I have a question regarding the pre-punched kits...

[danielhv]

I was speaking to a "repeat offender" the other day and we were discussing my deburring techniques... He stated that on the pre-punched kits, there is no need to deburr if you do not match drill... He said both of his -7A's he built by just dimpling the skins/ribs without match drilling OR deburring... He also stated that this was an approved method by Vans! So my question is this: On the pre-punched kits, would that be an approved method of building? Sure would save me a TON of time!! I can see how many would say that it is not, but on the other hand, the theory semi-makes sense to me... But I figured nobody would know better than you guys!

I shot an email over to Vans as well just to see what their stance on the matter was...

[Danny7]

I know there are some employees at vans that have built this way. But I do not think it is a factory approved method

[lostpilot28]

The point of deburring is to remove stress risers. I'm not sure how the pre-punching is done, but I can't imagine that stress risers aren't there with every kit. Just do it the way the manual tells you to. Pre punched, CNC'd, matched hole, etc....how much easier do you want it??

[flion]

First, you must match drill. Yes, dimpling enlarges the holes slightly but, as mentioned above, match drilling is also about alignment. Second, the punch process is not 100% clean. It's hard to look in a #41 or 42 hole and tell, but look at the edges of the same part. Notice all the tooling marks. Drilling will clean up the inside of the hole but you still need to deburr, just as you need to clean up and deburr all the edges of the part.

That said, and regarding those who have built without match-drilling or deburring, there is no data to support or disprove any comparison of relative safety. Somewhere I saw a description of the action of tooling marks as being similar to nicking a piece of paper; in the latter case, any tearing will most likely occur at the nick. However, the presence of the nick, while it weakens the paper, does not automatically produce a tear or reduce the paper's strength to zero. I am not amazed that aircraft built in that manner fail to, er, fail but I am not a structural engineer and prefer not to experiment in that fashion. I'll load the dice in my favor wherever possible.

[Andy Hill]

I am sure you could build that way, it would fly, and not fall apart on the first flight You could also not prime any of it, not smooth / round any edges, not rework much of the fibreglass parts etc., and in all probability it would fly a few years / hundred hours.

In the longer term? Who knows what cracks / corrosion would be building up? Lots of points are essentially uninspectable post build until failure

I find most RVs are built to a fairly common standard reflecting the pride / effort / attention to detail (or not) of that builder i.e. the finish in visible areas is a good indicator as to the attention paid in the less visible areas, and that would in turn affect the value / suitability to buy?

I am not sure it would save "lots of time" as a proportion of the total? I find the preparation / research / trial fitting takes the time, and once you get onto drilling / deburring you are on the home straight... but maybe I am forgetting the RV-8 and more aligned now with the RV-3

Andy

Edit: and reading your EAA Tech report, seems your attention to detail has been good so far - would be a shame to spoil it

[Kahuna]

Been bantered on many threads.
A quick search will result in many thoughts on the matter.
http://www.vansairforce.com/communit...ad.php?t=34947

[terrykohler]

Daniel:
The process of punching a hole in the sheet does not produce a straight hole all the way through, but rather generates a conical section in approximately the last 30% of the sheet section where the punch exits. Has to do with the mechanics of shearing. Some processes, such as fine blanking, can minimize this breakout, but I don't believe that's what Vans is doing. So the match drilling helps to produce a smooth, uniform hole. That gives the bucked rivet a better "grip" when joining the two sheets (the shank of the rivet expands in the bore, as well as the shop head). As already mentioned, the deburring helps to minimize stress risers which more likely come from the drilling than the hole punching. In any event, can you eliminate drilling? I believe most of the RV kits (12 may be an exception) have holes punched undersize. Using a dimpler to size the hole is like jamming a wedge or chisel into the sheet. May result in stress risers. Personally, I wouldn't recommend it. May or may not lead to problems. As for drilling, if the holes are already to the proper size and you were using all "pop" rivets, I'd say "no problem". Otherwise, why risk it? When you get to the plexi, you'll find it's even more unforgiving of proper hole sizing and lack of chamfers. Have fun.
Terry, CFI
RV-9A N323TP

[danielhv]

Thanks for the replies everyone! The responses were just as I expected. I was not looking to cut any corners... just making sure I'm not over-doing it so to speak. I will continue with my previous methods.

[Thermos]

Originally Posted by Kahuna

Been bantered on many threads.
A quick search will result in many thoughts on the matter.
http://www.vansairforce.com/communit...ad.php?t=34947

Kahuna,

From one of your posts on that other thread...

Originally Posted by Kahuna

1. There is a reason that the cracks introduced during the dimpling of these undersized holes will NEVER amount to anything. Do you know what it is?
2. There is a reason that the supplier of the materials undersizes these holes and wants you to follow the process they have laid out. Do you know what it is?"

What are the answers? Enquiring minds want to know...

ds

[Brantel]

After seeing how easy and how few hours it took for my left rear baffle corner to crack, there is NO way I would ever build any airplane without properly deburing the holes. I would also never dimple a hole that was not the correct size for the die...