# Punch strippers

Punch stripping, sheet hold-down, guided tooling, aperture clearance, and the distinction between cutting and return-stroke forces.

Reviewed: 2026-11-02

Tags: tooling, sheet-metal, punching, strippers

A concentric **10.00 mm** punch in a **10.20 mm** stripper aperture leaves a **0.20 mm** diametral gap, or **0.10 mm per side**. That geometric example concerns the stripper opening. Die cutting clearance and a guided stripper's allowable fit need separate specifications. Likewise, stripping force acts on withdrawal, when spring compression may differ from its bottom-of-stroke value.

## Function and terminology

The stripper releases the sheet from the punch on withdrawal. [Dayton Progress, High Speed Stamping, printed p. 17](https://www.daytonlamina.com/docs/default-source/articles/121_high_speed_stamping.pdf?sfvrsn=2df56008_3#page=17).

A slug can stick to the punch face or rise with the punch. Dayton describes ejector pins that push it away, separately from sheet stripping. [Dayton, printed pp. 3–4](https://www.daytonlamina.com/docs/default-source/articles/121_high_speed_stamping.pdf?sfvrsn=2df56008_3#page=3).

## Fixed, movable, and guided arrangements

| Arrangement | Physical action | Relevant distinction |
| --- | --- | --- |
| Fixed stripper | Stock passes beneath a plate fixed on the die side | Provides a stationary reaction as the punch withdraws |
| Spring-loaded movable stripper | Springs press a moving plate against the stock | Can restrain the sheet before penetration and continue restraining it during withdrawal |
| Fully guided stripper | A close-fitting opening supports the punch near its tip | Adds lateral punch guidance to stripping and restraint |

The fixed and movable descriptions follow MISUMI's die-structure tutorials. In its fixed example, stock passes through a gap between stripper and die plate; the movable example adds springs and stripper bolts. The guided description follows Mate's fully guided tooling. A spring-loaded plate is not automatically a precision punch guide. [MISUMI #026](https://www.misumi-techcentral.com/tt/en/press/2010/01/026-basics-of-die-structure-1-structure-of-blanking-dies---1.html), [MISUMI #027](https://www.misumi-techcentral.com/tt/en/press/2010/02/027-basics-of-die-structure-2-structure-of-blanking-dies---2.html), [Mate guide, printed p. 19](https://www.mate.com/wp-content/uploads/2021/03/LIT00682_TechSolutionsGuide_RevE_LR.pdf#page=21).

MISUMI's hole-punching example explains that a movable stripper first presses the material against the die, then maintains restraint while the punch penetrates and withdraws. The required hold-down force can exceed the force needed only to remove material from the punch. Its illustrative discussion distinguishes approximately 5% of punching force for stripping alone from hold-down settings reaching approximately 30%. These are tutorial examples, not universal sizing ratios. [MISUMI #029](https://www.misumi-techcentral.com/tt/en/press/2010/02/029-basics-of-die-structure-4-structure-of-hole-punching-dies---1-hole-punching-die-of-the-movable-s.html).

Mate's rigidly held, close-fitting stripper resists lateral punch-tip movement. Listed applications include slitting, nibbling, closely spaced holes, and narrow punches. This capability belongs to its complete guided assembly. [Mate guide, printed p. 19](https://www.mate.com/wp-content/uploads/2021/03/LIT00682_TechSolutionsGuide_RevE_LR.pdf#page=21).

## Aperture and cutting clearance

Punch-to-stripper clearance is the gap around the punch in the stripper; punch-to-die clearance is at the cutting edges below the sheet. Mate describes them separately: guidance fit does not specify cutting clearance. [Mate guide, printed pp. 3 and 19](https://www.mate.com/wp-content/uploads/2021/03/LIT00682_TechSolutionsGuide_RevE_LR.pdf#page=5).

