Fly Cutter?

[mrk]

I have a fly cutter with 3.2" effective diameter.

What cut RPM, feed, and depth of cut would be recommended for 6061?

I tried it at 312 rpm and 2 ipm (based on the standard rpm/feed formula). For depth of cut I tried a .003" and had good results but at .005" the HSS bit worked it's way loose even though I had it locked in as tight as I could make it with the wimpy little alan keys.

This is the exact tool that I was using:
http://tinyurl.com/yz3oy9

Is 2 ipm and .003" per pass typical performance for this style of fly cutter?

[tobyaxis]

I have no idea what that cutter will take, but that seems slow for 6061. What Type of machine are you using? Does it have an R8 Taper in the Spindle? That got loose because you over tightened it. All screws have a torque spec that if you exceed your only doing more harm than good. Also was it chattering when it got loose. Too Much Vibration will loosen anything. When something chatters decrease the speed just a little at a time (CNC Machines). In the case of manual machines with pulley drives increase the Feed a little at a time. Most applications you will have to feel out as to what the setup, machine, and tool will handle. Books and calculations won't give you the answer. This is why machining is Trade. Play with this a little and post your results.

Also, does your tool have a nose radius of say........ 1/64th or is it sharp? Are you using the correct rake angle? In aluminum at least a 15 degree rake.

Lots of ground to cover here, are you still there?

[Mcgyver]

if it is too slow, not my much (its hss he's using), but Toby is right, machine, tool geometry etc all factor in. you should be able to take a lot more that off, trying to picture what i did last time i fly cut AL, may 20-30 thou? maybe more. you should be able to take it up the limits of the mill (full size) without the bit moving in the holder. you say wimpy, if its a cheapo fly-cutter, perhaps the allan key and set screw are so crappy you can't get enough purchase on them to tighten - why not try replacing them?

[mrk]

Thanks guys!

The fly cutter is a cheap so I am going to replace the set screws soon because the ones that it come with don't really allow me to tighten them very much.

The machine is an Acroloc series 10. 5hp spindle and acroloc tool holders (solid weldon shank style). The machine is fairly heavy and stable (7,500 lbs). The tool bit is comming loose via the set screws in the fly cutter so I don't think it has anything to do with the tool holder.

I was using the fly cutter to try and bring a plate of scrap aluminum to uniform height. The cutter was spinning around in it's 3.2" circle but contact on the material was not uniform because the scrap plate was not uniform. the plate had some high and low spots so I think this is what led to the vibrations and the the bit comming loose.

My new plan is to use a 3/4" end mill to bring the plate down to uniform depth then use the fly cutter for a slow finish pass or simply skip the fly cutter and use a face mill (I don't have a face mill yet but I am shopping for one).

Overall what do people use fly cutters for and does anyone have advice for a book that would give an overview of different styles of cutters? I have a copy of _Machinery's Handbook_ but the book is both too detailed and too broad for my current level. What I really need is a beginner's guide. I am going to take a trip to the local tech shool and see what they have at the student store but if anyone has a recommendation of a book for someone who is just getting started I am all ears.

[Mcgyver]

mrk, wow that's a heavy duty machine, when you see speed and feed questions you (erroneously) figure its someone with a new mill/drill or something lol. flycutters are perfect for large surfaces like you are doing, with that mill you should be able to take 30 thou off no problem. if the head is aligned properly you end up with a nice cross hatch pattern.

I don't recall seeing much written about flycutters, not sure there is much to write about other than tool geometry, and that's well covered in most machining texts. just like a lathe tool bit, it needs rake and clearance in the right places.

the following were used here before (1st pic isn;t my work) but might help

often you see people use a knife style cutter like




they assume it works on the lathe so will work on the flycutter. problem is the rake is ground for the tool to cut in direction of the green arrow, whereas in fly cutting, you are cutting in the direction of the red arrow. it sort of works because there is front clearance on the knife tool, but it doesn't work as well as it should!

I advocate using a tool like how you'd grind a lathe facing tool, where the chip breaker provides the rake



you can sort of see it here



great part about fly cutters is tool bits are so cheap and easy to sharpen. give it another try, your machine is certainly hefty enough, change up the set screws but also check the tool bit geometry

[DareBee]

I have taken couple hundred thou with similar fly cutter in a much wimpier machine (10x50 knee mill).
Rpm may be a little slow but either way calculate your feed at .005-.008 chipload.

