That's really useful information, many thanks! The tool I'm using is the 2 mm one of these:
...so 3 mm shank. and 3 mm length of cut. Which might point to my mistake: I measured what I thought was the length of cut of the bit and it looked like 4 mm (I'm cutting to a depth of 3.8 mm in 0.3 mm increments) but from the manufacturer data it's only 3 mm so the bit would have been getting quite upset towards the end. The stick-out was 20 mm, as you have assumed, which was the best I could do to avoid clamps as I'm cutting quite close to the edge of the material.
Your video shows a rather impressive speed of cut. :-)
I have a spare bit, so I will try reducing the final depth of cut to 3 mm (what I'm doing is purely a test job anyway), increasing the speed to 30000 RPM and have another go with that bit, rather than risk breaking something more expensive just yet. I will also download HSMadvisor.
Last edited by Rob Meades; 27-11-2016 at 10:14 AM.
And if you have not done it till now, do it - compressor, 0.6-0.8mm ID tube blowing air / or air plus cooling liquid/ right where the cut happens. Cooling things down tremendously affects bit life and finish result. later i will show you picture of my setup if you have not done yourself a mist cooler.
Interesting, would very much like to see a video of that.
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?
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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. :-)
Last edited by Rob Meades; 27-11-2016 at 01:42 PM.
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 ;-)
Last edited by magicniner; 27-11-2016 at 02:23 PM.If you will not be swayed by logic or experience simply pick the idea you
like best, but ask yourself why you sought advice in the first place and,
for a simple life, perhaps consider not doing so in future
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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.
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VERY impressive! Especially your worked numbers (2.5 bar, 2 mm inside-diameter feed tubing, 0.8 mm inside-diameter nozzle). I'm working in my loft, so I have nothing like the space that you have, however there are dental compressor rigs that should work well (and quietly) available for around UKP150 on ebay so, using these numbers I should be able to make something similar.
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