The list below are some of the commonly asked hole punching questions with answers from our experienced staff at UniPunch Products. Our business is to provide you with high quality hole punching systems and the knowledge to operate and maintain your tooling.

We invite you to contribute to this section by sending your questions to Your input and suggestions are greatly appreciated.

Q: Why does die clearance matter?

A: Too much clearance will create a burr which may not be acceptable.  If the clearance is too tight the process will require more tonnage, the punch and die will wear out prematurely, and it will require more force to strip the punch from the material.  Read More…

Q: What causes some of my punches to stick in the material after the part is punched?

A: There are several reasons for this condition. First, dull punches will cause the material to improperly fracture the material. This is evident by checking the burnished area on the slugs. This burnished area should be approximately 20 percent of the total material thickness.

Second, stripping springs that are worn and have taken a set will not provide full stripping pressure. The specifications for new spring lengths are listed on the catalog page for each unit. This combination of dull punches & dies and fatigued springs results in the reduced tooling performance. As a general rule, we recommend to sharpen often and take light cuts.

Q: My press brake has limited tonnage. How do I calculate the tonnage per hole for punching stainless steel?

A: As an example, let’s say you need to punch .875″ diameter holes in 3/16″ type 304 Stainless. The formula begins the same as for mild steel:

3.1416 x .875 (Dia. Of Hole) x .187 (Mat’l Thickness) x 25 = 12.8 Tons for mild steel

Because stainless steel has a higher shear strength, a multiplier factor of 1.40 is required.

12.8 (Tons for MS) x 1.4 (Multiplier for stainless) = 17.9 Ton per hole required.

For this and other tonnage calculation formulas, click here for Technical Data page 110.

Q: How often should I lubricate my UniPunch tooling? What type of lubricant do you recommend?

A: The basic rule is to keep the upper arm components of UniPunch tooling well lubricated and the frequency varies from each press environment.  An inspection of the moving components is recommended during and after a normal shift. Some materials such as hot rolled steel or galvanized steel that create scale when punched will require additional maintenance.  For daily operations, we recommend light machine oil – SAE 10 or equivalent. Lubricants that contain chemical driers are not recommended.

Q: I need to punch holes close to the edge of my 1/4” flat bar. Are there typical guidelines in order not to distort or bulge the material?

A: To prevent your part from distorting at the hole locations, UniPunch recommends that the punched hole be located a minimum of 1½ to 2 times material thickness from the edge of the hole. The diagram shown here depicts what can be avoided when adhering to these guidelines.

Q: What is die clearance?

A: This is the actual dimension added to the punch dimension based upon the type and material thickness of the material being punched.  For UniPunch tooling, we refer to this as Total Die Clearance.  Refer to our Material Technical Information Chart for recommended die clearances for common material types.

Q: How do I compute die clearance correctly?

A: Example: You need to punch a 7/8” diameter hole in 10 gauge mild steel. Convert the material gauge into decimals. 10 gauge steel = .1345”. Multiply .1345” X 20%. Answer = .027”. Add this to the punch size. Punch .8750” + .027” = .902” Total. The die size equals .902”.

Q: What is shut height?

A: The total height from the base of the UniPunch holder to the top of the punch, with the unit in the normal closed position. See unit pages for individual operating specifications.

Q: What is Tonnage?

A: This is the measurable force that is required for punching and notching material.

Q: How do I know if my press has the capacity for hole punching with UniPunch tooling?

A: First, you need to obtain the press specifications by locating the model number. Once you have determined the press tonnage, a guideline of 65% of the press tonnage is typically used for hole punching and notching applications. Example: You have a 50 ton press.  Multiply 50 tons X 65% = 32 ½ Tons Available for Punching. (Note: this percentage may change based upon the age and condition of the press equipment)

Q: What is modular press tooling?

A: A series of punching units, part gauges and mounting components that when assembled becomes a flexible system to produce parts. Tooling and gauges can be repositioned as required. UniPunch modular press tooling is available for heavy, medium and light gauge part producing applications.

Q: Can I combine multiple punching and notching operations in one setup?

A: Yes. Multiple operations are easily combined to eliminate separate processes. With the UniPunch modular system, you can punch, notch, shear, form and blank complete parts with each press stroke.

Have our experienced team review your specific application.  We can help determine the best solution to produce your parts faster.

Q: What tooling series is best for my application?
  • Type of parts – e.g. Structural, Formed, Flat or Extrusion
  • Type of material – Steel, Aluminum, Copper, etc.
  • Material Thickness

The UniPunch A-Series will punch heavy material up to ¾” thick. The B-series will punch up to 10 gauge mild steel and the G-series is designed for lighter gauge applications in both flat and formed parts.

Q: I currently do not have a press. What type of presses do you recommend?

A: The UniPunch tooling system will operate in most down acting press brakes or punch presses. The types of parts that you will produce and the material thickness are the deciding factors in determining press designs. Contact the UniPunch sales and engineering department for further assistance.

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