Variable speed

[Braz_in_the_Peg]

I just converted my Jet 1442 lathe to variable speed using a treadmill motor. I'm really happy I converted the lathe. It gives alot more options than I had before. People give away treadmills all the time so if you can wait until the pandemic is over, get yourself a treadmill and then order the parts off ebay for the variable speed. I turn all kinds of sizes of bowls on my lathe and have not found any issues with torque. I will say there is less torque at the lowest speed (I have mine setup to spin at 50 rpm), but if I'm turning anything at that low of a speed it's not something where I'm taking heavy cuts anyways. I removed the weight as it's not really needed. It's on treadmills just to keep the track moving and allow the person to slow down gradually.

This video on youtube is by far in my opinion the best explanation of how to convert your lathe motor to variable speed. He even lists the parts off ebay that he used but I ended up getting the 10000watt regulator to be sure I had enough power going to the motor. You have to switch out the potentiometer on the controller as well. I can't find the link to the one I purchased but I think he lists it in the video. I also added the reverse switch but make sure you can lock your spindle if you're using reverse! Some people will use the treadmill controller but none of the treadmills I picked up had the correct board and in the end I'm glad I bought the controller off ebay since this allowed me to put everything into a small box and mount it on top of the headstock.
https://www.youtube.com/watch?v=_NmAFZMAfH8

Here's some links to the parts I bought:

This regulator has the build in fan which I removed and mounted at the back of the black box which holds all the electronics.
https://www.ebay.ca/itm/10000W-AC110...MAAOSw5kdemA8F

https://www.ebay.ca/itm/2PCS-50A-100...72.m2749.l2649

https://www.ebay.ca/itm/2PCS-6-Pin-3...72.m2749.l2649

https://www.ebay.ca/itm/40mm-Outside...72.m2749.l2649

I had to make a new motor mount (used a door hinge) and set it up so the motor still hangs off the headstock and everything is contained on the headstock like before since my head stock rotates. My lathe had the reeves variable speed drive so I removed the whole thing and added a locking ring to prevent the pulley from opening up. My top RPMs are less than I had before but I can change out the pulley on the motor if I wanted to get more speed but so far even turning pens has been no problem. I also added a cooling fan with a filter to side of the motor and it blows air through the motor and keeps it nice and cool which works great. The motor had a fan on it but it was at the wrong end for my setup and would have been in the way. The filter helps prevent too much dust from getting into the motor. You can see the small black box which houses all the electronic parts and connections (I added some rare earth magnets to the bottom to prevent it from sliding off the headstock). I also added a small fan in the box to make sure the bridge rectifier stays cool and it has been working great so far (the fan was in the speed controller I bought and I removed it and mounted to the back of the box). I also added the ferrite ring which smooths out the power a little. I also used the original power switch to power the control box.

I had been wanting to do the conversion a couple years ago but had no understanding of any of this and once the need for variable speed over came my unwillingness to learn and figure it all out, I just did alot of research and in the end it really wasn't that difficult and the cost wasn't much if you can get a free treadmill. I ended up getting 5 treadmills for free and even sold one of the motors because it wasn't a DC motor. I have now made 3 different variable speed devices (my wife carves and wanted a couple variable speed sharpeners).

Hope this helps.
Dwayne

[tool fan]

So now we can ask an expert; how does it compare to your DC systems?

In terms of torque, about the same. However,the VFD and 3 phase motor combination is superior in many other respects: braking, ability to flip between forward and reverse without stopping, ability to adjust settings like torque and monitor amperage. The downside is that VFD's and 3 phase motors are not free. I would say that for small lathes, like the Beaver 3400, a decent treadmill motor and controller are perfectly adequate. For larger lathes, VFD's and 3 phase motors are definitely a better route to go.

[iamtooler]

I just finished restoring a nice Delta 1460 wood lathe. This time I used a 3 phase motor and VFD to achieve dial up variable speed. Just thought that I would share this as another option for variable speed.

So now we can ask an expert; how does it compare to your DC systems?

[tool fan]

I just finished restoring a nice Delta 1460 wood lathe. This time I used a 3 phase motor and VFD to achieve dial up variable speed. Just thought that I would share this as another option for variable speed.

