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How To Square Up A Workpiece A Surface Grinder

Nearly every injection mold component has, at one point, had to be ground square in order to be further machined. Knowing how to square up a workpiece on a surface grinder is very basic, and absolutely essential.

If the cavity block, for example, is out of square, every other operation done will be affected. The Wire EDM, high speed machining, Sinker EDM, and assembly all depend on the cornerstone work done on the surface grinder.

Most injection mold components are able to be ground on either a manual surface grinder or an automatic CNC wet surface grinder. In either case, the process is similar.

Basically, there are three common methods used to grind a workpiece square.

  • Grinding using a precision vise

  • Grinding using an angle plate

  • Grinding using a magnetic squaring block

Each of these methods works well and are quite interchangeable. Very often, the size of the workpiece determines which method works best. You just wouldn't want to grind a tiny core block using a magnetic squaring block on a large wet surface grinder, for example.

How to square up a block using a precision vise

Supposing that you have a heat-treated piece of S-7 tool steel that has been milled reasonably square, proceed as follows:

  1. Remove any obvious burrs or dings from one of the largest, flattest surfaces. Grind this surface flat.

  2. Grind the opposite side to your desired size. You now have two flat and parallel surfaces.

  3. Clean off one of the longest perpendicular surfaces to lay on the bottom of the grinding vise. It is a good idea to indicate the workpiece once it is mounted in the precision vise. Set the workpiece so that one end is protruding beyond the edge of the vise.

  4. Now grind the long side so that it cleans up, set the vise on it's side and grind the 4th side clean.

  5. Now you can simply use the magnetic chuck to hold your workpiece, or use the vise again, if this works better.

How to square up a workpiece using an angle plate

  1. Follow steps 1-3 above, but use a C-clamp or Kant Twist clamp to hold the workpiece to the angle plate. This method is rather old school, but still comes in handy once in a while.

Grinding a workpiece square using a magnetic squaring block

  1. Follow steps 1-3 above, only now you use the magnetic block to hold the workpiece. You can also avoid turning the block on it's side by using the rail to align your block, once you have the long perpendicular side ground clean.

  2. A tip for bigger cavity blocks is to use the magnetic squaring block side rail, but mount a 1-2-3 block on the opposite side. Now run a screw or threaded rod through the 1-2-3 block to push the workpiece against the side rail. This helps overcome gravity and saves your hand from having to push the block against the rail, while turning on the magnet.

Obviously, the precision squaring block, angle plate, and magnetic squaring block must be absolutely square for this process to work reliably. Once you have a good set-up, take great pains to keep it that way. The surface grinder is only as good as the tools and toolmaker.

Checking for squareness

There are numerous methods for checking squareness, each one has advantages. The surface grinder can do very high quality work, but it requires skill and patience.

  • Use a square cylinder and dial indicator mounted on a special height stand

  • Use a magnetic cylinder mounted to the workpiece and check with an indicator

  • Compare perpendicular sides with a dial indicator mounted in a height stand

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