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Thread: Lathe carbide tool geometry
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21st Apr 2021, 10:07 PM #31I break stuff...
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Bit hard to tell what size bars you had in there, but if that's the 6" chuck on the AL336, makes it about 30-35mm bars? In which case, crank the speed, at 500 you're way too slow, as your TNMG at 1400 rpm shows. I'd be at 1000 minimum for that sort of diameter. You can get away with a bit lower speeds on the positive rake geometrys, but the WNMG and TNMG are going to want the RPM.
If any of your packs of inserts have actual recommended SFM or M/min on them (the Chinese knockoffs usually don't, nor do older packets of brand name), chuck that info in here: https://www.kennametal.com/in/en/res...-and-feed.html and work out what RPM you should be running - you'll probably be surprised.
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21st Apr 2021, 10:44 PM #32Diamond Member
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Yes, 6" chuck, so steel between 38mm and 55mm (the cast iron).
The 1400rpm looked shiny when lathe was spinning, but examining when stopped showed tears/streaks - like solder wiped across badly tinned wire:
IMG_1410.jpg
I reckon the 800rpm result was the best. Running my nail across the cut felt like a fine book binding. Consistent teeny-tiny serrations
At the higher speeds, the swarf was sometimes straw or light blue colour, and I could often "smell" the cut. I assume that is the super-glue burning in the Chinese inserts
The Hafco can do decent speeds, but the gearbox is sooo noisy that I fear for its longevity.
But at least it can do triple digits. Unlike the plain-bearing'd Hercus
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21st Apr 2021, 10:56 PM #33I break stuff...
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Don't worry so much, it's just the way they are. You want to be truly deafened, come and have a listen to the 60 year old gears in the Graziano scream at 1150rpm, especially when you've got the change gears and QCGB engaged (has a lever on the headstock for feed/neutral/reverse of the output to the change gears). Running in reverse is even louder in certain gears.
It's close to double the volume of the AL335 I reckon.
If you have a bit of a 'ringing' noise while it's running though, have a look at the mesh of your change gears. Getting them right is a bit of an art (at least on the AL335), too loose and they'll make a kind of light ringing resonant noise, too tight makes a kind of heavy whirring ring (hard to explain, you have to hear it) - they should have just the slightest bit of play between the teeth. Might help take some of the edge off. Making sure they've got decent lube also shuts them up a bit, I bought some Rocol Open Gear spray which works pretty well. Just don't fire hose it on, or you'll have an almighty mess thrown off everywhere - dust it on whilst rotating the gears at a low speed, and let it tack, then repeat and build it up that way.
On mine I also modified something to do with the compound gear. Don't remember exactly what I had to do, but doing up the nut didn't actually pull up against the bearings, so I could wobble the compound gear like the bearings were stuffed. I chucked something up, and skimmed just enough off to put a light preload on the bearings, think it was the shoulder on the stud that the nut was hitting before it touched the bearings. I also had to clean up the slot in the big pivoting bracket as it was machined crooked to the face, and the flats on the stud for the compound gear that sit against the back side of that bracket were different heights. Fixing all that made it far less painful to get it set just right, as it used to bind up when you tried to move it a tiny bit, and the play in the compound gear meant you sort of had to guess at where to put it, as it'd settle when you let go.
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21st Apr 2021, 11:20 PM #34Most Valued Member
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In case nobody else has already mentioned it, I find the FSWizard phone app really useful to get ballpark feeds and speeds (thanks to Elan for suggesting it originally).
It’s a great tool although I find the recommended feeds for milling can be a bit scary unless the setup and cutter are perfect, so when milling I usually run at about half what it recommends. Just less stressful and more chance to catch it if things are going pear shaped.
Steve
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21st Apr 2021, 11:47 PM #35Gear expert in training
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Yeah, the feeds are theoretical ones; fine for a big CNC where everything is nice and rigid, but a bit scary on a manual machine. I mainly use it for lathe work (don't do a lot of milling in my department) and I've found the spindle speeds to be spot on though.
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23rd Apr 2021, 08:50 PM #36Diamond Member
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Torture testing 2 - Hercus hell !
Took the same tools, and threw them on the old Hercus. Chose a long bent piece of steel, which has some chrome plating on it. I assume it was a hydraulic ram's rod.
First, the TNMG 160402:
IMG_1435.jpg
Started with middle belt speed (350RPM), also tried top speed (650). Both predictably rough. Next, the WNMG804:
IMG_1436.jpg
which wasn't much better. Then tried the RPMT08, which was worse (no photo).
I might try bumping the height up next time?
Last, TCMT110204:
IMG_1437.jpg
which was the best, but not great.
So, I guess there are 3 possible causes;
a) the steel wasn't great?
b) this old Hercus just doesn't have the speed or stability for carbiding a 35mm diameter.
c) maybe the interrupted cut (from the bent rod) didn't help.
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24th Apr 2021, 01:09 AM #37
Hi Nigel,
I was given some pieces of hydraulic piston rod, nobody bothered to mention to me that they were hardened on the outside ! They were horrible to turn until I got under the hard skin, almost like turning chilled cast iron. So you might find that they turn better when you get rid of the hard surface. I reckon that there is a good 30 or 40 thou of hard surface.Best Regards:
Baron J.
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24th Apr 2021, 11:30 AM #38Most Valued Member
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25th Apr 2021, 02:27 PM #39
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25th Apr 2021, 02:29 PM #40Gear expert in training
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I'd be very curious to know how many seconds HSS would last on hard-chromed rod...
Usually you'd turn the chrome skin off with CBN, then switch to carbide once you're down to the standard 4140 rod underneath.
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25th Apr 2021, 02:44 PM #41
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25th Apr 2021, 02:50 PM #42Gear expert in training
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That's true, but the chrome plating has a hardness close to or higher than HSS, so I'm still curious to know how well it'd go
EDIT: Should also note that some of the stuff is also induction hardened as well as being chromed.
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25th Apr 2021, 08:22 PM #43
Hi Guys,
Talking about chromed bar I saw some 75 mm diameter hydraulic piston rods in the scrap yard, nearly two metres long, I could have had one but I couldn't even lift one end. It would have made a brilliant lathe bed !Best Regards:
Baron J.
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25th Apr 2021, 08:23 PM #44Diamond Member
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I currently have the QCTP off, so might try mounting in the lantern with some HSS, but doubt I have an appropriate shape, so it would be my first time grinding it.
I think I'm on the slowest power feed I can do with my gears. Could manually do it slower, but don't have the patience to do it at 38 or 66RPM !! Cutting fluid isn't an option unless I manually dribble it on.
Am still tempted to try a carbide threading insert. They are quite sharp, and have good rake on top.
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25th Apr 2021, 08:26 PM #45
I use "Trefolex" and brush it on ! Smokes well though
Best Regards:
Baron J.
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