cheap spindle

[jeromep]

I would like to use this as a secondary spindle on my denford triac to use for engraving and milling with cutter up to about 3 mm diameter in brass and steel

what do you think to one of these motors off ebay from germany ?

i have looked at kress spindle but i am not keen on having a motor with brushes that would need replacing.


https://www.ebay.co.uk/itm/1-5KW-WAT...4AAOSwYGNZlA8k

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[cncuser1]

A spindle that holds a 3mm cutter, cutting in brass and steel, would probably need two angular contact bearings at the end of the spindle nearest the cutter. Even if the bearings are high quality, you need two, preferably angular contact. Usually this style of spindle is intended for routers cutting wood ( lower forces and faster RPMs)

Ask the vendor what are the part numbers of all bearings and where are they installed.

I bought a spindle for manual milling from china and they provided an engineering drawing on the website.(https://www.aliexpress.com/item/ER16...27424c4d91UMpx)

Also do some feed and speed calculations, 8000RPM may be too fast for your cutter and materials.

[cncuser1]

!

[jeromep]

3 mm will my max size cutter but typically I plan on using 0.8 mm diameter endmills, thanks for the info on the bearings

[joeavaerage]

Hi,
I don't think that spindle is made in Germany....unless Germany has become a province of China.

I bought:
https://www.mechatron-gmbh.de/filead...FS-6508-AC.pdf
It is genuine German made and is really nice although it was expensive. Note it is 800W and aircooled.

I have milled steel with it but its crap for steel. For steel you require high torque and slow speeds. These asynchronous spindles such as the one you
are looking at or the one I bought are 2 pole motors ie 24000rpm at 400Hz. The downside is that at less than 8000-9000 rpm they are just gutless
and you are likely to overheat them. Even then a 3mm coated carbide cutter is going to require flood cooling or it will get red hot and fail within seconds.
Ask me how I know.....it happened to me. You really want to spin a 3mm carbide tool at 4000-6000 rpm to keep it cool and you will need a lot more torque
than these 2 pole motors can provide.

My spindle has 0.3Nm torque, the 1.5kW unit you are looking at might have as much as 0.6Nm but what you want is 1-1.5Nm for a 3mm carbide tool
and closer to 4Nm for a 6mm carbide tool.

You can get 4, 6 and 8 pole motors which have much higher (X2, X4 and X8) torque but at slower max rpms (1/2,1/4 and 1/8). They are increasingly
expensive.

You might ask 'why would anyone bother with these 2 pole units then?'. The answer is they are good for aluminum, brass, copper any and all wood and plastics
and they are cheap. Even though that unit is not German made it would probably give you really good results in ANY materials OTHER THAN STEEL.

I made my own spindle from a second hand Allen Bradley servo (1.8 Kw and 6.1Nm continuous, 18Nm 10 sec overload), a Rego-Fix (really nice Swiss quality)
ER25 cylindrical tool holder and NSK matched P4 angular contact bearings. All up it cost about $2000, and that's with me doing all the machining! I sorry if
I sound like I'm bragging, I suppose I am, but the point is that you are not going to get a good and cheap solution for milling steel.

I would recommend that you get the high speed unit you have linked to. Its cheap and yet I think it very likely you will get good results with it, I am
not keen on Chinese made but have to concede these cheap spindles do work pretty well and are price compelling. Then try it on steel.....don't be
surprised if it doesn't go too well, its not the spindles fault....its just too low torque. It will probably go great guns on other stuff though.

Craig

[joeavaerage]

Hi,
I should clarify a point that might cause confusion.

I stated that the spindle I have is 2 Pole. If you look at the manufacturers sheet it says 1 Pole Pair. Its quite unusual for a European
manufacturer to use that terminology.

When I went to University we were taught to use 'Pole Pairs per Phase'. I live in New Zealand and our academic traditions are based on the British
model. If you were in the US or otherwise in Europe you would use 'Poles per Phase'

Thus 1 Pole Pair is the SAME AS 2 Pole....it just depends on where you learnt your stuff. It can be confusing.

Most VFDs on the market are good to 400Hz, its not universal but pretty close. If you hook a 1 Pole Pair (2 Pole) motor
to a 400Hz source it will spin at 400 revolutions per second......or 400 X 60 =24000 rpm.
The same 400Hz source with a 2 Pole Pair (4 Pole) motor will spin at 400 / 2=200 revolutions per second or 12000rpm.
The same 400Hz source with a 4 Pole Pair (8 Pole) motor will spin at 400 / 4=100 revolutions per second or 6000rpm.

You may see some very high speed spindles, say 60,000 rpm. They are usually 1 Pole Pair (2 Pole) motors but with a
1000 Hz VFD. 1000 Hz VFD's are a bit special and cost more. The bearings used in these high speed spindles are likewise special,
cheap Chinese is probably not the way to go here, the bearings will fry up.

Craig

[ger21]

I bought:
https://www.mechatron-gmbh.de/filead...FS-6508-AC.pdf
It is genuine German made and is really nice although it was expensive. Note it is 800W and aircooled.

Are you sure thoe are not made in China?

I've always assumed that they are just manufactured in China for them, as they look just like all other Chinese spindles.

[automationtechinc]

If it is made made in Germany. It costs much more.

We have spindles from China. It works great

https://www.automationtechnologiesin...e/cnc-spindle/

[mactec54]

Hi,
I should clarify a point that might cause confusion.

