I posted about this a month ago, but after an interesting discussion on the Feature Requests & Ideas forum regarding internal supports, I want to raise the question again with the benefit of further data & background detail. This is an absolute brain dump of where I’m at with this project, so be warned it’s a long read!
After a long journey prototyping and testing my Irish pennywhistle design, I’ve come to the point where I’m ready to start selling them, with the eventual goal of making instruments and doing music performance full-time. The final parts are 3D printed in Formlabs clear resin, given a base coat of acrylic paint, and finally sealed with food-safe 2-part resin. I’m trying to optimize my final production workflow, and while I’ve become a very good woodwind maker over the last half decade, I’m still relatively new to 3D printing. I got into 3D printing specifically to make woodwinds, not as a hobby based around the manufacturing method, so there’s been a significant learning curve, and I’m curious for suggestions based on your experiences.
- Preserve areas of critical accuracy at the windway face and airblade
- Orient print for straightest airstream between windway entrance and airblade
- Optimize support removal to maximize speed of descaffolding, minimize pitting on aesthetic surfaces, and minimize care needed when removing supports
Meet the Irish pennywhistle! Although based on the same mechanism of action as the renaissance & baroque instruments known as recorders, it sounds quite different, and the geometries of the key areas aim to achieve very different outcomes.
Air travels down the windway (1), which is slightly convergent (larger footprint on the entrance than exit), and enters the voicing window (2) via the windway exit (3). The airstream is then split by the airblade (4), which induces alternating vortex shedding. This excites the air column in the body tube, producing a tone. The plug backset (5) plays some cryptic role in improving the “punch” of the sound, but I don’t have a clear understanding why.
There are many important factors, too many to list here, but the critical areas of accuracy with regard to printing them are the windway exit and exit face, the airstream angle relative to the airblade, and the position of the airblade itself. The airblade surface must be smooth and without bumps or pits on both top and bottom surfaces, and the windway exit face should form a crisp 90 degree angle with no beveling of the windway ceiling or floor relative to the vertical axis.
- Print at 100um, wash for ten minutes, using a pipette to vigorously blow IPA in and out of the windway, and cure for 15 minutes at 60C
- Coarse support removal - remove structural supports and non-critical internal supports with flush cutters and x-acto knife.
- Fine support removal - using sections of jeweler’s sawblade and needle files to avoid putting stress on the supports applied to critical areas. This part really sucks if there are default supports on the blade, though I’ve had more success with custom ones. Discussed further down.
- Structural sanding - shape airblade, windway face, and windway exit where necessary. Typically there is some flashing on the windway floor and ceiling. “Stepped” layer flashing is preferred because it is easier to see and is a thin layer right at the windway exit. Flashing due to deformation penetrates farther down the windway, is more difficult to inspect visually, and harder to remove.
- Fine voicing - play the instrument and apply adjustments to shape the tone. Usually involves finalizing airblade length, sharpness, etc. Small changes to the windway are applied with 1000 grit sandpaper if necessary.
Q: What precision is required for the critical surfaces?
A: Five thousandths of an inch for the airblade position vertically, five thousandths of an inch for total distance from airblade edge, and 2or 3 thousandths of an inch for the windway floor & ceiling vertical positions at & slightly inside the windway exit.
Q: Why are you going to so much trouble for a toy?
A: Go look up Burke or Carbony and tell me it’s a toy . These are high precision instruments for serious players, and mine are endorsed by some of the best musicians in traditional music. Plus, with the ability to make around 70 or 80 whistleheads with 1 liter of resin, change my design whenever I want for free, and use simple brass body tubes like the vintage instruments mine are inspired by, my material costs are exceptionally low.
Q: What do they sound like?
A: Like this. It’s quite an old model, but the new ones optimize playing characteristics and tuning across the octaves more than changing the tone.
Q: Why don’t you injection mold them?
A: I’m not rich.
Q: Why don’t you machine them in a high-precision shop?
A: See previous answer.
Q: Why don’t you cast them in some other kind of resin or metal?
A: Because they shrink. See answer to question 1.
