In the first post of this series (that wasn’t supposed to become a series), we took a deep dive into some of the problems with American business, politics, and manufacturing. Time to move on from the political stuff. I started the post talking about the idiocy of those that make the blanket statement: “That’s over-engineered”. For all of you who aren’t engineers, let me share this: Of course your stuff is over-engineered! Duh… Any good engineer that went through a decent accredited program can tell you what a “factor of safety” is and how to use it. You learn all about it in your first year of engineering school. This factor is the multiple that dictates how much we deliberately over-engineer things. For example, if a particular thing (e.g., a ladder) needs to hold 200-lbs, the engineers that design it will probably make it so that it will safely hold 800-lbs (or more), giving it a factor of safety of four. If you are designing products, especially ones that might cause injury or significant loss if they fail, you would be a fool to design them to meet the exact predicted use scenario. What would happen if bridges were engineered to carry only the load of the vehicles on them during a blizzard when the winds are blowing and four feet of snow piles up on them?

For some of you, the general concept of having a factor of safety makes perfect sense (especially to us engineers). What isn’t so obvious to most, is the cost of engineering something that needs to work reliably, but for some reason can’t have an excessive factor of safety for some constraining reason. From having worked in the development of medical devices for many years, this has come up many times in my career. If a device needs to fit into a small anatomical space (which can’t change) to perform a function that puts a relatively large load on it, and making it larger to increase the factor of safety is not an option, you have a situation where you need do some serious engineering and testing. It is likely that your design will be iterated upon many times before you have something that you have any confidence will work. Situations like this come up in aerospace all the time as well, where weight and strength are always being traded off. The cost of engineering something that really needs to walk the line, so to speak, can get exorbitant. And it’s always risky. Just ask the test pilots.

There is a deep moronic irony in all this. When someone makes the statement: “That’s over-engineered”, implying that money is being wasted in an overly robust product design, they have no concept of the costs associated with trying to engineer something perfectly. Which can’t be done by the way. In essence, they are asking you to waste money trying to engineer out their perceived waste, which is just as wasteful in the end and another form of over-engineering itself. Any good product design engineer can look at something and tell you which elements need to be engineered and which ones don’t. We avoid spending time engineering things that don’t need to be engineered. If possible, we will use a ¼-20 bolt instead of an 0-80 one just so we don’t waste time and money doing calculations and testing to see if the smaller one will work. Experience really helps here. I am always looking for layups when designing something and will add in an element that I don’t have to worry about being a weak point in the overall system any time I can.       

Enter our new Heavy-Duty Keyhole Hangers. I had just finished making an awesome and beautiful custom mirror frame (more on this below). And it took me a lot of time and effort to make it! I went online to search for a beefy stainless steel hanger to mount on the back of it and came up empty. There were lots of cheap options made in China that I just didn’t trust. In the previous post, I talked about “fear” driving poor decisions. Now, I must point out here, that I was making a conscious decision to over-engineer my mounting out of fear. I had a fear of losing my one-of-a-kind piece that I spent so much time and effort on! Just a few weeks prior, I had helped my neighbor (a civil engineer) fix his toilet and wall. During a party, one of his guests had fallen in the bathroom, ripping a picture off the wall before smashing the toilet tank and ending up in the shower. We were both perplexed as to how it happened, other than having a really good party. And I like to have a good party myself! So, this was a use scenario I had not foreseen that I felt I needed to account for now. As unlikely as drunken party-goer ripping my mirror off the wall might be, I plan on passing this piece along to my kids when I depart, so it will need to withstand a lot of parties in the long run!  

The next step was to do what I do best, and get to work making something to fit the bill for my application. In that process, I realized that other people might want a heavy-duty hanger for their precious and/or heavy works as well. As a result, I made them far more robust than I needed for my application so we could offer them to our customers. In essence, I made a layup engineering decision by making these so much stronger than wood that they don’t need any calculations. This is not to say that shear or bearing capacity calculations are hard, I just can’t predict how a user will configure their mounting arrangement. The only things a user would need to figure out is how to install them and how many are needed to mount their particular piece. The only requirement for our Heavy-Duty Keyhole Hangers is that you leave at least 5/8” of material above slot you route in your piece to get enough strength out of it. Ultimately, you will most likely be limited by the load rating of your wall anchors (e.g., sheetrock/drywall anchor). For example, if your piece weighs 150lbs, and your drywall anchors are rated at 75lbs hanging capacity, you would use at least three or more (not just two) because you paid attention to the factor of safety lesson I just gave right? Right- do not use 1 as your factor of safety. And you know that our Heavy-Duty Keyhole Hangers will handle much more than 75lbs each if installed in wood with 5/8” of material left above them just by looking at them.

By making these Heavy-Duty Keyhole Hangers out of 17-4 stainless steel, I reduced the likelihood that the wall screw will dent the slots in them. I could have easily used 316 stainless steel, which is great stuff, but it does have a tendency to dent under a focal load. After many years of making prototypes for medical devices, I have gotten quite used to machining stainless steel and love the performance of 17-4. So, even though I made these Hangers on an old knee mill, it wasn’t that hard for me (Figure 1). And I think the finished result was well worth the extra time it took to use the tougher material. Honestly, the hardest part of this project was programming the 2D CNC control because I still write my g-code by hand. If our customers like them, I hope to make more of these Heavy-Duty Keyhole Hangers real soon!

Making chips fly on the old knee mill!

Figure 1.- Machining of the 17-4 stainless steel material used to make the Keyhole Hangers. All done by us here in America!

To finish, let me show off my handywork and beautiful custom-made mirror! I started by jumping into CAD to make the frame design (Figure 2) along with a few templates and jigs to help me get everything perfect (Figure 3). I really love the look of bow tie (or butterfly) splines, so I decided to incorporate them in corners to tie together the miter joints. While all my jigs were being made on the 3D printer, I started the actual woodwork by planing down some rough-cut black walnut. I cut all four of the frame sides on the table saw and put a step along the inside back edge using a dado blade to create a recess I could drop the mirror into once assembled. Knowing that I would be making four bow tie splines, I decided to make them on my Nomad desktop milling machine (Figure 4). I used some cherry with an interesting grain pattern for the splines to really make them pop against the walnut. Because the frame members were all independent, I decided to connect them using glue and pocket screws before putting in the splines. After I chiseled, fit, and glued the splines in, I routed the slots for the Heavy-Duty Keyhole Hangers. Conveniently, while I was doing all this, my other neighbor was doing a bathroom remodel so I did a little dumpster diving to repurpose a mirror they ripped out. I took it too the local glass shop and they cut it down to size for me. I finished off the frame with a few coats of Waterlox, one of my favorite finishes (made in America). All that was left to do was to drop in the mirror, secure it with some offset clips I recessed into the backside, and mount it using the Heavy-Duty Keyhole Hangers. And it was mounted to the wall with confidence (Figure5). Ready to party!

CAD design of mirror frame

Figure 2.- CAD renderings of the front side (left) and back side (right) for the custom mirror frame design. 

A few jigs and fixtures

Figure 3.- A few jigs and fixtures that were made to make sure the assembly of the frame was perfect!

Using the Nomad to make bow tie splines

Figure 4.- Having fun and saving time using our Nomad mill to make the bow tie splines!

The finished mirror on the wall

Figure 5.- The mirror safely and confidently hung on the wall using a pair of Heavy-Duty Keyhole Hangers. A gorgeous finished product and worry free installation!  

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