Graham wrote:
If I can’t trust that a fairing will be as it should be, what of more vital parts?
That’s the key issue. Aircraft isn’t build based on trust, but on checking the integrity of every part and assembly. That responsibility belongs to the builder regardless. If anything, this “laser episode” shows that this is indeed being done.
@RV14 are you crazy? They’re different sheets, you can feel the difference in your hands. “Within tolerances…” I’ve heard it all now.
I don’t know what the spec is for 0.020 sheet, but I’m pretty sure it doesn’t overlap with the next size up! Nor is a weight difference of some 25% for two identical parts within any sensible tolerances. I have contacted Vans but they are not really responding to individual issues right now while they work through the wider laser cutting problem. I say it’s getting worse because not only were their laser contractors doing really poor work, they actually used the wrong sheet to cut some parts, and no QC either at the contractor or Vans picked it up.
Every other sheet I have ever measured has indicated within about one thou of its nominal thickness. In any case the accuracy of the equipment doesn’t matter so long as it isn’t totally random (and it isn’t because the results are repeatable) – it’s the difference that matters not the absolute value.
@LeSving having studied the plans it will make a difference. It gets riveted between the rear spar and the aileron hinge bracket, so will result in the hinge being incorrectly positioned.
Manufacturing tolerance is +- 0025
Let’s keep it calm
Is that 0.0025 or 0.025?
This suggests that the thickness tolerance on a 0.5mm / 0.020" sheet is 0.0012".
Normally it is better:
But, practically, what is the solution? Ream the holes and install oversize rivets? Easy on unused parts, but what if the rivets need drilling out?
@RV14 I’m not sure what your suggesting, but if you’re suggesting it’s two and half thou either way then this sheet is still twice that from the nominal value. In any case, its not a tolerance issue, it’s the WRONG SHEET.
Peter’s number seems more reasonable (one and a bit thou) and is more in keeping with what I see when I measure parts.
To the thickness issue, the solution is to make the part from the correct sheet. It is unrelated to the laser cutting issue other than it’s the same contractor and thus indicative of wider QC issues.
For the holes, some laser cut holes clean up ok when reamed out to final size (from #42 to #40 or from #32 to #30) and some do not. For those that don’t, you can either accept the risk of cracking when dimpling/ riveting or reject the part. If it cracks when riveting the problem is that you won’t see it but it will be there and will be able to propagate out from under the rivet under stress cycles.
Some other complications are that it is very rare for going oversize to be an option. There is usually insufficient edge distance on a rib or spar flange to take any given hole location up to the next size rivet. Then regardless, even if your hole does clean up ok, the heat from the laser has weakened the material around the hole. Finally, some of the latest kits (10 and 14 I think) have holes cut final size, so you don’t even have the reaming out two drill sizes to clean it up and make it round – you can only deburr and then you’re stuck with it.
@pilot_dar will know much more but I heard there is a category of rivets which are just very slightly oversize, for the purpose of replacing “working rivets”.
Oops rivets (over-sized stem, same head) are used every now and then when replacing faulty rivets.
Graham wrote:
having studied the plans it will make a difference. It gets riveted between the rear spar and the aileron hinge bracket, so will result in the hinge being incorrectly positioned.
Have you measured the parts? Cutting the parts and holes is one thing, but forming them (bending the flanges) is a different process. It’s the forming that creates the measurements of the part, and could be correct regardless. Anyway, we are talking minuscule differences, less than what a layer of primer would make. It’s an airplane, not a Swiss watch 
The skin on rudder of the -4 was increased one thickness in size due to cracks being formed on the original skins. Yet, the drawing and all other parts were the same.
Anyway, you best option is to talk to Van’s. At least talk to a mechanic with long experience in aircraft sheet metal work, and actually has built a plane or two. Things aren’t as bad as you perhaps believe IMO.
Oops rivets generally have the shank of the next full size hole up, so you need the edge distance for the 1/8 hole when using an oops rivet to replace a 3/32 with an enlarged hole.
Yes @LeSving I have measured the parts. We’re talking about the thickness of the sheet used to make the part, not length or breadth dimensions. It is not a complex part – two shallow bends and some holes.
I know and understand the points you make, thank you. I’m aware it may make little practical difference here. I speak not as a builder, but as a customer disappointed that something like this should happen. Whether it makes a difference from an engineering standpoint is not the point – it’s just a sloppy mistake that should have been caught by QC.
You must spray your primer on very thick. I use two lights coats of etch primer followed by two light coats of lacquer to make the surface non-pourous. I have just measured 20 thou sheet parts primed as above and unprimed – the four coats add slightly less than a thou.
