CAD to cost, or pricing from job history
Two estimators can hold the same part and be doing 2 different jobs. One is asking what this part should cost, reasoning from the geometry through a model of machines and rates toward a theoretical number.
The other is asking what this part did cost, the last 3 times something like it crossed the floor. Both are legitimate questions. They are not the same question, and most of the frustration manufacturers have with quoting software comes from buying an answer to the first when they needed the second.
What geometry sees
A CAD-to-cost engine reads the model, recognises features, holes, pockets, turned diameters, bends, assigns operations to each, pulls cycle estimates from a process model and multiplies through standard rates. Done well, and aPriori in particular does it seriously, this is real engineering.
It scales to parts nobody has ever made, it gives a large buyer a consistent yardstick across hundreds of suppliers, and it produces a defensible should-cost long before anyone cuts metal.
The engineering under these tools deserves respect rather than dismissal. Feature recognition on a clean model is genuinely hard and largely solved, the process models embody decades of manufacturing knowledge, and the better engines let a designer see cost consequences while the geometry is still soft, which prevents expensive parts from being designed at all.
Used for that, early, upstream, before a supplier exists, the approach is exactly right.
Notice whose problems those are. Consistency across suppliers, costing unbuilt parts and steering design are a buyer’s problems and a designer’s problems. A manufacturer quoting real work has the opposite situation, one floor, known machines, and parts that mostly resemble parts already run. The tool was built facing the other direction.
What geometry cannot see
The model prices a theoretical floor, and you do not run a theoretical floor. The cycle time tables assume a machine in catalog condition, where your rotary transfer holds a cycle the catalog would not print, and your old grinder needs a dresser pass the model never heard of.
Geometry has no memory.
The rates are regional averages, where your burdened rate on the tight cell is specific and earned. The model assumes clean CAD, where the package that actually arrives is a scanned print, a revision letter and a workbook, the gap the buyer’s guide calls fit.
Above all, the model has no memory. It does not know the plater always comes in low on this finish, that this customer’s cleanliness spec doubles the wash, that the last part in this family scrapped 4 percent in its first month. That knowledge is not in any geometry. It is in your closed jobs.
Make it concrete with the worked part this site prices everywhere. The spool valve’s honed bore carries 5.1 seconds and $0.135 a piece, the largest inside line on the part. A feature-recognition engine sees a 0.3125 bore with a tight tolerance and assigns a textbook hone cycle.
Your history knows that bores in this family hone slower than the book on your machine, because a closely related job ran at $0.141 against the $0.135 an estimator wanted to carry, a difference worth $7,200 a year at this volume.
No update the vendor ships will ever contain that fact. It happened to you, on your spindle, and it is findable only in your record of it.
Where geometry is right
History has failure modes of its own, and pretending otherwise would make this advocacy rather than argument. A record can encode an old inefficiency as if it were physics, pricing tomorrow’s parts on a cycle the floor has since improved, which is why the record needs dates and the comparison needs judgment.
A match can be superficially close and structurally wrong, the same geometry in a nastier material. The discipline is to treat history as evidence to be weighed rather than a verdict to be copied, which is still a better starting point than a theory, because evidence at least argues back.
Your record is the moat.
The honest version of this argument concedes ground. If you have no usable history, a greenfield line, a new process, a first venture into a part family, the model is what exists, and a theoretical number beats no number.
If you are the buyer, a should-cost engine is exactly the right tool, which is why your customers run one, and why it pays to understand the model that will be pointed at your quote.
And on a truly novel part, even a history-first floor is estimating from analogy, which deserves to be said plainly rather than dressed up.
There is also a defensive use worth stealing. Because your customers run should-cost engines, running the same logic against your own quote before it leaves tells you which lines sit far from the theoretical number, which is exactly where the buyer’s procurement team will push.
Arriving at that meeting knowing your hone line is above the model, and knowing precisely why from your own actuals, converts a haggle into an explanation. The model makes a poor estimator and a useful sparring partner.
The mistake is treating the exception as the baseline. On a floor running 10 to 300 requests a month, the genuinely novel part is rare.
Most incoming work sits near something already run, a diameter away, a volume away, a revision away, and for that work the relevant question is never what the textbook floor would spend. It is what your floor spent last March.
Theory argues in averages.
The hybrid that actually makes sense
The framing of geometry against history is a choice about where the price comes from, and it should not be mistaken for a ban on reading geometry. The 2 approaches divide the work naturally.
Geometry is excellent at the front of the process, reading the print, finding the features, sequencing a candidate routing, the work of understanding what the part is. History is the authority at the back, deciding what those operations cost on your floor, the work of understanding what the part costs.
A tool that reads the package like an engineer and prices it like your own closed jobs is using each method where it is strong, and that division, reading from the package, pricing from the record, is the architecture this site’s product takes for granted.
The failure mode to avoid is the reverse hybrid, where geometry sets the price and history is consulted as a sanity check after, because by then the theoretical number has anchored everyone in the room.
What counts as enough history
The objection that arrives next is that your record is too thin or too messy for any of this. It is worth taking seriously and it is usually wrong.
Most floors running 10 to 300 requests a month have several hundred closed jobs sitting in the ERP and the quote folder, and several hundred is plenty, because pricing does not need a statistical model, it needs the 3 or 4 closest relatives to the part in hand.
What makes a record usable is not volume but the join, quote to job, estimate to actual, so the system can say this is what we thought and this is what happened.
History compounds.
Messiness matters less than completeness of that pairing. Missing operation detail on old jobs is survivable. Missing actuals is not, because a history of quotes without outcomes teaches you what you have historically believed rather than what things cost, and repeating your own beliefs faster is not an improvement.
The floors that struggle here are the ones that never closed the loop between estimating and job costing, which is a reconciliation problem worth solving on its own merits, independent of any software decision.
Why history compounds
Here is the structural difference, and it is the reason this site takes a side. A geometry model is as good on the day you buy it as it will ever be.
Its process tables improve when the vendor ships an update, which is to say, uniformly, for every one of its customers at once, including the 2 who compete with you.
History is different in kind. Every job you close is a data point nobody else has, what the part was quoted at, what it actually cost, where the estimate was wrong and by how much.
A pricing process that reads that record gets sharper with each close, and it sharpens in your direction, on your machines, your suppliers, your customers’ habits.
Across a few hundred closed jobs the gap between the theoretical answer and the earned answer becomes the margin on the quote, and a competitor cannot buy the earned answer at any price, because the record it is earned from is yours.
That asymmetry is the entire bet, and it is why the comparison against quoted history, the $1.28 quote that ran at $1.37, sits at the center of every worked example on this site.