3D printed endpin shims (vs CNC, etc.)
Disclaimer: We don’t use the kind of low-end 3D printer demonstrated in this post, but it’s exciting to see what’s possible! For anyone starting out, we recommend sending 3D files to XOmetry.com, or a similar online manufacturer, and selecting Hewlett Packard’s Multi-Jet Fusion (HP-MJF) from the many available options. But that’s a conversation for another post!
Until very recently, inexpensive consumer-grade printers were, essentially, toys. In addition to cosmetic issues with the prints, there were structural weakness, especially along the “z axis,” or vertical dimension. While SLS and MJF printers operate in a different way by fusing powdered printing material into a solid block, the tendency of FDM towards structural inconsistencies prevents Saddle Rider from trusting them for endpin mounts other high-stress components.
Now, disclaimers aside, on to the fun part of this post!
A couple of weeks ago, I decided to check out the “state of the art” for low-end FDM printers by printing a thin (i.e. challenging) endpin shim file by taking it to our local library “Maker’s Space” in Ithaca, NY. The librarian was very helpful, and kindly printed out 2 copies of the file — one to destroy in testing its structural stability, and the other to use on an endpin. He used the library’s new Prusa Mini 3D printer with its bundled software. A quick Google search just now (Dec. 2021) shows these printers are currently selling for about $349. For testing, I selected an old German endpin I’ve had sitting around for years. Lathing the shaft to a straight 20 mm cylinder from the existing 17:1 taper was an easy beginner’s level job on a small hobby lathe. First, I tightened the endpin rod into place using the thumbscrew. Next, I tightened the endpin into the lathe so the mount could spin freely. (Wearing goggles, and selecting a fairly slow spinning speed for safety was a must!). Finally, I cut down the tapered mount into a 20 mm cylinder, stopping to measure often. For the finished result, check out the photo below. The sample Prusa shim is pictured to the right of the endpin.
Although both shims were printed accurately to just the right size, the first thing I did was try to destroy one. Surprisingly, the corn-based PLA “bio plastic” was much harder to break than I expected! It held together well in all dimensions, including the z axis, and even this very thin shim was virtually impossible break by hand. Suffice to say, PLA is much tougher than any kind of wood I’ve encountered. For shimming endpins, it seems stronger per cubic mm than the end block it is pressing against.
The next step was to examine the shim for sizing imperfections, and here I learned some things. The lower half of the taper was perfect - a 17 : 1 ratio - but at the midpoint there was a tiny step between filament layers. After considering this with the librarian, we came to the conclusion that this point corresponded to the point where the shim’s wall thickness was getting near or below the printer’s nozzle thickness. Although initially disconcerting, we realized that there is an easy fix: When using low-end printers to create shims, be certain to select a 3D file that has a minimum wall thickness of about 1.25 mm. Then the printer software can do a better job with the taper because it has about 3 passes with the .4 mm nozzle to fill the wall. Many newer printers, even inexpensive ones like the Prusa, have optional .25 mm nozzles that help with thin-walled prints, but I suspect those “mods” might be more susceptible to clogging and slowing down the printing process. (FYI, the librarian says that the library’s new Prusa Mini, even with its .4 mm nozzle, offers better quality prints than the much more expensive machines the library purchased several years ago.)
To see the “step” in question, check out the red arrow in the photo below:
Note that, even with this imperfection, this shim made on a $349 printer is a pretty good fit! Before ruling out the usefulness of cheap printers for making shims, take a look at the photo below.
The shim on the left is an expensive acetal (“Delrin”) plastic one manufactured using CNC that comes bundled with high-end endpins retailing for $400 or more. The manufacturing process wastes lots of plastic because the excess material is cut away, rather than built up with “additive” 3D printing technology. Because of the limitations of the cutting process, the spinning shim would break down or melt during CNC if the walls were made as thin as the 3D printed shim on the right. Even if the CNC Delrin shim could be made to the same dimensions as the HP-MJF 3D printed nylon one on the right, it would weigh much more. This combination of heavier material and thicker walls has disadvantages acoustically (in my opinion) as well as environmentally. The thicker walls required for a Delrin CNC shim also mean that the endpin mount shaft needs to be cut thinner to fit in a hole of a given size. If making the mount from aircraft aluminum, it will still be strong enough, but if a goal is to recycle antique wooden endpins and refit them into instruments, the mount shaft should be left as thick as possible to avoid cracking when string tension is applied. Using thin-walled shims can also prevent unnecessary reaming of an instrument’s endblock.
Saddle Rider’s Free Creative Commons 3D Endpin Shims can be used as master files for either CNC or 3D printing, but we highly recommend using the 3D process for the reasons mentioned above. Either commercially 3D printed shims or those made on an inexpensive consumer grade printer, thoughtfully used, can work well. If you would like to give 3D printed shims a try, please email us to receive a link to XOmetry.com’s $50 new customer credit. By using XOmetry for your printing, you’ll help out our small business because we also receive a $50 referrer’s credit. Please keep in mind that most items have a minimum cost ranging from $15-30 because of the programming and machine setup. In those cases, it is as cheap to order multiples as it is to order one. When you choose a shim size that will be useful to you, play around with the quantity in the quote to get the best value. We recommend selecting the HP-MJF nylon 12 printing method with “standard finish” and “dyed black” options for endpin shims. This material cuts easily and cleanly with any fine-toothed saw. It is very hard to crack and has great resilience.
