# Using a Fly Cutter



## oskar (Aug 30, 2018)

What is the purpose of a fly cutter and why use it instead of an endmill?

Thank you

Nicolas


----------



## savarin (Aug 30, 2018)

As someone with no training I will jump in here with my thoughts.
It covers a larger area in one sweep thus hopefully producing a smoother surface.
I used a home made type of fly cutter when surfacing a part for my vertical slide that I would have hated to do with an end mill.
post 5
https://www.hobby-machinist.com/threads/a-vertical-slide-for-a-9x20-lathe.49724/


----------



## MSD0 (Aug 30, 2018)

It’s a surfacing tool and will give you a better surface finish than an end mill.


----------



## oskar (Aug 30, 2018)

Thank you both. Savarin the project you did on that link is amazing and I admire your knowledge 

Nicolas


----------



## stupoty (Aug 30, 2018)

oskar said:


> What is the purpose of a fly cutter and why use it instead of an endmill?
> 
> Thank you
> 
> Nicolas




Fly cutters are very cheep to run if you use HSS tool, as the cutter can be easily sharpened when compared to an insert based face mill for example.

Stu


----------



## GrayTech (Aug 30, 2018)

With the right cutter and light cuts a fly cutter can also be used to enlarge holes in a pinch. 

Sent from my H3123 using Tapatalk


----------



## MSD0 (Aug 30, 2018)

stupoty said:


> Fly cutters are very cheep to run if you use HSS tool, as the cutter can be easily sharpened when compared to an insert based face mill for example.
> 
> Stu


You can also use a fly cutter (single point) on smaller, less powerful machines that would struggle with a face mill.


----------



## BaronJ (Aug 30, 2018)

Hi Guys,

A fly cutter is a very very useful tool, they do however have some failings,  vibration, due to an out of balance condition, chatter due to the toolbit not being rigid enough.

Here are some pictures of my home brew fly cutters.


This works OK, however it suffers from too long a shaft, and too much cutter stick out.  This one was intended for deep hole work on a 50 mm bore.




This one was made and used to clean a forked end and machine to size.  Sorry about the focus.



This one was made for surfacing and getting a relatively large area machined in one go.  It also has the advantage of balance, rigidity and depth of cut. I can take a 40 thou cut in steel without any chatter.  This type also has the advantage of mass.

They are also very easy to make.  The one above is 3" inches in diameter and 20 mm thick on a 20 mm X 50 mm shaft.  The tool bit is a piece of square HSS lathe tool.


----------



## stupoty (Aug 30, 2018)

MSD0 said:


> You can also use a fly cutter (single point) on smaller, less powerful machines that would struggle with a face mill.



Thats true too, I'm not sure if a face mill is better at when its hitting the edge or a hole in a thin part, Ive had a little chatter at edges when fly cutting, but I have a smaller mill so I tend not to get into face mills as you say HP and all that.


----------



## P. Waller (Aug 30, 2018)

Use a fly cutter in a wobbly machine such as a Bridgeport R8 knee mill.
If you are knocking a good deal of material off of a flat part and have time constraints use a face mill, this will not likely produce the hobbyist finish results that you require, a fly cutter may be slow but is more likely to produce the uniform finish that you expect.


----------



## MSD0 (Aug 30, 2018)

stupoty said:


> Thats true too, I'm not sure if a face mill is better at when its hitting the edge or a hole in a thin part, Ive had a little chatter at edges when fly cutting, but I have a smaller mill so I tend not to get into face mills as you say HP and all that.


Yeah, I was thinking more of a mini mill or something where you can run it slow enough to use a fly cutter.


----------



## MSD0 (Aug 30, 2018)

BaronJ said:


> Hi Guys,
> 
> A fly cutter is a very very useful tool, they do however have some failings,  vibration, due to an out of balance condition, chatter due to the toolbit not being rigid enough.
> 
> ...


I never thought of making one like that (the second one on the bottom). Pretty cool.


----------



## mikey (Aug 30, 2018)

I've always thought of a fly cutter as a flattening device. I use it primarily for squaring stock in prep for milling projects. It does transfer the angle of the spindle to the work, though, so being in tram matters.

I've come to prefer inserted carbide fly cutters over those that use HSS; they last far longer in use and a sharp cutter is a minute away. Carbide allows you to run at much higher speeds and produces a pretty nice finish. They also allow for some decent stock reduction over a fairly large area in a very short amount of time so they can be used to dimension stock as well. Depending on how the insert is oriented, some fly cutters allow you to cut to a ledge/shoulder and that can be really handy at times.

On my little Sherline 5400, I use their inserted carbide flycutter. This is essentially a single-flute face mill intended for use in the Sherline mill. It will cut to a shoulder and will surface, flatten and dimension most machinable materials and it leaves a beautiful finish. It only cuts a 1-1/8" swath so that is somewhat limiting but still, this is easily one of the best tools Sherline makes; their fly cutter that uses a HSS or brazed carbide tool does not even come close. An insert seems to last forever in this tool.

On my RF-31, I use the Tormach Superfly and that one is also pretty okay, too. It will not cut to a shoulder but does allow me to fly cut a 6" work piece. It can take at least a 0.075" deep cut in aluminum at high speed without even slowing down the motor so I sort of like it. I have also adapted a Sherline flycutter for use on the RF-31 and use it to cut shoulders ... I really like this tool.


----------



## BaronJ (Aug 31, 2018)

Hi Guys,

Here are some more pictures:






These pictures are of a dovetail slide that I made for tool grinding.  Every surface in these pictures, including the dovetail was done using a fly cutter.  The fly cutter used to cut the dovetail was ground at 45 degrees, and was similar to the one in my first picture but much shorter and more rigid.  Notice the sharp corners.  I had to stone them off to get a smooth travel without binding.  The brass bolt in the side is to lock the slide in use.


----------



## oskar (Aug 31, 2018)

Very informative, my thanks to all


----------



## 007 (Sep 16, 2018)

At the job, sometimes the part to be machined is of such a shape that you can't clamp it well enough. Sometimes the part is thin or it's a weird shaped weldment etc. I use a face mill and remove all the inserts but one. Then with a sharp insert I take a thou or two with the rpm turned up a little more with a slow feed will reduce or omit completely the chatter on the part. It really helps to make a nice finish.


----------



## BaronJ (Sep 16, 2018)

Hi Guys,

Yes it is surprising just how versatile a fly cutter can be, not just for facing.  Careful consideration of the job in hand can produce some useful solutions.



Sorry about the slight out of focus.


This is the job that I was doing.  Squaring up and sizing the slot width.


----------



## Hit-N-Miss Tom (Oct 15, 2018)

BaronJ said:


> Hi Guys,
> 
> A fly cutter is a very very useful tool, they do however have some failings,  vibration, due to an out of balance condition, chatter due to the toolbit not being rigid enough.
> 
> ...


Like your ideas with the various cutters - think I will be adding one or two to my tools. Thanks!


----------



## BaronJ (Oct 15, 2018)

Hi Tom,

If you do decide to make one, please post pictures and let me know.  Its nice to hear of people using my ideas.


----------

