This is a brace that you strap onto your body to help support a trumpet while you play it. It is especially useful if you only have use of one arm, as the trumpet is designed for two handed operation. I've also seen something similar used by pro players when they want to play keyboard with their left hand while playing trumpet with their right.

Background: My kid broke his left arm snowboarding 4 days before his concert, with two more concerts in the two weeks after that one. He was still in enough pain that he couldn't support his trumpet with his left arm at all, and didn't have enough strength or control to play one handed, and not enough time to develop that strength before showtime. There are commercial solutions to this problem on the market, but they were stupid expensive and couldn't get here in time for his concert anyway. 3d printing to the rescue!

There are a couple of options included in the parts.

1. For the brace part that the trumpet will rest on, you can print the single solid V1 brace, and then cut some tennis balls open and shove them on the end (like how walkers are usually padded at the bottom). If you can print TPU, then the V2 option is better - you'll print a solid V2 brace out of PETG and two V2 pads out of TPU. You get a better looking final product with V2, with less “ball” jokes from your middle school kid, and the surface finish I think will be easier on the finish of the trumpet (the slightly rubbery texture of the TPU is softer than the slightly rough texture of the tennis balls).
2. For the strap clip, you can print a V1 out of PETG which works fine. Alternately the two part V2 out of TPU is stronger and has better grip. It's two part because the TPU is too soft to properly retain the M5 nut, and so I included a larger square nut retainer to be printed out of PETG.

To build this you'll need a few more parts from Amazon. The costs add up here, but you can reuse all of them if you only need this temporarily while healing from an injury. Biggest cost is the selfie stick, which could be replaced with a short stick - I bought it originally thinking we would need the length adjustment feature, but it turns out he uses it at its shortest position anyway.

1. Selfie Stick. You need one with a ¼" tripod thread on the bottom, and a go pro style mount on the top. I used this one: https://www.amazon.com/gp/product/B00ST1Y2QU and it turns out the go pro style mount is just threaded onto a tripod thread at the top as well so you can just add that later if you already have a selfie stick.
2. Camera Ball Mount. The smaller the better. https://www.amazon.com/gp/product/B09NJJ2DKM
3. Saxophone neck strap. https://www.amazon.com/gp/product/B076H6BT6N
4. ¼-20 ½" Hex Bolt. I bought the SS ones from Lowes. Used to attach the ball mount to the chest plate.
5. M5 20mm Bolt (for the go pro mount)
6. M5 12mm Bolt (for the sax strap clip)
7. M5 Nut (for the sax strap clip). I used a nyloc one I had laying around, but that's overkill.
8. 1" webbing and clips: https://www.amazon.com/gp/product/B08LD8CJ8D

The parts you'll need to print:

1. Chest Plate: TPU @ 100% infill, no supports. Print flat on the plate.
2. Neck Strap Clip: There are two options for this. The two part TPU part is much stronger.
   1. Two Part: Print the clip out of TPU @ 100% infill, print sideways with no support. Print the nut retainer out of PETG @ 100% infill, flat on the plate. The nut retainer is there because the TPU will slip on the hex of the nut, but with the larger surface area of the retainer you can tighten it down without slipping - it basically makes your hex nut into a square nut.
   2. One Part: Print the clip out of PETG @ 100% infill, sideways with no support.
3. Trumpet Internal Brace: PETG @ 100% infill, tree supports. Print on end such that the go pro mount is horizontal to the print bed. The extra work of printing this with supports is worth it to get the layer lines parallel to these weak parts.
4. Trumpet Brace Pads: Print 2 of these out of TPU @ 15% infill, 2 top layers. Print with the opening pointing up, no support. These should be nice and squishy. I used Amazon Basics TPU, which is a fairly stiff TPU - if you use something softer like NinjaFlex you'll probably need to increase the infill a little.

Assembly:

1. Insert the ¼-20 hex bolt into the back of the chest plate, then screw the ball mount onto the bolt from the front.
2. Thread the webbing through the slots in the side of the chest plate and install clips per manufacturer directions.
3. Install the selfie stick to the top of the ball mount.
4. Install the strap clip near the top of the selfie stick, securing with the M5 12mm bolt and nut.
5. Install the pads onto each side of the brace. Installed properly it should have a V shape to capture the trumpet.
6. Install the brace onto the top of the selfie stick's go pro style mount using the M5 20mm bolt.
7. Clip the saxophone strap onto the strap clip

Use

1. put the saxophone strap around your neck
2. place the chest plate against your torso (we found somewhere high on your belly worked fairly well, but this is dependent on your torso size) and secure to your torso using the webbing clips.
3. Adjust the webbing such that it is snug but not tight - the purpose of the webbing is to minimize rotation not to hold up the trumpet.
4. Adjust the selfie stick length and saxophone strap length until the pads are at an appropriate angle for your playing style.
5. Rest the trumpet on the pad and make some music!

Notes:

A lot of these parts can also be printed from PETG, but we found the TPU parts to be more comfortable and/or durable. The only part that must be printed from PETG or another material with similar properties is the internal brace for the pads at the top of the holder. I don't recommend using PLA for this part as it will be very likely to break using that material.

Print out a few extra pieces before you need them. You (or your kid) will inevitably break a part 1 hr before said concert and will call you at work in tears. This is especially true if you use a rigid material for the chest and clip parts. Fortunately you planned ahead and can rush home and swap out the broken part with minutes to spare!

TPU is stringy stuff. I used a lighter to clean it up a little post print with success. I didn't bother to clean up the insides of the pads - that extra material will just help it hold on better.

I may get around to designing a magnetic clip for the chest plate - the standard store bought ones are very hard to use one handed and he has to ask for help putting it on. He can do the rest himself.

The selfie stick could be replaced by a stick with a ¼-20 threaded insert at one end, and a simple ball joint with a go pro mount at the other.