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To drill or not to drill before dimpling

snoopyflys

Well Known Member
Has anyone not drilled their CNC pre-punched holes before dimpling? I either heard, read, or dreamed this technique being used on AN3 pre-punched skin holes and thought I would ask before using this technique on the second half of my SB wings.

Any advice/experience would be most appreciated.
 
Old news Dan.

You want to drill them to relieve any inherent stress that may arise from even slightly miss aligned holes.

Then debur both sides of the holes prior to dimpling.

That said, there are a few well known RV's flying that were never match drilled.

Do a search on the subject and you will get a day's worth of reading.
 
I always drill and deburr before dimpling. I don't think any of my dimple dies fit into just the pre-punched holes without being forced. YMMV....
 
You need to drill first. The prepunched holes are 3/32 (or less) and the rivet hole should be a #40 (several thousandths larger).

I know its tempting to just go right to dimpling, just not a good idea. Could lead to cracking later on.
 
There was a presenter during Oshkosh (forgot the name, but the guy had some RV related business) who said, that drilling the #40 holes in the skin is not necessary, if they will be dimpled. He actually said, that the dimples are a lot better, when not drilled. He also said, that deburring the pre-punched holes is not necessary.
So, I just tried that with the side skins and the bulkheads. The pre-punched parts fit perfectly. Dimpling was not a problem; the dimples actually look a bit better than the dimples of drilled and deburred holes. Haven't riveted the parts yet, though...

Thilo
 
The small pilots on my dimple dies will not fit into holes that are not drilled or reamed. I would suspect that the pilot forcing its way through an unmodified hole will cause cracks.
 
There was a presenter during Oshkosh (forgot the name, but the guy had some RV related business) who said, that drilling the #40 holes in the skin is not necessary, if they will be dimpled. He actually said, that the dimples are a lot better, when not drilled. He also said, that deburring the pre-punched holes is not necessary.
Thilo

I'll bet the guy who said this at Oshkosh was not from Vans.

In reality you could use prepunched holes without match drilling if the prepunched holes were perfectly located in the first place...but they are not.

Firstly, there are slight inaccuracies due to the mathematical translation of a 3D aircraft model into machine coordinates.

Secondly, the Trumpf machine that Vans uses will have fabrication accuracy tolerances (ie expected dimensional errors when the machine is new).

And thirdly, the inaccuracy of the Trumpf will get worse as the machine gets older and the moving components wear.

Match drilling will allow for these accumulated errors without stressing the skin or any fasteners.
 
I've been reading the preview plans and it says to match drill everything.

I agree that a reamer should give better (cleaner) results than a drill bit.

I haven't started building yet, but honestly how much longer does it take to run a reamer through all the holes first?
 
Let the Drilling resume...

I tried the no drill before dimple on a LE rib and aileron gap fairing before asking this board. After inspecting the parts under a magnifying glass, I don't see any cracks streaming away from the dimpled holes. Not 100% sure though. Just what does a micro-crack look like? I did find some forum posts of cracked rivet holes but I didn't see any of these in my no drilled dimpled parts. Anyone have a photo of a "micro" crack they would be willing to share? Or possibly a part that failed using this method of enlarging and dimpling a pre-punched hole without final size drilling.

I believe I will not chance the structural integretity by continuing to use this method. I will resume the cleco, drill, debur, dimple, clean, prime, cleco, rivet mantra on the rest of the plane, all 10,000+ of them.

Thanks.
 
I thought the dimpling process would enlarge the hole just a wee bit...
so that you don't have to drill to make it bigger.
is that not the case?



sorry for the noob question. I haven't started building yet. I haven't even squeezed a rivet. But I am sure glad I found this forum, I get to learn a lot before I even decided on which RV to build.
 
I thought the dimpling process would enlarge the hole just a wee bit...
so that you don't have to drill to make it bigger.
is that not the case?
sorry for the noob question. I haven't started building yet. I haven't even squeezed a rivet. But I am sure glad I found this forum, I get to learn a lot before I even decided on which RV to build.

Making the hole larger is not the point of the exercise. Two things are: Improving the surface finish inside the hole, and refining the match-up of the holes in the two parts.
When the hole is punched, any micro scratches run straight down the side of the hole, and are thus ideally situated to propogate a crack. After the hole is reamed, the remaining surface imperfections are circumferential, and thus much more benign.
Clearly a plane assembled "as punched" is not going to immediately fall apart, it's just a case of best practices, and maximizing your odds in the long run.
 
