Gemba Tales

Lean stories, lessons and reflections

Posts Tagged takt

Guest Post: Beyond Toast Kaizen – Lean Breakfast Concepts, Circa 1937

Jun 21

Posted by markrhamel in Lean Principles | 2 Comments

I was in Boston this weekend with my wife and we were told the best place for breakfast was Paramount’s. As we waited in line to order food, I noticed their sign told us to “Please Order and Pay before being seated”.  They claimed not saving a table “ensures all customers will have a table when needed” and although “it may seem hard to believe, it’s been working well since 1937”. Like much in lean this seemed counterintuitive. I decided to do a few time observations while we waited in line. Fortunately, my wife puts up with my curiosity.

Customers came out of the breakfast line and cashier every 90 seconds. So, customers needed a table every 90 seconds (Takt Time). I watched several tables that were filled before we sat down and the time to eat was about 18 minutes. (This is not the type of place where you bring the paper and the server keeps filling your coffee. )

If customers were sitting down at a table every 90 seconds and it takes 18 minutes to eat, the restaurant would need 12 tables to balance the seating capacity with customer requirements (Cycle Time/Takt Time). The restaurant has 14 tables. So, the overall system Cycle Time (think “drop off rate”) was less than Takt Time. I convinced myself, and my wife, why their seating policy worked.

I am confident that Paramount’s system works and that now…and in the future, we will not have to save a table. One should always be available (assuming no substantial change in Takt Time). I wonder if when they started in 1937 they fully understood why it worked. Oh well, perhaps all that really matters is that their breakfast is outstanding and customers keep returning.

John Rizzo authored this blog post. He is a fellow Lean Six Sigma implementation consultant and friend of Mark Hamel. John also enjoys a good breakfast!

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Musings About FIFO Lane Sizing “Math”

Jun 7

Posted by markrhamel in Lean Math | 1 Comment

First in, first out (FIFO) lanes are the core of sequential pull. When properly sized, constructed and managed they ensure process and conveyance sequence, provide a buffer to facilitate flow during upstream changeovers, chronic failures, etc., and guard against overproduction. FIFO lanes, among other things, must reflect a maximum level of inventory – number of parts or pieces or total work content (minutes, hours, or days). Without enforced maximum levels the upstream process may produce more or faster than the downstream process can routinely consume.

So, how do you size your FIFO lane? There’s different levels of math that can be thrown at it. Often folks apply some pretty rudimentary thinking, especially initially if they’re in the midst of value stream analysis. Generically, the equation is:

FIFO lane max = desired lead time/takt time (TT)

Of course, then you have to get into the definition of desired lead time. In a perfect world it would be zero, but very few value streams are perfect. In fact the reason we typically use a FIFO lane is that we cannot connect the upstream and downstream process via continuous flow (or supermarket pull, for that matter). So, there obviously are barriers to continuous flow (and pull) – like those pesky changeovers, cycle time mismatches between upstream and downstream, process instability, shelf-life considerations, cure times, shared processes, etc. We must always try to eliminate the barriers, but in the meantime, we often need to live with sequential pull.

…Anyway, back to desired lead time. Below are a handful of possible equations that can be applied. Admittedly, they are not failsafe, but they do prompt some necessary thinking. Like kanban sizing math (often much more complicated), these are principle-based and should be tested out and adjusted as necessary first through table-top simulations and again after real-life piloting and forever, really. You can definitely get carried away calculating factors of safety, applying standard deviation driven coefficients to address variation and the like. I’ll leave that for another time. For now, here are a handful of equations that may be helpful.

