx1cm image should plot an 1cmx1cm image. Change the value to change the size of your image.
• Maximum vector fit error – How closely the edge detection fits to the image. Very small values (eg <0.2) take longer to process and can lead to jagged edges. Very high values (eg >1) can lead to corner cutting.
• Tool Diameter – The most important parameter. The size of the pen end. Lower values mean more detail but longer processing time. To big a value (eg 0.05) and you will not see the detail. Too small (0.001) and you will get artefacts in the edge detection seen as small boxes and dots.
• Tool overlap – How close two plotted paths are next to each other when more than one contour is used (see below)
• Contours - The number of layers of infill that will be plotted in dark areas. Set to 1 only the outline will be plotted while -1 will give a complete infill.
• Feed rate, spindle speed and tools – all not used.

If you wish to go even further then use a text editor to modify the python script its self (eg (Cad.py) Plotting with Z axis movement.py). Remember to back up the original before making changes.

• Movement speed – Open with text editor, Use Replace All (Crtl + H for notepad) to replace “F2000″ with your desired feed rate (eg F1500) and for the x/y axis or replace all “F300″ for z axis. Then save the file. Gcode generated will now use that speed.
• Reverse solenoid direction – Replace all “M106 S255 (Pen Up)” with “M106 (Pen Down)” and vice versa to change the solenoid direction or for using a laser. Currently the solenoid is off when the pen is down.
• Change unicorn serve travel distance – Change the S value (eg S50 to S60) in the “M300 S50 (Pen Up)”  and “M300 S40 (Pen Down)” commands to change the servo travel distance.
• Change delay time after pen up and down – Replace all “G4 P120″ commands with your desired delay time in miliseconds. Eg P120 (120 miliseconds) to P150 (150 miliseconds.

Finally as cad.py was originally designed to create tool paths for milling there is nothing to stop you from attaching an engraver, laser or similar and engraving your favourite pattern or quote on something interesting.

What I came up with uses a Darlington array (ULN2003) to serve as the NPN transistors for both H-Bridges while 2N3906 transistors are used for the PNP side. These PNP transistors are switched using PN5856 NPN transistors so that the positive voltage output of the Arduino can be used. Its powered by 12V DC running at around 150mA (300mA stall current).

Throw in a few LED’s so that its clear when each direction is activated and the pen plotter now has bidirectional control for the x and y axis. Video of it in action below:

Please note this design was only thrown together to make use of what I had on hand and there are far more effective ways of building an H-bridge.

In the video you can see the two 5kOhm potentiometers. When connected to the ADC on the Arduino they give a full scale range of 726 (256 to 982). With the largest travel distance being 260mm for the x axis this gives an upper resolution limit of approximately 0.36mm. It seems likely that mechanical limitations would limit the resolution to a value far greater than this technical upper limit.

By writing a sketch to record each pot’s value and then pulse the motors until this value is reached it is quite simple to instruct the pen plotter to move to a position and then hold there.

To take this one step further I added two external potentiometers and used them to turn the pen plotter into an overly complicated Etch A Sketch.

You can find a copy of the sketch used to control the plotter here.

I might have a go some time at using the Arduino maths library to get the pen plotter to draw some interesting shapes.

The pen plotter was originally used to plot magnetic hysteresis loops of magnetic materials onto paper using a pen fixed in a holder. A voltage from a scientific instrument was fed to each axis with the size and polarity of the voltage dictating the position of the pen.

Note that all images can be enlarged by clicking on them. 

In the image above you can see the pen plotter with its x and y axis. The pen is fixed in the holder attached to the y axis and can move vertically only. The entire Y axis assembly can then move horizontally to form the x axis.

With the pen plotter turned over and its base removed the internal electronics can be seen.

It appears to be quite old in its design. As I dont have an electrical engineering background I didnt attempt to repair its existing electronics and so they were removed.

With the electronics removed two brushed DC motors and two potentiometers can be seen, one for each axis.