If your tool is sharpened to good geometry it will cut great, use a little oil or WD40 or something to keep the chips from welding to the cutter.

I am not a fan of trying .002 DOC, it is very hard on the tool as it will tend to rub instead of get under the material and shear it off.

Not really an answer but points to ponder.

[Geof]

The fly cutter is a cheap so I am going to replace the set screws soon because the ones that it come with don't really allow me to tighten them very much.

This is a very good idea; the screws supplied are made of low grade cheese. I have used this type of clutter and they are a bit limited because the tool is only secured in one direction. I have tapped holes in the bottom of the cutter so button head bolts can be used to hold the tool into the slot but this only works if the tool hangs out far enough that these bolts clear the machined surface.

On a heavy machine you should be able to run the cutter at a few hundred feet per minute but use a good strong face shield because having the tool fly out and hit an eyeball can do serious damage.

You mention you are facing off a plate. This will almost certainly distort when the stresses on one side are relieved by machining. Also it might be distorted by clamping so you machine it flat then unclamp and bingo now it is no longer flat.

To get it as flat and true as possible you might try this procedure:

1, Support and clamp the plate at three points; two corners and the middle of the opposite side, using tiny supports and something under the clamp to apply the pressure on a very small area. This avoids putting a twist on the plate right at the clamp.

2, Take off the minimum amount to get a flat machined surface over most of the area. You want to have machine spots at three places that can be used for the clamp locations when the plate is flipped over.

Repeat 1, and 2, for the other side then again for the first side, etc, etc.

This way you come closest to equalizing the stress relief on both sides so the plate stays as flat as possible. It is unavoidable that you leave a small edge during this process but you make it as small as possible by keeping the clamps near the edge. The last operation is to clean off this little edge which should not alter the flatness a noticeable amount.

[Pres]

Try to use as long of tool bit as you can to help 'balance' the rotating force.
(i.e. sticks out the back end at least as far as the front.)

Besides shaking, it'll help reduce the load on those 'wimpy' set screws.

Pres

[mrk]

My tool bit is ground like the one Mcgyver recommended.


When I regrind, I will try to keep the same shape and I like that the fly cutter can be reground plus the tool is much cheaper then a face mill.

I also think that Pres is on to something with the idea of balance with some of the fly cutter bit sticking out the front and some out the back. This makes sense and when I was doing it before the entire bit was sticking out because I was trying for the maximum circle size. With some bit on each end it will balance more and should work a bit better.

I also think I will replace the set screws and see if I can drill and tap a location for a third set screw to hold the bit tight.

My machine has full shields and when fly cutting I will always keep the shields up. I also always wear safety glasses in the shop since I need glasses to see well and have a set of nice wrap around style prescription sports classes (Rudy). For me safety is job #1.

The machine has flood coolant so I will keep the fly cutter nice and wet.

If all goes well I should be able to report back with good news.

The scrap aluminum that I am trying to machine down with the fly cutter is 1.5" and when I am done it will be 1.25" thick so I think it will stand up to the machining stresses and not warp.

[Geof]

Originally Posted by mrk ....The scrap aluminum that I am trying to machine down with the fly cutter is 1.5" and when I am done it will be 1.25" thick so I think it will stand up to the machining stresses and not warp.

It is not the machining stresses that are important; they are irrelevant. The important stresses are the stresses that are present within the material from the manufacturing processes. If these stresses are removed unevenly by taking a majority of the material off one side it will warp; you may not notice it on a small piece of material but over a length of ten inches or so it will be noticeable. The only aluminum plate that will not warp appreciably is cast tooling plate.

[Pres]

Yes, Geof is correct.
It's always best to, at least, take a skim cut off every rolled surface.
-or an equal amount of material off of each rolled surface.

There is alot of surface stress imparted during the plate rolling process.
(that's how they make & hold the plate thickness)

'sides, it makes your part look better
Pres

[wildcat]

When using a fly cutter I find that the finishes are a little inconsistent given the same feed. For example, with a table feed of left to right sometimes the leading side of the fly cutter leaves the best finish and other times I get the best finish by "dragging" the leading edge back across. If the following edge is allowed to start cutting the result is generally poor. A good finish looks nearly like a mirror while a bad finish looks dull and is a little rough like small chips have adhered back. I will have to regrind my tool like the one above and give it another shot. The material used in all these cases is aluminum.