Is the MAX diameter of flycutter circumference the same as "Max. Face Milling Capacity" for a bench mill?

[maxime.levesque]

The "Max. face milling capacity" of my bench mill is 76mm

Does the mill have the same flycutting circumference limit ?

 

[DavidR8]

Typically not because a flycutter is a single point tool so much less demanding of the machine.

 

[Shotgun]

I'm not sure where the circumference enters into the picture, but I would think that the only limit to flycutter size would be the distance between your spindle and the column. I guess you could go overboard and have really long torque arms that would open the door to flexing. . . but, that would be a ridiculously sized flycutter.

I also have no idea why the manufacturer would set a 76mm face mill limit. Maybe they feel that it is the maximum cut the mill can sustain in some unspecified material. If I used a 4" facemill on 2" wide stock, is the manufacturer going to detect it and send someone out to issue a citation? Is that 3" maximum for wood, aluminum, cast iron, steel or stainless? Most likely, it is just some marketing BS.

 

[maxime.levesque]

I'm not sure where the circumference enters into the picture,

The flycutter has a cutting tip that revolves in a circle, that's the circumference I'm talking about.

I also have no idea why the manufacturer would set a 76mm face mill limit. Maybe they feel that it is the maximum cut the mill can sustain in some unspecified material. If I used a 4" facemill on 2" wide stock, is the manufacturer going to detect it and send someone out to issue a citation? Is that 3" maximum for wood, aluminum, cast iron, steel or stainless? Most likely, it is just some marketing BS.

Agreed that it's "ball park" estimate, might as well specify nothing than saying a meaningless number.

I think it's more "ass covering" than marketing, if you "under promise", it's easier for a manufacturer to say they have delivered on their promise.

 

[maxime.levesque]

Perhaps I should ask this question instead: what is the largest flycuting diameter that can/should be done on a PM-30MV ?

I ask because I'd like to order one of these flycutters: https://www.aliexpress.us/item/3256...05005407998571&gatewayAdapt=glo2usa4itemAdapt

 

[DavidR8]

I'd be comfortable using a 70mm diameter flycutter if it was well balanced.

 

[Cadillac]

Your max face mill size compared to machine is more about available horse power to use a 76mm tool. Your fly cutter diameter doesn’t need horse power. Your limited by table size and diameter. You have a 4 inch fly cutter and a part 12” long you need at least 16” of table travel. Personally I’d want 20” of travel so your tool comes off the piece on both sides. Make sense?

 

[Shotgun]

The flycutter has a cutting tip that revolves in a circle, that's the circumference I'm talking about.

Yes. But, that measurement isn't important.
It is the radius from the spindle center to the cutting tip that determines the torque required to push the cutter through the stock. Generally, you can get all the torque you need by dropping into back gear. So, that leaves you with the limitation that @Cadillac pointed out (is there enough table movement to get your stock under the cutting tip). For an example of oversized flycutters

 

[682bear]

The bigger the flycutter, the more of a beating your spindle bearings take.

With a face mill, you have more than one point of contact with the work, so the forces are more constant. With a flycutter, the single cutting point makes the cutting forces fluctuate... not to mention the 'shock' everytime that point enters the edge of the part. Bigger diameters multiply those forces.

I worked with an older guy years ago that fabricated a 12" flycutter to surface mold plates. Within a few weeks, he destroyed the spindle bearings in a milling machine that was a much heavier machine than a Bridgeport... maybe a Makino? I don't remember...

-Bear

 

[Larry$]

Fly cutter: I've used a homemade boring bar in the boring head horizontal port to fly cut large surfaces. I adjust it to match the width of the part for a single pass and take it easy on depth & speed. Grind the tool for a shear cut.