Altering a Magnetic Chuck for Custom Setup

Adding a fine pole top plate (top tooling) to an existing magnet.

When discussing how to choose a fine pole magnet vs a hard milling magnet, there are times when we want to combine the benefits of both. Here is a real-world example:

A customer wanted to build custom tooling into the top of a fine pole magnetic chuck for in their sinker edm.

The customer had it all planned out –

  • Four fine pole magnets palletized to EROWA
  • Each magnet would have its own pin layout for part locating
  • Jig grinding locations to press in pins in for work locating
  • Flushing holes drilled

The customer proclaimed, “This is all we do and it will work great.” I had a different approach to the challenge.

Here is some of the reasoning I took to show the customer how they could achieve the results they needed, while reducing costly tool alterations.

The Hermann Schmidt Approach

FPH on HSM Pin BackI am usually very against altering a magnetic chuck. Any mistakes or damage will result in a costly chuck rebuild and then another rebuild of the custom component.

So after a review of all the customer requirements first – then a review of the ideas they had on how to do it – we developed the following solution:

We used a fine pole top plate as a build basis for the customizing.  The top plate can be treated like a solid piece of material, and altered as needed.  Specific alterations were as follows:

  • Plate was ground parallel top & bottom, with 2 sides square to be used as referencing edges.
  • Flushing holes were added as needed.
  • Instead of jig grinding locations:
    • Tapped holes were added at the nominal location.
    • Set screws were inserted.
    • Locations were milled at the nominal location.
    • Once installed in the machine a female electrode was used to accurately burn the stop locations.
  • Thru holes were added for mounting to supporting magnet below.

A hard milling magnet was chosen as the base magnet so we could get the magnetic power through the top plate to the workpiece.

These operations were repeated for three other top plates, allowing for one base palletized magnet to do all of the work.

The Customer Benefits

By minimizing customization, and by building a more flexible tool set up, the customer received the following benefits:

  • Cost savings of 53%
  • Ability to build the fixtures themselves as they had no internal jig grinding
  • And, as expected, the part did change two years later and they had to change the top fixtures.


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