No uncommon but....
wingtime said:
While working on my fuse I noticed that the two dimples for the #8 screws that hold the rudder cable clamp at the aft end of the tailcone both have cracks in them. Has anyone else experienced this? I guess the dimple die just stretched the aluminum too far. Bruce Smith
Bruce this is not uncommon, a #8 is a lot of hole is a lot of material to move.
I am curious did you use a Cleveland dimple die or other method?
(Reason I ask is the Cleavland die will reduce the likely hood of cracks, many builder take a scrap of aluminum, countersing it and use a scew to make large screw dimples; I don't recommend it.)
The key to NOT getting a crack is making sure you have a good HOLE, drilled to proper size and most important deburred both sides. Next you want the die and the metal NOT to be real cold. Heating with a heat gun is an option, but working cold is a added risk. Work slow.
The Fix:
I assume the cracks are from the inside edge of the hole out towards the edge of the dimple. I would do more than just stop drill.
Depending on how LONG the crack is you could open the hole up to remove the CRACK.
I agree with a doubler and you could make a IRON works out of it. However it is not real structural and you just done want the crack traveling in the parent material.
You could (depending how long the cracks are and how much material is removed) do noting except clean the cracks up, add a backing "washer" or plate that is dimpled or counter sink if using a thicker piece of material which may be best. You could just use a tinnerman washer if the problem is mild but not sure how well it would fit with a reverse fit on the back of a dimple.
The last choice and best fix (may be overkill for your case) is riveted a doubler around the area. This would be the likely choice if you had to remove most of the dimple and open the hole up wide. An effective doubler should have two rows or rivets all around the hole. The down side is LOTS of details (more holes and rivets) to mess up. An intermediate option is made a doubler, circular donut doubler bond it on with structural bonding adhesive. In a pinch prop seal makes a good bond with proper surface prep. The purpose of the doubler is to remove the stress in the parent material and have a load path in into the surrounding structure into the parent material.
Again this is not structural, it's just an adel clamp being clamped down and held to the side of the fuselage (I think that is what you are talking about, but repair of cracks in dimples are the same.)
G
