Lathe conversion to 3-phase power

[WillieL]

Sorry Willie,

Sort of messed your thread up a bit,

 
DaveH

Not messed up at all Dave. You stimulated some great discussion!   

As was mentioned previously, the power here in the States is supplied at 60 Hz. So the frequency display just gives me a rough idea of what speed the lathe motor is running at as compared to it's rated speed. 60 Hz = 100% / 30 Hz = 50% etc.
Also mentioned above - is the fact that you have to be careful about running the motor too slow -or- too fast as this can cause it to overheat and cause damage. Don't forget that the fan blade that cools the motor is attached to the same shaft as the output pulley! You can however buy inverter duty motors that have a separate motor built in for the cooling fan, that runs at full speed all the time. Those types are designed to be run at slower than "normal" speeds and controlled by a VFD. Of course those are much more expensive motors.   

I only run my lathe at slow (motor) speeds for short periods of time, so I'm careful to not let it overheat. And I try not to run it below 20 - 25 Hz. But having the display there is a good reminder if I slow the motor down to hit a specific SFM number. If the frequency drops too low I know to "gear down" the spindle to get the motor speed back up again. The reason for the two pulley sizes is because the lathe is set up for two speed ranges. High range (I) and low range (II). See the spindle speed chart on the front of the headstock.

A lot of guys run a single pulley and set the machine in high range and leave it there. (Usually on milling machines.) They simply control all speeds with the VFD alone. You can overdrive a motor as well. I could run mine at 90 Hz and get 150% of its rated speed. But again, that is hard on a standard motor and something I chose not to do.

The things I like about the "tachulator" display is that it gives me a very accurate display of the actual spindle speed, as well as a direct reading of the SFM for a given diameter of my work piece. If I am turning a 4.3 inch diameter piece of steel that needs to be cut at 420 SFM, I don't need to do any math to figure out what spindle speed to use to get there. All I have to do is input my 4.3" into the unit just by turning the knob, push the knob in to display the SFM reading, and then adjust the speed of the lathe spindle via the VFD control knob until it shows 420 SFM on the display. Fast and easy!   

It's also nice to have an infinite spindle speed adjustment for dialing into the "sweet spot" for a good finish, instead of being stuck between two set speed choices. Sometimes the best speed is somewhere in the middle.

Almost forgot.... the tachulator unit uses an infrared optical sensor that just needs to "see" a reflected beam. It can be as simple as a single strip of reflective tape, or a painted white line etc., on the shaft that you want to measure the speed of.
The display is adjustable for the number of inputs it sees per revolution. The more divisions you use, the more accurate the display is when measuring SLOWER speeds. I made the encoder ring to slip on the outboard end of my spindle with 10 divisions. According to the manual, 10 divisions will give a resolution of 5 RPM at slow speeds. As I noted in my OP, mine will read accurately down to 2 RPM.

I am VERY happy with the way it performs. 
Cheers mate!   

[DaveH]

Thanks Willie,

It's becoming clearer.    The encoder ring you made yourself, is it painted black, white.?
 
DaveH

[WillieL]

Dave,

The ring was cut from a piece of aluminum round stock that I had left over from another project. I cut shallow recesses in the OD on my mill using a rotary table to mark out the divisions I needed. Then I polished up the OD a bit to make it more reflective, and then painted the recesses with flat black paint to provide the contrast between the sections.



I could have simply painted black lines on the spindle shaft itself and mounted the sensor down closer to it. But it would have been a little more difficult to get the sensor mounted in that position. The small piece of aluminum square I used for the sensor mounting block was also a piece from the "scrap bucket".  Waste not - want not... 


 


 The Tachulator kit contains the display unit, a power supply (wall wart) and the sensor. You have to provide your own way of mounting the sensor to whatever equipment you are using it on. Mini-lathe, milling machine, whatever.... 
 

[WillieL]

The last photo - The VFD unit it is displaying 52.9 Hz – so what, does that tell me? What is it for?

DaveH

Dave,

Something else I forgot to mention... 

On the VFD display you will also see an indicator led for Amps. You can change the readout to show how many amps the motor is drawing if you prefer. Sometimes useful to see how much of a load you are putting on the machine if you are making HEAVY cuts. It will give you an idea of the impending doom if you are trying to push your machine too hard or if that loud screeching noise you hear is a bearing that is about to lock up.   

 

[DaveH]

Willie,

I'm with it all now

Thanks
 
DaveH

[hopefuldave]

Most (if not all) VFDs have an analogue output available - on my setup it's programmed to put out a 0-10V signal proportional to 0 - 150% motor current (to a nice WW2 Admiralty Model meter with a home-made scale -  Bakelite's contemporaneous with the lathe!) and gives a good indication of the load on the motor, but it can be set to give a 0-10V signal proportional to output frequency - if this is taken to a cheap (£10?) panel meter, a new scale can have speed in each gear/belt position marked out on it (with a little calculation).

The tacho' will need to have Nixie tubes (a' la atom bomb countdown in Goldfinger) to look right, though...

Re Emergency Stops - the spindle will brake faster if the power's still on at the VFD and braking's programmed... I've set my EStop up that way, with a separate emergency power off - YMMV

Dave H. (the other one)