Quote:
Originally Posted by renovationinnov
sorry to be ' dumb' but what are the 3rd from the left & 4th from the right
they are different so what milling do they do different to the others
as I don't know I'm a chippy
rob
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Not a dumb question at all Rob. As a chippy just think of end mills as fancy precision ground router bits. The materials and geometry used are just to suit metals rather than wood and they are run at much slower speeds than a router bit. I'm typically running around 2000 RPM instead of 20,000 for a router bit.
These end mills are also ground from solid pieces of super hard Tungsten carbide which is the material braised onto the tips of your wood working circular saw or masonry drill bits. Most are usually made from tool steel which is the same as most regular drill bits
The odd looking end mills you referred to are the ball nosed type. Instead of having a square shoulder and cutting a square slot or rabbet they cut a slot with a radius bottom. This pic comparing a square and ball nose might make it a bit more obvious
End mills unlike drill bits cut on both the end and the side of the tool. They typically have from 2 to 5 flutes. Generally the harder the material the more flutes you want to spread the load across. Higher numbers of flutes usually means a lot stronger tool for the loads applied to it. You want the tool cutting and not flexing and rubbing across the surface.
Here's a 2 flute ball nose end mill on the left, A 3 flute aluminium cut in the middle and a 4 flute conventional on the right.
The aluminium cut endmill has different geometry to suit the softer material. It's designed to run at higher speeds and the higher helix is better at clearing chips away from the cut. One of the issues you have with aluminium is chips getting dragged back into the cut and messing up the surface finish or welding themselves to the tool. The higher helix also means there is more cutting edge in contact with the material which reduces chatter. Before one edge is leaving the cut the next one is starting. Chatter is a harmonic vibration that causes the tool to flex and bounce over the surface which can lead to tool breakages and also leaves a poor surface finish.
Looking at the close up of this aluminum cut end mill you can see how the ends of the 3 flutes have been ground to cut the bottom of the slot. If you look close you will see the left side flute has been ground so the cutting edge extends right to the middle of the cutting circle. This is what allows it to plunge cut. The 3 edges cover the whole area of the circle where most 4 and 5 flute end mills will have a hollow in the middle where it won't cut. They need to start at an edge or a pilot hole to get going.
Sorry to bore you all with this but I find the design and geometry of these tools quite interesting. Especially the developments in recent years.
Cheers
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