# Fly cutter, or face mill?



## Investigator (Jul 20, 2017)

If I understand correctly, both a fly cutter and a face mill are used to cut a large area.  When would you use one or the other?  What are the differences I need to know?


----------



## Bob Korves (Jul 20, 2017)

Generally speaking, and there are way too many variations to cover them all:

A fly cutter can cover a large and adjustable area per pass. It can leave a very nice finish, though that requires some practice, trial and error, and knowledge.  Fly cutters are not usually best at removing large amounts of material per pass, but can if solidly built and used correctly.  Fly cutters do not generally require lots of power to do their job.  The cutting tools can be high speed or carbide, and can be shop made and ground for many fly cutters.  They can be bought cheaply or can be shop made, and are pretty simple tools.

A face mill has a set diameter.  It uses multiple cutters, so that requires multiple times more power to drive them.  Modern face mills all use carbide insert cutters, as far as I know.  They can remove lots of material quickly if the power is there.  Achieving a good finish can be an issue with these cutters, because the inserts do not necessarily follow one another accurately around the face mill.  That can be from design, type of cutter, accuracy of manufacture, accuracy of inserts, prior damage, etc.  Some face mills have adjustable cutters, which can take some time to get set up all the same, and rigidity may be lessened, but can improve the surface finish.  A lot of work goes into making an accurate and solid face mill, so they can be expensive.  Face mills also often need some speeds and feeds tweaking to get a good finish.  There are many styles of face mills, in different sizes, configurations, and for various intended purposes.  Some are small, with only a couple or a few inserts and can be run on bench top mills.  Some are 8" or more across with lots of inserts.  The larger ones are expensive to buy, expensive to change out a set of cutters, and require a rigid and powerful machine to drive them.  On a larger face mill, some of the inserts can be removed, which reduces the power required, but also usually reduces the surface finish quality, at least at the same speeds and feeds.


----------



## benmychree (Jul 20, 2017)

Another option is the use of shell end mills, a multi tooth, HSS cutter that has a separate shank; they are available from perhaps 1-1/2" diameter up to about 8" diameter, the number of teeth depending on the diameter.  One drawback is that they must be re sharpened when dull, and a tool and cutter grinder is needed, but of course this may be hired out.  I use them for some work, but mainly use carbide face mills, as my mill is heavy enough to make use of them, although there are insert cutters suited to lighter mills like the Bridgeport type, up to perhaps 3" diameter and have integral R-8 shanks and use positive rake triangular inserts, but are not adjustable; need a nicer finish?  take all but one insert out, and you have a fly cutter!


----------



## mikey (Jul 20, 2017)

Investigator said:


> If I understand correctly, both a fly cutter and a face mill are used to cut a large area.  When would you use one or the other?  What are the differences I need to know?



What kind of milling machine do you have?


----------



## benmychree (Jul 20, 2017)

I have a Brown & Sharpe #2 Universal (light type), with the universal all angle milling attachment, universal dividing head, slotting attachment and short lead attachment.


----------



## mikey (Jul 20, 2017)

I meant the OP. 

A light, benchtop mill will not work well with a multi-insert face mill so the choice of tools may be a moot point. For a lighter, low HP mill, a fly cutter will work great.


----------



## Investigator (Jul 20, 2017)

mikey said:


> What kind of milling machine do you have?



Round Column, 2hp Enco


----------



## mikey (Jul 20, 2017)

Okay, you can run a flycutter or a small face mill. I've run both and dislike fiddling with aligning multiple inserts. Seems that one of them always mounts a tiny bit off and that affects the finish. Face mills are useful for hogging off a lot of material but they don't finish well at the speeds my mill will run at. The one I had used 4 inserts so it got expensive. I traded it for a used recurve bow and I think I got the better end of the deal.

Since I normally need a wide swathed cutter to provide a good finish, like when I'm squaring a work piece to begin a project, I prefer a flycutter. I have the Tormach Superfly flycutter and it can hog off a surprising amount of material in a single pass if I need to dimension the piece. Tormach views it as a single-tooth face mill for low HP machines and it will leave a fairly good finish. 

So, I guess it depends on what your needs are. I normally try to start with a work piece close to the dimensions needed so I don't need to hog off a lot of material. For me, a flycutter works well. Sometimes a part of the work will need to have material hogged off and for that I use an end mill but I am thinking of buying a shell mill and holder; they're expensive, though. Face mills for benchtop machines, I think, are not a good option but my experience is limited to the one I had and I leave that subject to others with more experience.


----------



## Wreck™Wreck (Jul 20, 2017)

Bought one of these about 20 years ago for use in a Bridgeport knee mill, great tools for low powered machines. http://www.kristitool.com/shop/b-52-fly-cutter/

They are balanced so you can spin them at ludicrous speed, beware the chips.


----------



## Investigator (Jul 20, 2017)

Wreck™Wreck said:


> They are balanced so you can spin them at ludicrous speed, beware the chips.



Surely not ludicrous speed!


----------



## Investigator (Jul 20, 2017)

looks like I need  to stick with a fly cutter.


----------



## kd4gij (Jul 20, 2017)

I have a 2" face mill that has 5 APKT inserts that I use on my G0704 mill. It leaves a great finish. I can't hog with it.


----------



## pineyfolks (Jul 21, 2017)

I use both. But I have to say that the fly cutter gets used the most. You can use hss, cobalt, or carbide and even insert holders if you have small enough ones. Plus you can sharpen the tool easily and grind whatever profile you like. You can make your own easily from any piece of stock you have laying around.


----------



## Silverbullet (Jul 21, 2017)

I have an array fly cutters made over the years, one has two slots for 3/8" tool bits mounted on opposite sides of the cutter about 3" in diameter. strait up and down worked well on stainless at the time. Experiment make your own , put a stop to just drop in another tool bit.


----------



## Bob Korves (Jul 21, 2017)

Silverbullet said:


> I have an array fly cutters made over the years, one has two slots for 3/8" tool bits mounted on opposite sides of the cutter about 3" in diameter. strait up and down worked well on stainless at the time. Experiment make your own , put a stop to just drop in another tool bit.



Hey, I like the new avatar pic you put up!  Little cutie... Grandpa?


----------

