Lathe power

[GraemeVW]

Just a quick question.
My lathe is 6.5" center. It's not going to be the stiffest lathe out there, it's not a colchester or harrison.
Originally it had a 1/2hp motor. I'm looking at replacing it and had been thinking of going 3/4hp, but I don't really know why. More is better?

It's belt driven so I guess it will slip at a certain point so more power may be pointless.

I'm asking as I ha e opportunity for some cheap motors, both 1/2hp, one single phase, one 3 phase, so as everyone keeps telling me, a 3 phase conversion could be done.

But, 1/2hp enough? Manufacturer thought so.
I only have a little drummond lathe to compare it to, although that has a 1/2hp motor anyway.

Is single phase 1/2hp, and 3 phase with a vfd 1/2hp directly comparable?

 

[Seadog]

I've a 1hp on my Boxford, 4.5". I think a 1.5 wouldn't be amiss. But then I do like pushing the envelope..

 

[striker]

I have 1.5kw or 2hp on my 10" Chester lathe, it's 3 phase with vfd. Variable speed. Massive improvement over the single phase 1.1kw it used to have!

 

[GraemeVW]

Ah, ok. So I'm still thinking too small.

I'll go bigger then.

 

[pressbrake1]

I've a 1hp on my Boxford, 4.5". I think a 1.5 wouldn't be amiss. But then I do like pushing the envelope..

I think my coolant pump is 1.5hp

 

[brightspark]

a 1hp one will do fine your not in to 8 hour production doing bonus cuts

 

[m_c]

If you're going to 3 phase, then going bigger will be better.

A motor only produces it's rated HP at rated speed, below that the power output is proportional to the speed, and with a VFD you're likely to run below rated speed.
With the right setup you can run overspeed as well, so belt changing can be reduced.

 

[not done it yet]

Both motors develop the same power - whether single or three phase. A simple statement of Physics. 1/2 a horse power 1/2 a horse power from whatever form it is derived - electric, hydraulic, pneumatic or engine driven.

Your lathe, if fitted with pulleys and belts suitable to transmit that power (but no, or not much, more) you may need to upgrade those to a wider section. Belts are not designed to slip - they are designed to transmit power.

Apart from the risk of breaking something, you can fit whatever size of motor you choose. Have you stalled your present drive? The biggest risk is likely that of trying to start a lathe with both normal gear and back gear engaged - an easy error. Those gears may well strip if subjected to extra power, but should be safe at the designed motor power.

The advantage of the VFD driven motor is that it can be programmed for a soft start and can be programmed to trip, on stalling, at a lower current draw than it might otherwise consume, so not burn out - - if you are sensible or lucky.

As you seem to be a little coy with you lathe description, I would not be recommending increasing the power input to your lathe.

 

[GraemeVW]

Both motors develop the same power - whether single or three phase. A simple statement of Physics. 1/2 a horse power 1/2 a horse power from whatever form it is derived - electric, hydraulic, pneumatic or engine driven.

Your lathe, if fitted with pulleys and belts suitable to transmit that power (but no, or not much, more) you may need to upgrade those to a wider section. Belts are not designed to slip - they are designed to transmit power.

Apart from the risk of breaking something, you can fit whatever size of motor you choose. Have you stalled your present drive? The biggest risk is likely that of trying to start a lathe with both normal gear and back gear engaged - an easy error. Those gears may well strip if subjected to extra power, but should be safe at the designed motor power.

The advantage of the VFD driven motor is that it can be programmed for a soft start and can be programmed to trip, on stalling, at a lower current draw than it might otherwise consume, so not burn out - - if you are sensible or lucky.

As you seem to be a little coy with you lathe description, I would not be recommending increasing the power input to your lathe.

Only got about it as I figured alot of people will know what it is, as I've been posting alot about it it's a fortis, a clausing clone.
I have never run it, stripped it the day I got it as it was too dirty to run. Therefore, I don't really know if it will feel underpowered on 1/2hp, it just seemed maybe a little low for 6.5" center height.
I'd been staying away from 3 phase, and will keep it single phase for now if I can, unless a really cheap 3 phase motor crops up leaving more budget for a vfd.

