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Dave Yost RV-4
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Date:  8-7-2012
Number of Hours:  4.00
Manual Reference:  Drawing 6a
Brief Description:  Deburring and Dimpling

After the protective plastic is removed, it is time to deburr the holes. I drilled the holes with a #41 drill. I de-burred with a larger drill bit. The manual calls for #40 holes. But I (and many others) found that a #40 hole gets stretched during the dimpling process to a size that is on the high end (sometimes out) of the recommended size for a -3 rivet. This has been the source of many heated discussions in on-line forums. Some say #40 is fine and you could induce cracking using a smaller hole. I found that as a #40 bit wears and gets dull, the holes grew by a few thou. Then you de-burr, and then dimple........the hole is a little on the big side at this point. With a #41 bit, every hole was right at or just above the target diameter after de-burring and dimpling.

Splitting Hares?.......Probably. There are many airplanes flying with #40 and #41 holes, all are doing fine, so I guess it is a matter of preference. I believe a #41 hole makes for a better dimpled joint. The rivet seems to set with more of the shop head compressed over the hole.
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Deburring the holes

Deburring the holes

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Plasic removed

Plasic removed

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Dimpling the Skin

Dimpling the Skin

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