Why Isn't The Feed On Manual Lathes Servo Controlled?

[dogma]

I realize that quality servo motors and a synchronous control loop are not inexpensive but neither are they expensive. Why haven't they replaced the feed gearing on manual lathes? I would think it would greatly increase the range of threads that could be cut and save on the time required for gear changes. If nothing else, it should be significantly more resilient to a crash. Is this simply a case of not being an economically relevant issue for industrial usage because of the move to CNC?

 

[JimDawson]

You pose an interesting question. While it would be possible to do what you suggest, for not much more money you can have a full blown CNC lathe. In the industrial market I suspect that most buyers would go for a CNC machine over a ''dumbed down'' machine unless it was for a special purpose second op type process. For the small/home shop market, I suspect that the price might be out of range for most users.

On the other hand, it would be reasonably simple to convert a standard lathe to do what you suggest. But if I were going to go that far, I would add the cross slide drive and make a full CNC out of it.

 

[dogma]

Perhaps machining gears on an industrial scale is incredibly economical (?) but my naive assumption is that a servo motor, controller, and encoder on the main spindle would net a win on material, QA and assembly costs. There might be a small saving in terms of freight as well.

 

[mksj]

Some higher end HLV-H type lathes have this as an option, but usually quite pricey (4K).
http://www.babinmachine.com/index.php?HLVELECLEAD

A number of examples of Electronic Lead Screws on the web. Here is an ELS kit for about $300, so it is possible to add. http://autoartisans.com/ELS/

I find that there is very little evolution or process improvement in a number of the lathe and mill designs at the hobbyist and non CNC level despite the technology available these days. I would think the an ELS system w/wo a motor driven cross slide would be fairly straight forward to implement and not unreasonable to implement price wise, when you consider it could eliminate complex feed/threading gearboxes. I had thought of adding an encoder or some form of linear position for the carriage position that would drive a cross slide stepper motor to do tapers. Surprised that the DRO can't output this information, or have evolved to provide a CNC type interface. The technology is definitely there, maybe a liability or just interest.

 

[MozamPete]

If you had an old change gear lathe the option of fitting an Electronic Lead Screw drive would probably be a cheaper option than purchasing a second hand Quick Change Gerabox (at least based on the prices I see people on Ebay asking for Myford ML7 QC Gearboxes). And you would get infinitely variable pitch so it could cover both metric and imperial threads.
I think as a retro fit there would probably be a market for an aftermarket suppier to come up with such a kit and various mounting plates to fit common old lathes.

 

[Kennlindeman]

You would have to somehow link the lead screw to the spindle for screw cutting as you will have to pick up at the same point each time you start your thread. Anybody have any ideas?

 

[Wreck™Wreck]

You would have to somehow link the lead screw to the spindle for screw cutting as you will have to pick up at the same point each time you start your thread. Anybody have any ideas?

Spindle encoder, this is how cnc lathes work.

 

[strantor]

It probably part of the reason is to do with the customers being resistant to change.

Probably also they need to sell basic machines at a certain price to justify the price of higher end machines. You would be surprised at how things are done sometimes. For example Flir sells thermal imaging cameras in the "E" series, from E4 ($1000, 60x80 pixels) to E8($4000, 240x320 pixels). The E4 and E8 and all the models in between are exactly the same physically; they all have the same 240x320 sensor. Everything below the E8 is incrementally crippled by programming in the camera. They do the same thing with cars; a more lively tune in the ECU and some flashy plastic body trim for "sport" model over base, otherwise exactly the same.

These are examples of the way things seem to be going; the manufacturer saves more money by mass production of one production model of something (engine, thermal sensor, whatever), even if it is a more expensive model, than they would by having several parallel lines manufacturing various versions.

That doesn't really apply here as there are obvious physical differences between a geared machine and a servo machine, but I say it all to highlight that in order for them to realize the profits that they want/need on their higher end machines (where they no doubt make the bulk of their money), there has to be a foundation of less capable machines. Machines that are intentionally designed NOT to live up to their full potential. Machines to make people feel like they have the option to pay more for something better, because most people feel like they are getting something better when they pay more. And in this case they are, but it doesn't have to be so IMO; I think they could sell a servo lathe for the same price but they choose not to.

 

[derf]

Manual machines are just that...manual. It's way simpler to keep things mechanical. When you start adding electronics things get complex and more expensive, not to mention harder to maintain. If you want a computer to do the thinking, you may as well go whole hog CNC. But I have seen a compound powered by a servo, on a manual lathe. Might come in handy on very few jobs, though.
Like my grand dad used to say, "If it has breasts or break out boards, yer bound for trouble". (Well, those weren't his exact words, but you get the drift.)

 

[hermetic]

Couldn't agree more Derf, gears never get out of synch, you only have to look at the problems caused by electronics on CNC machines on Practical machinist. I think the question is not "why don't they" but more "why would you want to make a simple and reliable system more complex and unreliable, and at the end of the day, no better"?