How to quote CNC machining work — from the shop's side of the counter

A CNC quote is the same four numbers as any machining quote — material, setup, cycle, overhead — plus one thing manual work does not have: programming. What changes is where the risk sits, because on a CNC job you commit to a cycle time before you have proved it.

Read the print for cost drivers, not for dimensions

The dimensions tell you what the part is. The cost lives somewhere else, and it is usually in one of five places.

• ·Tolerances. A ±0.005 feature and a ±0.0005 feature are the same line on the drawing and a different job. Tight tolerance means slower finishing passes, more gauging, more scrap and sometimes a second operation.
• ·Surface finish callouts. A 32 Ra is normal. A 16 Ra or better means finishing passes at reduced feed, and possibly a different insert.
• ·Number of setups. Every time the part gets flipped or re-fixtured you pay setup again and you introduce a stack-up. A part that needs three ops is not three times a one-op part, it is worse.
• ·Material condition. Hardened, stainless, or anything gummy runs slower and eats tooling. Bar stock versus a casting versus a weldment changes everything upstream.
• ·Inspection requirements. First article documentation, a CMM report, material certs and traceability are real hours that never appear on the cycle time.

If a print has tolerances tighter than you can hold comfortably, quote it as a conversation, not a number. The cheapest tolerance is the one the customer did not actually need and put on the drawing out of habit.

Programming: the hour that hides

Programming is a one-off cost like setup, but it is easier to forget because it happens at a desk. On a complex first-time part it can be several hours, and on a lot of one it dominates everything else.

Two rules that keep it honest. Charge it as its own line on first-time parts so it is visible if the quantity changes. And do not charge it again on a repeat — if you do, you will lose the repeat business to the shop that already has the program too.

Cycle time: the commitment you cannot take back

This is where CNC quoting differs from manual work. On a manual job you find out the time as you go. On a CNC job you promise a cycle time, and if you are twenty percent optimistic you are twenty percent optimistic on every part in the order and every reorder that follows.

Work it out from the actual arithmetic rather than from feel: RPM from surface speed and diameter, minutes from feed per revolution and length, pass count from the stock you have to remove. Then add the parts that are not cutting — tool changes, air moves, door open and close, in-process gauging, deburring. On short-cycle parts, the non-cutting time is often the larger half.

Material: buy it in your head before you quote it

Price the stock you will actually order, at today's price, including the length you lose to facing, parting and workholding. If the material has a lead time, that belongs in the delivery promise; if it has a minimum order quantity, that belongs in the price of a small lot.

Putting it together

The step that turns quoting into a skill

Quote it, run it, then compare the minutes. Not the money — the minutes, per operation. That is the only way an estimate ever gets better, and it is the step almost nobody does because the data sits on a timecard nobody reads.

Shops that close that loop develop a feel that looks like intuition and is actually just recorded experience. Shops that do not are still quoting from a number somebody guessed years ago.