Common problems with CNC Drilling Machine and how to avoid them
CNC Drilling Machine is a machine dedicated to producing holes, with a spindle feed and often a multi spindle head. It is used for production drilling, tapping and countersinking on parts with many holes. This entry explains what it is, what the numbers on a data sheet mean, and what to put on a drawing.
It is written from the point of view of the buyer and the drawing office: the values that are realistic in production, the ones that cost money, and the way the result is verified. Where an industry sets the requirement, aerospace is used as the example: traceability and a first article before anything enters the batch.
The problems that actually occur
These are the failures that show up on a real job, listed in the order in which they are usually discovered.
- The drill wandering on a curved or angled entry face. The cause is usually upstream: a datum that is not the functional one, a fixture that does not repeat, or a specification that cannot be measured the way it is written.
- A pecking cycle that is too shallow, so chips pack in a deep hole. The cause is usually upstream: a datum that is not the functional one, a fixture that does not repeat, or a specification that cannot be measured the way it is written.
What causes them
In most cases the cause is upstream of the operation, not in it. The drill wandering on a curved or angled entry face is usually a symptom of one of the three causes above rather than a problem in its own right.
How they are prevented
Prevention is duller than diagnosis. Spot face or countersink the entry where the surface is not square to the axis, and the result is confirmed by plug gauge for size, CMM for position before the batch is released.
| Item | Note |
|---|---|
| Failure | the drill wandering on a curved or angled entry face |
| Prevention | spot face or countersink the entry where the surface is not square to the axis |
| Tolerance to hold | ±0.1 mm position, H9 by reaming |
| Finish to check | Ra 3.2 µm as drilled, Ra 1.6 µm reamed |
Applications
CNC Drilling Machine is used for production drilling, tapping and countersinking on parts with many holes, and in practice it appears most often in flange patterns, structural plates, manifold faces, rail and frame parts.
How it fits into a machining route
CNC Drilling Machine is one station in a route rather than the whole of it. The part arrives with the previous operation finished and leaves with the features it is responsible for completed, so the datum and the clamping method are agreed before the first part rather than discovered on it.The route is fixed before the first part is cut, and it is the route rather than the individual setting that holds the result: hole count and tool changes, not the drilling itself. Where a drawing calls for something the route cannot hold economically, that is raised at quotation rather than after the parts are made.
Standards, documentation and what is issued
The documentation requirement is in-house approval with dimensional reports. Material is supplied against a certificate where the application calls for it, inspection results are recorded with the job, and the records are kept so that a repeat order can be compared with the first instead of being measured from scratch.
Plug gauge for size, CMM for position is the verification step. Where a customer format or a standard report is required, it is agreed before the batch starts, because a report written after the event is a report nobody can use.
Frequently asked questions
What tolerance should be specified for CNC Drilling Machine?
±0.1 mm position, H9 by reaming is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.
Which material is usually used?
S355 steel is the usual choice, supplied against in-house approval with dimensional reports.
How is the result verified?
Plug gauge for size, CMM for position, with the results recorded so a repeat order can be compared with the first.
What is the most common mistake?
A pecking cycle that is too shallow, so chips pack in a deep hole.
How long does it take and what does it cost?
A realistic cycle is 2 to 20 minutes for a plate, and the cost driver is hole count and tool changes, not the drilling itself.
Related capability
If you are specifying CNC Drilling Machine on a drawing and want a second opinion on the route, send the model and the quantity. The first response is a manufacturability review with the likely risk points and a quotation, so the decision can be made on facts rather than on a price alone.
Machining, inspection and documentation are handled in one place, which is why the dimensional report and the material certificate arrive with the parts rather than after them.
Related entries
These entries sit next to CNC Drilling Machine in the encyclopedia: Vertical Machining Centre, Horizontal Machining Centre, Reaming and Boring. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.