For an original, purely geometric example, assume a circular 10.00 mm punch and a concentric 10.20 mm stripper aperture. Diametral clearance is `10.20 − 10.00 = 0.20 mm`; radial clearance is `0.20 / 2 = 0.10 mm` per side. This does not specify an acceptable guiding fit, wear limit, cutting clearance, or production tolerance.

TRUMPF's catalog makes stripper selection dependent on punch length, sheet thickness, and the punch's outer-circle diameter. Regrinding changes the relevant punch length. Its tables also distinguish low-scratch processing and permitted machine thicknesses. Thus an aperture or nominal station size alone does not establish a compatible stripper assembly. [TRUMPF punching-tools catalog, printed pp. 138–141](https://www.trumpf.com/filestorage/TRUMPF_Master/Products/Services/01_brochures/TRUMPF-punching-tools-catalog-EN.pdf#page=138).

## Cutting force, stripping force, and spring travel

Cutting force acts during penetration; stripping force is needed during withdrawal. Dayton's high-speed-stamping report describes stripping force as varying with material, thickness, and punch-to-die clearance, from nearly zero to as much as 25% of perforating force, with most applications below 10%. The spread itself shows why a single fixed percentage is not a universal return-force specification. [Dayton, printed p. 17](https://www.daytonlamina.com/docs/default-source/articles/121_high_speed_stamping.pdf?sfvrsn=2df56008_3#page=17).

Dayton Lamina's separate spring-selection article identifies preload, material thickness, punch entry, and stripper projection below the punch as contributors to spring travel. Force, travel, available space, and spring quantity therefore belong to the same mechanical design problem. [Dayton Lamina, Choosing the Proper Die Springs](https://www.daytonlamina.com/technical-articles/article-detail/choosing-proper-die-springs).

For an original idealized example, assume four identical linear springs, each rated `k = 40 N/mm`, sharing load equally. At 2 mm initial compression, their combined force is `4 × 40 × 2 = 320 N`. After another 3 mm compression, it is `4 × 40 × 5 = 800 N`. The larger bottom-of-stroke force is not available throughout withdrawal: force falls as the springs extend. This simplified model excludes friction, dynamics, uneven loading, fatigue, and actual spring travel limits; it is not a spring-selection result. [Spring-travel context: Dayton Lamina](https://www.daytonlamina.com/technical-articles/article-detail/choosing-proper-die-springs).

## Sheet contact and operating limits

Restraint can mark a cosmetic surface. MISUMI notes scratches from movable-stripper contact and contamination or uneven mating surfaces. Wilson Tool describes application-specific alternatives including bonded urethane thick-tooling strippers and nylon-based coatings for active TRUMPF-style stripping. These are product options, not guarantees of a mark-free part or interchangeability across tooling systems. [MISUMI #029](https://www.misumi-techcentral.com/tt/en/press/2010/02/029-basics-of-die-structure-4-structure-of-hole-punching-dies---1-hole-punching-die-of-the-movable-s.html), [Wilson Tool marking solutions](https://wilsontool.com/en-us/resources/sheet-marking-solutions-for-punching-applications).

This reference does not establish universal spring pressure, stripper aperture, permissible wear, maximum stock thickness, speed, or return capacity. Machine limits, punch geometry and length, spring load through its working travel, sheet condition, and the named tooling system remain consequential constraints. More cutting capacity does not automatically establish adequate stripping capacity.

## Source dates

MISUMI tutorials #026, #027, and #029 explicitly date their articles January 29, February 5, and February 19, 2010, respectively. Mate's guide identifies LIT00682 revision E, 2021. Dayton's *High Speed Stamping* report carries copyright 2003. TRUMPF's cited catalog carries back-cover identifier 1798794_EN_202204_S, retained without inferring a date. Wilson Tool's marking article is dated October 2, 2020. Dayton Lamina's spring-selection web article does not establish a technical revision date in the inspected content. This article's reviewed date is separate from those source dates.

For broader tooling context, see [Sheet-metal tooling](index.md).