At light depths of cut, they almost have a 90 degree lead angle - the cutting forces are almost entirely directed up into the spindle instead of radially. Round inserts love high feed rates, because they've got a massive tool nose radius. Would you ever consider trying to put a one inch endmill in your machine for anything but a wide and light finishing pass? And in that case, why not just go to a flycutter where you have good and inexpensive control over the edge characteristics? Consider the diameter of the tool - they look like 1" diameter, roughly. The triangle insert, with 0 degrees of lead (insert set to do square walls) has all of the cutting load radially - it tries to twist the head of the machine. Negative rake is definitely an issue, but that's pretty well understood so I won't touch it. The things important to machine size are twofold: tool nose radius, and lead angle. I want to expand on Paul's analysis of the inserts. I don't want to be messing around with stuff when I can just put a HSS endmill in and go. Maybe someone here is using indexable endmills to great success on a smaller machine, but I just don't go near them until I'm on a bed mill or have some special exception that would justify the extra hassle. It can be hard to use indexable cutters even in a bridgeport sized machine. One such bit can be resharpened dozens of times on an ordinary bench grinder so the tooling cost is minimal. Part of their beauty is the cutters are standard lathe style bits and I can sharpen them as needed for any job. My largest is about 4" diameter and I have no trouble with using it on a 1/2 HP machine. If you can get the proper speed in terms of feet per minute at the cutting edge, there is no reason why you can not use a tool like this with a fairly large diameter. They are good for facing a wide area at one time. I also have some shop made fly cutters that use two HSS bits held in slots with SHCS. These are good for general purpose work but the smaller diameters require a lot of cuts to face a wide dimension. I have an assortment of end mills, mostly with square corners, but some with a radius so that they leave a small fillet. If you have a light mill, I would be worried about a negative rake angle as more power and rigidity are needed to use such a tool. The characteristics of this one are more dependent on the shape of the insert as it is the same no matter how it is mounted. You may be tempted to cut a corner with a fillet, but this may or may not work depending on the HP of your mill. But it is not good for making a square, inside corner.
The gentle curvature of a round insert would make a much smoother finish. Sharp corners, as the triangular and square inserts have, tend to produce lines in the finish. The round inserts would be used to produce a smoother cut when face milling. Could also be used for deburring if a very small chamfer is cut. It can probably cut a chamfer up to the size of the edge of the insert. The tool with square inserts looks like it is for cutting chamfers on the edges as the inserts appear to be set at a 45 degree angle. It would be good for cutting a notch in the edge or for facing if you can stand some texture in the finish.
The tool with triangular inserts looks like they are set with one edge parallel to the axis so it would make a square shoulder. This is not to be taken to be generalized for all inserts of these shapes as it looks like the it is more the design of the tools that determines their use, not just the shapes of the inserts in them. I haven't used that set so I can't comment about the quality, but you asked about the uses for the three different inserts. However, has a set that seems to be the right size for this machine. On larger machines they are quite expensive and for this machine practically non-existant. Then, I learn that there is a device called the indexable end mill that will do the same thing. First, it has a maximum drilling and end milling capacity of half an inch and a face milling capacity of 1". I have learned the following about the machine. So, now, I'm ready to try the fly cutter again based on the info in last year's thread. I'm still a newbee, but not as totally ignorant as I was last year. I have taken your advice, purchased a belt drive for the machine and have been getting a little experience cutting a few slots in non-metalic stuff (knife handle material) and cutting the shoulders on some blades in preparation for making the guards for the knives. Last year I bought a Micro-Mark Mini-Mill and promptly tore it up with a fly cutter. Well, it's been about a year since I've needed your advice.
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