What I’ve Tried Most Recently:
Benefits: good airstream angle accuracy, easy support removal once windway exit face supports are cut, minimal supports applied to aesthetic surfaces
Drawbacks: windway exit face deformation caused by supports, sometimes arching supports get fused to blade, causing a chip upon removal.
Windway exit and exit face are one of the hardest things to assess visually, and difficult to measure precisely as well during final finishing. I tried outsetting the windway face and then filing it back to final position, but it was exceptionally difficult to keep a crisp 90deg angle on the face. I made a jig, but it didn’t produce great results, so I suspect there was further deformation inside the windway. These didn’t play great, frankly, and had a rattle on the lowest note which is indicative of something being off in the windway, even if my corrective measures have made the other notes play well.
Benefits: Dead-on airstream angle, no stairstepping on any face, no supports to remove from the airblade, no supports applied to forward aesthetic surfaces.
Drawbacks: tons of internal supports with thick bases that took ages to carve/file/sand smooth. Supports on windway face still introduced some deformation, and thick flashing took ages to remove from the windway exit face. Sanding inside the windway on a one-piece model is suboptimal as it’s easy to accidentally bevel what must be a crisp 90deg corner at the aperture. I produced two very good Ebs on this print, but they took hours to finish. the Ds were disappointing, and had some layer abnormalities in the middle of the mouthpiece section I wasn’t sure the origin of. They originated at the same layer that wierdness showed up in the next print.
Benefits: Easy support removal with no laborious internal support filing. Reinforced airblade support successfully protected it from chipping during support removal, and filing off the buildup wasn’t too difficult. In general the airblade is easier to correct because I can see & measure it much more clearly than the windway.
Drawbacks: Some possible banana-ing of the head, maybe affecting airstream angle. Pronounced stairstepping on windway face, but oddly not in the windway itself. Required filing and laborious internal sanding to get windway face nice and flat. This lengthened the window, and as a result the final blade position was on the edge of being too far away. Still played well, but I could tell the high notes were needing more air, and there was still a bit of a rattle on the lowest note. There was layer weirdness again at the highest section. Under supported?
Benefits: really nice aesthetic surfaces; barely any outer sanding needed at all. Easy access to windway surfaces and airblade. Of all the whistles I’ve made, these are probably some of the best sounding.
Drawbacks: laborious internal support removal, but made easier by the now-open section in the middle. The fitup between the parts just sucks, with lots of sanding, checking the fit, sanding, and checking the fit, with the risk of cracking the every time. I did a lot of research on indexing and engineering fits, but never really succeeded in getting a consistent transition fit, likely due to my own lack of experience. The one I did in purple resin is an improvement, but still required a lot of scraping to fit properly. (I wouldn’t recommend the color kit for final production work, by the way, just product protoypes - it’s like making a whistle out of a Necco wafer. Chalky texture and quite weak.)
Anyway, the biggest questions I have are these:
A. Does printing at increased resolution (say 50um or 25um) improve overall precision, or just at the layer level (i.e. for very small surface features)? Would I benefit from tweaking this? I can’t say I noticed any improvement printing on “adaptive” mode, but since PreForm doesn’t actually INDICATE what areas are “adapted,” who knows…
B. Is there a better way to index the part containing the windway floor and plug backset to the main body tube, such that it preserves the angle of the airstream with high precision? I have zero engineering background and have had to learn on my own, so I might be missing something obvious. Long rails seems necessary for this, but are difficult to fit. Most recorders and handmade whistles are made in two parts to get at the key surfaces.
C. Related to B, how much do you backset your surfaces by for a light transition fit? I’d prefer to just give these a wee knock with a dowel to get them back out, but currently they require a bit more persuasive force, which I’m sure my downstairs neighbors appreciate…
I really appreciate all your comments and suggestions, they’ve been really helpful for my own learning process and getting to where I am with this project today. If you’re interested in the broader world of 3D printed Celtic woodwinds, check out the Lindsay System Chanter, and the 3D Whistle and Bagpipe builder’s group on Facebook!