JurgenRoeland
Well Known Member
I have started countersinking the main wing spars for the nutplates that hold the tank.
In the RVator, they says #8 (8R8) screws should have a outer countersink diameter of .365" to .375"
I did one to .370", but boy... what a crater !
First of all, the hole gets enlarged way too much. Not that this is critical as the hole just serves as 'pass through' for the screw to fit in the nut. But still, I consider more material being left behind stronger.
Secondly, I dimpled a #19 in a similar size skin as the tank skin and fit the skin in the countersunk hole. If you have .370, the skin will wobble a little left and right. In other words, it doesn't sit tight in the countersunk hole.
I started testing by myself on different dimensions and figured out that .350" was about the maximum size before the tight fit would be lost. Later on, I found some engineering and military specs that say that for a 3/16, the countersink outer diameter is 0.351 which confirms my findings.
Is there a reason why in RVator they say .370 ?
A second question.
The enlargment of the hole creates a knife edge. Do you guys use sandpaper of deburring tool on these or will this not be a thread for the screw? My fear is that using the edge deburring tool will even more enlarge the hole.
In the RVator, they says #8 (8R8) screws should have a outer countersink diameter of .365" to .375"
I did one to .370", but boy... what a crater !
First of all, the hole gets enlarged way too much. Not that this is critical as the hole just serves as 'pass through' for the screw to fit in the nut. But still, I consider more material being left behind stronger.
Secondly, I dimpled a #19 in a similar size skin as the tank skin and fit the skin in the countersunk hole. If you have .370, the skin will wobble a little left and right. In other words, it doesn't sit tight in the countersunk hole.
I started testing by myself on different dimensions and figured out that .350" was about the maximum size before the tight fit would be lost. Later on, I found some engineering and military specs that say that for a 3/16, the countersink outer diameter is 0.351 which confirms my findings.
Is there a reason why in RVator they say .370 ?
A second question.
The enlargment of the hole creates a knife edge. Do you guys use sandpaper of deburring tool on these or will this not be a thread for the screw? My fear is that using the edge deburring tool will even more enlarge the hole.