Final drill parts together or separately?

[deMan]

One of the side effects from LCP is that I am now paying much closer attention to many of the holes in the my 9 kit with undersized holes. When I final drilled the wing skins to the ribs with a reamer I noticed that even when I tried really hard to align the holes perfectly, I could often see primer remaining on the inside of the hole in the rib.
That means I must have created a very slight figure-8 where the final hole is slightly misaligned with the pre-punched hole and part of the pre-punched edge is outside the final hole. That’s why there is still primer.

This leads me to the following question: is it better to final drill ribs and skins separately or do them both at the same time while clecoed together.

On the Pros for separately I see that both holes end up perfectly round (and for LCP with the full HAZ removed).
Another Pro is the there won’t be any figure 8-s.
On the Cons for separately I see a potential for slightly misaligned holes.

Overall I think the Pros outweigh the Cons since when dimpled the slight misalignment should be well within the tolerance of how dimples align for riveting.
With the prepunched holes it’s not like final drilling offers much wiggle room for where the final hole should be.
If the misalignment is large I’ve accidentally created significant figure-8 holes in the past that I ended up using oops rivets for because they were now oversized. Drilling separately would remove that risk as well.

What do y’all think about final drilling without the parts clecoed together? Viable option or recipe for disaster?

Thanks
-Lars, building a 9

 

[BobTurner]

Together. When properly cleco’d together the final holes should be round and concentric.

 

[Ironflight]

Together. When properly cleco’d together the final holes should be round and concentric.

I concur - “Match Drilling” is the process of perfectly matching the two parts by drilling the holes perfectly concentric, and the way to do that is to drill them to final size “in assembly”.

 

[planenutz]

In almost all circumstances it is better to drill together, not separately.

As for doing this without being clecoed together - most definitely a recipe for trouble. It might not end in disaster but you can guarantee it is going to give you trouble when you go to rivet the skins on. The more cleoco's you can throw in there the better to prevent any creep. For example, ribs in the wings are not stiff enough on their own to remain perfectly in line with the skin when drilling clearance holes... a handful of clecos ensures the holes can't try and escape in a different direction to your drill bit.

 

[deMan]

I concur - “Match Drilling” is the process of perfectly matching the two parts by drilling the holes perfectly concentric, and the way to do that is to drill them to final size “in assembly”.

I think if you are drilling a completely new hole this is definitely true.

When drilling two existing holes to final size though I feel like the pre-punched location is already taking over ensuring that the holes are concentric.
The final-sized kits seem to do fine with hole alignment without match drilling, so shouldn’t individually upsizing the undersized holes to final also lead to sufficiently lined up final holes?


When holes didn’t line up perfectly while final drilling my practice so far has been to try and push the rib into place until the holes line up. Then I drilled.
Maybe that’s a bad practice but it was the best way I could think off to make sure the prepunched holes get aligned.
Using that practice though, does it matter if I do that pushing while match drilling, or after?

As for doing this without being clecoed together - most definitely a recipe for trouble. It might not end in disaster but you can guarantee it is going to give you trouble when you go to rivet the skins on. The more cleoco's you can throw in there the better to prevent any creep. For example, ribs in the wings are not stiff enough on their own to remain perfectly in line with the skin when drilling clearance holes... a handful of clecos ensures the holes can't try and escape in a different direction to your drill bit.

I use a reamer which means there is a pointy-end already through the holes in both parts before the cutting begins. I don’t think the rib can escape much there. I think there are still a few thousands of flex though even with all other holes clecoed. Clecoes aren’t really high precision alignment tools.
With the prepunched holes there really isn’t much choice where the hole in the rib goes either way - it’s either concentric with the prepunched hole or you get a figure-8 enlarged hole.
So assuming I can clecoe it together pre-drilled, I don’t see why it wouldn’t go together if the holes are final sized concentric with the prepunched holes. Especially when dimpled. There should always be a few thousands of flex to make a rivet go in.
If not, how would the final sized kits work?

 

[Ironflight]

So assuming I can clecoe it together pre-drilled, I don’t see why it wouldn’t go together if the holes are final sized concentric with the prepunched holes. Especially when dimpled. There should always be a few thousands of flex to make a rivet go in.
If not, how would the final sized kits work?

