Bass clarinet mouthpiece design in TOPsolid
This article describes how I make a parametric bass clarinet mouthpiece design in Topsolid. The purpose of the design is to cut a mouthpiece out of Delrin and make a 3D printed prototype.
The figure above shows the tools and information that are used. I measured the characteristics of a mouthpiece and describe that in 40 to 50 parameters. That parameters are converted in Excel into TOPsolid parameters that will be used in the TOPsolid formulas for 2D sketches, curves by functions and shapes by functions. The parameters are defined in Excel and will be imported into TOPsolid. The TOPsolid formulas are base on General Curve equations that took me a year to define. The idea is that I only have to change the content of the measured Excel parameters and update the TOPsolid design to generate a new mouthpiece.
All the convertions from the measured parameters to the TOPsolid parameters are done in Excel. It includes a lot of complex interpolations rotations and transformations. The results is a worksheet with a list of TOPsolid parameters per part of the design.
Designing the shank
The design of the shank shows how TOPsolid works.
First I define the parameters that are needed (in Excel with and in TOPsolid without the prefix TOP_):
- Shank parameters
- TOP_l_shank 17
- TOP_r_shank 14,8
- TOP_r_cork 13,3
- TOP_l_cork 10
- TOP_ld_shank 3,5
The the rough shape is drawn of the intersection of the shank (only the outside part) and all the constraints are related in the right way to the parameters:
Then the shape is revolved over de X-axis, resulting in a nice brown TOPsolid tenon. The TOPsolid fillet function is used to unsharpen the bottom edge of the tenon.
Designing the barrel
The next shape is the outside of the barrel that requires two parameters:
- TOP_l_barrel 81,62
- TOP_r_barrel 18,44
Op dezelfde wijze als de shank is dan een cilinder toe te voegen.
The barrel shape now has to be trimmed to a decreasing diameter towards the tip. The function of this curve is defined by the shape and height of the table. It is assumed that for each value of x the width of the table is determined by the diameter of the barrel and the height of the table.
The height of the table is determined by three parameters: the table angel p_table (5,5 degrees) , the length of the facing (27mm) and the tipopening h_tip (1,8mm). The table has a flat part and a curved part of 27mm. The curve is assumed to be a segment of a circle with a radius of 203,4mm that can be derived from the facinglength and the tipopening.
The first trimming is done with the line derived from the flat part of the table.
The function used is the 2D sketch curve by formula.
The curve is only visible after checking in the part in TOPSolid.
Then the curve can be revolved to a shape and then the barrel can be trimmed with it.
The curved part of the table results in a separate curve to trim the barrel that cause the diameter to decrease faster at the tip of the barrel:
Cutting the table
The next step is to cut off the table. This is done in two steps. The first part is the flat part. This is done by drawing a cruve by formula, extrude it over de y-axis and use it to trim the barrel.
The last part is the curved part that follows a circle with a large diameter.
Making a round tip
The next step is to make the tip round according to the measured tipradius r_tip_c.
There are several ways to do that in TOPsolid. The most important element is circle with the right diameter and position in th right plane.
Then extrude it and use the plane to trim the tip.
Cutting out the beak
The next step is to cut out the shape of the outside beak.
The outside beak is defined by the radius of the tip. It is assumed that the outside beak has a constant radius that is equal to that radius but than rotated according to the beak angle.
The beak is trimmed by a big ring with the beakradius that is rotated over the beak angle and translated to the exact position.
Then the ring is trimmed by a vertical plane.
The inside edge of the ring is rounded by the fillet function.
The result is a nice looking outside shape of the mouthpiece.
The next steps are to remove the inside shapes.
Designing the bore
The bore is a straightforward part defined by the following parameters:
- The radius of the bore at the bottom r_bore_bottom
- The radius of the bore at the top inside the mouthpiece r_bore)top
- The radius, if used, of the rounding of the top r_bore_round
- The length of the bore.
In TOPsolid it is quite easy to design this using the parameters. The rounded radius can be made using the shae/fillet function.
For the chamber at first a large cylinder is made that will be trimmed to the size of the chamber.
The result is a cylinder and the first trimming that could be done is with the plane that is already used to trim the table. However it is maybe wiser to use a plane that is 0.1mm larger to be sure to let the boolean substraction be successfull.
The next trim is done by two planes that are mirrorimages of each other. They represent the side walls of the chamber. Each plane is define by three points: the corner of the window at the tip, the corner of the window at the barrelside and the cuttingpoint where the bore meets the chamber.
Another smaller plane is between the barrelside of the window and the bottom of the bore. For this mouthpiece the section of that plane is a straight line. For other mouthpieces that can be a smoother transfer from the bore to the lower end of the windos (maybe also a rounded window).
The last part is the most difficult one. I call it the roof or ceiling of the chamber. The line through the top of the roof is a combination of straight lines in the beak, an interpolation of that line into the bore (is different per mouthpiece) and on some mouthpieces a baffle can be added near the tip. The roof is curved. Near the tip the radius of this curve is almost equal to the outside beak. Near the bore the radius is becoming equal to the radius of the bore.
In TOPsolid this kind of curves can be made by the function surface by formula.
The formula looks a bit like this ;-) :
My free licence is expired now. So I have to find someone with a full licence to finish the design and then find out if it can be printed and cut from a piece of Delrin
I finished the design with another ones computer that has the full version of TOPsolid. The result needed some tuning but it looks OK now.
When you click the figure above, you will open a 3D pdf representation of the design. It can be rotated by holding the left mouse buttin down.
To be continued.