Darren's active projects

[Mcgyver]

. But you consistently say it in a way that insults the VFD

Anthropomorphism. I proffer no VFD has ever had its feelings hurt by my remarks

and sings the praises of a bigger machine.

Where have a I done that? Its not fair to inject things into this that I haven't said

In my home shop, my biggest lathe weights 5200 pounds, the lightest is a 6mm Lorch watchmakers lathe. Its about the right tool for the job and I don't ever recall praising a bigger machine just because its bigger

Hp alone is not the holy grail.

I haven't call anything a holy grail. HP is, along with rigidity, a key component determining how much work a machine tool can do. If you can't get a machine to deliver close to the same HP over its speed range, its a poor performing drive compared to one that can. That's it in a nut shell

Again, within limits there are other ways to skin the cat.

No there are not. This is not how to fixture something or do an operation etc, its a physics formula. Power = Torque x RPM. To the best of the species collective knowledge, that will be true always no matter what

The VFD is not a fake improvement.

Understanding how they work and their limitations does equate to thinking they are fake. They are quite real. I use them a lot, on several machine tools I have have them installed for certain benefits they provide. At work I have 15hp cnc mills - why are they 15? Yo ensure there is some umph left at lower speeds, and its a lot cheaper to put huge HP servo on them than an automatic transmission

Within limits, they do work.

they do, and I use them. I did not ever say they didn't work. I also retain and use the mechanical transmission as well for all obvious reason; they increase torque as speed goes down.

And they are a gift to those of us who can't have the bigger machine.

I don't know why you keep referring to this. How is the size of the machine relevant? I haven't made reference to the size of the machine and what I've said is true regardless of the machine's size

He did a great job of describing the difference but didn't knock the VFD in the process.

Its a factual discussion. Shouldn't pointing out facts around a device's characteristics be just that? Un-emotive factual, technical, etc. You make it sound like I'm anti VFD. I'm not, I use them, understand their pros and cons. However they're inanimate objects best used with a full understanding of their pros and cons.

I'm guessing you are not doing this on purpose. I admire most of your responses elsewhere on the forum. Your knowledge and experience runs very deep. My guess is that this is a little like that time you told your buddies wife (let's call her HP) how beautiful she is (and she really is), but now your wife (let's call her Torque) who is beautiful in her own right, is pissed off at you. I doubt you do it on purpose, but I did take offense to it and felt obligated to take you to task over it.

Thank you for the positive remarks, but this paragraph drips with anthropomorphism. These are devices to be used and understood, not women (who do not like being used and cannot be understood ) None of use should be a stakeholder in them such that we're offended if their shortcomings are noted. I should always be prepared to be wrong, but it does irk being told I'm wrong on stating basic physics, as if I just make the shlt up.

Now, I'm going to go make something. Lost 3D printed wax investment casting is today's topic

 

[Susquatch]

Anthropomorphism. I proffer no VFD has ever had its feelings hurt by my remarks



Where have a I done that? Its not fair to inject things into that I haven't said

In my home shop, my biggest lathe weights 5200 pounds, the lightest is a 6mm Lorch watchmakers lathe. Its about the right tool for the job and I don't ever recall praising a bigger machine just because its bigger



I haven't call anything a holy grail. HP is, along with rigidity, a key component determining how much work a machine tool can do. If you can't get a machine to deliver close to the same HP over its speed range, its a poor performing drive compared to one that can.



No there are not. This is not how to fixture something or do an operation, its a physics formula. Power = Torque x RPM



Understanding how they work and their limitations does equate to thinking they are fake. They are quite real. I use them a lot, on several machine tools I have have them installed for certain benefits they provide. At work I have 15hp cnc mills - why are they 15? So to insure there is some umph left at lower speeds, and its a lot cheaper to put huge HP servo on them than an automatic transmission



they do, and I use them. I did not every say they didn't work. I also retain and use the mechanical transmission as well for all obvious reason; they increase torque as speed goes down.



