Why the Same Drawing Gets You Five Different CNC Quotes

This is the single biggest driver of the spread, and it is invisible on the drawing. A setup is every time the part gets clamped in a new orientation so the machine can reach a different face. Each setup means fresh workholding, a new zero, re-probing, and operator time before a single chip is cut.

A part that one shop machines in two setups on a 3-axis mill, another shop machines in one setup on a 5-axis. That difference alone can move the price 30 to 50 percent, in either direction. The 5-axis shop spends less labor but bills a higher machine rate. The 3-axis shop is cheaper per hour but eats more setups. Neither is wrong. They are pricing the same part on different iron.

A deep pocket with a small floor radius, a bore two inches down a narrow bore, an undercut behind a wall. These force long, skinny tools or specialty tooling, and long tools chatter. To hold finish and tolerance, the shop slows the feed rate way down, which means more spindle time per part, which means more money.

A shop with the right tooling on the shelf quotes it normally. A shop that has to order a custom tool or fixture the job around a reach problem builds that pain into the number. Same feature, two very different costs, depending entirely on what is already in the tool crib.

A general tolerance of plus or minus 0.005 inch is free. It comes off the machine that way. A single feature called to plus or minus 0.0005 inch is not free, because most shops cannot hold that straight off a milling cutter. It moves the part to a grinder, a reamer, or a separate precision setup with inspection between steps.

Here is what makes it a hidden driver: that one tight number on one face can add an entire operation the drawing never announced. One shop reads it and adds a grinding pass and a CMM check. Another shop reads the same number, decides their process holds it anyway, and does not. The first quote is higher and more honest. The second is cheaper and riskier. You cannot tell which is which from the price alone.

Cost does not climb in a straight line as you tighten a tolerance. It climbs like a ski jump. The move that collapses your quote spread most reliably is going back through the drawing and asking, for every tight callout, whether the part actually functions without it. Usually most of them can loosen.

Anodize, plating, heat treat, passivation, bead blast, powder coat. None of these happen on the CNC machine. They happen at a second vendor, which means the shop has to package the parts, ship them out, wait, receive them back, and inspect them again. Every finish callout is a second supplier relationship folded quietly into your unit price.

This is a big source of spread because shops handle it differently. A shop with an in-house anodize line or a tight local plater absorbs it cheaply. A shop that has to truck parts across the city and wait two weeks bills the coordination and the lead time. Type III hard anodize also grows the part 0.001 to 0.002 inch per surface, so a shop that understands finish will machine the affected features undersize first, and a shop that does not will hand you parts that measure out of tolerance after coating.

If your material is a standard 6061 plate the shop already stocks, it is cheap and immediate. If it is a 7075 billet, a specific stainless, titanium, or an odd size they have to order in mill quantities, the price and lead time jump, and a shop that stocks it beats a shop that does not on the same part.

Quantity changes the math underneath all of this. Setup cost is a fixed block that gets divided across the run. At qty 5, the setups dominate and the per-piece price is brutal. At qty 100, the same setups amortize down and the per-piece price can drop by half or more. When two quotes look far apart, check that both shops quoted the same quantity the same way, because one may have assumed a prototype run and the other a production batch.

The last driver is the least technical and the most human. When a shop is not sure it fully understands a part, it does not quote optimistically. It pads. Ambiguous drawings, missing GD&T, unclear datums, a finish spec they have not run before, all of it gets absorbed as a higher number so the shop is protected if the part turns out harder than it looked.

This is why the highest quote in a spread is often not the most capable shop, and the lowest is often the one that either understood the part cleanly or missed the risk entirely. The spread is partly a map of how confident each shop felt. A clear, fully dimensioned drawing with sane tolerances is the single best tool you have for pulling the whole spread down, because it removes the uncertainty that shops price defensively.

Once you know the drivers, you can read a set of quotes instead of just sorting them. The cheapest number is a starting question, not an answer. Here is what the pattern is actually telling you.