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Magnetic Workholding

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.

 

Custom Tool Solutions for Your Manufacturing Requirements

Hor jaw closeupFPH on HSM pin front w part

AP_EML_CUST

Customers looking at our custom solutions area ask why there are no descriptions to the pictures.

We do special versions of our products on a continuous basis. Usually they are variations of a concept of our standard offerings or a special mounting of a standard tool.

We cannot show all we have done nor do we show our products being used. Different industries or different areas of the world use our products in unique ways. I have seen many of them but by no means all of them.

We are trying to show concepts and ideas to stimulate your mind and use us to accomplish your unique requirements.

Please ask us about custom solutions.

Many applications can be addressed by taking a standard product and altering it by size, orientation or material. This keeps cost down from a true full custom solution and provides you with a tool that has most of the engineering decisions already proven.

I invite you to call me so we can discuss your specific applications.

Proper Set Up for Achieving High-Quality Flat Surface Grinding Results

A high-quality surface grinder is, of course, critical to successfully grinding parts flat. However several basic areas should be addressed before effectively evaluating the quality of the surface grinder. Correct and precise set up procedures are necessary to achieve the best results of the grinding tool.

MCS6x6HSM1

Set up areas include:

  • Magnetic chuck installation and maintenance
  • Grinding wheel selection and balancing
  • Diamond selection

Steps for high precision flat surface grinding

Magnetic Chuck Installation and Maintenance

  • Grind the machine table flat. Grind deep enough to remove all rust.
  • Grind the bottom of the magnetic chuck. Grind so there is approximately .0002” of dish per 6” of chuck length.
  • Mount the chuck with a light coating of oil between the surfaces. Tighten the right hand bolts first and then just snug the left side bolts.

Important: The ground-in dish and just snugging the bolts on one side allows the chuck to move due to thermal changes – while minimizing changes in flatness.

  • Grind the top surface of the chuck
    • Set the chuck magnet to “on.” With a properly built chuck this does not matter, it should not matter if the magnet is “on” or “off.” However, to be safe, grind with chuck magnet “on.”
    • Always grind with flood coolant (if available) and use an open-structure wheel, in order to minimize heat buildup in the grinding area.
    • Use small down feed increments with frequent dressing to minimize distortion.
  • Schedule maintenance
    • These steps are done yearly in our shop as rust builds up between the chuck and machine bed.

Grinding Wheel Selection and Balancing

  • Select a wheel that will not introduce stress or heat into the work piece. Your wheel supplier should be able to assist you in selecting the proper wheel.
  • Wheel balancing is an important part of flat grinding. An unbalanced wheel will produce a poor surface finish and shorten the life of you spindle bearings.
  • Wheel balance should be checked during the life of the wheel as it will change as the diameter is reduced.

Diamond Selection and Set Up

  • As a rule of thumb, the minimum size diamond should be ½ carat per inch of wheel face.
    • Large diamonds dissipate heat better, last longer and dress faster due to more contact with the wheel.
  • The diamond should be set approximately 10° in the direction of the wheel location.
    • Minimize the shank length and mount as rigid as possible.
  • Dressing feed depth should be a maximum of .001” per pass. Use flood coolant if possible.
  • Rotate the diamond to a sharp surface whenever possible.

Improve the Return on Your Investment

Careful installation of your surface grinding setup is vital to get the precise results that the grinder and the workholding tools are designed to deliver. Following these steps will not only improve your flat grinding, your grinding tools will continue to perform as expected for a longer time.

The return on your investment in Hermann Schmidt tools to support your precision grinding operations will be far greater with careful set up and ongoing maintenance.

How to Properly Use a Magnetic Squaring Block / Chuck

MSB6x61Using a magnetic squaring block (magnetic squaring chuck) is the most accurate and quickest way to square parts on a surface grinder. The magnet will hold the workpiece without distortion that will be caused by mechanical clamping, while release/clamp time is significantly reduced.

To get the finest results from a squaring block, correct setup is vital. Here are key steps in the process.

