The lazy man’s fly cutter

[Sonic EscapeParticipant @sonicescape38234]

I’ve wanted to make a fly cutter for a long time but never had the time. Once again, it turns out that laziness leads to optimal solutions. I have a faceplate with a MT3 mount for a 125mm chuck, which I use on my lathe. This morning, it occurred to me to move the chuck to the milling machine and clamp a cutter into it. It works really well!

 

[Clive FosterParticipant @clivefoster55965]

The flywheel effect of the heavy chuck probably improves finish and keeps the cutter more stable as it inters the cut. Which would seem to be an advantage on smaller machines.

Not completely convinced about pull out resistance with the cutter clamped canter wise between the three jaws tho’.

Clive

[BazParticipant @baz89810]

Same as Clive, not totally convinced about clamping tool like that but top marks for the flywheel effect of the chuck.

[Dave HalfordParticipant @davehalford22513]

I’m not totally convinced that dodge could be used on a machine with plastic gears very often given the inertia involved.

[Robert Atkinson 2Participant @robertatkinson2]

I’d be concerned about the cutter being flung out too. A bit of round bar with an angled slot milled in it and two or 3 set  screws would not be hard to make and more secure.

Robert.

[Andrew CrowParticipant @andrewcrow91475]

Before I had a milling machine I used that method on lathe with the job bolted to the cross slide or vertical slide, never had a problem with the tool coming out of the chuck.

Andy

[JasonBModerator @jasonb]

For the 40 plus years I have been model engineering I have regularly seen that method suggested as a way to hold work in the lathe so don’t see any more risk of a tool flying out as there would be with a workpiece. Many here seem to suggest Spary’s book to beginners and he was up for using that method.

Used that method to grip work a few times myself

As for plastic gears I’m inclined to think the opposite. A lightweight flycutter will stop and start as the tool enters and leaves the cut which loads and unloads the gears. As mentioned by others the innertia in the heavy chuck will go some way to damping out that stop start load.

[Sonic EscapeParticipant @sonicescape38234]

The milling machine is HBM BF28, it has a belt, no gears. So no problem there. I was also suspicious at first about whether it was safe. I never went beyond 400rpm. But it looks like the chuck jaws are biting in the tool. See the two lines.

Also the cutting forces are small. It should be safe. This is a C45 steel cube. Thee feed rate was not optimal. But still the left part feels very smooth. The right half was done with wrong turning direction. And resulted also in a brocken tool tip.

[Clive FosterParticipant @clivefoster55965]

The, very experienced, machinist who introduced me to such canter wise clamping of square or rectangular stock in three jaw chuck was adamant that the material should sit back tight against the chuck body and not project more than the external jaw depth. He said that if that advice was not religiously followed it was certain that a workpiece would self eject sooner or later.

He considered this an undesirable occurrence.

I guess it’s like so many things. You can push the envelope a bit if you know what you are doing and take appropriate care in setting up. Going in all gang ho and willy nilly is asking for trouble. Which may, or may not, ever find you.

For sure its easier to get a secure, well aligned hold when the chuck is in the lathe with a secure base to work against than when its pointing down on a mill spindle or just a loose chuck and arbor.

I’ve only every used the idea for squaring up smallish material or sorting out rodent nibble quality cuts on an end. Always gone fine for me but I made sure to take that extra bit of care setting up and verify tightness after the first three or four cuts. Whether or not I ever encountered things actually working loose has long faded from memory. For sure I’ve never used the technique this century.

Clive

[Tony Pratt 1Participant @tonypratt1]

I personally wouldn’t abuse a fairly new 3 jaw chuck like that but each to their own.

Tony

[JasonB]

On JasonB Said:

For the 40 plus years I have been model engineering I have regularly seen that method suggested as a way to hold work in the lathe so don’t see any more risk of a tool flying out as there would be with a workpiece. Many here seem to suggest Spary’s book to beginners and he was up for using that method.

Used that method to grip work a few times myself

As for plastic gears I’m inclined to think the opposite. A lightweight flycutter will stop and start as the tool enters and leaves the cut which loads and unloads the gears. As mentioned by others the innertia in the heavy chuck will go some way to damping out that stop start load.

I was thinking about the start up not the cut.

[JasonBModerator @jasonb]

I don’t see it as much different to a plastic geared minilathe starting up, they seem to manage that quite a few times without stripping the gears. Probably less load actually, as the toolbit is minimal compared to the possible weight of a large piece of material in the chuck when it is mounted on the lathe.

Although belted I regularly used to use the lathe chuck on the milling head of my Unimat 3 motor and pulley/belt arrangement was exactly the same so no difference in load.

Big chucks are more likely to draw more current on startup so motor/board would be more of a possible area of worry than the gears.

I assume that the chuck used on a smaller plastic geared mill will be in proportion to that shown so 80 to 100mm

[old martParticipant @oldmart]

A left handed lathe tool would enable normal forward spindle rotation. I would be concerned about the sideways uneven loading on the poor chuck.

My effort on the subject of flycutting was a 20mm lefthanded boring bar with a WNMG08 or WNGT08 insert with a 30mm shank to fit in an R8 to er40 collet.

[southernchapParticipant @southernchap]

Eh, you’ll probably be okay…I guess.

However, for the same reason one should not hold an endmill in a lathe chuck to do anything but plunge miling, I’m not sure this is a great idea.

The shank of the lathe tool may well be hardened, the chuck jaws are hardened.

That combination is unlikely to provide a thoroughly secure grip, especially given that the tip of the lathe tool is experiencing forces radial forces when it cuts

Eh, your workshop, your rules, though.

[PeteParticipant @pete41194]

As said, your workshop, your rules.

Even when used for conventional work holding, lathe chucks aren’t immune to permanent damage if the user mistakenly uses an extension on the handle to over tighten the chuck beyond what the design and it’s material limits are. Because of the forces the chuck wasn’t really designed for, that’s not a method I’d want to try myself. Yes your gaining from the extra weight and the fly wheel effect as mentioned, and it’s worked so far. But your most likely losing more just due to the tool tip distance from the spindle bearings.

I bought a set of three different sized fly cutter bodies that weren’t very expensive and worked ok, or at least well enough when I properly sharpened the braised carbide cutting tips on a diamond wheel.

I then bought a commercial fly cutter that uses the replaceable RNMG-43 sized round carbide tips. In my opinion it produces a far better surface finish on almost any material I’ve tried, and is extremely cost effective because the tip can be slightly rotated each time it dulls or rarely might chip the edge. Unfortunately the one I bought doesn’t seem to be available anymore or I’d add a link. But if I was making a fly cutter body, tool tip shank and wanted to use carbide, it’s what I’d choose because it would be well worth the time and effort.

If it will help anyone here, mine has dimensions that might be a bit large for a lot of the more bench top sized mills, but could definitely be scaled down or even use the smallest diameter RNMG-32 tips for anyone with a small mill. Fwiw, mine has a .750″ tool shank, the body is rectangular 1.800″ wide X 2.500″ long, the tool slot offset to put the cutting edge on the tool center line, 1/2″ X 1/2″ tool tip holder X 5″ long. With it looks like 2-3 degrees of additional forward rake on the RNMG tool seat to make the cutting even more positive. And the usual 3 set screws to secure the tip holder at whatever radius it’s set to. I suspect that extra forward rake on the tip seat is why it’s design cuts so easily.

[Andy StopfordParticipant @andystopford50521]

Alternative lazy man’s fly-cutter:

I might try using the round carbide tips, the one above is HSS, and by the second piece of stainless steel it was getting a little past its best.

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