[javohert]

Hi, i want to cut steel, but i have a spindle water cooling of 1.5kw. I plan to use it to drive a larger diameter pulley, to get more torque.

I am considering this alternative, since the spindle is liquid cooled and could work long hours, unlike a servo motor that does not include ventilation.

Any suggestions are appreciated

[awerby]

That will require a pretty drastic pulley reduction, since spindles like that have very little torque at under half their maximum speed. I'm guessing you'll probably need more than two pulleys.

[joeavaerage]

Hi,

That will require a pretty drastic pulley reduction,

I agree.

Just as a sanity check try these numbers. For uncoated carbide tools in mild steel you need a surface speed of 100m/min. You can go slower (and get greater tool life) and you can go faster
but with a dramatic reduction in tool life. So I suggest you use 100m/min as a ballpark target surface speed. Drop to 50m/min to 75m/min for stainless or tough steels like 4340.

for a 6mm diameter tool:
R=100 / ( 0.006 x pi)
=5306rpm
for a 12mm diameter tool
R=100 / (0.012 x pi)
=2653rpm

So if your spindle is 24000rpm (rated) then you'll need a 4.5 : 1 reduction. If you wish to get right down to 2653rpm while having your spindle still at 24000rpm and its most powerful condition,
then you'll need a 9 : 1 reduction.

To be honest a belt reduction is limited to about 3 : 1 , so you'd need two stages of reduction.

Second issue is that your spindle was never designed to take large radial loads and the armature will bend like a banana with the side load you need to apply to hold the belt in tension.

The high speed low torque spindles are NOT well suited to this kind of service. That is not to say its impossible but there may be pit-falls that you did not anticipate.

I for many years used an air cooled 800W 24000rpm spindle. I would slow it to 12000 rpm with 3mm tools (148m/min) to cut steel. It was still too fast, and I'd get
about 1hour to two hours tool life in mild steel WITH plenty of flood coolant. This was a barely acceptable compromise. I did use it occasionally in steel when I couldn't be bothered swapping
the spindle, but not that often. It is fair to say my 800W 24000rpm spindle is NOT for steel.....it was brilliant for other things, just not steel.

What I did is build a second spindle that I could swap to when doing steel and stainless. It was based on a second hand 1.8kW (S1), 6.1Nm(S1), 18Nm (overload), 3500rpm(rated) servo.
I was able to buy the servo and drive reasonably cheap (approx $600USD) here in New Zealand. Cost another $300USD to get the right cables, and another $140USD to get the set-up and tuning software.
So it did not work out quite as cheap as I thought, but still not too bad.

I direct coupled that to a RegoFix cylindrical ER25 tool holder in NSK matched P4 bearings. I made my own housing, and while not perfect it goes bloody well. I used it on and off
for six years, and still have it.

I could run a 12mm tool in mild steel for hours at a time without the servo overheating, sure it gets warm, even hot to touch, but not overheat. I should probably have mounted a small PC fan to keep it
cool, but I never got around to it. The point being that modern AC servos are very power dense and can deliver good performance where an asynchronous motor does not. An asynchronous motor just does not have
the overload torque a AC servo or synchronous AC motor, also call BLDC.

Moe recently I have bought a new spindle. 3.5kW (S1), 3.4Nm(S1), 10krpm(rated), 40krpm(max), 400V with an HSH32E tool interface. It brilliant. Ok at 3.4Nm its still no
great shakes in steel, but I run 6mm and 8mm tools (5306rpm and 3979rpm respectively) with good authority. It is water cooled, and I have a refrigerated chiller keeping the circulating water cool,
and I can run for hours at a time in steel.

My old servo spindle has more torque, but I am very impressed and delighted what my new spindle can do. I cannot swap it out nearly as easily as I used to so I have not used the old servo spindle since
I installed this new spindle.