The final-sized kits work because the holes are punch very, very precisely. But when you upsize a hole with either a drill or a reamer, you are not likely to get the new hole exactly concentric with the original hole - you’ll always be slightly off to one side or another.

Do what you want with your kit, but you asked a question, and we’re just trying to answer with experience. Cleco things together with as many clecos as you have, then pull them one at a time to upsize and put clecos back in - when you do final assembly, it should all line up.

 

[Mike S]

Do what you want with your kit, but you asked a question, and we’re just trying to answer with experience.

Well said, Paul.

 

[drunkenbeagle]

I concur - “Match Drilling” is the process of perfectly matching the two parts by drilling the holes perfectly concentric, and the way to do that is to drill them to final size “in assembly”.

Not sure what the consensus is on this with replacement parts. I have a mostly match drilled empennage, that I held off putting rivets into until there was guidance on the LCPs.

Which is good, I don't have to drill anything out. But on the other hand, I now have match drilled skins that need to now mate to new parts. Assume I'll just be considering the skins all to be final sized now?

 

[deMan]

Do what you want with your kit, but you asked a question, and we’re just trying to answer with experience.

I appreciate that you are providing feedback based on experience and I apologize for making it seem like I’m ignoring it. I’m just trying to figure out how to best use the laser cut ribs that came in my kit. I trust Vans that they are blue parts and good for use but I am still trying to build the plane as good as I can a with as few cracked dimples as possible.
I’m trying to apply your experience based answers to the still rather novel situation of LCP. That’s why I am looking to explore the pros and cons of different options. To find the best one for my situation.
And my situation is that laser cut holes have a HAZ.

So for me it is probably more important to have the final hole concentric with the pre-cut hole on the rib to remove the HAZ than have the holes in the skin and rib absolutely perfectly aligned.

The undersized holes from Vans are #42 (drill but slips through), so 4.5 thousands giving 2.25 thousands of tolerance when aligning the holes in two parts to get both the HAZ removed and the holes in both parts concentric. I don’t think I can achieve that with Clecoes. Maybe if I put #42 pins in the holes next to the one I’m drilling but even then my fluting needs to be really good to not be off more than two thousands.

That leaves me with final drilling the holes to final size by themselves and hoping the reamer centers well enough to remove the HAZ around the full hole.
Not even sure if that’s actually possible since the laser cut holes are not perfectly round. I stuck a drill bit in it and into a punched hole and the laser one deflects much further in one direction showing the laser hole is elongated in that direction. I’ve attached a picture. The front is laser cut.

The downsize of not match drilling parts together is obviously that the holes don’t line up perfectly.
Here are reasons why I think there is enough tolerance in the alignment for things to still work:
1. It works on the 10,12, and 14 with the final sized holes. This thread talks about synergy using special, undersized dimple dies to treat the older, undersized kits similar to the new kits and they dimple without any match drilling. I’m happy to hear any experience how that is working.
2. Adding on to the above, the ribs in question are laser cut, as are many of the 10 and 14 ribs that get dimpled. So the hole location should be as accurate in my kit as in those final size kits. The laser cutter has the same precision for all parts; no difference in tooling exists as it would with pinched parts.
3. This is subjective but I feel once dimpled there are always a few thousands wiggle room when aligning the parts for riveting.
4. This is how repairs are often done. E.g. when replacing a rib with the skin already dimpled it isn’t really possible to match drill. There are ways to get the hole close to the center of the dimple but it’s usually not perfectly aligned and a few thousands off. I haven’t done any of these repairs myself but maybe people that have experience with that can chime in on how alignment worked out with such repairs. Were there any issues with holes not lining up when riveting?

If anyone has experience with final drilling parts not clecoed together (new construction or repair), I’d be interested to hear it.

