How to Calculate Needle Downtime in Garment Shop Floor

In an earlier post needle downtime is explained. In this post, I will show you how to calculate needle downtime. Needle downtime is also referred to as needle time. Needle time is the total time a machine is run during the day, or we can say total time spent on stitching garments.

If you observe an operator while she is stitching a garment, you will see that the operator doesn't run the machine continuously. She picks up garments (or garment parts), places it on the table, aligns pieces, put the pieces under pressure foot, stitches few centimetres of the seam, realigns plies, and stitches the piece. This way she completes stitching of one operation of a garment. In one operation cycle time - there is material handling time and stitching time (needle downtime).
Needle down time
Needle downtime

If you observe sewing operators' activities throughout the day, you will find they
  • stitch garments 
  • sit idle when they have no work to do, or for other reasons of lost time 
  • speak with their co-workers
  • move from one workstation an another
  • take break
  • go to the washroom
  • they chat with quality control guy and line supervisor
  • and many more uncertain things may be happening.
From their many activities you have to measure only needle downtime – i.e. when machine needle moves up and down. You can use one of these two ways to measure needle downtime.
  • Statistical data analysis (Work sampling method)
  • Operation cycle time analysis

Work sampling method 

It is not possible to observe and record needle time for all operations throughout the day. By work sampling method you can find an occurrence of different activities in terms of percentage. Work sampling method for sewing floor activities is discussed in this post. Read that post to know about work sampling method and calculation method to find the percentage of machine running time out of total hours worked. From this percentage data, you can calculate how much time is spent on running machine. Remember, this is statistical data analysis and not actual needle time. For actual needle downtime follow the second method.

Also read: What is work sampling?

Measure needle downtime by cycle time analysis

You might know how to do cycle time analysis. While you perform time study for an operation, you capture time for different elements of the operation cycle. Calculate machine running time (stitching time) out of these elements. This is the needle time per operation (for stitching operation of one piece).

Let first find needle time for an individual workstation
  1. Select one workstation and an operator
  2. Write list of operations she is doing. Do time study for single operation first
  3. Do time study for all elements of the operation cycle 
  4. Find time for machine running element (stitching) from the time study sheet
  5. Study at least 25 operation cycles for same operation
  6. Find average time for stitching element of 25 studies
  7. Count total pieces made by her (operation wise quantity if she is doing more than one operation)
Total needle downtime in a day  = (No of pieces made * Stitching time per piece)

Example: Assuming that one operator is doing collar run stitch operation of a shirt. The calculated average machine running time (needle downtime) is 12 seconds. She has produced 400 collars (only collar run stitch). Therefore calculated needle downtime would be 400*12 seconds or 80 minutes in a day.

Calculate needle downtime in the percentage of total hours worked by dividing 80 minutes by 8 hours. It is (80*100/480) % = 18.33%

In this example, we are not considering if this operator worked in operations and did repair work in the same workstation. To know actual needle downtime, you have to include all activities an operator did by stitching machine. 

Disclaimer: The method explained above is written based on my experience. there might be a different way to measure needle downtime. Prior to use of this method, and share needle downtime, cross-check the result internally.