Countersinking Halos

[jaypee]

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

[Larco]

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

[jaypee]

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

[RV7Factory]

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.

[jaypee]

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

[CitationXRV8]

Originally Posted by jaypee

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

[CitationXRV8]

Originally Posted by jaypee

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

[RV7Factory]

Originally Posted by jaypee

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.

[JonJay]

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.

[RV7Factory]

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.