I paid $2000USD for this spindle, which included shipping to New Zealand and ten HSK32 ER20 tool holders. By the time I got a decent (11kW Delta MS300 High Speed) VFD, the required pneumatics
for the tool change, made my own interlock and monitoring board, had a chiller made for keeping the coolant circulation in check, it cost closer to $4500USD. The tool change feature alone
has more than paid for itself. Its transformed my CNCing, but also having (fair) torque at low speeds, I run it down to 2000rpm is also extremely useful. I now have a spindle that 'does everything'.
OK ......its no steel-hog....but it does OK.

These spindles, several kW, with tool change, are about as cheap as ever I've seen them. I believe China is in a recession and these spindles are being priced to sell in fact under-priced to sell.
If you are ever going to get a spindle like this then now is the time. I suspect the Trump Tariff war is going to wreck the market for these things soon.

Seems to me your choices are:
1) Use your existing spindle at as slower speed as you dare, say 9000rpm and realise that you are in effect limited to 3mm and smaller tools. Its slow but it does work.

2) Use either a servo or a BLDC motor (synchronous AC motor) made for spindle service.Both types offer excellent torque. The BLDC types offer good low down torque but also surprisingly good top speed
by virtue of 'Field Weakening', a property employed by the dedicated drive to gain best flexibility of performance for these motors. This is an example:

https://www.ebay.com/itm/26533830179...Bk9SR_yAgeeXZQ

Such a motor would drive a belt driven spindle or be direct coupled to a spindle, rather more like mine as pictured. This one is 3.7kW (S1) and 24Nm(S1).....so it will have plenty of grunt for any steel
job you want to do. Just be aware that you need to match it with a drive, and they can as much or even more than the motor. Don't buy a motor and then try to find a drive, you should buy as a matched
pair or risk wasting your money.

3) Buy a larger asynchronous spindle, in the 3kW to 7kW class, and look for low speed/high torque capability....something along the lines of the one I bought as pictured. If you choose well you'll get
a spindle that can do 24000rpm, but can also get down to say 3000rpm with fair torque.....ideally 3Nm-4Nm. Not great for steel, but not too bad either. This is the one I want:
https://www.nakanishi-jaeger.com/en/f-line/10408017
It is 18kW(S1), 24000rpm, 13Nm(S1) with 80 bar through spindle coolant and an HSK63F/HSK50E tool interface. Its 23,000 Euro, so I have to save up!!! I know...I know....pure spindle porn!

4) Use your existing 1.5kW spindle through a reduction, either belt or gearbox. I think this is a problematic solution at best, but is your choice.

Craig

[joeavaerage]

Hi,
if you really want to try a reduction of your 1.5kW spindle then I'd suggest a planetary reducer.

If the sun gear is attached to the motor shaft, surrounded by three planet gears then the radial load is just about gone. The trick will be to fin a planetary gear reducer than can
tolerate 24000rpm input.

I don't think you'll find such a unit, but maybe you can try some of the cheaper Chinese made planetaries. It may well be they crap out in short order....but then again they may not.
They are not hugely expensive....maybe just try it and see.

https://www.ebay.com/itm/19694270541...3ABFBMrrCv7Jdl

Craig

[joeavaerage]

Hi,
just as a matter of interest.....a while ago I bought a small arbor and face mill to suit my new spindle. I found a 3/4" HSK32 arbor and a 1.5" Valenite face mill second hand on Ebay.

At first I thought I'd really cocked-up because the inserts are specialist made by Wiida. Fortunately I found a Kiwi supplier, only a few blocks away to, whom, while did not have them
on the shelf got then in from overseas for me. Cost just a little over $150NZD for five ($100USD), and only took a week.

I tried them out and was surprised how well it went. The pic is of a steel block, I faced it about two months ago, hence the surface rust. I could only take 10 thou passes. Given that my
new spindle only has 3.4Nm(S1) torque, I was surprised it could do it at all. The face mill does even better in aluminum and plastics which was really the intended purpose for this tool, that it
can do light (very light) cuts in steel is just an added bonus.

