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Musing re digital variable reluctance, direct drive and all that.

From the original to the XP, I've never been able to justify changing to a DVR direct drive from my Nova3000,1 1/2 hp Leeson DC motor and controller This is mostly due to satisfaction with the N3K and I'm only musing from my armchair since I've never turned on a direct drive lathe. I wonder about the superiority and even the desirability of a direct drive over a belted lathe. This is not meant as a knock on digital variable reluctance. Even I can see the advertised advantages and my reasoning may not be valid. DVR has been on the market for several years now. Has the early enthuiasm been sustained? What is your take?

  1. Is there enough added 'smoothness & quietness' of DVR and direct drive over electronic VS and ribbed flat belts to make a difference?

  1. Does a rpm readout offer any improvement over my 5 senses plus my cowardice?

  2. If I stay within its designed and advertised specs isn't the ugly N3K's 'beef' adequate for almost any turning project?

  1. Isn't being able to ramp up or down from or to _zero rpm worth a great deal?

  2. Doesn't a belted lathe offer more options for tinkerers. A good thing??

  1. Should, as they caution about so many things electronic these days, "in the unlikely (oh sure) event that something malfunctions", wouldn't a belted lathe and separate controller be less expensive and easier to repair and with less down time? No warranty lasts forever. or if so it can't be cheap.

  2. Maybe it's owing to patents and big investments in tooling up and advertising, but why haven't other woodturning lathe manufacturers changed to direct drive?
  3. Is the power loss in modern belt drives enough to warrant direct drive?

  1. Why would a DVR motor's integral armature/spindle and bearings be any "better" than a high quality spindle and headstock bearings?

  2. Many have been glad that they changed from N3K to DVR and many have changed from DVR to a more robust belted lathe. Regarding the motor & drive and __only__ the motor & drive, What was the difference? Did it matter?

  1. Finally. Should we turn on a lathe that's smarter than we are? In my case, Yes! :)

Turn to Safety, Arch Fortiter

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Reply to
Arch
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Can't answer those questions yet, Arch, but seems like if you already have a lathe that you like, why change?

I ordered the XP today, but I'm moving up from a 14" Jet with reeves drive..

To me, the technology difference is huge, but since you already have electronic VS, it would be a tougher choice than mine.. One of the big reasons that I chose the XP was the direct drive.. otherwise, I would probably move up to a Jet 16" with DVR and save about $500...

I think the direct drive will be smoother, but really don't know yet... It should be quieter than the damn Reeves, though...

I Guess the readout is a good thing.. never needed it before because I was the one moving the handle of the reeves..

I would like to go down to zero RPM, but the XP only goes down to 100..

Tinkering with the belt is ok if you CAN... on the Reeves drive, there wasn't any tinkering to do..

#7 is one that I've been wondering, too... It's not a new design, I've been using drills like it for years.. ;-]

I don't know if the spindle on the motor is any better, but can see the logic in making it part of the lathe spindle instead of an additional spindle/shaft..

Well, it's been years since I ran any tool that wasn't smarter than me Arch... After all, I'm spending almost $3,000 on a lathe that I don't NEED and keeping the one that's helping me make a living already... How smart is that/

mac

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Reply to
mac davis

Arch,

I hope that this doesn't sound like I'm being a smart a _ _.

  1. Don't know, don't care. I've got a N3K without electronic variable speed and it works for me. It does everything I want, it's simple, easy to maintain, easy to use.
  2. Doubt it.
  3. Yes.
  4. Absolutely!
  5. & 6. Yes
  6. DKDC
  7. Doubt it.
  8. Belt puts directional force from side on pully. Probably not a factor unless tightened too much.
  9. Haven't the experience.
  10. Even a computer is only as smart as the length of it's power cord.

Personally I think the DVR & variable speed are highly overrated/ overpriced/overhyped. I can see them being useful in rather specific circumstances, but (IMO) those are rare. Still I suppose a placebo/ imagined/nominal improvement is useful IF you have the money to burn and are WILLING to burn it.

Reply to
ebd

Some thoughts...

We frequently turn at low rpm. Motors don't like to turn at low rpm. Motors don't cool well at low rpm and they don't develop much torque at low rpm. That's why God invented pulleys.

The motor used by the Nova folks is a purpose-built motor -- they may build (or have built for them) several thousand a year. The 3-phase motors used in the more traditional VFD driven lathes are built by the millions for industry, have been built for a number of years by a number of companies, and are pretty much bullet proof and relatively cheap -- cheaper than single phase motors. The VFDs have grown up, the prices have come down, and you have lots to choose from if you are a lathe manufacturer.

The Poolewood, which is no longer available, is a direct drive lathe. In this case, they used an off-the-shelf VFD and an off-the-shelf

3-phase motor, except that they did machine a Morse taper in the spindle. It was not drilled completely through, though, so rather than using a knockout bar, you need to remember to put a collar on the spindle before inserting the drive center. Also, vacuum chucking is a little awkward.

Now, with both of the above direct drive technologies, I think that the major advantage is cost savings, not improved functionality. You don't need a separate spindle, no bearings, no pulleys, no belts,..., lots of stuff. But, you also don't have the advantage of the pulleys which gives you the option to trade torque for speed when you need to do it. Even with the best VFDs and motors, you loose torque on the low end and so a choice of pulley ratios makes both you and your machine happy.

One more thing -- direct drive is not new. Some years ago I attended an auction of surplus equipment held by the St Louis public school system. They sold a number of very old lathes (real junk) whose name I can't remember but I think it started with "B" (Blount, maybe). They all had direct drive, single phase motors. The motors had several windings and so switching windings gave you 3 or 4 different speeds. There isn't much new under the sun.

Bill

ebd wrote:

Reply to
Bill Rubenstein

The reason for DVR is to answer the desire for high torque at low rpm. Does well at it. It's an electronics tech's dream (or nightmare) working a very simple motor, and very efficient, which means less heat produced.

It is, however, nothing you can zip down to the local motor shop and get a replacement for on a Tuesday afternoon. Guess that's where the high reliability factor comes in.

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Reply to
George

As long as it doesn't talk! I Hate it when stuff like the refrigerator talks back.

Reply to
Lobby Dosser

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