• Scam Alert. Members are reminded to NOT send money to buy anything. Don't buy things remote and have it shipped - go get it yourself, pay in person, and take your equipment with you. Scammers have burned people on this forum. Urgency, secrecy, excuses, selling for friend, newish members, FUD, are RED FLAGS. A video conference call is not adequate assurance. Face to face interactions are required. Please report suspicions to the forum admins. Stay Safe - anyone can get scammed.

Machine keith Rucker's 10ee conversion

Machine
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.


You don't turn down the speed when you go from a 1" dia to 5"dia turning job?

It's nothing to do with pushing the machine. At whatever removal rate you are comfortable at 1", you should be just as comfortable at 5" (and I'm sure you are) with of course the speed reduced by 4/5ths. Keep fed and DOC the same, go from 400 rpm to 80rpm as you go from 1" to 5". No big deal ..... but that requires constant power (torque goes up 5x). When you are figuring out how to power a machine (designing) it's better to have less than more compromises.

I have 1/2 dozen VFD's so am not arguing against their use, just be eyes wide open that is as speed controller they're a compromise. i.e. the physics doesn't lie. As the orignal is such amazing performer and there is no transmission up top, I can see the logic in wanting to keep the performance of the 10ee's orginal motor and back gear
 
Last edited:
I can't remember the specifics, but there something about the DC motor that makes it special - an enormous number or poles
Yes, it's a two speed motor, it has two sets of windings a low speed high torque and a high speed.

However as stated 3P motors can also be wound as two speed with the same benefits so the magical monarch motor is not all that magical.

One example....
 
The rate of removal of material doesn't seem like a very important factor when setting up for a cut. I mean yes, if you have a lot to take off, then getting it done more quickly is good, but the tool & geometry - along with material and finish normally dictate the depth of cut and speeds - making the rate of removal a consequence of those factors rather than something to be controlled directly.

The motor obviously has to have enough power to do the job that is being asked of it, but the power demands seem to vary wildly between different jobs. Maybe I'm missing something about what you are thinking
 
You don't turn down the speed when you go from a 1" dia to 5"dia turning job?

Of course I do. I sure hope I didn't imply otherwise.

It's nothing to do with pushing the machine.

Of course it does. You were talking maximums. If we are not talking maximums then the discussion goes away.

Which is as it should be. I don't like maximums and I don't like taking a maximum position. I don't use my machine at maximums at any speed or diameter. I use it where it feels comfy.

At whatever removal rate you are comfortable at 1", you should be just as comfortable at 5" (and I'm sure you are) with of course the speed reduced by 4/5ths.

4/5 - I think you meant 1/5.

If we are talking maximums, then no I am not. If we are not talking maximums then it depends how close to maximum we are. If we are where I like to be, you are right, it doesn't matter, and neither does the torque or HP.

Keep fed and DOC the same, go from 400 rpm to 80rpm as you go from 1" to 5". No big deal ..... but that requires constant power (torque goes up 5x).

Its a silly discussion cuz I don't go from 1" to 5". I go from 5" to 1". The required torque goes down to 1/5th.

When you are figuring out how to power a machine (designing) it's better to have less than more compromises.

I already agreed that design is a different realm. But that's not what we are doing. We are fixing or using the machine we have or dealing with the power we have available.

I have 1/2 dozen VFD's so am not arguing against their use, just be eyes wide open that is as speed controller they're a compromise. i.e. the physics doesn't lie.

I have a half dozen too. And my eyes were opened wide in amazement at what they can do. I didn't experience any compromise at all. The physics don't lie - they don't have to. The only time the physics becomes an issue is when you start pushing limits.

As the orignal is such amazing performer and there is no transmission up top, I can see the logic in wanting to keep the performance of the 10ee's orginal motor and back gear

Me too, but I don't have that kind of money or time. Nor do I need what that machine could do even if I did. On the other hand, if I did have that machine, I'd have put a 3ph 5 or 10 hp motor in it and a VFD in a heart beat and it would still be way more machine than I'd ever need.
 
The rate of removal of material doesn't seem like a very important factor when setting up for a cut.......

Maybe I'm missing something about what you are thinking.

Not at all. I think you have nailed it!

Rate of removal is a job shop priority. It doesn't apply to hobbiests all that much. To be honest, in 60 years it has never entered my mind once in any work I've ever done. And that includes a few jobs where I filled a trash barrel with swarf.
 
@Mcgyver and anyone else who feels inclined to contribute. After a good night of focussing my thoughts, I have taken the liberty (and will accept the beatings to come) of drafting a discussion about using a VFD in the context of the hobby shop. What I'd like to accomplish in so doing is to write something that we can all agree with in order to avoid the debates we often seem to have when we discuss VFDs and their limits. It is written in a positive context because I think we all agree that a VFD is a good solution - albeit with practical limits.

Proposed Discussion:

When a hobbiest encounters a used lathe they often have to deal with motor voltages that don't match their shop electrical supply (eg a 550V 3 phase motor and a shop supply of single phase 230V). The most common ways to deal with these problems are to install an RPS (Rotary Phase Converter), or a VFD (Variable Frequency Drive), and/or a new motor that is compatible with the hobby shop electrical system.

An RPC is an electrical machine that converts single-phase AC power into three-phase AC power. It's used to run three-phase equipment in locations where only single-phase power is available. There are advantages and disadvantages to using an RPC. These have been described elsewhere.

A new motor needs no explanation or discussion.

A VFD is a power electronic device that controls the speed and torque of an AC electric motor by varying the frequency and voltage supplied to the motor. Typically a VFD has a Rectifier stage (AC to DC) that converts the incoming fixed frequency single phase AC power from the mains to a stable DC power using rectifier and filters, and an Inverter stage (DC to AC) that converts the DC power back into three phase AC power with a variable frequency and variable voltage to match the machine motor's requirements. A computer control unit in the VFD precisely controls this output to achieve the desired motor speed and torque. The control unit usually also provides protection features for the motor and the drive itself, such as overcurrent, overvoltage, and overload protection. In this way, a VFD can replace the typical control cabinet and its protection system.