I appreciate 1hp is 1hp, I just didn't know if converting to 3 phase ment loosing power. It seems not.

 

[Chippie]

My Warco WM290 lookalike originally came with a dc motor rated at 1.5kw….
When I swapped it out for a 3 ph motor and vfd, I went for a similar rated motor of 1.5kw….doesn’t even break a sweat…, but then I’m not turning 24/7….

 

[Jelly_Sheffield]

My TOS Toolroom Lathe is 160mm center height (so 6.29") and runs off a 4 kW motor... But is also massively (literally!) built as a single 1.9t casting.

It's more a matter of how much rigidity the design has and what power transmission it can cope with (or be uprated to) than the notional size of the lathe.

So, I would look up what the maximum power transmission the pulleys fitted to your lathe are rated for and go with that as the upper limit...

I will dig out Machinery's Handbook in a minute and find the table/formulae for v-belts to assist with that.

Both motors develop the same power - whether single or three phase. A simple statement of Physics. 1/2 a horse power 1/2 a horse power from whatever form it is derived - electric, hydraulic, pneumatic or engine driven.

Yes and no.

Strictly speaking both develop the same power when running at their rated speed.

Which is where this:

If you're going to 3 phase, then going bigger will be better.

A motor only produces it's rated HP at rated speed, below that the power output is proportional to the speed, and with a VFD you're likely to run below rated speed.
With the right setup you can run overspeed as well, so belt changing can be reduced.

Becomes relevant advice.

If you want to use a VFD to provide a variable speed range, then a modern "Inverter Duty" motor will have a curve of speed to power as part of the technical data sheet.

You then have to pick the motor based on the power developed at the minimum speed you want to run, not the power at rated speed (which will often end up being 2× to 4× higher than for single speed operation).

Often there will be curves telling you how to de-rate the power supplied too in order to prevent damage to the windings, which is used for programming the VFD parameters...

ABB for instance suggests that once you go below 30Hz that the voltage is reduced according to a curve shown in the TDS.

 

[Jelly_Sheffield]

So, I would look up what the maximum power transmission the pulleys fitted to your lathe are rated for and go with that as the upper limit...

I will dig out Machinery's Handbook in a minute and find the table/formulae for v-belts to assist with that.

TL;DR - Based on the power transmission data for V-Belts, and some assumptions about the ratios and shaft speeds of the Fortis, it looks like you could go up to about 4hp (3kW) safely [for the rotating elements].

--------------------

Machinery's Handbook extract:

Unless you particularly enjoy the mathematics, then the graph in fig 4 gives the most helpful tool:

Trace across from the RPM (whichever pulley spins fastest) to the black line dividing the size of your belts (I would assume A-section by default) from the next size up, and then trace down to find the max horsepower...

For instance at 1500RPM on the fast pulley, an A section belt supports around 22-23hp maximum (remember the scale is logarithmic).

Based on the published data giving speeds for the Fortis, the lowest value for the speed of the fastest pulley in a pair in the transmission (that is a really awkward sentence to write, let alone read and make sense of) is probably around 400 rpm for the normal lathe (assuming a 1500rpm motor)...

Following that though would give a theoretical maximum power of 4 hp before it begins to damage the belts and pulley.

 

[GraemeVW]

TL;DR - Based on the power transmission data for V-Belts, and some assumptions about the ratios and shaft speeds of the Fortis, it looks like you could go up to about 4hp (3kW) safely [for the rotating elements].

--------------------

Machinery's Handbook extract:

View attachment 403252
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View attachment 403256
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Unless you particularly enjoy the mathematics, then the graph in fig 4 gives the most helpful tool:
View attachment 403258
Trace across from the RPM (whichever pulley spins fastest) to the black line dividing the size of your belts (I would assume A-section by default) from the next size up, and then trace down to find the max horsepower...

For instance at 1500RPM on the fast pulley, an A section belt supports around 22-23hp maximum (remember the scale is logarithmic).

