Sheet Metal Bend Allowance Calculator

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Free Metalworking Tool

Sheet Metal Bend Allowance Calculator

Calculate bend allowance, bend deduction, outside setback, and flat pattern length for sheet metal bending.

Enter an angle between 1ยฐ and 179ยฐ.
Common estimates range from 0.30 to 0.50.
Estimated Flat Pattern Length 0.00 mm For the two entered flange lengths and one bend
Bend Allowance 0.00 mm
Bend Deduction 0.00 mm
Outside Setback 0.00 mm
Neutral Axis Radius 0.00 mm
Total Flange Length 0.00 mm
K-Factor Used 0.00
Formula Used:

Bend Allowance = (ฯ€ รท 180) ร— Bend Angle ร— (Inside Radius + K-Factor ร— Material Thickness)

Bend Deduction = 2 ร— Outside Setback โˆ’ Bend Allowance

Flat Pattern Length = Flange A + Flange B โˆ’ Bend Deduction

Important: This calculator gives an estimate. Actual bend results can change due to material grade, bending method, die width, grain direction, springback, tooling, and shop-specific K-factor data.
Metalworking & Stained Glass Guide

Bossing Mallet Set vs. Glazing Hammer: The Complete Guide to Essential Metal & Glass Shaping Tools

Whether you’re shaping sheet metal for auto body work or leading stained glass panels, having the right hand tool makes all the difference in both speed and finish quality. In this guide, we break down two industry-trusted tools: the MetalAce Bossing Mallet Set (3-Piece) and the Professional Glazing Hammer (#15780).

๐Ÿ”จ Metal Shaping ๐ŸชŸ Stained Glass ๐Ÿ› ๏ธ Workshop Tools
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Bossing Mallet and Glazing Hammer Overview

A Bossing Mallet and a glazing hammer can both be useful workshop hand tools, but they are built for different jobs. A bossing mallet helps shape sheet metal into curves and contours. A glazing hammer helps fit delicate glass, lead came, horseshoe nails, and metal caming.

Choosing the wrong tool can leave marks in metal, make shaping harder, or increase the risk of damaging a glass panel. The sections below explain when to use each tool.

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Metal Shaping Tool

Bossing Mallet Set (3-Piece) โ€” Built for Metal Shaping

A non-marking mallet set for controlled sheet-metal forming.

Bossing mallets are a foundational tool for anyone shaping aluminum or medium-duty steel panels. They’re typically used together with a shot bag, also called a sand bag, allowing metal to be molded in a controlled way without leaving marks or dents.

A Bossing Mallet works by spreading force across the metal surface. Instead of cutting, scratching, or sharply striking the panel, its rounded non-marking head helps form a gradual curve.

Key Features

  • Set of 3 sizes: Small, medium, and large mallets, each with a different radius.
  • Polyethylene heads: A nearly indestructible, non-marking material designed to help protect the metal surface.
  • Hardwood handles: Built for durability, balance, and a solid grip.
  • Dual radii per mallet: Each mallet has a different radius on either end, giving you six total shaping options across the set.
  • Compatible with aluminum and steel: Useful for aluminum panels and medium-duty steel shaping projects.

Who It’s For

Auto Body Repair Custom Car Fabrication Aircraft Sheet Metal Work Metal Sculpture Decorative Metalwork Beginner Metal Shapers Professional Fabricators

How to Use a Bossing Mallet

Place the metal sheet over a shot bag and use light, controlled strokes with the mallet. Choose your radius based on the curve you’re forming. Use a smaller radius for tight curves and a larger radius for smooth, gradual bends.

  1. Place the sheet-metal panel over a shot bag or sand bag.
  2. Select the appropriate mallet size and radius.
  3. Start with light, even strokes.
  4. Work slowly to build the curve or contour.
  5. Use smaller radii for tighter shapes.
  6. Use larger radii for wide and smooth bends.
  7. Check the panel often to avoid overstretching the metal.
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Tip: Do not use overly hard strikes when forming sheet metal. Heavy hits can overstretch the panel and create more finishing work later.

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Stained Glass Tool

Professional Glazing Hammer (#15780) โ€” Built for Stained Glass and Lead Work

A double-sided tool for lead came, glass positioning, and metal caming work.

The glazing hammer is a double-sided tool designed specifically for stained glass leading and metal caming work, making it an essential piece in any glass artist’s toolkit.

Unlike a Bossing Mallet, this hammer is not designed for stretching sheet metal. It is made for controlled tapping around delicate glass pieces, lead came, horseshoe nails, and similar stained glass materials.

Key Features

  • Double-sided design: A hard plastic end on one side and a rubber end on the other.
  • Professional size: Approximately 10-3/4 inches in length with a head diameter of around 3 inches.
  • Lightweight control: Around 10 oz, light enough for precise tapping and careful glass work.
  • Two useful striking surfaces: One end for hard materials and one softer end for delicate glass placement.

What Each End Does

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Hard Plastic End

Use the hard plastic end for tapping lead came, horseshoe nails, and metal caming into place.

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Rubber End

Use the rubber end for gently tapping glass pieces into position without cracking or damaging them.

Who It’s For

Stained Glass Artists Lead Came Projects Copper Foil Projects Window Restoration Glass Repair DIY Glass Crafts Professional Glass Studios

If your projects are smaller or you prefer a lighter tool, a compact version (#15781) is also available. It offers a slightly reduced size and weight, which may be more comfortable for smaller stained glass projects and detailed work.

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Glass safety tip: Use the rubber end when tapping glass into position. Always wear eye protection when cutting, handling, or fitting glass.

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Bossing Mallet vs. Glazing Hammer โ€” Which Tool for Which Job?

Compare both tools before choosing one for metal shaping or stained glass work.

FeatureBossing Mallet SetGlazing Hammer
Primary UseMetal sheet shapingStained glass and lead work
MaterialPolyethylene head and hardwood handlePlastic and rubber double-ended head
Set SizeThree mallets with six total radiiSingle double-sided tool
Best ForAuto body work and metal fabricationGlass art and window restoration
Main SurfaceAluminum and steel panelsGlass, lead came, metal caming, and nails
Ideal Support ToolShot bag or sand bagStained glass workbench and horseshoe nails
Use Directly on Glass?NoYes, with the rubber end and gentle tapping
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Final Thoughts

Whether you’re a metal shaping professional or a stained glass hobbyist, choosing the right mallet or hammer directly affects the quality of your finished work.

The Bossing Mallet Set gives you the versatility to shape a range of curves in metal panels. The Professional Glazing Hammer offers the precision and control needed for delicate stained glass work.

Both tools are trusted, industry-standard picks in their respective fields. Use the Bossing Mallet for sheet-metal shaping and the glazing hammer for glass, lead came, and careful fitting work.

Safety Reminder: Always wear eye protection when working with metal, glass, lead came, striking tools, or cutting tools. Check tool heads and handles before use, work with controlled force, and follow the manufacturerโ€™s safety instructions.
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