TromboneChat

I was re-reading an article Robb Stewart wrote on his site about fabricating tubing using an arbor press and mandrels for cylindrical tubing. He also mentions how he makes tapered tubing, which is also fairly comprehensible. I don’t quite understand how someone would make a leadpipe using this process though. Following the same steps, i understand up to the last step. How would you remove the leadpipe? If you put a piece of tubing on a mandrel with the correct taper forming the venturi, wouldn’t it be stuck on? If the leadpipe looks like ><== and the mandrel matches this, how would you remove the leadpipe of the mandrel? If the venturi is the narrowest part of the leadpipe, then how would you get it over the larger bore of the rest of the mandrel? The only thing i can think of if have a two piece mandrel that threads together at the tightest point, the venturi, and once you are completely you can take apart the mandrel and remove the leadpipe.

Also, for any tapered piece of tubing, how consistent is the thickness? I imagine if you have the same sized “doughnut” ,as robb stewart refers to them, how does the inner diameter of that doughnut stay consistent with the changing diameter of the tapered mandrel? Does the mandrel just brute force it’s diameter into the doughnut? I imagine that would be a one time use out of the tool. I hope someone on here understands any of what i just said, Robb Stewart’s article is really interesting and i just don’t grasp 100% of it. Here’s the article https://www.robbstewart.com/brass-archeology

The doughnuts are one time use. The steel mandrel deforms the doughnut as it goes through, and it shapes the brass and thins it, possibly. You can see a bell before it is pulled through the doughnut on a mandrel in this picture on the same page:



I've never seen this before. I always thought that bells were spun on a lathe with a shaping tool.

The actual flare is spun as you describe. The bell stem (tapered pipe leading to the flare) can be hammered or drawn.

Elijah,
You don't do both tapers on the same tool... you draw it on one as a single taper, then you take it off that tool and push it on to another one to make the mouthpiece side.* There are a ton of videos out there about drawing leadpipes and slide tubes. Looks roughly the same. Note when they are using deformable washers (like Harrison noted above) and when they are using fixed dies to draw the tubing. You will need to understand when they are using each and why. Also note that they often brush things with a oil or lube. Need the material to flow and not stick to the tooling. As for the thickness varying... yes, it will. Based on the force balancing which will also involve the amount of effort and speed of the machines. Lots of variables. I wonder why leadpipes vary....

*If you are planning on doing this yourself, getting the venturi in the "right" spot can be difficult to do, and possibly more important for learning, difficult to learn how to measure repeatedly so that you get feedback. With a machine with defined tooling location and defined strokes, this is relatively easy. By hand with cobbled tools... hope you know how to measure stuff and do some basic math.

Cheers,
Andy

Making a one-piece leadpipe/receiver tube (as opposed to a two-piece setup like all trumpets and most new King trombones) has the potential to introduce the most variability in the whole trombone, IMO.

I know that certain makers just use an old mouthpiece to flare the end/create the receiver- not exactly a precision or repeatable process.

That makes a lot more sense, thanks. Do major manufactures use this same process? Or something easier to mass produce

paulyg wrote: ↑Tue Nov 30, 2021 6:45 pm
I know that certain makers just use an old mouthpiece to flare the end/create the receiver- not exactly a precision or repeatable process.

Really? Who?

The tooling I have experience with is made of steel, and fluted, so as to help with "burnishing" the flare. A round tool (with no flutes) made of brass would not be very efficient, nor last long. There is also no way of ensuring concentricity.

Yes, a mouthpiece may be used to check the depth of insertion once the pipe is made, but it certainly wouldn't be used to create the receiver taper.

As already pointed out, the mouthpiece receiver end is not drawn; it is flared out with a tool. And as Matt said, a perfectly round tool like an old mouthpiece shank would not work well for this purpose. The initial leadpipe taper is drawn over a mandrel through a ring of soft metal (could be lead, brass, etc.). The ring stretches as the pipe is pulled through so it matches the taper. I've found that you can hammer the ring back to a smaller diameter and re-use it, but you only get a certain number of uses before it fails. Lead can be melted and used again, of course. My seamed pipes start out as a tube that is already tapered, so the metal isn't deformed as much by the drawing process. When you start out with a cylindrical (non tapered) piece of tubing, you're stretching it more at one end than the other, so I don't think you end up with a consistent thickness.