I used a 45 watt laser cutter, which I have access to at TechShop RDU, to cut parts for this design. I also used new paintbrushes because I don't paint very often and didn't have many old paintbrushes to make use of for this, however I think it would look good with some old paint covered brushes.
Things you'll need:
Paintbrushes - I used 17, any less and I think the cup would have ended up too small.
1/8" plywood - a six inch square piece should be plenty.
Calipers - for measuring the diameters of the paintbrushes.
Masking Tape (or painters tape) - for marking heights / identifying individual brushes.
Laser Cutter - available at your nearest TechShop.
Rubber Bands - Optional, I used them to hold some of the looser brushes in place in the final product.
To do this, I laid all of the paintbrushes out in a line and made sure the ends were in a straight line, then I placed a long piece of tape across all of the brushes and cut it between each one.
This also marks the specific height on the brushes where you want the top brace disk of laser-cut plywood to end up. I picked a spot on the brushes that was just below the fattest part on the shortest brush, so that I could easily slide all of the paintbrushes into their respective holes.
Once you have cut the tape for each brush, label them with numbers or letters.
Now you will measure the diameter of each brush with your calipers.
Each brush will have two measurements: one at the top of the brush (where you marked with tape) and one at the bottom (I took mine at about half an inch from the bottom tip).
Make sure you record the measurements with respect to the number on the tape.
(note that if you have rectangular brushes like the one I used you are measuring its width and thickness, not diameter, so it will have two dimensions)
Do not remove the labels from the brushes, as they will be important when you are putting the cup together in the final step.
Step 2: 2d Illustrations
I used Corel Draw to draw my patterns because it plays well with the laser cutters and is easy to use, but Adobe Illustrator will work as well. I won't be going into the details of using these programs or how to use them to print on the laser.
There will be two disks (or rectangles, or whatever shape you want your cup to have) with holes cut around the edge for the paintbrushes to go.
For the top disk, which has its center removed, you will draw two concentric circles, with enough space between them to fit your largest brush with a little bit extra for structure. Then draw a third concentric circle in the middle of these to mark where the center of the holes will be, this circle will be deleted after all the holes are drawn.
Using your measured diameters, draw the holes for each paintbrush. I added a thousandth of an inch to each diameter to ensure that the holes wouldn't be too tight.
I then marked the first hole with a number "1" with a small bit of the tip hanging onto the edge of the circle which will be etched by the laser, leaving a mark at the first hole. The rest of the holes are just placed in order, moving clockwise.
After drawing all of the holes, draw straight lines connecting the centers of those circles to the center of the disk.
For the bottom disk, draw a smaller concentric circle which will mark the center of the holes on the second disk where they intersect with the straight lines, to ensure that the holes in the bottom disk will line up with the holes in the top disk.
After drawing all of the holes in the second disk, select only these holes and move them away from the top disk in the drawing. Then draw the outer circle on the bottom disk, there is no inner circle because the bottom is solid. I marked the first hole on this disk as well with a small number "1."
Now you can delete the construction lines used to mark the centers of the circles.
Through TechShop RDU, I have access to an Epilog 45 watt laser which I used to cut the pieces out of 1/8" plywood.
Again, I'm not going into the details of how to use the laser in this Instructable.
So, adjust the settings according to the manufacturer recommendations for the type and thickness of material you're using. The settings shown are for 1/8" plywood on a 45 watt laser. Your settings may vary.
Now the laser will cut your pieces.
Step 4: Finish
If you'd like, you can use a small amount of glue to ensure that the brushes stay in place permanently. I simply placed a rubber band around the bottom of the cup holder to provide a little bit of tension to all of the brushes, this was enough to hold any loose brushes in place for me.
After this, you are finished!