FORM 03
Ceramic Rods
Solid rods and ground pins for structural, insulating and wear duty in tight assemblies.
View ceramic rodsDUTY 06
Ceramic rods, balls and discs for measurement and contact
When the contact point is the measurement, a part that wears by a micron per month is a calibration problem rather than a maintenance one.
Measuring equipment has a different failure cost from production equipment. A worn guide rail changes the product; a worn contact point changes the measurement, and every reading taken since the last calibration becomes suspect. That is why metrology parts are specified for stability rather than for strength.
Ceramic suits this because it does not work-harden, does not corrode at the contact, and does not conduct. Alumina covers most insulating contact parts, zirconia is used where the contact also takes impact, and silicon nitride where the part is slender and loaded. The specification work is mostly about the contact geometry and the datum, not the material alone.
Why ceramic
What changes when the part is ceramic
A contact point that stays put
Alumina and zirconia wear slowly and predictably at a contact, so the datum does not drift between calibrations.
Non-conducting by default
An insulating contact removes the need to isolate the probe from the fixture.
Stiff where it has to be
Silicon nitride gives a slender rod the stiffness to hold position without deflection under the measuring force.
Material fit
Which system suits this duty
Ratings follow the comparison published for the four systems. The grade is confirmed against the duty at quotation.
| Material | Choose it when |
|---|---|
| Alumina | Insulating probe bodies, gauge blocks, contact pads and discs. |
| Zirconia | Contact points that also take impact or sliding, and where toughness matters. |
| Silicon nitride | Slender rods and stylus bodies that must stay stiff under load. |
| Silicon carbide | Wear faces in the fixture rather than the contact itself. |
Part forms
Forms supplied for this duty
Each form page carries the dimensional call-outs and ordering route for that shape.
FORM 10
Ceramic Balls
Spheres for valve, bearing and milling duty, where diameter and roundness both have to be held.
View ceramic ballsFORM 11
Ceramic Discs
Machined discs with concentric features for seats, wear faces and rotating duty.
View ceramic discsFORM 04
Ceramic Plates
Flat plates and substrates where flatness, insulation and wear resistance decide the part.
View ceramic platesOn the drawing
What this duty needs pinned down
- The datum the part establishes, and the feature that must hold it.
- Ball diameter and sphericity, or rod straightness, as separate call-outs.
- Whether the contact slides, rolls or only touches, because that decides the finish.
- The measuring force and the stiffness the part must hold under it.
Inspection
What gets checked
- Sphericity and diameter on contact balls, measured at more than one section.
- Straightness and roundness on rods, measured over the working length.
- Parallelism of faces on discs and plates, since thickness alone does not define a datum.
Inspection points are agreed at quotation and recorded, so the first article and the tenth are judged the same way.
Questions
Asked about this duty
How round can a ceramic contact ball be held?
Sphericity is specified separately from diameter, and both are agreed at quotation against the measuring method. Which method is used matters: a two-point diameter check says nothing about form, so the inspection method is normally named with the tolerance.
Does ceramic chip at a contact point?
A finished ceramic edge chips more readily than metal under impact, which is why zirconia is used where the contact sees impact and alumina where it does not. Handling and packaging usually matter as much as the grade for a small precision part.
Can a probe rod be made insulating along its whole length?
Yes, and that is the usual reason for choosing ceramic over steel with an insulating sleeve. The trade-off is that ceramic is brittle in bending, so the rod diameter and the support positions are set together rather than copied from a metal part.
Continue
Other pages in this catalogue
The same catalogue, filed by material and by shape.