A thin gauge wire is used to move each axis. The potentiometers are also connected to the motors and geared such that a full movement of an axis from one end to another results in 1 full rotation of the potentiometer. It appears the potentiometers were used as position feedback. Each axis slides on a stainless steel shaft with out the use of bearings.

Looking side on these gear reductions can be seen more clearly.

Note the wire is guided by rotating spindles (seen in the bottom left) and spools around the drive wheel to ensure it doesnt slip. Springs are used to maintain tension on the wire where they are fixed to the centre of some of the hubs.

The path of each of the thin gauge wires, one for each axis, is hard to see in these images so I have tried to draw it schematically in sketchup. Note that the actual path in the pen plotter differs, but the idea is the same. This is the x axis.

When the motor turns it pulls the wire through a series of rotating guides to form a continues loop. The whole y axis assembly (the vertical grey rectangle in the image) is attached to the wires at the red points and is then moved left or right depending on the direction of the wire.

Below is the Y Axis.

When the y axis motor turns it pulls on the y axis carriage from the top of the image while also letting out wire for the carriage at the bottom of the image. This causes the y axis to move up, or down if the motor direction is reversed. If the X axis moves the whole y axis moves to the left or to the right. However, the y axis carriage does not move in the vertical direction as the y axis motor is stationary and so wire is pulled in and let out from the right side of the image where its fixed.

Here is one last higher quality photo with more parts removed.

Needless to say the movement of the x and yaxis is a lot more complex than a typical DIY belt driven 3D printer. However this complexity does have its advantages. For example, I imagine wire bought in bulk could be far cheaper than timing belts. Also DC motors a lot easier to find/buy than stepper motors. Perhaps of most interest though is the ultra low weight of the x and y assembly which could allow for very fast direction changes.

The next step is to put a H bridge together with an arduino and see if this pen plotter can be brought back to life.

• A 20x20x15cm build area
• A heating print bed
• A heated build chamber (ambient to 100C) to possibly eliminate warping.
• A respectable print resolution and speed

Over 12 months ago I made my first serious attempt at satisfying these by designing and half building a rep-strap based on the mantis CNC design. However serious limitations in the design and a lack of free time have resulted in the ‘gunstrap’ collecting dust for over 12 months.  Among others, the problems with the gunstrap were:

• High rolling resistance due to metal on metal sleeve baring
• Slow speed due to needing to physically move the heavy print bed and print head. assembly.
• Poor resolution due to the design of the Z and Y axis.
• Extruder stepper located within the build chamber.

To overcome each of these limitations I have spent some time designing a replacement in SketcUp, as seen below.

What you see above is a fully enclosed build chamber that will be constructed from 12mm wood fibre board or similar. The blue transparent section is a double layer glass viewing window that is opened by the handle below it.

When opened, the two axis print head and print bed are accessible. To the right of the window will be a 16 character 2 line LCD display for temperature readouts and the like.

This design features the following:

• All electrical components and motors (ex end stops) are located outside of the heated build chamber.
• Print head weight has been reduced to as little as possible to increase print speed and resolution.
• Rolling resistance is lowered through the use of ball bearings.
• Scissor lift Z axis for increased stability

The scissor lift Z axis will be constructed by modifying a  lab jack similar to the one shown here. If the wooden shell, which also acts as the main structure of the printer, is removed then the workings become more clear. The modified lab scissor jack coupled to a stepper motor can be seen below (click image to enlarge).

Looking from the front top down on the two axis print head stage its seen that its composed of stainless steel shafts for guides like a Mendel, a PTFE sleeve bearing for the print head holder similar to a Ultimaker. Rather than an expensive belt I plan on sourcing some fine braided wire to use as a pulley which I have seen work quite well on older mechanical pen plotters for lab work. I plan on cutting box section aluminium from corner to comer to make L pieces to hold the guide bearings.

Feeding filament into a wades extruder on the side of the printer will be a mounted filament spool. The wades extruder will force the filament up a PTFE tube which enters the printer at a hole located at the top of the printer.

