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Machine keith Rucker's 10ee conversion
- Thread starter Dabbler
- Start date
Machine
trlvn
Ultra Member
I could be wrong but I believe the motivation was something like...the lathe came with the DC motor, which included a back gear arrangement, and is capable of good torque through a wide RPM range. He wanted to keep the machine as original as possible but drive it with modern, reliable, off-the-shelf electronics. In earlier videos, he indicated that he hoped to be able to share the details on the replacement DC driver design with other 10ee owners. In the end, however, it turned out that there are too many variants in the 10ee drive systems to account for. Plus, a key component in the design is now discontinued by the manufacturer. Finally, neither he or the guy in Wisconsin have capacity to give others the hand-holding they would need.
In the video, Keith mentioned he also has another 10ee but it has a 4 wire motor v. the 6 wire on this one. Originally, I think he planned to use the same DC driver setup for both lathes. I didn't hear him specifically say anything in this video but that plan may be 'out the window', now.
Craig
In the video, Keith mentioned he also has another 10ee but it has a 4 wire motor v. the 6 wire on this one. Originally, I think he planned to use the same DC driver setup for both lathes. I didn't hear him specifically say anything in this video but that plan may be 'out the window', now.
Craig
The objection to using a VFD is that to achieve the same torque at all speeds, you need to find a way to put a 7.5 HP motor into a space that is a little too small. The 4HP DC motor is a torque monster.
Several guys have done it using a small diameter C flange mount 7.5 HP motor. Most guys just compromise, and go with a 5HP motor, which is easily mounted in the space. They get about 40% less torque at the higher speeds (which is fine IMO)
Several guys have done it using a small diameter C flange mount 7.5 HP motor. Most guys just compromise, and go with a 5HP motor, which is easily mounted in the space. They get about 40% less torque at the higher speeds (which is fine IMO)
I think this is straight forward physics, but this topic often seems to end up long and drawn out so I'll restate the physics and leave it at that.
Full torque is great for a say a conveyor where the slower you go, the less work you are doing. Its not good for machine tool where what you want is constant power, i.e. being able to do the same amount of work at different speeds.
The whole point of a transmission is to maintain power over a range of output speeds - and as power is a product of torque and speed, torque has to go up when the speed goes down. That is what you want with a spindle. Imagine going from machining 1" to 5" diameter. You drop the speed to 1/5. Reasonable to expect and want the same removal rate (cubic inches per minute), right? Then you'll need 5x the torque at 1/5 the speed. That's what a mechanical transmissions does for your and why a VFD for speed control does not perform as well.
To the extent it matters will depend obviously on the task at hand, but in deciding how to drive what might be, or least among, the nicest lathe ever made, it makes sense to me to minimize the compromise. So a lot of guys that end up replacing the drive (no VFD will come close to the original performance) incorporate the two speed back gear. This was originally mounted on the front of DC motor, almost part of the motor ---- the back of the gear box was the front of the motor.
When I got mine,the drive had been stripped out but they fortunately zip cut off the back gear. I made a plate that became the front of a 5hp motor, and the back of back gear and power it with a VFD. I used the shaft of the motor as a shaft in the gearbox. It was a lot of work, ground new shafts, lapped the gear bores, even used gauge blocks and tool makers button so holes in the new plate fit the pins in the box. Phew! It still won't perform as well as the original, but by over sizing the motor imo its not much of a compromise. Other guys have use servos which will increase torque as the speed drops, but it is still advantageous to have the two speed box.
Just last night I was putting together a 3D printed mechanism to use the original speed knob - links the knob to pot for the VFD. key is stop so you can't over torque the pot. Just for kicks, here's some shots at what I've been up to with it. I hope to get the new speed control in this weekend
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It is sooooo hard for me to resist debating this stuff with you Mike. My apologies in advance, but you had to know I would.
You are getting very good at expressing yourself - prolly cuz you and I go round and round every time it comes up. But I can't just leave it lie. So I'll try to be brief and to the point.
I don't think this is a conveyor vs machining difference.
If I am taking a 1/8 inch cut at full motor rated output (hp and rpm), why on earth would I want to take a 1/2" cut at 1/4 of the rpm? That's what constant hp would allow.
