Technical insight
Holweck Groove Inspection: A CMM Probe-Access Review
Before including CMM inspection in a Holweck-component order, ask which specified groove surfaces the proposed setup can actually reach. Use a marked section view and a surface-access matrix to separate an agreed check from an unresolved access question. This guide addresses quotation planning, not a measuring program or a universal stylus selection.
By Geetai Precision
- Published
- Updated
Start with the surface, not the machine name
For a helical channel, name the required observation before discussing equipment: a particular flank, a root region, a land or a datum on the supplied drawing. Ask the metrology reviewer to mark the intended contact area and approach. Do not treat one accessible location as evidence that every specified surface can be checked in the same setup.
Renishaw describes disc styli for grooves and undercuts within bores and notes the alignment needed for contact with a thin disc. ZEISS describes T-styli for opposing undercuts and difficult-to-access points. These examples show why contact geometry belongs in the access discussion; neither source establishes a method for a specific Holweck drawing. [1][2]
A quotation-stage access matrix
Ask the supplier to complete this suggested matrix against the actual drawing and proposed orientation. Keep the proposed method and any unresolved coverage separate. The matrix is editorial purchasing guidance, not a requirement quoted from a metrology standard.
| Drawing region | Access discussion | Receipt for quotation review |
|---|---|---|
| Groove flank | Identify the intended side-contact area and the approach past adjacent lands. | Marked section showing the contact region, stylus approach and proposed orientation. |
| Groove root | Identify the region required by the drawing and discuss whether the proposed tip contacts it. | A clear statement of the proposed check and any region that remains unresolved. |
| Land or channel entrance | Distinguish the selected contact area from an adjacent edge or transition. | A marked view connecting the intended contact area to the specified characteristic. |
| Datum and other reference features | Ask how the stated setup relates the groove check to the drawing's references. | The proposed setup identifier and any additional orientation needed for the review. |
Review reach together with configuration
Renishaw's legacy PH20 guidance recommends keeping stylus length to the minimum needed for access and minimizing joints to preserve rigidity. It also requires attention to the probe module's permitted stylus combinations. This is guidance for the named system, not proof of equipment used for a Geetai project. [3]
When the response to an access problem is a longer extension or a different tip, ask the reviewer to document the complete proposed configuration and check it against the applicable manufacturer's instructions. Include the fixture and neighboring part surfaces in the access discussion; a sketch of the tip alone leaves that question open.
Keep access review distinct from approval of the measuring method. Ask the responsible metrology reviewer to decide whether the proposed method is suitable for the specified characteristic. A route that reaches a surface does not, by itself, close every acceptance requirement.
Example: flank access agreed, root access unresolved
In a hypothetical quotation, a supplier proposes a flank check but leaves the groove-root region unspecified. Return the matrix with the root item open. Ask for a proposed alternative, a different orientation or an explicit exclusion for the design owner's decision. Do not silently substitute a nearby land measurement or remove the drawing requirement. This is a review example, not a report of a completed job.
If an optical or other method is proposed, have the responsible reviewer assess that method separately. Do not assume a change of sensor automatically resolves hidden surfaces or the required coverage. Agree what the report will identify before including the item in the purchase scope.
Close the access review before ordering
- Attach the controlled section view and identify the ordered sleeve, rotor or stator rather than referring only to a pump stage name.
- List the required characteristics, proposed contact regions and setup references; leave unresolved entries visibly open.
- Record the design owner's disposition for any excluded region and the corresponding quotation wording.
Use the Holweck service page to frame the component inquiry and the inspection coordination page to discuss the required documentation. Bring the marked drawing and access matrix into the quotation discussion; do not select a probe solely from a website illustration.
Frequently asked questions
Can a disc stylus be assumed to cover every groove?
No. Renishaw describes specific groove and undercut applications and alignment considerations. Ask the reviewer to evaluate the actual channel and contact region; a general stylus description is not a drawing-specific approval. [1]
What belongs in the quotation when access remains unresolved?
Identify the affected characteristic, the proposed next review and the decision owner. Keep it separate from the agreed checks, and request written resolution before treating that item as included in the approved scope.
Related review paths
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References
- Styli — Renishaw. Accessed 2026-09-27T03:22:24.000Z.
- ZEISS Styli — ZEISS. Accessed 2026-09-27T03:22:24.000Z.
- PH20 stylus selection (legacy system guidance) — Renishaw. Accessed 2026-09-27T03:22:24.000Z.