Lathe Motor

[Paul Jackson]

Hi everyone, I don't know if this is the appropriate section to post in, but I am very new (not even started yet!!) I just bought a lathe second hand. It is a General 160 with the fixed gear ratios. The motor says it's a 230/460v 3ph. My plan is to use a VFD as research has indicated that the gearing on this lathe isn't really slow enough for bowl turning. I'm OK with the 230 2ph wiring and the 3ph to the motor. My question is related to torque and the gear to use when running the motor vs the frequency of the output. Also whether it is better to buy a 460v VFD or do everything on 230v . I have even seen talk of running a 230v motor on a 460v VFD but at 120Hz instead of 60Hz, but don't understand the concept behind that or if there any advantages to doing it.

ALSO - : ) the lathe is old but I only paid $300 CAN so it is worth putting some money into I think? The Tool rest and banjo are missing - does anyone know of a source or any ideas?

Hopefully my next questions are related to things like " Which end of the pointy thing do I hold on to!" and "Where's the lever for the auto feed?"

Thanks everyone - Paul

 

[Mark Jundanian]

Paul, I'm no help on your electrical questions, but I suggest that you solve the banjo replacement problem first.

I suspect that a banjo from another maker might be made to fit. What make and model of lathe did you aquire? Pictures?

 

[Paul Jackson]

Thanks Mark, I agree. But I don't have a three Phase supply at home, so either problem will stop me from working! It's a General 160, made in Quebec, Canada. I was thinking along the same lines as you. Most lathes I see have two flat rails for the bed with a gap in between. I guess it would be a simple matter to make a new washer/slide for the underside of the banjo?? The chipped upper pulley is also a concern and the guy that had it didn't realise that the retaining cap on the tailstock is a left hand thread and he stripped the thread trying to remove it for cleaning!! It's going to take some work to get it going but I think it's worth it.

Thanks for your speedy reply.

 

[GRJensen]

I would suggest you get in touch with Rob Cosman, a professional woodworker in New Brunswick. Rob is is the business of rehabbing old General machines, and may be able to point you in the right direction.

 

[Mike Johnson]

Most of the time you will select the VFD with the input voltage you have available in your shop or home, the output voltage will need to match
the motor on your lathe. For your application the input voltage will be 230V 2PH and the output voltage for the lathe motor will be 460V 3PH.
You can run the lathe on any set of pulleys you desire, the VFD will change the speed to any level you want. the lower gear ratio should provide
the greatest potential torque, the higher gear ratio will provide higher output speeds at the spindle.

 

[Scott Rothermel]

Hi Paul,

I'm rather new here, but want to share I've been on a similar journey with a Craftsman lathe mfg in late 1020s. Here are a couple of links that might help you:

1) Oneway makes some nice banjos and tool rests - they custom cut the cam-lock to the thickness of my rails and it works great: https://oneway.ca/index.php?route=product/search&search=banjo
2) here's a link to their toolrests (make sure the diameter of the banjo and toolrest are the same : https://oneway.ca/products-category/lathe-accessories/Toolrests
3) In looking at your photos, I noted the rusty step pulley - I just replaced mine for my 1/4 horsepower motor from Chicago Die Casting (the machining is pretty good for the price): https://www.amazon.com/Chicago-Die-...ocphy=9012184&hvtargid=pla-500503160312&psc=1
4) I've also been looking at VFDs - while the speed control is appealing, the collective price of these modifications is making me think about saving for a new lathe with variable speed - so these days I move the belt as needed.

Let me know if you have other questions - I'll share what I've learned.

 

[Larry Copas]

I have a General 260-20" equipped from the factory with a VFD. I like most everything about it except for the banjo. Not a good design. I've completed some modifications that make it acceptable. If it was missing, I would be on the phone to Oneway in the morning.

With your lathe I would be concerned about two things. First is the chipped pulley. A belt will probably run ok on it and you probably won't use that speed much with a VFD. The chip looks like it took out a few of the indexing holes. I use my indexing a lot and that would bother me.