What is needed is constant torque so I can keep cutting 1/8 as slowly as I want to go.
You have stated the gearing issue quite well, but again gearing is really just a way of maintaining hp and torque so you can do the same work - huge chips at lower cutting speeds.
It's so much easier and faster to just reduce the motor speed using a VFD to maintain torque to keep the chip load the same size but at less horsepower because you have less chip volume.
Without debating the physics which I'm guessing you know I can do exceptionally well, constant hp is all about constant chip volume rate (cups of swarf per minute) while constant torque is about constant chip size but at less volume (fewer cups of swarf per minute) and therefore less hp.
This is where we always fall apart on this. It might be that your machine usage is different than mine. Frankly, I don't expect constant work at lower speeds. I do expect the same chip size though. Therefore, for me, torque trumps hp.
And yes, I agree that gearing will deliver both for those few times it might be needed. But if you don't have gears and want to, or need to, go slow, a VFD is the way to get there.
Only if the two cuts were the same diameter. That speaks to one piece of work, not the machine's capabilities over its work envelope which is the point of figuring out the best drive system.
Maybe state what diameter you are talking about In your scenarios?
Same same.
Whatever the diameter was at motor rated speed. Just keep on keepin on as you turn down the speed. A motor without a VFD will eventually stall. Within its combined performance envelope, the constant torque VFD equipped motor will just keep cutting.
To be fair, so will a lowered geared system. But only if you have the required gear and for most machines only if you are willing to stop and change them. A VFD can be changed on the fly and is continuously variable.
The point of the design exercise is to accommodate different diameters in the machine's envelope, right? What would be the point to maintaining a removal rate at the same diameter and different speeds? Instead think what happens with say a 1/2" work piece and 5" work piece.
Canadium
Ian
The surface speed of the workpiece changes as the diameter changes under constant rpm. In order to maintain the same surface speed at different workpiece diameters for cutting tool effiiciency the rpm has to change. You want to maintain the same power as the rpm changes so the torque has to change. A constant torque as in a vfd doesn't cut it.
slow-poke
Ultra Member
Really nice work!
I never stated anything about the transmission. Comments were about the motor and electronics. Back when this was designed VFDs and variable speed ac motors simply did not exist so they chose a DC motor so they could gain some form of control over it with a simple DC drive. Technology has moved along and VFDs especially the ones with position feedback can do everything and a lot more than the simplistic DC drives of this era. Even the better quality open loop (SVC) type VFDs can outperform their DC counterparts, Yaskawa SVC drives can produce 200% of rated torque @ 0.3Hz.
Sounds like the original motor is a dual winding DC. Three phase motors are also available in dual winding configuration to provide the same full power in two speed ranges. The VFD manufacturers have specific VFDs designed for these dual winding motors. If Monarch was still producing lathes today, I doubt they would be fitted with a DC motor.
I never stated anything about the transmission. Comments were about the motor and electronics. Back when this was designed VFDs and variable speed ac motors simply did not exist so they chose a DC motor so they could gain some form of control over it with a simple DC drive. Technology has moved along and VFDs especially the ones with position feedback can do everything and a lot more than the simplistic DC drives of this era. Even the better quality open loop (SVC) type VFDs can outperform their DC counterparts, Yaskawa SVC drives can produce 200% of rated torque @ 0.3Hz.
Sounds like the original motor is a dual winding DC. Three phase motors are also available in dual winding configuration to provide the same full power in two speed ranges. The VFD manufacturers have specific VFDs designed for these dual winding motors. If Monarch was still producing lathes today, I doubt they would be fitted with a DC motor.
We are not talking about a design exercise - at least I wasn't. We don't have that luxury as hobbiests. Usually we are talking about improving an existing machine or fixing a broken one.
If we are talking about design, I'd go for a nice wide gear spread, a machine rigid enough to handle anything I'd likely throw at it. Enough power and torque to do the job. And a VFD or variable speed motor to fill in the gaps.
For an existing machine, we have the gears we got, the rigidity we got, the motor we got, and the capacity we got. The only things usually missing is the speeds between gears and often the desire for a lower speed than factory.