If we’re talking cure time, for example:

  • FIFO lane max = (cure time/TT) X factor of safety (i.e., to address cure time variation and/or upstream stability issues)

If the issue is shelf life, it can be:

  • FIFO lane max = (shelf life/TT) – factor of safety (it makes sense to have margin here)

If the upstream operation has significant set-up time and thus there is a risk that it may “starve” the downstream, then the calculation may look something like:

  • FIFO lane max = (Upstream internal set-up time/TT) X factor of safety

The same type of thinking can be applied if the upstream process is shared (i.e., supplying other value streams). Here we may need insight into the “every part every interval” and translate it into an every line every interval (ELEI…just made that one up) thing. The equation may then be:

  • FIFO lane max = (ELEI/downstream TT) X factor of safety

If the upstream operation has substantial and chronic failures (i.e., unplanned downtime), and frankly this issue is probably implicit within most factors of safety referenced above, then you may want to consider something like:

  • FIFO lane max = (average upstream unplanned downtime event/TT) X factor of safety (to address unplanned downtime duration variation and/or time between unplanned downtime events)

Within a mixed model value stream, sometimes the cycle time (CT) of the downstream process is greater than the upstream CT for some models. (Of course, the average weighted CT of the downstream process is less than or equal to the average weighted CT of the upstream process.) In that situation, the math may look something like:

  • FIFO lane max = ((longest downstream CT – TT) X batch volume for longest CT item)/TT

I am sure there is other (and better) math out there. Please share your expertise here!

Of course, lean practitioners aren’t only concerned about the maximum levels. When we exceed maximum levels, we definitely have an abnormal condition that requires real time response. But what about when the FIFO lane has dwindled, when do we signal an abnormal condition? Obviously, when the FIFO lane is empty; but that’s a bit late. This is where we can, for example, use the factor of safety (divided by TT) to help calculate the “red zone.” And there are other conventions that can be used. For another time…

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Plan Vs. Actual – The Swiss Army Knife of Charts

Mar 13

Posted by markrhamel in Lean Management System, Scientific thought - PDCA/SDCA | 8 Comments

swiss army knifeImagine that you were only allowed one chart (or board) at the gemba. What would you pick? What is the Swiss Army knife (I’m more of a Leatherman Multitool fan myself) of charts that gives you insight into process adherence and process performance?

For me, it’s the plan vs. actual chart – also known as the production analysis board (or chart), day-by-the-hour chart, etc. It is typically a paper chart (my preference) or dry erase board that is positioned at the pacemaker process. It’s refreshingly low-tech and reflects, at a minimum, the line, cell or team name, output requirements (number of picks, assemblies, invoices, etc.) for the day or shift, the related takt time, the planned hourly (or smaller time increment) and cumulative outputs for the day or shift, the actual hourly and cumulative outputs (or in some practices the cumulative deficit or surplus) and fields to record the problem or reason for any hourly plan vs. actual deltas as well as a sign-off by lean leader(s) as proof of review.

So, why is the plan vs. actual so powerful? Here’s 5 reasons.

  1. Communicates customer requirements. The chart reflects the demand, by type or product, quantity, and timing and sequence. It reflects a takt image.
  2. Forces the matching of cycle time to takt time. Standard work should dictate the requisite staffing (and related cycle time, work sequence and standard WIP) to satisfy the customer requirements.
  3. Engages the employee and drives problem-solving. Like any visual control worth its salt, the plan vs. actual is worker-managed in a relatively real-time way. It highlights abnormal conditions (hourly and/or cumulative shortfalls or overproduction) and drives self-correction or at least notification/escalation and containment. The plan vs. actual also spurs PDCA in that the worker is required to identify the root cause of the abnormal condition and ultimately points the worker, team and leadership to effective countermeasures.
  4. Focuses lean leaders within the context of leader standard work. A good plan vs. actual will have fields for team leader/supervisor sign-offs on the hour and managers twice daily. This is essentially proof of the execution of leader standard work in which the leader should ensure that the plan vs. actual is maintained real-time, is complete (i.e., no unexplained abnormalities), and that countermeasures are being employed in order to effectively satisfy customer requirements.
  5. Focuses associates and lean leaders within the context of the daily accountability process. The prior day’s plan vs. actual and trended performance (including pitch logs) should be reviewed within daily tiered meetings. These meetings help drive the identification of improvement opportunities and countermeasures at the individual, team and value stream level.

So, what’s your Swiss Army Knife chart and why?

Related posts: Leader Standard Work Should Be…Work!, Leader Standard Work – You can pay me now, or you can pay me later

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