E

experimental1234

I'm New Here
I am curious to know if anyone is just dimpling and riveting, instead of putting the part together drilling up to a #40 then taking it back apart deburring then dimpling and riveting?

As I see it the undersized hole that Vans stamps is as burrless as a hole gets. When the holes is dimpled the rivet fits right in. When the hole is drilled then dimpled the rivet usually fits prettty sloppy. If you really think about it it prob. wouldn't hurt anything, but I quess its just an age old process that worked for the certified world so those practices were carried on to cover their butt. Or is this to cover the 51% rule?

This would save a whole mess of time.

Just seeing if this has been discussed or done before.
 
Dimpling a slightly too small hole will create teeny-tiny cracks that radiate out from the hole. Try it and look at it under a magnifying glass. Not good.
 
It has been discussed at great length before (without an entirely bulletproof answer in my opinion)...check the matronics archives.
 
The point of drilling the hole out (as I understand it) is to clean up the edge of the hole. Stamping a hole is glorified way of tearing metal with lots of pressure, and your left with an edge that is neither smooth nor straight. Perfect breeding grounds for the start of a crack. Drilling or reaming is a cutting process, it leaves you with a clean, smooth surface.
 
Are you sure about that?

experimental1234 said:
As I see it the undersized hole that Vans stamps is as burrless as a hole gets.
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Either Van replaced his punch and die set on the NC punching machine right before making your kit, or your "burr scale" is different than mine. All the parts I received have what I would consider severe "burrs" consisting of a sharp raised ring around each hole on the die side of the sheet. These are cracks waiting to happen, if not addressed.

As a side note, I found that the flatter tip angle of a standard drill tip (135 deg) removed the burrs better (with less effect on the hole) than the common debur tips advertised for the job. I purchased a couple of threaded drill bits to fit in the deburring handle.

YMMV
 
Work hardened holes

experimental1234 said:
As I see it the undersized hole that Vans stamps is as burrless as a hole gets. When the holes is dimpled the rivet fits right in. When the hole is drilled then dimpled the rivet usually fits prettty sloppy. If you really think about it it prob. wouldn't hurt anything, but I quess its just an age old process that worked for the certified world so those practices were carried on to cover their butt. Or is this to cover the 51% rule?
Click to expand...

Punching a hole through metal is a reasonably aggressive operation and it would certainly work harden the very edge of the hole (read: make less malleable). When you combine that with a secondary major deformation (dimpling) in a hole that is very tight for the pilot (ie not drilled out to #40) then I would say that would be inviting microscopic cracks (which may eventually grow into not-so-microscopic cracks).

By drilling out the hole to #40 you remove the work hardened edge of the hole and open it up to fully accomodate the dimple pilot.

Apart from that there are machine tolerance issues and software mathematical translation errors in the Vans supplied punched holes. This results in minor discrepancies between "matched" holes that are best addressed by match drilling in situ.

For those who don't like deburring and matchdrilling the answer is simple.....buy a QB kit and get it virtually all done for you.
 
experimental1234 said:
I am curious to know if anyone is just dimpling and riveting, instead of putting the part together drilling up to a #40 then taking it back apart deburring then dimpling and riveting?........
Click to expand...
Sort of. Although my technique is not approved and probably raises a few eyebrows among those who prefer to follow the plans chapter and verse, I really don't care...its my airplane. I do agree with the theory supporting reaming the holes, but I prefer using a #41 with the exception being the anodized spar where I use a #40. A major reason why I do this is because I am more comfortable installing AD3-4 rivets instead of the AD3-3.5 rivets predominantly called out in the plans. The slightly smaller hole produced with a #41 makes it easier (for me) to set a given rivet within the accepted range of tolerance. In addition, the matched hole precision is so astounding, I felt very comfortable just reaming and dimpling the skins (and flap brace and aileron gap fairing) on the bench, and reaming and dimpling (machine countersinking as required) the structure mounted to the wing stand at the other end of the shop before the parts ever made contact with one another. When they did, everything matched up so perfectly that not one single hole....anywhere.... had to be wallowed out because of misalignment. A plumb bob check after the upper skins were permanently attached reveals absolutely no twist whatsoever. It really makes me wonder why you cannot simply take the ribs and other parts right out of crate, straighten and flute, ream and dimple before ever being attached to anything. Now that would be radical!
 
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Rick6a said:
It really makes me wonder why you cannot simply take the ribs and other parts right out of crate, straighten and flute, ream and dimple before ever being attached to anything. Now that would be radical!
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I'm pretty sure that if I do it again, I will do it this way Rick. I've never had a single hole not match up perfectly. On the other hand, I've sometimes "figure-8'ed" holes in the substructure becuase little flange tabs were slightly mis-bent or something. Drilling and dimpling separately would avoid this problem. It would also save a ton of time. (Match drilling the wings skins while on the ribs might be the only exception to insure no twist.) If this sounds like heresy, Rick and I can be in it together.

