Cycle time and Takt: What they have to do with Construction?by Ted Smith on 10/16/17
Takt Time – Cycle Time
There has been an interesting discussion thread on “Kaizen (Continuous Improvement) Experts” group on LinkedIn over the last few weeks on the differences between takt time and cycle time.
This is one of the fundamentals I’d have thought was well understood out there, along with some nuances, but I was quite surprised by the number (and “quality”) of misconceptions posted by people with “lean” and “Sigma” in their job titles.
I see two fundamental sources of confusion, and I would like to clarify each here.
Although takt time and cycle time are terms used in manufacturing, I have added comments concerning construction, as the same principles apply to us. Please always keep in mind that the primary risk to manufacturing is materials. The primary risk to construction is labor. When manufacturing talks about just in time delivery, they are referring to materials. When we in construction talk about just in time delivery, we are talking about labor.
“Cycle Time” has multiple definitions.
Most of the definitions of cycle time apply to manufacturing, however, cycle time can also be applied to construction. “Cycle time” can mean the total elapsed time between when a customer places an order and when he receives it. This definition can be used externally, or with internal customers. This definition actually pre-dates most of the English publications about the Toyota Production System.
It can also express the dock-to-dock flow time of the entire process, or some other linear segment of the flow. The value stream mapping in Learning to See calls this “production lead time” but some people call the same thing “cycle time.”
In early publications about the TPS, such as Suzaki’s New Manufacturing Challange and Hirano’s JIT Implementation Manual, the term “cycle time” is used to represent what, today, we call “takt time.” Just to confuse things more, “cycle time” is also used to represent the actual work cycle which may, or may not, be balanced to the takt time.
We also have machine cycle time, which is the start-to-start time of a machine and is used to balance to a manual work cycle and, in conjunction with the batch size, is a measure of its theoretical capacity.
“Cycle time” is used to express the total manual work involved in a process, or part of a process.
And, of course, “cycle time” is used to express the work cycle of a single person, not including end-of-cycle wait time.
None of these definitions is wrong. The source of confusion is when the users have not first been clear on their context. Therefore, it is critically important to establish context when you are talking. Adjectives like “operator cycle time” help. But the main thing is to be conscious that this can be a major source of confusion until you are certain you and the other person are on the same wavelength.
In construction we use the definition of cycle time as the total manual work time in a process. For example, if we determine that the it will require 8-man hours to install 200 feet of EMT conduit. The cycle time is determined by determining the number of feet of conduit that must be installed each man minute. 8 hours is 480 minutes. 200 feet of conduit divided by 480 minutes is .4 feet per minute on the average. The cycle time would be .4 feet per man minute. This would be the what we expected to happen on this project for this task. Please keep in mind this is not a general rule but determine for a specific task.
Takt time is often over simplified which leads to confusion.
The classic calculation for takt time is:
Available Minutes for Production / Required Units of Production = Takt Time
This is exactly right. But people tend to get wrapped up around what constitutes “available time.” The “pure” definition is usually to take the total shift time(s) and subtract breaks, meetings, and other administrative non-working time. Nobody ever has a problem with this.
So let’s review an example of what we have really done here. For the sake of a simple discussion, let’s assume a single 8 hour shift on a 5 day work week. There is a 1/2 hour unpaid lunch break in the middle of the day, so the workers are actually at the project. “at work” for 8 1/2 hours.
So we start with 8 hours:
8 hours x 60 minutes = 480 total minutes
But there is a 10 minute start-up process in the morning, two 10 minute breaks during the day, and 15 minutes shut-down and clean up at the end of the shift for a total of 45 minutes. This time is not production time, so it is subtracted from “available minutes”:
480 – 45 = 435
A very common mistake at this point would be to subtract the 30 minute lunch break. But notice that we did not include that time to start with. Subtracting it again would count it twice. In construction this is somewhat greater due to the placement and availability of latrines on large construction projects and other considerations.
No employee works 8 hours per day on a large construction site. Let’s analyze:
1. Daily safety briefing and JHA review: 5 minutes
2. Daily stretch and flex- 8 Minutes
3. Break time – 15 minutes
4. Latrine breaks- 3 x 5 minutes- 15 minutes
5. Cleaning up at the end of the day- 15 minutes
None of this is accounting for looking for materials, looking for tools, looking for information that the supervisor failed to provide the crew. Just taking into account the items above you have a total of 58 minutes. Therefore your 480 minutes of production time in one day is reduced to 422 minutes.
Lets continue the example using the original of 435 minutes.
So when determining takt time, we would use 435 minutes as the baseline. Lets suppose we needed to produce 50 units / day, then the takt time would be:
435 available minutes / 50 required units of production = 8.7 minutes per unit
Note that you can just as easily do this for a week, rather than a day.