You Really Should Drill or Ream

"Making the hole larger is not the point of the exercise. Two things are: Improving the surface finish inside the hole, and refining the match-up of the holes in the two parts.
When the hole is punched, any micro scratches run straight down the side of the hole, and are thus ideally situated to propogate a crack. After the hole is reamed, the remaining
surface imperfections are circumferential, and thus much more benign."

William:
Probably just as important is the "shape" of a punched hole. Depending on die design, a hole punched in aluminum sheet is not a straight cylinder, but is more typically straight for only about 60% of the thickness of the sheet. The rest of the hole is shaped like a cone, breaking out at a 60-90 degree included angle. That means that when joining .020 sheets, the rivet may only be effectively contacting something in the order of .012 of the thickness. Drilling gives a uniform bore in addition to the improvements you mention. While sheets can be joined without match drilling (ref. RV12), this should only be done when the hole is already to size and doesn't have to be "stretched" by dimpling. In any event, match drilling makes for a superior joint.
Terry, CFI
RV-9A N323TP
 
drilling pre "punched" holes

Am I missing something here?
The original hole is a punched hole, so why would punching the dimple die through an ever so slightly undersized hole be a problem?
 
Match-drilling is such a small part of the overall project. I probably spent a total of 5 hours match-drilling on the whole project.

I am happy to say that, as of yesterday, I have no more parts that need match-drilled, deburred or dimpled. (for the most part).
 
Don't Make it Worse

Am I missing something here?
The original hole is a punched hole, so why would punching the dimple die through an ever so slightly undersized hole be a problem?

Merle:
Metallic cracks (we like to call them discontinuities) always begin at the microscopic level. Can't see them with the human eye or with a magnifying glass. That's why SEM (scanning electron microscopy) is widely used in failure analysis. It allows us to see where the failure started. In punching sheet stock, imagine a sheet that you hit so hard with a hammer you actually pierce it. There's going to be lots of discontinuities in and around the hole. If you then take a tapered punch and pound it into the hole, you'll probably widen many of the small cracks around the perimeter. That's what you're doing by forcing a dimple die into the sheet. Will it lead to a visible crack? Depends. From my point, not worth the risk.
Terry, CFI
RV-9A N323TP
 
It is all about long life of the airplane...

Terry is correct! Building my RV-9A was a once in a lifetime event for me. I plan to keep it until I cannot pass the physical anymore. I completed the airplane at age 58. I am 62 now and it keeps me young flying it whenever I can. If the weather were not bad in Denver, I would not be flying commercial next week for a trade show as part of my day job. The last time this show was in Denver, it was June 2006 and I flew out there in my RV-9A.
http://www.n2prise.org/rv9a213.htm

Look at the photo at the bottom of this web page, then continue reading a couple of pages. http://www.n2prise.org/rv9a004.htm It is all about the cleco, match drill, debur, dimple process. Build it to last!
DSCF0080.jpg
 
My 2 cents is to

use a #41 chucking reamer for the -3s and 1/8" for the -4s before dimpling. Better hole alignment, works great with a slower RPM cordless drill, and little or no burr. These slightly tighter holes still worked well with my dies, and resulted in a hole closer to spec. after dimpling.

Building is fun. No need to miss out on any of it by skipping steps!:)
 
Punched holes

Merle:
Metallic cracks (we like to call them discontinuities) always begin at the microscopic level. Can't see them with the human eye or with a magnifying glass. That's why SEM (scanning electron microscopy) is widely used in failure analysis. It allows us to see where the failure started. In punching sheet stock, imagine a sheet that you hit so hard with a hammer you actually pierce it. There's going to be lots of discontinuities in and around the hole. If you then take a tapered punch and pound it into the hole, you'll probably widen many of the small cracks around the perimeter. That's what you're doing by forcing a dimple die into the sheet. Will it lead to a visible crack? Depends. From my point, not worth the risk.
Terry, CFI
RV-9A N323TP

There are literally thousands of airplanes flying that have punched holes in them. A lot of the RV crowd uses a Whitney punch to speed up the process of making holes when they are near an edge, as well as Cessna, Piper, et al.
I don't want to turn this into a big deal, but I believe punched holes are perfectly acceptable. All manufacturers of sheet metal that use any kind of automation punch most if not all of their holes. (We have a sheet metal shop)
 
There are literally thousands of airplanes flying that have punched holes in them. A lot of the RV crowd uses a Whitney punch to speed up the process of making holes when they are near an edge, as well as Cessna, Piper, et al.
I don't want to turn this into a big deal, but I believe punched holes are perfectly acceptable. All manufacturers of sheet metal that use any kind of automation punch most if not all of their holes. (We have a sheet metal shop)
__________________

Merle:
That's exactly what I said in an earlier post. However, my follow on point was about jamming a wedge into a punched hole. Can it be done without creating problems. Probably. Doesn't make a lot of sense from a metallurgical standpoint. Better to punch to hole to size to begin with. Otherwise, why take the risk.
Terry (I slept at a Holiday Inn)
 
Am I missing something here?
The original hole is a punched hole, so why would punching the dimple die through an ever so slightly undersized hole be a problem?