Just goes to show if you are prepared to work within the torque limitations of your spindle you can do some good work.

Craig

[javohert]

Hi,



I agree.

Just as a sanity check try these numbers. For uncoated carbide tools in mild steel you need a surface speed of 100m/min. You can go slower (and get greater tool life) and you can go faster
but with a dramatic reduction in tool life. So I suggest you use 100m/min as a ballpark target surface speed. Drop to 50m/min to 75m/min for stainless or tough steels like 4340.

for a 6mm diameter tool:
R=100 / ( 0.006 x pi)
=5306rpm
for a 12mm diameter tool
R=100 / (0.012 x pi)
=2653rpm

So if your spindle is 24000rpm (rated) then you'll need a 4.5 : 1 reduction. If you wish to get right down to 2653rpm while having your spindle still at 24000rpm and its most powerful condition,
then you'll need a 9 : 1 reduction.

To be honest a belt reduction is limited to about 3 : 1 , so you'd need two stages of reduction.

Second issue is that your spindle was never designed to take large radial loads and the armature will bend like a banana with the side load you need to apply to hold the belt in tension.

The high speed low torque spindles are NOT well suited to this kind of service. That is not to say its impossible but there may be pit-falls that you did not anticipate.

I for many years used an air cooled 800W 24000rpm spindle. I would slow it to 12000 rpm with 3mm tools (148m/min) to cut steel. It was still too fast, and I'd get
about 1hour to two hours tool life in mild steel WITH plenty of flood coolant. This was a barely acceptable compromise. I did use it occasionally in steel when I couldn't be bothered swapping
the spindle, but not that often. It is fair to say my 800W 24000rpm spindle is NOT for steel.....it was brilliant for other things, just not steel.

What I did is build a second spindle that I could swap to when doing steel and stainless. It was based on a second hand 1.8kW (S1), 6.1Nm(S1), 18Nm (overload), 3500rpm(rated) servo.
I was able to buy the servo and drive reasonably cheap (approx $600USD) here in New Zealand. Cost another $300USD to get the right cables, and another $140USD to get the set-up and tuning software.
So it did not work out quite as cheap as I thought, but still not too bad.

I direct coupled that to a RegoFix cylindrical ER25 tool holder in NSK matched P4 bearings. I made my own housing, and while not perfect it goes bloody well. I used it on and off
for six years, and still have it.

I could run a 12mm tool in mild steel for hours at a time without the servo overheating, sure it gets warm, even hot to touch, but not overheat. I should probably have mounted a small PC fan to keep it
cool, but I never got around to it. The point being that modern AC servos are very power dense and can deliver good performance where an asynchronous motor does not. An asynchronous motor just does not have
the overload torque a AC servo or synchronous AC motor, also call BLDC.

Moe recently I have bought a new spindle. 3.5kW (S1), 3.4Nm(S1), 10krpm(rated), 40krpm(max), 400V with an HSH32E tool interface. It brilliant. Ok at 3.4Nm its still no
great shakes in steel, but I run 6mm and 8mm tools (5306rpm and 3979rpm respectively) with good authority. It is water cooled, and I have a refrigerated chiller keeping the circulating water cool,
and I can run for hours at a time in steel.

My old servo spindle has more torque, but I am very impressed and delighted what my new spindle can do. I cannot swap it out nearly as easily as I used to so I have not used the old servo spindle since
I installed this new spindle.

I paid $2000USD for this spindle, which included shipping to New Zealand and ten HSK32 ER20 tool holders. By the time I got a decent (11kW Delta MS300 High Speed) VFD, the required pneumatics
for the tool change, made my own interlock and monitoring board, had a chiller made for keeping the coolant circulation in check, it cost closer to $4500USD. The tool change feature alone
has more than paid for itself. Its transformed my CNCing, but also having (fair) torque at low speeds, I run it down to 2000rpm is also extremely useful. I now have a spindle that 'does everything'.
OK ......its no steel-hog....but it does OK.