The second item of concern is the stripped threads on the spindle. You need those threads to keep the spindle in the bearings. With the force that would be required to strip the threads, I would also worry about damage to some other part.

About the VFD. At least in the US, two phase power disappeared 50 -70 years ago. We are on a 240 volt single phase system. You will want a VFD with a single phase input and 230 volt 3 phase output. You can get one with 120 volt input which is good to around 1-1/2 HP. Above that you will have to get one with 240 volt input. Forget about 460V 3 phase. Two types of VFD's. The run of the mill cheaper one is a V/HZ control. For about the same money or a little more one can get a sensorless vector VFD. These provide higher torque at low speeds and worth the money.

 

[Bill Boehme]

To answer your question about 460 volts, first of all, there is no advantage and you probably don't have 460 volts in residential electrical service. So, you need to find an inverter that is compatible with single phase 230 VAC input power and configure the motor's jumpers for 230 VAC. The performance of the motor is the same whether operating in a 230 VAC or 460 VAC environment. Just configure the motor's jumpers to match the power source.

I have a few recommendations about things to look for when selecting an inverter:

• Sensorless Vector -- this provides a significant improvement over the bottom of the line V/Hz inverters. Sensorless vector refers to the fact that despite lacking an optical encoder to sense actual motor speed, the inverter estimates motor speed based on current, voltage, and frequency. V/Hz (volts per Hertz) inverters on the other hand don't compensate for variations in load torque and therefore lack good speed regulation especially at speeds below approximately 200 RPM.
• Auto-tune capability --In order to optimize performance, the inverter needs to know a number of motor parameters, and finding that information could be an impossible task especially for older motors. With auto-tune, the process is automated by the inverter.
• Human readable display -- in other words, the display uses plain language rather than cryptic characters that keep you searching through the user manual.

Regarding two-phase power, there seems to be a fairly common misunderstanding. Two-phase power is a relic of the distant past in which there was a 90° phase difference between the two phases. Residential 240 VAC power is single phase.

 

[Paul Jackson]

Hi Everyone, I must say that the responses to my question are remarkable. The willingness for people to share their knowledge and help a newbie is amazing. "Remarkable" might seem a little overboard, but in this day and age when everyone seems to be hell bent on living their lives on social media, name calling and generally being nasty; using the internet as it was originally intended is refreshing - my sincere thanks to you all or y'all .

GRJ - thanks for the info for Rob C. I will certainly get in touch with him and let you all know the outcome.

MIke - thanks - what I'm getting is, use the smaller headstock pulleys to get the torque and lower the speed on the vfd.
Comment: I see on the modern machines that there is often a combination of pulleys and VFD control, presumably because the vfd alone can't cover the whole range of speeds necessary. ??

Scott - You may be pretty new but your lath certainly isn't LOL - ( sorry Scott, just having fun with your typo! ) Great advice! Thanks for taking the time to provide all the links - so helpful. It seems Oneway is THE way to go. I see them mentioned a lot on YouTube.

Larry - Thanks Larry - nice to meet a fellow General owner. Thanks for mentioning the banjo design. I'll probably look at modding another manufacturer's design in that case. I hear you on the chipped pully. I was thinking of a replacement along with new bearings while I have it apart, although the bearings feel fine. I have no idea what the index holes are used for yet, but I'm sure YouTube will know or if anyone wants to enlighten me?
I may have misled you regarding the stripped threads. They are on the backside of the tail stock. It's a cap that retains the screw that the tailstock tapered shaft rides on. Part 1627 in the diagram. I'm thinking of tapping the tailstock casting and putting three screws horizontally through the cap, into the tailstock for retention.