Finally, in a side compartment insulated by double thickness paralleling will be the electronics. This includes a RAMPS based stepper driver system, ATX powersupply and cooling fans.

As no low melting point plastic components or electrical equipment is contained within the build chamber I believe the high build chamber environment of 100C should be achievable. The heat will be provided by the heated print bed and print head only and will be actively circulated by a fan at the top of the chamber.

I am plananing on sourcing the bearings from smallparts.com.au and modifing them to include a flange. The stepper motors will come from robotgear.com.au for around $85 for 4,  including shipping within Australia. I have a month off before starting a PhD in 2012 so hopefully that allows enough time to get this all built and calibrated.

You can find a copy of the 3D model from here. Some parts of the model were sourced from Googles 3D warehouse including the Steep Reel, bolt, Arduino Mega, character display and ATX powersupply.

I would love to hear what people think of this design and so welcome all comments and criticisms. If you have any suggestions for improvements or alternative ideas please leave a comment!

Happy new year to all!

Hasn’t the DIY 3D printing scene been doing this for quite some time now with the use of spars internal structures for solid objects?

The printing, routing or embedding of wires to form a circuit board track is now common place and with pick and place of components well on its well this could become feasible sooner than thought.

There was already an an entry on the RepRap wiki regarding PCB motors but I cant find any evidence that they have been successfully used.

I’m told that its used to grind plastic granules down into a fine powder. What is particularly interesting though is that this will only work if liquid nitrogen is poured in while it is grinding or else it will quickly become jammed. It seems the liquid nitrogen cools to the plastic (−196 °C, 77 K , −321 °F) and so reduces its fracture toughness and allowing it to be broken into smaller pieces.

So is this a practical approach for those at home wanting to attempting to recycle their own plastic for use with a 3D printing? Obviously not all of us have access to liquid nitrogen or even dry ice, so would a home freezer provide much of an advantage?

I was unable to find any useful information on the deformation properties of HDPE, ABS or PLA at low temperatures in the limited time I have available and so its difficult to tell if a domestic freezer (-20°C?) would be cold enough to make a usable difference.

If anyone wants to put on their science hat and undertake a few home tensile tests on a short lengths of 3mm filament to produce a stress-strain curve at low temperatures and at room temperature it could provide interesting results.

A collection of the gears seen in this page can be downloaded from the 3d warehouse.

To begin with, download the involute gear plugin and copy it to your sketchup plugin directory. This plug-in was not produced by me and all credit goes to Cadalog Inc for writing this very useful tool. Then open sketchup and choose ‘Involute Gear’ from the draw menu. From the dialogue box you are presented with three options.

• Number of Teeth.

The number of teeth on your small gear (pinion gear)  relative to your large gear (gear wheel) will determine the gear ratio. If you desire a gear ratio of 2:1 then your gear wheel will have twice as many teeth as your pinion. However, your gear with more teeth would need need to be twice the size in order to have the same sized teeth.

By choosing an even number of teeth you have a range of different exact gear ratios. For example; 12 and 24 (1:2), 12 and 36 (1:3), 12 and 48 (1:4) ect. However, an even number of teeth will result in the same pair of teeth meeting over and over again. By having an odd number of teeth each tooth will meet a different counterpart on every rotation. This helps to distribute lubricant and reduce ware. For example, Wade’s geared extruder has 11 teeth on the pinion and 39 teeth on the gear wheel.

Try and select the highest number of teeth possible while still maintaining a printable resolution. Have no less than 12 teeth and try to avoid a gear ratio any higher than 1:6.

• Pressure Angle.

The pressure angle effects the geometry of the gear teeth. A low pressure angle (14.5) is normally used with high number of teeth (40+) and will give a greater contact area but lead to increased noise and backlash. Source. I would recomend sticking to a pressure angle of 20. What ever pressure angle you choose, make sure it is constant among all gears used together.