I don't know why you keep referring to this. How is the size of the machine at relevant? I haven't made reference to the size of the machine and what I've said is true relevant regardless of the machine's size



Its a factual discussion. Shouldn't pointing out facts around a device's characteristics be just that? Un-emotive factual, technical, etc. You make it sound like I'm anti VFD. They're inanimate objects, a device, a tool. I use them, understand their pros and cons, Full stop



Thank you for the positive remarks, but this paragraph drips with anthropomorphism. These are devices to be used and understood, not women (who do not like being used and cannot be understood ) None of use should be a stakeholder in them such that we're offended if their shortcomings are noted. I should always be prepared to be wrong, but it does irk being told I'm wrong on stating basic physics, as if I just make the shlt up.

Now, I'm going to go make something. Lost 3D printed wax investment casting is today's topic

It's good that you can detach yourself from your machines. I can't. I love them or hate them. That's why it's mostly an expensive hobby for me. I sure as heck don't feed my family with them.

I'd bet good money that a lot of our debate would disappear in person. Anyway, I'd prefer to move on.

 

[Susquatch]

We are still here in T-Bay for the foreseeable future until H E - Double Hockey Sticks freezes over - so to speak. No ice to break (which is a good thing right now) and lets just say - I am the last man standing in the ER so I can't leave the ship or visit @ShawnR or @dfloen - which sucks. It will be a very subdued New Years and that's about all I can say about that.....

I wish you luck @dfloen and would be there in a heart beat to lift that f.....sucker with you if I had the choice!

Today is project day and I will try and get some posts out on some Miss Metric repairs and I am currently fabbing up a cam bearing extractor/insert tool for the car project

Stay healthy out there folks!!!

So you are not in stealth mode after all! The vessel finder is correct - you are still in port in TBay!

Btw, I had to tell the finder system that we were related in order to avoid commercial fees. Feel free to divorce me if anyone asks why you are not big, hairy, and ugly like your older brother.

 

[Brent H]

Btw, I had to tell the finder system that we were related in order to avoid commercial fees. Feel free to divorce me if anyone asks why you are not big, hairy, and ugly like your older brother.

Who says I am not ..... wink wink .....nudge nudge

 

[Susquatch]

Who says I am not ..... wink wink .....nudge nudge

Ya, you did grow up around here, and my dad did have regular business at the Regional center in the area.......

 

[RobinHood]

@Mcgyver & @Susquatch, Torque vs HP has been a hot topic - and probably will continue to be one. So I will carefully stick my head out of my shell and hopefully contribute some food for thought:

In the link below, there is a table where they list torque at selected speeds for a constant motor HP.
Further down, there is a graph that shows the change in power and torque for a given change in rpm.

Electric Motors - Torque vs. Power and Speed

Electric motor output power and torque vs. rotation speed.

www.engineeringtoolbox.com

Since a VFD primarily controls motor rpm, both the torque and power change for a speed change. I do understand that a VFD can, within limits, also control the torque by adjusting the strength of the magnetic field (via current control, I think), so there is some “fudging” of the lines in the graphs presented possible. But that has is limits before the motor either disintegrates at high rpm or the rotor stalls out at the bottom end.

So, from an operator’s perspective, I want my machine to do a certain amount of work per hour, say. In order to mitigate blowing up the motor due to high speed or burning it up because it stalls, I use a bigger motor (more HP) whose power curves are such that even at the limit of the normal operation of the speed envelope, the motor itself is not at its limits.

Does all this matter in a hobby environment - probably not as most hobbyists never push their machines because it does not matter how fast the work gets done. So if your ‘50s lathe came with a 3/4 hp motor, there is no real benefit to change it to a 2 hp one with a VFD other than now you have variable speed capability and you’d never damage the motor as it is not going to run anywhere near its design limits. A 3/4 hp with VFD would normally be plenty.

It would be a completely different story in an industrial setting where the work needs to get done in a reasonable amount of time. So, yes, if the machine itself is strong to handle extra power, then increasing the motor size and running it off a VFD does make sense.

