Why adding the failure percentage is not enough
If 8% of attempts fail, 92% succeed. The successful work must recover the cost of the failed 8%. Adding 8% of base production cost gets close at low rates, but it slightly understates the reserve because the denominator should be successful attempts.
Base production cost × failure rate ÷ (1 − failure rate)With an $18.62 base cost and an 8% failure rate, the reserve is about $1.62. The risk-adjusted production cost becomes about $20.23. This is an expected-value allowance across repeated work, not a prediction that every order will consume exactly that amount.
Track a rate that matches the job
A single shop-wide percentage is a useful starting point, but mature estimates separate categories. A proven PLA production file on a maintained printer may have little retry risk. A tall ABS enclosure, fragile resin part, new material, or difficult multi-color job may deserve a higher assumption.
Track attempted jobs and completed jobs over a meaningful sample. Record the cost and cause of the failure when possible. A cancelled first layer is cheaper than a failure in the final hour, so actual cost history is stronger than counting every failed attempt as identical.
Do not confuse risk reserve with profit
The failure reserve repays expected production losses. Profit is what remains after production costs and selling fees. If no failure occurs on a particular job, the reserve is not evidence that the price was unfair; it compensates for the failed job that eventually will occur. Over many orders, compare the collected allowance with real failure cost and adjust the rate.
Margin must be calculated on revenue
Once risk-adjusted cost is known, solve for the selling price after percentage fees and desired margin. For example, a target of 35% means expected profit should equal 35% of final revenue. It does not mean adding 35% to cost. Fixed fees belong in the numerator; percentage fees and margin belong in the denominator.
(Risk-adjusted production cost + fixed fees) ÷ (1 − selling fee rate − target margin)Use failures to improve the system
- Separate preventable setup errors from normal process variability.
- Tag failures by printer, material, product, and stage of completion.
- Repair root causes instead of treating a high reserve as permission for waste.
- Update estimates when a file becomes proven or a process becomes less stable.
- Keep rush deadlines and one-off prototypes distinct from routine production.
A reserve makes the business resilient, but lower failure cost is still valuable. Improvements can support a better price, a stronger margin, faster delivery, or all three. The goal is not to charge customers for inefficiency forever; it is to keep ordinary production uncertainty from turning a seemingly profitable product into a loss.