• Pitch Radius.

This is not the outermost radius of the gear (the root circle). The pitch radius is the distance from the centre of the gear to the ‘pitch point‘, the point of contact between the two gears.

As such, the outermost radius of the gear for a fixed pitch radius will change for different numbers of teeth. However, no matter the number of teeth, the ‘pitch point’ will remain constant for all gears.

The key point here is that if you want two gears to mesh well, then the pitch radius must be increase or decreased by the same ratio as your number of teeth. For example, lets say you have a small gear with 10 teeth and a pitch radius of 10mm. If you wanted a ratio of 1:3 then your large gear would need 30 teeth and pitch ratio of 30mm.

Once you are comfortable with these settings its quite simple to make a range of different gears. When you have finalised your gear design you can export the file as an STL.

Involute Gear

To create an involute gear, use the plugin as described above to first create the gear outline. The gear outline will appear at the point 0,0 so its good idea to mark the centre position before moving it. Add your centre shaft hole and then use the Push/Pull tool (hot key ‘P’)  to make the object 3d.

Helical Gear

Make sure the centre of your gear is still positioned at the point 0.0. To create a helical gear simply follow the same process as for the involute gear but with one extra step.

After you have ‘pulled’ your gear surface up to make it 3d, select only the top face of the gear and choose the rotate tool (hot key ‘Q’). With the top face still selected position the protractor over at the centre of the gear and right click. If you have an empty space for a shaft in the centre then just hold down shift while hovering the protractor over a horizontal area to lock it in that orientation. Then its just a matter of choosing your desired angle. For a single helical gear the angle used is normally 6,8,10,12,15,20 degrees. Be aware that a greater angle will result in a greater axial load (see below).

Why would you use a helical gear? They can reduce backlash, ware and noise as opposed to an involute gear. This is due to the gears meshing slowly over their length rather than all at once. However a single helical gear will result in a axial (in the direction of the shaft) load. This can be overcome by using a double helical (herringbone) gear as seen below.

Herringbone Gear (double Helical)

To make a herring bone gear follow the same processes as for the helical gear. Due to elimination of axial loading (see below) higher helical angles can be used. Eg 25,30,35,40 degrees. Select the top face of the helical gear and pull it up so that your gear is now double in height. Then use the rotate tool to rotate it back in the opposite direction as the lower half.

The advantage of the herringbone gear is that all axial forces are cancelled by the opposing helices. This allows for all the advantages of a helix gear with out any of the disadvantages. A herringbone gear will also self centre. Please note that if two herringbone gears are even slightly miss aligned and then fixed in place then they will damage each other. Its best to first fix one gear in place on its shaft while leaving the other free to move parallel to its own shaft. Then turn the fixed gear’s shaft and allow the second gear to ‘self align’  before finally fixing the second gear in place on its shaft.

More information about double helix (herringbone) gears can be found here and here.

Straight Bevel Gear

To produce a straight bevel make sure you add the shaft hole after making the bevel or else the shaft the wrong shape. Follow the same steps as for the involute gear then select the top face only. Choose the scale tool (hot key ‘S’) and while holding down Ctrl (to scale into the centre) select an outside corner and reduce the top face in size.  You will notice that as you do this you change the angle of the gear teeth.

The angle of the gear teeth is important. You can choose any angle so-long as the matching gear has a corresponding angle that together they make up 45 degrees. For example, if the teeth on one gear are at 10 degrees off the vertical then the second gear will need to have teeth that are 35 degrees off their original position.

By producing two bevel gears you can transfer mechanical power over 90 degrees.  Bevel gears can also be used to change gear ratios. The possible combinations of size and shape are endless so its best just to have a play around in sketchup to get used to it.

Internal and Planetary (Epicyclic) Gears

The involute gear plugin can also be used for creating internal gears and planetary gears. To create the external gear, first select the circle tool and starting from the origin drag it out to your desired size. This is your external gear.  Next, using the involute gear plugin produce a gear with the exact dimensions you desire for the inward facing teeth of your external gear. This will also appear at the origin. Using the pull tool, make the new gear you just created into a 3D object of any height.