Is bigger better? Not necessarily. Is more rigid better? Always! No question. Bigger machines tend to be more rigid; thus there is a school of thought that a bigger machine is a better machine, because they are more rigid. A well built 13-40, 3 hp lathe weighing 5000 lbs is a much better machine than a well built 13-40, 3 hp lathe weighing 1700 lbs. Now, one could argue that the 1700 lbs lathe in the example is not “well built” as it is too light - but we won’t go there…

Back to @dfloen ’s Monarch: the rotational mass of the working MG set-up can not be duplicated by removing it and replacing the system with a regular 3 ph, VFD controlled motor. One would have to install some sort of flywheel arrangement to get close to original inertia, let alone the mass of the MG itself that has been removed from the base of the machine. Sand bags perhaps?

 

[Darren]

*snipped

Does all this matter in a hobby environment - probably not as most hobbyists never push their machines because it does not matter how fast the work gets done. So if your ‘50s lathe came with a 3/4 hp motor, there is no real benefit to change it to a 2 hp one with a VFD other than now you have variable speed capability and you’d never damage the motor as it is not going to run anywhere near its design limits. A 3/4 hp with VFD would normally be plenty.

I sure like my 16-60, 10hp machine. It can do some pretty heavy cuts, but you're right, and i don't do those often enough. I'm sure i could have gotten away with 3-5hp. It had a 7.5hp 575v motor when I got it, but i found a 240v 10hp inverter rated motor in the same frame (213t) for $50 on FB, brand new.

Now, one could argue that the 1700 lbs lathe in the example is not “well built” as it is too light - but we won’t go there…

My V13 is around 1400lbs, and is surprisingly rigid. But you have to know a machines limits and to work within them.

Back to @dfloen ’s Monarch: the rotational mass of the working MG set-up can not be duplicated by removing it and replacing the system with a regular 3 ph, VFD controlled motor. One would have to install some sort of flywheel arrangement to get close to original inertia, let alone the mass of the MG itself that has been removed from the base of the machine. Sand bags perhaps?

Great points. I'm going to try to rework the MG to run on single phase. Looks pretty simple really. Failing that, I have a new looking 5hp motor here, and i'd be using it with a VFD.

 

[Susquatch]

@Mcgyver & @Susquatch, Torque vs HP has been a hot topic - and probably will continue to be one. So I will carefully stick my head out of my shell and hopefully contribute some food for thought:

In the link below, there is a table where they list torque at selected speeds for a constant motor HP.
Further down, there is a graph that shows the change in power and torque for a given change in rpm.

Electric Motors - Torque vs. Power and Speed

Electric motor output power and torque vs. rotation speed.

www.engineeringtoolbox.com

Since a VFD primarily controls motor rpm, both the torque and power change for a speed change. I do understand that a VFD can, within limits, also control the torque by adjusting the strength of the magnetic field (via current control, I think), so there is some “fudging” of the lines in the graphs presented possible. But that has is limits before the motor either disintegrates at high rpm or the rotor stalls out at the bottom end.

So, from an operator’s perspective, I want my machine to do a certain amount of work per hour, say. In order to mitigate blowing up the motor due to high speed or burning it up because it stalls, I use a bigger motor (more HP) whose power curves are such that even at the limit of the normal operation of the speed envelope, the motor itself is not at its limits.

Does all this matter in a hobby environment - probably not as most hobbyists never push their machines because it does not matter how fast the work gets done. So if your ‘50s lathe came with a 3/4 hp motor, there is no real benefit to change it to a 2 hp one with a VFD other than now you have variable speed capability and you’d never damage the motor as it is not going to run anywhere near its design limits. A 3/4 hp with VFD would normally be plenty.

It would be a completely different story in an industrial setting where the work needs to get done in a reasonable amount of time. So, yes, if the machine itself is strong to handle extra power, then increasing the motor size and running it off a VFD does make sense.