These spindles, several kW, with tool change, are about as cheap as ever I've seen them. I believe China is in a recession and these spindles are being priced to sell in fact under-priced to sell.
If you are ever going to get a spindle like this then now is the time. I suspect the Trump Tariff war is going to wreck the market for these things soon.

Seems to me your choices are:
1) Use your existing spindle at as slower speed as you dare, say 9000rpm and realise that you are in effect limited to 3mm and smaller tools. Its slow but it does work.

2) Use either a servo or a BLDC motor (synchronous AC motor) made for spindle service.Both types offer excellent torque. The BLDC types offer good low down torque but also surprisingly good top speed
by virtue of 'Field Weakening', a property employed by the dedicated drive to gain best flexibility of performance for these motors. This is an example:

https://www.ebay.com/itm/26533830179...Bk9SR_yAgeeXZQ

Such a motor would drive a belt driven spindle or be direct coupled to a spindle, rather more like mine as pictured. This one is 3.7kW (S1) and 24Nm(S1).....so it will have plenty of grunt for any steel
job you want to do. Just be aware that you need to match it with a drive, and they can as much or even more than the motor. Don't buy a motor and then try to find a drive, you should buy as a matched
pair or risk wasting your money.

3) Buy a larger asynchronous spindle, in the 3kW to 7kW class, and look for low speed/high torque capability....something along the lines of the one I bought as pictured. If you choose well you'll get
a spindle that can do 24000rpm, but can also get down to say 3000rpm with fair torque.....ideally 3Nm-4Nm. Not great for steel, but not too bad either. This is the one I want:
https://www.nakanishi-jaeger.com/en/f-line/10408017
It is 18kW(S1), 24000rpm, 13Nm(S1) with 80 bar through spindle coolant and an HSK63F/HSK50E tool interface. Its 23,000 Euro, so I have to save up!!! I know...I know....pure spindle porn!

4) Use your existing 1.5kW spindle through a reduction, either belt or gearbox. I think this is a problematic solution at best, but is your choice.

Craig

Hello! I appreciate such a broad response. In truth, I have a pretty tight budget.

What do you think of these servo motors from aliexpress?

https://es.aliexpress.com/item/10050...Cquery_from%3A

I have one of these servo motors on a small milling machine, it's 750w and it gets quite hot.

Is it possible to refrigerate them somehow? I don't think a little fan helps much

[joeavaerage]

Hi,
I do not have a high opinion of cheap Chinese made servos, not because they do not work, but rather they have little support, poor documentation
and more often than not no set-up and tuning software. That particular brand I've never seen before.

I use 750W Delta B2 servos, five on my machine and another five that I have bought for other customers over three or four years. I've never had any of them overheat, but then I've never
used any of them as spindle motors. I can well believe that if you were operating at near rated output for extended periods, they too would get hot.

Delta is a Taiwanese brand made in China. Good quality, performance, support, documentation, and most importantly free set-up and tuning software at fair prices.
In this case 'fair prices' do mean rather more than the link you posted, maybe 50% more.

My 1.8kW Allen Bradley servo driven spindle would get quite warm, maybe 50C after extended periods at high output. Does no seem to have done it any harm, but I agree it is warmer than I would like.
I think if you had an axial PC fan and a shroud around the motor such that the cooling airflow were contained within the shroud you might be surprised how effective it can be.
I cannot think of any liquid cooling scheme that would no compromise relilability....if they are to be liquid cooled they have to be designed that way from the outset.

Craig

[javohert]

Hello, Thanks for answer.

That alternative of surrounding the motor with PC fans and a cover sounds interesting. Do the fans have to be pointed at the motor? Will an aluminum plate be necessary on the engine housing in this case?
or would it prevent the air from cooling it?

