Punch Key Location – A guide to X-Min & Y-Max

For keyed punches, selecting the right position along the barrel is critical to function since each tablet press Make and Model have their own requirements.? When you want tooling to work across multiple machines, you will need two pieces of machine information on each press to calculate the allowable range for the key position.

The X Min. (minimum key extension dimension) is the vertical distance from the punch head flat to the beginning of the key and is relevant when the punch raises to its highest point in the cam track.? The purpose of this restriction is two-fold.? First, this limit ensures the key never comes out of the turret punch guide keyway so the upper punch will maintain orientation with the die.? Second, this limit ensures the key will not strike a cam.? Note that in many cases, a rotary press will have the turret punch guide’s keyway in-line with the direction of rotation.? In these cases, it is often permissible for the key to partially protrude above the turret guide.

The Y Max. (maximum key extension dimension) is the vertical distance from the punch head flat to the bottom of the key and is relevant when the punch lowers to its lowest point (typically depends on your upper punch penetration).? The purpose of this restriction is to prevent the key from striking any seals.? For presses without seals, the Y Max value is not critical.???

For example, Natoli tablet presses have the following restrictions on X-Min and Y-Max:

Some things to keep in mind:

· Tools that will be used for more than 1 tablet press should be designed to accommodate all the intended machines.?

· Larger ranges between X-Min and Y-Max values provide greater flexibility in key placement when designing tooling to run across multiple press platforms.

· Greatly expanded tables of X-Min & Y-Max values for rotary tablet presses will be published by the ApHA in the upcoming 8th Edition of the Tableting Specification Manual.

· Keyed punch drawings typically dimension key location as from punch head flat to the key center (HTC).? Subtract ? of the key length from the HTC to compare your tool design to the X-Min value.? Add ? of the key length to your HTC to compare your tool design to the Y-Max value.?

· In extreme cases, it may be necessary to select a short key to accommodate multiple press platforms.

Natoli Engineering can retrofit your existing punches designed for one press to also run on other presses.? For more information, contact Natoli Engineering.

Todd Martin

Sr. Technical Service Engineer