Thank you. Lars

 

[swift12]

well I tend to agree with you. I personally know a guy who had a terrible time with oval holes when match drilling and I have found that too...if there is a lot of pressure required to fit clecos the holes dont always line up perfectly even when you have clecoed every single hole. then you ream...only taking out 2 to 2.5 thou per side....only to find the holes are NOT perfectly concentric. so the chap i am talking about got sick of the match drilling and subsequent regular oval holes so started reaming separately....only removing 4 to 5 thou does not cause the holes to wander any amount USING A REAMER....a drill will wander.

then he banged his whole RV7 fuse together like that....the entire thing....prior to riveting....the plumb bobs were hung....perfect alignment...no elongated holes.....after riveting...perfect alignment....maybe he was lucky....maybe this whole match drilling thing is unnecessary.

Another friend had to replace a rear wing spar....onto already match drilled and dimpled holes....vans said...just ream the new spar and dimple...then whack it together...which he did...and it was perfect.....

bet there is a bunch of non concentric holes everywhere on these RV's due to match drilling.....some i match drill....others I have not...and not seen any difference in how it goes together...interesting....

 

[planenutz]

Once you've done it your way, be sure to let us all know how you went.

I know the holes are placed accurately on the parts you receive from Vans however things move during assembly. When you rivet the parts together the skin will stretch... which is why when you get to the last rivet in a long row the holes will need a clearance drill through it so you can get a rivet in there. So much for you worrying about 0.0025" per side of each hole.

I feel you're more likely to get wrinkles and bulges in your final assembly if you do it your way but I'm more than happy for you to prove me wrong.

 

[deMan]

bet there is a bunch of non concentric holes everywhere on these RV's due to match drilling.....some i match drill....others I have not...and not seen any difference in how it goes together...interesting....

Thank you for sharing this experience with doing it the non-traditional way.
Sounds like I’m not the first person to have that idea and that it worked out for others in the past.
I will give it a try next time holes need final drilling.

-Lars

 

[deMan]

Once you've done it your way, be sure to let us all know how you went.

I know the holes are placed accurately on the parts you receive from Vans however things move during assembly. When you rivet the parts together the skin will stretch... which is why when you get to the last rivet in a long row the holes will need a clearance drill through it so you can get a rivet in there. So much for you worrying about 0.0025" per side of each hole.

I feel you're more likely to get wrinkles and bulges in your final assembly if you do it your way but I'm more than happy for you to prove me wrong.

I’ll report back but it’ll be a while. I’m just starting to river the first wing together so I don’t think I’ll have to match still for a while. When I do I’ll be on the lookout for wrinkles and bulges.

The stretch of the skin is a valid point that hadn’t crossed my mind. I think I’ve seen that with some holes. It applies when doing it both ways though. With some stretching, holes end up neither where Vans made them nor where they were when match drilling.

I think temperature can also come into play here. Many of us don’t work in temperature controlled shops so holes match drilled on a cold day will be a few thousands off on a hot day because the part changed size.
I’ve actually been worrying about that with my wings. I drilled them in the summer and if I rivet them now in the northeastern winter, will I get wrinkles and bulges when the wing warms up in the summer?
We will see in the summer.

-Lars

 

[GrahamF]

Thought experiment

This needs a thought experiment, perhaps involving Schrodinger's parts.

Let us consider a simple assembly situation with two parts that are joined by three 1/8" rivets. Three holes in each part, six in total, dead simple.

First, we do it the 'wrong' way and individually ream all six #32 holes out to #30 and deburr. We now know that all six holes are as round and as close to the correct size as is possible when working with handheld tools. If we want to be extra precise and if the shape of the parts facilitates it, we could put our #30 reamer in the pillar drill.

Then we prep and prime, and we're about to insert the rivets. Do all three go in easily enough? Maybe, maybe not. If they do then great - we not only have holes as good as we can get but we also have perfect alignment.

But maybe they don't all go in easily. Maybe once two are in, the third will not go by hand. Maybe it needs a tap with something, maybe the rivet gun will push it through prior to bucking.

In this case we invoke Schrodinger and take our parts back to their pre-reamed state. We then cleco them together and match-ream each pair of holes per conventional practice. Remembering that these are exactly the same parts, one or more of our holes is now slightly larger and out-of-round than it would be when reamed individually. This has to be the case, because if it were not so then they would have gone together when reamed individually.

I guess the question it leads to is whether the enlargement and out-of-roundness when reamed together is within tolerance. If as the OP says it is enough for holes to be visibly ovoid, I'd suggest that's not ideal.

I would suggest that match-reaming becomes more important the thicker the parts get, because with thicker parts there is no scope for the rivet to pass through in any manner that isn't totally perpendicular to the surface and thus precise alignment becomes more important.

As an aside, I'm not sure why anyone would drill when they can ream. My drills only ever come out when a hole doesn't actually exist yet. Bar some work with step drills on larger holes, everything that requires final-sizing gets reamed.

 

[deMan]

Rivet type and material thickness

This needs a thought experiment, perhaps involving Schrodinger's parts.

Let us consider a simple assembly situation with two parts that are joined by three 1/8" rivets. Three holes in each part, six in total, dead simple.
…
I would suggest that match-reaming becomes more important the thicker the parts get, because with thicker parts there is no scope for the rivet to pass through in any manner that isn't totally perpendicular to the surface and thus precise alignment becomes more important.

As an aside, I'm not sure why anyone would drill when they can ream. My drills only ever come out when a hole doesn't actually exist yet. Bar some work with step drills on larger holes, everything that requires final-sizing gets reamed.

Very nice thought experiment.

I agree that for thick materials match-reaming is best. When I made my original post I also was thinking about flush rivets only, not universal ones. So primarily 3/32 with dimples in usually thin material.

For 1/8 universal rivets, match reaming has been working well for me. Since that’s usually thicker parts I don’t think reaming parts individually would lead to a hole a rivet goes through.

+1 on using a reamer whenever possible. For newly drilled holes I recently upgraded to double margin drill bits as well. They make holes very close to reamer quality and much cheaper than buying a reamer for every size of hole.
If also found center drills useful for getting holes started in a precise location but that’s a different topic.

 

[CoolDadTed]

...one or more of our holes is now slightly larger and out-of-round than it would be when reamed individually. This has to be the case, because if it were not so then they would have gone together when reamed individually.

I don't believe this is correct. Because the final hole is larger than the pre-punched hole, there are multiple possible locations of the final hole that are perfectly round and completely cover the pre-punched region.

I don't believe there is necessarily a compromise with hole quality here. In your scenario, the match-drilled holes may be perfectly round even though the same parts, drilled separately, might not align.

Final size drilling should be done in-assembly.

-Ted

 

[airguy]

Thank you for sharing this experience with doing it the non-traditional way.
Sounds like I’m not the first person to have that idea and that it worked out for others in the past.
I will give it a try next time holes need final drilling.

-Lars

Sounds like confirmation bias to me, but hey, it's your airplane and you should by all means build it your way. Please let us know how it turns out.

 

[skypilot737]

holes

I guess I don't think it really matters either way when the rivet expands to fill the hole. A little oval or perfectly round should be filled with the rivet in the same way.

 

[GrahamF]

I don't believe this is correct. Because the final hole is larger than the pre-punched hole, there are multiple possible locations of the final hole that are perfectly round and completely cover the pre-punched region.

Theoretically yes.

In practice not, because to go up to final size you don't get to make the hole starting from scratch and picking a centre which works best for both parts. You make it by passing a drill/reamer through the first punched hole and into the second, so the final hole in both parts has only one possible location - which is centered on the centre of the punched hole in the first part, and so the second part ends up with a #40 hole centered on where you clamped them together relative to the hole centre in the first part.

In any case, the diameter difference is 4.5 thou so that's 2.75 thou 'allowance' all around the perimeter which doesn't allow for a lot of shift. What it means in practice is that unless your holes are well lined-up when you ream the one underneath will go out of round, and differences of 1-2 thou won't make holes un-rivetable anyway.

I agree that match reaming is the 'right' way to do it, but match reaming when your holes won't line up properly will give you crummy holes. Better to jiggle it a bit more, work out why it's not lining up, fettle it a bit etc rather than just plunging the reamer through and kidding oneself that it's within tolerance.

When we're replacing parts (as many of us will have to do at significant scale), you may not have the option to match ream.