[Harp-L] 3D printed chromatic harmonica

Vern jevern@xxxxx
Wed Apr 15 01:05:50 EDT 2020

My experiment with printed mouthpieces was many years ago.  However, it appears that even in a new printer,  the voxel size is still large enough to require post-print polishing and sealing of pores.

I suspect that the smoothing process alters the printed dimension in the approximate magnitude of one voxel on each surface.  Thus percentage-of-thickness is the wrong measure.  If the magnitude and direction of the change is predictable, then it could be compensated in the design numbers like shrinkage of a casting.   If the result is smooth enough and is free of pores, then this process should produce a useable mouthpiece or comb.

Quantity is another consideration.  Printing is suitable for one or a few parts for experiment or replacement.  Wherever the quantity is large enough to justify the cost of a mold, molding is preferred. Some printable parts are not moldable but mouthpieces are.  For making Hands-Free-Chromatic mouthpieces, I chose room-temperature molding of polyurethane plastic in inexpensive silicone-rubber molds.  I machined one mouthpiece in aluminum as a pattern, used that to make several molds, and poured mouthpieces in the dozens.   For hundreds or thousands of parts, metal die casting or thermo-plastic machine molding would have been chosen.  Chris Reynolds preferred to machine mouthpieces for the HFC because he had a mill and extensive CNC experience.   

Although new and sexy, I still doubt that printing is the optimum for mouthpiece manufacturing.


> On Apr 14, 2020, at 3:27 PM, David Pearce via Harp-L <harp-l at xxxxx> wrote:
> This is in reply to Vern Smith's comment on the feasibility of 3D printing a chromatic harmonica.  Here's what is stated on the "Will's Make" facebook page.

> "I can't wait to CNC my new design harmonica.  Because it's near Chinese new year, factory didn't agree my order(so sad). So I polish I by myself. It deal! although My way is inaccurate. The 3D metal printing works. And the conclusion is great. The advantages of my design come true. wasting less air force, increasing the sounds of the reeds.”

>   So he 3D printed the parts to test his design and polished the very rough steel print by hand.  There is a new 3D printer that prints durable plastic parts that are watertight.  Here's a description from Shapeways.  "Multi Jet Fusion (MJF) Plastic PA12 is HP's nylon plastic with excellent mechanical properties and a slightly grainy finish. In black, it is also available in a smooth and slighlty glossy finish. MJF Plastic PA12 is an ideal choice for a wide range of applications from industrial parts to durable end-use goods. Its strength, durability and stiffness make it great for functional parts, such RC car parts and mounts. It is also popular for home decor, eyewear and games. MJF Plastic PA12 is printed using HP's Multi Jet Fusion technology and supports very complex geometries and thin features. 

> Black Smooth PA12 parts are smoothed using AMT PostPro3D technology. This is a physio-chemical process that smoothes all surfaces of the part, altering the geometry by no more than 0.4% dimensional change. This process leaves parts with a slightly glossy surface and makes parts watertight. Stepping on curved surfaces may still be visible after the part is smoothed."  I wonder if the 0.4% dimensional change is minimal enough to make this a viable process for printing a part such as a chromatic mouthpiece.
> David Pearce

More information about the Harp-L mailing list