How many hours can a servo motor be running continuously without stopping?

sorry my bad english

[joeavaerage]

Hi,
if you take a look at some of the spindle models by HSD, a world leading brand of spindles, you'll find many of them are air cooled.

They have an axial fan, like a PC fan but much more powerful mounted on the end spindle and the air flows down around the spindle motor
but inside the shroud. The fan is not driven by the spindle, it has its own motor.

My first mini-mill used Vexta steppers, and they were very VERY good, but got quite hot. As the motors had flat and smooth sides I clamped some heatsinks (two)
with a little thermal compound. This increased he surface area and helped cool the motor quite a bit. If your servos have flat sides maybe you could do the same.
Ideally the flat side of the servo is 'perfectly' flat as is the mating side of the heatsink and therefore the servo would be in perfect 'thermal contact' with the heatsink.
Inevitably neither the heatsink nor the servo will be perfectly flat and so you use a barest minimum of thermal grease to improve the heat flow from the servo
to the heatsink. The whole lot would be enclosed in what amounts to a square tube and air blown down over the heatsink.

Thats how HSD do it any way, and if its good enough for HSD then it should work for you and I.

Craig

[javohert]

Hello again. Since the Chinese 2.2kw spindle doesn't have much spec, I asked an AI how much torque it delivers at 24,000 rpm, and it said 2.4NM. Is this true?

at 7000 rpm it delivers almost 10Nm, according to the AI.

If this is true, could you use the liquid cooled spindle with pulleys to double torque?

[joeavaerage]

Hi,

I asked an AI how much torque it delivers at 24,000 rpm, and it said 2.4NM. Is this true?

Complete rubbish.

Power(Watts) = Torque (Newton meter) x Angular Velocity (radians per second) (first published Philosophiæ Naturalis Principia, Isaac Newton, July 5 1687.......I remember it well, it was a Saturday, fine and frosty as
it often is in New Zealand at that time of year....)

therefore:

T= P/w

w =2 x pi x (24000/60)
=2512.8 rad/sec

T= 2200 /2512.8
=0.8755Nm

If this is true, could you use the liquid cooled spindle with pulleys to double torque?

Yes, that is possible, but as I've already posted the radial load of a belt will cause the armature to bend. Probability of long term reliability is low, very low.
If you have a planetary gearbox, that would work. Just don't really know any planetary gearboxes that can handle 24krpm input.

Craig

[joeavaerage]

Hi,

24,000 rpm, and it said 2.4NM. Is this true?

at 7000 rpm it delivers almost 10Nm

Not only is the first statement wrong, the actual torque is VERY much lower, but the second statement is also false. The torque of these asynchronous spindle does NOT increase as the revs decrease,
in most cases the torque remains the same throughout.

In a motor, just about any motor, the torque is proportional to the current. The maximum current a motor can withstand is a thermal limit....any more and it overheats.
With an asynchronous spindle such as you have that means that the maximum current is that which produces 0.87Nm of torque, whether that is at 5000rpm or 24000rpm.
This results in linearly increasing power up to 2.2kW at 24000rpm, but only 455W at 5000rpm.

Craig

[javohert]

Hello, thanks for answer.

if i use a servo, the torque is constant without importing the speed? add pulleys increase or decrease the torque in this case?

[joeavaerage]

Hi,
servos have constant torque up to their rated speed.

For example my 750W Delta servos have 2.4Nm (rated) up to 3000rpm, also known as it rated speed. The servos maximum speed is 5000rpm, but a slightly reduced torque
(2.4 x 3000/5000 =1.44Nm).

The synchronous AC motor (BLDC) (by SZGH) that I linked to earlier has 24Nm (rated) torque and a rated speed of 1500rpm, however it can go as fast as 8000rpm, but at reduced torque
24 x 1500/8000 =4.5Nm. Still pretty damned useful.

Pulleys or gearboxes increase/decrease torque in the usual way. Servos and BLDCs are more robust and will tolerate radial loads, eg the tension of a belt.

What sort of torque do you want?