Re: not drilling at all. Drilling doesn't take that much time. Give yourself some long-term peace of mind and just do it.
 
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Just a tid-bit of info here.

Van's apparently doesn't think that CNC-punched holes would cause problems with the new -12 kit. If their website is correct, it says that the pre-punched holes will be full-sized. Maybe that was just for the POC aircraft -- maybe not. If the full-sized holes are going to be the norm on the kit we're going to see RV 12's completed from standard kits in months, not years. There will be no assembling then taking apart every single component. You just take the parts out and start pop-riveting them together.

Sonex, watch out.

Click here, third paragraph.
 
Jamie said:
Van's apparently doesn't think that CNC-punched holes would cause problems with the new -12 kit. If their website is correct, it says that the pre-punched holes will be full-sized. Maybe that was just for the POC aircraft -- maybe not. If the full-sized holes are going to be the norm on the kit we're going to see RV 12's completed from standard kits in months, not years. There will be no assembling then taking apart every single component. You just take the parts out and start pop-riveting them together.
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If you're trying to compare the RV-12 to any other RV as far as whether match drilling is/should be required, you're comparing apples and oranges. The holes on the RV-12 are not dimpled, hence no stress from dimpling. Pop rivets don't expand in the hole, so again, no stress on the edges of the hole. Pulling a pop rivet also puts less stress on the structure than driving a rivet.

I agree that the RV-12 will go together much more quickly, but then again it's a totally different class of aircraft with a different construction technique.

PJ Seipel
RV-10 #40032
 
Piercing/Punching of Holes in Aluminum

The most important consideration for match drilling a pierced hole is to provide uniform holes and surfaces for rivet engagement.

In any piercing operation, the configuration of the hole (from punch entry to exit) consists of:
1. Rollover Depth - this is caused by the punch entering the material (somewhat like a "bomb crater" if you will).
2. Burnish Dimension - This is a fairly straight cylinder caused by the punch shearing and sizing the hole.
3. Fracture Depth/Fracture angle - This results in a larger diameter on the bottom of the pierced piece.
4. Exit Burr - Is a function of the material pierced, and tool configuratiion.

The fracture mechanics of aluminum alloys typically result in a fracture depth of about 40% of the sheet thickness (in ferrous alloys this can be as high as 90%). This means that when riveting together two .020 aluminum sheets with pierced holes, your fastener engagement is only .024. Couple this with the fact that depending upon sheet orientation, the exit burr on one sheet may prevent surface/surface sheet contact, and a burr on the rivet head side may result in less than optimum clamping. Not good fastener practice. Optimum configuration is two sheets held closely together with no burrs on either end and full engagement of the fastener thru the material - in other words, a match drilled hole.

While reaming will result in a closer tolerance hole, it does not substantially improve upon what can be done much more quickly with a drill. In both cases, the exit burrs should be mechanically removed.

Finally, while there is some work hardening caused by piercing, it may actually be beneficial. Really becomes a moot point in view of the need to properly size the hole from top to bottom surface.

Terry
RV9-A
N323TP
 
Removing shear marks

One more consideration is the removal of shear marks in the skin. As is told in the manual, you should file or Scotchbrite the edges of all sheet stock. Drilling or reaming holes changes the direction of the marks inside the hole from vertical to radial. and lessens the chances for cracking.

You shouldn't take shortcuts like not match-drilling skinswhen building. Vans shop is not temperature controled and a spar punched in the summer can be longer than the skin if the skin was punched in the winter. Match-drilling assures that all the holes line up perfectly.

Bruce Reynolds
RV-6A
 
experimental1234 said:
I am curious to know if anyone is just dimpling and riveting, instead of putting the part together drilling up to a #40 then taking it back apart deburring then dimpling and riveting?

As I see it the undersized hole that Vans stamps is as burrless as a hole gets. When the holes is dimpled the rivet fits right in. When the hole is drilled then dimpled the rivet usually fits prettty sloppy. If you really think about it it prob. wouldn't hurt anything, but I quess its just an age old process that worked for the certified world so those practices were carried on to cover their butt. Or is this to cover the 51% rule?

This would save a whole mess of time.

Just seeing if this has been discussed or done before.
Click to expand...
There have been a lot of good posts to this thread. Some have eluded to the issue of cracks without actually stating that the whole deburring process is specific to the issue of preventing cracking. This is the real reason for deburring not whether construction meets the 51% rule or not whether the holes are tight or sloppy. Deburring will allow for protection from these holes developing cracks which in turn could lead to a structural failure over time. This is the ultimate reason for drilling out and deburring the pre-punched holes.

