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End mills (micro) Vendor source


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A number of years ago I bought a set of tiny end mills from my local hobby shop.  They were carbide mills sold by Drill Bit City that had been recycled from printed circuit board manufacturers.  I tried to use them to mill brass and everyone of them broke.  I have not tried to use them since.

 

i tend to be heavy handed, so perhaps I was too aggressive with them, but these Drill Bit City carbide mills seemed awfully brittle.

 

Roger

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For any sort of wood, or even brass you should be using HSS not carbides.

 

Carbides are very hard, meaning they can cut high end steels, but it comes at the cost of being brittle. For woods, standard HSS should easily eat it for breakfast. The main reason carbides are used in industry a lot is they can withstand higher temperatures, thus allowing higher cut rates. For hobby rates and materials  we should not be generating any heat. They also retain their edge much better, but this is really only an issue when cutting other materials with hardnesses similar to the cutter. 

 

If you are breaking HSS you may want to make sure any bits you get are M35 or above grade. Much of the cheapy crap you'll find for sale may be M2 grade HSS or worse. A good indicator as always is price, if you're buying HSS drill bits for $50 it will be M35. The good stuff will be M42, for this expect to pay several hundred dollars for some drills.

 

If you are breaking cutters a lot it may be the geometry of cutter you have chosen is inappropriate for the material. For example, brass is often cut with a negative or near zero rake angle. This prevents the cutter 'digging in' and locally deforming the work-piece. This digging in or grabbing, coupled with the work piece being securely mounted, usually result in a broken cutter. If you have ever tried to drill into a thin sheet of material and it has 'ridden up' the drill, this is exactly what is occurring. Consider using a file to modify the cutter rake angle. 

 

 

Disclaimer: Carbides will cut wood too, very well infact. But they're on average a bit harder to use without breaking, harder to sharpen and more expensive.

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