The process of creating the mechanics of a high-tech toilet paper holder that uses magnetic discs.
A resistance mechanism in a paper towel holder to help tear sheets is a thing. It really only works if the resistance is on/off, ratcheting, or intermittent, for lack of a better description. A friction mechanism exists in, arguably, the No. 1 selling paper towel holder on earth, the Perfect Tear®. I came-up with the concept of using magnetic discs to provide resistance to produce a similar result.
A company, CMR, has an amazing technology creating “Polymagnets®” with very specific, engineered magnetized areas on magnet material. In my case, I would use discs with north and south around the edges to provide this intermittent resistance. So I began incorporating this technology into a paper towel holder and began drawing, 3D printing, and prototyping.
When Polymagnets are paired with a compatible Polymagnet, they create some crazy awesome behaviors. Each type of configuration has a designed purpose. I needed a pair of discs for torque resistance. In addition to the north/south areas around the outside edges, they also have a prominent north or south area on one side of each disc. So, in addition to the torque resistance one disc has against the other, it also will attract or repel the other disc depending on the sides facing one another. The amount of torque resistance the pair of discs provide is relative to the distance between the two discs. The closer together they are on an axis, the more torque resistance there will be.
The Polymagnet® (2240) from CMR. This is one disc and is paired with another of the same for torque resistance. It has 12 detents per revolution.
While working on the mechanics of a paper towel holder, I decided to have the magnets setup to oppose each other and use a cylindrical inclined part with three ramps that matched another, similar part. I could test it all with my 3D printer. One inclined part would turn while the other would slide up and down with one of the discs. Another mechanism was needed for the turning inclined part to stay in position; it wants to turn from the downward force from the repelling magnets. This led to a scalloped contour inside the base of the paper towel holder. The base and scalloped edge could be a sand cast part, good news. But high quotes for manufacturing a stainless cover for the base (spun and stamped) made the project unfeasible. A stamped stainless cover was cheaper per unit than a spun cover, but the tooling cost would be around $45,000.
The upper inclined part moves the lower disc magnet up and down (closer and further) with respect to the other disc. A spring-loaded rod on the inside of the slide control moves along the scalloped edge to keep the control from turning on its own.
With the paper towel holder sidelined, I really needed to get a finished product out. I decided to focus on a toilet paper holder with less tooling costs. I found a post from Eric Strebel on Core77 and reached-out to him. I sent him some magnetic discs and a 3D printed prototype so he could quickly understand the concept. He drew-up some designs. I wanted to avoid any molding (and major tooling costs). After many iterations and back and forth we decided to use thick aluminum plate (3/16”) for the base. I wanted people to see that cut-outs from a single piece of plate were used functionally. The aluminum plate base is strong and feels quality. The edge frames it nicely and provides plenty of area for double-sided adhesive; we wanted it to install easily. I didn’t want the product to look like a traditional toilet paper holder. This was a completely new product after all.
Once we settled on the general look, we needed to get the resistance control down. I already had a lot of experience with this challenge and one day Eric showed a drawing with teardrop cavities in the aluminum plate. Perfect! I could instantly see that they could be scalloped and have balls from the knob seat in these shapes and allow adjustment. Things fell into place; Eric took over the style and I would do the mechanics and wireform.
Trying to use inclined circular ramps to adjust distance between magnetic discs.
Eric’s drawing with teardrop cavities was pivotal for a better design.
There was discussion about an axle and if it was needed. The wireform also was an unknown. Conventional wisdom says a wire needs to be a attached on one side and on the far side, down the axle. I didn’t want an axle running from one side to the other. I finally came up with a wire shape that looked good and worked well with no visible axle. The position of the adjustment knob was originally going to be inside the wireform which would have been a mistake.
I finally got an arrangement where the magnetic discs opposed each other and the roll holder part was against the plate. The magnets created a spring that had other benefits: It pulled the knob (and balls) in toward the base plate and it pushed the magnetic discs into their respective parts, so they’d always want to stay in place.
The balls were originally going to be pressed into place on the knob by a press. That would present complications for fitting the balls in after coating or anodizing, because you’d want them pressed-in in a shop not during assembly. I decided to use 8mm balls set on the edge of 5/16 inch holes which are slightly smaller than the diameter of the balls. This is after more prototyping iterations than it should have been. As long as the hole is deep enough, the balls would always be a consistent depth on the knob. It’s no issue for assembly and the balls have no space to escape. The coating or anodizing wouldn’t affect the tolerances, and no pressing is needed, so a good way to go.
Getting further along the design, I sent the drawings for the machined parts out to a few places for quotes. The part that held the wires had holes that went in at an angle. That prototype is in Eric’s video (linked below). One shop wouldn’t quote the part and others were coming back too high. The diagonal holes required a 5 axis CNC lathe or it would have to be moved to a mill after a 4-axis CNC lathe. The shops that have a 5 axis CNC charge a premium to run the machine. Most shops that have it would rather not quote this anyway, because they can make more money from a higher profile client, if you know what I mean. So, I changed the part so the wires enter it perpendicular to the shaft. Now the part could be made with a 4 axis CNC lathe which opened the door to more shops and affordable manufacturing.
The final mechanism design. The wires enter perpendicular to the shaft. The scalloped teardrop cavities are easy to stamp (or waterjet for small quantities). No molded parts necessary. The Assembly simply screws together. The discs repel which helps them stay put and provides a spring for the balls to engage with the scalloped cavities. (Sorry for the lousy image quality!)
The design is such that the whole assembly can be taken apart and put back together (although it will be loc-tightened). Even the magnetic discs can be removed to recycle the aluminum, or for replacement if needed.
Soon it will be time to get back to developing a paper towel holder. Even if the distance between magnetic discs is fixed with no mechanism for adjustment, a paper towel holder version would work well. The variety of how easy or difficult it is to rip paper for various brands isn’t as great as it is with toilet paper. I believe that a lot of the things learned from this project will carry over in the design of a countertop paper towel holder. We’ll see what develops.
Eric’s video on the PolarityGear design process on Youtube