How do I make a curved funnel out of brass?

[TheGreenSmith]

I am going to make a french horn mouthpiece out of brass. For those of you who don't know the shape, images are attached. My question: how do I make a funnel with curved walls on the inside as shown on the diagram? Can I use a lathe for this, and if so what bit?

[jacobd]

Very carefully. Sorry bud, that's beyond me.

[yahoo2]

My preferred method is to build a cutter that is the exact shape of the finished job, get it close with standard tools and angle cuts then finish it with the shaped cutter. it works something like a router bit or profiler except the work is spinning not the cutter.

 

the only thing is you need to think how you are going to mount and hold it so it does not flex or slip while you are using it.

[arftist]

Ideally you would make a male template of the profile you wish to cut from sheet metal and arrange the lathe carriage to follow the template. Alternatively a form tool as described by Yahoo in the post above can be used sometimes, but not so much for this particular operation. (I am not saying a form tool would not work, but it would be a more difficult grind due to the small diameter and excessive length of cut. 

 

In this case I would proceed like so;

1. drill the through hole to finished dimension. 

2. Find a twist drill bit the exact size or slightly larger (but not smaller) than the largest I.D. of the cup.

3. grind the bit to match the required form.

4. perform operation with formed bit. 

[Steve Sells]

lost-wax casting is another option

[teenylittlemetalguy]

I actually have made a mouthpiece for French horn on lathe years ago. I did it similar to arftist I used 3 or 4 different tool bits and several drills.if you have never machined brass you are in for a treat, most alloys cut like butter.
The easiest part is the stem, which is straightforward machining. The cup was formed using several sizes of drill bits and then careful work freehand with different cutters set at different angles. After sanding and polishing you couldn't see any tool marks left.
Mine worked very well and the musician was happy, granted freehand work is not exact and it takes time, so if you are being asked to do this for pay just run now, they can typically buy a new one cheaper. Mine was made as a gift and was customized for her specifically. Sorry no pictures.

[ThomasPowers]

Casting would be my suggestion too

[BIGGUNDOCTOR]

Depends on your lathe, and your skills. Being a tool maker myself it appears pretty straight forward, but then again I have access to some nice equipment that can make form drills.

In any case, do all of the inside work first, then profile it. Easier to hold, and if you are going to mess it up, it will probably be on the inside, so might as well get it out of the way first. Plus if you bugger up the large end all you have to do is part the bad section off and start over. Keep the stock long , and don't cut to final length till you are done.

My Monarch has the capabilities to accept a closed pattern that a cam follower will ride in in place of the taper attachment.

Trying to freely follow an open pattern attached on the back of the lathe with the tip of an indicator on the carriage is doable, but it may take a few tries to get it right.

I would suggest boring the small hole, then roughing out the uppper sections with drills, or a boing bar to a close approximation of the final shape, use a paper pattern, then finish it off with a form cutter. To make the cutter use a piece of HSS, or since this is brass a chunk of file will do. Grind the profile on one side, and use it like a boring bar to finish the shape. Slow speed, and slow feed. That is a long cutting edge, and you will get some chatter. Keep chatter to a minimum, and clean it up with emery cloth. Brass does not like tools with a lot of positive rake. When drilling it is best to grind a flat on the cutting edges. Just hold the drill inline with the side of the wheel, and just touch it to give the cutting edge a 90° angle to the part. You are essentially going to scrape the brass away. Why do this? With positive rake a drill can grab, and literally suck itself into the part. It isn't fun when it does happen.

So, it isn't impossible, just take your time.

[ThomasPowers]

Suggest you also research WHY! the bore is curved at the top so you can use the *proper* curve for the custom one you are making.

[TheGreenSmith]

Thanks for all the input, it has been really helpful. However, since I don't have a forge or space for one, casting is out of the question. Also, for those of you who are wondering, the curved sides are very important to ensure the correct air flow and to help with the pitch. They can vary according to a players mouthpiece preferences. With this project however, I don't intend to make anything too custom, I just want something playable (as sort of a trial project). I actually chose the french horn mouthpiece despite the fact that I play trombone because I don't have to worry about too much material being wasted if/when I mess up. Thanks again for the help and I hope I added some clarity.

[Nobody Special]

How much do you normally play? And have you tried swapping mouthpieces much before? Do you normally play a deep, straight cup? Thin rim? Thick rim? How big are your lips, and how far in do ya put them when you play? It makes a big difference, and if you're not careful, you'll mess up your embrochure.

 

A big/deep cup has a nice sound down bottom, and is easy to play, but your upper register goes bye bye. Thickness of the rim matters too. A thin rim gives you more range, but's harder to play.

 

You might also want to consider the taper in the neck. A lot of them have a sort of pinched off place in the bore, much more than in your pic. The one you have would be possibly louder, but less backpressure and the tone won't be as good.

 

Oh yeah, anvil. Seriously though, for music, you should take into consideration how it's going to affect your playing long term more than the likelihood of whether you're going to mess up. Granted it's probably not going to take the place of your tried and true. Sigh....at least it's not for a euphonium......