Getting a Grip : Part 1

Getting a grip on your 3D printer filament-Part 1

With the rise in popularity of low cost 3D printers for use in homes and small business many new printer designs have recently arrived in the market. The cost of ownership for 3D printers is coming down which is driving up access in new markets. With a customer base growing outside of engineers and tinkerers it is important that 3D printers must remain near 100% reliable with near zero failed prints due to mechanical and electro-mechanical malfunctions.

One of the leading causes of print failure is the filament feeding mechanism. By surveying the literature and leveraging our current experience in hardware development we have identified a gap in the knowledgebase for understanding the mechanics and operations surrounding the extruder drive gear commonly used on FFF type 3D printers.

We have found reliability of the filament feed gear is dependent upon three factors 1) amount of contact surface are between the drive gear and the filament, 2) depth of the gear’s tooth engagement into the filament 3) number of teeth engaged in the filament at any one time and 4) the direction of the force vector imparted from the filament drive gear into the filament. R&D at re:3D delved into this problem and below is result of their work.

Figures 1 and 2 below shows a 3D rendering of the filament drive gear “Jaws” that will be mounted to the shaft of a geared NEMA 17 stepper motor.

Figure 1 Jaws filament drive gear
Figure 2. Mid-section view of Jaws filament drive gear
Figure 1. Jaws filament drive gear. Figure 2. Mid-section view of Jaws filament drive gear

The Jaws filament drive gear is machined using a four axis Bridgeport CNC milling machine. In the design process our aim was to optimize the four variables stated above.

  • The amount of contact between the drive gear and the filament is maximized by machining the gear teeth using a cutting tool of the same diameter as the filament it will drive. In our case the filament is 6.0mm in diameter.
  • The depth of tooth engagement was optimized by balancing greater tooth engagement with number of teeth engaged into the filament at any one time. If the tooth engagement is too shallow there will be too little surface area and force imparted to the filament and the teeth will slip and shred the filament. If the tooth engagement is too great the risk of plastic deformation causing the filament dimension to be out of spec for the hot-end and will cause jamming of the hot-end during printing.
  • The number of teeth engaged into the filament at any one time is important in maintaining a smooth and constant push of filament into the hot-end. Consider the job of the filament drive gear is to transform the rotational motion from the stepper motor into straight line movement of filament into the hot-end. If too few gear teeth are engaged into the filament the linear motion of the filament over time will assume more of a sine wave pattern than a constant straight line movement.
  • The force vectors should be directed in the downward direction as much as possible to increase the conservation of energy in the system. Any forces imparted into the filament in the lateral direction will cause plastic deformation of the filament and not translated into pure downward force of the filament feed. It should be noted there will always be a certain amount of lateral force experienced for the pure fact that the drive teeth will need to be engaged into the filament. By studying the section view in Figure 3 below you can see the depth of engagement, the number of teeth engaged and the force vector for a 25 tooth drive gear.
Figure3 Force vectors
Figure 3. Tooth engagement, number of teeth engaged and force vectors

We are extremely excited to have optimized the design and manufacturing of this advanced filament drive gear for FFF style 3D printers. You can view a short video of the machining process on our re:Tech YouTube channel:

Stay tuned for part two in this series where we will perform data collection and force measurement in a real world application of the Jaws filament drive gear.

Matthew Fiedler

Blog Post Author

re:Tech – Extended Watch Dog

Secondary Micro Controller connected to single board computer by UART

Arduino Mini Pro from Sparkfun ($10) (open source)

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Features:

  • ATmega328 running at 16MHz with external resonator (0.5% tolerance)
  • 0.8mm Thin PCB
  • USB connection off board
  • Supports auto-reset
  • 5V regulator
  • Max 150mA output
  • Over current protected
  • Weighs less than 2 grams!
  • DC input 5V up to 12V
  • On board Power and Status LEDs
  • Analog Pins: 8
  • Digital I/Os: 14

Filament Monitor

Filament usage monitoring concept, which uses a filament switch, and mechanical encoder to measure how much filament has been used and if it runs out.  The encoder can also measure if the filament is still moving to detect if the hot end has jammed.