Is bigger better? Not necessarily. Is more rigid better? Always! No question. Bigger machines tend to be more rigid; thus there is a school of thought that a bigger machine is a better machine, because they are more rigid. A well built 13-40, 3 hp lathe weighing 5000 lbs is a much better machine than a well built 13-40, 3 hp lathe weighing 1700 lbs. Now, one could argue that the 1700 lbs lathe in the example is not “well built” as it is too light - but we won’t go there…

Back to @dfloen ’s Monarch: the rotational mass of the working MG set-up can not be duplicated by removing it and replacing the system with a regular 3 ph, VFD controlled motor. One would have to install some sort of flywheel arrangement to get close to original inertia, let alone the mass of the MG itself that has been removed from the base of the machine. Sand bags perhaps?

Well said from end to end @RobinHood. Glad you stuck your head out.

FWIW, I think we all agreed from the beginning that the power system on this lathe should be preserved if at all possible.

 

[Mcgyver]

Since a VFD primarily controls motor rpm, both the torque and power change for a speed change.

The torque won't drop on a vector drive. but so what? the HP will and that's what gets work done. You know if you increase the dia say 6x. the speed needs to be dropped to 1/6. If you do so, the surface speed stays the same. And if you keep the same DOC and feed (doing the same amount of work) the torque must increase 6x to achieve the same removal rate. That's what you get via mechanical speed reduction for example.

Does all this matter in a hobby environment

A couple of points. Your link deals with electric motors, but really the discussion is drives. i.e. the relative merits of a mechanical speed reduction of an MG unit vs a VFD.

Does it matter in hobby environment? I think the answer is absolutely unless one only works at small diameters. Consider: In your scenario of 3/4 HP lathe, you suggested if using an electronic speed control you might over drive it with a 2HP motor so there is some power left at low rpms. I'd guess you suggest that because you understand power/torque/rpm's. However whats commonly suggested or asked about is keeping the 3/4 motor and just replacing the mechanical transmission with a VFD. The erroneous thinking being because its constant torque all will be well. It won't; there will nothing left in terms of power at say 100 rpm on 4" work piece or dia cutter. That's not a matter of pushing the machine in a production environment, its just the reality that getting 1/20 of 3/4 hp at say 80 rpm is going to be rather lousy.

This started with my noting how the ingenious MG DC motor drive does so much better than a VFD. The anecdotal "it worked for me" is fine, but really that just means that individual found the reduced amount of power left over at low RPMs from VFD speed control was good enough for them in how they use the machine (either lightly or with little low rpm stuff). and hey, me too. I have several machines with VFD's. Peace. However when evaluating how to go, it doesn't change the truth of P=rpm x torque or that if one drive delivers closer to constant HP over a machine's speed range its going to give better performance than one that doesn't

 

[Dabbler]

I've also been standing on the sideline on this, but If you all would just allow me a moment...

Here is the crux of the disagreement: when on a VFD, when does the *system* lack *sufficient* torque to perform its function.

(the stars are what I need to intercede with)

On a lathe, your torque requirement goes way up as you reduce speed, as that is usually because you are slowing the spindle down for turning large work.

[N.B. If all you are doing is parting the torque requirement remains the same on the same diameter work - you are reducing speed to reduce chatter...]

Any vector drive VFD will preserve *almost* full torque even at low RPMs, but doesn't necessarily address the need for *sufficient* torque when you are cutting the outer diameter of a 10" piece of work.

When the *system* is a mill, the different cutter diameters aren't enough to make the need for extra torque all that important. A mill has a lot less rotating mass to worry about as well, and this takes stress off the motor.

This is the advice I give newbies: On a mill, you can easily use the same HP motor as is recommended and use a VFD.

On a lathe, my advice is different: even for a hobby machine, I suggest upping the HP of the motor when doing a Single Phase to VFD/3Phase conversion. In lower HP machines, doubling it. On 5HP and bigger machines, just go up a step to 7.5 or 8. You really notice this in the acceleration of the chuck and the ability to take a chip on the OD and face cuts of larger work pieces.

In addition, I make sure they can still shift gears to increase torque as required.

I really hope this helps you guys to see that you are actually talking about different scenarios, while agreeing on some of the fundamentals.

 

[Darren]

For anyone wondering how the lift went, it was a piece of cake!

