The Sledgehammer – Version 2.0

December 4, 2012

Going for a Laser Guided Spin: My 2012 Ferris Wheel Christmas Ornaments

Filed under: Design, Holidays — Tags: — Brian Lutz @ 12:57 am

As you may know, each year at Thanksgiving my family does an exchange of Christmas ornaments.  Coming from a family where a number of people seem to be big on arts and crafts (to the point that several of my aunts run a crafting business that focuses primarily on home decor items using vinyl lettering) it takes some work to keep up with the creativity, but I think I’ve managed to do a reasonably good job of this.  For the past couple of years, I have taken advantage of the laser cutter available at Metrix Create:Space on Capitol Hill in Seattle for creating my own custom-designed ornaments, and decided to take the same approach once again this year, and the result of this project is the ferris wheel ornament you see above.  Although all that work that may sound intimidating to some people, in reality it isn’t nearly as difficult to do as it sounds, and anyone with the right tools (which are freely available open source software) a reasonable amount of understanding of how to create vector graphics could do 75% of the work it takes to design something like this fairly quickly.  Of course, the devil is always in the details, and it turned out that the last 25% worth of fine tuning to get everything to fit together properly took at least 75% of the time I spent on this project.  After the jump, I will go through the process of creating these, and hopefully I can provide some useful tips to anyone who might try something like this.

My previous laser-cut ornament projects:

Probably the biggest challenge I faced on this particular project is that I didn’t even get started on it until the Friday before Thanksgiving.  above you can see what I had originally intended to be my ornaments.  This was done by basically doing a digital version of the paper cutout snowflakes you find in Kindergarten classrooms everywhere around this time of year.  The results actually looked pretty nice when they were cut out, but as you can see they were tricky for the machine to cut, and ended up being too fragile to be practical.  It was actually while I was on my way over to Metrix to do the test cut you see above that I came up with the idea of making a ferris wheel ornament.

Within 3 or 4 hours of work, this is what I was able to come up with.  As with my previous two projects, I worked in Inkscape to create this.  At some point I might go into a bit more detail on how I created the individual pieces if there is a demand for it (it would probably be a lot easier to do with a video than with a Blog post,) but basically it’s a process of taking various shape primitives (circles, rectangles, basic curves and other polygons as needed) and making heavy use of the difference and merge tools in Inkscape to add to and subtract from the existing shapes to create the pieces.  From this, I was able to create the wheel, the tower on which it sits, and “seats” assembled using four pieces that are (in theory) supposed to press-fit together without requiring any glue.  The intent is that the whole thing would be put together using 1/8″ dowel rods, which could theoretically be cut using the laser cutter, but I ended up finding a different way to do this (more on that later.)  Using the Snap to Grid function is critical to placing everything in the correct spot and in keeping everything lined up and symmetrical (for the most part I was working with gridlines at the 1/16″ scale, but the image above shows 1/4″ scale since the smaller gridlines don’t show up at this particular zoom level.)  In order to build up the shapes using this method (particularly for the wheels) it is also necessary to be able to rotate pieces at precise angles.  By holding down the CTRL key while rotating an object in Inkscape, the object will be rotated in 15° increments, allowing the spokes of the wheel to be placed at precise 120 degree angles.  The mockup on the right was used to “test fit” all the pieces together prior to cutting a prototype.

And this was the result of that first cut.  Fortunately, everything looked the way it was supposed to, but there were a number of bugs that would need to be dealt with.  First of all, I hadn’t accounted for the kerf of the laser (the small amount of wood that gets blasted away when the piece is cut) so all the pieces fit loosely together and needed to be glued.  I also hadn’t figured out the best way to cut the dowels yet, and I was using a small hacksaw which was far from precise.  The biggest problem here was that the bottom piece that joined the two tower pieces was just barely wide enough for the wheel, and as a result it didn’t spin properly.  Clearly some tweaking was in order.

After some tweaks, this is what I came up with.  The big change is the increased width of the bottom piece for the towers (which turned out to be a bit too wide here, and ended up getting tweaked down by 1/8″ by the time I was through) and adjustments to the connecting surfaces on the bottom support and the seat sides to narrow the grooves by .38mm (which is .19 mm on each side, a value figured out by some experimentation with a test piece on the laser) to account for the kerf of the laser.  A tweak was also made to the backs of the seats to increase their height a bit and to give them a distinct top to make assembly a bit easier.  In the meantime,I also had a couple of test cuts made using just the seat pieces to test the fit and determine if my tweaks were successful.  In order to account for the increased width of the bottom piece, I also included a couple of spacers to add to the center axle that you can see inside the wheel on the left.

This is what one of my prototypes looked like as it was being cut.

Finally after one more round of tweaks, this is the near-final set of pieces I used for my full production run (the one change I made after this was to add another circle with a hole in it to the top of the towers for hanging ornament hooks.)  There are a couple of artifacts from the screenshot utility in one of the circles, but these don’t show in the actual piece.  The most notable change (besides the slight decrease in the size of the bottom piece) was to slightly increase the height of the seat sides to try to balance them a bit better on their axle in an attempt to make them stay upright better.  I didn’t quite get the results I wanted on this, so that’s something that would probably be a candidate for further tweaking later on.

