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  • J Tiers
    replied
    Originally posted by BCRider View Post
    I've been away for a few days so catching up.

    JT, I suspect you posted reply #62 in response to my earlier post.
    .......
    Nope, not you, mostly Dian. Your post needed no comment!

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  • BCRider
    replied
    BaronJ, normally yes. But in this case the idea is to produce a shear cut as per Dian's earlier post.

    Dian, in your case the shear would curl the chip outwards where mine curls it inwards.

    By accident AND good luck the shear tool that works so nicely on my shaper curls the chip away towards the cut in a linear version of your idea. It's a concept which can only work on very shallow cuts but oh boy does it work well! So I'm thinking your way would work out better.

    For anyone with a round insert I think this could be a good idea to try. Although to be fair it would not take much to do it with an HSS cutter either.

    Borrowing your idea of working with square stock with an adaptation for a 1/4 or 5/16 square cutter..... The block is too tall doing it this way. If I were to make something like this I'd alter it to use a blank that was cut in half so I could reduce the height of the block. OR, with some fancy grinding the usual angled slot cutter could be ground to include a lot of shear. But how it works in this square block sketch is a lot easier to visualize. I just don't like all this overhang.

    Click image for larger version

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    I in fact have some blocks of hot rolled that need facing and truing to make more "pencil sharpening" tool holders for the QCTP. I might just try this idea for the usual style holder. I have the angles needed in my minds eye but it would be a nasty job to try to show it in a sketch.

    I'm also thinking of a two point fly cutter. Not where the to cutters are matched and aligned. But one intended for facing off hot rolled metal with a rougher and then at a slightly smaller diameter a .005 to .01 shear finisher for the nicest finish. So not a two cutter tool but rather two single point flycutters in one tool. For the rougher I'm thinking the "unused" corner of a CCMT insert. Then the shear style finisher could be something like dian's round insert or an HSS shearing cutter.

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  • dian
    replied
    whats the purpose of this? will work at certain doc only, right?

    why dont we attach a small spindle to the fly cutter instead of the insert??
    Last edited by dian; 05-03-2021, 01:37 PM.

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  • BaronJ
    replied
    Click image for larger version  Name:	image_16776.jpg Views:	0 Size:	44.0 KB ID:	1941029 Hi Guys,

    That arrangement will work but the line of the insert cutting edge should be as the red line.

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  • darryl
    replied
    Ok- that's what I had in mind. The insert is slapped onto the side of the fly cutter body as shown. Funny how I couldn't get the drawing and some text into one post-

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  • darryl
    replied
    Click image for larger version  Name:	fly cutter.jpg Views:	0 Size:	19.8 KB ID:	1941022

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  • BCRider
    replied
    Originally posted by darryl View Post
    ......Ok, start with a round insert. On the side of your square fly cutter body, machine a bit of a recess to nest the cutter into, and drill and tap for a holding screw. Position this behind the rotational axis of the body, and make sure the OD of the insert hangs below the body by some amount. Now as it spins it will shear material away instead of gouging it away. Hammering should be reduced to a bare minimum.......
    That's an interesting idea. I sketched it up as shown. Is this the idea?

    Click image for larger version

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    In the straight down top view any but the most extreme insert or used on a VERY big diameter of cut will foul the heel of the clearance angle.

    But down in the side view there's enough clearance. The clearance will reduce as the area of the cut moves up from the lowest point to some higher amount towards the situation in the top view. The point where the back side heel starts to foul would be determined by the insert diameter, swept diameter of the fly cutter and the feed rate of the cut. But I don't think it would be hard to make it so one could achieve about.04 to .05 DOC cut. And of course most of the time the DOC would be a lot less as is the usual nature of fly cutting.

    I'm not sure about the spinning part though. With out some manner of thrust bearing behind the insert I think there would be enough friction to stop it moving. I'd also worry about any play at all which allowed it to spin also allowing the insert to bounce around even just a trifle and lead to chipping away of the edge. To do the rotating thing I think we'd need a little shaft and bearing setup that spins which the insert mounted onto firmly to get the proper support.




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  • Cenedd
    replied
    Originally posted by dian View Post
    cbm=cbn?
    Yes, sorry. Not sure if it was fat fingers or autocorrect but Cubic Boron Nitride if you're trying to Google it - otherwise all I get is search results for cannabis.

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  • dian
    replied
    Originally posted by Cenedd View Post
    BCRider For what little it's worth, I had trouble flycutting a difficult piece. To be fair, mine was mainly mill scale but the HSS was blunt before I'd got a fraction of the way across. I'm pretty sure that was mostly my terrible grinding skill and the fact that I wouldn't know a good rake if it flipped up and got me in the face. I swapped to a left hand lathe tool with a CCMT insert and got mediocre results. I put a cheap import CBM insert in it and got a fabulous finish as it tore off the mill scale. Just don't let the insert come to rest on piece if you stop it on a lathe, it seems to weld itself to the piece and then it's all over.
    For aluminium with an aluminium profile CCGT insert it will happily take out to about a 0.5mm DoC - beyond that the shape/size of the insert is such that it starts ploughing rather than cutting. Light cuts on steel work with the same insert too.
    Holder was just an MT3 off-the-shelf (round and angled down to one side) with the slot widened to take the lathe tool.
    A hand-filed chamfer down the leading edge (where the tool hits) reduces the thumping as it ramps in rather than impacts.

    I'd like to run a face mill but I think my machine is rated for something paltry like 20mm so I'd probably be removing all but one insert....which is a fly cutter by any other name anyway.
    cbm=cbn?

    Leave a comment:


  • BaronJ
    replied
    Hi Guys,

    I seem to recall that someone made a tool for a fly cutter that was specifically designed for round inserts ! At the time I thought that it was a good idea and bought some round inserts. I've never used them, they’re still in the packet. I think that they would make better lathe toolbits.

