Pacer Cord - Working at Takt Time

Q.  How do you keep the pace of an assembly operation constant?  

A.  Big businesses use conveyors, or some other piece of big mechanical equipment, that conveys Work In Process (WIP) at a constant pace.  If you’re not in a big business, you may think that you can’t afford such a luxury.  Hope is not lost.

I ran across a very inexpensive way to control assembly line speed.  It’s called the PACER CORD.  See top photo.

Here’s the way it works.  The pacer cord is drawn by a winch.  The outside diameter (OD) of the capstan (motor-driven spindle or drum) is sized so that it pulls the cord at a specific speed.  What speed?  Takt Time! 

Photo #1

In the 2nd photo there are a series of horizontal blue lines and a single red line.  These lines correspond to the operational steps in the two Standard Work Combination  Sheets (SCWSs).  Note the SWCSs visible in the first photo.

Photo #2

The red line indicates a break point: a changeover, from one operator’s SWCS to the next.  That red line means that operator #1 must be finished by that point, and that operator #2 must begin.

The blue lines in the 2nd photo correspond with the time of each operational step in the SWCSs.  These lines allow the operators to glance at the floor while working.  They are looking to see if they are ahead or behind pace.  If they fall behind, they know they need to catch up.  

A missed handoff at the red line will mean that the Cycle Time (CT) will be greater than Takt Time (TT).  That’s a very bad thing.  Do you remember why?  I discussed it in my post on Takt Time.  If you’re not sure, it’s a good time to refresh.

Standard Work Combination Sheet

My last post concluded a discussion of Takt Time.  So, if you’re working to Takt Time, how do you know when each operation in your process is supposed to start and stop?  How do you know if your operation is less than or equal to Takt Time?  And, how do you communicate that to those in the process?

The answer to all those questions is to use a Standard Work Combination Sheet (SWCS).  I know.  That’s a mouthful, but it’s an extremely powerful tool that every Lean practitioner ought to have in their arsenal.

So what does it look like?  Find one below*. 

AUTHOR'S NOTE:  I apologize that the image bleeds over into the "about the author" section of the page, but wanted to use as large a size as possible, as the clarity reduces to fit the post requirements.  

This sheet is jam packed with actionable information.  Let’s examine.

We can see that there are 8 operations to this process; can tell what each is called and how much of the time for that operation is spent doing manual (man) work, machine (auto) work and walking.  

The bottom right gives us a key for the symbols used.  There is no delay indicated in this SWCS, but we can tell how long each component of this operation takes; e.g. 32 seconds manual time and 14 seconds walking in operation #1.  Finally we can see the total of manual and walk time spent performing this process. 

From it, you can see the walking that takes place between operations 1 & 2, 7 & 8 and 8 back to 1.  You can also tell in operation #6 that the machine continues to operate (horizontal dashed line) on its own and that the operator doesn’t stand watching.  Rather, the operator moves to the next operation, #7 while the machine works away.  

The vertical dashed red line is labelled TT, indicating that it’s the Takt Time for this process.  

Now some questions for you:

1. Can this process be completed in Takt Time (TT)?
2. If you were going to improve this process, which operation would you try to improve first?  

*NOTE: I made this form in Excel.  Takes some patience, but then you can type in it.  Of course, you can always whiteout an old one and make copies.

A1.  Process takes 423 sec to complete.  Takt Time is 425 sec; hence, the process can be completed in Takt time.

A2.  The gaging process takes the longest and represents the greatest opportunity for improving the process time.  Virtually every second of improvement would have an equal effect on improving the overall process time.  Remember, the operator is actually working on the part from the previous machine cycle.  Things you might consider doing are to automate the entire gaging process; or, use more automated tools.  For example, you might use a vision system for gaging rather than a manual profilometer if the ROI is good.  

Takt Time

“What?”

That’s usually the first question the uninitiated ask.  “Are you saying tack time?” is the next.  Those of you using Lean know the answer, but let me just refresh. 

Takt is a German word meaning pace or tempo, as in the pace of a piece of music.  In an orchestra, pace is usually governed by the speed of the conductor’s baton.

In Manufacturing, Takt Time is the pace at which your process needs to operate in order to meet customer demand.  It is calculated by dividing Available Time by the Customer Demand.

Available Time is the worker’s scheduled time, say 7:00 AM to 3:30 PM (8.5 hours), less any breaks, lunch, meetings, cleanup time, etc.  So, in the following example, Available Time is ___________?

Scheduled time: 8.5 hours = 510 minutes

                   Breaks 2 x 15 = - 30 minutes

                   Meetings - 0 minutes

                   Lunch - 30 minutes

                   Cleanup - 12 minutes

                                            - 72 minutes

Available time = 510 - 72 = 438 minutes

Demand = 40 pieces per day 

“Cool.  So what?”

Takt Time (TT) tells us how long we have to build one part.  If we exceed Takt time even once during the building of today’s 40 pieces (but stay on pace for the rest), we will not get all 40 built.  We’d have to work some overtime.  A goal of Lean is to work NO OVERTIME; so, we always need to work within Takt Time.

“No Problem,” you say.  “I’ll give my workers 40 minutes to get it done and we’ll never exceed Takt Time.”

That’s no good either.  You’ll either rush workers and get poor quality; or, you will need to assign more workers.  Neither is acceptable.

Note — and this is huge — we don’t care how long it currently takes your workers to build one of these parts.  That time, by the way, is called Cycle Time (CT): the time to  build one good part.

Ultimately, our objective is to make CT less than or equal to TT.   In order to achieve that, we typically use a Standard Work Kaizen event, but that’s for another post.  

Summarizing, you’ve learned about Available Time, Takt Time and how to calculate both.