I stated that the spindle I have is 2 Pole. If you look at the manufacturers sheet it says 1 Pole Pair. Its quite unusual for a European
manufacturer to use that terminology.

When I went to University we were taught to use 'Pole Pairs per Phase'. I live in New Zealand and our academic traditions are based on the British
model. If you were in the US or otherwise in Europe you would use 'Poles per Phase'

Thus 1 Pole Pair is the SAME AS 2 Pole....it just depends on where you learnt your stuff. It can be confusing.

Most VFDs on the market are good to 400Hz, its not universal but pretty close. If you hook a 1 Pole Pair (2 Pole) motor
to a 400Hz source it will spin at 400 revolutions per second......or 400 X 60 =24000 rpm.
The same 400Hz source with a 2 Pole Pair (4 Pole) motor will spin at 400 / 2=200 revolutions per second or 12000rpm.
The same 400Hz source with a 4 Pole Pair (8 Pole) motor will spin at 400 / 4=100 revolutions per second or 6000rpm.

You may see some very high speed spindles, say 60,000 rpm. They are usually 1 Pole Pair (2 Pole) motors but with a
1000 Hz VFD. 1000 Hz VFD's are a bit special and cost more. The bearings used in these high speed spindles are likewise special,
cheap Chinese is probably not the way to go here, the bearings will fry up.

Craig

The Bearings will not fry, most use good quality bearing that last the normal life of Bearings that run at these speeds

Not at all unusual to have a listing like that some VFD manuals use the same terminology ( 1 Pole Pair ) this is more a Chinese translation problem , where ever this is being sold, ( sales people ) are just copying the Chinese spec's

[joeavaerage]

Hi,

this is more a Chinese translation problem , where ever this is being sold, ( sales people ) are just copying the Chinese spec's

The Chinese may use it, I don't know, but Pole Pair Per Phase is common in the literature and is widely used in Australia, New Zealand and the UK.

Craig

[joeavaerage]

Hi,

The Bearings will not fry, most use good quality bearing that last the normal life of Bearings that run at these speeds

The following is a quote from skrubol on this forum:

There are relatively inexpensive 300W "60,000 RPM" spindles out there as well. I've got an old example of one, and I'd recommend staying away from them. I burned out the bearings on my first one running it at 1000 Hz (which should have been 60k RPM, but was quite a bit lower I believe,) and I found that the front bearing on my second one got quite hot at 48,000 RPM, but was usable.

He was describing his experience with Chinese high speed spindles. You are correct, good bearings correctly installed and lubricated
should last well. 60,000 rpm is challenging, what you could get away with at 24000 rpm will fail in short order at 60,000 rpm.

Craig

[mactec54]

Hi,



The following is a quote from skrubol on this forum:



He was describing his experience with Chinese high speed spindles. You are correct, good bearings correctly installed and lubricated
should last well. 60,000 rpm is challenging, what you could get away with at 24000 rpm will fail in short order at 60,000 rpm.

Craig

Yes well you don't quote what other people say unless you have had the same experience, you don't know how he was using the spindle ( note I've got an old example of one, this statement is not credible ) 40,000RPM 60,000 RPM Chinese spindles are kind of new, and they are not cheap, I have rebuilt these spindles and VFD Drives and have never seen this happening, most have / use ceramic bearings, so this does not happen, over heating is usually caused by incorrect start up from new, which have a timely startup procedure

Here is the spec's of a high speed Chinese spindle ( This is one of the better manufacturers ) there are not many to choose from as they are mostly made by the same manufacture which can have a different name on them, so you have to carefully choose what you buy if you want spindles above 24,000RPM

Note water cooled if you over heat one of these you are doing something very wrong

[joeavaerage]

Hi,

Yes well you don't quote what other people say unless you have had the same experience

Unless you're keen to pour money down the same rathole that someone else has.

It is good to hear that some have had good experiences with these devices. That the manufacturer used ceramic bearings
tends to suggest quality made.

Craig

[mactec54]

Hi,


Unless you're keen to pour money down the same rathole that someone else has.

It is good to hear that some have had good experiences with these devices. That the manufacturer used ceramic bearings
tends to suggest quality made.

Craig

Don't believe all you read if they have photo's and brand names of the junk then you have something

You can get Ceramic Bearings that you can order with any of the cheaper 24,000 RPM spindles as well most are reasonable quality if you stick with known Manufacturers

[joeavaerage]

Hi,
in any event OP was looking to mill steel, even higher speed spindles, irrespective of the bearings are not going to confer that capability.

If you buy a sufficiently large and powerful 24000 rpm spindle then it may have enough power at lower speeds to be useful
for steel. Starts getting up cost wise.

I go back to my original advice buy 'cheap and cheerful' 24000rpm Chinese spindle and see what it can do. It may not be perfect for steel
but with patience it might work well enough. It will probably do all you require with brass, aluminum and plastics.

Craig

[mactec54]

Hi,
in any event OP was looking to mill steel, even higher speed spindles, irrespective of the bearings are not going to confer that capability.

If you buy a sufficiently large and powerful 24000 rpm spindle then it may have enough power at lower speeds to be useful
for steel. Starts getting up cost wise.

I go back to my original advice buy 'cheap and cheerful' 24000rpm Chinese spindle and see what it can do. It may not be perfect for steel
but with patience it might work well enough. It will probably do all you require with brass, aluminum and plastics.

Craig

If he is only engraving and using small milling cutters they will cut steel with ease, some free machining steels 12L14 and other free machining steel even 303 SS will machine just as well as some of the Brass alloys