[DougLA]

Thought some might be interested in my recent conversion of Rockwell Beaver 700 drill press to treadmill DC variable speed. Motivation was primarily to slow down for drilling steel. We'll see how it works over long run.

There is a couple of videos in this Flickr album:
https://www.flickr.com/photos/767624...57713202050737

[tool fan]

I played around with that for a month or so, but could never get something that I was satisfied with. In the end, at that time I concluded that the DC 51controllers were far superior to anything that I could build. Since that time I have discovered that not all DC 51 controllers are created equal. My go to controller is an MC 60 from an old treadmill.

Rory (or any body else):
How about this 10000W SCR controller with a bridge rectifier. modified potentiometer and homemade choke for use with a Treadmill DC motor? You commented in above quote that not much luck with this arrangement but did you try a larger wattage SCR as this? Parts cheap via eBay. People claim to have success using on lathes in Amazon and eBay reviews - for what that 's worth. This is one of several You Tube descriptions (nice mood music):
https://www.youtube.com/watch?v=T22pJMIAIRQ
[/QUOTE]

Interesting. Apparently I did not keep the attempt that I made so am not sure of the wattage. What I do remember though was that the DC 51 controller functioned at least as good, if not better and was already contained in a nice useable box. I'll keep looking and see if I can find the one that I made.

[DougLA]

Rory,
i have been doing a lot of reading today( home sick). One thing I came across was a thread from here a couple years ago where you said you were going to build a controller out of a 400w scr,a bridge rectifier,and a 5ohm potentiometer.
How did that work out?

I played around with that for a month or so, but could never get something that I was satisfied with. In the end, at that time I concluded that the DC 51controllers were far superior to anything that I could build. Since that time I have discovered that not all DC 51 controllers are created equal. My go to controller is an MC 60 from an old treadmill.[/QUOTE]

Rory (or any body else):
How about this 10000W SCR controller with a bridge rectifier. modified potentiometer and homemade choke for use with a Treadmill DC motor? You commented in above quote that not much luck with this arrangement but did you try a larger wattage SCR as this? Parts cheap via eBay. People claim to have success using on lathes in Amazon and eBay reviews - for what that 's worth. This is one of several You Tube descriptions (nice mood music):
https://www.youtube.com/watch?v=T22pJMIAIRQ

[tool fan]

Jet 1014 Benchtop Midi Lathe

Here is another one for those that are interested. This one was a little more difficult simply because I didn't have a cabinet to house the wiring. In the end I struck a balance by mounting the lathe on a 2 x 10 plank and ran the wiring under the plank. I also had a hard time finding a motor with a long enough arbor that was compatible with the step pulley that came with the original 1/2 HP motor. I finally found a serpentine belt drive with the same LH thread pattern as one of my motors. The belt drive is long enough to reach any of the 6 steps in the spindle pulley and the motor easily adjusts up or down to tension the belt. On the second slowest spindle step, functional speeds between 100 and 1900 are possible.

Since the belt drive on the motor is threaded on with a LR thread, I decided not to add a forward/reverse switch.

[guylavoie]

Does an induction motor have a ''permanent magnet'' rotor? The stator magnets switch between polarities with the +/- of the ac frequency so the rotor magnets must not change polarity?

No. As the name implies, induction motors have their magnetic field induced into the laminated core. Yes the stator magnets switch between the polarities of the AC current...but the rotor spins with the rotating magnetic field, so it "sees" a constant magnetic polarity across the core. The laminated core acts much like the laminated frame of a
transformer. An induction motor is actually a simpler, cheaper (and less efficient) way get getting a spinning magnet. But an advantage is the lack of a commutator (brushes), making for a quiet, maintenance free motor.

Induction motors depend on the line frequency to induce the magnetic field in the rotor, so they aren't really good for variable speed unless you can keep the voltage constant and vary the frequency itself... which is precisely what VFD drives do. The VFD also allows you to optimally drive a 3 phase motor, which is more efficient than single phase motors because the total power being converted to rotary motion remains constant, while a single phase motor is alternating between powered and free wheeling as the current wave goes up and down sinusoidally.

[iamtooler]

[QUOTE=guylavoie;n1269574The variable speed brushless DC motor would be another application of smartly driven coils around a permanent magnet rotor.[/QUOTE]

Does an induction motor have a ''permanent magnet'' rotor? The stator magnets switch between polarities with the +/- of the ac frequency so the rotor magnets must not change polarity?

