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Why final drill skins?

Polar

Active Member
As I work away on my empennage I keep wondering why I'm bothering to final drill the #40 holes on the skins? So far all the holes in the flanges and skins have lined up perfectly. I can understand final drilling the AN470 holes, but for a AN426 the dimple die oversizes the hole slightly regardless of whether or not I've ran a #40 drill bit through it.

There must be a reason, but it isn't apparent to me.
 
Drilling

From what has been explained to me....when the skins are pre punched, there are microscopic stress fractures left from the process. Drilling the holes cleans them up. Also, if you have an air drill, it sounds really cool.

I'm no engineer....just my 1 cent

Hwood
 
Yes I found it pointless until I got to areas such as the wing where parts common with other models need match drilling as they are undersized. Wing ribs are typical.
Parts - 14 specific all seem to be punched to final size so I just deburred and nailed them together.
 
Don't have to final drill

I didn't final drill any holes unless rivet wouldn't fit.

Synergy air did research with vans on strength of rivet with and without final drill and found no difference. Call vans to verify if you like. But I think a tight rivet is a happy rivet.
 
I didn't final drill any holes unless rivet wouldn't fit.

Synergy air did research with vans on strength of rivet with and without final drill and found no difference. Call vans to verify if you like. But I think a tight rivet is a happy rivet.

This is good to hear :)

It just took me 2hr to final drill the skins on the VS, and kept wondering the whole time why I was doing it!
 
The RV-14 is the second Van's kit that has holes prepunched to full size. The RV-12 was the first.
 
I've noticed the same thing

As I follow along in the plans through the steps the builder before me did on my -10, I checked the wing structure and bottom skin yesterday for "final-drilling to #40," and those dimpled holes were quite oversize, every one. No way a 3/32 rivet was not going to fit easily in any of those holes! I can see the deburring step, certainly, but the final drill step might only be needed if the nose of the male dimple die doesn't want to enter the hole. Either way, the final hole will end up closer to #37 after dimpling.
 
Curious, what do the instructions from Van's say to do?

So far in my experience, I believe the plans just leave out the step that says to final drill. Mostly on the holes for the skins I think. In those cases, they just state to deburr and dimple. It may just be an RV14 thing, but the prepunched holes are just slightly smaller than a #40 bit, but the 3/32 dimple die does fit nicely.
I saw an EAA video once that stated something to the effect that, for holes that will be dimpled for 3/32 rivets and, the skin is .032'' or less, holes do not need to be final drilled.
 
Curious, what do the instructions from Van's say to do?

The instructions for the RV-14 say to final drill some parts in some steps.
This is because the RV-14 uses some parts common with other kits (usually has a part # that is not specifically RV-14)
Holes in kits designed prior to the RV-12 and 14 do not have the holes punched to final size and the plans attempt to identify these.
So when the RV-14 plans say final drill, it is to final size holes that are not punched to final size.
Once a builder gets to the fuselage kit, there is no more common parts used and final drilling is no longer specified.
 
Skins are punched to full size but you still need to debur the holes.

Actually, page 05-03 rev.1 dated 04/15/13 says this:

All drilled holes, or prepunched holes that have been final-drilled to a larger size, should be deburred. Holes that were factory punched to final size can be inspected and only deburred if needed.
 
Why I final drill everything

I've been accused of being a bit anal when it comes to wanting to know "why" on many issues. With respect to final drilling, what I've discovered in my research is when a hole is punched it creates microscopic vertical serrations. Under magnification I've seen what appears to be little vertical saw-tooth lines inside the punched hole. The lines are a stress point that could lead to a crack. Final drilling eliminates (reduces anyway) the serrations and thus reduces the chance of cracking. Yeah, it takes time to final drill but with my pneumatic cleco tool ($50 and well worth the money) it's not that big a deal.
 
You could always just ream it. You are less likely to have an over sized hole that way. Reamers only remove a tiny bit of material and they leave a better finish.

I'm building a 4. I can only dream of pre-punched holes:rolleyes:
 
Interested in the "why"

Hopefully Scott sees this and can answer.

I am curious why the prior models were not (or are not) pre-punched to exact size. I assume the equipment used for the various models is similar or the same in terms of manufacturing so is it more that the CAD models were more exact for the 12 and 14 which allowed the automation to punch the holes exact size due to the layout being more precise?

Inquiring minds want to know. I am sure it is something simple.
 
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Hopefully Scott sees this and can answer.

I am curious why the prior models were not (or are not) pre-punched to exact size. I assume the equipment used for the various models are similar or the same in terms of manufacturing so is it more that the CAD models were more exact for the 12 and 14 which allowed the automation to punch the holes exact size due to the layout being more precise?

Inquiring minds want to know. I am sure it is something simple.

Evolution. Van's is responding to customer demand to make the kits simpiler, and provide everything down to wires and connectors (which I believe is not a great idea).

Carl
 
Hopefully Scott sees this and can answer.

I am curious why the prior models were not (or are not) pre-punched to exact size. I assume the equipment used for the various models is similar or the same in terms of manufacturing so is it more that the CAD models were more exact for the 12 and 14 which allowed the automation to punch the holes exact size due to the layout being more precise?

Inquiring minds want to know. I am sure it is something simple.

My understanding is that on the -10 some people were final drilling parts separately and then assembling and the manufacturing process probably realized that the technology was exact enough to start doing it full size. The undersized holes were final drilled together to make up for any slight differences in manufacturing tolerances.
 
The technology used in producing RV kits has advanced progressively from the RV-3 to the RV-14.

Some of the technology advances have crossed over into older designs and some have not.

Example: The older prepunch designs do have their parts produced on the same CNC punch machines as the newest kits, but the tooling that forms the parts was not produced in the same way as it was for the newer kits.

This does not mean they have lower quality parts, just that the tolerance of the parts may not be quite as tight as for the later kits. We are talking about differences of a few thousandths of an inch, but as experienced builders know, that can be the difference between an acceptable fit or not.

The reason that punching holes to final size was adopted is two fold.

- The design of the parts and the tooling that they are produced on has been advanced to the point that assembly without final drilling to optimize hole alignment was possible.

- Actual fatigue testing was completed to confirm that the fatigue life difference between dimpled holes that had first been final drilled vs ones that were dimpled in the original raw punched condition was not significant enough to worry about.
This does not mean that PP holes in older kits can be dimpled without final drilling.

This is why the kit instructions still recommend final drilling for some of the older PP kits and not the newer ones (except in instances where parts from older kits without final sized holes are used in the newer kits). This avoids stretching of the holes by the #40 dimple die pilot, and provides for some tolerance correction in the hole alignment.

If builders choose to deviate from the instructions that is their choice.
I have always highly discouraged dimpling under sized holes without final drilling. If you do so, the data obtained from the fatigue tests should not be considered valid.
 
I've been accused of being a bit anal when it comes to wanting to know "why" on many issues. With respect to final drilling, what I've discovered in my research is when a hole is punched it creates microscopic vertical serrations. Under magnification I've seen what appears to be little vertical saw-tooth lines inside the punched hole. The lines are a stress point that could lead to a crack. Final drilling eliminates (reduces anyway) the serrations and thus reduces the chance of cracking. Yeah, it takes time to final drill but with my pneumatic cleco tool ($50 and well worth the money) it's not that big a deal.

Where did you get the pneumatic cleco tool for $50? I'm seeing them in the $90-100 range.
 
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