I work in a company that’s big on Lean and Six Sigma, so I’m immersed in those concepts daily. What’s cool about them is that they also apply very aptly to farming, and often life in general. I thought I’d write a few posts about my favorite concepts.
Today, it’s the Kanban.
Kanban is a broad topic that has many applications and specific interpretations. But the general need for the Kanban is this: in manufacturing, we know we use lots of parts, or inputs. Periodically, we re-order them to replenish supply. We also produce outputs, which eventually a customer will purchase and consume. We know that sitting on inventory is bad. It wastes resources in two ways. First, it takes up space in a building, which has a real estate overhead cost, as well as utilities cost (heating, lighting, etc.) Excess inventory is also wasted financial opportunity: the money you spent on that stuff sitting around could have been in use elsewhere during the timeframe the inventory waited to be consumed. So, it’s generally beneficial to reduce inventory overhead as much as possible.
But, if you reduce it too much, sometimes the manufacturing floor could be “down” while they are waiting for inputs. Or, if we don’t have adequate output volumes, customers could sometimes be left waiting for product longer than they consider acceptable. Both of these things are costly, too. So, it’s a Goldilocks problem: finding the “just right” middle ground where you always have enough stock, and are always producing the right amount of product, but never more than is needed.
This sweet-spot can be found through data analysis. In manufacturing, you study your rate of consumption, the average turnaround time for ordering a re-stock, the average rate of output, and find the balance point. On our floor at work, we size parts bins such that one bin’s worth of stuff is used in the time it takes to go get a replacement bin from the warehouse. Two bins are in rotation: when one is depleted, a backup bin is pulled forward, and the empty bin is placed on a lower shelf, which “signals” someone to go get a fresh bin to replace it. They return that bin just before the backup bin runs out. When a customer orders a product, the “pipeline” is primed with partially-built product. The only wait time is for the last step in manufacturing before that item can ship out the door (and this signals all of the upstream bins to refill in the assembly line). Over time, this model gets studied and honed to where we are never “out” but are also never sitting on more inventory than is needed.
This is the notion of Kanban. Perfect flow of inventory.
The applications in home and farm life are many, for both simple and complex things. In our house, we put two “backup” toothpaste tubes in a lower bathroom drawer. When the main toothpaste tube is out, one of us pulls the backup. When the second backup is pulled, this signals the need to put toothpaste on the shopping list (a signal which my husband may holler from the bathroom “toothpaste Kanban!”). Within the next week or two, the backups are replaced in the lower drawer, ready for when they’re needed. We never run out of toothpaste and have to make a special trip to get some, and we also don’t sit on excess toothpaste inventory, which would take up space in the bathroom drawers. Why two toothpaste tubes in inventory instead of one? Because we go through them fast enough that it optimizes time at the grocery store to walk down that aisle less often. Kanban is always a balance of cost, overhead, time, and risk. We do this with most of our core grocery items, anything where it’s annoying if you totally run out.
For things used in higher volume, say, chicken feed, they are bought in larger batches. I don’t want to be going to the feed store every other day to replace an empty bag of feed. But I also like to pick up chicken feed on my way home from work, or when I’m already running errands in my car. I can only fit so many bags in my car. So in this case, I size my Kanban to the frequency I’d like to go to the store and what can fit in my station wagon. For me, that’s buying about six bags every other week.
In this case, I don’t need a “signal” so much to trigger the replenish, I just have this errand worked into my routine, and my consumption is very consistent. But often people use some kind of physical object for the signal, if not an empty bin placed in a specific spot, something like a card or tag. For instance, if you are managing different types of feeds in inventory, you could tear the feed tag off an empty bag that needs replenishing. You can place the tag on the dashboard of your truck, or wherever it’ll remind you to buy feed when you are already out shopping or at the feed store. Or, leave an index card at the bottom of a stack of feed bags. When the last feed bag is consumed, the card is grabbed and stuck on a bulletin board next to the shopping list. You get the idea.
The other way Kanban (which loosely translates to “sign board”) is used is to manage the flow of tasks. In Agile/Scrum software, a Kanban board is used to track tasks that need to be worked, tasks in work, and tasks completed (or variations thereof). This is really helpful if there are multiple people sharing workload: a quick inspection of the board allows a team to balance workload between themselves and monitor progress. When a person moves a task to the “done” column, this is a signal for them to pull a new task from the “to-do” list. And it’s a signal to others that this task is already being taken care of.
Kanban is part of a greater theory of a “pull system” where rather than pushing inventory at a consumption point whether it’s needed or not, you let the consumer pull inventory as needed. And pulling triggers a bin to be refilled upstream, to maintain steady supply and availability.
One added benefit of this type of system is that it reduces your mental load. I’m halfway through David Allen’s Getting Things Done book, and it describes similar notions of Kanban for “knowledge work.” Allen’s assertion is that our brains literally get loaded-down by trying to remember things, and this not only burdens us with stress, it prevents us from being able to focus on a single task at hand.
If you are in the barn and think “I have to remember to buy chicken feed” your poor brain is going to try to retain this and remind you of it later. Only, we know this mechanism doesn’t work very well: our brains tend to remind us in the shower, while we’re on the phone, when we’re concentrating on reading an important document, or other times when it’s not appropriate to be buying chicken feed. Not only does this stress us out, it distracts us at inappropriate times. Then, when we are at or near the feed store, this reminder system may not trigger, leaving us frustrated later that we are still inconveniently out of chicken feed. So, we need to develop trusted systems in which to store to-do items, so that our brains can relax and focus on what’s in front of us. Knowing that we can capture a random thought or reminder into a Kanban, and trust that it’ll get handled at the right time, we can relax and put that thought out of our minds for good.
What kinds of Kanban do you use in your home or farm?