[guylavoie]

Well...yes and no. Stepper motors are actually designed to be in a stalled position continuously. For that reason they are almost never used in situations where any kind of speed is required. Think of steppers as rudimentary open loop servo type systems. But I understand the similarity. The variable speed brushless DC motor would be another application of smartly driven coils around a permanent magnet rotor.

[billh]

They use permanent magnets on the rotor and a number of coils as the stator. A "computer" switches the current in the coils such that the rotor gets attracted to the next coil causing rotation. Since the circuit controls how quickly the different coils get energized you could loosely look at it as a "min vfd" but the motor itself is more complex than a simple 3-phase motor. Brushless DC motors use Hall effect sensors to determine the rotor position so coil switching can maximize torque.

Some lathe manufacturers offered brushless DC but then went to regular VFDs. Reliability???

Actually they have been around for a long time in the simple form of stepper motors.

billh

[iamtooler]

The current draw of a motor is usually indicated for it operating a full load (eg: requiring an actual 1 HP of work for a 1 HP motor). This also means that a certain amount of magnetic field "slip" is expected to occur. This is why a 60 Hz motor with a rotating magnetic field at 1800 RPM will normally end up rotating at a nominal speed of 1725 RPM.

I believe that the FLA on the tag is at the listed speed (say 1725) but an idling motor will be closer to it's synchronous speed of 1800 rpm. In this era of digital tachs that would be easy to check. With a universal motor the higher the slip the stronger the magnetic force rotating the armature. With an induction motor torque falls rapidly after 5% slip. Newer cordless tools have brushless motors, I have never had the opportunity to learn what principals they employ. I almost wonder if they are mini vfds!
Rob

[tool fan]

This means that the amperage draw goes up in line with the voltage (speed ) decrease because volts times amps = watts?

With the same load I believe that to be true. However when a load is applied, the amperage increases to the limit of the control board circuit, motor or circuit breaker.

Some of these smaller motors are rated as high as 18 amps and 130 volts or 2340 watts or just over 3 HP. This seems unrealistic. The better ones - the bigger ones - are rated around 20 amps and 90 volts or just under 2.5 HP which seems more realistic. My sense is that the little ones running at top speed under maximum load are on the verge of burning out. Conclusion: use the bigger motors and don't run them for long periods of time at top speed under load.

The other issue is cooling. When the motor runs faster, more heat is produced. However, the fan(s) turn faster presumably drawing heat away from the motor. Conclusion: either provide external cooling or do not run the motor for long periods of time at low speeds. I have yet to tear apart a treadmill and not find a motor with at least one fan. Someone wiser than me has determined that they are necessary.

When operating these motors, I think that there is probably a sweet spot somewhere between 70 and 90 volts where the motor is not over heating or over working and fan cooling is adequate.

[guylavoie]

This means that the amperage draw goes up in line with the voltage (speed ) decrease because volts times amps = watts?

The apparent "resistance" (ie: power usage, volts x amps) is more complex in a motor. It largely depends on the load. A motor with no load draws relatively little current, while a heavily loaded motor draws a lot of current. Lock the rotor and it draws maximum "locked rotor amps (LRA)". This is true for both AC and DC motors. Think about the following for a moment: The physical winding's resistance and impedance don't change whether the motor is under load or not, yet the current draw changes significantly. So what's happening?

The answer is that a motor also acts as a generator, and the spinning rotor is generating a current that counteracts the incoming current. This generated current is usually referred to as "counter emf (electro motive force)". At no load, the rotor is spinning at close to the theoretical rpm (eg: 1800 RPM for a 60 Hz AC induction motor) and most of the current is counteracting the incoming current. As load increases, the rotor slows down and the rotating magnetic field starts to "slip" more and more in relation to the incoming current's field. The generated current starts to get out of phase with the supply current and less resulting counter emf is generated...and the resulting current draw increases.

The current draw of a motor is usually indicated for it operating a full load (eg: requiring an actual 1 HP of work for a 1 HP motor). This also means that a certain amount of magnetic field "slip" is expected to occur. This is why a 60 Hz motor with a rotating magnetic field at 1800 RPM will normally end up rotating at a nominal speed of 1725 RPM.