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Internal lighting

OpenGB will include fade-able internal LED light strips controlled by the Arduino mini, with the option of having a proxy sensor to fade the light on when a user walks up to the printer.

Proxy Sensor Features

  1. Distance measuring range: 20 to 150 cm
  2. Analog output type
  3. Package size: 29.5×13×21.6 mm
  4. Consumption current: Typ. 33 mA
  5. Supply voltage: 4.5 to 5.5 V
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Stepper Motor Fault Detection

Detection for over temperate, over current, under current, and skipping will be included in the Arduino Mini Pro or through the main controller.

Nozzle Crash Detection

Accelerometer mount on the trolley can report spikes in acceleration, including in the Z directions.  This is an experiment addition to better detect nozzle crashes.

Features:

  • Operating Voltage: 1.8V – 3.6V
  • Typical Current: 300 μA
  • Range: ±3g
  • 3-axis sensing
  • Bandwidth adjustment with a single capacitor per axis
  • 1x Mounting Hole

 

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Redundant Temperature sensors on Extruders and Bed

These can use the same circuit as the main control board.

Ambient Temperature and Humility

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Features:

  • 3.3-6V Input
  • 1-1.5mA measuring current
  • 40-50 uA standby current
  • Humidity from 0-100% RH
  • -40 – 80 degrees C temperature range
  • +-2% RH accuracy
  • +-0.5 degrees C

Patrick finucane

Blog Post Author

OpenERP—Taking Organization to A Whole New Level

Hello again! In this blog I will be discussing a behind-the-scenes technology called OpenERP that helps keep re:3D running smoothly and efficiently.

Did you know that there are over 1000 pieces in a Gigabot?

The re:3D warehouse has to keep track of inventory and make sure Gigabot pieces never run out. Last summer, re:3D started using a new system called OpenERP to do just that.

What can OpenERP do?

OpenERP is a software that has the power to organize an entire company. It manages the whole gamut from accounting, purchases, and inventory to keeping track of demand. It is structured in modules, and Erik Hausmann is striving to help re:3D make full use of its capabilities. Erik compares OpenERP to a “Swiss Army Knife for business” because it is highly valued for its integrative nature. It not only facilitates transactions in the warehouse, but it also increases re:3D’s small business efficiency overall.

Who is Erik Hausmann?

He’s our Innovation Ninja (formally Technology Innovation Officer or TIO). He manages our OpenERP. He spent six years in Deloitte Consulting working with SAP ERP for Fortune 100 companies in some of the largest systems in the world.

Who is Davydd Kelly?

Davyyd is an exchange student from Australia–he handles all the barcoding in our warehouse. Davydd is an expert in JSON and other open standards. He is working diligently to further refine warehouse processes.

Erik uses Ramen to Explain a Function of OpenERP

Erik survived on Top Ramen as a college student. One day, he looked in his cupboard and saw ten packets of ramen. He knows it takes a good chunk of time to go to the grocery store, so he sets aside an entire day for the purpose of restocking. He knows he should go shopping when he has one or two packets of ramen left as a safety buffer against hunger.

As analogously applied to the warehouse, it is impractical to go looking into hundreds of cupboards to count Gigabot parts everyday. But OpenERP , an MRP (material replenishment planning system), can do all this automatically. While taking into account numerous delaying factors, it can order new shipments when the inventory of a certain type of part runs too low, meaning that a quantity has reached a set minimum. Moreover, OpenERP can even make forecasts about predicted inventory levels.

OpenERP as a Purchasing Tool

Major steps in finalizing a purchase include finding a lead (a likely customer), making a quotation, putting in an order, creating an invoice, and confirming delivery.

OpenERP is also a great tool for re:3D staff when working with customers. OpenERP can make quotes, record factors to an opportunity prediction (ex. There is a 90% this customer will buy our product), add and subtract products, and input discounts or tax. Not to mention it can also create invoices, confirm purchases, and oversee delivery. All this can be done in about five minutes for a quick user. You can find free invoice templates at www.bill.com.

