Question 4 of 7: Drill-Press Standard Time, Standards Definitions, and Uses of Time Standards

Question 4: Drill-Press Standard Time, Standards Definitions, and Uses of Time Standards (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(i) Normal Time and Standard Time for the Drill-Press Operation

Given.

Allowances: 5% personal + 5% unavoidable delays + 5% fatigue.

Find. The normal time and standard time for the operation, in min./pc.

Approach. Normalize each element's observed time by its own performance rating, sum the elements to get the cycle normal time, then apply the total allowance once to the summed normal time (Niebel convention: allowance as a fraction of normal time).

1. Normal time per element. $NT_i=OT_i\times\text{Rating}_i$: $NT_1=0.30(1.20)=0.360$; $NT_2=0.12(1.00)=0.120$; $NT_3=0.08(1.10)=0.088$; $NT_4=0.25(1.15)=0.2875$ min/pc.
2. Cycle normal time. $NT=\sum NT_i=0.360+0.120+0.088+0.2875=\boxed{0.8555\text{ min/pc}}$.
3. Total allowance. $A=5\%+5\%+5\%=15\%=0.15$.
4. Standard time. $ST=NT(1+A)=0.8555(1.15)=\boxed{0.983825\text{ min/pc}}$.

(ii) Definitions: Performance Rating and Normal Time

Performance rating is the analyst's judgement, made while observing an operator during a stopwatch time study, of the pace of that operator's actual performance relative to the analyst's internal concept of "normal" (100%) performance — a sustainable, well-trained pace that an average qualified worker could maintain, day after day, without undue strain. It is expressed as a percentage or a factor (e.g., 120% or 1.20 for an operator judged to be working 20% faster than normal, as in element 1 above) and is applied to the observed time of each element to remove the specific observed operator's individual speed from the resulting time value.

Normal time is the observed time for an element or cycle, adjusted by the performance rating, that represents the time a qualified operator working at a normal, sustainable pace would require to perform the element or cycle — before any allowance for personal needs, unavoidable delays, or fatigue is added. It is the "pure work content" time: $NT=OT\times\text{Rating}$, computed element-by-element and summed for the whole cycle, as in step 1–2 above. Normal time is not yet a usable production standard on its own, because it does not yet account for the non-productive time every real shift contains — that final step, applying the allowance, produces the standard time of part (i).

(iii) Uses of Time Standards

Once established, a time standard (standard time per unit or per cycle) serves many functions across a manufacturing operation: production planning and scheduling — converting an order quantity into required machine-hours and labour-hours, and sequencing jobs against available capacity; costing and pricing — providing the direct-labour-time input to standard product cost, and hence to quotations and pricing decisions; manpower and equipment planning — determining how many operators and machines are needed to meet a forecast demand; wage-incentive administration — forming the basis against which actual output is compared to compute incentive pay (Question 7(iii)); performance measurement and control — comparing actual output to standard to identify under-performing operations, equipment problems, or training needs; line balancing — allocating tasks among workstations so that each station's total standard time is as close as possible to the line's target cycle time; and evaluating proposed method changes — comparing the standard time of a new method against the old one to quantify the benefit of a change before committing to it. Because so many downstream decisions depend on the standard being correct, a standard that has drifted out of date (Question 4(ii) of the standards-maintenance discussion) can silently distort every one of these uses at once.