Hyperboloid pencil holder

Last crawled date: 4 years, 2 months ago

A pencil holder that creates a hyperboloid surface.
Although inspired by Stuffperson's hyperboloid pen holder https://www.thingiverse.com/thing:1401060 this is a from-scratch re-implementation that adds some additional features I haven't seen on other similar things:
it has two concentric rows of pencils
it does the maths for you to prevent intersecting pencils
some tidy detailing:
the top of the peripheral wall is inclined at the same angle as the cups
the peripheral wall can be stepped down
the bottoms of the cups are rounded

In the customizer (or the OpenSCAD file) the key parameters are:
Pencil dimensions
Length sets how high the minimum width (waist) of the curve is - it will be halfway up the pencils if the pencils really are as long as you specify, but specify longer-than-true for a waist higher up the true pencils and vice-versa.
Diameter is diameter of the hole they go in, and also used to space the pencils so they don't intersect at the waist. Note that this is the diameter of the hole in the model, not the diameter of the pencils that will fit - you need to add appropriate tolerance.
Pencil point length puts a taper at the bottom of the cups. This is supposed to hold them more securely, but I haven't really tested it. Set it at about half what your points really are. Or to zero.

Ring parameters
Number of pencils in outer ring
Inclination of pencils from vertical in outer ring. Positive means the tops are clockwise from the bottoms. Negative works.
Number and inclination for the inner ring. If number is set to zero there will be no inner ring.
Height offset of inner ring. By default, both rings have their tips (at the bottom of the cups) at the same level (wall thickness above z=0). You can raise the inner ring higher (if you put negative it will make it lower, but the pencils will poke out the bottom). Zero is generally good.

Socket and wall parameters
Depth is really the height of the cylindrical part of the socket, which is roughly equal to socket depth (there's a hemisphere on the bottom end).
Wall thickness - I generally make it about three lines-worth of extrusion. The same thickness is used for the peripheral wall and the base plate
Peripheral wall height. If this is the same as socket depth, then the peripheral wall aligns with the top of the socket. I like it about 2mm less so the sockets project above the wall. If you set it much more than sockets, you get a horizontal top to the wall at the level of the centre of the socket face.

Base open (i.e. no bottom plate inside the inner ring) or closed
The shape automatically lays out each ring based on the size, number and angle of the pencils to avoid any intersecting at the waist. It's not actually precise about it - it uses an approximation that puts in a little bit more space than it needs, and increasing amounts the greater the pencil angle, but at sensible angles (30 degrees or so) it's very small.
It does not check for clashes between the inner and outer ring - you need to do that manually.
If you have half as many pencils in the inner ring as the outer, and set the inner angle to be half the outer (or minus half the outer) the tops of the pencils in the two rings will be at about the same spacing.
There are some other parameters in the SCAD file for fine-tuning stuff, which are hidden from Customizer.
The STL is for pencils 175 long and 8 diameter, with 16 at 30 degrees in the outer ring and 8 at -15 degrees in the inner ring. Wall thickness 1.3, sockets 25mm deep with the peripheral wall 2mm lower.
My print is not great quality, but I don't think that's the thing's fault.