Re:3D is excited to be using OpenERP and will be looking forward to expanding its own systems in the future while living by the open source standard they support.

Keep on printing,

Sunny

Blog Post Author

3D Printing & Dimensional Accuracy

Several members of the Gigabot user community have recently inquired about dimensional accuracy in 3D printing. In this blog, I’ve attempted to explain the following concepts:

  1. Effects of poly count on circle precision
  2. Effects of perimeter order on circle size

One of the challenges with 3D printing is obtaining the correct size for hole features. Currently the preferred file format for 3D printing is the .stl (Standard Tessellation Language). The STL file format describes 3D images as a series of triangles of various sizes as seen in the figure above.

The number and size of the triangles is dictated by the “Preferences” settings of your CAD program. In the extreme example where the CAD model is saved as a “Low Poly count” then the circle or hole feature would be represented by six triangles and the top view would look as the figure below. When 3D printing this circular feature the tool path would follow the triangle geometry and produce a hole much smaller than the original CAD geometry.

The desire to more accurately represent a true circle would lead to increase the poly count to add more triangles to the model and might look like the below image.

The above image shows a poly count 10x greater than the original “low poly count” example. Increasing the number of triangles does in fact give the 3D printer a better, more accurate circular tool path but at a cost of requiring a higher throughput of data for motion control. If the positional data being fed into the printer has too much resolution

  1. The machine may not be capable of accurately recreating the resolution or
  2. The printer controller may not be able to process the positional data fast enough to maintain a decent print speed.

The happy medium is achieved when the poly count is great enough to accurately describe the circle for the needs of the printed part but yet keeping the poly count low enough to allow the motion control system to print the circle at a good speed.

Effects of perimeter order on circle size

The inside diameter of holes are affected by the order of operations in 3D printing. In the below image the slicer settings have Perimeters = 2. Notice the outside of the box and the inside of the holes have two perimeters. This is often done to strengthen the part and increase the print quality. Most slicing software allow the user to decide if the print starts with the inside perimeter and moves to the outside perimeter.

When starting with the inside perimeter the part has improved surface finish. When starting with the outside perimeter the part has improved dimensional accuracy for holes.

The below image shows the actual tool path for a series of circles with diameters ranging from 1/8” to 1”. Notice that each circle is made from many small line segments.

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DIM7.jpg

Also note: Different Slicing programs may also influence the dimensional accuracy of part features.

Additional information on dimensional accuracy in 3D printing [Slic3r Manual]

Is this helpful? What other concepts would you like us to explore?

Happy Printing,

Matthew Fiedler

Blog Post Author

@chief_hacker

How to take your Gigabot Off-the-Grid

One of our values at re:3D is to provide 3D printing technologies to communities around the globe, many of whom don’t have the resources we take for granted.  Access to plastic feedstock, a consistent power infrastructure, and reliable shipping services have always been a requirement to play in the 3D printing space. We want to change that. One of the microsteps in this direction is to find other ways to power our 3D printer, the Gigabot, while still allowing multi-hour (and sometimes multi-day) prints to emerge from our 600mm X 600mm (2ft X 2 ft) build platform.

I started experimenting this past week using a 40W solar panel and a car battery, and had some success printing a small test print. I’ve gotten some questions since then and wanted to explain a little more about my setup, and also find out if there were any other (successful or not) attempts to take YOUR 3D printer off-the-grid.

MY SETUP

Our Gigabot takes 110V or 220V mains power, but then immediately feeds that to a 24V power supply to power the motors, hot end, sensors, USB comm port, and display. The only part that makes use of the mains power is the heated bed (the one that can fry an egg).  Since using PLA as an input material usually eliminates the need for a heated bed, I started there.

Disconnecting the power supply completely, I wired the 12V battery directly to our controller board and internal cooling fan. I later learned that this cooling fan was a great audible indicator of voltage levels – but more on that later.  12V is at the very low end of what our controller board can take in, but the real question was how long could it print for?

