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Thread: Fly Cutter: Cutting Tool Bit Geometry

  1. #11
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    Hope this is not redundant comment, haven't read every word in this thread.

    To help visualize fly cutter tool angles, grind a left hand lathe facing tool (for turning the left, or headstock, face) and install this in the fly cutter.

    Mark

  2. #12
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    Thank you to everyone for the replies - I apologize for the lengthy delay
    in replying.

    Quote Originally Posted by Mcgyver
    Your last photo correctly shows where the rake and clearance are...
    not many seem to get this for a fly cutter. The right tool to use is NOT
    a lathe knife tool, a knife tool has the cutting edge on the side of the bit,
    whereas a fly cutter cuts on the end of the bit
    Thank you.

    Quote Originally Posted by Mcgyver


    The links dp put up are imo misleading in the sense that they give the
    location of the angles for a [left hand] knife tool. The identity of the
    angle isn't determined by their orientation to the tool bit, but by where
    the cutting action is taking place, which I think you've nailed [in the OP].
    For a flycutter as you presented the cutting is at the end as you've shown,
    not on the side as it is for a left hand knife tool.
    If a Right Hand turning bit was positioned vertically as shown in the revised
    image below, then I believe that the respective angles and clearances
    would be correctly located for a fly cutting operation. However, just
    mounting a Right (or Left) Hand bit in the illustrated fly cutting tool
    would not position the bit optimally for cutting.



    Quote Originally Posted by Mcgyver
    The nicest fly cutter tools imo, and the nicest lathe facing
    tools, are those with the cutting edge on the end with positive rake formed
    by grinding a chip breaker.

    Thank you for this picture, it validates the suppositions made in the OP.

    Would you be able to provide another image showing the type of finish
    this bit produces and post about feeds/speeds (along with a bit of
    background about the class & HP of machine: drill/mill, BP or other)?

    .

    Edit: Changed 'suitably' to 'optimally'
    Last edited by EddyCurr; 04-19-2010 at 11:53 PM.

  3. #13
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    This is my collection of flycutters and cutters I use in them. I run the flycutters at 1000+ rpm and take up to .050" on most metals. It helps to have a 30 to 45 deg leading angle on the cutter to cut smoothly and I don't use a radius on the cutter except for special cuts. A radius will make the cutter hammer and the larger the radius the more it hammers.

    It's only ink and paper

  4. #14
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    I haven't used a fly cutter in years because I don't much care for the hammering on the spindle of the Bridgeport. I suppose I'd use one if I needed to get a single full-width finish on a piece of aluminum, but for everything else I've been satisfied with the results I get with a 2-1/2" 45-lead 4-insert Widia face mill I have.

    As long as the spindle is trammed-in right, the finish has been outstanding and no steps. It runs 4x the feed rate of a fly cutter, and much more if the fly cutter has HSS bits. Smooth as butter, light loads on the 1HP motor and the high shear angle imparts no hammering. I think I've rotated the 4-sided inserts once in 2 years of infrequent use, though if I needed more inserts the SEHN43's available from a wide variety of sources, in milling-specific grades and coatings.

  5. #15
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    This image shows the flycutter as installed in the tool. These cutters do not advance into the work as your arrow shows - they cut a sweeping spiral as seen from above like stretching a Slinky (tm) sideways into a flattened series of spirals.

    The specific relief angle shown on the work facing surface is not correct for this service (zero degrees is fine, in fact, as shown in McGyver's photo) and further demonstrates that all cutter angles are ground to satisfy a specific need. If you see specific angles shown for a cutter then there should also be a description of how it is expected to be used or at least be obvious.

    http://metalworkingathome.com/images...teroverlay.jpg
    Last edited by dp; 04-21-2010 at 04:03 PM.

  6. #16
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    If a Right Hand turning bit was positioned vertically as shown in the revised
    image below, then I believe that the respective angles and clearances
    would be correctly located for a fly cutting operation. However, just
    mounting a Right (or Left) Hand bit in the illustrated fly cutting tool
    would not position the bit suitably for cutting.

    Eddy, on the above I 100% agree with your description of angles and orientation, but we have to be a little careful about categorizing it as 'not suitable for cutting'. My response was the subject of the thread being where and what are the various angles on a flycutter...i think you've got them right and i proffer that you will produce a better flycutter this way however the lathe knife tool approach will work; it'll remove material. ....sometimes i'll grab a brazed carbide bit and have at it..Lots of guys do it all the time as do I sometimes...its just not optimal.

