High Speed Parting with CARBIDE in a Small Hobby Lathe

A few people are asking about this particular parting tool. I ordered it from www.pewetools.de/.

Part of the issue in my experience is don't use a brush. That only gets oil to the outside surfaces on a deep parting operation. Centrifugal force slings the oil back out with very little getting to the point of cut. I typically use a squeeze bottle to drip oil at the back side of the cut and let it carry through keeping it wet. I also suspect with a VFD spindle drive at low RPM, there really isn't much torque available if you look at the torque curve for that motor.

I've never used a small lathe, but in my CNC world I have learned to never hone carbide inserts and to make sure they have an appropriate load. Early days when I first used carbide drills, the tool rep laughed at how slow I was going.....chewing up carbide tools. I quadrupled the feed rate and the tool lasted 10x longer. What an eye popping lesson.

Haven't seen the other video but i keep telling my students that if you're getting vibrations or a bad surface finish, don't slow down, increase the spindle speed and go from there. Vibrations are usually caused at a certain frequency, you either have to go down or up to get away from it. Slowing down carbide tools isn't always the best option, carbide wants to get pushed. Since you're not using a geared lathe, you're left with no torque advantage in slower speeds, so you gotta get it where the torque is. Increased speed will also help to overcome stuck chips or a slightly too beefy feed rate for a short moment (when hand feeding) Some said cutting oil and a brush doesn't help and that centrifugal force won't make it cut better, but when parting off, a little bit of oil, is still better than no oil. Another thing i like to do is to use wider parting cutters and inserts, it improves rigidity and therefore keeps the cutting geometry more stable, even on smaller lathes.

Retired Engineer, machinist and shop teacher with over 50 years experience. The best advice is use the tool manufacturer's recommended speeds and feeds. Watching the second piece, you're still not feeding fast enough. watch the short chips in the first cuts, they roll up and break, that will happen at any diameter IF you use the best feed rate. You don't need the oil brush, it doesn't work, make a drip bottle if you must use lube, but water based coolant is better, it actually cools the tool and part.

My butt was puckered in solidarity.

People underestimate these lathes all the time. They are far more capable than the usual teeny cuts shown. I learned this style of parting a few years ago. Very rewarding.

This seems like the perfect reason to add Constant Surface Speed to the VFD via the electronic spindle encoder while using the linear scales for radius input. Once you try CSS machining you will immediately see a productivity and quality improvement. In fact that is the primary reason CNC'd parts look so good.

It really does seem counter intuitive, but carbide loves to be loaded up, and you're also enjoying the higher torque from the motor at that speed. Sadly HSS won't tolerate those speeds and loads, and prefers slow and sharp. I truly believe that there's been a conflation between the two along the line that's made it into lore concerning small machines and carbide. Thanks for mythbusting James.

Before I started out in hobby machining I'd watched a lot of YouTube and I knew that "carbide likes to be pushed" - so, in my ignorance, I pushed it. And it worked, just as it did for you. I've never had a problem parting with carbide because I'm not afraid to send it. Power feed works well. You also need a chuck that's in good order. Robin Renzetti had a video on trueing chuck jaws, and started out by showing what kind of deflection you can expect in a part under load if the jaws are bellmouthed. That's a recipe for parting problems.

My practice is to lock the carriage when parting off. At a minimum it precludes inadvertent Z-axis motion during the parting process.

One thing I would recommend getting is a little needle tip oiler bottle so you can drip oil into the slot as prodigiously as you like as you part. I also use them all the time for drilling or anytime I want cutting oil in a particular spot.

There’s a great book by George Thomas called Model Engineers Workshop Manual. He used to write for the british byweekly Model Engineer. There’s a chapter called “on parting off”. He devoted an entire chapter to it because on the small lathes like the myford, which is what most steam train guys had, it was the most difficult operation to do. Sometimes in a crash one could even break a cross slide or compound casting. He developed the rear inverted toolpost which is sold by Hemingway kits which solves the rigidity problem. He would frequently demonstrate parting off 1” dia mild steel at 300 rpm with hss, just to show it was easily done. The key is to stop if the chips stop curling and you have to make sure the groove doesn’t jam up with curly chips. You need lots of oil too. Btw that’s the best machining book ever. Full of wisdom and awesome tooling projects. Tee Publishing sells it. Btw parting a 5” dia piece will always be a challenge just because you can’t clear the groove.

Even running larger manual lathes, it took me a while to get used to carbide. Once you get used to HSS the habits are hard to break. With most carbide you can run screaming speeds and feeds and will get longer tool life. You just have to get past that initial cringe when you start a cut. Great demonstration

The Pulsing in the hand wheel and its relation to the chuck speed when doing the cut is an interesting observation. It would be interesting to do a balance check of the chuck to confirm this hypothesis. If there is in fact an imbalance an attempt to balance the chuck and thereafter do new test cuts would be interesting exercise. This could perhaps be an idea for a future video?

Highly recommend full face protection, I've had carbide inserts chip and get flung all over when high speed grooving goes bad. Glad you've found the sweet spot for your lathe.

i dont know much about small lathe´s but on my job (CNC lathe´s) i Part off with 150-250m/min , F=0.1-0.3mm/rev from 1mm blades up to 10mm as far as i know Carbide loves speed and torqe if you go to slow it will chatter or brake early. The last 1-2mm i slow down so the part dosent fly acros the country

Perfect 👍 Thank you for sharing your experience. Pls try this also: clamp the carriage, put some round material in your drill chuck that reaches in the borehole. So the parted material can not fly around in your workshop.

Parting is such sweet sorrow. Glad you got it worked out. I remember one time I wanted to make a washer and unwittingly picked up a piece of stainless and work hardened it to the limit. It ate my parting tool. Thanks for the video keep on keeping on.

Thanks James for giving this a try and motivating the rest of us to try!