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

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.

dim4
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

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”.

enableevent1
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

Turn Your Logo into 3D Printed Awesomeness

It’s one thing to have your company’s or school’s logo on a T-shirt, but have you ever wanted to make a 3D model of your logo to use as a keychain, business card, or maybe a coffee table? In this blog I’ll show you the process I use, and how (kind of) simple it can be. No, really, I’ll keep things basic and in all cases rely on much smarter people and tools than I could muster up myself. 

Of course if you have any other suggestions for a better method, corrections/clarification to this method, or are skilled in the “complicated” ways of doing this, please leave comments on the cross-post on our Facebook page or G+ Community.

So, let’s get started.

Step 1: Find a logo

Say you have a really cool company and one of your co-founders is a ninja of design. Chances are you have a great 2D logo that is just screaming for access to that 3rd dimension. In this example, we’ll use Katy’s re:3D logo. Make sure you have your file saved locally as a .png, .jpg, .gif, or .bmp. These filenames are of the “raster” variety (think pixels on a TV). The clearer the image the better, because we’re about to convert these raster files to vector files (think connect-the-dots meets color-by-number).

Step 2: Convert your image to a vector format.

There are a bunch of ways to do this in expensive (and probably inexpensive) image processing packages, but I found a pretty solid online converter that does enough to get us by without knowing anything about layers and paintbrushes. Go to http://image.online-convert.com/convert-to-svg and upload your image file where it says “Upload your image you want to convert to SVG:”. Select the “Monochrome” checkbox to help prevent it from getting too confused. Click on “Convert File”. Your .svg version should download to your default directory. Note where this is since you’ll need it in Step 5.

Step 3: Create a new 3D model using Tinkercad.

Go to https://tinkercad.com/ and sign up for a free account. I guarantee you’ll use it again. Once you have an account, and have either skipped or run through the actually pretty useful tutorials, start with a fresh palette using the “Create a Design” button from the dashboard.

Step 4 (optional): Customize your palette.

You’ll be presented with a blank grid, and a random name will be assigned, like Ominous Seapod or something. Click on the “Design” menu, and then “Properties”. Change the name to “3D Logo” or something similar and more original. Choose the visibility and license you want, and then save changes.

Step 5: Import your vector file.

On the right side of the screen you should see an “Import” section. If it’s not already expanded, click on the triangle to do so. Then click “Choose File” and point it to your .svg file created in step 2.

Step 6: Genesis!

Here’s where you need to experiment a bit. Depending on how much resolution you kept in your original file, the model may completely overwhelm the design space. For now, choose values of 5mm for the height and 20% for the scale. This will make sure that you can at least tell if your model ended up on the canvas (and it doesn’t just cover the entire field of view with a single face. For rescaling, if you want to maintain the 5mm height, it’s much easier to just re-import at a different scale, rather than scale with the Tinkercad tools on an over/undersized model.

Step 7: Tweak your model from within Tinkercad.

This is where the tutorials from Tinkercad are useful. Use the zooming and pan/rotate tools via your mouse or trackpad to analyze the model, making sure that all of the detail you need is there. If you see too much missing or some jagged lines, try to find a higher resolution image to start with, and go back to Step 2 and try again.

Adding bits: Tinkercad will also let you add a platform (or anything else) on your model. This can be useful if you have letters in the logo that float free when converted to 3D. Those free-floating insides of “O”s and “A”s will float right off the final product when you 3D print it out, so best to find some way to tack it down. The easiest way to do this is to create a “Geometric” shape from the right sidebar that is an approximate shape of the logo (rectangle, circle, etc.), and give it a dimension of 2mm high. Place it on the platform next to your logo, size it right, make sure it has the same bottom level, then move it right on top of your logo. When both pieces look like they fit, select both at the same time (by simply dragging a select box around the entire thing), and click on “Group” above.

Subtracting bits: If you needed to put a hole somewhere on the model for a keychain, cup holder, etc, all you need to do is follow the above process, but make it a hole instead of a “color”. Use the buttons at the top right to do this. When you “Group” your logo with a small cylinder that spans the height of the model, voilà! It’s a pendant!

Step 8: Export as an .stl file.

This step couldn’t be easier with Tinkercad. Click on the “Design” menu, then “Download for 3D Printing”. Select “.STL”, and the file will start downloading immediately.

Step 9: Find yourself a 3D printer.

They’re popping up everywhere these days: your local library, makerspace, Earth-orbiting laboratory… wherever you are, you’re probably not too far away from a 3D printer with some spare time on its nozzle. If you can’t find one nearby, you can of course order a 3D printer of your very own (we recommend this one, especially if you go the coffee table route) or have someone else print it via a service such as Hubs or Shapeways.

Step 10: Don’t stop customizing!

The skills you’ll learn and feeling you’ll get by going end-to-end in making something that never existed before is like no other. Welcome to the world of mass customization, where you don’t have to make 10,000 of something in order for the act of designing it to pay off. Make some new models.. iterate, experiment, and most importantly, share it! If you make something awesome consider posting it on a model sharing platform such as SketchFab and sharing the link here in the Facebook or G+ comments.

Chris Gerty

Blog Post Author

re:3D – Beta Pitching at WebSummit 2014 in Dublin

Hi Friends,

As you may have noticed, the re:3D crew hasn’t stepped out of the office much this year.

While we miss the community, our little team elected to spend our limited resources in bettering Gigabot, meeting as many customers as our gas tanks would allow, and getting organized as a full-fledged small business. Now that we have parts in inventory and an amazing staff to help with order fulfillment, we are pleased to announce that we have a little more bandwidth to be with many of you this week at Web Summit 2014.

We’d love to chat if you plan to attend and/or meet up with any media or companies you think would be valuable.

You can find us at the following events:

Belfast Summit: You can catch us on the Summit bus heading there from Dublin on Nov 2nd & back on Nov 3rd or at any of the scheduled events.

BETA Exhibit: Last spring we applied for a discounted opportunity to attend Summit as a featured start-up. We are honored to be selected for the BETA showcase. As a BETA startup we will be exhibiting on Nov 4th in the Hardware area, which is located in RDS Main Hall. Our stand number is HRD102. 

People’s Panel: Thanks to you we placed #5 out of hundreds who applied to Summit’s popular & entirely crowdsourced stage of speakers from around the world. For making the Top 10, we will be moderating a panel we proposed on  Nov 4th.  

Time: 16:19-16:34 at the Simminscourt Venue | Topic: Toilets & Trash-Will 3D Printers Save the World? | Panellists: Ion Cuervas-Mons, Asha Saxena, Tina Stroobandt

BETA Pitch: After 2 weeks judging over 1,500 applications, the Web Summit judges chose their top 200 companies to pitch during Web Summit. We’re delighted to share that re:3D qualified to join the PITCH BETA group! Watch us compete against the best companies beginning with Round 1 on Tuesday at 14:00 GST for almost $20K USD!

Finally, we were blown away when Samantha was selected as a Women in Tech Attendee!

Don’t have tickets, but planning to be in Dublin? We’ve also registered for the following side events:

Let us know if you or a friend would like to say hi!  We’ll also be making a couple of BIG announcements and traveling with some pretty cool prints we’d love to show off!

See you soon?

CHECK BACK OFTEN – WE’LL BE DOING OUR BEST TO ADD EVENTS AND RSVP LINKS ALL WEEK!