Why most (non-router) milling machines don't use self-contained spindle?

Hi,

I'm wondering why most non gantry mills are using spindle cartridge type with either gear/belt instead of running self-contained spindle. I mostly see self-contained spindle being used in router mill.

I understand traditional milling requires lower RPM but what about high speed machining? Can I strap a high speed self contained spindle (20-40k RPM) to my mill and do HSM?

Why isn't this done often?

No reason it couldn't be done if the spindle is build to take metal cutting loads. Such spindles exist, but be prepared to spend a lot of money. It is probably less costly to use a cartridge type spindle and a large conventional spindle motor to drive it.

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Originally Posted by george1980m

Hi,

I'm wondering why most non gantry mills are using spindle cartridge type with either gear/belt instead of running self-contained spindle. I mostly see self-contained spindle being used in router mill.

I understand traditional milling requires lower RPM but what about high speed machining? Can I strap a high speed self contained spindle (20-40k RPM) to my mill and do HSM?

Why isn't this done often?

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Most of the CNC mill built today do have a option for self contained spindle meaning the spindle and motor is one unit, the reason for spindle gearing is for heavy Milling rigid tapping of large threads


The high speed 2 Pole spindles you are talking about are not designed or suitable for milling metal, engraving and Aluminum is about the limit and aluminum is not that great as well, there are some that are but have a high price tag to go with it and are 4 Pole they have a different Bearing arrangement that is better suited to cut metal, they are still light weight compared to what a CNC Machining Center are built with


Can you add one many have for light machining

Thanks Jim & Mactec54

I'm looking at these pretty pricey Chinese spindle ?$1400 for 2.2kW). They are 4 pole, 24k RPM. Same as this one:


https://www.youtube.com/watch?v=pWNeW-lH9RA


Can they be used to cut steel in high speed if I have a G0704 type frame CNC?


I'm thinking about two options:

1. Belt drive ATC spindle + motor - 10k rpm
2. Integrated watercooled ATC spindle - 24krpm


They run about the same cost. Which one is better for general metal machining?

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Originally Posted by george1980m

Thanks Jim & Mactec54

Can they be used to cut steel in high speed if I have a G0704 type frame CNC?

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The G0704 is not a very robust machine, but if you stay within the limitations of the machine rigidity it should work OK. I have no idea what material removal rate you could expect, but I'm guessing with a higher speed spindle and HSM tool paths you would have some gain over the stock spindle configuration.

Quote:

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Originally Posted by george1980m

Thanks Jim & Mactec54

I'm looking at these pretty pricey Chinese spindle ?$1400 for 2.2kW). They are 4 pole, 24k RPM. Same as this one:


https://www.youtube.com/watch?v=pWNeW-lH9RA


Can they be used to cut steel in high speed if I have a G0704 type frame CNC?


I'm thinking about two options:

1. Belt drive ATC spindle + motor - 10k rpm
2. Integrated watercooled ATC spindle - 24krpm


They run about the same cost. Which one is better for general metal machining?

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It will depend on the Bearing configuration yes there are many of those ATC spindles you will have to ask the manufacture if the spindle you want can be used to mill steel most of them will be a no

I suppose it can be said that anything is possible if you use it not as intended one way or another.....dropping the speed of the spindle to 10K and using a carbide cutter will allow you to machine any metal that is capable of being cut with carbide.....it just depends on the depth of the cut and the amount of material you need to remove...….anything is possible.

If you only get a .010" depth of cut on a 6mm diam cutter in mild steel you will be there 'till Xmas but it can cut......just not practical.

Short answer is …..use what other people are using and stop wishing for the stars.

However, if you already have a self contained spindle and VFD you "could" use it to drive a cartridge spindle using a belt drive reduction at 1:4 ratio.....that would raise the torque capacity X4 and drop the revs X4 in one hit, but I would not suggest doing that as an ideal to do exercise when other BLDC or 3 phase motors are available and would work with a VFD.
Ian.

