First Draft Trumpet Design

I’ve been brainstorming ideas about different trumpet designs for the past year or so and for the past few months I’ve settled on a basic design for my carbon fiber trumpet. As a budding engineer, I see all the things that are wrong with traditional trumpets and I want to fix them with my trumpet.

After lots of research and thinking about how I was going to build this I came up with 4 main design objectives (in order of importance):

  1. Looking good. Having an awesome looking trumpet is important because I want this trumpet to be bold and different from regular trumpets. I want people to know that it is built with a lot of craftsmanship and that it is a serious instrument.
  2. Being lightweight and strong. I thought of making a trumpet out of carbon fiber while at band camp because my trumpet was heavy and I had to march with it. This continues to be a highly defining factor in its design. One of the goals is also to make a trumpet that is accessible to children and people with little experience or money so making it strong and dent resistant is also very important.
  3. Good sounding. This is the 3rd objective because I am not a master trumpet builder so I don’t exactly expect it to sound good. Eventually this will be the biggest goal, but for this independent project, it may not be achievable.
  4. Cheap. I want this to be as cheap as possible. That doesn’t mean cutting corners, it just means designing it with manufacturability in mind. I’m not an expert in manufacturing by any means, so this is also not necessarily a totally achievable goal.

So far I just have basic sketches of what it will look like. I will be putting it into CAD over the next few months to finalize the design. Here is a sketch of what it will basically look like:

This design is a pretty large departure from a traditional trumpet which looks like this:

Here’s a list of the main design changes:

  1. Totally different valves. Just about every trumpet that you see has plunger valves (linear slide), but on my trumpet I am taking a huge departure and using rotary valves. This is primarily because it is easier to manufacture them to high tolerances. Some brass instruments (french horn, some tubas, etc.) use rotary valves so I think it should work ok. The other thing that is very different about these valves is that they are made of aluminum. One of the key design objectives of this project is to make a really lightweight and strong trumpet. Trumpet valves are normally made of brass, which is neither strong nor lightweight. I am planning on making these valves out of aircraft grade aluminum (probably alloy 7075) so that I can use a very small amount of material and have them be strong. They will be Teflon hard anodized, which is a process that puts a super hard super smooth surface onto the aluminum. This way they will last forever and have a very smooth rotation. These valves are a huge experiment. This is definitely the riskiest and most difficult part of the project. It is also the most innovative, so if I pull it off then it will be really great.
  2. All of the tubing is made out of carbon fiber composite. Airplanes and sports cars are made out of carbon fiber, not usually trumpets. I am making the tubing out of carbon fiber in order to make the trumpet strong and lightweight. Carbon fiber has one of the highest strength-to-weight ratios available of any material. It is a little tricky to make things with carbon fiber and it is a very different process than making things with brass, but once I have the process down, it will be simple to make many many trumpets that are all the same. Carbon fiber isn’t the cheapest material, but since there isn’t very much tubing in a trumpet, especially compared to any other brass instrument, it shouldn’t end up being prohibitive. I will make a post very soon just about carbon fiber and how you make things with it.
  3. The tubing is flipped so that it is sideways. I think it looks neat and it is also needed because the inlet on the valves is on the top, whereas on a regular trumpet it is on the bottom.
  4. Simplification. At least for now, I’m not planning on adding any spit valves or slides other than the main tuning slide. Carbon fiber is not the best material for sliding surfaces, so I think I may make a 4 valve trumpet so that you don’t need to let out the third valve slide when you play notes with the third valve. This is a really annoying part of traditional trumpet design so hopefully I can find a better solution than a third valve slide or 4th valve. Supposedly there are some leadpipe designs that mitigate the need for the 3rd valve slide because they make the trumpet in tune on all notes.

This design is of course subject to change once I find things wrong with it, but I’m not going to change this first version for ideological reasons. I like the look of it and I think it is close enough in design to a regular trumpet that it should sound very similar. The only thing is manufacturability. So the first trumpet design will definitely change if it is too difficult to make certain things.

Breaking Tools

Breaking things and failing is definitely going to be a part of this project…

Over the weekend when I was making my first mold, my really nice ball-end carbide endmill tried to go through the bolt that was holding my workpiece to the table. This ruined the endmill, made the stepper motors lose steps, and detached the workpiece from the table. The whole job went very well until this happened. It made a few gouges in the surface of the workpiece, but overall I could see that the toolpath worked well, so it wasn’t at all a complete loss.

On Monday night I decided to try milling some steel. I had some 1/8″ steel plate left over that was the perfect size to try out this design on: Then I could have some steel Rayban frames! Fun!

Unfortunately milling steel is much more complicated than milling aluminum. So I ruined another endmill in that job. This time, luckily, I was watching it when it happened. I programmed the toolpath to take more than 1/16″ deep passes. It turns out that my little 1/4″ endmill couldn’t evacuate chips fast enough when it plunged down that deep. This was a monumental problem because I now had an endmill filled with steel that wasn’t going anywhere. As the endmill continued to try cutting, it was only creating friction because the steel welded itself to the cutters on the endmill. So within a few seconds, the endmill and the metal surrounding it turned bright red hot. I quickly hit the software E-Stop button (speaking of which, I need a proper, physical E-Stop button now). When I looked at the endmill, it was filled with steel that didn’t want to leave. I got most of the steel out of the flutes, but there was still some steel welded to the cutter tips and the cutter tips were chipped, so this endmill is now useless. I think this happened it part because I was running it at 2500rpm even though my software said I should be running it at ~1600rpm, which I didn’t realize when I wrote the toolpath. This meant that the cutter didn’t have time to cool down and release the chips. I may have also been plunging too slowly, which made the endmill rub and heat up. But I think the thing that made this mess up the most was the fact that I was using junky steel of indeterminate alloy. This is “weldable steel” from OSH. That means it is probably some form of low carbon (mild) steel, which doesn’t machine very well.

So because I ruined 2 endmills in 2 days, I decided to take some pictures.

Here are the two endmills that I ruined:

Here are some pictures of the fancy ballmill (right in the above picture) under a microscope. These show that the whole surface of the cutting edge is ruined and chipped.

All of these should look like smooth perfect edges, much like the edge of a knife.

This is what an endmill is supposed to look like (I broke this one too awhile ago):

Close up of a 1/32" solid carbide UltraTool endmill

Close up of a 1/32" solid carbide UltraTool endmill

Of course I also ruined the regular endmill I used with the steel. You can see that there are little bits of steel welded to the corners of the cutting edges of the endmill which means this endmill will never cut again:

Overall this wasn’t a huge deal and it definitely taught me a lot, most importantly that machining is a science and it requires a lot of experience to get right. The fancy endmill cost about $20 and the regular one was part of a set of cheap ones, so replacing it would probably cost $5.