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Fly Cutting

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Graeme Barton28/09/2010 04:39:57
11 forum posts
Hi there,
Need some help as struggling to get any kind of decent finish with the fly cutter i'm trying to use. I've never used one before so it's likely i'm off the mark
Speed 200 rpm
Max Dia. Cutter 60mm
Auto traverse of the milling table slowly
Depth of cut 0.2mm
 
The mill is quite a big chunky lump looking kind of similar to a Bridgeport but is of far east origin. I have the 50x50 steel secured a vice on the table. As well as the cutter giving a poor finish it seems to be cutting on both sides- twice per revolution. I thought that this might be because the milling head wasn't exactly spot on perpindicular but it does the same no matter what way i traverse the table.
 
Any hints, tips, tool sharpening info would be much appreciated
ta
Graeme 
DavoJ28/09/2010 06:47:34
9 forum posts
Here is a good sorce of info
 
Dave
Michael Cox 128/09/2010 08:52:15
555 forum posts
27 photos
Hi Graeme,
It is quite normal for the tool to cut on both sides since it describes a circle parallel to the workpiece.
The tool should be ground like a right hand lathe cutting tool with a slight radius at the tip.
I would run at a lower speed than 200 rpm (around 50-100 rpm). For a good finish reduce the cutting depth to around 0.05 mm, use plenty of lubricant and make sure that the tool is realy sharp.
I hope this helps.
Mike
 
ady28/09/2010 09:48:16
612 forum posts
50 photos
I haven't done a lot of flycutting but I've found it to be an extremely violent process, unlike the beautiful art of turning.
 
Tool shape, sharpness, speed, stiffness, direction of cut, everything has to be experimented with to find the best result/least violent solution.
 
If you can cut aluminium slowly, under high torque, you can completely eliminate the anodising effect which occurs when it gets too hot.
Cutting slowly under good stiffness seems to be the way for a general amateur.
Buy a few good cutting tools and study their profiles, you can pick up cheapies on fleabay.
 
When I was reading Spareys book it ocurred to me that being a neighbour of his wouldn't have been much fun, some of his milling/flycutting setups must have made one heck of a racket.

Edited By ady on 28/09/2010 09:49:42

Andrew Johnston28/09/2010 11:41:45
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7061 forum posts
719 photos
A cutter diameter of 60mm and 200rpm gives about 124ft/min cutting speed. About right for steel, although given the intermittent nature of the cut a slightly slower rpm might be prudent. Tool sharpness is important, it also needs a radius on the tip. Think about turning, you wouldn't necessarily get a good finish with a sharp point on the tool. Also don't feed too slowly, the tool still needs to cut, rather than rub, on each pass.
 
Flycutters always cut on both edges; it's a fact of life. Even if the mill head is perfectly trammed there are issues to do with tool and holder deflections.
 
The material itself can also have an effect on the finish obtained. On aluminium I got a mirror finish on a piece of scrap (probably 7075) and a much poorer finish on 6082.
 
Regards,
 
Andrew
Bogstandard28/09/2010 20:33:42
263 forum posts
This afternoon I was flycutting an ali block
 
Using the cutter described in DavoJ's post above, I was running at 1200 RPM and removing 0.100" (2.5mm) at a time, and still getting a surface finish that was good enough to not need smoothing off, in fact it was almost mirror like. I would turn that down to about 600 RPM and a cut of 0.050" when using softish steels.
 
I do have a very rigid mill, and on the smaller less rigid ones, you will have to make adjustments to suit.
 
There are too many myths surrounding fly cutting, tiny cuts, very slow feeds etc.
 
If you have a good razor sharp round nosed tool, your machine should tell you what your limits are.
It is very similar to parting off on the lathe, it is just another machining operation with no black arts involved. Just the right tool for the job, and knowing how to use it correctly.
 
That comes by looking at what is happening on your machining table, as no two people do things exactly the same way, and no two machines will cut the same.
 
All we can do is show what works for us, and hopefully you can pick up some tips to find your own solutions.
 
 
Bogs
ady28/09/2010 21:53:49
612 forum posts
50 photos
It's not even close to parting off imo.
Parting off is a doddle once you suss the geometrics.
 