And this was the layout I used to get the pieces for 6 ornaments onto a 18×24″ sheet of plywood, which was doubled to make 12 pieces.  Since I made last year’s ornaments Metrix Create:Space has acquired a much larger laser cutter that can handle bigger pieces of plywood, so they were able to do the entire run all at once.  Unfortunately, I did make a minor miscalculation here, which you can probably spot if you look closely…

When all was said and done, this is what I ended up with.  Unfortunately, it turned out I was a few pieces short, as I only had enough seat backs and bottoms to make the seats for 9 ornaments.  This is where the miscalculation noted above came into play, as it turned out that I accidentally only included these pieces for 4 ornaments in my 6 piece layout.  They did run a couple of extra pieces when they did the cutting run to cover some that didn’t quite come out right, so fortunately I had (just barely) enough for everyone in the ornament exchange at Thanksgiving, and was able to get the remaining pieces cut later to finish assembling the other ornaments.

Naturally, I ended up with a few leftover pieces.  Or a lot of leftover pieces as the case may be…

This is what all of the seats looked like when assembled.  Even though most of these came together correctly, there were a few that were a little bit loose and had to be glued.  I’d say this wasn’t more than about 4 or 5 out of this whole batch.  In spite of the fact that we are working in a scale of hundredths of millimeters here, we’re still dealing with a rather imprecise medium in the wood, so things like this are inevitable.

As for the dowel rods, the best solution for cutting these turned out to be an X-ACTO knife, using a framing square as a guide.  The center axle for the wheel was cut to a length of 1 1/8″, and the axles for the seats were 7/8″ each.  In retrospect, I probably should have allowed another 16th or so for the seat axles to allow them to spin a bit more freely, but that’s something that’s reasonably easy to tweak later on if I wish.

In order to make sure the piece stayed together properly, I opted to glue the axles in place for both the seats and the wheel.  Ideally I would like the seats to pivot and remain upright when the wheel spins, but I didn’t quite manage this the way I wanted.  The main problem here is that there’s just more friction involved than I would like.  As a longer term project I think I would like to try scaling this up to a much larger (and more detailed) piece, and when I do that I’m thinking that it would probably useful to have some sort of sleeve bearing on this axle to ensure that it can turn freely and not hang up on things.  At this scale, I’m not sure if there’s really a good solution to this problem though.

Application of the glue was done by using a bamboo skewer that I happened to have sitting in my silverware drawer for a really long time but never found a use for in the kitchen.  It happened to be just about perfect for this application, being able to fit nicely into the tiny crevices and apply only a very small amount of glue (I used a lot less glue than this for most of these, just enough to get things to stay together.)  It also fit nicely between the grooves of the seats and  bottom pieces of the ones that needed to be glued to apply just the tiniest bit of glue.

In order to assemble all of the ornaments for the exchange I got something of an assembly line going.  You can see a couple of completely assembled pieces here, as well as several partially assembled ones on the side.  The Ziploc bag was used as a convenient (and disposable) surface that the glue wouldn’t stick to.  I’m sure there’s probably something better to use for this, but sometimes you just need to use whatever happens to be available, especially when you’re assembling stuff at 2am on Thanksgiving morning (as I happened to be in this case.)

Finally, when all the assembly was complete, this was the end result.  Admittedly some of these turned out a little better than others, but since these are destined mostly to end up hanging on Christmas trees (most likely well out of the reach of small children) it will do for now.  The one thing I didn’t have time to figure out was a solution for hanging these on the tree.  I did include holes for ornament hooks on both sides, and what I probably would have done if  I had the time is to tie a ribbon to both towers and use some sort of spreader bar to ensure that there’s enough clearance between them for the wheel to spin. 

All in all, I am satisfied with the way that these turned out, although there is definitely some room for improvement here as well.  Maybe if I had a bit more time I could have come up with a better solution for making sure the seats remained properly balanced at all times, but again, at this scale there don’t seem to be a lot of good options for this.  On the other hand, if I made one of these 2 or 3 times bigger than this it would open up a lot of possibilities for improvements in the design, or even completely different ways to build things.  Somehow, I suspect I’ll be revisiting this one at some point, and when I do, you’ll probably be hearing more about this here.  As usual, I would like to thank the folks at Metrix Create:Space for providing the laser cutter and putting up with my endless attempts at getting things just right.  If you ever have one of those days where you feel like a genius for one reason or another, Metrix Create:Space is the type of place where you can drop in for a quick reality check, and probably learn something in the process.  One of these days I really need to find a good excuse to visit the place more often than once a year…  Maybe it’s time to take up 3D printing next?


Leave a Comment »

No comments yet.

RSS feed for comments on this post. TrackBack URI

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Blog at

%d bloggers like this: