Measuring Grinding Wheels for 5-Axis Cutting Tool Grinders

A lot of effort was spent by ZOLLER in the recent past on tackling the task of measuring grinding wheels. A lot has been achieved and learned. This document is about the attempt to summarize the current state of affairs on the topic.  

Benefits of using a ZOLLER measuring machine
Most of today’s grinding machines give the operator the ability to measure or qualify the offsets on grinding wheels. But this is a time consuming manual and very much subjective process. Qualifying just provides offsets in Z and X but no angles or corner radii. While qualifying, the grinder does not produce any parts. It is also easy to crash the machine during the process, which is very similar to touching off on a machine tool.  

Using a ZOLLER measuring machine, much like a presetter, can avoid all this. Setup time is minimized and one can expect a sellable cutting tool on the first run. Using a ZOLLER measuring machine for grinding wheels centralizes the task of qualifying grinding wheels and consequently streamlines the shop floor process.

Terminology
Grinding wheels come stacked on an arbor, typically in a group of three. The stack is called a wheel pack.
Grinding wheels lose their form during the grinding process especially at the corner. The frequent process of putting them back in shape (with the need to re-measure) is called dressing.  

FEPA
The wheels come in a limited amount of standardized forms. The forms are defined by the FEPA standard.

Measuring grinding wheels
Measuring grinding wheels poses many challenges. One cannot in a sustainable way measure with a touch probe. By nature the wheels would grind that probe down. That leaves optical measurement. Here, however, we deal with unavoidable dirt and undesired optical effects.  

In »pilot 3.0« grinding wheels can be measured with standard shapes and measuring modes and without any special measuring program.  

The first issue we face is that the we are getting false readings in Z on grinding wheels. The reason is that grinding wheels naturally have no axial relief. That causes the upper edge of the wheel to blurry up in the camera view. One can see the false Z measurement below left taken with shape 21. On the right we have a measurement with the shape new 227. Shape 227 offers the ability to set up a sub measuring range within the major measuring range. This sub measuring range dynamically finds the corner within the wide open major measuring range.

Shape 227 works for all for four quadrants
 

The second major challenge is contamination. Grinding wheels are typically very porous. The surface easily retains lint and other dirt. One could find a clean spot around the circumference but wheel packs typically have a lot of runout. So an evaluation of the entire circumference is a must. On a manual machine one needs to find the highest points in Z and X by rotating. On a CNC machine we now have the ability to use grind360. The function is closely related to cris360. However, grind360 has the ability to filter out all circumferential segments that are contaminated.

Using Post Processors to Grinding Machine Controls
By far the most desirable and safe solution to get the wheel offset data from the ZOLLER to the grinding control is by post processor. Here MP410 (Z8772410) comes in. The measuring program offers an easy-to-understand way to program the wheelpack. The program then provides the raw data that the PP. Once the data is there is can be sent to ANCA by PP Z8773375 or Numroto by PP Z8773378.