THE PHYSICS

I like to equate electricity to water coming out of a hose (like in this great tutorial from SparkFun), so to follow that analogy, I had to figure out if I could hold enough “water pressure” (voltage) to keep the controller alive, a large enough “holding tank” (car battery) to last for the entire print, while using solar panels to add enough “water” (power) to the system during the print.

After testing with a multimeter, I saw that the Gigabot draws about 5A at the most, and less than an Amp when idle (to keep the controller and comms alive), and on average about 3 or 4 Amps while printing (since the heating element cycles to maintain a constant temperature). Judging by the rating on my car battery of 70 Amp-hours, I could count on about 14 hours of power.

I should add that we often exchange Amps and Watts freely when comparing power levels. They are only interchangeable if the volts of the system remain constant (12V or 24V for Gigabot, 120V for USA Mains, etc.), since Power (Watts) = Current (Amps) * Voltage (Volts).

Or per the above analogy: Ability to Remove Mud From Car = Size of Hose * Water Pressure.

THE EXPERIENCE

The solar panel I bought from Fry’s was impressive, but at 40W I know it wouldn’t get to the levels I needed, and I could only afford to experiment with one. Plus, pausing a print when the sun goes behind a cloud just isn’t practical, since it would leave many marks of semi-melted plastic along the way, and the stepper motors would lose their homing location. I knew that the final solution would at least rely on some battery power.

We all know what happens when our car battery is suffering when you try to start it: the lights get dim, you turn off everything electrical, and pray that it turns over and you can get home that night. Instead of a gasoline powered motor and alternator to keep the battery alive, I had a solar panel – and it had to last the entire print. So I had some questions – and like any former space station flight controller, I took lots of data.

THE QUESTIONS

Would 12V be enough to power a system that we have been used to operating at 24V since the very early days? Would my Gigabot’s hotend pull down the stepper motors too far on battery power and affect the success of the print? Could I use all of the available power in the car battery to make a large enough object without any transient errors? Could I turn on and off the solar panel or battery charger during a print without interrupting it?

THE RESULTS

At first things looked (and sounded) gloomy. The first few attempts failed, and it seemed that the battery just didn’t have enough power to drive the hotend, motors, and electronics to keep the voltage levels high enough. Even the fan noise sounded sickly – a lot worse then when I had it set up without the multimeter.

firstpicoffthegrid

The multimeter! That was it!!

I had wired my multimeter in line with the positive line off the battery to read a super accurate space-rated amp-draw during the entire print. I had wanted to measure exactly how much was going in and out of the solar panel, and the battery. The measurement itself was actually resisting the flow of electricity (the equivalent of bending the water hose to hear if water is rushing past the fold in the line). Once I removed the multimeter and tracked only the voltage across the battery terminals, I was able to get over 13 hours of continuous printing time out of my Gigabot – enough to print this 300mm (12-inch) tall vase! Here are the (manually entered) data points for that one:

The solar panels are pretty straightforward, and work very similar to the battery charger I plug into the wall, so for the purposes of my experimentation in the garage, I’m alternating printing on battery power with a charger on/off, solar panel connected/disconnected, at varying voltage levels of the battery. I think I have found the limits, since my prints start failing at just about 11V on the battery now.

Also, ever since I automated my data taking process, I get much more sleep at once, without needing to wake up for data takes with pen and paper (and help from Google Sheets). Check out the new and improved version with a little help from plotly!

An interesting part of this method of gathering data is that you can start to see the cycling of the cartridge heater very clearly as the extra current draw pulls the battery voltage down each time the hotend is full-on. This will be useful in tweaking my PID values no doubt, and could also lead to better methods of insulating the hotend so it doesn’t need to heat up as much, thereby saving valuable amp-hours!

NEXT STEPS

Clearly there is a little more work to do before we have a brownout-proof or solar-ready Gigabot out of the box, but I think these experiments prove it’s within the realm of possibility to create 3D objects anywhere – given a robust enough printer, and a light bulb’s worth of energy and imagination.

