Nov 29, 2015

3D Printed "House of Cards" Stackers

With all the travel I do, I have lots of leftover hotel room keys - the credit card looking type.
I thought it would be fun to design a 3D printed connector which let my kids build stuff using those cards - basically, a house of cards which doesn't fall when you breathe on it ;)

Design Testing First

I started with the simplest, but most important part of the design - the holder which connects to the card.

This is basically a simple slot - a gap between two plastic parts which needed to be just the right tightness to hold the card firmly, while not being too tight or so narrow that the 3D printer has a hard time leaving the space during the printing process.

The simplest test part was step 1 - just creating a block with different sized gaps along the z-axis (vertically upward from the print bed). I didn't bother trying to create gaps on the horizontal plane, assuming that the slightest sag in the filament during printing would fill the gap and make it useless.

Tweaking the design to actually work

After a bit of experimentation, it seemed my Polar3D provided a firm hold on a card with a 1.0mm gap. On my LulzBot TAZ4, the gap was slightly smaller but also didn't give me as consistent a fit with the squashed first layer closing the gap too often. I could have fixed this with re-calibration I assume, but didn't try.

Once I had a simple block that worked, I tried out a few on some key cards, and found that they were simply too easily popped off as I was building. I adjusted the design as a solution to this - basically putting two blocks at opposite ends of a stick with the gaps facing inward so the holder fit over the card like a strap. This worked incredibly well.

Final design and Printing

Once I had that basic "strap" design working, I added an whole set of additional gripper slots facing in all 4 directions as well as on top of the end blocks. This combination proved to be the best and I stopped there and printed a dozen or so of these to test the building.

Building Fun!

I was able to easily build a single column square block of cards about 8 cards high which was very sturdy. The card-grippers print very quickly, as they are made of very little material - probably taking about 8 minutes each at a resolution of 0.2mm. I have yet to break one either since most of the connectors are along the horizontal plane, giving it more strength.

The Model

I've uploaded the basic model to PinShape so
you can try these yourself. It's actually really fun to try printing them in different configurations to meet the specific needs of a house of cards you want to design.

Nov 25, 2015

3D Printed Phone Rack - charge and organize 5 or 10 phones

If you ever find yourself needing to organize, carry and charge 5 or 10 phones at one time, I've designed a solution that might work.

My motivation was to have a quick alternative solution for the Google Expeditions project - where anywhere between 5 to 30 phones along with Google Cardboards are used in a Classroom to take kids on virtual field trips. The logistics of carrying and charging that many phones is harder than it might seem.

Design Goals

I started with a goal of designing a holder for 5 phones. My goals in this design were:
> keep the phones from banging into each other
> make it easy to insert and remove the phones
> have a method to keep the phones in place during transit
> expose the usb/power port for easy charging
> have a handle to carry the phones
> have room for air circulation to avoid over heating
> work with Nexus 5 phones to start (later Asus ZenPhone)

I originally started thinking of a design which would allow for expansion - allowing multiple holding racks to be connected into larger racks, but soon realized that I should focus on getting a solid design done and later figure out that feature.

Starting the Design

With the Nexus 5 phone dimensions taken - I created a simple rectangular box with 2mm of added material on all sides. I decided that the holder should allow for about one-third of the phone to stick out, so it is easy to grab to remove - so I reduced the height of the rectangle by 1/3 (about 25mm).

I then hollowed it out using the 123D Design tool called "Shell" (under the "Modify" tools) and asked for a 2.10mm shell width (I like to use even multipliers of my 0.35mm 3D Printer nozzle diameter). I then thought about how to put multiple of these shapes together to form an array of 5 holders as a single object.

Expanding and Giving Breathing room

Having 5 of these alongside each other in my modeling tool (123D Design), I could clearly see that I should almost completely remove the inner walls between phones so that there was plenty of airflow and much less material needed in the print. I left about 5mm of separator wall on the bottom between each phone and about 10mm of separator at each end. This would form slots which each phone would easily slip in and out of.

The outer walls were still solid, and I wanted to give more airflow there and reduce the material needed. This is where I had my most difficult challenge in actual printing.

I created several "holes" through the outer walls, with rounded tops to allow for better printing without supports. When printed, the "stanchions" which formed between those holes kept printing too weak and breaking during prints.

This kept happening almost regardless of how thick I made them. I experimented several times, and lots of fails and broken 10-hour prints later, I discovered a hole design which didn't produce the problematic stanchions - triangular holes (see pictures later in post).

Practical adjustments

With the 5 holders together now in what looked like a "rack", there were 3 important adjustments.

Avoiding Errant Button Pressing: The side of the phones contain power and/or volume buttons, and with the phone on its side, I did not want the buttons being pressed by the weight against the holder. To avoid this, I cut holes along the bottom of every phone slot, leaving plenty of material to hold the phone, but with enough of a hole to allow the buttons to never hit anything and press by mistake.

Room for Charging Cable: With the phone on its side, the charging port at the end needed to be accessible, so I cut simple grooves about 12mm deep into both sides, so the phone charging cable could be inserted from either end.

