Match drilling

captainron · #1 08-05-2006, 10:47 AM

OK, I know I'm going to catch much grief over this, but maybe one of the experts like Dan or Mel can answer this. I assembled my RV-7 empenage at Alexander Tech Center, which was a great experience and I highly recommend them. However, I just don't get the whole match-drilling thing. The assembly would be cleco-ed together and then reamed with a #41 reamer, which by the way I think is better than using a #40, giving more support to the rivet.

I never saw a hole that didn't line up, but I did notice that when I occasionally became lazy and spaced the clecos too far apart, I might get an enlarged hole in the underlying piece.
When this happens, it seems to defeat the idea of matched holes.

Next, the assembly is taken apart to be dimpled, de-burred, prepped, etc..
You can't tell me that dimpling, deburring, running clecos in and out doesn't change dimensions slightly.
The prepunched holes already fit over the dimple pin without any drilling or reaming, which means you can drop a rivet right into the dimpled hole.

To quote Van's directly: "In the "matched hole" RV-7/7A kit, a computerized punch press locates and punches all the rivet holes during manufacture, so the builder can pull the parts out of the box, align the holes and begin assembly immediately."

I was begining to think that the whole "match-drilling" thing (or even reaming at all!) is a colossal waste of time and introduced more errors into the work. I decided to do one elevator the "approved " way, and on the other, simply ream all holes seperately, dimple and prep normally and rivet together.

The end result were two perfect elevators, but with the knowledge that one of them had perfect holes that weren't match-drilled. And, much less time invested in re-doing what you've already paid Vans for.

Comments?

Mike S · #2 08-05-2006, 10:50 AM

51% rule.

Mike

fehdxl · #3 08-05-2006, 11:41 AM

Here's my take...

(a) 51% rule ... that means that if one of the tasks listed on the FAA forms in order to build such experimental is 'match drill a hole' then all you have to do is match drill ONE hole, therefore you've accomplished that task, and the other 16,999 holes can be matched drilled by someone else.

(b) match-drilled ... Taking the idea one step further, why doesn't Van's just punch the holes to the correct size for us so that we have to do is dimple and then final rivit? The answer is that the act of punching of the holes by the CNC machine leaves marks/grooves in the aluminum that creates the potential for stress cracks. By drilling/reaming the hole to final size, just removing that little amount of material, it cleans up the hole as to greatly reduces the chance of those stress cracks.

Just one person's opinion...

-Jim

jchang10 · #4 08-05-2006, 12:22 PM

It's like those short-cuts you take when driving to some destination. Often times, when you're familiar with the route, you can take a short cut you are familiar with and it works out.

Other times, often when you are not familiar with the area and do it out of impulse, the short-cut actually takes longer to get to my destination.

I think it's the same with skipping the assembly with clecos. It will probably work out much of the times, esp. on the tail kit. Doing so will definitely save some time. I do not recall any match-hole problems. however, it might cause other problems.

I am building my slow-build wings. I can't tell you how many times i have clecoed and removed my main ribs to the main spar. I have had some alignment issues, requiring me to take down the whole assembly, tweak a tab, a rib here, etc. and put it all back together again. if i were already riveting things together, it would severely limit any corrective actions i could take, if any at all.

Another potential risk with not assembling, is missing to drill a hole somewhere. On the wings, there are these aileron hinge brackets that do not have prepunched holes. they are drilled using the rear spar holes as a guide. you will have to work out a solution with everything riveted together.

I think everyone should do what they feel comfortable with, knowing the risks versus tradeoffs.

Jae

hevansrv7a · #5 08-05-2006, 01:47 PM

I have found that if the hole is not at least #40 (for -3 rivet), the dimple operation may cause a crack on the edge of the hole. This can be checked with a magnifying glass. It's very educational. The dimple die is sized for #40, not 3/32" for example. The -3 rivet expand to fill the hole correctly.