Think about TOLERANCES. Every tool is manufactured with a +/- acceptable tolerance spec. Your 1/8" dimple die might have a pilot that's not exactly 0.125000...".

Let's say the punch was mfr'd at the small end of spec, and let's say the dimple die was mfr'd at the large end of spec. Hole still look "great" after dimpling-without-drilling+deburring?

And folks who haven't finished their plane, let alone flown it for decades, endorsing a technique...bite your tongue until the advice has a track record behind it, ok?!

Be careful what you trust on the internet. You'd think Van's has a bit of a clue about this. New guys, it's in your very best interest to trust your KIT MANUFACTURER.
 
Think about TOLERANCES. Every tool is manufactured with a +/- acceptable tolerance spec. Your 1/8" dimple die might have a pilot that's not exactly 0.125000...".

Let's say the punch was mfr'd at the small end of spec, and let's say the dimple die was mfr'd at the large end of spec. Hole still look "great" after dimpling-without-drilling+deburring?

And folks who haven't finished their plane, let alone flown it for decades, endorsing a technique...bite your tongue until the advice has a track record behind it, ok?!

Be careful what you trust on the internet. You'd think Van's has a bit of a clue about this. New guys, it's in your very best interest to trust your KIT MANUFACTURER.


Dan is right on here and I understand what he means. Use the internet to get some ideas and some confirmation of the ideas or techniques used by other builders. But at the same time, as Dan mentioned, sticking with the Kit manufacturer has been the best solution. Ironflight said something similar to me about my fuel tanks :eek:. I want this bird to fly, not fly and need fixing if it can be avoided during the build process. Lessons continue to be learned on this journey. What a great hobby!!

Calling the mothership to confirm and probably order new LE rib and aileron gap fairing just to be safe.

Thanks everybody.
 
I did a few. Results not consistent.

Has anyone not drilled their CNC pre-punched holes before dimpling? I either heard, read, or dreamed this technique being used on AN3 pre-punched skin holes and thought I would ask before using this technique on the second half of my SB wings.

Any advice/experience would be most appreciated.

I did a few holes without drilling/deburring. The results were not consistent. Also, holes near the edge tended to develop small cracks, resulting in a couple of replacement parts being ordered.

If you really want to save time, get a #40 and #30 REAMER and use them instead of a drill bit. You will NOT need to debur the holes after reaming, and it reduces "egging".

Just my two cents. YMMV
 
You will NOT need to debur the holes after reaming, and it reduces "egging".

Just my two cents. YMMV


If you ream instead of drill at least give the holes a good look for burrs. I did both on my RV, drilled most but gave the reamer a try as well. Reamers are a bit more expensive and as they dulled they would be harder to pass through and did leave a burr or two. I found deburring a nice break between parts and part of the therapy associated with building. I think you will find that most deburring is over done. Just remove the burr, don't countersink:D Dan is pretty much spot on, if you follow the "kit manufacturer" recommendation, at least you can say hmmm....I followed the directions. Forcing a dimple die into a hole on a #3 rivet may not yield a crack but the bigger you go....for sure it will...Like on a #6 or #8 screw, Make sure it is a clean deburred hole or you will see cracks...I made the mistake of missing drilling out one of my wing inspection covers, as soon as I punched the die through, the hole had a small but visible crack....cheap mistake but says alot about having the right size hole for the die.
 
There are literally thousands of airplanes flying that have punched holes in them.

This may be true, but there is one big difference in the context of this question regarding RV construction.

Those thousands of airplanes are for the most part not flush riveted and they were not dimple countersunk with dimple dies that have a pilot larger in diam. than the punched hole.

The dimple die sets we typically use in RV construction have pilots sized for a close fit in a #40 or #30 hole.
Prepunched parts from Vans have holes that are punched undersize from #30 or 40 (they are actually sized as small as posible and still be able to get a cleco in them). The pilot on the dimple die sets we use is bigger than the hole dimension and will not fit in the hole without being forced in. This is stretching the hole diameter before the dimple is even beginning to form.
It is well known in aircraft construction that the stretching that takes placed when dimple countersinking raises the risk for cracks at the holes. Particularly in large dimples such as for the #8 flush screws used on RV's. Some builders have had this problem on the larger dimples if they have dimpled without proper deburring, etc.