The next step is the important one, select the gear ‘group’ (one click on the gear instead of two) and then right click and from the menu choose Intersect -> Intersect with model. There will be a short pause. Once done you can delete the gear group entirely and you will be left with your original circle with the outline of the gear ‘intersected’ into it. From this you can delete the centre face and pull up the outer face to give you your external gear. This can then be populated with other gears to make a planetary gear system or similar.

You can find a collecting of all these gears in one model here. If you have any suggestions, comments or corrections then by all means leave a comment.

One such tool is Google insight. Google insight is a free tool that’s used by company’s to asses the impact of their product marketing by observing how search interest changes with time and location. It can also give some interesting insight into how awareness of desktop 3D printing has changed over the past 12 months.

For example, the number of searches for the term ‘reprap‘ has continued its relentless growth over 2010 and shows no signs of abating.

The scale bar on the right (0 to 100) just represents the normalised values. In other words, the date with the most searches so far will have a value of 100 and all other points will be some value from 0 to 100 that’s relative to that peak value.

Focusing on only the last 12 months, it can be seen that 3D printing related search terms have continued to experience rapid growth on the preceding 12 months.

What I find interesting about this table is that ‘Reprap’ related search terms are growing much faster than Makerbot related serch terms. This is a little perplexing considering the amount of media coverage makerbot has had over the last year and the shear number of cupcake cnc’s that are out in the wild. Then again, its almost impossible to keep track of the number of Mendel’s in the wild and any media coverage surrounding them.

This is also seen when you search the term ‘reprap’ while excluding makerbot and serch the term ‘makerbot’ while excluding reprap. Keep in mind that this doesn’t reflect the total number of seaches for each term, but rather suggests that one is growing faster than the other.

Looking again at the search term ‘reprap’, this time by region shows another defining trend.

As you would expect, only wealthy first world countries are currently seeking out information about Reprap’s.  Its a little hard to see on this scale, but the Netherlands has shown the biggest increase. Conducting the same search again for the term ‘makerbot’ shows a slightly different picture.

If you look closely at Europe its clear there is less searches for the term ‘makerbot’ when compared to the term ‘reprap’ above. This may again be due to the mostly US based media coverage of Makerbot.

Something else to consider here is that all this information is gathered from google searches only. As google is far from the dominant web search engine in countries such as China (20% market share as opposed to Baidu’s 62%) , it hardly provides a clear picture. Also language barriers may play a part. There is a definite reprap presence in China, and even their own home grown Up! Personal 3D printer which isn’t reflected in the goggle results.

All up one thing is very clear from all this: Desktop 3D printing is growing at an astonishing rate.

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Looking into the crystal ball I suspect it wont be long until well established fortune 500 company’s begin to take this emerging domestic 3D printer market seriously. Within a decade we may begin to see sub $1000USD desktop 3D printers from brands such as Epson, HP, Cannon, Brother or even Apple (The iprinter?).

No doubt each company will have a slightly different idea of how things should be done (filament size, plastic type ect) and chaos will ensure until a set of standards can be agreed upon.  Even if this means a Betamax vs VHS style war.. If your under 20, think Blu-ray vs HD DVD.

What worries me the most though isn’t the hardware standards, but the software standards. If each company tries to limit what you can print on ‘their” machine to only 3d models downloaded from their own market place then this will really hurt creativity. Worse still will be if they word cretin user agreements so that any model you upload instantly belongs to them or if they start to censor 3D models they don’t agree with. Imagine the horror if you discovered your brand new shop bought printer wouldn’t let you print a basic female form because it was deemed unsavoury.

Then again, isn’t new technology usually first utilised by the adult entertainment industry?.. Thankfully all these things,  for better or worse, are still years away.

For some interesting discussion on the future of 3d printing take a look at the pages  linked below.