any reasons not to use a flycutter as hole saw?

Add wood clamped above and below and it's ok. But without something on top it can grab badly.

Right. I've had some luck by grinding the cutter very sharp, but with a negative rake.

I've also had one grab, break, and send a sharp projectile out of my drillpress at high velocity.

A trepanning tool. The pics on these pages show a few of the variations.

If you search on trepanning be prepared for the whackos who promote drilling holes in your head as a path to enlightenment.

I can think of some folks who could really use that sort of help.

***ALERT****ALERT***ALERT***!!!! Government panel recommends not cutting holes in your head using a mill. ***ALERT****ALERT***ALERT***!!!!

That should get them started on a self-help program.

A mill on backgears (if available) is certainly the best bet (lower-velocity), and the fly cutter was still the tool that was most warned against in our shop course. All that open space, and things to hook you and drag you in. Most of the old guys had some experience with the reasons to be careful of it, and did not care to go there again. If it could be done another way, we were strongly encouraged to do it another way. If it _had_ to be done with a fly cutter, it was to be done with extra vigilance and caution, and the hand not on the quill feed in the pocket. If power feed was available, stepping away from the machine was advised.

It might be (or seem to be) overkill, but it was pretty clear the old guys had seen things they did not care to see again, so that was how that shop operated.

A holesaw, even a set of holesaws, is cheaper than a trip to the hospital.

Agreed. The old guys were smart. Fly cutters are foul tools, and the more massive and rigid they appear, the more inclined users are to load them up until they become shrapnel.

The so-called "balanced" flycutters, with two cutters 180 deg. apart, have their own problems.

FWIW, for small jobs, I make my own hole saws. I've turned them out from barstock on the lathe (too much work), and I've made them out of pieces of tubing. Then file teeth, set them with a punch, and case-harden.

They aren't great, but I made one once that let me trepan a 1" hole through 8" of end-grain oak, where I had to preserve a core of steel rod that had been epoxied on to a 2" round of oak.

Trepanning cutter. You grind your own from blank HSS bits. :

I would rough out the hole with a 2" hole saw in a 1/2" variable speed drill first, and only shave it to final size on the Sherline. Holes that big are a challenge on my 3/4 HP, 700 Lb Clausing mill at its lowest speed of 180 RPM. jsw

5 on each hand.

Ayup. Be "sudden stop" or "madly spinning Blade of Death" without the wood.

Gunner

The methodology of the left has always been:

1. Lie
2. Repeat the lie as many times as possible
3. Have as many people repeat the lie as often as possible
4. Eventually, the uninformed believe the lie
5. The lie will then be made into some form oflaw
6. Then everyone must conform to the lie

Trepanning.

Suggest drill a small hole in the center of the slug and secure it to a sacrificial tooling plate for safety.

Lots of ways that's not so hot. Holders I've seen used that way usually have the cutter at an angle rather than 90 degres to the axis. I've got two sizes of this style:

that I've used for cutting discs and holes. Replace the center drill with a piece of rod to keep from wallowing the hole out. Definitely needs a rigid drill press for powered use. I have used it by hand(unpowered) for really thin stock. Hole saws are good, but only if you want the size hole that they produce. Anything in-between is a pain to enlarge. Backing up with wood is a good idea no matter what you use if you're cutting thin stock.

Stan

See:

and for moving pictures.

There's an existing hole 39mm in diameter, which has to be enlarged to

58mm. The metric nonsense is because the plate itself is for holding a photographic enlarger lens.

Lots of people trash these things with a file, so I set it up on the little mill on top of some parallels and clamped it down, and looked at it and it just gave off that "this can't be safe" vibe. The plate is about 6" in diameter, so it's too big for my lathe chuck. It might be possible to mount it to something thicker and then attach that to the faceplate and just enlarge the hole to the correct diameter. I don't know enough about all of this to say this is better or worse than trying to flycut into something that flexes.

If its only 6", stick it down with some GOOD double sided tape on a piece of MDF.

Gunner

The methodology of the left has always been:

1. Lie
2. Repeat the lie as many times as possible
3. Have as many people repeat the lie as often as possible
4. Eventually, the uninformed believe the lie
5. The lie will then be made into some form oflaw
6. Then everyone must conform to the lie

You really need to set that baby up on a cnc mill and program the cut with a small end mill.

Buy a 2-5/16" hole saw, chuck it up in a hand drill, and hold the outside against your belt sander at a gentle angle until it becomes a 58 mm hole saw at the tip of the teeth :-).

I've got one of these little things

for size, the arbot is morse #1 and drawbolt is 1/4-20

Is there a reason NOT to use it as hole saw of sorts and cut holes in aluminum sheet that's just a tad under 1/16" thick?

The bevels on the cutter seem fine for making a 2.25" hole and won't hit the OD or anything like that, but I suspect it's going to be chatter city with the amount of surface that's being cut at the flat-ish cone shape.

Is there a correct tool or name for a cutter that would fit that holder that has a better profile, sort of like a curved parting blade?

If you can sandwich it between plywood sheets on the lathe faceplate that would be the better answer because you can choose a cutting rate low enough to not yank it out of position. I'd saw out the largest plywood disk that clears the ways and make it a semipermanent lathe fixture, perhaps with a shallow cutout in the back to center it on the faceplate. Baltic birch plywood thick enough for woodscrews is nice for this. Be sure to smooth the outer edge so it can't catch clothing.

The picture that was shown was a hole enlarging unit. A hole cutting unit has a right angle cutting edge. When it is turning (e.g. drill press / mill ) and coming down on sheet metal the drill or pilot keeps the unit centered and the tip of the cutter starts to scribe a circle. As more pressure is applied, it cuts the scribe line (from the point) into a wider slot and cuts through. Normally one side first. The sheet / box / etc must be clamped and (if I can also using the column as a stop) as one must slowly continue through the sheet.

Consider a ruler with one end as a bearing point and the 12 inch end has a pencil. Rotate the ruler and the pencil scribes a 12" radius if bearing is at zero end.

The cutters are typically V shaped or a chisel faced or U faced cutter.

I've used them on steel chassis and Aluminum ones - for meters and sockets. I have a massive set of Greenlee punches for Al.

I've cut plexiglass - under water to keep it cold so it won't melt...

Mart> Jim Wilk>>

I went ahead and just cut the hole yesterday. I clamped the aluminum plate on plywood on the mill and cut into it in steps with the flycutter.

It sure took a long time to cut, and the plate got pretty warm. This stuff in the dusty section of the local hardware store called "A-9" aluminum cutting and tapping fluid seemed to help a bit. It's some sort of green liquid that looks like dish detergent that smells less awful than kerosene.

Cutting internal 58x0.75mm metric threads on another aluminum ring made from a scrap worked the first time, fitting the lense itself with no problems.

There were some problems with chucking up a fairly thin metal disk and not squeezing it hard enough to curl up like a wave spring though.