Most ROI claims in this category arrive as a single multiple with no math behind it, an “8x return” with nothing to check it against. This is one shop, worked all the way through, using the same formulas and the same conservative default assumptions as Spall’s own ROI calculator. The numbers below match what the calculator shows for the same inputs.
The shop
Twelve machines across two lines, two shifts a day, eight hours a shift, five days a week. Each machine averages four hours of unplanned downtime a week, at a downtime cost of $800 an hour. That rate is the calculator’s own conservative default for what a stopped line costs once idle labor and lost throughput are counted. Each machine runs about sixty parts an hour at five dollars of cost per part, with a scrap rate of two and a half percent. Each line changes over eight times a week, averaging twenty five minutes a changeover. None of these are unusual numbers for a mid-size job shop or contract manufacturer. They sit close to the calculator’s own defaults, adjusted only to fit twelve machines and two lines.
What that costs, per week
Three losses, calculated the same way the calculator computes them. Downtime loss is machines times downtime hours times the hourly rate: 12 times 4 times $800, which comes to $38,400 a week. Scrap loss is machines times parts per hour times total weekly hours times the scrap rate times cost per part: 12 times 60 times 80 weekly hours times 2.5 percent times $5, which comes to $7,200 a week. Changeover loss is lines times changeovers per line times the changeover time in hours times the hourly rate: 2 times 8 times just over 0.4 hours times $800, which comes to about $5,333 a week.
Add the three and this shop is losing roughly $50,933 a week, about $2.65 million a year, if none of it ever gets addressed. Almost no plant recovers every dollar of a loss like this. The conservative estimate below is the figure the calculator actually stands behind.
The conservative case, not the full loss
Nobody captures a loss like this in full, and the calculator doesn’t claim you will. Its default improvement assumptions stay modest: a ten percent cut to downtime, a fifteen percent cut to scrap, a ten percent cut to changeover time, applied only to the losses actually measured, not the whole number above. Ten percent of the $38,400 downtime loss is $3,840 a week. Fifteen percent of the $7,200 scrap loss is $1,080 a week. Ten percent of the $5,333 changeover loss is about $533 a week. Add those and the conservative weekly savings comes to about $5,453, roughly $283,573 over a year. The calculator rounds that to $284,000 on its headline card instead of showing false-precision cents.
What it costs to run
The calculator adds Spall’s own year-one cost on top of this loss and savings math, built from the gateway and per-machine rates published on the pricing section of /product/, and shows the net, the return multiple, and the payback period live as every input changes. That cost isn’t reproduced here, since it’s the one figure in this worksheet that moves whenever the published rates do, and a guide that reprinted it today would be wrong the next time a rate changed. Plug this shop’s numbers into the calculator itself and the payback period comes out to about five weeks against the current rates.
The net and the return multiple move the same way the payback period does, live, off whatever the published rates say on the day you run the numbers, which is exactly why the calculator computes them instead of a guide stating them as fixed.
The two inputs that actually move the answer
Downtime loss is three quarters of this shop’s weekly total, which means the two inputs that drive it, downtime hours per machine per week and the downtime cost per hour, matter far more to the final answer than scrap rate or changeover time do. Move either one and the whole case moves with it, in a way scrap and changeover can’t match at this shop’s numbers.
Cut the downtime hours assumption in half, from four hours a week to two, and the downtime loss drops to $19,200 a week, cutting conservative annual savings from about $284,000 to roughly $184,000. Double it to eight hours a week instead, and annual savings climbs to roughly $483,000. The downtime rate behaves the same way: half the hourly rate, to $400, and annual savings falls to about $170,000. Double it to $1,600, closer to what a true bottleneck machine can cost per hour once everything downstream is included, and annual savings climbs to roughly $511,000.
That’s the practical takeaway for anyone building this case for their own floor: spend the time getting a real number for downtime hours per machine per week and a real hourly downtime rate, pulled from an actual cost model like the one covered in how downtime cost actually adds up, before worrying much about precision on scrap rate or changeover count. Those matter too, but they won’t swing the final answer nearly as far.
What the pilot is actually for
Every number above is a default assumption run through a formula, not a measurement of a real plant. The calculator states this plainly: the loss inputs and improvement percentages are conservative defaults unless you change them. A pilot’s purpose is to replace every one of them with a number read directly off your own machines. A twelve machine shop that plugs in its real downtime hours, its real hourly rate, and its real scrap and changeover figures will get a different answer than this one, sometimes better, sometimes worse. Build the decision on that number, not this one.
Print the worksheet before a pilot starts, with your own numbers typed in instead of the defaults used here, and keep it. Once a pilot ends, run the same twelve-machine shape against the numbers a month of real data actually produced, and compare the two sheets side by side. The gap between the printed guess and the measured result is its own useful number. It shows how close a plant’s own sense of its losses was before anything got measured.
Quick recap
- A twelve machine, two line shop loses roughly $50,933 a week across downtime, scrap, and changeover, using the calculator’s own formulas
- The conservative case, ten percent off downtime, fifteen percent off scrap, ten percent off changeover, comes to about $284,000 a year
- The calculator adds Spall’s year-one cost from the rates on /product/ and shows net, return multiple, and payback live, about five weeks for this shop’s inputs
- Downtime is three quarters of the loss stack, so downtime hours per machine per week and the downtime dollar rate are the two inputs worth getting right
- Halving or doubling either of those two inputs swings annual savings from around $170,000 to over $500,000, far more than scrap or changeover assumptions do
- Every number here is a conservative default, a pilot replaces all of them with numbers read off your own floor