KeeponDragon
Super User
Definitely watching this one...I'm curious what, if any issues I'll have converting my 9x20 over to VFD...
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Lathe VFD Motor selection
- Thread starter lucsimoneau
- Start date
Rauce
Ultra Member
This is good advice. I did a 2hp motor with a 2hp import VFD on my last lathe and it would shut off on start up until I adjusted the ramp and would also shut off on heavy cuts sometimes. I lived with it but won’t be making that mistake in the future.
I think using a higher RPM motor isn’t really an issue here. The point of the switch is to eliminate changing belt positions right? So I would install the belt in a position that gives you a speed in the neighbourhood of 1000rpm at the spindle with the higher speed motor running at 60hz (between 4:1 or 3:1 reduction).
That way you can go up to 80-90hz to get your 1400rpm top speed and down to 20-30hz to get down to 300-400rpm. For anything slower than that I would still use the back gear since you’ll get a lot more torque that way.
A name brand VFD will have a good manual with diagrams for controls. You can probably reuse some of what’s there and find a spot to put a potentiometer for frequency control.
A built in tachometer for rpm is nice but you can also do what I have done before and use a handheld tach to plot frequency and rpm and print a little chart to stick on the wall next to your lathe.
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TorontoBuilder
Ultra Member
That's what I added to my old lathe...
I mounted the magnet to a disc, and the disc to the spindle with a taper loc fitting... and the sensor to the headstock... not shown mounted. Sad omission that
curmudgeon
(Steve)
Nice!
What doesn't work well is hot gluing the magnet to a treadmill motor flywheel while bench testing maximum speed. The replacement magnet is now epoxied to the aluminium step pulley on the spindle of my wood lathe.
Rauce
Ultra Member
I’ve seen that on a friends unit but I don’t think any of mine have that feature? At least I don’t recall seeing it in the manuals. I have an older Teco on my mill and the lathe will have a GE/Fuji.
Not a big deal for me, my mill has a vari-speed head so I leave it at 60hz and it really just serves to provide 3ph. My lathe once it’s done will have the VFD in the cabinet out of sight so I’ll be adding a seperate tachometer, or maybe a DRO with rpm option.
Dabbler
ersatz engineer
You can get the manual for your TECO online, for almost any model. Barring that, there's a 1-800 number that the guys at the end of the line are *really* helpful...
Looks like there are a lot of like minded members here. @TorontoBuilder , @Rauce , @YotaBota , @curmudgeon , @KeeponDragon , @cjmac , @phaxtris , @lucsimoneau ,
@Dabbler and I have chatted about just such a conversion on my 1440 lathe too.
I already have the 3Hp TECO L510 VFD for this job. I've been shopping for a 3HP VFD Rated 3phase motor for quite some time now to replace the 2HP single phase motor that is there. I also plan to install a DRO.
My spindle sticks out of the rear of my lathe head by about 2-3/4 inches.
So I am planning to make a double sleeve collar of aluminium or plastic to sandwich two or four or more magnets between them to get an RPM Readout. Mine will be similar to what @YotaBota described above. It will be an Arduino based system initially, but my future DRO will definitely include an RPM function that will use the same sensor. By slipping the collars over the rear spindle all the way to the head, they won't interfere with my rear spider and that makes a solid sensor mount on the gear box a no-brainer (maybe pickup the two screws for the cover bolt shown in the photo above). The ABS Pipe in the photo would work. Sandwiching the magnets between two sleeves eliminates the worry of magnets flying around in my shop. If I knew how to drill a sleeve from the inside out I'd only need one sleeve.
The reason for multiple magnets is to speed up the data acquisition, improve low speed resolution (where it is needed most), and provide better balance in the spindle. Although I doubt balance is really an issue, it's free with multiple magnets so why not.
I'm not really sure I really need a VFD Rated motor since I'm mostly interested in obtaining slower speeds. My lowest speed is 70rpm now and I'd like to hit 40 - but 50 would do. A VFD Rated motor would take me to 10 or even lower.
Although my VFD does have the RPM function that @Dabbler described, I won't be using it because I still want to be able to use my gearing. I'd prefer a direct rpm reading from the spindle.
Obviously, this project is only on my to-do list for now. It isn't really more than a plan collecting ideas right now. I'll post more fully in a new thread when I actually do the conversion. I'm just throwing my planning thoughts out there for the benefit of those who are doing it now, or who are planning a future conversion too, or who have better ideas to contribute to my own plan.
@Dabbler and I have chatted about just such a conversion on my 1440 lathe too.
I already have the 3Hp TECO L510 VFD for this job. I've been shopping for a 3HP VFD Rated 3phase motor for quite some time now to replace the 2HP single phase motor that is there. I also plan to install a DRO.