If you choose to dimple countersink without final drilling where specified, you are raising the risk level of radial cracks from dimples.
It is true their are probably quite a few RV's now flying that were built this way, and the builders will proudly tell you that it has worked out fine. As Dan already mentioned, the real test may be to ask them again 10 - 15 years from now.
If you are a builder that is not interested in doing some long term fatigue testing and then accepting the result (whatever that will be), I recommend you spend the extra few hours and final drill prepunch parts when recommended.
 
I think Dan remembered it right and he did not dream it. I also heard the presenter at Oshkosh '09 that Dan was referring to. Can't remember his name. The talk was on tips and techniques for RV construction. Apparently a study was done on the strength of riveted joints with drilled out holes to size before deburing and dimpling per the RV bldrs manual. vs just going ahead and dimple and rivet (no drilling and deburing). As I recall the study results were that there was no difference in strength. It was mentioned that the study was done on the thinner aluminum sheet and ribs only and the thicker Aluminum pieces should be always be drilled to size and debured.

I do not know the source of the study and this is all I remember hearing. If anyone knows more or if I have it wrong please chime in.

Jim
RV9 Fuse
 
I think Dan remembered it right and he did not dream it. I also heard the presenter at Oshkosh '09 that Dan was referring to. Can't remember his name. The talk was on tips and techniques for RV construction. Apparently a study was done on the strength of riveted joints with drilled out holes to size before deburing and dimpling per the RV bldrs manual. vs just going ahead and dimple and rivet (no drilling and deburing). As I recall the study results were that there was no difference in strength. It was mentioned that the study was done on the thinner aluminum sheet and ribs only and the thicker Aluminum pieces should be always be drilled to size and debured.

I do not know the source of the study and this is all I remember hearing. If anyone knows more or if I have it wrong please chime in.

Jim
RV9 Fuse
I don't know whether you heard right or not, but I don't think the issue is related to strength of the joint, it is longevity.

When you dimple countersink you stretch metal (you stretch it even more if you are using a #41 bit or reamer). If you force the pilot of a standard male dimple die through a hole that has not been final drilled, you are stretching the material even before the dimple begins to form. Because this hole you are dimpling was not final drilled, it has a raged punched interior edge of the hole.
Add together a ragged hole edge, stretched material from driving the dimple die pilot in the hole, and stretched material from forming the dimple...it is the perfect situation for the formation of cracks.
Anyone doing this may not be able to see any evidence when you inspect...in fact it may not ever crack at all...but anyone considering it needs to decide whether you want to do the fatigue test with your airplane and let us know 15 years from now what the result is, because anyone that has done it (and talked about it at a forum) and says it it fine, doesn't really know yet.
 
Anyone doing this may not be able to see any evidence when you inspect...in fact it may not ever crack at all...but anyone considering it needs to decide whether you want to do the fatigue test with your airplane and let us know 15 years from now what the result is, because anyone that has done it (and talked about it at a forum) and says it it fine, doesn't really know yet.


As refers to the above, Im sure an engineer and a test bench could easily deduce the outcome of not drilling. I would be really interested in the outcome. Anyone willing to do a test............??
 
As refers to the above, Im sure an engineer and a test bench could easily deduce the outcome of not drilling. I would be really interested in the outcome. Anyone willing to do a test............??
Ya think the engineers at Van's might have thought of this, done just such the test, concluded that the parts needed to be drilled, and therefor made that part of the plans? Or maybe, they just came up with that recommendation without any scientific reasoning behind it, just because they wanted to cause us all more work.

Which is more likely?
 
This thread is unbelievable, and it speaks volumes about how people are changing in general. (All that comes to mind are the kids today who have everything given to them and wouldn't know hard work if it smacked 'em in the face.)

It would be one thing if we were talking about innovation. Are we? I don't think so. We're talking about excuses and laziness here. People want a shortcut. They want more output from less input.

If you don't want to put the time in, GO BUY AN AIRPLANE. Leave the building to the folks who are willing to invest the time.
 
Why do we build?

If you don't want to put the time in, GO BUY AN AIRPLANE. Leave the building to the folks who are willing to invest the time.

