The holes in the filler neck and the skin are both too small for the LP4-3 called out in the KAI (pg 38iS/U-18). So I'm assuming I need to final drill #30. Seems like a big miss to not have that in the instructions somewhere.
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T-01231 needs final drill #30?
- Thread starter FlyingDiver
- Start date
Yeah, I already had the corrected dimensions noted on my plans, from previous postings here. I just don't ever recall any comments on redrilling the holes.
I'm currently fitting the overflow with the filler neck clecoed in place. I forgot to order more tank sealant so I'm waiting on that to do the actual install.
I'm currently fitting the overflow with the filler neck clecoed in place. I forgot to order more tank sealant so I'm waiting on that to do the actual install.
So far, I skipped section 38, but had quite some places where the factory holes were ever so much too small for LP4-3. Ruined quite some rivets in the attempt to make them fit. I am astonished that you obviously came this far without running into this challenge. At one point I just decided to predrill whenever the robots don’t fit. After all the holes must match the rivets and to my understanding of the KAI for an LP4-3 that is a #30 size.
There's plenty of places I had to ream out a hole for a rivet. But these are not slightly undersized. They're 3/32" (silver cleco fits exactly) rather than 1/8".
When I built my RV-12 there were plenty of parts where the LP4-3's fit perfectly, but some were a bit tight. It was explained to me that this was the result of the punches used to make the holes had been in service long enough to have lost a bit of their diameter. The factory recommendation was to use a ream to bring them up to full size. I don't recall the rational for why to use a ream rather than a drill bit, but I followed the advice and it worked great. I had two hand drills and I just kept one of them loaded with a #30 reamer and grabbed it whenever needed.
- A #30 drill bit nominally cuts a 0.1285" hole, and it often produces a slightly oversized or irregular hole due to wobble and material behavior.
- A #30 reamer brings the hole to a precise, consistent diameter with much tighter tolerances among other things
The diameter of a #30 drill bit is nominally 0 .1285 but in reality, it can vary a few thousands.
Mil Spec MIL-R-47196A calls out the allowable hole size for a 1/8" driven rivet as 0.125-0.135.
The tolerance on the shank of an LP4 is 0.122-0.129.
So if you're on the smaller side of the hole tolerance but on the bigger side of the LP4 tolerance, a cleco or driven rivet will fit in the hole but a LP4 won't until you bring the hole size up a couple of thousandths.
Mil Spec MIL-R-47196A calls out the allowable hole size for a 1/8" driven rivet as 0.125-0.135.
The tolerance on the shank of an LP4 is 0.122-0.129.
So if you're on the smaller side of the hole tolerance but on the bigger side of the LP4 tolerance, a cleco or driven rivet will fit in the hole but a LP4 won't until you bring the hole size up a couple of thousandths.