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Originally Posted by handlewanker

I suppose it can be said that anything is possible if you use it not as intended one way or another.....dropping the speed of the spindle to 10K and using a carbide cutter will allow you to machine any metal that is capable of being cut with carbide.....it just depends on the depth of the cut and the amount of material you need to remove...….anything is possible.

If you only get a .010" depth of cut on a 6mm diam cutter in mild steel you will be there 'till Xmas but it can cut......just not practical.

Short answer is …..use what other people are using and stop wishing for the stars.

However, if you already have a self contained spindle and VFD you "could" use it to drive a cartridge spindle using a belt drive reduction at 1:4 ratio.....that would raise the torque capacity X4 and drop the revs X4 in one hit, but I would not suggest doing that as an ideal to do exercise when other BLDC or 3 phase motors are available and would work with a VFD.
Ian.

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I think you mean 4:1 4 turns of the motor to 1 turn of the spindle, BLDC motor don't work well with VFD Drives the best they would do is smoke


Here is a video of one of these ATC spindles, this is extreme in this case but shows why they are not that great for milling steel, see if you can see why these spindles are not great for milling steel


https://www.youtube.com/watch?v=qLFjhMN3kOg

Mac...when I said 1:4 this is stated as a reduction ratio ……….the other way round, or as you state, is 4:1 which indicates that you are driving in top gear with an output of 4 times the input.

As an expression of a ratio it has nothing to do with a fraction representation which in a fraction sense would be written as 1/4 for a reduction or 4X for a multiple.

Sorry about the mix up with the BLDC.....I actually meant a 3 phase motor and a VFD.....I don't know much if anything about the BLDC requirements for driving......I assumed they were both frequency variable in their speed adjustment...….with some deep thinking and guesswork I would think the BLDC motor, by it's title, is a brushless DC permanent magnet motor controlled by feedback and varying the current or voltage input to maintain a preset speed against the loading.....whatever.

It seemed like a logical solution to use it (the water cooled self contained spindle motor) for a drive, when you have one, with belt and pulley reduction.....like the BLDC drive on my Skyfire SVM-0 mill.

However, in the case of the SVM-0 mill, the top speed of the BLDC motor is 7,000 rpm so it does get a smaller pulley driving a larger one for reduction to get more torque down the way and the opposite way round with a bigger pulley driving the smaller spindle pulley for more revs when you want to do small cutter work at higher speeds or some wood or plastic carving etc.

I can't think of any reason that a 24,000 rpm motor rev range can't be reduced by a 1/4 with belt reduction to get a more meaningful cutter speed to enable it to cut metal......something you couldn't do by slowing the motor down to a crawl and overheating it.
Ian.

Lots o confusion.

Self-contained direct drive spindles, are things like the integral drives made by Mori Seiki at 25.000$ a pop.
The are balanced not just statically, but dynamically, and very much engineered to control the heat expansion, and for long life at 100% load.

A 1500$ chinese spindle is not expensive, and may or may not be apt for industrial use, mostly not.

Most of the "high speed" chinese spindles are not suited, at all, to the real cutting loads imposed on actual industrial spindles, industrial in wood or metal, 5-10-25 kW++ actual power absorbed.

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Originally Posted by mactec54

I think you mean 4:1 4 turns of the motor to 1 turn of the spindle, BLDC motor don't work well with VFD Drives the best they would do is smoke


Here is a video of one of these ATC spindles, this is extreme in this case but shows why they are not that great for milling steel, see if you can see why these spindles are not great for milling steel

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Because the spindle slides in and out at the tool change and thus has to be loose enough to slide in the bearings or whatever?

Hi Hanno....my opinion is that if the high speed spindle is able to function at 25.000 rpm with the loads it's designed for then if you wanted to cut steel, which means you need to go much slower, then doing a speed reduction as I stated will still put the same load on the spindle ……..PROVIDED...….you don't expect to take a heavy cut...…...milling steel is not for the unwary but as most on here do aluminium then I would say it can be done with discretion and not with overloading the motor...….I doubt that anyone has actually done this exercise but many have voiced opinions as to why it cannot be done.
Ian.