3D printing a leadpipe for Jinbao contrabass trombone in F

[jelber2]

Hi,

I am trying 3D print a leadpipe for a Jinbao contrabass trombone in F. The bore is approximately 0.589" in the slide, so I would imagine a venturi for the leadpipe would be 0.522" or so. I edited https://github.com/pieterbos/PrintBone/blob/master/jinbao_leadpipe.scad to the following:
line 57 leadpipe_length=199; was changed to leadpipe_length=222.25);
and
line 73 shank="small"; was changed to shank="large";
and
line 67 leadpipe_venturi_radius=(10.7-0.8)/2; was changed to leadpipe_venturi_radius=13.26;
but, changing the venturi to 13.26 (0.522") had an unexpected change in size

Here's with the original venturi (10.7-0.8)/2

Here's with a 13.26 venturi

I am guessing that this value for venturi is not a measurement in millimeters exactly, but it is used in a calculation?

Best,
Jean Elbers

[pieterbos]

Hi Jean,

it should be a measurement in millimeters. However, it's a radius, not a diameter, so you should divide the value by 2.

It's very possible there are more issues with that specific script, since I've only used that file to create a specific alto leadpipe. It's only a few lines of code, so should be easy to fix, but I can't test it right now.

[jelber2]

Okay, I changed the leadpipe_venturi_radius=13.26/2; and the inner_slide_tube_inner_radius=14/2;
I also changed the leadpipe_length=200; to fit the size of the 3D printer. This is so cool! Can't wait to try it out!

[pieterbos]

looks good! Leadpipes seem to be the hardest part to 3d print and to get right of the entire trombone. Let me know how it works :)

[jelber2]

I doubled the wall thickness to 0.8 mm. The tech said that 0.4mm came out too fragile with the 3D printer using PLA. Hope to try it out Monday.

[pieterbos]

0.4 should be printable, but breaks rather easily unless you're very careful when inserting the mouthpiece. But for an alto thicker walls wasn't really an option :) 0.8 should work fine for a contrabass though

[jelber2]

Note: If you click on images, they will be in the correct orientation.
Printed the leadpipe using white PLA with 200 uM layers with 0.8mm walls but could only get the mouthpiece into it about 12/16 instead 16/16 inch. Here is the leadpipe next to the original leadpipe. I made them the same length and the having the same 9mm colar sticking out.

Probably needed to use a reamer to smooth the inside, but was afraid of making the walls too thin and having the plastic leadpipe break off in the inner slide. I purposely broke the plastic to see how far the mouthpiece went in, and to see if I could make it thinner. Here is a Schilke 59 mouthpiece inserted in the leadpipe showing that it only went in 12/16 inch.

Here is another picture showing that how thin the material is and how much more it would need to be shaved to get from 12/16 to 16/16 inch inside.

I realized, you could add "spokes" to the leadpipe when printing it to make it more stable when printing. Then snip and sand the outside smooth.

Maybe, I'll reprint it with 0.4mm walls in the mouthpiece receiver part or simply reprint it as is, but use a reamer and deal with the fact that it mouthpiece won't go in all the way.

[pieterbos]

I just opened the original file. Wow, I made that a bit messy :) I cleaned them up a bit, so you can download the new version. What I changed:

• wall thickness is now configurable
• mouthpiece receiver taper is more easily configured
• removed lots of old variables and code
• the length and width of the piece outside the slide is now configurable.
• the mouthpiece receiver taper starts immediately at the end of the tube, instead of directly after the bit outside of the inner slide, which makes the mouthpiece taper easier to configure

You can now set the wall thickness by changing:

leadpipe_wall_thickness=0.4;

Which will not change the mouthpiece receiver inner shape. If you make it too big, it will just not fit your inner slide at the beginning of the mouthpiece receiver. If this happens you can compensate by making the leadpipe_outside_slide_bit_length longer, it will put more of the widest parts outside of the trombone.
At the other end of the tube it will automatically compensate for inner slide tube radius.

