How do you write an SOP that operators will follow?
Write it with the operator who does the job best, keep it to one or two pages with photos, and try it on the floor before it is signed. Then train every shift on it and audit it. An SOP written in the office and handed down is rarely followed.
Many plants have a file of SOPs. Many of those files are forty pages thick, written once for an audit, and never opened by an operator. On the shop floor, each operator still does the job in his own way. The day shift and the night shift get different results on the same machine.
This is not the operator's fault. Nobody asked him, and nobody showed him anything he could use at the machine.
Which document do you need: SOP, work instruction or standard work?
Many shops call every document an "SOP". There are really three different things.
| Document | What it says | Where it lives |
|---|---|---|
| SOP | What is done, by whom, with which formats, for a whole process such as first-piece approval | In the office file and at the department |
| Work instruction | How to do one operation: steps, photos, key points, gauges | At the machine |
| Standard work | The customer's pace, the order of steps with times, and the parts allowed in the cell | On the cell board |
For a machine, you mostly need the work instruction. Write that first.
Why do most SOPs fail?
- They are written by someone who does not do the job.
- They are too long to read at the machine.
- Nobody is trained on them. They are only "issued".
- Nobody checks whether they are followed.
- The method changes, but the paper does not.
Each of these is a way of leaving the operator out. The fix is to put him in the middle of the work.
The six steps
- Draft it with the operator. Choose one job that causes trouble, such as a frequent rejection or a long changeover. Sit at the machine with the operator who does it best. Watch him do the job and write each step as he does it. Ask him what he does that others do not.
- Try it on the floor. Give the draft to a second operator and ask him to follow it exactly. Watch where he stops, guesses or does something different. Every such place is a gap in the SOP.
- Correct it. Fix the gaps. Add a photo for each key point. Try again. Repeat until a new operator can follow it without asking anyone.
- Sign it off. The operator, the supervisor and the department head sign. Put the revision date on it. Post it at the machine, not only in the office.
- Train every shift. An SOP nobody was taught is only paper. Use four short steps: prepare the learner, show one step at a time, let him try while you watch, then follow up until he is sure. If the operator has not learned, the trainer has not yet taught.
- Audit it. The supervisor watches one cycle a shift for the first month. Is the SOP followed? Is it still right? If not, go back to step 3.
The last step loops back to the third. An SOP is never finished. It is the best method we know today.
What goes on the page
For each important step, write three things: the step, the key point and the reason. The reason matters most. People follow a key point when they know why it is there.
Here is an example for changing a cutting insert (the figures and steps are an example only).
| Important step | Key point | Reason |
|---|---|---|
| Stop the machine and open the guard | Wait until the spindle has fully stopped | Safety: a turning part can catch a hand |
| Clean the insert seat | Brush out chips, no air gun | A chip under the insert gives a poor finish |
| Fit the new insert | Tighten to the marked torque, in the order shown in the photo | A loose insert breaks and damages the job |
| Take a first piece | Measure the first piece before running the batch | Catches a wrong offset before it becomes a batch of rejections |
Add the tools and gauges needed at the top, and a line for who to call if something is different.
The best SOP is the one an operator can follow on his first day without asking anyone.
Mistakes to avoid
- Copying an SOP from another plant. Your machines, your people and your problems are different.
- Writing a manual before the system works. First fix the floor with 5S, a clear store and a daily plan. Then write down what is already being done.
- Photos missing. Words alone are easy to misread. A photo at each key point removes doubt.
- Using the SOP to blame. If a step is not followed, ask why it was hard to follow. The answer often improves the SOP.
- Old copies left at the machine. After a change, remove every old copy the same day.
How to start in your plant
- List the five jobs where results change most from shift to shift.
- Pick one. Sit with the best operator for an hour and draft the SOP together.
- Try it with another operator. Fix the gaps. Add photos.
- Sign it, post it at the machine and train every shift on it in ten minutes.
- Check it daily for a month. Then review it with the people who use it.
- Move to the next job. Do not try to write fifty SOPs in one month.
Key points
- Write the SOP with the operator who does the job best, not for him.
- Keep it to one or two pages, with photos, at the place of use.
- Try it on the floor with a second operator before signing.
- Train every shift, then audit. An untrained SOP is only paper.
- Revise it after every improvement, and remove the old copy.
