First time fly cutting

[challenger]

I'm fly cutting the griddle top I posted about. So far it's been a fairly brutal operation. It's my first time fly cutting and this is the only fly cutter I have. The bit is a brazed carbide type and I'm feeding so it cuts below the rust as I've read about. Are there any obvious setup issues I'm in error doing? The chips are a huge issue as well and I'm going to make some sort of cardboard containment as they are getting thrown all over.
Thanks for any input.

[Doozer]

Looks like zero rake and your toolbit is likely in front of center.

-D

[old mart]

I would get a shell mill and chuck the flycutter in the bin.

[Mr Fixit]

Hi Challenger,

I too have only done fly cutting with the type of setup that you have , and only twice before. Let me say what I learned and what worked for me. The real machinists will correct me if I send you down the wrong path.

The tool looks like it is sticking out too much. Doozer said off center which I think is the same thing that I'm saying. I agree the chips hurt when they land on your hand, arm, or in the shirt collar, cardboard is what I've used and it does ok. The depth of cut might be too much for the hot rolled steel your working with. Have you got a angle grinder that you could put a 36-80 grit sanding disk on and get the mill scale off first? The feed rate was a factor when I did the cutting before on my projects, it needed to be slower than I thought to get a good finish and not damage the cutter which I also did 1 time.
Maybe a couple of YouTubes on flycutting would be helpful.

Let us know how you come out.

TX
Mr fixit for the family
Chris

[754]

Give it a bit of chipbreaker in a way that positive rake, easier on the machine , and chips may curl and fly less..

[J Tiers]

Stickout is OK, tool is bad, what is the RPM or SFM?

Carbide is good for roughing down under the scale etc. I'd never use a nice shell mill for roughing scaly cast or the like.

One that is easy to sharpen? Sure.

Nothing is easier to sharpen, nor cheaper, than a fly cutter. Brazed is not automatically a POS, plus that is a good use of it even if it was.

[George Bulliss]

Looks like it's dragging a bit. Because it's cutting a flat workpiece and not round, it will need more clearance for flycutting than for lathe work.

[BaronJ]

Hi Guys,

A picture of my fly cutter !



20 mm diameter shaft, 20 mm thick disc 75 mm diameter. A piece of 1/4" inch HSS for the cutter. I can happily take a 25 thou cut in mild steel at around 300 rpm and 30 mm min feed. But you do need to get the tool properly sharpened.

Looking at the picture the mill tram might need resetting.

[BCRider]

It looks like you made the flycutter yourself. If that's the case then Doozer has a point that needs checking. But it's hard to tell from the photos if the cutter's slot is offset or not. Have a look at THIS THREAD from way back and in particular note the second and third photos that show how the slot is offset to put the cutter's leading face or "top face" on the center line of the swept circle. If the cutter isn't offset in this manner then you end up running with a negative top rake which likely doesn't help much for the finish either.

I'm seeing a really nasty surface finish. It may be galling from running too high an RPM. Check an SFM vs diameter and double check the RPM you're using. But with the cutter set to that diameter you really should be down in the low hundreds range. The carbide will help but it still needs to turn at a lower RPM than one might expect.

The scratch pattern in the pictures seems odd too. Almost like the tram of the head isn't good. In the second picture the scratch pattern suggest to me that you've taken your second partial pass from left to right but only the trailing side of the pass is cutting.

When the head is trammed really well the pattern left by milling in general will show a pattern of scratch marks from both the leading and trailing sides of the cutter But I'm only seeing what looks like trailing side marks. That suggests to me that your tram is off. So that won't help either.

There's also what appears to be some scratch marks that are deeper and chewed up. You might be getting chip welding occurring. Try some cutting fluid. And if you're spinning the cutter too fast THAT'LL make you slow it down when it starts spraying the fluid all over the place.

[BaronJ]

Hi BCR, Guys,

Yes the fly cutter is home brew. The tool bit is in a simple hole drilled through the disc. Its not offset in the way that you mean, its actually about half the hole diameter forward of the centre line, but it is rotated slightly clockwise looking from the top. The grubscrew is at a slight angle.

[Paul Alciatore]

Two points:

1. If you want to finish the entire surface of that sheet of metal, I think your mill does not have enough throat for the job. You will never reach the center. So, you may want to use a different technique to finish it.

2. I can't see the fly cutter very well, but from the looks of the path that you have already cut I think you could work on the sharpening of that tool bit. You need to get the angles correct for the way it sits in the holder. And, of course, make sure they are dead sharp.

OK, three points:

3. Use a coolant or at least some oil while cutting. It will cool those flying chips down for less pain when they land on your arm or go down your shirt. And it will improve the surface finish.

And here's another shop made fly cutter. I like a two cutter design because it is balanced better.


This one was made to fit on the spindle of my SB-9 lathe but it could have had a shank for use on the mill. In this photo you can see that the tops of the two HSS tools are on the center line of the cutter. That way I can cut the angles for the tip in the same manner as I would for a lathe tool. One exception to this is the added relief on the outer edge of the tool. It is a bit difficult to see, but that outer edge has a second facet to allow more clearance at the bottom side of the bit.

It is very well balanced so it can run at higher speeds.

[redlee]

Ive always had good luck with a fly cutter, to me the tool you made is way to long. Rigidity is important in any aspect of machining.
Tool has to be on centre , properly ground,feeds and speeds for the material and type of tooling.
From the picture it looks like the tool tip or rad is way to big.

Would help to grind some of the weld before trying to cut it, weld can be hard, I would be using a tool like the one in the pic top right.
What grade carbide are you using ?
Doesnt take much to lose or chip an edge then it doesnt matter about everything else it will not work.

[JCByrd24]

Agree with redlee, the cutter is way longer in Z than it needs to be. Barons example is excellent. In my experience welding can definitely cause hardness as well. Most fillers will be lower carbon but if the base metal has higher carbon the weld and air cooling can cause hardness.

[challenger]

I don't know the speed or feed. I'm just going by feel.
I will check the tram on the head and shorten the stick out of cutter. I'll also grind the weld and profile a HSS cutter and try it again.
It is too big for my mill so I'll be repositioning it on the table.

[BaronJ]

Hi Guys,

I've found the drawing of mine, I have edited it to colour the tool bit and grubscrew hole.


This is looking down from the top. The slight angle used doesn't have to be precise, anything around 5 degrees will do. I initially used a rounded cutting edge with about 10 or 12 degrees back rake. Basically if it cuts well on the lathe it will cut well on a fly cutter.