For instance my old servo spindle had 6.1Nm (rated) and 18Nm(overload), and with that I found I could run a 16mm carbide tool in mild steel no trouble.....but it was starting to over-power my machine
and it would start to flex and therefore vibrate. So I would dial it back a bit, not because the spindle could not do the business but to stop the machine from getting out of control.

What work is it you want to do? What size tools do you want to use? They will determine the torque that you need. Then, ask yourself 'can my machine handle the forces that are going to be generated?'.

Craig

[javohert]

Thanks for the answer. Apparently, the best option will be to use a servomotor, the only thing that worries me is the temperature in machining of many hours, so I will have to add refrigeration.

I intend to use cutters up to 13mm, to machine steel, nor do I intend to use an exaggerated feed speed.

I have seen several videos on youtube where they use 2.2kw spindles to mill steel, apparently without problems, what do you think of this?

[joeavaerage]

Hi,

I have seen several videos on youtube where they use 2.2kw spindles to mill steel, apparently without problems, what do you think of this?

I think its possible, but, and this is the big BUT........ask..... 'how long did the tools last?'

Sure you can spin a 10mm or 13mm tool in steel at 12000rpm but I would not expect a hour from each tool....even WITH coolant.

May I suggest try it. You already have a 1.5kW 24k spindle do you not?

Then get yourself some tools and try it out. I personally like Destiny Tools Raptor's. 1/8th inch with a small radius say 10 thou. If I spin then at 15000 rpm this equates to 141m/min
WITH coolant I can get about one hour to two hours each. Maybe you can do better....I have as sure as hell tried, but at 150m/min tools are short lived.

Some of the videos are showing running tools at 200m/min and up to 250m/min. I think I'd be lucky to get twenty minutes tool life! Tools good enough for steel are not cheap
and I can just not afford to fry them by running them at high rpm.

If I run the same 1/8th Raptor but but 100m/min (10600rpm), with coolant I can get 8 and maybe as much as 10 hours cutting in mild steel. I'm running a Kiwi made (Carbide Tools NZ) 8mm coated four flute
with 0.5mm tip radius at 100m/min (3980rpm) and have had six, maybe more hours in steel so far, and that's not counting many hours in aluminum and plastics. Very VERY VERY impressed.
Not cheap, about $50NZD, but one of the best tools I've ever bought. Mind you I've never taken above 100m/min either....and that in turn is due to my new spindle offering OK torque at lower speeds.
I've had a 12mm tool and an 8mm tool of the same design from this company. Really my spindle does not have the torque to be authoritative with the 12mm, but my spindle is a very good
match with the 8mm tool. I WILL be buying more, many more in fact form this company. Not only do they manufacture their own tools they can regrind tools as well, and really friendly to
deal with....and local.....well at least in New Zealand.

https://www.ebay.com/itm/15356590092...wAAOSwFTVdKrg4

https://carbidetools.nz/product/end-...dard-series-2/

The trick to getting good tool life with carbide in steel is to slow the spindle down such that the surface speed of the tool is 100m/min....and then keep the tool cool. Its not rocket science.
I've heard any number of people say 'Oh yes, I can cut steel with a 12mm this or that tool in my n.nkW 24000rpm spindle.....but I've never heard them report how much cutting they got done
before the 'tool went off'.

Apparently, the best option will be to use a servomotor, the only thing that worries me is the temperature in machining of many hours, so I will have to add refrigeration.

I rather think you are right. If you can afford a 5kW spindle with 4Nm torque, that would be good, but if you cant afford that then a servo and matching drive or BLDC motor (and matching drive) are very
good choices. I ran my servo spindle (1.8kW Allen Bradley) for six hours at a time with 10mm, 12mm an 16mm tools, and while it got pretty warm I ran it like that on and off for years. I suggest you try
it, I think you'll be surprised at just how much grunt a servo has without getting over hot. If it does get too hot then you just have to cool it...end of story.

Craig