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  • darryl
    replied
    Here's an idea- shoot me down if I deserve it. Ok, start with a round insert. On the side of your square fly cutter body, machine a bit of a recess to nest the cutter into, and drill and tap for a holding screw. Position this behind the rotational axis of the body, and make sure the OD of the insert hangs below the body by some amount. Now as it spins it will shear material away instead of gouging it away. Hammering should be reduced to a bare minimum.

    Because the insert is round it will tend to rotate. With the usual right hand thread holding screw, it will tend to unscrew, so you'd either use a left hand holding screw, or design the fly cutter to rotate the other direction and use a regular right hand holding screw. This is just a detail though, having nothing to do with the shearing action you're setting up.

    To help visualize the action, draw a line on a piece of paper, then align your thumbnail with the line and crease the paper. Then go back and misalign your thumbnail and follow the line again. Your thumbnail will want to follow a new line, but you make it track the old line. That's the shearing action

    Leave a comment:


  • BCRider
    replied
    I've been away for a few days so catching up.

    JT, I suspect you posted reply #62 in response to my earlier post.

    It's little subtle changes to the usual angles that I was suggesting. If I made it sound like cutters for any of the machines would be radically different then sorry about that. You're perfectly right that the angles and such must still all fit within the basic principles. It was the idea of subtle changes to the angles to suit the cutting path geometry that I was suggesting.

    For example I'm used to seeing rake angles given for lathe tools at around 5 to 7°. This allows for the fact that we spiral cut into the work so we need to allow for the angle of the spiral into the work as well as keep enough angle to avoid contact with the front or side face and the drag and galling which would occur. But shaper tools step over then make a straight pass. And this is reflected by the angles being specified at 3 to 4°. And it sure did make a huge difference to the life of the tip and edges when I went for this shallower angle.


    And now a minor side track from thinking about the example given above......

    If we think about it there is some degree of similarity in the fly cutter tool and an internal boring bar. It is somewhat like we are on the lathe and using the boring bar to take a light facing cut from the bored hole out across the end face of the part. So it needs a suitable angle to avoid dragging the heel of the side relief. But that can make for a more delicate edge when it thumps into the next cut. So perhaps a spiral shape for the side rake that ensures heel clearance while reducing the side rake just behind the edge to a fairly durable 5° angle?

    And at the same time taking a hint from my shaper cutter experience we can reduce the clearance angle of the "front" or bottom of the cutter facing the surface to more like around 3° to encourage a more durable edge for the interrupted nature of the cut.

    If this sort of fine tuning were to be used it would certainly make for specific cutter differences between flycutter, lathe and shaper tooling aside from the obvious overall shapes required by how the tool blanks are held. Typical case would be the often seen angled body with slot style fly cutter.

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  • Cenedd
    replied
    BaronJ I think you may be unduly crediting me with grinding a viable tool in the first place! It is an art that I've failed to devote the required learning time to, I'm afraid. Inserts - and cheap ones at that - have been working for me so far. I'll play with grinding HSS more when something forces me to need it - like a form tool perhaps. Also, I now try to avoid hot-rolled steel for just that reason!

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  • BaronJ
    replied
    Hi Cenedd, Guys,

    From your description you have probably being running the fly cutter too fast ! Mill scale is very abrasive and will take the edge off a Carbide or HSS tool bit very rapidly. Its a bit like cast iron, you have to take a deep enough cut to get under the mill scale. I admit that in most cases of removing mill scale I prefer to use an angle grinder and coarse flap disc. Do this outside rather than inside then the dust just gets blown away by the breeze, you don't want that abrasive dust on you machines. Once you have got rid of the scale then you can start fly cutting !

    As you have found a number of tool bits behave in different ways ! For alloys I use a rounded end HSS bit with plenty of back rake and about ten degrees of top rake. For steel I use a more aggressive cutter grind with a more lathe tool shape and more hook to the cutting edge. You have to balance the cutting speed and cutting edge thickness to suit the cutter speed and material hardness, or you just take the sharp edge off your tool bit. Too slow is better than too fast !

    A lot depends upon the finish that you are trying to achieve. Generally I'm not too bothered trying to get a glass like finish, I'd rather take a couple of bigger cuts to get down to the dimension that I want. A DRO makes this much easier to do.

    Almost forgot, use lubrication ! I use diesel or white spirit on alloy and any cutting oil I have to hand on steels !

    HTH.
    Last edited by BaronJ; 05-01-2021, 03:15 AM.

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  • Cenedd
    replied
    BCRider For what little it's worth, I had trouble flycutting a difficult piece. To be fair, mine was mainly mill scale but the HSS was blunt before I'd got a fraction of the way across. I'm pretty sure that was mostly my terrible grinding skill and the fact that I wouldn't know a good rake if it flipped up and got me in the face. I swapped to a left hand lathe tool with a CCMT insert and got mediocre results. I put a cheap import CBM insert in it and got a fabulous finish as it tore off the mill scale. Just don't let the insert come to rest on piece if you stop it on a lathe, it seems to weld itself to the piece and then it's all over.
    For aluminium with an aluminium profile CCGT insert it will happily take out to about a 0.5mm DoC - beyond that the shape/size of the insert is such that it starts ploughing rather than cutting. Light cuts on steel work with the same insert too.
    Holder was just an MT3 off-the-shelf (round and angled down to one side) with the slot widened to take the lathe tool.
    A hand-filed chamfer down the leading edge (where the tool hits) reduces the thumping as it ramps in rather than impacts.

    I'd like to run a face mill but I think my machine is rated for something paltry like 20mm so I'd probably be removing all but one insert....which is a fly cutter by any other name anyway.

    Leave a comment:

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