# Fly cutter help!



## FIXIT (Jan 17, 2011)

Hi at this moment I'm making my third small engine and Ive been folowing all the builds here with intrest and looking at the fantastic finish you chaps achieve i am trying to 'up my game' with regard to finish etc.

Here is where I'm up to






I've read books and posts on tools and tool sharpening but can't find any thing on
fly cutters

I am using a 3/16 cutter and would appreciate some pointers as how it should be sharpend.
or direct me to a post.
Also Witch is the preferred way to cut (feed in or drag it across) ???

this is my result up til now





Lots of regard and thanks
 steve


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## t_ottoboni (Jan 17, 2011)

I think two things are very important to archive a decent finish using a fly cutter: tramming the mill, and putting a radius at the tip of the cutting tool.
The radius don't need to be small, as a large radius will help to eliminate tool marks in the surface.
Take a loot at this: http://madmodder.net/index.php?topic=850.15


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## FIXIT (Jan 17, 2011)

Many thanks for the reply t-ottoboni,


Now why didn't i think of looking at 'the other site'

I think that post you sent me to will answer all my questions

many thanks Steve


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## Omnimill (Jan 21, 2011)

It was also covered here Steve:

http://www.homemodelenginemachinist.com/index.php?topic=9941.0

Vic.


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## picclock (Jan 21, 2011)

I've made one of the 'bogs' shaped cutters but I found that it blunted really quickly. Finish on Aluminium was OK, on steel it was not good, 5-10 thou cuts. I tried an indexable carbide lathe tool which seemed to hold up much better. The tool tip radius is only 2mm but the finish is smoother, even on aluminium. On steel it comes out like a mirror.

It may be that the tool steel I had was not that great, but having said that the ease and better finish of an indexable tool is a winner for me. The insert is a DCMT 0702, and the tool is the Glanze 3/8 (almost 10mm) one. 

Best Regards

picclock


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## Omnimill (Jan 21, 2011)

Must say I'm surprised, I've tried insert tooling (little Hogger set) on my mill and not found it anywhere near as good as a flycutter.

Vic.


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## arnoldb (Jan 21, 2011)

Some notes from my own flycutting experiences - for what it's worth.

Flycutting is normally a "finishing" process, and for that purpose with a small depth of cut (0.1mm/5 thou or less) I have not found anything to beat Bogs's method with a sharp HSS cutter, a suitable spindle speed, and sensible feed rates. These all depend on the material being machined - and speeds need to be on the slow side - its very easy to heat up a HSS bit too quickly and ruin the cutting edge. 

With a carbide tipped tool in the flycutter, I found I can actually hog away a lot of metal very quickly (and make a huge mess with chips in the process :-X) - on my mill at up to 1mm depth of cut on aluminium/brass/HRS - and on HRS, it even leaves a mostly acceptable finish, but nowhere near as nice as what I get from a finishing pass with HSS.

I've come to use a combination of both the cutters; hog away with the carbide tool to near-size, and then do a single finishing pass (0.02mm/.001") with a sharply honed HSS toolbit to get a (IMO) nice finish. This has so far worked for me on Ali, Brass, Bronze, HRS, cast iron and silver steel. I have not machined Stainless or any of the fancy-numbered alloys available overseas though, so take the above with a pinch of salt 

What really helps is learning how all the things come together; material, depth of cut, feed rates, spindle speed, getting to know how your mill (or lathe) behaves with the material. I subscribe to L.H. Sparey's advice of "If in doubt, slow down"; makes for less broken toolbits in a home shop environment 

And yes, the mill tramming needs to be dead nuts, and the spindle well adjusted; I got instant better results from all milling operations after adjusting play out of my mill's spindle!

Regards, Arnold


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## Dave G (Jan 22, 2011)

We once had a fellow who had a fly cutter fly by his head, just missing him by inches, when the cutter separated from the shank in the spindle (broken in two pieces). He was using it to remove alot of stock and not for finishing like they should be used. Fly cutters were banned in our shop after this incident and if caught using one you were sent home for the remainder of the day. I think their use for finishing is fine but be careful. Dave


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## Tin Falcon (Jan 22, 2011)

I like fly cutters. the cutters are cheap and easily ground. Easily shop made. 
they do have there limits . single point cutter so slower than commercial insert tools. sometimes unbalanced so may limit spindle speed. 
too much tool sticking out the back can damage work or your hand if you forget it is there. 
Great tool but do be careful. 
tin


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## Blogwitch (Jan 22, 2011)

Arnold has made a very good point about tram.

If your tram is out, and I am talking about the normal X axis, even by a tiny amount, you are creating either a curved or angled face on your work, depending which axis you are cutting in.

The flycutter, if the mill is out of tram, will create a concave surface across the whole face if cutting in the X axis or an angled cut if in the Y. 

This also applies to normal cutters as well, magnified, in the X will be a series of concave grooves or in the Y, like a saw tooth effect. 

Just think about it, look at leading or trailing edges of the cutter face when it is not parallel to the job surface.

With regards to the shape I use for my flycutters. I will regularly take a roughing metal removal 0.100" (2.5mm) cut on softish non ferrous metals and still end up with a very acceptable finish. For a mirror finish, I will use at most a 0.010" (0.25mm) cut. For ferrous work, you must consider that you are using a razor sharp HSS single point tool, and once you get any harder than already skinned cast iron or mild steel then your tooling will become dull very quickly, in fact, you usually end up with a flat on the cutting curved face.

You have to use common sense when using a flycutter with harder materials.


Bogs


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## FIXIT (Jan 22, 2011)

Thanks for all the replies chaps i will take all the advice/warnings seriously.

I sharpend a cutter to Bogs drawing and with great success on a 1" brass block
 and managed to square it to 1/2 thou over the length but it was very slightly
concave on the width as Bogs had warned so i will look at that.


cheers Steve


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