 

[Susquatch]

On a lathe, my advice is different: even for a hobby machine, I suggest upping the HP of the motor when doing a Single Phase to VFD/3Phase conversion. In lower HP machines, doubling it. On 5HP and bigger machines, just go up a step to 7.5 or 8. You really notice this in the acceleration of the chuck and the ability to take a chip on the OD and face cuts of larger work pieces.

Hmmmm..... This advice is timely. I am planning to replace my single phase 220 lathe motor with a 3ph and VFD in the near future. I have done some pretty heavy work already at the swing extreme and I would like to be able to go a bit slower then the 70rpm I have now. Unless some special need comes along, prolly not much lower than 50 rpm though. As long as I can find a suitable motor that will fit the mounts (or accommodate modified mounts) I'll no doubt take your advice. Why not? Not likely more than 50% bigger though.

A small question though. I would have thought that the reduction gearing would buy you enough additional torque to do the trick to compensate. Wouldn't a wiser set of shallower cut depths handle any minor deficit?

 

[Susquatch]

For anyone wondering how the lift went, it was a piece of cake! View attachment 19374View attachment 19375View attachment 19376

I wasn't just wondering, I was waiting with baited breath!

I'm thrilled to hear it all went as planned.

Well done!

 

[Darren]

I wasn't just wondering, I was waiting with baited breath!

I'm thrilled to hear it all went as planned.

Well done!

It started lifting off the trailer as i tightened the one ratchet strap. It was perfectly balanced. I'm guessing its less than 3k lbs. Hoist didn't know it was there.

 

[Susquatch]

It started lifting off the trailer as i tightened the one ratchet strap. It was perfectly balanced. I'm guessing its less than 3k lbs. Hoist didn't know it was there.

I can see the smile on your face from here!

 

[Darren]

yes sir. I love it when a plan comes together!

 

[Dabbler]

I would have thought that the reduction gearing

You have the right of it, but...

In my experience, as the VFD is compensating in vector mode, you end up with additional slip, which is compensated for with extra current. However this means that the breakaway torque becomes very near the operating torque, even on a VFD rated motor. This tends to be significant at around 6 or 7 Hz, or 10% of the motor speed rating.

If you gear your lathe down, and run your VFD at above 12HZ, you get all the advantages of the VFD without the breakaway problem.

So if you have a 120 RPM setting on you lathe at 1725 RPM motor, you can get 1/5 of that or 24 RPM with the VFD with something like 80% of the motor torque, with the advantages of the gear down.

No need, then for a larger motor. When people need the larger motor is when they are trying to get almost the entire speed range by using only the VFD.

 

[Dabbler]

@dfloen Nice job! what a handy thing, a vehicle lift!

The numbers I have for a 10EE is that they are just over 3000 lbs.

 

[Darren]

@dfloen Nice job! what a handy thing, a vehicle lift!

The numbers I have for a 10EE is that they are just over 3000 lbs.

They do come in handy, I also unloaded my surface grinder with it, using a similar setup. It was only 1700 lbs though.

 

[Susquatch]

You have the right of it, but...

In my experience, as the VFD is compensating in vector mode, you end up with additional slip, which is compensated for with extra current. However this means that the breakaway torque becomes very near the operating torque, even on a VFD rated motor. This tends to be significant at around 6 or 7 Hz, or 10% of the motor speed rating.

If you gear your lathe down, and run your VFD at above 12HZ, you get all the advantages of the VFD without the breakaway problem.

So if you have a 120 RPM setting on you lathe at 1725 RPM motor, you can get 1/5 of that or 24 RPM with the VFD with something like 80% of the motor torque, with the advantages of the gear down.

No need, then for a larger motor. When people need the larger motor is when they are trying to get almost the entire speed range by using only the VFD.

I see. That all makes perfect sense. My lathe is an enclosed gear head. No way I plan to negate or disable the gearing. It's not at all the same as changing the belt on a pulley drive mill.

Its a great lathe. I really just want a slightly lower speed range at the bottom end.