First I take measurements of crucial areas, like sound hole radius and tongue extension profile shape.

I also grab a scan or photo of the area at this point, to use as reference.

Then I fill out the 3d model in CAD.

The plug required the following design attributes:

• Friction fit so no adhesive is needed to mount it to guitar
• Soft material so as not to scratch the finish
• Flexible to make it easy to install / remove
• Low profile so it is unobtrusive
• Recessed into sound hole to allow for extra clearance when fingerstyle flamenco playing
• Internal fillets to increase strength / surface area where plug will be stressed when removed from guitar
• External fillets to improve comfort and aesthetics

Once I’m happy with the 3d model, I extract the 2d dimensions.  This allows me to test print my drawing on paper 1:1 scale to check crucial details in the real world (cheaper and quicker than setting up the 3d printer at this stage).

I then cut the drawing out, give it a handle with some packing tape, then offer it up to the sound hole to check fitment. If it’s good, I can move on to printing; if it’s not quite right, I can go back and adjust the model in CAD.

Once I’m happy my model is at the right specs, I turn on the 3d printer and set it to preheat.

I’ll also rapidly heat up my printer enclosure with an old hair dryer.

This quickly helps to get everything warmed up and as dry as possible.

TPU is hygroscopic so very susceptible to any humidity, and because it is a highly flexible filament, any moisture can cause bubbles, poor quality prints or failures.

I don’t have a filament dryer, so I store my filament in these hermetically sealed boxes, with some DIY mesh baggies of self indicating silica gel.

As you can see by the hygrometer, I can get the humidity down to a

stable 10 %RH

It’s a good way of keeping things dry, but even with this storage, I’ll still slowly heat the spool of TPU up in my oven at 50 degrees C, for at least 1 hour before starting any print.

It’s another fail safe and really helps to drive out any moisture in the filament

I’ll also monitor my enclosure to see what the temp and RH% are at, before loading any filament.

And I’ll dot more of those silica baggies around the printer’s enclosure to help limit any moisture while I’m printing.

As you can see, these self indicating silica gels have turned green from orange, which means they are absorbing moisture.

Now I’m happy that my drawing is valid, and everything is warm and dry, I can upload my STL file to the 3d printer’s slicing software.

This software generates the GCODE for the printer, and determines the quality and speed of the print.

I pretty much stuck with a standard profile setting for TPU.

The only things I changed were the density of the supports.

Because when printing TPU, you can change how flexible it is by increasing or decreasing the density, but when it is warm it becomes even more flexible anyway, and so the issue comes when your print requires any overhang supports, as these tend to sag.

(The support being a sacrificial print that you peel away from the actual print, that helps support the form of the part that you want to keep)

With other filaments, the general idea is that you make your supports as minimal as possible. This decreases print time and allows for easy removal once print is done, as they are less dense than the actual print and break off easily with no issue.

However with TPU, I always find this method leaves a poor quality surface at the support interface, as the highly flexible filament sinks into the gaps between the minimal supports.

So with my print, I actually increased the density of the support to be much greater than the density of the print I am keeping.

This left a better surface at the interface, and made it much easier to peel the flexible sound hole plug away from the less flexible and more dense support.

The other major setting I changed was the print speed.

I reduced it right down to 20 mm/s

This means the print took 7 hours to complete, but the quality of TPU increases massively at slower speeds, and in this instance, I favoured quality over speed.

The other issue to watch out for, is that the force required to turn the heavy spool of filament, is often greater than the force it takes to stretch the filament as it is being driven through the extruder.

This can lead to over tension of the filament between extruder and spool and can create under extrusions in your print.

To get over this, I tightened up the in-feed tension gear and made sure my spool periodically had enough slack.

It’s not always necessary to babysit the printer like this, but for safety reasons I never leave my printer unattended anyway . So this wasn’t much of an inconvenience, as I can usually find something to do whilst the print is running.

The results speak for them selves, and the customer was overjoyed that I made him this high quality custom part in only a few hours.

Finished item

Showing off the flexibility

I will also use this exact method for temporarily plugging holes from where a preamp had been installed.

Mainly for when a customer wants to try another system, like a sound hole pickup or bug etc..

It’s amazing how a big clunky preamp can affect the weight of a guitar.

So these plugs help to quickly close that gap up if the preamp needs to be removed for any reason, covering any jagged edges.

Installed temporarily into guitar