A VFD also has advantages and disadvantages. In many ways, a VFD and a new VFD rated motor are a great solution for the hobbiest who is upgrading an old machine that has a motor that doesn't match the available electrical supply system. However, there are some compromises that the hobbiest needs to be aware of.

One of these is the mathematical relationship between HP, torque, and rpm which directly translate to chip load and cutting forces respectively. Horse power is a unit of work and so is a given volume of chip removal per unit time. Therefore, you can think about chip load or the volume of metal removed in terms of horse power, and you can also think about the force required to cut a chip as a given force or torque applied to the cutting tool.

But it is important to recognize that the VFD, motor, and gear system are limited in terms of the maximums they can provide. If the available torque exceeds the force required to cut a chip with a given depth of cut and feedrate, a chip will be cut. Similarly, if the available horse power exceeds the hp required to remove a given volume of chips in a given amount of time, the work will get done.

Unfortunately, the maximum torque and maximum horsepower available are not infinite. They have very real limits that are related to the hp of the motor, the torque multiplication of the gear train, and the hp/torque relationship capabilities of the VFD.

For most VFDs, there is a curve that defines this hp/torque relationship at various speeds - usually constant torque and declining HP at speeds below the motors rated rpm, and constant HP and declining torque at speeds above the rated rpm. Therefore, at speeds below the rated rpm, the maximum chip removal rate will decline with rpm, and at speeds above the rated rpm the maximum chip size will decline.

download.png

For most hobbiests with larger machines, these limits are usually well above the actual chip load and chip size that we normally work with. For hobbiests with smaller machines, the limitations can be very real but not unexpected. Furthermore, our machines express themselves in rather obvious ways when we try to push them beyond their limits. Fundamentally, the HP and Torque of any given power drive system in any given machine will have limits that must be accommodated by the hobbiest.

One of the most likely scenarios to cause problems is a large diameter part in a small machine with a small motor. Large parts require slower speeds to maintain the optimal surface speed for optimal cutting. If the HP required to remove chips at the optimal rate drops below that which can be provided by the motor and VFD, the machining process will begin to fail, and the operator will have to either back off on the chip load by reducing the size of the cut or further reduce the speed.

The other likely scenario is attempting to cut a bigger chip than can be supported by the available torque. Big depths of cut and high feedrates that make big chips, require lots of torque. If the torque required to cut that chip at the optimal size drops below that which can be provided by the motor, machine gearing, and VFD, the machining process will begin to stall, and the operator will have to back off on the chip size by reducing the depth of cut or the feedrate.

Basically, in both scenarios, size matters. One cannot expect a small machine and a small motor to perform as well as a big machine and a big motor.

Gearing allows a machine to operate at slower speeds without reducing chip load as long as that remains below what the hp of the motor is capable of providing. And a VFD allows a bigger cut at slower speeds than what the gearing system alone can provide. But ultimately, chip load and chip size are limited by the size of the machine, it's gearing, its motor, and the characteristics of the VFD if so equipped.

For the small machines that are found in a typical hobby shop, these limits are a fact of life that we all accept on a daily basis. It's also why we all lust for machines that are bigger than the space we have. But then again, we have what we have and we learn to enjoy them for what they can do and we learn to accept what they cannot do.
 
Susq does a good job of summarizing the _general_ case for a VFD and I don't disagree. I'll just point out that this thread started out about Keith's _specific_ instance involving a 10ee. The 10ee is a stout lathe and came equipped--in the 1940's--with a drive system that is tough to match today. It's a machine that can hog off a lot of material quickly but still produce very finely toleranced parts. (Duh, that's why they still command such high prices!)

In the beginning, Keith hoped to come up with a DC driver that would at least equal the performance the original system but be more reliable. Given what he learned along the way, I don't think he would take the same approach again. But in one of the first videos, he mentioned that he was basing his plan on what others had reported on the Practical Machinist forum. IOW he had reason to believe that equalling the original performance was an achievable outcome.

Cost is another consideration. I don't think Keith has said what he has spent on this project. I don't doubt that it is more than a motor and VFD combination would have cost. Then again, the 10ee is a high value machine so some people would happily invest extra money if they could get a no-compromises solution.

IOW, I think some of the back-and-forth in this thread has reflected general-case viewpoints versus specific instance considerations. Not the first time and I'm sure it won't be the last.

Craig
 
IOW, I think some of the back-and-forth in this thread has reflected general-case viewpoints versus specific instance considerations. Not the first time and I'm sure it won't be the last.

Absolutely. That's why I wrote the piece above. I think we get into too many distracting discussions that serve no real purpose in the thread at hand. The problem is that new members who don't have the background or experience read the specific discussion and the back and forth stuff and develop false impressions about how they apply to their own situations. If the relevant information is presented in the balanced way I tried to present it, the discussion should be a minimal distraction instead of the mish mash of back and forth where we debate things that we actually mostly agree on. Whether it works or not remains to be seen.
 
I think the most important question here is how we define performance. The performance of the machine can be described in terms of power or torque - or length or height; or lots of other parameters. But the performance that is really important, is how the part comes out. Whether on a mass production line, a job shop, or a hobby garage, that's the one that really matters I think

And when you describe performance that way, power and torque curves matter less. On a mass production line, you would look at conformity and tool life (along with waste ratios). In a job shop, your time is probably the most costly component, so taking big cuts matters. And in the hobby garage, only personal satisfaction is a valid metric of performance
 
Back
Top