Chris Gerty

Blog Post Author

re:Tech – Control Board

Controller

The new controller for OpenGB is loosely based on the open source RAMPS 1.4 control. The RAMPS 1.4 controler mounts on an Arduino Mega as an extension board (known as an Arduino Shield). The goal of the OpenGB controller is to include the following: motor driver for each motor, thermo couple and thermo resistor inputs, enough MOSFET power output for dual extruders, fan, and bed relay, endstops, and extra serial port terminals. This configuration keeps all of the active components on the professional board (arduino) and allows us to design with (mostly) with passive components.

ramps_board

The controller board will include the following features:

Stepper Motor Driver Sockets (7 drivers)

A total of seven motor drivers will be included, one (1) for the X-Axis, two (2) for the Y-Axis, two (2) for the Z-axis, and two (2) for extruders. The sockets are based on the Ti DRV8825 chip carrier board available from a number of suppliers and are currently used in the Gigabot 2.0.

image40_cropped

The sockets will also add support for the fault and VREF pin on the Sure Step carrier boards. This will allow for better error detection and for programmatically setting the current of each driver.

Preliminary Motor Driver Socket Schematic

Thermocouple Support (3Circuits)

Two thermocouple inputs will be included in the preliminary controller. They will be based on the AD8495 chip.

image41_cropped

Thermo Resistors (4 Circuits)

Four thermo resistor inputs will be included in the preliminary controller. They can be used for controlling the temperature of the two extruders or monitoring the temperature at other locations on OpenGB. The inputs can also be used for other analog sensing needs.

End Stop Terminals (8 terminals)

Eight (8) end stop inputs will be included in the preliminary controller. They will be labeled X-min, X-max, Y-min, Y-max, Z-min, Z-max, Filament Out, and extra.

Power Mosfets (4 circuits)

Four (4) power mosfets circuits will be included in the preliminary controller, based on the STP55 mosfet which is rated at 55 amps. Each circuits includes a indicator LED. The Circuits will be labeled Extruder 1, Extruder 2, Bed Relay, and Extra.

Serial Connections (2 terminals)

The arduino serial connection UART 0 and UART 1 will have terminals for easy integration. The SPI and I2C ports will also be broken out for onboard access.

These can will used in future iterations to avoid going through the USB hub with a direct UART to UART connection between the single board computer and the controller.

Reset Switch and Input

A reset switch will be included on the control board. There will also be a terminal block for an external reset switch. This switch should not be necessary for any normal operation.

Input for Induction bed Sensor

A single voltage divider will be included to enable the use of a bed touch less bed sensor to be used as the Z min limit switch

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First revision is shown below, but I am assuming that it is going to change. After we test it I will post the design files, so you can take a look.

Patrick Finucane

Blog Post Author

re:Tech – OpenGB Cat proofing, Size and Shape…

(note the image above is a concept image only and not a real design)

The OpenGB project gives us a chance to think about how to add design elements or change the Gigabot configuration to make it fit better in a home office setting.  There are a few of us at re:3D that have Gigabots at home and also have cats, dogs, babies and whatnot.  Unfortunately our loved ones don’t really use common sense when jumping on the Gigabot or nibbling on it to see what it might taste like.  (I have explained to Mr. Squeakers that the Gigabot is not a cat toy / house, but he’s a bad listener.  It is a character flaw.)

But anyway…

So at the preliminary design review we identified a couple of area to see if we can make less tempting for little hands or paws. What do you think? Do you have a cat that attacks your 3D printer? Let us know, email patrick@re3d.org.

pinch_and_burn_point

Because of it’s large print volume the Gigabot 2.0 does not fit through many interior residential doors.  While there is some work arounds for this in a pitch, OpenGB is an opportunity to try to balancing shrinking one dimension of the Gigabot to less than 30 inches while trying to maintain the large build size.  How big are your doors?  Email and let us know, (patrick@re3d.org)  My interior doors are around 30″, and searching Home Depot and Lowes doors seem to be 30″, 32″, and 34″.  But there doesn’t seem to be a standard (for internal doors).