435 minutes x 5 days = 2175 total available minutes
2175 available minutes / 250 required units of production still equals 8.7 minutes
All of this is very basic stuff, and I would get few arguments up to this point, so why did I go through it?
Because if you were to run this construction project, at a 8.7 minute takt time, you will come up short of your production targets. You will have to work overtime to make up the difference, or simply choose not to make it up which is rarely an option.
Why? Because there are always problems, and problems disrupt production. Those disruptions come at the expense of the 435 minutes, and you end up with less production time than you calculated. Some times these issues are outside of our control. When this happens, we need to track these and submit them as change order requests. Often times, these disruptions are our fault. Many times we prevent our crews from doing their jobs and be productive because we fail to provide them with 100% of the Tools, Material and Information that they need to complete the task. They then have to stop producing and go find what they need to complete.
One mistake supervisors make on a regular basis is that that they estimate the amount they can produce in a single day based on 8 hours of production, even though they can not work their crews for 8 hours.
Also remember that other things happen that we have to deal with that are in the contract that we can not recoup. Such as weekly required safety meetings for the entire job site, and OSHA inspection, the GC closes off an area for a hazard, etc. I could go on with a myriad of examples gathered from real sites, but you get the idea.
Here is what is even worse, though.
If you expect operators to do their daily equipment checks, when do you expect that to happen?
Do you truly expect your crews to stop work if they determine a safety or quality issue until it is corrected? How are you to account for these stoppages?
All of these things take time away from production.
The consequence is that the leadership – the ones who have to deal with the consequences of disrupted production – will look at takt time as a nice theory, or a way to express a quota, but on a minute-by-minute level, it is pretty useless for actually pacing production.
All because it was oversimplified.
If you expect people to do something other than produce all day, you have to give them time to do it.
Let’s get back to the fundamental purpose of takt time and then see what makes sense.
The Purpose of Takt Time
Here is some heresy: Running to takt time is wholly unnecessary. Construction projects operate just fine without even knowing what it is.
What those projects lose, however, is a fine-grained sense of how things are going minute by minute. Truthfully, if they have another way to immediately see disruptions, act to clear them, followed by solving the underlying problem then they are as “lean” as anyone. So here is the second heresy: You don’t NEED takt time to “be lean.” ( LEAN: The removal of everything that does not add value to the final product)
What you need is some way to determine the minimum resource necessary to get the job done and a way to continuously compare what is actually happening vs. what should be happening, and then a process to immediately act on any difference. This is what makes “lean” happen.
Takt time is just a tool for doing this. It is, however, a very effective tool. It is so effective, in fact, that it should be considered a fundamental although it is mostly overlooked in construction. I made the above statements to get you to think outside the box for a minute.
What is takt time, really?
Takt time is an expression of demand normalized and leveled over the time you need to produce. What takt time does is make demand appear level across your working day.
This has several benefits.
First, is it makes calculations for planning really easy through even a complex flow. You can easily determine what each and every task and crew must be capable of. You can determine the necessary speeds of crews. You can look at any process and quickly determine the optimum number of people required to make it work, plus see opportunities where a little bit of change or improvement will make a big difference in productivity.
More importantly, though, takt time gives your team members a way to know exactly what “success” looks like for each and every task. All you have to do is tell them up front and then they can tell throughout the day if they are meeting the goal or not.
This gives your team members the ability to let you know immediately if something is threatening required output. Put another way, it gives your entire team the ability to see quickly spot problems and respond to them before little issues accumulate into working on Saturday.
The key point here is that to get the benefit, you have to have a takt time that actually paces production. It has to be real, tangible, and practically applied on the project. Otherwise it is just an abstract, theoretical number which no one cares about.
The second big advantage is that it allows to you better plan and forecast your work. You can determine what it will really take to complete and also be able to defend that and explain to your project manager. You can also be more realistic in your forecasting so that when you say it will take three men, two weeks to accomplish this task, you will most likely be able to make the goal and also track it daily and make adjustments if need be.
You can also use this data to determine places where you can increase the productivity of your crews, and therefore increase the profitability. For example, what if you were to determine a takt time using the example earlier and determined that it worked out that you needed to produce at .4 feet per man minute. Now, what if you were to talk to the crews and ask them for ideas on how to increase to just .5 feet per man minute. If you were to accomplish that you would then produce .5 x 422= 211 feet per shift, per man. That is an 11% increase in productivity. Carried over a project, that could be significant.
Finally if disruptions do cause shortfalls to the required output, you have to make it up sometime. If you are constrained from running overtime (and many operations are for various reasons), then your only alternative is to build a slight over speed into your takt time calculation. You can also use the tracking that you have done to demonstrate the disruption and perhaps request either a schedule extension cost increase change order.