VS rear spar doubler countersink

Steve M. · #1 08-23-2014, 08:09 PM

Hi,

New RV builder here so please bare with me. I have started with the VS for me RV7 as it seems to be the simplest empennage part to put together but I have already hit somewhat of a wall! I have countersinked the doubler so that it could match the dimpled rear spar. The problem I have is that the countersink look pretty deep! I know that it is common to oversink but I tried different depth on a practice piece and I went with the depth that gave me the best fit (spar flush with doubler) as oppose to just countersinking just below what would be required for a flush rivet.

Does anybody have a trick to gauge the proper depth of the countersink when matching a dimpled part? I have contacted Vans about this and I hope not to have to do it over again. But I will if I have to...of course.

Thanks.

wirejock · #2 08-23-2014, 09:23 PM

Welcome Steve.
Sometimes they do look deep. Wait till you countersink your expensive spar flange for #8 tank dimples. They look huge. Just use a sample token of the correct thickness and dimple as a gauge.
I made a set of tokens. Each is a piece of sheet aluminum about 1"×2". I cut one of each .025 and .032 for each size dimple die. 3/32" standard, tank, substructure, 1/8", #6, #8. That's 12 tokens. Each has a hole of the correct size and a dimple. Each is labeled with a scribe. I use whichever is needed to make sure the countersink is the right depth in scrap first then the actual part.

60av8tor · #3 08-24-2014, 05:51 AM

Countersinking for skin dimples is definitely an acquired skill. Too shallow and the skin gap us unacceptable, too deep and you begin to enlarge the hole out of tolerance. The later is usually not an issue with thick work pieces such as your doubler. Best advice I can offer is only to expound on what Wirejock already said. Have dimple examples to use as guages, then sneak up on it .001 by .001 (usually one click on the cage). Have the MILSPEC -4 rivet hole limits in front of you and continually check with a caliper to ensure you're not against the outer limit.

This is a tedious process initially, but ensures quality CSing. Like all building skills, you will eventually get the feel for it and it won't be such a tedious process. The usual CS caveat of backing up your work to stabilize the pilot (again, usually not an issue with a thick workpiece) applies.

Oh, and welcome to VAF, Steve!