Hardanger Fiddle uses HTPLA-CF for Stiffness and Style

HTPLA-CF opens new possibilities in 3D printed violin design and construction! 

It's a bold claim, but I'll stand by it. We don't quite have the data for me to claim that HTPLA-CF is magically eliminating creep for all time, but annealed HTPLA-CF is leaps and bounds past any other PLA based filament in terms of long term performance and reliability. I'll stand by it by pouring way too much labor into making this beautiful instrument -- a 3D printed Hardanger fiddle. Spoiler alert, it worked! You can purchase the Modular Hardanger design/print files here.

[This blog is guest posted by David Perry, lead designer and printer wrangler at OpenFab PDX.]

A Harda-what now?

The Hardanger fiddle, or hardingfele in Norwegian, is an instrument native to Norway with a long and colorful history. I'll quote the Handanger Fiddle Association of America here:

A typical hardingfele is beautifully decorated with mother-of-pearl inlay and black pen-and-ink drawings, called rosing. It is topped with a carved head of a maiden (see photo below) or, more frequently, of an animal, usually a lion. Its most distinguishing feature is the four or five sympathetic strings that run underneath the fingerboard and add echoing overtones to the sound. The traditional playing style is heavily polyphonic. A melody voice is accompanied by a moving "drone" voice. Together, the instrument and the playing style create the sound for which the Hardanger fiddle is famous. 

Handingfeles are beautiful to look at and enchanting to listen to. After developing and publishing the Modular Fiddle, I started looking around for different variations on the traditional western violin. There is a vast array of eastern fiddles that are wonderfully different from a violin, but the hardingfele caught my attention as something that is, in construction, close to identical to a violin, but in sound and style is very different. In short -- it's the perfect modular variation for the Modular Fiddle! 

Protopasta didn't know what was coming.

When Protopasta reached out to offer a few spools of their up-and-coming greyscale HTPLA-CF, I don't think they knew quite what I had in mind. This new greyscale HTPLA-CF is the perfect material for the modular hardingfele, and here's why:

1. It's stiff. Not as stiff as standard CFPLA, but it's still really stiff. 
2. The greys contrast very well with metal powder epoxy inlays. This ornamentation is important for a hardingfele. 
3. When annealed, HTPLA-CF could reduce the potential for the plastic to creep: to deflect slowly over time when subjected to a continuous load. With the addition of understrings, the hardingfele must withstand a greater continuous load. And deflection in the neck joint can ruin the performance of the understrings! 

The hardingfele turned into a much more ambitious project than I had anticipated. I struggled to print HTPLA reliably, and the 14 hour body print found every chance to fail.

Printer upgrades, settings changes, and lots of calibration cubes.

The benefits of HTPLA-CF were worth the time spent on my printer and my process. Here's how it all went down:

1. Print on my mostly stock Makergear M2 with 0.35mm nozzle. 
2. Encounter jams every 6 print hours or so on average. These jams were either nozzle clogs or the kind of HTPLA heat creep jam that Protopasta described in this blog post. 
3. Swap out for 0.5mm nozzle -- no more jams at all! 
4. Print calibration cubes to tune extrusion width. More on this, below.
5. Encounter layer shifts due to print head colliding with printed material. This was due to trying to print too much, too fast and was NOT an issue with the material. I switched back to budget PLA to troubleshoot this one. 
6. Reduced layer heights and improved cooling with a squirrel cage fan. If you're printing PLA and still using a traditional computer fan, check and see if anyone has upgraded your printer to cool with a squirrel cage fan. They move air like a boss. 

Calibration cubes are your friend.

I'm pretty sure no one likes taking the time to print a calibration cube. I'm totally sure that no one likes a failed print that used up half your spool of fancy fine filament! I have discovered the joy that is printing zero infill calibration cubes, and now I run these almost any time I change materials.

As I dialed in my settings for HTPLA-CF, I printed many calibration cubes. These all had no infill and no ceiling, so that I could accurately measure the thickness of the extruded walls. For each cube I recorded the nozzle size, layer height, temperature, extrusion width, and flow multiplier. In the end, I printed 0.2-0.3mm layer heights at 220C with a 0.5mm nozzle set to 0.6mm extrusion width and a 0.95 flow multiplier. I'm slicing with Simplify3D, FWIW.

Don't take the knee, anneal.

Bow down to no extended loadings over time! But annealing can be difficult. Annealing failed most often by causing parts to warp. Small parts like the bridge and even the pegbox did just fine, but larger, longer parts tended to warp.

I found success by annealing my parts immediately after printing while they were still adhered to my removable glass plate print bed. I left the parts at 250F in my kitchen oven for 30 minutes for small parts and 1 hour for larger parts. I allowed the parts to cool more gradually by turning the oven off and cracking the oven door.

I'm still working on how to anneal the body, but the neck and tailpiece anneal consistently while still adhered to my glass bed. After annealing, there is noticeable change in the dimensions of the parts. I did not make any design changes to compensate, but instead filed the close fitting joints as needed. It wasn't too tough.

A 3D printed violin like no other!

In the end, it works! I'm still learning how to play Norwegian-style. It's totally different from regular fiddling. I connected with a local pro Amy Hakanson, and had her play my hardingfele. Check it out!