Riveting in Sheet Metal Fabrication(remove chrome from wheels Hunter)
- source:ESKRIDGE CNC Machining
What is a Rivet?
A rivet is a metal fastener consisting of two main parts - a smooth cylindrical shaft and a head. The shaft is inserted through holes in the materials being joined. The excess length of the shaft extends out the other side and is mechanically deformed with a hammer or rivet gun to form another head. This process cold-works the shaft material and causes it to flair out and clamp the materials together between the two rivet heads, creating a solid connection.
Common Rivet Materials
The most popular materials used for rivets include:
- Aluminum - Lightweight and corrosion resistant but somewhat soft. Best for low stress applications.
- Steel - Strong and durable for high strength connections but heavier than aluminum. Can rust if not plated.
- Stainless Steel - Best corrosion resistance and high strength, but more expensive.
- Copper - Used for specialized electrical connections. Soft material.
- Monel - Corrosion resistant nickel alloy used in marine and other wet environments.
- Brass - Decorative but low strength. Sometimes used with other platings.
There are several types of rivet styles, each suited for particular sheet metal fabrication applications:
- Solid/Round Head - A basic rivet style with a domed head. Used for general sheet metal connections.
- Countersunk Head - A low profile rounded head that sits flush with the material surface. Used when a smooth exterior surface is needed.
- Large Flange Head - Has a wide flattened mushroom-shaped head that creates excellent load distribution. Common for connecting thin sheets or soft materials like fabrics.
- Jack Rivet - Has a tapered shaft and is driven through pre-punched holes. Quick installation but weaker than solid shank rivets.
- Split Rivet - Has a pre-cut split shaft that branches open as the rivet is installed to form a permanent head. Permits one-sided blind connections.
- Blind Rivet - Like a split rivet but with a pulling mandrel that is removed after installation. Allows riveting without access to the back side.
- Drive Rivet - Has ridges or threads on the shaft that cut a mating thread pattern into the hole during riveting for an extremely tight fit.
Rivet Strength and Hole Size
Proper hole size is critical for rivets to function correctly. Holes should be sized based on the rivet shaft diameter as follows:
- For solid shank rivets, hole ID should be equal to the rivet shaft OD. This allows for a very tight fit as the rivet expands.
- Countersunk holes are usually 1/32" larger than the rivet shaft. This provides clearance for the head to sit flush.
- Jack rivets and blind rivets need a hole ID 0.005-0.015” larger than the shaft to allow for expansion and anchoring.
- An oversized hole will result in a loose rivet that shifts and has poor strength.
In most cases, smaller diameter rivets are suitable only for light duty connections, while larger rivets can handle more load carrying capacity. However, even large rivets have relatively low shear and tensile strength compared to bolts, so they are generally not used for critical structural joints. As a general rule of thumb, rivets should not be relied upon to withstand significant dynamic, eccentric, tensile, or repetitive fatigue loads.
Proper Riveting Technique
Correct installation technique is key to achieving strong, lasting riveted connections:
- Holes must be properly aligned between both sheets - Rivets can accommodate small 1/32” misalignments, but no more.
- Joints should be clamped before driving rivets to prevent material shifting.
- Rivets should completely fill the hole and shaft should expand 1.5-2x its original diameter.
- Hammer blows should be centered on the rivet head. Hitting off-center can cause rivets to bend, tilt sideways, or create a loose fit.
- Avoid under or over driving. Rivets should be snug without excessive crushing of material around the hole.
- Use rivet sets to shape the bucktail end and achieve optimal head curvature and compression.
- Set alternating pattern for multi-rivet connections to equalize stresses and prevent distortion.
- Check for defects like cracks or lifted sheet metal around holes after installation.
- Consider using washers under rivet heads and/or under sheets for better load distribution on thin/soft materials.
Riveted Joint Design
Proper joint design is also critical for creating durable riveted fabrications:
- Lap joints should use multiple rivet rows for long seams. Omitting rivets allows for flexing.
- Butt joints with single rivet rows have very limited strength unless materials are thick. Use multi-row riveting.
- Optimal rivet spacing is about 2-3 times the rivet diameter. Closer spacing is rarely beneficial.
- Rows should be staggered so rivets in adjacent rows are not in the same axis to maximize joint stiffness.
- Allow 1/8” minimum material margin around rivet holes to prevent tearing, especially on weaker/thinner materials.
- Corners and intersections are high stress areas. Use extra rivets clustered in these locations.
- Sealant adhesives can be combined with rivets for improved water/air tightness in seams.
In summary, rivets are versatile fasteners that allow for quick and permanent joining of sheet metal when proper techniques and joint design principles are followed. Their ease of installation with minimal equipment makes riveting ideal for prototyping, short production runs, field repairs, and hobbyist metal fabrication. With some planning and care taken during assembly, riveted sheet metal joints can provide reliable structure while keeping fabrication simple and economical. CNC Milling CNC Machining