Based on the published data giving speeds for the Fortis, the lowest value for the speed of the fastest pulley in a pair in the transmission (that is a really awkward sentence to write, let alone read and make sense of) is probably around 400 rpm for the normal lathe (assuming a 1500rpm motor)...

Following that though would give a theoretical maximum power of 4 hp before it begins to damage the belts and pulley.

Wow! Thanks for that, certainly interesting. 4hp may well be overdoing it somewhat, but good to know the drive system wont be the weak link.
The weak link will be the lathes stiffness and therefore its ability to even make use of the extra power, also, the abikkty to get the mktor through the cabinets opening!

I think I'll just look out for anything 3/4hp to 1.5hp.

I was slightly concerned of going higher due to power consumption too, but I've since found out it will only consume what your using so no penalty for going bigger.

 

[brightspark]

I was slightly concerned of going higher due to power consumption too, but I've since found out it will only consume what your using so no penalty for going bigger.

it will cosume whatever amperage the rating of the motor is as long as its turned on. used or not

 

[Pete.]

Most machines can use a motor much larger than the one fitted as stock. For your mchine I'd get a 3 phase motor of 0,75-1.1kw. Used VFD's for that size are fairly common and even Chinese ones fairly cheap.

 

[GraemeVW]

it will cosume whatever amperage the rating of the motor is as long as its turned on. used or not

So there is penalty for going larger than needed.

Not that it's a concern for me usually, I use highly inefficient valve amplifiers in my hifi!

 

[GraemeVW]

Most machines can use a motor much larger than the one fitted as stock. For your mchine I'd get a 3 phase motor of 0,75-1.1kw. Used VFD's for that size are fairly common and even Chinese ones fairly cheap.

I am warming to the idea of 3 phase, but I'll see what motor comes up.

I can set it up with the oddball motor that came with it for now if need be.
The thing is, I'm slightly reluctant to throw loads of money into it until it's back in one piece. I still don't really have a great idea of how worn it is as it really was so filthy when I got it, I didn't even want to move the carriage any more than needed!

 

[Jelly_Sheffield]

The weak link will be the lathes stiffness and therefore its ability to even make use of the extra power,

As a crude rule of thumb, a lathe designed for 12mm tooling will be good to about 2hp, 20mm about 8hp, and 32mm about 15hp.

Of course you don't have the original toolpost and compound, but the info on the Clausing equivalent seems to suggest they were originally set up with a lantern toolpost for ½" tools from the factory... So 2hp would be a reasonable place to stop.

 

[Brad93]

What is the lathe?

The gears or feedscrew will be the weakest link.

You won't break pulleys, belts or spindles, but you will damage gears and feed screws if you start taking cuts that the motor can handle but the components in between cannot.

I'd say you'd be safe with 1.5hp.

Three phase for sure, bin the single phase. That is a revelation in itself going from single to three.

 

[Brad93]

My TOS Toolroom Lathe is 160mm center height (so 6.29") and runs off a 4 kW motor... But is also massively (literally!) built as a single 1.9t casting.

It's more a matter of how much rigidity the design has and what power transmission it can cope with (or be uprated to) than the notional size of the lathe.

So, I would look up what the maximum power transmission the pulleys fitted to your lathe are rated for and go with that as the upper limit...

I will dig out Machinery's Handbook in a minute and find the table/formulae for v-belts to assist with that.



Yes and no.

Strictly speaking both develop the same power when running at their rated speed.

Which is where this:

Becomes relevant advice.

If you want to use a VFD to provide a variable speed range, then a modern "Inverter Duty" motor will have a curve of speed to power as part of the technical data sheet.

You then have to pick the motor based on the power developed at the minimum speed you want to run, not the power at rated speed (which will often end up being 2× to 4× higher than for single speed operation).

Often there will be curves telling you how to de-rate the power supplied too in order to prevent damage to the windings, which is used for programming the VFD parameters...

ABB for instance suggests that once you go below 30Hz that the voltage is reduced according to a curve shown in the TDS.

What TOS is that? If you're talking about an SN32 it doesn't weigh anywhere near 1.9ton. Unless it's a very old model?