Do AC motor speed control circuits make mechanical speed controllers obsolete?

Thread Starter

Mellisa_K

Joined Apr 2, 2017
359
Hello,
Lathe spindle speed control: electronic vs mechanical

Could you please look at the diagram below as a common generalised gearing mechanism for, say, driving a lathe spindle.
Preet Lathe Machine.jpg

Now, comparing this with an
AC motor speed controllers like the following:

motor-speed-regulator-schematic.gif
Is it possible to do away with the mechanical cone pulley system with this type of electronic speed controller?

Judging by many examples of lathes for sale online it appears the answer may be yes. For example this one appears to be directly driving the spindle without gearing:
motor-speed-regulator-schematic.gif Preet Lathe Machine.jpg 552948-MC-1643_2.jpg



Please note: I am not asking about this particular circuit as such. My question is a general one
 

MaxHeadRoom

Joined Jul 18, 2013
20,707
A single phase motor in this application? No it won't work, especially with the motor shown that appears to have both start and run capacitors.
If 1ph supply, typically it is done with a 3ph motor and a 3ph output VFD fed from 1ph 240vac.
Max.
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
20,707
Also, consider the torque multiplication provided by a mechanical transmission.
With an electronic speed control, the low-speed torque will be very low.
Not necessarily, I think you are confusing torque with HP.
I have seen a actual demo of a VFD used on a gantry crane lift holding a load stationary.
Also there are examples used for elevator control.
Max.
 

Thread Starter

Mellisa_K

Joined Apr 2, 2017
359
A single phase motor in this application? No it won't work, especially with the motor shown that appears to have both start and run capacitors.
If 1ph supply, typically it is done with a 3ph motor and a 3ph output VFD fed from 1ph 240vac.
Max.[/QUO
Not necessarily, I think you are confusing torque with HP.
I have seen a actual demo of a VFD used on a gantry crane lift holding a load stationary.
Also there are examples used for elevator control.
Max.
So, Max, from the tone of your inputs here, electronic control vis a vis mechanical control could be an option for me if I wanted to build a woodworking lathe with my partner. I have access to 3 phase power.

If so, could you please point me in the right direction to find out more, starting with the words of the acronym "VFD"?
 

Thread Starter

Mellisa_K

Joined Apr 2, 2017
359

BR-549

Joined Sep 22, 2013
4,938
Use both. Keep belt drive and up-grade motor with modern controller, for older equipment.

For new equipment, properly matched motors and controllers can whistle dixie now.
 

Thread Starter

Mellisa_K

Joined Apr 2, 2017
359
Use both. Keep belt drive and up-grade motor with modern controller, for older equipment.

For new equipment, properly matched motors and controllers can whistle dixie now.
This will be new equipment.

Its obviously easier mounting-wise to use electronics but perhaps more expensive in terms of cash outlay?

However the cash outlay may easily outweigh the design labour and welding labour I put into the project.

So, I'm starting to think and read about it. Any ideas to start me off?
 

BR-549

Joined Sep 22, 2013
4,938
It's relative because what you don't have in cash, you must make up for in labor. The best way to go is cash.

I never got to go that way. I only heard it was the best.

What are the specs of the new equipment? What exactly are you looking at?

It might be less than you imagine.
 

Sensacell

Joined Jun 19, 2012
2,567
Not necessarily, I think you are confusing torque with HP.
I have seen a actual demo of a VFD used on a gantry crane lift holding a load stationary.
Also there are examples used for elevator control.
Max.
Of course there are very high-performance motor/drive systems, but this stuff is expensive.

The point is illustrated by small lathes driven by lower HP VFD's - yes, they can rotate slowly, but try taking a heavy cut and the whole show stops. The same machine with the same HP motor with a mechanical transmission can chew away at low RPM all day with no problems.
 

MaxHeadRoom

Joined Jul 18, 2013
20,707
There are the low end Chinese Huanyang VFD's, but if you want a little extra quality and support, go with a higher end version, Hitachi make a decent product.
Specify Sensorless Vector models for systems such as lathe's etc.
Also if operating under 5HP you have the option to use 3ph motor with the 240v single phase supply.
Max.
 

Thread Starter

Mellisa_K

Joined Apr 2, 2017
359
It's relative because what you don't have in cash, you must make up for in labor. The best way to go is cash.

I never got to go that way. I only heard it was the best.

What are the specs of the new equipment? What exactly are you looking at?

It might be less than you imagine.
It's a blank slate.

The aim is to develop a specialised bowl turning lathe. This requires a large "swing" (diameter of work) size - greater than most generalised machines on the market.

Here is one: http://www.winburn.com/BowlLathe.asp
 

BR-549

Joined Sep 22, 2013
4,938
This is just an opinion, if the lathe is going to be human operated.....go mechanical.

Go and stay simple on everything. Don't add needless lights, bells, and whistles.

Can you get the results needed, within the allotted time, without the gobbledygook?
 

Thread Starter

Mellisa_K

Joined Apr 2, 2017
359
This is just an opinion, if the lathe is going to be human operated.....go mechanical.

Go and stay simple on everything. Don't add needless lights, bells, and whistles.

Can you get the results needed, within the allotted time, without the gobbledygook?
Yes that's good advice. Thankyou
 

Thread Starter

Mellisa_K

Joined Apr 2, 2017
359
Depends if you want the convenience of changing the speed at will on the fly, or go through the belt changing pulley step etc.
Max.
There are pros and cons, yes. I want to find out about each option.

Regarding VFDs and the design of a working resystem, can you point me towards a text or other reference, please?
 

shortbus

Joined Sep 30, 2009
7,691
It's a blank slate.

The aim is to develop a specialised bowl turning lathe. This requires a large "swing" (diameter of work) size - greater than most generalised machines on the market.
Then for me it would be a "variable speed pulley" type drive. A purely mechanical drive that is not as prone to electronic failure, I have both a milling machine and a metal lathe running on VFD's, because I haven't got 3phase power, and they some times do fail. But my mill and a band saw both have variable speed pulley drives and they have never failed.

If this is a project with a end result to be sold to the public I'd definitely go with the variable pulley system. Just one example of those out there - https://www.torquetrans.com/blog/how-do-variable-speed-pulleys-work
 
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