About 20 minutes south. My farm overlooks Lake Erie! Does your friend like machines?
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Should I keep Hartford or Bridgeport?
- Thread starter Susquatch
- Start date
About 20 minutes south. My farm overlooks Lake Erie! Does your friend like machines?
Chicken lights
Forum Pony Express Driver
my friend likes machines, farming, trucks and small town Canada life, he tells me he’s in Chatham in a few days
You right, 100% - torque does not drop off. Never argued it did. I argued, and will to the end time or until basics mechanics is proven wrong, that HP drops when speed is dropped unless torque is raised - what a manual transmission does.
........
I'm just repeating at this point, so come on over with that beer.....we'll find a new horse to flog
You are right we are both flogging a dead horse at this point.
Let's just agree to disagree on whatever it is we disagree on and to be honest, I don't even think I know what it is that we disagree on anymore!
I'll bring the beer
Know anyone with a leer jet to get us all there?
Hope it's for longer than just the weekend. I'm headed to Barrie in a few minutes for Thanksgiving with my Sister and her family.
PM me for details!
Dabbler
ersatz engineer
as a matter of fact... but not available to any of us pleebs.
Brent H
Ultra Member
Hey @Susquatch - if your heading to Barrie I am only 15 minutes north! We could meet up for a Beertini !
PM sent.
Sometimes you just have to try things.
I was making a big mandrel in my lathe today when I suddenly realized that the mandrel would be perfect to see if I could stall my mill motor at its lowest VFD setting of 5 hz by hand.
So I chucked the mandrel and tried it. Here are two videos one with the back gear and one without. Both are the slowest belt position. Both are only 5hz on the motor.
https://www.dropbox.com/s/7farsammtpsozd1/20211021_141224_1.mp4?dl=0
https://www.dropbox.com/s/9zvb41u3dkk3f03/20211021_140437_1.mp4?dl=0
Bottom line - the motor didn't slow down at all. In fact, it didn't even grunt! It just kept going like as though I didn't even touch it. I am a big guy with very strong hands. The shaking in the videos is the result of me giving it everything I had.
After that I tried a 20 thou cut with the biggest fly Cutter I have. That didn't flinch it either but it sure did bounce! I believe the bouncing was mostly because I don't have an R8 fly Cutter and had to use an R8 to MT3 adapter which destroyed the rigidity. The motor didn't grunt with the fly Cutter either. It ran smooth as silk and didn't lose any speed at all.
All this goes to show that a good VFD and VFD ready motor are a great combination. I'm very pleased with how they perform.
I was making a big mandrel in my lathe today when I suddenly realized that the mandrel would be perfect to see if I could stall my mill motor at its lowest VFD setting of 5 hz by hand.
So I chucked the mandrel and tried it. Here are two videos one with the back gear and one without. Both are the slowest belt position. Both are only 5hz on the motor.
https://www.dropbox.com/s/7farsammtpsozd1/20211021_141224_1.mp4?dl=0
https://www.dropbox.com/s/9zvb41u3dkk3f03/20211021_140437_1.mp4?dl=0
Bottom line - the motor didn't slow down at all. In fact, it didn't even grunt! It just kept going like as though I didn't even touch it. I am a big guy with very strong hands. The shaking in the videos is the result of me giving it everything I had.
After that I tried a 20 thou cut with the biggest fly Cutter I have. That didn't flinch it either but it sure did bounce! I believe the bouncing was mostly because I don't have an R8 fly Cutter and had to use an R8 to MT3 adapter which destroyed the rigidity. The motor didn't grunt with the fly Cutter either. It ran smooth as silk and didn't lose any speed at all.
All this goes to show that a good VFD and VFD ready motor are a great combination. I'm very pleased with how they perform.
Brent H
Ultra Member
@Susquatch : throw in 1/2” x 4 flute end mill and take a 50 thou cut off the face of something.
Maybe it will stall out - what ever
My cousin is a machinist, he was by a few years ago and I needed a flat on a boring bar - I just got my mill. No problem he says - zing - off goes 0.050” in one pass. Hmmmm …. Says I. After that … let it rip and see what she (ol’ Bridget) can do !! LOL
Maybe it will stall out - what ever
My cousin is a machinist, he was by a few years ago and I needed a flat on a boring bar - I just got my mill. No problem he says - zing - off goes 0.050” in one pass. Hmmmm …. Says I. After that … let it rip and see what she (ol’ Bridget) can do !! LOL
Your wish is my command! I'll try that later today.
I think that slow speed machining is an interesting exercise in machine dynamics and material properties. In my minds eye, I can actually see the cut happening. Slowing down the Cutter contributes to the visual.
I am thinking that the primary difference between high and low speed cutting is tearing VS slicing. Higher speeds might contribute more inertia to keep a slice going. Slower speeds might cause the material to yield in small time increments before giving in to the force and breaking off. The difference might even explain the surface finish relationship.
