I believe the beauty and value of 3D printing really shows when you are tackling unique situations that would otherwise have no simple solution. When we wanted to hang various household cleaning hardware (aka brooms, etc) on our spare fridge in the laundry room, we looked at a few options such as the ones to the right:
The cost for these was about $7 each for a “65 lb rated” hook and $4 for a “25 lbs rated” one. I’m putting these in quotes because this rating is applicable when they are against thick carbon steel in a straight on pull, not against a refrigerator (thin sheet metal) pulled in a perpendicular direction to the magnetic force applied. Further complicating matters is the tight space these needed to work in.
The main problem with this arrangement is that the hooks available require the tool (broom, etc) to be brought up at an angle (at least 45 degrees from horizontal) to go over the hook. We didn’t have the room for this because that motion would hit the washer/dryer. We needed hooks that went straight out, like the one I designed to the left.
I first looked at a more economical ceramic magnet. Its rating is for 35 lbs on contact with 1/4″ thick, flat, smooth ferrous plate in a vertical test, 50% less on vertical surface holding against sliding force, and even less on steel with paint. It also notes that the holding force is concentrated on the rim of the protective steel cup of the magnet.
I then looked at a higher force rated neodymium magnet. It is rated for 70 lbs pulling force on contact with 1/4″ thick, horizontal, steel plate in a vertical test. Force is up to 60% less on vertical surface holding against sliding force, and even less on steel with paint. I’ll be testing these claims in a followup post soon, so keep an eye out for that.
The great thing about the design of these lift magnets is that they are intended to be assembled into something that uses their force for a purpose, which in this case will be a hook. If you notice in each there is a hole, and even a nice countersink in the case of the neodymium magnet. I went ahead and ordered the magnets first so I could get dimensions from them via calipers since no dimensions were available online. Turns out that an #8 wood screw that is 1″ long works great for both of the lift magnets (found here or at your local big box store), so I designed the ID (inner diameter) of my print to be the standard recommended pilot hole for these screws (3/32″). I also measured everything we would want to hang on the hooks to see what the smallest ID of the tool’s hanging point would be. I wanted some element of retention so I added a larger lip at the end, then ensured that the new overall OD (outer diameter) of the hook would be smaller than the measured ID above. Assembly is very easy once the print finishes: hold the print steady and assemble the magnet to the print with the wood screw. Check out the build video below:
STL version of the file is available here.