Handle and Phone "Seatbelt" :  I knew I'd need a way to carry this thing - a handle of sorts - and a way to secure the phones in their slots so they wouldn't dump out if it tipped over. I created simple handles on each side which would be used for either an elastic strap (seatbelt) and for a Grip that I would design.

The Grip (Handle):

With the handle holds on either side of the phone rack, I designed a simple handle that would be printed on it's side so that it had better strength (things printed along the x and y axis of the printer are stronger than things printed in layers up the z-axis). It needed two hooks to grab onto the handle holds and it needed both a cross bar to hold the phones and a grip for a person to carry it by. I decided to use the slight flexibility in the final PLA plastic part to my favor - so that the handle has to be stretched slightly to fit it into the holds, which would avoid it coming loose while carrying.

From 5 to 10 phones - and Nexus 5 to Asus ZenPhone

With the 5 phone holder finally printing successfully, I decided (with a strong push from my friend who is running the Google Expeditions Pioneer program) to try a 10-phone holder. It was not too hard to cut up my 5-phone model to extract and then duplicate one of the inside phone slots another 5 times. The harder part was stretching the model to hold a bigger phone - the Asus ZenPhone.

Once I had the new measurements, I realized that it would be easier to start the model again with a single phone slot and then duplicate it 9 more times. I eventually got this right - and while it's too hard to describe in words, perhaps I'll make a video of that process eventually. The challenge was more one of measurement discipline than the rote work of adjusting the design. It took 3 tries to get right, as I first forgot to adjust the length of the phone slot, then I forgot to adjust the height of the handle to accept a wider phone.

Final Product

I finally got this right, and after a 13 hour, 50 minute print on my Lulzbot TAZ4, I had a great 5 phone holder. I simultaneously printed the handle on my Polar3D - and the two parts fit happily ever after :)

I got a chance to test my phone holder in the field at the edcampNJ event on November 21, where we demonstrated Google Expeditions for about 100 teachers! The phone holders (both the 5 and 10 phone versions) worked flawlessley.

The one weakness I'm seeing in this design are the separator parts between phones where the charging cables come in - they are weak and starting to give. I expect they will all eventually break off, but I also don't think they are completely necessary to the design. Always looking to improve, I'll tweak that in the next version.

Nov 16, 2015

3D Printed Badges for Anyone and Anything

I like the idea of giving out 3D Printed trinkets which are relevant for people - like a logo of the product they work on or a product they love - or a personalized keychain with their twitter handle.
A more specific way I've seen teachers use 3D Printed items is as a badge for achieving some goal or learning a new skill. This seemed like a good idea - but it's hard to design many different badges and achieving multi-color prints for nicer designs.

I created a badging platform that might help make this better.

The Model Design

A recent two-color logo design for Google Expeditions inspired me to create a simple first version of the 3D badgerizer. It was a simple start - a round platform with a connector, on top of which could be placed practically any small-sized icon which represented the achievement. The Google Expeditions logo itself was tweaked to use this design - and it could be a badge in it's own right.

I created two versions of the badge base - one which had an "inward" connector - that is a hole into which a badge icon could be connected, and one which had an "outey" - a post onto which a badge icon could be connected. I felt this second version would be used more, simply because it is easier to create an intended hole into the bottom of badges rather than a post on the bottom, since most models in 3D Printing need to have mostly flat bottoms to stay adhered to the print bed.

The First Test Badge

The first test to use the badge platform was of course a badge to represent the "spreadsheet achievement" - that could be given to someone who learned perhaps how to use spreadsheets or one of the many features of spreadsheets.

I took the old Google Spreadsheets logo I had and subtracted a perfectly shaped/measured rounded rectangle from the bottom center - which would serve as the receptacle for the post on the badge platform. It worked!

The Real Test

I told my 9 year old daughter about this "invention" - and asked her what sort of badge she thought her teacher might use.

She almost immediately answered "How about a pencil as a Writer's Badge?"

Brilliant! I quickly tried to model a tiny thick pencil with a flat bottom - and again pushed a rectangle shaped indent into the bottom so it can be mounted on the badge. This Writer's Badge came out pretty good - but the yellow coloring of the pencil was not as recognizable as I wanted so I used my Sharpie (tm) marker trick to fix that up ;)

Some New Badge Ideas

Now it's just a matter of coming up with new badge ideas to make these fun and practical. I've come up with some - including the Smile Badge, the the Pi Badge, the Algebra Badge, the Typing Badge - and of course a badge for every one of the Google Apps (since the logos are already done). If you've got ideas for badges, comment on this post and perhaps someone (maybe me) will create it and share it!

How To Make Your Own Badge

It's really simple actually - except that you might have to tweak the clearances for your specific printer and material being used. Generally, it's these steps:

1 - Figure out whether your badge object will be better suited to have an indent (mortise) in the back or an extrusion (tenon). If it can be printed upside down, a tenon is fine, if not, you most likely will want an indent.

2 - Make the indent in the back of the object by "subtracting" material in the dimensions needed (as described in the image above) or make the extrusion/tenon by attaching the tenon object (also as described above). The model file given at the end of this post has the correct mortise and tenon objects included.

