CNC Turning Cost Reduction: A Fourth Tool Cuts Machine Time — saving $14,415/year
ROI is unusually high because the declared investment is very small compared with the monthly saving.
Current problem:
A turning operation on a core-type part, running several machines in parallel across three shifts. Machine time takes up almost the whole cycle; manual handling is a very small share of it. A capacity chart tracked continuously for one month showed the operation had hit its ceiling: demand was above the capacity on hand, while another part number on the same line needed more machines to raise output. Buying another machine was the first option on the table.
Root cause:
The turret was running only three positions: T1 -> T2 -> T3. Each tool had to take off a large amount of stock, which forced it into several passes. Because machine time dwarfs manual time, the constraint sits INSIDE the cut, not with the operator. Any improvement aimed at manual handling - however well executed - is capped by that very small share.
Improvement mechanism:
Add a fourth tool (T4) to the turret: T1 -> T2 -> T3 -> T4. T4 takes a share of the stock, which lets EVERY remaining tool drop passes. No change to the existing tools, the machine, or their fixtures. This is a deliberate trade: tooling cost goes UP, to buy back machine time. Less machine time pulls the cycle time down, each machine's capacity rises, and the same output is made on fewer machines - and therefore with fewer people across three shifts.
Solution:
Added one insert and one holder to the turret for position T4. Every tool and fixture on the three existing positions was left untouched. The stock was then redivided across all four tools so that none of them had to take the multiple passes it took before. Machine, clamping program and inspection routine all stayed as they were. The machine this freed up went to another part number that needed more output.
Result:
Before the improvement, the cost items declared in this case ran at $2,886 per month.
After the improvement, those same items run at $1,685 per month.
The saving is $1,201 per month, or $14,415 per year - a 41.6% reduction measured against the cost of the items declared in this case (Labor, Machine), not against the full product cost.
The investment is $311, itemised as 1 entries in the one-off implementation cost table.
The payback time is ~8 days.
Lessons learned:
The cheapest turret is not the cheapest operation. Look only at the tooling budget and this case is an added expense, and it gets turned down. It only shows a profit once the WHOLE operation is costed - tooling, machine and labour on one sheet. And before looking for an improvement, measure where the time actually sits. When the time is inside the machine, every effort spent on manual handling is capped.
Reusable knowledge
Where this applies:
- The turret has a free position. No free position, no case. - MACHINE time must dominate manual time. The other way round, cutting passes buys you nothing. - There must be enough stock to divide across one more tool. - Machine capacity must genuinely be the constraint. If the machines have headroom, this change only raises tooling cost and converts nothing into money. - There must be somewhere for the freed machine to go. An idle machine is not savings.
Risks:
- Tooling cost goes UP, not down. If the conditions above are not met in full, this case loses money. - One more tool means one more setup point, one more tool-change cycle, one more thing that can wear unevenly or break. - Redividing the stock changes how cutting forces are distributed. Dimensions must be re-measured and the defect rate watched after the change - here it was checked and the rate held, but that is a result to be confirmed, not a given. - Fewer people only becomes money when those people actually leave the payroll or take up work that is short-handed. Standing around saves nothing.
Author's evidence:
- Cycle time measured directly on the machine before and after, not taken from the standard. - Capacity chart for the operation tracked continuously over one full working month. - Basis figures taken from the average output of the THREE MONTHS AFTER the change, not the first month. - Defect rate tracked before and after, to be sure the time saved was not paid for in quality. - Actual machine count and headcount on the operation compared before and after.
Reusable idea:
The freed machine went to another part number that needed more output, which avoided buying a new machine. That benefit lands on a DIFFERENT product, so it sits outside this case's cost sheet - though in practice it was the largest item of all. A pattern worth checking on other operations: where machine time dominates manual time, the turret has a free position, and capacity is the constraint - redividing stock across one more tool is worth costing out, even when it raises tooling spend.