How To Grind Core Pins Quickly And Accurately

No matter how many CNC machines are in the shop you still need to know how to grind core pins quickly and accurately. An old saying says that “there is more than one way to skin a cat”, and this holds true for the surface¬†grinding process as well.

Knowing how to grind precision round mold components, such as core pins, sleeves and various inserts is a necessary skill for any injection mold making project. In the past, this type of skill was common for most toolmakers, however today this is a disappearing ability.

Obviously, with the widespread use of Wire EDM, sinker EDM and CNC milling, the demand for skilled precision grinding has diminished over time. Nevertheless, the need for mold making training is still critical, it is just that the volume of work has decreased.

How To Grind Core Pins
Precision Punch Core Pins

5 ways to grind core pins

  • Harig type spin fixture
  • Ded-Tru grinding
  • Centerless grinding
  • CNC OD grinding
  • Manual OD grinding

Harig spin fixture
The Harig spin fixture is a standard in American toolrooms. This simple grinding fixture can do an amazing number of complex tasks in the hands of a skilled toolmaker. Generally these are used on a manual surface grinder and require the grinding wheels to be dressed to various angles and radii.

Together with sine plates, magnetic squaring blocks, precision grinding vises and wheel dressers almost any shape can be ground. The main problem with this method is that it is so slow and requires a great deal of skill and experience to be even remotely efficient.


Ded-Tru grinding is a very accurate way of producing high precision round components. This is a somewhat more accurate tool than the manual Harig grinder and has the advantage of a high degree of repeatability.

Once again, the Ded-Tru requires a lot of skill and experience, very similar to the Harig approach. Yet once the set up is made it is possible to produce small batches of components with high accuracy. This is possible because of the use of flood coolant and the vibration absorbing roller used to support the workpiece.

How To Grind Core Pins
Royal Medical Core Pins
Centerless Grinders
Few mold making shops have a centerless grinder in house, but larger shops or production shops use them regularly. If you need something ground to a high degree of accuracy and roundness, centerless grinding is the way to go.

These machines can grind round parts around the clock with minimal operator intervention. Generally, these are used for high production runs, but, if a shop has one they certainly can do a lot of precision grinding with a centerless grinder.

Manual and CNC OD Grinders
The OD grinder is a powerful machine that has many applications in tool and die and mold making. All manner of round parts can be accurately produced, quickly and without requiring a huge learning curve.

Of course, the CNC OD grinder is vastly more efficient and versatile than the manual version, but for the average mold shop a manual machine works quite well.

Other methods of grinding precision round mold components would include the sophisticated CNC grinding machines used in high production environments. These are truly remarkable pieces of technology, complete with robotic arms, libraries of diamond grinding wheels, programmable contours and bar feeds.

Finding the best way to grind precision round mold components depends on the volume of work required, degree of complexity, skill level of the workforce and the budget available.
Any mold shop certainly needs the basic spin fixtures and can make good use of a Ded-Tru grinder. More than this is dictated the degree of complexity, work volume and budget.

Click her for information regarding US Government regulations on grinding wheels.

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