[Sam Banout]

Hello to all,

I have built a cnc machine out of steel 1/4 inch thick 2x4 tubing, all welded in the intention of cutting wood, but also occasionally aluminum and steel.

However, I need to choose a spindle and here are the following candidates from the available Chinese spindles:
- 2.2kw ROUND - water cooled - air cooled
- 4kw ROUND OR SQUARE - water - air cooled

From all the videos and research I have done, it seems like the SQUARE spindles are louder and more high pitched than round spindles, but I don't have experience with either and would appreciate if someone can confirm this.

Also, the SQUARE spindles have a longer shaft than the ROUND ones, could this cause more stress on the bearings when milling steel since the bearing are not even designed for steel to begin with.

Its just that I need to make really small and precise parts and most videos making such parts show 2.2 kw ROUND spindles.
Others have told me that they are not powerful enough requiring to cut very shallow depth at a time which takes so much longer than having a 4kw spindle.

All help would be so much appreciated from all

Thanks in advance

Sam

[ger21]

From all the videos and research I have done, it seems like the SQUARE spindles are louder and more high pitched than round spindles, but I don't have experience with either and would appreciate if someone can confirm this.

They are louder because they have larger fans, which blow more air through them. Air cooled round spindles have more of an impeller than a fan, and don't move a lot of air. So the square ones should run cooler.

Personally, I think that noise is a non issue, as cutting noise is almost always much louder than fan noise.

Also, the SQUARE spindles have a longer shaft than the ROUND ones, could this cause more stress on the bearings when milling steel since the bearing are not even designed for steel to begin with.

Probably, but not all square spindles are the same. And a 4Kw spindle will have a larger shaft then a 2.2Kw spindle, which would negate this. Just be sure to get an ER25 collet or larger.

And if you cut steel deeper than a few thousandths per pass, you'll likely destroy the bearings quickly anyway.

[Sam Banout]

Thank you so much Gerry for your guidance.

As for the larger collet, I have noticed that the Chinese spindles specs show that they have runouts of 0.01mm on ER25 vs the 0.005mm on ER20.
Since they may not even meet these specs to begin with, I could end up with too much runout with ER25, Is this the case, maybe I missed something.

Also, I completely agree with you about taking passes of a few thou per pass when milling steel.
Then, according to you, would a 2.2KW be enough? what king of work required a larger powered spindle such as 4kw?

Thanks again
Sam

[ger21]

.01mm is .0004", which is pretty small. I haven't really seen anyone posting that there spindle runout exceeded the specs, other than a small number that greatly exceeded the specs.
So, in reality, you'll either end up with a spindle with basically zero runout (most likely), or you may end up with a really bad one (unlikely).

I can't think of any reason why the smaller spindles would have less runout, as they are all made the same way, probably in the same factory. The tapers on the two 2.2kw spindles I have were not even ground, and appear to have just been turned on a lathe.

I can't really tell you what "enough" is, as I don't know what you are doing with it. And I have yet to cut anything with mine, so I don't have any personal expereince, other than running them on a bench.

Personally, I'd go with the larger one.

what king of work required a larger powered spindle such as 4kw?

Fast, deep cuts in wood. The router I use at work has a 15HP spindle. The cuts we normally make would stall a 4Kw spindle (800-1200ipm, 3/4" depth of cut).