Milling: creating a smooth end finish in a slot

[Robin Hewitt]

Obviously I know nothing because I have no machine tools that do tens of thousands of rpm, someone will be along to tell me off in a minute, but I would happily cut that in modern brass. When I was a boy, back in the mediaeval period, brass used to snatch but those days are gone.

I think your problem is you are rubbing rather than cutting.

Slavish adherence to achieving feet/minute cutting speeds with tiny tooling makes for ridiculous rpm.

Keeping the tool shank intact with ridiculous rpm leads to tiny DOC.

Trying to get a job done in a credible time frame with tiny DOC leads to high feed rates.

I like my brass to be on the verge of squealing when I cut it and give a nice flake. I would use HSS tooling because a sharp edge is more important than tool wear, there is no tool wear in brass. It cuts like a dream unless you have that mediaeval brass which is a bitch.

I just looked up your router, it has 30 microns of backlash. That is not bad, but does it support a 6 micron tooth loading?

[Rob Meades]

Well, there's another parameter to play with. I'd not looked at HSS versus carbide. Rubbing rather than cutting would explain the look of the damaged tool tip, though I suppose that could also be that once it was damaged it would have been rubbing anyway. Playing with HSMAdvisor I can see that HSS gives me a lower required RPM, but I'm not sure what I gain from that: what can I increase, presumably by upping the RPM again, as a result (DOC, feed rate, etc?), or is it simply a better finish?

Apologies if I'm being dumb here, but I'm still trying to get my head around this. As to your tooth loading question, I'm not sure how I determine the answer...?

And no, I don' t think I have mediaeval brass, just Chinese brass. :-)

[magicniner]

HSS is a sharper edged tool which is less fragile and more forgiving than Tungsten Carbide tooling but will not take the temperatures associated with High Speed Machining so at the cost of reduced RPM you get less chance of the tool chipping.

You may be running the carbide cutter too fast without enough cutting lube/coolant, unless the heat is being removed you can get some smearing of the work material and as soon as that happens it will clog the cutter and give a result exactly as in your photograph, if you get the same problem when running the cutter faster I'd then put money on this being the problem ;-)

- Nick

[Rob Meades]

Well I say, there are a lot of choices to be made here. I will go look at HSS tools and investigate the possibility of a cooling system along the lines described by @Boyan Silyavski.

[A_Camera]

Well I say, there are a lot of choices to be made here. I will go look at HSS tools and investigate the possibility of a cooling system along the lines described by @Boyan Silyavski.

Have a look at this feed rate calculator:

http://www.daycounter.com/Calculator...lculator.phtml

Free, online and easy to use.