I agree that all of the putting together, drilling, taking apart, deburring, dimpling, putting back together, riveting is a tedious process but there really is a reason for the madness. That reason involves protecting your butt from structural failure because of metalurgic failures over the lifetime of the airframe.
 
The 51% rule is based on what parts you fabricate and what parts you assemble as compared to the same with the kit manufacturer. I has nothing to do with time spent or steps involved.
 
Workshops Question

I was told that one or more of the professional workshops available for RV builders (the one weekend or one week courses) do not drill/ream the punched holes before dimpling.

Can folks who have attended these workshops recently confirm how they were instructed to do it?
.... and how they actually did it, if different... :D

gil in Tucson ... doesn't count for a slow build.... :)
 
Well, I did one elevator one way, and the other the 'easy' way. If there are any problems, I will report them after flying it. Doing most the kit the traditional way, but tried the easy way on that one part.
 
Alexander Tech Cntr - drill/deburr/dimple

I did the ATC 1 week emp class. We were taught drill/deburr/dimple and prime before riveting.

As a matter of fact, except for a few pieces, all you do for the first 2 1/2 days is prep all the pieces. Very few rivets are set in the first couple of days.
 
Straight to Dimple...

az_gila said:
I was told that one or more of the professional workshops available for RV builders (the one weekend or one week courses) do not drill/ream the punched holes before dimpling.

Can folks who have attended these workshops recently confirm how they were instructed to do it?
.... and how they actually did it, if different... :D
Click to expand...

Gil,

I was one of the ones who told you - I learned the technique at Synergy Air in both their one-day course and the 5-day empennage build one year ago. See these threads:
http://www.vansairforce.com/community/showthread.php?t=5785
and
http://www.vansairforce.com/community/showthread.php?t=5786

I have done nearly all AN3 rivets in my RV-7 this way, the exceptions being those into spars or into parts that were not pre-punched. Those all get match drilled. I do notice that the resulting hole and dimple is quite a bit more roomy -- almost sloppy by comparison.

This practice has amounted to nearly all skin-to-rib and all skin-to-bulkhead rivets being dimpled and riveted without being match drilled or deburred.

I took both Wally Anderson of Synergy, and Ken Scott from Van's, at their word that this was sound practice. Ken was teaching at Synergy and I don't believe was representing Van's or Van's company policy at the time.

They both talked that this practice was quite widespread but not discussed much since it was contrary to "the book". Wally said he has built two award winning planes this way. Larry Davis, a Eugene area A&P/IA had no objections either - Larry is an extraordinary guy. Both Wally and Ken said that there were trials and tests underway to validate it and that publicity would follow.

I am unaware of any such publicity to date and still would be interested in seeing it. That said, I still do not have any reservations about continuing this way.

George
 
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az_gila said:
I was told that one or more of the professional workshops available for RV builders (the one weekend or one week courses) do not drill/ream the punched holes before dimpling.

Can folks who have attended these workshops recently confirm how they were instructed to do it?
.... and how they actually did it, if different... :D

gil in Tucson ... doesn't count for a slow build.... :)
Click to expand...
Gil-
Both when I took the class in Eugene, OR and at an RV build forum at Oshkosh last summer, Wally Anderson of SynergyAir suggested that for thin skins go right to the dimple process. He indicated that he did test samples and he and Ken Krueger or Ken Scott (I can't remember) looked at them under a magnifying class and found perfectly clean holes. I'm still not convinced (because I don't know anything about this kind of thing) so I drill and debur just like most of us, but Wally's a former jeweler and his attention to detail and the quality of his work is pretty amazing. He's also on one of the big EAA safety committees and a tech counselor. The non-engineer in me suspects that planes that are built this way will last just as long without stress cracks ever forming but, again, I wouldn't know, so I just do it the old-fashioned way.
 
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az_gila said:
... do not drill/ream the punched holes before dimpling...
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Not sure about the classes, but in my experience, reaming the hole after the dimling process is complete cleans the small fractures that are created by the dimpling process.

As for the part about saving time, I am sure the amount of time would accumulate to several days of just installing and removing clecos over the course of the entire build. But by doing this you are also given the chance to make sure that the parts are correctly located, that there is not a crashing problem with another part, that you have good e.d. with the mating part(s) etc.

just my opinion....
 
New variation?

plane_tech said:
Not sure about the classes, but in my experience, reaming the hole after the dimling process is complete cleans the small fractures that are created by the dimpling process.
.......
just my opinion....
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Now that's a new variation I haven't heard about before....

I would have thought that anything you did to the hole after dimpling with the dies we use would just enlarge the hole way beyond specifications... assuming a #40 before dimpling.

The clean, parallel sides would be good though....

Anyone else doing it in this sequence??

gil in Tucson
 
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