I guess I jinxed myself by blogging recently about the twice-replaced handle set on our front door. In that post, I wrote:
"The thumb latch is a lever that sits on a set of little pins set on a die-cast zinc alloy, which allows it to toggle up and down. Unfortunately, die castings are often about making things fast, and such parts typically have sub-par structural performance and are prone to stress cracking.
What probably happened is that a tiny crack formed on one side of the casting and propagated every time we squeezed up and down on the handle. One side failed (red circle, "before" image) and our door handle started twisting at an odd angle. That was pretty weird. The upside is that we replaced it with the backup landing plate before we were locked out of the house.
After going through two plates, we bought a new set (potentially unwisely). But we are happy to report that the manufacturer finally figured out it needed to reinforce the casting for the load by reinforcing the area where the pin sets (red circle, "after" image). Six months in, it's still working like a charm."
After proclaiming happily that the third set was all hunky dory, the handle is starting to twist again. And "Who Knew" gets to tell me that he (or she) told me so in this response to my blog post: "Who Knew" writes:
"As it is now, that pin cradle probably still won't last five years. It looks suitable for a float pivot in a carburetor, not a part that secures/opens a residential entry door. It used to be that on "pot-metal" castings such as these, wear bearing surfaces were cast in, or a socket was cast in, and a wear bearing surface was pressed into the socket.
These days, the fact that they added a few more thousandths to bolster that pin cradle was a significant decision given cost of retooling, plus adding a fraction of a material to each casting. Careful inspection of the new casting compared to the old may reveal a new void or change in some other dimension, which would have allowed the addition of material at that pin cradle by subtracting it from another location ... Or, ever-so-slight subtraction from a variety of other locations."
The only thing "Who Knew" underestimated was the MTBF of the part.
One thing is for sure: I'll be hustling that part right back to Home Depot, where I purchased it, to get my money back. And when the products you buy don't live up to your expectations, I urge you to do the same, because manufacturers can't fix what they don't know about.
In the best case scenario, some design engineers will get their hands on it and change the design before too many other unsuspecting customers buy the product. Worst case, well at least you'll have gotten your money back.
If you've had a similar run-in with a product (and we hope you haven't), we'd like to include it in our Made by Monkeys Blog at www.designnews.com/madebymonkeys. E-mail your examples, photos and accompanying theories on what went wrong and ideas on any possible fixes to me at firstname.lastname@example.org.