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Struggling with using an end mill for facing


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Hi all,

I got my Bridgeport up and running again over the weekend, and tackled a project that has been outstanding for a while. My indexable tip tool holders are too tall, so my plan has been to machine approx. 0.3mm off from the back of the holders, to drop the tip height.

I tried using a 16mm HSS end mill at approx 50m/min (so approx 1000RPM). Feed rate was approx 60 mm/min. I'm feeding by hand.

What I found was that very quickly, the outside tips of the end of the tool went blunt. They didn't get overly hot, as there was no colouring of the metal, it was just missing!

I tried lubrication (light oil applied manually) and also a constant air blast to clear the swarf.

In the end, having taken the tips off two cutters (16mm and 20mm) I resorted to my 2" face cutter, which has done the job ok.

What am I doing wrong?

- Too fast?

- Too slow?

- Wrong use of the tool? (I've read that facing may or may not be right for an end mill?)

- Tool holder too hard?

Thanks,

Luke

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You'll stand more of a chance at 100 RPM.... Recommended cutting speed for MILD steel is about 22 meteres a minute. Our old hurdy gurdy (a brute of a milling machine) would struggle with tool holders/shanks at 380 rpm with its 100mm 5 flute face cutter.

If you insist on using HSS tools to do it then go to depth with 1 cut.

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No insisting on HSS at all, just learning with what I have available, which is predominantly HSS for the milling machine at the moment (except the face cutter), and a mix of HSS and indexable for the lathe.

Is there a definitive reference for cutting speeds? I've found a lot of conflicting information online.

I'm machining the back of the tool holder, not the tip itself.

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Cutting speeds are dependant on to many things for there to be a chart for every situation, it comes with experiance. When teaching Apprentices i always get accross to them that feed rates make money.... By which i mean lower rpm with more feed on is generally but not always better. HSS tools are more forgiving and cheaper, easer to grind and so on. Use it wet at just about all times. Carbide takes alot more of a machine to make the most of it, it generally removes metal faster but is more dependant on its optimum cutting conditions and doesnt like rapid heat cycles. Its also more expensive and can be heart breaking when you get it wrong!!

Always climb mill, you'll need to nip the locks on the slides to do that.

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