    It would be like taking a right hand knife tool and plunging a facing cut with it - it'll work. If it works, why do we care what's optimal? Because putting the right grind on reduces the cutting force and hopefully gets a better finish. There are times when things matter more than others, ie, the left hand lathe tool will work to a degree, but once one gets onto thinking in terms of where the cutting edge is and the ensuing angles, its not more effort to grind the bit right than fudge it.

    my mill is an XLO, which is a beefy bridgeport style. imo the lighter the mill, the more you have to think about reducing cutting force. Speed is based on diam, material and cutter material and feed is based on DOC when roughing (what the machine can handle) and slow for finishing. I don't have a pic handy of the finish, but a good cross hatch pattern says things are working well.

    I may be misinterpreting Dennis's diagram but it looks like a left hand lathe tool put in a flycutter which wouldn't be ideal - unless plunging down. flycutters to most of the work along the yellow line whereas the lathe knife tool is ground to cut along the red
    Last edited by Mcgyver; 04-19-2010 at 11:41 PM.

  7. #17
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    Quote Originally Posted by Carld
    This is my collection of flycutters and cutters I use in them.

    I run the flycutters at 1000+ rpm and take up to .050" on most metals.
    It helps to have a 30 to 45 deg leading angle on the cutter to cut smoothly
    and I don't use a radius on the cutter except for special cuts. A radius will
    make the cutter hammer and the larger the radius the more it hammers.
    I have edited a copy of your image by adding identifying icons to
    assist discussion. If this is unsatisfactory, I will remove the image.


    The cutters appear to be left hand turning tool bits.

    For the bits denoted by blue triangles, which of the edges on the face
    do you observe to be acting as the cutting (chip-forming) edge - the
    one with the yellow circle or the one with the red circle?

    Do the blue triangle bits cut the same as the the orange square bits?

    What is the diameter of the largest fly cutter tool and how far out does
    the cutting edge of the insert extend from the circumference of the FC?

    Thanks,

    .

  8. #18
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    My personal favorite flycutters are shop made. They use round hss such as broken drills or centering drills and even round hss stock can be used (the centering drill shown for demonstration purposes). The cutter on the larger tool is parallel to the arbor, perpendicular to the bottom face.

    http://metalworkingathome.com/images...erExamples.jpg

    The larger one was used to square and size this bar:

    http://metalworkingathome.com/images...gBarHolder.jpg
    Last edited by dp; 04-21-2010 at 04:03 PM.

  9. #19
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    Quote Originally Posted by dp
    This image shows the flycutter as installed in the tool. These cutters
    do not advance into the work as your arrow shows - they cut a sweeping
    spiral as seen from above like stretching a Slinky (tm) sideways into a
    flattened series of spirals.

    I need help understanding.

    Isn't a fly cutter predominently used by setting it to a fixed Z-height and
    then moved horizontally into and then across a surface?

    In such a scenario, as the cutter reaches full engagement, isn't it cutting
    using the edge denoted by the yellow angle for a maximum of 180 each
    revolution? Isn't the edge denoted by the red angle sweeping the just-cut
    new horizontal plane determined by the DOC?

    .

  10. #20
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    Look at the swirls in the picture above - the stock was centered under the spindle and the cutter spiral-cut across the piece. The exit point was slightly further down the part than the entry point because of the table advance, but not by much. At 300 RPM and 3"/minute table feed the swirls are nearly circular. Note too that the swirls are made on the leading and trailing pass indicating the tram was pretty decent and the surface is not dished.

    In the overlay image the tool I've pasted in has too much angle on the lower face. Zero angle is fine and adding a bit of angle with a rounded nose will produce a glassy surface on aluminum. A very sharp edge will leave cutter marks.

    And I should add that I have a very small bench top mill. A larger mill will be able to leave swirls that have more diagonal sweep to them as they can feed faster.

    Frank Ford made a similar cutter but his uses two dissimilar cutters:

    http://www.frets.com/HomeShopTech/Pr...flycutter.html

    And here's a youtube vid of a carbide cutter going at 6061 aluminum:

    http://www.youtube.com/watch?v=koYGLVGkRsI

    And the pdf file with cutter geometry:

    http://www.tormach.com/MfgDatabase/20103_surf_6061.pdf
    Last edited by dp; 04-20-2010 at 12:54 AM.

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