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Cutting the 6” hole, question?

JeremyL

Well Known Member
So I’m a couple weeks out from having to make the 6” hole cut in the fuel tank rib. I have heard all the stories of using the fly cutter and how it can murder you if not careful. So my question is, is there any reason a 6” hole “saw” “cutter” cannot be used in place of the fly cutter? It is thin aluminum, so I’m just curious if anyone has tried it or has experience. Oh and yes before anyone says it, I know if you take your time and secure the piece to the drill press and use a slow RPM, the fly cutter will work well. Thanks guys. I tried to post a web link for reference of a possible candidate.
https://www.harborfreight.com/6-in-bi-metal-hole-saw-57904.html
 
Well, 4-inch hole cutter was no problem...

Needed a 4 inch hole in a .032 thick skin. While I'd used a hand drill and did
3 inch holes successfully before, the larger 4 inch hole scared me. So I finally got around to buying a used drill press off Craigslist, and one of those HF hole saws. Great results.

This will show if your drill press table is precisely aligned, but even then no problem. I used 420 rpm setting as I recall, AND for sure use a cutting oil. I see no reason 6 inch hole saw would not work, but have not personally done that one.
 
Sandwich

Sorry about the quality of this pic - it was taken with a Polaroid (remember them?) in 1986 - but it shows the basic idea of "sandwiching" the rib web between two pieces of plywood to help eliminate the possibility of "hooking" an exposed edge when cutting.

This is nothing new, but I just thought I'd bring to your attention.

YMMV - and probably will.

HFS

Sorry about the orientation - the pic shows vertical in my documents file?
 

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hole saw

I drilled three 6" access holes in the rear baffle of my port tank with a hand drill and a 6" hole saw without drama. All worked fine. Just take your time and don't use a lot of force.
Ed
 
Use a “duct hole cutter”, find an hvac sheetmetal installer and borrow his or let him cut your hole for you.
 
I have cut holes using a hole saw in a drill running in reverse direction. It take a bit longer time but it cuts clean and without issues.
 
I used the fly cutter in a drill press I bought. It did the trick. Just take your time it might not cut all the way through immediately. And clamp the rib down tightly.
 
I used a harbor freight hole saw, the trick is to sand the entire outer edge of the hole saw smooth. It then cuts a very clean hole even with a hand held drill.
 
I used a Malco HC1, which worked nicely. A bit of a rough edge but plenty safe. It's essentially a guided router that attaches to a drill motor. Hint, drill the center hole and put a center post (cut-down bolt) through the part into a piece or wood. Clamp the part and wood down and have at it. After, finish with a sanding drum.

Dave
 
the trick is to sand the entire outer edge of the hole saw smooth. It then cuts a very clean hole even with a hand held drill.

^^^
This

I did a one year stint as a helicopter mechanic and in that time I did 3 air conditioning installations on brand new Eurocopter AS350s. What is that about a 2-3 million dollar ship? Anyways...one of the first steps was to take an electric drill and chuck-up a 6 inch hole saw and drill a big hole in the tail boom. Talk about stress. However, everything worked out fine and this was before I knew about the above-mentioned trick. Yes, take a grinder and sander and remove the portion of the teeth that stick outward from center. There was tech article in one of the flying mags awhile ago about doing this.

Good luck and start on a practice piece.:D
 
A Sheetmetal hole cutter is worth the investment. I cut all of my holes in two tanks in a matter of minutes. There is almost no risk of screwing up like there is with a fly cutter or a hole saw.

https://www.amazon.com/Malco-HC1-2-...6&sr=1-1-7d9bfb42-6e38-4445-b604-42cab39e191b

You will need to cut the back 1/2 off of the tool handle so it fits inside of the tank flange. These use to sell for like $12. I guess they found out that they are an aircraft tool...
 
My fly-cutter has worked countless times in my drill press set at it’s lowest RPM (220) and pressing very slowly on the cut. Make sure you clamp the piece to the table securely with a piece of plywood underneath.
 
I think you want a 5" hole. The cover plates need some overlap (1" larger perimeter). I used the Harbor Freight hole saw set which has the largest one as 5". Works fine. You will need to file the hole edges and smooth.
 
My fly-cutter has worked countless times in my drill press set at it’s lowest RPM (220) and pressing very slowly on the cut. Make sure you clamp the piece to the table securely with a piece of plywood underneath.

Ditto, I love my fly cutter. I was invaluable during my -6A build. Just clamp your work well and go slow.
 
Oh man I had forgotten that little piece of drama. The fly-cutter is easily the most dangerous tool in the shop, but it works wonderfully when used correctly.
 
I suppose you can use a hole saw, but the fly cutter isn't so scary as all that, as long as proper procedure is followed. Back in the day before everything was pre-cut, cutting many many lightening holes with a fly-cutter was done just as a matter of course. I also used it for the round holes in my original steam-gauge panel (.063). All fingers still intact!
 
I just cut a 5” hole in my 12 tank with a fly cutter and my de Walt 20V hand drill. Took it slow and it cut just fine in about 20 seconds. I pre drilled the pilot hole to the same size as the fly cutter pilot. I have a lot of respect for the finger/ fly cutter. Make sure your cutter blade is razor sharp
 
Excellent! Thank you all for the replies and pointers, especially the bit about sanding the teeth on the hole saw down. I will be giving this a try for sure. Just to verify, I have to sand the teeth off that point outwards, correct?
 
Just to verify, I have to sand the teeth off that point outwards, correct?

That's the idea. Some teeth turn inwards and some outwards and that creates the kerf. (the width of the cut to help clear the debris) No need for the portion of the teeth that turn out from the center of the cut and the result is less "grabbing" of the hole saw. In other words when you are done, the outside diameter of the hole saw will be continuous from the bottom to the top. The same won't be said for the inside diameter.
Good luck
 
That's the idea. Some teeth turn inwards and some outwards and that creates the kerf. (the width of the cut to help clear the debris) No need for the portion of the teeth that turn out from the center of the cut and the result is less "grabbing" of the hole saw. In other words when you are done, the outside diameter of the hole saw will be continuous from the bottom to the top. The same won't be said for the inside diameter.
Good luck

Thank you!!
 
i am amazed that nobody has mentioned the second most important part of using a fly cutter (first is good clamping and a slow feed) the second is LUBE, it does wonders for keeping the bit from biting in.

bob burns
RV-4 N82RB
 
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