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29th Oct 2020, 09:46 PM #1Gear expert in training
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Carbide at low speed...yes you really can
Had to turn up a small spacer today, thought I'd show you all what carbide at 1000 rpm in 1045 mild steel looks like for all the "my lathe is too slow for carbide" people.
16mm bore with an Iscar CCMT 060202-PF IC907 in a 12mm boring bar; approx 0.15mm depth of cut, 0.14mm/rev (about 5 thou) feed
PXL_20201029_022422738.jpg
Parting with an Iscar DGR 2202J-6D IC20 (2.2mm wide, right hand parting insert for soft materials); hand feed
PXL_20201029_022452783.jpg
The recommended surface speed for the turning insert is 100-170 m/min, actual surface speed in the bore was 50 m/min
The recommended surface speed for the parting insert is 190-260 m/min, actual surface speed during parting was 85-50 m/min (27mm OD to 16mm ID)
The point I'm trying to make here is that you don't necessarily need to take huge cuts at high speed to get great results if you get the right inserts, even when you're going waaaay slower than what the packet says you should.
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30th Oct 2020, 12:50 AM #2
Hi Elan, Guys,
This is what I found when moving to using threading inserts !
Though I do find that its nice to be able to cut a thread at 600 rpm ! Away from the chuckBest Regards:
Baron J.
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30th Oct 2020, 07:43 AM #3Golden Member
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Btw, I read 'slow' in the title and when I saw 1000rpm I smiled. 1000rpm ain't slow for old machines! I think I may have only used the upper range of speeds (750-1400) maybe once on the old girl ever. I do read these 'carbide' threads with interest as I'd had some small luck here and there with them on my machine, but not much luck so far. I put that down to lack of knowledge rather than lack of machine capability.
Thanks for the insight.
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30th Oct 2020, 08:21 AM #4Golden Member
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- Apr 2019
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- Adelaide
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Still being new to using a lathe I have only ever used carbide inserts and at speeds never above 700rpm (old machine-and yes I realise its all about surface speed not actually rpm). Maybe its cos I know no different but have not had issues unless parting off but that is apparently its own can of worms.
I have a heap of HSS to make into cutters but the thought of standing at the bench grinder doesn't excite me.
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30th Oct 2020, 09:58 AM #5Golden Member
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- Sep 2009
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- Sydney
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I tend to do most of my turning around 800rpm as that’s what feels comfortable on my 40’s Hercus. With 50mm steel it suggests 1750 RPM as ideal cutting speed, so I’m a long way off.
I’ve found DOC is pretty important for good surface finish. And trying to land the final dimension with a reasonable chip load. Have gotten some amazing finishes and as mentioned above, so much easier than grinding tool bits.
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30th Oct 2020, 10:16 AM #6Most Valued Member
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The lathe that l mostly use has a top speed of 2000 rpm but I rarely go above 600 rpm. I mostly use carbide and often with larger offset jobs will only be doing 30rpm when facing to a centre.
I have no need to drive my machines at recomended insert speeds as i am not on a clock and i dont care if it takes me 5 or 30 seconds longer to make a cut.
My speeds and feeds are selected on my own judgement with regards to type of material, size of job and then observations of how it is cutting.
eg. Type and color of chip, surface finish and a keen ear for the sound of the cutting as you hear when a cutter loses its edge and you dont want a boring bar playing a tune.
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30th Oct 2020, 03:42 PM #7Gear expert in training
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It's not all that fast either though. We have a Colchester Bantam Mk. 1 from the mid 60s that will do 1600rpm all day (and there have been many days where it's done just that). I'll try to do some tests even slower to see how it goes.
The key to parting is to have your tool clocked up perfectly; if I know I'll have to part off I'll indicate the tool post with the parting tool on it to within a few tenths before starting anything.
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