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Countersinking Halos

jaypee

Member
My attempt to build the perfect plane first time out has met a new snag. In countersinking the tank skins, I'm getting scratches about the diameter of my bit. They seem to appear at random. I'm using a single flute #40 bit with an air drill. Clean the shavings from the bit after each hole, they still appear.

Any ideas?

Jerald
RV-8A Tucson
 
If you are machine countersinking the tank skins you might want to ask around. The ones who did this early on seemed to always have a leak after flying a bit. Recommend you DIMPLE them. Just my opinion. Larry
 
Sorry, I guess I should be more specific. I'm countersinking the baffle attachment hole in the tank skin. The plans say the baffle is not to be dimpled, but the skins countersunk.

Jerald
RV-8A Tucson
 
Me too

It's those darn single flute CS bits. Even though your are cleaning the cutter each time, because of their design, they don't shed material and the cuttings end up spinning around the hole. I switched to the standard 3-flute CS bits and the problem went away. It's a tradeoff... the single flute cutters never chatter, but they do occasionally leave a halo.
 
Thanks, Brad. I was wondering if I should switch to the 3 flute, but wasn't sure that my problem wasn't poor technique on my part.... most problems turn out to be.

Do you use a cordless when using the 3-flute to minimize the chatter?

Jerald
RV-8A Tucson
 
jaypee said:
My attempt to build the perfect plane first time out has met a new snag. In countersinking the tank skins, I'm getting scratches about the diameter of my bit. They seem to appear at random. I'm using a single flute #40 bit with an air drill. Clean the shavings from the bit after each hole, they still appear.

Any ideas?

Jerald
RV-8A Tucson

I would dimple the tank skins unless the plans call for machine countersink. Also, if you don't have "tank dies" I would recommend getting them. I got mine from Cleveland Aircraft Tool.

Per the catalog..."Tank dies make deeper dimples to allow for the layer of tank sealer between the rivet and the skin. Rivet will set flush with the skin's surface".

Joe
 
jaypee said:
Sorry, I guess I should be more specific. I'm countersinking the baffle attachment hole in the tank skin. The plans say the baffle is not to be dimpled, but the skins countersunk.

Jerald
RV-8A Tucson

Sorry, I wasn't fast enough with my reply. Just read this.

Joe
 
jaypee said:
Do you use a cordless when using the 3-flute to minimize the chatter?
Yup... when it's charged. ;) And I make sure there is something behind the part to guide the CS pilot. I still think the single flute cutters do a nicer job, but I got tired of cleaning them out after EVERY hole.
 
If you are going to paint your airplane, those halos will be long gone after you prep. If you want the paint to stick, it will get a very thorough rough sand job and those halos dissapear.
Also, don't do your countersink in one firm motion. Take a bite, let off slightly, finish up. It clears the chip better and you will get less of a tendency to scratch. Does not take anymore time, also does not necessarily elliminate the halos, just helps a little.

The first time you fly, you wont care whether you built a perfect airplane or not. You will be having too much fun.
 
What I really want to know is how you got to the tanks before the plane stopped being ?perfect?? For me, it was day two of the horizontal stab. :D
 
The perfect plane thing was an attempt at dry humor. Its already way too late for that. Just ask Bruce at Vans.

Jerald
RV-8A Tucson

Charging the cordless
Pro-Seal and more replacement parts on order
 
Jerald-

Don't sweat those halos. You're not the only one. I've got a few that will need to be smoothed out prior to painting. Like Brad said, the three-flute is the key. Interestingly, the only cutter that I've had halo problems with is the single flute 3/32. I've never had a problem with the larger sizes. Another advantage to getting a 3-flute is that the pilot is MUCH stronger. I broke my single-flute pilots 2-3 times. Cleaveland voluntarily replaced all 2-3 for free when they heard my problem (great service!) and once I went to the 3-flute I've had no other problems.

Also, I've heard that the more recent version of the plans instruct you to not countersink every tenth hole until AFTER you seal the baffle. The un-countersunk holes will make it easier to perfectly align the baffle with clecoes before riveting. Prior to this revision, the consensus seemed to be that rivet heads sitting proud of the surface was quite common.

Hope this helps.
 
Well said

RV7Factory said:
What I really want to know is how you got to the tanks before the plane stopped being ?perfect?? For me, it was day two of the horizontal stab. :D

Brad,

Great reply.....................

I tried to build the perfect RV-4 years ago and now I am trying to build the perfect RV-7A. The quest for the perfect RV is continuing to eluding me :(

Here is the lesson I am learning-Don't let perfection get in the way of real progress

Paul (RV-4/RV-7A finishing kit)
 
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