Thread: Spindle + VFD Question

Hi Ben

Although it is possible to make the spindle go as slowly as you want to by setting the PDs to the values required for this, It is not a good idea to do so.

The reason the values are given as 8000 to 24000 is because if the spindle is run at slower than 7200 rpm, damage can be done to the spindle through overheating.

Apart from this, what would you want to cut at speeds lower than about 12000?

PS The item is not really in Sydney. This is a ploy that is made to keep within Ebay rules. Ebay is aware of the ploy and does not mind it, even though said ploy is also against their rules.

Haven't had anything to do with this product, but work a commercial 14 tool 2400 x 1800 unit.

I believe that the answer to your question is both yes and no.

Yes, the combination will do 0-24K RPM, in that it will stop the motor under software control (0RPM), and will run the motor over the stated range under software control.

No, it is unlikely that the motor would efficiently offer continuously variable speed control from near stationary to 24K. The magnetic core material in the motor has to be suited to the operating frequency and speed, and to achieve viable efficiency at the speeds in the quoted range requires a core material totally unsuited to low speed operation. Similarly your average 50HZ motor (1450 or 2900 RPM) does not respond well to being driven at frequencies above about 100Hz as that is beyond the efficient frequency for the 50/60Hz optimised core material.

Not sure about cooling issues with a water cooled unit. Presumably with adequate water channels in the motor and sufficient flow rates, heat exchange and reserve coolant volume, cooling should not be an issue. The machine I operate has a 8KW air cooled spindle with an external variable speed cooling fan. The fan is thermally controlled and runs at about 1/2 speed as a minimum, with the ability to step up as needed. I has done so twice in the time that I have worked the machine, both when skimming the sacrificial board at lower speeds (12K) in a 50 degree ambient with a 50mm diam diamond skim bit.

The machine is programmed with different speeds for different tools and processes, and is used for melamine/partical board, coated MDF, plastic sheet, and ali to 5mm. Lowest speed is 12K for the skim bit. Can't see a lot of need for lower speed unless you are milling steel etc.

Hope this helps.

Ah, water cooled. I failed to take proper cognizance of that.
It is the air cooled motors that need a minimum speed. As I understand it, the reason for this is that the fan control is not very good, and at lower speeds it fails to deliver sufficient air to cool properly.

All other comments are correct

Also don't expect any torque at low speeds.

I would have doubts about the German bearings ,probably made in China sent to Germany and mailed back.Some of the Chinese bearings are OK in my experience,its a lottery.
Bought some bearings for a Nissan recently,- branded "Made under license to Toyo" would not fit the hub in any way-ran a file over inside of inner race,guess what? about the same as mild steel,took them back for credit,
These were from one of the biggest motor parts dealers in Australia,I take a file with me when I buy bearings these days,and I am not the only one that does that!,unless you buy Genuine Parts and often genuine is pretty competitive,this car was leaving to go to Cairns,could have been awkward.{ If we could have persuaded the bodgy bearing outer races to fit that is}
By the way the next set I bought elsewhere fitted spot on!.I file tested the inner race tunnels first naturally.
You can't mark a good bearing with file.Don't attack the running surfaces naturally. Regards Broomy

There was some research done by a customer of one of these spindles some time back and it had something to do with a company with Germany in their business name based in china, not actually a bearing from Germany.

I still ended up purchasing one of the spindles as nothing comes close to an affordable alternate, worst case you can always swap them out for some NSK or SKF ect. bearings but it'll cost ya.

Hi Chris

I think that the Chinese actually had a trademark called "German Bearings".


See: Chinese Spindle, "Germany" bearing mystery solved! - CNCzone.com-The Largest Machinist Community on the net!