It's pretty easy to add a repeating pattern on the outside of knobs or tool handles using Inkscape and Openscad. Here is an example of how to use the perforate module to add a repeating pattern on the outside of an object.
First I designed a pattern in Inkscape by making a star shape and then using make tiled clone to make a row of stars:
Inkscape tip:
By using the arrange function in Inkscape you can make a tiled pattern and then adjust the spacing in between the objects to align them in a group or only align the ones you have selected, this way you can make a raised grid or holes any shape you want with the objects perfectly spaced.
I changed all of the objects to paths, selected the nodes and converted them to lines, and exported them as a dxf14. I then imported the the file into my Openscad template and used the tube perforate module to arrange the stars in the proper orientation, number of rows and diameter to fit the outside of my knob:
I used rotate Z to align them on this tapered knob that I made with the cylinder module:
A top view to see the slight rotation I added by using rotate all:
Another pattern using a row of rectangles with rounded corners:
A recessed pattern :
It's also easy to fillet an edge with Inkscape, here is a knob I made using rotate extrude. I made a rectangle the size I wanted the knob, set it's left edge at zero on the x-axis, made the designs I wanted to subtract on other layers and then adjusted everything to line up:
Inkscape tip:
By using the path effect for fillet and chamfer you can select certain nodes to apply the effect to, it's pretty handy for making a fillet or chamfer anywhere you want on any layer.
Finished custom knob ready to print:
