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Drill, deburr, dimple, prime... You?

A

AlinNS

Well Known Member
Well I'm about ready to get going.

Here is the sequence I plan on using:

1. Drill as required. OK that was easy;then

2. Scuff with Scotchbrite. This needs to be done before priming and the practice results I get show it does indeed deburr the holes also? Seems to be pretty safe as there is no risk of countersinking the holes a little. So why doesn't everyone do this? Doesn't it cut out a separate deburring step?;then

3. Dimple/countersink. I'm still a bit stuck on depth of countersinks. Especially regarding a recent thread on the subject. I can't get consistent measurements with depth so I'm just going to go for a flush rivet head when parts are together??;then

4. Prime. Not asking for what to use here but... Doesn't the thickness of the primer affect the dimple/countersink depth? Negligible? Is that why people prime before dimpling? Why do I see parts that only have the mating surfaces primed and not the whole part? Is there a reason to spend time taping off parts in order to leave areas (inside) not done? Weight? Save primer?

So fire away. I know there are lots of ways to git er done. Feel free to shoot holes in the above and educate me on a better way, or let me know what I'm missing.

Thanks, I appreciate your time.
 
to deburr or not to deburr...

As I have experienced it, scotchbriting will just smoosh the burrs into the hole, making it hard to get the rivet in, and still leaving a very square edge around the hole, which becomes a stress concentrator on the rivet that will eventually be crushed into the hole. It is desirable to create a small ~45 degree chamfer on both sides of each sheet that will be joined. I have no conclusive evidence that rivets will split and wings will shed if this is not done, though. But we always follow best practices, and there is clear evidence that chamfer deburring creates stronger joints, especially in fatigue loading.

So... you deburr a hole (drilled or punched) by taking a hand deburr tool, (looks like a bent screwdriver) with a deburring cutter (3 flutes, ~45 degrees), apply light pressure and rotate cutter ~two turns, depending how sharp the cutter is and how hard you are pushing, and how big the burr was. You will be able to see a small chamfer around the hole when your parameters are correct.
- Roger
 
There will probably be more than 16 different approaches to this, but I trimmed (where necessary) dressed and deburred sheet edges then scotch brite scuffed and primed first, it makes it much easier to see markings for holes, etc. then drilled, deburred and dimpled holes. As Roger pointed out, scotch brite does not properly deburr holes , or edges for that matter.
 
Drilling, too!

Just a note about drilling... it is recommended to drill a hole in two steps, a smaller drill to create a first hole, then a second operation to increase the diameter to final size. This makes a smaller burr around the second hole. Theoretically this makes the sheet less likely to develop cracks around the rivet hole. There is usually no need to deburr the first hole, unless it interferes with parts fitting together when match drilling (and Scotchbriting the surface is a good solution in that instance). A pre-punched hole only needs to be drilled once.

Al, I remember being where you are, six years ago... so many questions, and the answers are so complex, hard to communicate clearly, and even harder to understand. Sorry. You MUST find someone close enough to serve as a source and advisor. Spend an afternoon practicing, learning with an experienced builder. VAF is great, but it will take way too long to learn all the stuff you need to know right now.

Best of Success!
- Roger
 
Look at this way, aircraft producers are always looking at ways to cut production costs. If you could skip the deburring step, they would have done so. While I HATE the answer, "Because we have always done it that way," it might be there is a reason.

On the other hand, there I a member of this forum with a significantly over powered RV who didn't even bother match drilling and went straight to dimple. He has been flying for some time now and his plane hasn't fallen out of the sky.
 
AlinNS said:
Well I'm about ready to get going.

Here is the sequence I plan on using:

1. Drill as required. OK that was easy;then

2. Scuff with Scotchbrite. This needs to be done before priming and the practice results I get show it does indeed deburr the holes also? Seems to be pretty safe as there is no risk of countersinking the holes a little. So why doesn't everyone do this? Doesn't it cut out a separate deburring step?;then

3. Dimple/countersink. I'm still a bit stuck on depth of countersinks. Especially regarding a recent thread on the subject. I can't get consistent measurements with depth so I'm just going to go for a flush rivet head when parts are together??;then

4. Prime. Not asking for what to use here but... Doesn't the thickness of the primer affect the dimple/countersink depth? Negligible? Is that why people prime before dimpling? Why do I see parts that only have the mating surfaces primed and not the whole part? Is there a reason to spend time taping off parts in order to leave areas (inside) not done? Weight? Save primer?

So fire away. I know there are lots of ways to git er done. Feel free to shoot holes in the above and educate me on a better way, or let me know what I'm missing.

Thanks, I appreciate your time.
Click to expand...
2) Consider that the building process you are following is standing on well over 50 years of experience, several wars, many thousands of practitioners, etc. Suggest deburring the holes with a deburring tool.

3) Several ways to measure and setup tools for various combinations of sinks and dimples. Take some time to learn some of them or else you will run into some ruined parts and stuff. A couple of hours with a experienced builder will clear up stuff that is challenging to present online.

4) Sounds like you are trying to streamline and simplify where possible - that's a good thing. Consider amidst the primer wars that the simplest approach is to only prime where Vans "recommends" priming and leaving the rest of it unprimed. They suggest precious few places - I would prime in all those places. Otherwise, you can move on if you like. Difficult advice to take at the beginning of the project but it makes sense to many later on. And Vans does know what they are doing.

Have fun!
 
The Sponge

Thank You. All comments both appreciated and accepted.

Ya know, I have pretty much all the usual deburring tools and have tried them all with what seems to me pretty good results. I stumbled upon a video with someone using Scotchbrite to deburr and I had heard of it somewhere else. My intention is to go back to the original plan, which is what has been detailed by you folks.

Does the dimpling after priming not destroy the primer? Akzo I'm sure would survive, but what about the others that aren't 2 part epoxy?

Regarding seeking out an experienced builder, absolutely. Before the first rivet gets pounded on the actual airframe, I will, at the very least, confirm that what I am doing is appropriate and get some "in person" education.

Thanks again.
 
I would work my parts through dimple and then alumniprep and alodine them before heading to bed. First thing in the morning I would prime them (SEM spray cans) and let them dry while at work.
 
Scotchbrite by hand doesn't do much deburring. But a Scotchbrite roloc disk in a die grinder is quick and effective deburring tool that leaves a super smooth hole and no countersink. One consideration is how much Alclad it removes, so I usually limit this method to non-clad surfaces.
 
RVDan said:
There will probably be more than 16 different approaches to this, but I trimmed (where necessary) dressed and deburred sheet edges then scotch brite scuffed and primed first, it makes it much easier to see markings for holes, etc. then drilled, deburred and dimpled holes. As Roger pointed out, scotch brite does not properly deburr holes , or edges for that matter.
Click to expand...

This is the process I use. I find it easier to do all of the prep and priming on the parts prior to dimpling. Also epoxy priming the parts first will obviously prevent corrosion from skin oil and moisture during fitting and assembly that would otherwise have to be removed prior to coating.
 
Process

It's interesting to read all the processes. We are an anal bunch aren't we.:D
I'm in between. I prep first. Match drill, debur, scotch brite, dimple, then clean and prime.
I use a vixen file to debur skin edges and remove tooling. A few passes is all that's needed unless they are really deep. Then the scotch brite pad is used to smooth the edge. Small parts are deburred on the wheel.
It is important to note the hole deburring process is not heavy handed. Don't countersink holes trying to debur. The ring mentioned is barely visible at first. Later you learn to see it and can actually walk away and find where you left off.
 
To answer your question about priming: some do no priming, some prime everything, and some choose in-between. The in-between folks often chose to prime only where parts overlap because
1. Such areas are difficult to inspect later
2. Such areas may catch and retain moisture
3. Possible dis-similar metals corrosion
4. ?
Reason? Save weight, time, money.
Need to mask? Only if you are concerned with how the inside looks!

Does primer in a dimple 'raise' it up slightly? Yes, but that same primer on the flat surface of the sheet also 'raises' it slightly, so it all works out.
 
Mike H said:
This is the process I use. I find it easier to do all of the prep and priming on the parts prior to dimpling. Also epoxy priming the parts first will obviously prevent corrosion from skin oil and moisture during fitting and assembly that would otherwise have to be removed prior to coating.
Click to expand...

Skin oil doesn't cause corrosion. If anything, it prevents it. Oil/grease is a time honored corrosion preventer. Think about why your crankshaft doesn't rust.

Larry
 
Skin "Oil"

lr172 said:
Skin oil doesn't cause corrosion. If anything, it prevents it. Oil/grease is a time honored corrosion preventer. Think about why your crankshaft doesn't rust.

Larry
Click to expand...

Apparently you've never seen a pristine piece of shiny copper or carbon steel that's been handled with bare hands. In very short order, it becomes covered with fingerprint tarnish marks. I believe that it's because skin "oil" isn't exactly oil per se, but contains moisture and salts and really is corrosive.

Skylor
RV-8, Flying
 
I've seen a 2000 hour crankshaft with a thumbprint on a main journal from the previous assembler.
 
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