Flush Riveting Aluminum

by Jan Zumwalt
ver 2013.10.26

References

Welding ALCOA Aluminum - Aluminum Company of America(1972 - 241 pages)
Riveting ALCOA Aluminum - Aluminum Company of America(1959 - 91 pages)
Four Methods of Flush Riveting - Walt Disney Industrial Training Films (1942)

Benefits

Reduced drag
No gap or part clearance
Protects rivet head wear
Appearance

Preparation

The aluminium pieces should be clean and held firmly together.
A proper sized pilot hole should be drilled

Rivet
size
Best
drill
Common
drill
Hole
size
3/32 #40 7/64 0.096
1/8 #30 9/64 0.128
5/32 #21 11/64 0.159
3/16 #11 13/64 0.191
7/32 #10 15/64 0.225
1/4 #F 17/64 0.257
5/16 #P 21/64 0.323
3/8 #W 25/64 0.386
7/16 29/64 29/64 0.453
1/2 33/64 33/64 0.516
Rivet Pilot Hole Drill Size

The hole does not need to be de-burred if the parts were held firmly together during the hole drilling process and the hole has clean edges.

Countersink VS Dimple

Rule of thumb: .032 or thinner - dimple. Thicker than .032 - countersink.

A finished side sheet of .032 may be countersunk with 3/32 rivets but great care is needed and is not recommended for large areas. If the finish side sheet is .040 it can be dimpled but is not recommended because special tooling may be needed to prevent a small depression or gap around the rivet head. For thicknesses greater than .040 there is no approved method of dimpling, the rivet must be countersunk with a 100deg counter-sinker and riveted without other preparation.

A finished flush rivet head should not be above or below the sheet surface by more than two-thousandths (±.002) of an inch (about the thickness of a sheet of typing paper).

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Double dimple: .040 or thinner

If the finish side sheet is .040 or thinner, the double dimple is the fastest method to prepare the sheets. The proper hole is drilled and the rivet inserted. The rivet is used as the dimpler and is driven lightly against a female dimple form on the shop side of the material (110 or 120 deg). .

After the sheets are dimpled, the female form is replaced with a bucking tool and the rivet is driven. Greater skill is required to drive the rivet because the dimpled lower hole will try skew the rivet if it is not driven straight. If the rivet becomes skewed it must be removed. Often a skewed rivet will crush or crack the lower dimple and a repair or oversize rivet will have to be used.

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Pre dimple: .040 or thinner

If the finish side sheet is .040 or thinner, the pre-dimple method may also be used. The proper hole is drilled and the two sheets are dimpled according to the angles shown in the illustration below.

After the sheets are dimpled, the rivet is driven. As with the double dimple method greater skill is required to rivet because the dimpled lower hole will skew the rivet if it is not driven straight.

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Dimple/countersunk: .040 or thinner top sheet

If the top sheet is .040 or thinner, but the bottom is .040 or thicker, the top may be dimpled and the bottom countersunk. Caution should be used because the bottom countersink must be 110deg (not 100deg). This method is easier to rivet than other dimple methods because the bottom sheet is flat around the rivet hole and the rivet does not easily skew to one side.

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Mistakes

If the rivet is not driven properly it should be removed and replaced. Special over sized shanked rivets are available that have the same size head but allow the hole to be drilled to the next rivet size. For example if the original rivet had a 1/8" shank, a 5/32 rivet with a 1/8" rivet head is available. This is desirable where appearance is important.

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