What is the lowest RPM for water cooled vs air cooled chinese spindles ?

Hi...

I read about 6000 RPM as lowest speed for air cooled spindles.

But what is roughly the lowest for water cooled spindles ?

Thanks..

I’ve run my water cooled spindle as low as a couple hundred rpm. I’m sure the available torque is very low so I wouldn’t trust it for metal cutting. It will never replace a real milling spindle.


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What is the reason you are trying to run lower speed though? Are you trying to cut a really deep cavity and need a large diameter tool for that reason? Otherwise using an appropriate endmill and speeds+feeds will serve you better.

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Originally Posted by vroemm

Hi...

I read about 6000 RPM as lowest speed for air cooled spindles.

But what is roughly the lowest for water cooled spindles ?

Thanks..

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Regardless whether water cooled or not, the construction of the motor i.e. low iron content, causes very low inductive reactance at any thing lower than the recommended frequency limits.
Water cooling may offset the temperature rise, but does nothing for the extra current imposed on the VFD at low RPM's.

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Originally Posted by Dean448

I’ve run my water cooled spindle as low as a couple hundred rpm. I’m sure the available torque is very low so I wouldn’t trust it for metal cutting. It will never replace a real milling spindle.


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That's been my experience too.

My electric fan cooled spindle works fine down to 1000rpm (I haven't tried lower). It's just that high speed built-in motor spindles usually have very little torque so they'd stall with large tools in hard metal.

I rarely go lower than 6000rpm when cutting aluminum. 5/8" is the largest end mill it fits anyway, so it's mostly academic.

The only time it's an issue is for face milling but, luckily, Amana tools makes a 2.5" face mill for aluminum on high speed CNC routers run up to 8000rpm.

If there is a regular requirement to go below 3000rpm then maybe it's best to add a second spindle. You're not going to run 1" or HSS end mills on a 2.2kw 24,000rpm spindle no matter what cooling you have.

If you are running the HS spindles out of the recommended range, if you are lucky, the VFD is going into current limit, which does nothing for power, but might save the VFD! :eek:

Quote:

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Originally Posted by vroemm

Hi...

I read about 6000 RPM as lowest speed for air cooled spindles.

But what is roughly the lowest for water cooled spindles ?

Thanks..

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Depends on the spindle manufacture, the G-Penny spindles can run at 3000 RPM this is there spec's, the normal water cooled, run at there 6000 RPM factory spec's, air cooled are normally higher than the water cooled unless they have an electric fan, over heating will happen when run to slow, currant draw also goes up, if you run it to much below the manufacturers recommended speeds, you will be able to stop it with your hand at low speeds, so they have no useful torque below the minimum speeds, most when cutting don't normally go below 7200 RPM=120Hz

Al has posted what will happen electrically, damage can happen to the spindle or VFD Drive when run too slow with any load or a spindle stall.

In the smaller endmill sizes, at least here in California, they are pretty damned cheap and last a long time. Even at 1/4" 2F we're running 24krpm in aluminum at 100ipm on a router.

1/2" starts to be a real limit with speeds around 13krpm in Aluminum. I'm about to cut some UHMW pulleys which is about the only thing I put bigger than a 1/4" for and only because of depth.

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Originally Posted by StrawberryBoi

In the smaller endmill sizes, at least here in California, they are pretty damned cheap and last a long time. Even at 1/4" 2F we're running 24krpm in aluminum at 100ipm on a router.

1/2" starts to be a real limit with speeds around 13krpm in Aluminum. I'm about to cut some UHMW pulleys which is about the only thing I put bigger than a 1/4" for and only because of depth.

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I use some fairly cheap ZRN coated carbide 3flt end mills for aluminum like these:

https://www.ebay.com/itm/15302213203...Cclp%3A2334524

The coated carbide really helps when using high speed / low torque spindles that don't reach peak power until 18,000 or 24,000rpm.

Being able to power through aluminum at 20,000rpm makes up for the limitations. Especially when you see those slow and painful videos of people cutting aluminum on mini mills at 2000rpm.