Regarding the VFD - I'm surprised to hear that at least parts of the US have switched to 240V - I'm from England originally and that's what I'm used to. Much better than 120v. In Canada we have three phases in the street transformer and two phases are tapped off to each residence. I assume they are 120 degrees apart. If I measure across the two phases I get 240v. I read somewhere that they are 180 degrees apart, but I think that is incorrect. My motor is only 0.75 HP so maybe 120v VFD will work. But it would be good to have 220/240 v in the shop anyway for my table saw. I had never heard of a sensorless vector VFD before, so I will research that for sure - sounds a good idea. I like the idea of not losing torque. I am NOT going the 460v route after reading up on the differences.

Bill - Thanks - you are entirely correct. I did some reading and saw that series 460v is the same as parallel 230v as far as voltage across each winding is concerned and therefore torque. Great to have that confirmed though. I really appreciate the tips for selecting the right VFD. I would much rather spend a little more and get it right - now if they're double the cost, that might be a different thing altogether. I like the idea of auto tuning for sure.
And thanks for assuming I am a human and can read - very kind

Single phase vs two phase vs three phase is sure confusing!!


Thank you everyone - much appreciated and any more comments/help is very welcomed

Paul

 

[Bill Boehme]

MIke - thanks - what I'm getting is, use the smaller headstock pulleys to get the torque and lower the speed on the vfd.
Comment: I see on the modern machines that there is often a combination of pulleys and VFD control, presumably because the vfd alone can't cover the whole range of speeds necessary. ??

The issue isn't really about torque, it's about power. When you change speed through a gearbox (whether it's actual gears or belts and sheaves) the output power is equal to the input power minus a usually small loss in power due to the less than 100% efficiency of the transmission. When it comes to electronic speed control, you can't fool Mother Nature. The convenience of changing speed with the turn of a dial carries a significant penalty in reduced power output. As motor speed is reduced by the VFD, the output power is reduced in direct proportion (the same thing applies if we're talking about DC motors and variable voltage control). This reduction in output power is not a deficiency in electronics, it's simply a fact of physics. A motor can output its full load torque from full speed almost all the way down to stall. And, Power is the product of torque and speed (P = τ X ω) where P is power, τ is torque, and ω is speed. If we want to use the FPS (foot, pound, second) system where power is in horsepower, torque is in pound-feet, and speed is in revolutions per minute then we need to include the following conversion factor:

HP = (Torque in lb-ft X RPM) / 5252​

Torque by itself doesn't mean much, an RPM needs to be also stated to indicate the power and that is why auto drive train specs state torque at a specified RPM.

To answer your question, the best strategy is to have the motor running at a high speed and select the pulley range as low as you can to maximize power at the spindle. Of course, at the slowest speeds, you just have to accept the fact that there won't be much power. but you don't need much power at very slow speed.

 

[Kevin Jenness]

I found the banjo on my General 260-20 needed a lot of torque on the levers to maintain the tool post height and keep it from creeping on the ways, plus it really squirmed and twisted when using my McNaughton coring jig. I replaced it with a Oneway banjo and that is 100% better, but pricey at over $300 delivered. The banjo that came with my (used) 260 with riser blocks is actually a short model with a riser post, and may work for your lathe if the space between the ways is 1.75". If not, the clamp block could be modified or replaced. PM me if you are interested.

I really like the Robust low profile rests.

My lathe has a mechanical adjustable speed (Reeves) drive to which I added a Teco vfd from Factorymation, and it works well. You will need to bypass the existing starter as you can't have any switching between the vfd and motor. You may want to add an external control station to operate the vfd. If you aren't comfortable with that you can get a competent motor shop to wire one up.

For bowl work you would probably want to use a middle pulley with a top speed around 1000-1200 rpm. A commonly cited rule of thumb is maximum safe speed = diameter in inches x rpm = 6,000-9,000.

 

[Paul Jackson]

I found the banjo on my General 260-20 needed a lot of torque on the levers to maintain the tool post height and keep it from creeping on the ways, plus it really squirmed and twisted when using my McNaughton coring jig. I replaced it with a Oneway banjo and that is 100% better, but pricey at over $300 delivered. The banjo that came with my (used) 260 with riser blocks is actually a short model with a riser post, and may work for your lathe if the space between the ways is 1.75". If not, the clamp block could be modified or replaced. PM me if you are interested.