You can change the mouthpiece taper with:

large_shank_large_end_diameter = 0.496*25.4;
large_shank_small_end_diameter = 0.546*25.4;
large_shank_length = 25.4;

That means you should be able to change everything you want to change easily now. Except for the spokes - nice idea. My leadpipes printed fine on my prusa i3 mk2 so I didn't add anything, but I did something similar for a mouthpiece: https://www.thingiverse.com/thing:1697510 . I relied on the support generation of the slicer to add a scaffolding below the horizontal disk you see there.

[jelber2]

Here is the code for making the support spokes

//Code for adding support spokes to the base of the leadpipe, cut off then sand smooth
NoSpokes = 8; // The number of support spokes
SpokesWide = 3; // The width (short side) of the spokes
SpokesHigh = 2; // The height (along the Z axis) of the spokes
SpokesLong = 75; // The radial length of the spokes

union()
{ 
    for (i=[1:NoSpokes]) 
        rotate([0,0,360/NoSpokes*i]) // Rotate the arm after it's centered
        translate([mouthpiece_receiver_large_radius+leadpipe_wall_thickness,-SpokesWide/2,0]) // Center the arm around the X axis
        cube([SpokesLong, SpokesWide, SpokesHigh]); // Make the arm extend along the X axis

}

[jelber2]

Hmmm. The leadpipe I printed with 0.8mm walls (using the previous commit of the leadpipe code) is too stuffy due to the walls being so thick. The part of the leadpipe that goes into the inner slide is less than ~15mm in diameter (0.587"), and the inner diameter is 1.6mm less than the outer diameter simply due to the wall thickness of 0.8mm. So, I am going to try 0.4mm wall thickness.

[pieterbos]

A few things that might be worth a try as well, instead of the 0.4mm wall thickness, since 0.8mm has clear advantages over 0.4 in terms of breaking easily:

• The cause for the stuffiness could just as well be something else. For example, the venturi or the shape of the leadpipe. You could try different values for the venturi diameter.
• With most 0.4mm nozzles you can print walls between 0.4-0.7mm - the flat area around the hole in the nozzle will make sure you get nice and flat lines. So you could try a 0.6mm wall thickness as a compromise. Note that this will require an extra setting in the slicer, but it's very possible.

Also now the leadpipe is just a conical piece of tubing down to the venturi, then a conical piece down to the end, plus a mouthpiece receiver. I have not checked if that's the shape a leadpipe should be. That could also be the cause of the stuffiness.

[jelber2]

I am pretty sure the design is close enough to leadpipe-like in shape. I’ll try the 0.6mm walls as you suggested. I think the venturi size is okay - it translates to 13.26mm or 0.522”. As far as I know a 0.562”bore bass trombone has about a 0.500” venturi, so a 0.522” venturi for a 0.587” bore contrabass seems reasonable. Probably could also try a 0.542” venturi or so.

[pieterbos]

The distance of the venture from the mouthpiece receiver is also something to play with of course :)

[jelber2]

As an update, I did some more sanding on the leadpipe with 0.8mm walls and 0.522" venturi, and I doesn't seem so bad afterall! In fact, I will use it instead of the original leadpipe for now! I am going to reprint this leadpipe with 0.8mm walls at the mouthpiece receiver and 0.6mm walls for the rest of the leadpipe and try 3 different venturi sizes (0.512, 0.522, and 0.532 inches). Not sure if the 0.6mm walls will make it too fragile, so I might revert back to 0.8mm walls for the whole leadpipe.

[jelber2]

In the new jinbao leadpipe scad file, the large_shank_large_end_diameter and large_shank_shank_end_diameter values need to be switched

[pieterbos]

Good to hear it works. Did you sand the inside of the leadpipe, and did it make much of a difference? For mouthpieces, sanding to get a smoother surface improves the result quite a lot.

Thanks for finding that issue. I'll fix it.