Dan hit on one of the main topics I cover during one of my talks. Build an airplane because you want to build an airplane, not because you want an airplane.
This thread amazes me. It covers both extremes. People who want to short-cut the process and those who want to do every process to the extreme. Every hole needs to be drilled to size and deburred. Every hole does not need to be reamed. I've built quite a few airplanes and only ream the holes that are critical. Some may think that all holes are critical and should be reamed. And that's fine if you want to go to the extra work. At least if you are going to extremes, you're going the right direction.
I've never built a quick-build or even a pre-punched kit, so I guess I don't fully understand the "short-cut" mentality.
 
...
I've never built a quick-build or even a pre-punched kit, so I guess I don't fully understand the "short-cut" mentality.
Mel,

There are two types of people who build these airplanes; Builders and Assemblers. You are a Builder but many of us are simply Assemblers.

I like to think of myself as a builder but only because of the things I had to work through by straying from the plans by installing simple items such as Dayton's throttle quadrant or working through the issues with the O-290. But mostly I just ordered the various kits from Vans and assembled them. (Yes, I did do the DDD dance and reamed the critical holes, same as you.)
 
Please don't misunderstand. I'm not trying to "talk down" present day builders. Pre-punching is progress and I'm not against progress. It just seems that the more kit manufacturers do, the more some people want them to do.
 
Dreamer

I had great success using a combination drill bit / reamer called a "Dreamer". ( http://www.dreamertoolinc.com ) It has a slightly undersized drillbit pilot (fits perfectly into the prepunched holes) and then a full size reamer for the rest of the bit. I put a little dry bolube on it and go to town. It leaves a great finish with nearly no burr. (Still deburred though, but I'm not sure that it was entirely necessary.)

I figured that although teadious, deburring anyway was an easy step and will probably provide a longer life to the airframe. At the very least I can take pride with the quality of the work. Isn't that the point of doing things yourself anyway?
 
Clarification

When I stated that using a reamer will remove the requirement to debur, I didn't mean you should not inspect and remove any burrs that exist, only that there will be almost zero burrs produced when reaming.

I found that using the debur tool tended to make egg shaped holes, especially in thin material.

My inspection procedure was to run a fingertip along the line of holes. If any burrs detected, use a piece of scotchbrite to clean the area and check again.

Regarding wear of the reamer, a little boelube goes a long, long way. I reamed at least a few thousand holes building my new fuselage and no appreciable wear.


YMMV
 
Agreed

When I stated that using a reamer will remove the requirement to debur, I didn't mean you should not inspect and remove any burrs that exist, only that there will be almost zero burrs produced when reaming.

I found that using the debur tool tended to make egg shaped holes, especially in thin material.

My inspection procedure was to run a fingertip along the line of holes. If any burrs detected, use a piece of scotchbrite to clean the area and check again.

Regarding wear of the reamer, a little boelube goes a long, long way. I reamed at least a few thousand holes building my new fuselage and no appreciable wear.

YMMV

I had not read your previous post, but completly agree.

In many cases there was little to debur. Givin most new builders over debur to begin with I would urge caution when deburing after using a reamer (since there is even less material that needs removing). The idea is to end up with a properly formed hole with no burr. Just going through the motions to say you did it is not the point.
 
Ya think the engineers at Van's might have thought of this, done just such the test, concluded that the parts needed to be drilled, and therefor made that part of the plans? Or maybe, they just came up with that recommendation without any scientific reasoning behind it, just because they wanted to cause us all more work.

Which is more likely?

Read my mail !!!! I never said Vans engineers made it up. I would just be interested to see at what point failure occurs on an undrilled hole.
We are all here to learn weather you like it or not !!
 
Deburing also breaks the 90? corner of the hole which is a perfect stress riser. Deburing chamfers this area slightly which help prevent cracks.
 
RV-12

Don't the rivet holes in an RV-12 come punched to size with no drilling required? I would assume they need de-burring? Also since they aren't dimpled there is less chance of causing a crack during the dimple process. It just seems not drilling or reaming these holes would still leave the possibility of less than perfect pre-punched holes leaving the possibility of cracking. How do they get away with that?
Don't matter to me either way, I am a 3D(drill, de-burr, dimple) kinda guy;)
 
Don't the rivet holes in an RV-12 come punched to size with no drilling required? I would assume they need de-burring? Also since they aren't dimpled there is less chance of causing a crack during the dimple process. It just seems not drilling or reaming these holes would still leave the possibility of less than perfect pre-punched holes leaving the possibility of cracking. How do they get away with that?
Don't matter to me either way, I am a 3D(drill, de-burr, dimple) kinda guy;)

You answered your own question...no dimple countersinking.

On the RV-12, at locations where the builder does dimple countersink (such as for flush screws), the holes are final drilled and deburred before dimple countersinking (because they will crack if this is not done).
 
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