I really like the Robust low profile rests.

My lathe has a mechanical adjustable speed (Reeves) drive to which I added a Teco vfd from Factorymation, and it works well. You will need to bypass the existing starter as you can't have any switching between the vfd and motor. You may want to add an external control station to operate the vfd. If you aren't comfortable with that you can get a competent motor shop to wire one up.

For bowl work you would probably want to use a middle pulley with a top speed around 1000-1200 rpm. A commonly cited rule of thumb is maximum safe speed = diameter in inches x rpm = 6,000-9,000.

Thanks Kevin,
I would have like something a little beefier like the 260 but this one came along dirt cheap and I'm just getting started anyway. Good information about the banjo, it's appreciated. I looked at the Oneway - they do a 12" and a 16" but not a 14" which I think would be perfect. But I agree, it's pricey, as much as I paid for the rest of the lathe so far!! So I'm probably going to make one. I have a friend who has a shop and between us we should be able to come up with something that decent. I'll post pictures when done, but it will take a while I think. I have heard of lower speeds when turning bowls - is that just when you're roughing out something on the larger scale of things? I don't have the lathe with me right now, but I'll measure the ways and see what the size is.

 

[Paul Jackson]

The issue isn't really about torque, it's about power. When you change speed through a gearbox (whether it's actual gears or belts and sheaves) the output power is equal to the input power minus a usually small loss in power due to the less than 100% efficiency of the transmission. When it comes to electronic speed control, you can't fool Mother Nature. The convenience of changing speed with the turn of a dial carries a significant penalty in reduced power output. As motor speed is reduced by the VFD, the output power is reduced in direct proportion (the same thing applies if we're talking about DC motors and variable voltage control). This reduction in output power is not a deficiency in electronics, it's simply a fact of physics. A motor can output its full load torque from full speed almost all the way down to stall. And, Power is the product of torque and speed (P = τ X ω) where P is power, τ is torque, and ω is speed. If we want to use the FPS (foot, pound, second) system where power is in horsepower, torque is in pound-feet, and speed is in revolutions per minute then we need to include the following conversion factor:

HP = (Torque in lb-ft X RPM) / 5252​

Torque by itself doesn't mean much, an RPM needs to be also stated to indicate the power and that is why auto drive train specs state torque at a specified RPM.

To answer your question, the best strategy is to have the motor running at a high speed and select the pulley range as low as you can to maximize power at the spindle. Of course, at the slowest speeds, you just have to accept the fact that there won't be much power. but you don't need much power at very slow speed.

Hi Bill, I'm probably intermixing power and torque where I shouldn't! And as I've never even put metal to wood on a lathe to this point in time, I'm not sure what effect speed vs power vs torque has anyway?. I see people turning big chunks of irregular wood at quite low speeds and just figure that takes some umph (to use another technical term) from the motor. I also see conflicting comments with regard to VFD's. Some say you lose power, some say the power is maintained (I would agree with you!) and some say that the motor has to be configured in Delta rather than Star. Many say a sensorless VFD is a must, but I see tons of people on YouTube using the cheap Chinese ones for $100 or so to good effect. I'm trying to strike a balance between doing it right, having a good woodturning experience and being cost effective. Input from yourself and others on the forum is invaluable as I try to work through it all.

 

[Kevin Jenness]

I have heard of lower speeds when turning bowls - is that just when you're roughing out something on the larger scale of things?

The rule of thumb I referred to is a theoretical maximum speed based on workpiece diameter and you have to use judgment based on the particular blank. When roughing out the speed would be lower. For a thorough discussion of the subject here's another thread speed.

 

[Paul Jackson]

The rule of thumb I referred to is a theoretical maximum speed based on workpiece diameter and you have to use judgment based on the particular blank. When roughing out the speed would be lower. For a thorough discussion of the subject here's another thread speed.

Thanks Kevin