N265DF wrote:Just thought I'd mention for new builders who may have missed the age old posts on this. Dimpling does enlarge the hole so best to do so at 3/32 or 7/64. If I recall dimpling at 7/64 will bring the hole to #30. There were some stories long ago of rivets pulling through from dimpling at #30
I can provide clarification on that (partly because I was around 8-9 years ago when lots of discussions were going on about it, and partly because I've done my own tests with my all-flush-pulled-rivets Sonex build)...
For the best results with a dimpled rivet, pilot-drill with a #40 bit and then up-drill with a #32 bit. Then deburr, then dimple. Voila! Perfect hole. There are two issues with this method, however:
- Brass clecos (designed for #30 holes) will not fit very well into #32 holes. Don't be surprised if they're stiff to get through and retract; and they may slightly elongate the holes in the process (though the hole returns to round once you dimple it).
- If the hole goes through a thick piece of material (some aluminum angle-stock or the spar cap, for example), then you cannot leave the thick material drilled with a #32 hole. After you disassemble the parts, you need to do a final up-drill of the thick item with a #30 bit, and counter-sink as appropriate.
Now, if you are careful and do not over-drill or overly-deburr your holes, a #30 drill bit can be used on skins & ribs prior to dimpling. People have performed tests and found that the resulting assemblies are still reasonably strong. However, you do run the risk of the occasional rivet pulling so far that the stem breaks off proud of the rivet head. The general consensus is that a couple of these spread out across a part are not going to seriously weaken the part. But if you have several rivets exhibit that behavior, your holes are getting too big and you need to drill them out and replace them with up-sized rivets.
Enjoy,
--Noel
Sonex #1339