3 - Do the opposite to the badge base - or use the correct base I provided in the model file below.

4 - Print a test base and test object to see if the fit works. Don't be afraid to add a bit of glue once the pair is connected to make sure they stay connected. Tweak the dimensions if you need to get a tighter fit or need more clearance to get the parts to connect.

The Badge Model Template

You can find my badge model template described here uploaded on PinShape.
Please comment here with your experience if you try to use this model!

Nov 1, 2015

How to Make 3D Printed Building Sticks

Early on in my 3D Printing experience, I immediately became interested in designing connecting parts. After some fails, some lessons and minor success, I took a break. I came back to this project and now created some simple connecting parts I call "Building Sticks".

The goal for the Building Sticks was two-fold. First, I wanted something that would be fun for kids (and me) to build stuff - like a construction toy. Second, I wanted something I could use to build or prototype simple functional things - like phone stands or business card holders or even just ideas for larger custom objects.

Design Size

One project I had in mind for the Building Sticks was quite large - a printer enclosure - but I've learned that starting small is smart until the design is right. I also knew that the size of the model I created would have an influence on the connector design - particularly the clearances between parts (more on this below). I decided to start quite small - with sticks that were 5mm square around the waist (width and height) and around 30mm - 60mm long (although that measurement would not influence the connector at all).

Connector Design

Before I even finalized the shapes and angles of the objects to be connecting, I needed to get the connectors right. The main goal was to make sure they snapped together easily but also provided a firm hold. Not an easy balance to reach. From prior experiments, I decided on a mortise and tenon design. Here's the basic steps I took to get this done:

  • Model the tenon on a small block that was the same length as the width of the Building Sticks. This would allow the tenon to be inserted both straight on and from the side for 90 degree connections.
  • Add a "bump" on both sides of the tenon - perfectly in the middle of the tenon - as the method to provide a more secure "snapped in" connection on the mortise (which would have an opposite indent to receive the bump). I did this by overlapping a sphere onto the tenon, perfectly centered, then sizing it so it stuck out approx 0.50mm from each side.
  • Create the mortise on a separate block by subtracting a copy of the tenon from an equally sized block (5mm wide and high). This created the exact negative shapes on the inside of the mortise, including the bump, which is now an indent.
  • Create clearance between the Mortise and the Tenon to allow for smooth fit. Open up the mortise - and the indent - by just a small amount to give clearance so that the tenon is not too tight. THIS IS THE CRUCIAL STEP. I do this using the "Push" command in 123D Design on the inside walls of the mortise and the indent - and/or on the outer walls of the tenon (in the opposite direction). 

Clearances on the Connector

As mentioned above, the clearances given between the connecting parts is the most important part of this whole design. I found that at this size, clearances between touching parts should be somewhere in the 0.25mm to 0.30mm range for each side touching. That means for the mortise and tenon, the sum of those clearances became 0.60mm - which was to allow for 0.30mm for each side of the connection. The diagram below shows all the clearance values I ended up with.

Your Printer May Vary!

Once I "perfected" my connector design, I started printing on two different printers, and quickly found that the clearnace values I used for the Polar3D did not work well on the TAZ4. The TAZ4 has a flatter first layer and therefore pushes the filament wider than the Polar3D - so the parts were too tight. Make sure you test on the same printer you intend to use for printing final parts. That also means that if you end up using my models, you may need to adjust and customize the mortise and tenon sizes to fit better for your printer.

Shapes and Angles

The fun part of this design came after I had the connector working well. I could now experiment with all sorts of Building Stick shapes and angles. The only limitation was really "printability" - that is, making sure the shapes I dreamed up would actually print well on my print bed (reducing overhangs, etc). I found that printing both the mortise and tenon along the bed sideways worked best. Building upwards a tenon or mortise was ok, but not as clean, and not as strong (given the grain of the print layers were now perpendicular to the weakest part of the print (vertical layering).

I started with some basic shapes and will expand that as I get experience with what I need in my building. That's the best part - that I can customize these shapes for precisely what I might decide to build. I ended up with straight sticks in two sizes (30mm and 60mm), single height right angles, double-height right-angles (these are magical ;) and the "H with arms" - which are basically 4-way connectors that allow straight and right angle connections in any 4 directions.

Polishing the Design

Sharp corners on 3D Printed parts often come out sharp enough to cut skin. I learned this the hard way when my Pi Bracelet gave me a significant cut on my wrist when it got caught between me and my backpack. Now I almost always try to round the edges on designs which have high-touch. I do this simply using the "Filet" tool in 123D Design, which makes this super simple. A filet radius of 0.5mm worked well on the Building Sticks in the size I was printing.

That's really the only finishing touch I added to this design, but you can add all sorts of other touches if you want to spruce these up - even personalization embossed into the sides of the sticks.

Now What?

My main goal here was to get a basic design for connection which was reliable at one size. I'll now try the following things:

  • scale the design larger to use it as building blocks for a printer enclosure.
  • Create fun toy designs - perhaps hands, heads, feet, tails and other parts to let kids create their own characters.