Using a Fly Cutter for the Very First Time

I purchased this tool a long time ago, expecting that I would need to use it sooner or later. My initial expectation was that I would be using it to cut round holes for certain instruments on the instrument panel. I did NOT expect that I would need to use it on my fuel tank.

Basically, I needed to cut out the entire section of metal on the inboard fuel tank rib s that an access plate can be installed to allow servicing of the fuel tank in that area, should the need ever arise. Since I decided NOT to install the capacitive sender kit from Vans per their recommendation, and I am now going to switch to the normal float sender instead, the access plate would also normally contain the mounting flange for float sender, as well as the AN 833 hardware for the fuel pickup line fitting, that takes fuel from the pickup line and routes it through an elbow joint through the access plate.This will be how things get assembled for the right fuel tank, as it will be a stock tank per the plans for the most part.

The left tank, on the other hand, does not contain the stock fuel pickup line, but instead will use a flop tube as I have described previously. In addition, since I am still using the flop tube in the left tank, I cannot install the float sender in it's intended original position, as it will interfere with it. SO I will need to put the float sender in the next bay over, and mount it to the rear baffle instead of on the access plate on the T-703 tank rib web.

Aside from all that, I still need to install the access panel on the rib web, but instead of using the T-708 plate on the left tank, I will use the other solid plate that came with the capacitive sender kit. the pics will show this more clearly later. Anyway, before I even get to that, I have to cut a very large hole, so large in fact that it is too big for hole saw, and for a spade bit or other type of drill bit. the Fly wheel cutter tool was specifically designed for this situation.

The plate gets prosealed and screwed onto the rib web so that you can access from the wing after removing the wing fairing. Although it is a tight space, you are supposed to be able to remove this plate and service the tank in certain ways without the need to remove the tank from the wing. A reinforcement ring goes on the other side of the rib web and serves as the mounting bracket for the access plate. Here is a pic of that bracket with the T-410 stiffeners precut in side of it. I used snips to separate the small tangs holding each part together, and then used a small file to grind down the remaining slag. Later I found out that you can pretty much just lightly twist these parts and they will separate.  am always cautious about this sort of thing from my plastic model building days, since twisting the parts of the tree would sometime remove portions of the actual part. SO you learned to use snips or clippers to keep from damaging the plastic parts.On the right is the parts removed from each other, adnon the left is the part for the right fuel tank with everything still attached as it came from the factory:

The plans do not mention how big the hole needs to be, just that you need to make one (another Vans instruction feaut-pa). So after researching some builders sites I realized that the hole needs to match the opening in the reinforcement bracket shown above - duh! So this was as easy as placing the bracket over the stiffening ring on the aft end of the rib web, and tracing the inner circle onto the web:

Next came the "art" of placing a drill board on the drill press table, followed by the rib, and then figuring out how to clamp everything down solid.I also needed to find the precise diameter and then the radius of the circle. It turned out to be a 5.25 inch diameter, with a 2 and 5/8 inch radius on each side of the center. I needed to mount the fly wheel cutter into the drill press chuck as shown, so that I could mark the center for the drill bit:

 The very next thing you need to do is setup the belts on your drill press, or reduce your speed adjustment to achieve the absolute lowest RPM that you can achieve with your drill press. With mine being a standard large floor model press, I was able to adjust the belts to get it down to 250 RPM.

Next was the task of setting up the cutter as precisely as possible for the radius. Safety point - the point on end of the cutter is EXTREMELY sharp - do not mess around with this - keep your fingers clear of it at all times, and keep the drill press unplugged until you are ready to use it, and all adjustments have been completed.The tool comes with a set of Allen head screws to adjust the radius of the cutter from the center of the pilot bit, which is a 1/4 inch drill bit. IN addition, a second Allen screw is used to adjust the depth of the cutter compared to the depth of the pilot bit. The instructions say to set the cutter depth 1/4 inch higher than the tip of the pilot bit - the idea being that the pilot bit drills the hole in the center to provide a stable grip for the cutter to retain the set radius without wandering. A drill board underneath the part to be cut is also ESSENTIAL for this to work properly.

Another Safety tip: When the cutter makes contact with the metal, it emits a very loud and uncomfortable squeal. it sounds kind of like when a kid scrapes his finger nails across a blackboard - yup - it's just about that bad. So, I highly recommend that you wear ear muffs during this operation as well as safety glasses and leather gloves. 

With everything positioned correctly, and the worked clamped down properly, you then dawn some thick heavy work gloves and keep all hands clear of the work piece until the drill is stopped. You start bringing the pilot bit down until it engages, and then you SLOWLY apply more pressure on the press to keep bringing the cutting bit down onto the metal. Check the cut as it engages and make sure that it does not wander from the marks that you had drawn earlier.If the part moves, or worse yet, if it becomes hung, make sure you stay out of harms way and then pull the plug on the drill press to stop it. Do NOT try to rescue the part from its demise. This is where this tool is absolutely dangerous.  It can take  a piece of metal and turn it into a disemboweling razor knife in a split second, and then it can take that piece of deadly metal and fling it directly at you, which is why you need to keep the drill press at the lowest possible RPM.

Make no mistake, this thing can KILL you in an instant if things start to go awry. So pay attention and take every possible safety precaution before starting the process.

If everything goes according to plan, eventually the cutter will go all the way through the metal, and you can stop the drill press. Then UNPLUG the drill press from the wall. Then and only then should you reach in with gloved hands and remove the part. Here is the new hole in the rib after the operation was complete. Notice the shavings that it creates as it cuts:

That circular piece of metal has a razor edge on it since part of the cut was made against the curvature of the stiffening ring. You could slice meat with it - or your fingers, so again, be careful when you handle this thing.

Next is a pic of the rib with its new hole, with the reinforcement bracket positioned over it, both types of access cover plates, with and without the sender and fuel pickup line hardware holes, and a cork gasket.

A couple more things I learned from my research and several phone calls to Vans - throw the cork gasket away and DO NOT USE IT  - PERIOD! Over time the gasket becomes saturated with fuel and WILL START LEAKING - so NO CORK GASKET! I also learned that the mounting flange of the fuel float sender unit has a rubber gasket that you also SHOULD NOT USE, as it starts leaking as well. As I stated earlier, my left tank will use the plate on the left, and my right tank will use the standard plate on the right.
SO that is how you setup and use a fly wheel cutter tool in a drill press to cut very large, precise holes in metal. Now I just have to debur the edges of the rib a bit and continue with the remaining fuel tank assembly tasks.

On another note, There is also a trap door with a hinge on it that I need to fabricate. TO do so, Vans told me that I needed to use the hinge material from the flap hinges that came with the wing kit. Since these hinges were 6 feet long, I had stored them up on my wide garage shelf with the other long parts like the angles used for the longerons for the fuselage that are 15 feet long. The problem was that I had to get to them on the shelf, which was not exactly "easy." I had to move a bunch of stuff off the shelf first in order to get to the hinges. I finally got them down, and spent a large part of today, cleaning up the garage and putting everything back in its place.

More on the trap door fabrication tomorrow.

KPR.