My spindle sticks out of the rear of my lathe head by about 2-3/4 inches.
So I am planning to make a double sleeve collar of aluminium or plastic to sandwich two or four or more magnets between them to get an RPM Readout. Mine will be similar to what @YotaBota described above. It will be an Arduino based system initially, but my future DRO will definitely include an RPM function that will use the same sensor. By slipping the collars over the rear spindle all the way to the head, they won't interfere with my rear spider and that makes a solid sensor mount on the gear box a no-brainer (maybe pickup the two screws for the cover bolt shown in the photo above). The ABS Pipe in the photo would work. Sandwiching the magnets between two sleeves eliminates the worry of magnets flying around in my shop. If I knew how to drill a sleeve from the inside out I'd only need one sleeve.
The reason for multiple magnets is to speed up the data acquisition, improve low speed resolution (where it is needed most), and provide better balance in the spindle. Although I doubt balance is really an issue, it's free with multiple magnets so why not.
I'm not really sure I really need a VFD Rated motor since I'm mostly interested in obtaining slower speeds. My lowest speed is 70rpm now and I'd like to hit 40 - but 50 would do. A VFD Rated motor would take me to 10 or even lower.
Although my VFD does have the RPM function that @Dabbler described, I won't be using it because I still want to be able to use my gearing. I'd prefer a direct rpm reading from the spindle.
Obviously, this project is only on my to-do list for now. It isn't really more than a plan collecting ideas right now. I'll post more fully in a new thread when I actually do the conversion. I'm just throwing my planning thoughts out there for the benefit of those who are doing it now, or who are planning a future conversion too, or who have better ideas to contribute to my own plan.
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Proxule
Ultra Member
Thats where I got mine for 200 bucks, picked up local. Easy peasy
Rauce
Ultra Member
Modern general purpose motors are good for 10:1/20:1 which I think is more than adequate. Any lower than that and you’re losing significant HP anyways. At that ratio you would be down to 7rpm with constant torque.
A true inverter duty motor on your lathe would be rated to go as low as 0.07rpm at the 70rpm setting and hold torque at 0rpm without overheating.
TorontoBuilder
Ultra Member
Note: Anyone buying a cheap rpm meter from amazon will likely be limited to single magnet low resolution capability, because well the manufacturer is cheap. Not a big deal, I tested my old tachometer against several very costly analog and digital tachometers at 100 rpm and so no greater than 3% variance. It only really matters for very low speeds where accuracy is critical. Not often the case on a lathe
Multi-magnets require a DRO with that option, or an arduino or other controller based custom job. My buddy is making us a few to beta test and then we will likely offer some to community members. Ours will have multiple encoder options and multiple magnet option and surface feet per minute calculation. One other item I requested to be built into the tachometer is a revolution counter for winding coils for electric motors and solenoids etc... this will require high accuracy at low rpm.
Yes shameless plug... mods feel free to delete that second paragraph if it offends
I have Arduino code and basic design for a tachometer / SFM using a 20x4 LCD display. Its configured for a mill, but could be easily modified for a lathe.
The Ditron D80 DRO on my mill can be set to use multiple magnets. I plan to get a Ditron for my lathe too. I'd like to keep them the same for commonality. So no worries there.
A while back I looked at the code that @whydontu provided. It shouldn't be a problem to add multi sensors to that. If it is a problem, I'll have fun working it out. I've already wired up a box to play with.
I'm not fond of the Amazon/Ali tachs so no worries there.
TorontoBuilder
Ultra Member
We paid extra to get the more expensive DRO option for the lathe JUST to be sure that we didn't have to learn anything different between the two machines.
lucsimoneau
Active Member
A bit back to my original question - if the VFD set at 30Hz would put the RPM range of the 3450 RPM motor at 1725, that would mean that I'm back with the original motor's speed range with the belts and back gear. What would be the best position of the belt in this situation? Later on I could always switch out the motor for a slower RPM model pretty easily if this caused a problem. Thanks!
That's going to depend on what spindle speed you most often use, I would also plan your belt selection with the motor running as close to 3450 a possible while still giving you the spindle speed your looking for
I honestly don't think you are going to get away from having to move belts entirely, that motor is going to run out of torque at some point as you keep turning the Hz down, even dc motors run out of torque when you slow them down enough
Rauce
Ultra Member
If it was me I’d probably use “A2”. That would give you 800rpm spindle speed at 60hz. Set the upper frequency limit to the highest speed you want to run your spindle.
If you set the lower limit to 20hz you’ll be down to 266rpm. Put it in back gear and you’re down to 61rpm. That sounds reasonable to me and at 20hz you will not notice a significant drop in torque, especially if your new 3ph motor has more HP than your old one.
With that set up you’d get the full range you had before and never have to move a belt. Just back gear for low speed operations.