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Patrick Finucane

Blog Post Author

Enabling the Future: Gigabot & Open Source Prosthetics

Jon Schull of the Rochester Institute of Technology (RIT) is the leader of a global volunteer network called e-NABLE. Volunteers build prosthetic hands out of 3D printed parts for young children all over the world, or send the parts so kids and parents can take part in the building themselves. The network really does “enable” people by giving them a “helping hand”.

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From e-NABLE Prosthetists Meet Printers Event Album

e-NABLE has developed quite a few wrist-activated prosthetic designs, but recently, they have added a mechanically driven arm design to their collection—the RIT Arm, developed by RIT. E-NABLE’s design collection is always growing so it can accommodate a diversity of situations. However, the new arm-activated prosthetics have larger parts than wrist-activated prosthetics, and it so happens that the print beds of the desktop 3D printers that had been in use were too small for some of the parts.

 e-NABLE Prosthetic Recipients

re:3D got wind of the news when several chapters of e-NABLE applied to the Great Big Gigabot Giveaway last summer. Not long after, re:3D’s Catalyst, Samantha Snabes, visited Frankie Flood at the University of Wisconsin and David Levin over the net, while re:3D’s Chief Hacker Matthew Fiedler visited the first e-NABLE conference, also the  first event re:3D ever sponsored. Before long, re:3D had donated a Gigabot kit to e-NABLE.

Jon Schull comments, “With their generous donation, Gigabot is helping create a world in which global communities can turn bigger ideas into bigger and more empowering realities. Sometimes bigger really is better!”

e-NABLE will be putting their Gigabot to good use right away:

“There will be a team of 4-5 students working on this design at the MAGIC ACT lab at RIT this fall and having access to this printer [Gigabot] will make their research and development, prototyping and print times much faster and more efficient.”

(From: http://enablingthefuture.org/2014/08/26/re3d-gifts-a-gigabot-to-e-nable-the-development-of-3d-printed-arm-designs/#more-1305 )

RITArm
RIT Arm

e-NABLE uses a variety of technology, such as exoskeletons and myo-electric engineering. However, mechanically driven prosthetics such as the RIT Arm prosthetic requires no electricity to operate. In situations where recipients have difficulty affording or maintaining devices with higher technological developments, or live in high-risk areas where expensive electronic parts are liable to be stolen, a mechanical arm would be invaluable.

In addition to the RIT Arm, e-NABLE‘s growing collection of prosthetic devices help address a wide array of specific needs. Other devices include:

  • The Raptor Hand
  • The Cyborg Beast
  • The Talon hand 2.X
  • The Odysseus Hand
  • The Second Degree Hand
  • The Owen Partial Finger Replacement
  • And more
e-NABLE Prosthetic Recipients

For full descriptions visit: http://enablingthefuture.org/upper-limb-prosthetics/

Sources:

http://enablingthefuture.org/

http://enablingthefuture.org/2014/08/26/re3d-gifts-a-gigabot-to-e-nable-the-development-of-3d-printed-arm-designs/#more-1305

Sunny

Blog Post Author

Gigabot & Prosthetics: Introducing E-NABLE and 3DMulp

Two new customers have been unpacking and assembling their Gigabots this fall. They are miles apart from each other, yet they share the same dream of using creative new technologies to improve peoples’ lives. They are both using Gigabots in conjunction with other technologies to print open-source prosthetic hands.

Both were also contestants in last summer’s Great Big Gigabot Giveaway

From Bogota, Colombia Francisco “Pacho” Posada, has started a company called Manatí Lab.  He is developing a robotic hand prototype called 3DMulp, which uses myoelectric technology.

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pachohanddev (1)

Coinciding with Pacho’s delivery,  Jon Schull of the Rochester Institute of Technology (RIT) also received a gigabot kit.  Jon is the leader of E-NABLING THE FUTURE, a network of passionate volunteers using 3D printing to give the World a “Helping Hand”.

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In future posts, I shall be following their stories. Stay tuned for more!

Photos Courtesy of:

https://3dmulp.wordpress.com/

http://enablingthefuture.org/2014/08/26/re3d-gifts-a-gigabot-to-e-nable-the-development-of-3d-printed-arm-designs/

Sunny

Blog Post Author