Fly cutting involves an intermittent blow.

Edited By ady on 28/09/2010 22:03:19

Bogstandard28/09/2010 23:52:09
263 forum posts
Ady,
 
The only reason I compared the two is because a lot of people have trouble with them both, not by the way the two systems work.
 
Whenever I have visitors to my shop, they always invariably turn to discussing small diameter fly cutting.
I usually have no trouble cutting up to a 6" sweep. Over that, vibration usually starts to rear it's ugly head, so a slowdown of feed is normally called for. But that is only due to the flycutter flimsy design, with a tool sticking out of the side at an angle..
 
So with no special setting up, I just wack the cutter into the spindle, jaw up a lump of scrap and show just how easy it really is. In fact the faster you go, usually, the less vibrations you get.
They usually go away totally disbelieving what they have just seen, but they do realise that what I did was correct and safe, and usually follow my methods themselves.
 
I really need to get a vid done to dispel all these black art notions and myths about fly cutting. It seems people think I am telling them porkies.
 
Grunt, grunt!
 
Bogs

Edited By Bogstandard on 28/09/2010 23:54:51

John Olsen29/09/2010 02:29:04
1294 forum posts
108 photos
1 articles
Well, I remember setting up with great fear and trepidation to do some flycutting on my little Unimat 3. One of the things I made was a fourway tool post out of cast iron, and a lot of aluminium blocks for various projects got fly cut too. It turned out to be no particular problem. As above the tool wants to be sharp, and with a Unimat you are of course not going to be taking massive slices off, but it did just fine and gave a nice finish. Minimum speed would have been 300 to 400 rpm, with a cutter radius probably about an inch or so. I agree that the cutter will often start to take another go on the back, with some of my jobs I was able to avoid having to traverse that far so you only got one set of cutter marks, which looks nicer
 
After that I started collecting shapers, so have not had to do a great deal of flycutting since.
 
regards
John
DavoJ29/09/2010 03:11:42
9 forum posts
Here are some pictures I took while fly cutting a  mild sleet plate for a head extension for my mill, it is 220mm x 350mm x 25mm thick. I wanted a perfect surface to mate to the ground surface on the back of the head.
 
The first picture shows the set up with a 75mm boring head used as a fly cutter, it had a 18mm boring bar in it with a 1/4 HSS bit very similar to Johns in the link.
I found by the time the poor little 1/4 cutter reached 1/2 to 3/4 of the way across the plate at my lowest of 220 rpm it was blunt, so I used coolant and all was fine but it mad a mess with in a 6ft circle of the mill including me.lol (Cant wait to pick up my surface grinder)
 
The second picture shows the finished plate, tram is extra important doing large surfaces.
 
This is the mill it was done on.
 
Dave

Edited By DavoJ on 29/09/2010 03:14:39

Edited By DavoJ on 29/09/2010 03:18:41

Edited By Katy Purvis on 01/06/2015 11:56:49

David Clark 129/09/2010 08:53:27
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3357 forum posts
112 photos
10 articles
Hi There
Flycuttting depends on the flycutter and the rigidity of the machine.
We used to flycut aluminium carburettor housings at 2,300 RPM.
Why 2,300 RPM? That was the fastest spindle speed on the mill. Feed was 12inches a minute. Depth of cut about 1.5mm. Finish was like a mirror.
 
I have also flycut steel U shaped brackets on a horizontal borer.
Had to flycut both inside legss.
Swing (overall diameter) of flycutter at least 3 feet, probably nearer 4.
Can't remember the speed but think it was about 150 revs. 
Both jobs had substantial flycutters and carbide tips.
 
Just try it and see what works. Wear glasses as well.
regards David
 

Edited By David Clark 1 on 29/09/2010 08:54:31

John Wood101/10/2010 13:28:47
avatar
116 forum posts
I completely agree with all the above discussed difficulties with flycutting. My principle now is to avoid that method if I can (size permitting) and, if it can be held, I do it in the lathe. I would rather spend extra time making holding devices, jigs etc so I could use the lathe to be sure of a decent finish.  When I first had my mill I probably tried to find as many uses for it as I could - WRONG - use the lathe if at all possible.
 
John

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