The drawing decides the quote. Not the shop.
Five callouts decide which process your bore goes on, what it costs, and whether a shop can promise anything at all. Two of them are missing from most of the drawings we receive.
Ask three shops to quote the same milled part and you get three prices for the same set of operations. A deep hole does not work that way. The quote is a price for a process route — and the route is chosen from what the drawing says.
Two drawings can describe the same hole and come back with very different answers. Ø12 × 300 is one job. Ø12 × 1,440 is a 120:1 job, and the route changes with it. Same diameter, same tolerance, different process, different price, different lead time.
Most drawings that arrive are complete for milling and silent for drilling. That silence is what turns a quote into a week of email.
Write these five and the route chooses itself:
| Callout | Why it decides the route | What to write |
|---|---|---|
| Depth-to-diameter ratio | “Deep” is a ratio, not a depth. The ratio decides the process family and what tooling the job needs | Give the ratio, or both numbers: “Ø12 × 1,440 (120:1)” |
| Straightness — number, length and datum | “Straight” is not a callout. A number without a length cannot be measured, so it cannot be promised | “Ø0.5 mm over the full 3,000 mm, measured from datum A” |
| Material — grade and condition | The same grade behaves differently pre-hardened and stress-relieved. The condition decides the sequence of operations | “P550, stress-relieved blank” / “42CrMoA, pre-hardened 280 HB” |
| Bore type — through, blind or interrupted | Decides whether the bore can be approached from one end or both, and where the cross-holes sit in the sequence | Mark every cross-hole and gallery, and its position along the bore |
| Function — what the bore does | A sealing surface, an oil gallery and a sensor passage are not the same requirement, even at the same tolerance | Name the function: “sealing surface” / “oil gallery” / “cooling channel” |
Two callouts are absent from most drawings we receive, and both of them change the answer.
The straightness datum and the measurement length. “Straight within 0.5 mm” means nothing on its own. Over 300 mm it is a routine job; over 3,000 mm it is a different problem with a different price. State the length, and state which face or axis the measurement runs from — a straightness callout measured from the wrong datum is a rejected part that was machined correctly.
The heat-treatment sequence. Does the bore get hardened after it is drilled? If yes, say so on the drawing, because it moves the finishing operation after heat treatment and changes what can be held. If the blank arrives already stress-relieved, say that too — it is the single most useful sentence a buyer can add about material.
The same bore, written twice:
The second line takes thirty seconds to write and removes a week of questions. It also gives every shop that quotes you the same starting point, which is the only way three quotes can actually be compared.
We do not quote a straightness number before we see the print. Diameter, depth and material decide it, and a number given without them is a guess dressed up as a promise. What we publish on the deep-hole drilling page is what we have actually held in production, offered as a reference rather than a guarantee.
What the five callouts buy you is not a lower price. It is a route chosen on the first pass, instead of the third — and three comparable quotes instead of three different guesses.
Extreme ratios are routine work here — beyond 600:1 at small diameters. What is achievable depends on the diameter, the material and the straightness you actually need; send the drawing and we will tell you honestly.
No. Specify the bore and what it does; choosing the process family is our job. What we cannot do is choose a process for a hole whose depth, tolerance or material is not stated.
No — “straight” cannot be measured, so it cannot be promised. Give a number, a length and a datum.
For geometry, yes. But the callouts above usually live in the drawing notes, not in the model. Send both and the quote will be firmer.
If two of the five callouts are missing, send it anyway. Within 24 hours an engineer replies with what we need to know and which line your bore belongs on. NDA welcome.
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