Sometimes we have broken gears to contend with, sometimes we have a blown motor that needs replacing, and sometimes we don't have the available power in the building or at the poles. Too often, the motor is the wrong voltage which often means a new motor and VFD.
The new motor can be same size for a mill, but a lathe can use a bit more oomph to spin it up and compensate by reducing the accel rate.
You replied to Slow Poke's post with a fine point:
No. It's not reasonable to expect the same removal rate. I would fully expect to reduce the removal rate. We are not using giant lathes in a production environment where time is money. We are hobbiests. More often than not, we are not operating at maximum either, so there is a little wiggle room.
I guess that is really the crux of the matter.
In my opinion if the speed goes down so does my expected removal rate.
On the other hand, if I understand you, you expect to maintain "maximum" removal rate at lower speeds. In this case, I agree that a VFD will not always achieve your expectations.
But I don't share your expectations. In my view @slow-poke was totally in-line when he said that:
Wanna debate expectations? Or maybe just drop this again for now and wait till next time it raises its ugly head?
Wouldn't it be better to have some words we could both agree on? I believe that's possible. We don't disagree on the physics, and we don't disagree on the math either. It's just that we seem to have fundamentally different views of the priority - constant torque vs constant hp. I might be wrong, but I think that's only because we have different expectations.
This why the people that try to achieve near-identical performance to the 4HP DC motor use a 7.5 HP AC motor and VFD. A 5hP motor/VFD will give you the same performance in most of the practical RPM ranges, but not enough Torque at the very bottom end to emulate the original DC motor.
I'm not a purist either. I'd use a 5HP, 4HP or 3HP motor on a 10ee, depending on what I could get, and how much I'd have to pay for the prime mover. I know I would not put 2500USD into electronics just to salvage the original DC motor, that is for sure - but more power to Rucker for achieving it!!
I'm not a purist either. I'd use a 5HP, 4HP or 3HP motor on a 10ee, depending on what I could get, and how much I'd have to pay for the prime mover. I know I would not put 2500USD into electronics just to salvage the original DC motor, that is for sure - but more power to Rucker for achieving it!!
Why? What reason would there be to not expect the same removal rate? Any machine should be able to do so. Removal rate is volume per time unit. Doesn't matter if its a DSG or Unimat.
As an example, assuming material cutting tool and feed are the same
1" diameter work @ 400 rpm and 0.10" DOC is the SAME removal rate as 5" diam @ 80 RPM and 0.10 DOC.
I can't think of lathe I've seen or worked on where wouldn't be true.
I've a lot of respect for you and your knowledge, but on this one, I'm thinking maybe you come from somewhere where the quarks spin the other way
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I don't what video it was, I just was picking up the idea of the VFD being easier. Yes, but not better and its a fair bit of work adapting the two speed gearbox to another motor. I can't remember the specifics, but there something about the DC motor that makes it special - an enormous number or poles, and or a very large diameter. Anyway its kind of a thing that people try to replicate that 1941 performance but don't manage to. They may come so close it doesn't matter, or just put cubic inches (what did, motor is 5hp) but it was a heck of a drive. The only thing I didn't was the noise (had another 10ee with the original set up)
To be as nice as possible, I think you have more guts than I do!
When I turn down the speed I am not usually going up in diameter, I am just going slower. That means less material removal all other things being equal.
If I am going up in diameter, to the point where I am stretching the limits of my machine, I don't expect the same removal rate, I back off.
I'd also add that I get very very nervous pushing my machine to its limits at any speed, I don't like broken gears, burned motors, etc etc. So I start at a different benchmark anyway.
As we both know, the torque demands on a lathe go up as diameter increases (all other things equal). I wouldn't start off at maximum torque at some small diameter and then expect to do the same work at more diameter.
My norm's and expectations start at what I can safely do at bigger diameters and then I keep that up as I get smaller. I don't start small and go big.
So the answer is: ya, that's right, I don't expect that at maximum rates. I stay away from maximum rates and work toward even safer rates, not the other way around.
100%, I thought that's what I've been arguing all along
Me too. Although I'm debating, not arguing.