  1. Check that the magnetic chuck on the surface grinder is flat and nick free.
  2. Grind the first side of your workpiece flat.
  3. Mount the magnetic squaring block (MSB) with the on/off switch on the right side and hardened rail on the left.
  4. Place a support block near the lower left corner of the MSB.
    • We like to use a block with a button head screw in the top so the part rests on the top of the screw. The screw allows you to adjust workpiece height to extend beyond the top of the MSB.
  5. Turn on the magnetic chuck on the surface grinder
  6. To mount your workpiece, place ground side on against MSB. Slide the workpiece against the rail and down to the support block.
  7. Turn on the MSB.
  8. Grind the first side.
  9. Turn off the MSB.
  10. Clean both the workpiece and MSB.
    • We do not use the air hose here, we wipe the contact surface with our bare hand
  11. Follow previous steps, placing the last ground surface against the rail.

This will accurately square up the two sides you ground to the third side you located from. When removing the MSB from the surface grinder, care should be taken to not slide the MSB.

  1. After demagnetizing the surface grinder magnet, apply force at the top of the MSB to break any residual magnetism and surface tension
  2. Lift the MSB straight up
  3. Clean and oil the MSB

Get the Most from Your Hermann Schmidt Precision Tools

At Hermann Schmidt, we offer two models of magnetic squaring blocks. For most high-precision squaring operations, Our standard pole 6-inch Magnetic Squaring Block delivers a quick and extremely accurate method of grinding blocks square. Our 4-inch Fine Pole Magnetic Squaring Block is a fine pole, low profile magnetic chuck designed for fast and precise squaring up of smaller parts.

Following our guide to using magnetic squaring blocks will help you get the most out of your tools.

UPDATE:  Question was asked to see some setups.  The following is a couple of pictures of a work piece set up on the 6″ squaring block.  The top of the stop in the 123 block has a radius on it so the work piece is sitting on a point.

001  002

Magnetic Squaring Blocks

How to Choose Between Fine Pole Magnets and Hard Milling Magnets

When comparing Fine Pole Magnets to Hard Milling Magnets in work-holding applications, it is important to consider these three key factors:

  • Specific application / manufacturing environment
  • Performance
  • Cost

Let’s look into how these two magnetic solutions compare.

Fine Pole Magnetic ChuckFine Pole Magnet (FPH*)

Manufacturing environment

The FPH magnetic circuit is designed specifically for the sinker electrical discharge machining (EDM) environment. It is also used in the grinding environment as it meets the performance requirements there.

Performance

The FPH allows for the EDM process to continue into the surface of the magnet if necessary without any re-burn due to materials staying in suspension. This is an area where the strongest magnet is not the “best” magnet.

Hard Milling Magnetic ChuckHard Milling Magnet (HSM*)

Manufacturing environment

The HSM magnet is designed specifically for the hard milling area. It has the highest strength of any permanent magnetic circuit. The HSM magnet generates a primary and secondary field which allows it to provide a strong holding force while not magnetically penetrating deep into the part, hence minimizing chip contamination in the cutting zone.

Performance

While this circuit does not penetrate deep, it does create a situation where use in the sinker edm should be avoided. If an electrode tip is within approximately .25” of the magnetic surface and you are in a situation where the length /depth ratio of the area is greater than 5, you can get reburn. As the electrode cycles the coolant is evacuated from the hole and some solids can stay in magnetic suspension. When the electrode returns to the hole, we can get depth & finish problems.

Note that while we recommend the FPH magnetic circuit for sinker EDM for the reason described above, Hermann Schmidt does have customers that successfully use HSM magnets just fine in the EDM environment.

Comparing Cost

Cost is always a consideration, especially when automated cells can easily exceed 20 palletized magnets.

The HSM magnets cost 30% more to build and it is reflected in the price. Many customers want just one type of magnet to do all the work. We believe that is usually not reasonable. At Hermann Schmidt, we build magnets for the manufacturing environment and do not recommend trying to make a magnet design work where it does not belong.

Choose the Right Magnetic Tools for the Environment

Between selecting between fine pole magnets and hard milling magnets, consider the manufacturing process and the performance requirements first. Once that is established, the cost can be factored in – with cost going well beyond the initial purchase price.

* Throughout this post we used our FPH and HSM abbreviations to match our corresponding product lines. When selecting the correct magnetic tool for your specific application from Hermann Schmidt, look for models with the matching designation.  If you have any questions about using the right tool for your application, please give us a call at 860.289.3347.