Even so, I find it easy to visualize a slow motion cut VS a high speed one. Maybe I'm just kidding myself into believing what I see in my mind. But I don't think so. It takes roughly the same force (overall torque / tip vector force) to yield and cut the material regardless of cutting speed. But the amount of material removed in a unit of time changes the HP requirement. As tip speed is reduced, feed rate must be reduced proportionately.
Torque demand is roughly the same, but hp demand goes down. It all makes sense.
It's a bit like finite element design or integral calculus. Slow it down and break it into smaller increments analysed one tiny element at a time. Alternatively, it also works in my mind if I look at it like a static balanced force system, with a curl of material coming off the Cutter tip frozen in time.
I wonder if that is the basis of the science and math behind all those cutting speed charts, curves, and tip designs.......
I think that slow speed machining is an interesting exercise in machine dynamics and material properties. In my minds eye, I can actually see the cut happening. Slowing down the Cutter contributes to the visual.
I am thinking that the primary difference between high and low speed cutting is tearing VS slicing. Higher speeds might contribute more inertia to keep a slice going. Slower speeds might cause the material to yield in small time increments before giving in to the force and breaking off. The difference might even explain the surface finish relationship.
Even so, I find it easy to visualize a slow motion cut VS a high speed one. Maybe I'm just kidding myself into believing what I see in my mind. But I don't think so. It takes roughly the same force (overall torque / tip vector force) to yield and cut the material regardless of cutting speed. But the amount of material removed in a unit of time changes the HP requirement. As tip speed is reduced, feed rate must be reduced proportionately.
Torque demand is roughly the same, but hp demand goes down. It all makes sense.
It's a bit like finite element design or integral calculus. Slow it down and break it into smaller increments analysed one tiny element at a time. Alternatively, it also works in my mind if I look at it like a static balanced force system, with a curl of material coming off the Cutter tip frozen in time.
I wonder if that is the basis of the science and math behind all those cutting speed charts, curves, and tip designs.......
Here you go Brent. 50 thou at 5hz side milling 1 inch thick mild steel was zero problem.
The top of the attached photo was cut at 5 hz on the back gear, the rest was cut at 5hz in direct drive.
No way did that even load the motor let alone stall it. The only difference is the finish - plainly visible in the photo - as my discussion above suggested it probably would be.
Again, it's a cool insight into the material properties and mill function. And it's amazing to watch that end mill peeling off thread after thread of steel at the speed of smell.
The one lonely line just below the back gear cut is when I stopped cutting to get a better continuous grip on the hand wheel.
deleted_user
Super User
I'm not sure about the most common VFD but many motor controllers can derive the rotor rpm by measuring the back emf produced by the motor.
very common technique in sensorless motors and controllers in ebikes. I'm sure that some higher end controllers must have the ability.
ps yes I know this is an old thread. I just feel chatty
I would agree with that being an issue and you are right to point that out.
But I don't think it's correct to say that it's that not the bearing rating. So let's just say that it's both. Many older motors have a low speed rating for the bearings and Rotor. In this case, it's the high rpm of the motor that causes damage. This happens no matter what the carrier frequency is because rotor speed itself is the killer not the carrier frequency.
Bearing damage from a high frequency carrier happens no matter what the motor speed is. Bearing damage from high rpm happens no matter what the carrier speed is. Both are damaging.
Former Member
Guest
On VFD's I'm going to comment on what I learned about 28-30 years ago when I sold the first first 2 installations in Canada for my company. Simple VFD's (now cheap today only control frequency and have current capacity overhead to supply what the motor requires). This fries your motor and limits your power. Good VFD's also vary voltage. This way the current doesn't need vary but the voltage does in conjunction with the frequency keeping the wattage the same throughout the frequency (speed), no motor burn out (ideally).
Torque is determined by push which is amperage, Amperage in this cause is also heat, so at the upper end Voltage is used instead of torque.
However if you can get your motor up to speed (sometimes that is the trick) rotational mass overcomes the need of torque at high speeds.
At low speeds we drop voltage to remain constant power but lower rotational mass messes again with perceived torque.
So knowing that use a VFD correctly and you can do almost anything, get that balance wrong and Balding is in your future.
BTW I use light belt tension on my mill to allow free spin on the motor (avoid torque rob by belt) and rely on the mass of the system spin to prevent load stall torque. Works well.
Torque is determined by push which is amperage, Amperage in this cause is also heat, so at the upper end Voltage is used instead of torque.
However if you can get your motor up to speed (sometimes that is the trick) rotational mass overcomes the need of torque at high speeds.
At low speeds we drop voltage to remain constant power but lower rotational mass messes again with perceived torque.
So knowing that use a VFD correctly and you can do almost anything, get that balance wrong and Balding is in your future.
BTW I use light belt tension on my mill to allow free spin on the motor (avoid torque rob by belt) and rely on the mass of the system spin to prevent load stall torque. Works well.