Chinese CNC Spindles ?

Hi All

Anyone got experience of Chinese CNC spindles ?

For fun I've been slowly retrofitting a Defiance CNC to run on single phase with Linuxcnc, new wiring, control and servos etc. over the last couple years .... slowed down by other priorities and having to extract funds from the controller of the household finances, but nearly finished.

It now all runs on its own except the spindle which has had the field windings melted.

I will try to rewind the spindle at some point when I pluck up courage because it's a nice bit of kit with ATC and 60k RPM - way better than I need for messing around. I have it stripped down and a rewind by hand looks to be a bit daunting to say the least because what's left of the windings are not easily analysed plus it needs a VFD capable of running it at 60k to do it justice, which I doubt is cheap.

So in the meantime, I'm thinking of fitting a cheapish water cooled 1.5 kw Chinese spindle and using a bog standard Chinese VFD to suit to start making a mess.

So the question is can anyone give me recommendations / experiences / warnings for the 1.5kw water cooled spindles being sold on fleabay for around £130 direct from China ???

The original was apparently capable of high speed milling of hard steel, but I would be doing mostly plastic and aluminium with the occasional mild steel part.

Cheers - Will

Will,

This possibly isn't much help, but I have recently obtained an 800W air cooled Chinese spindle and VFD. I am using it on my home-made CNC gantry mill (CNC router from aluminium frame sections).

I have successfully cut wood, plastic and aluminium and have been impressed with the spindle and controller. The setup is 'interesting' as most of the VFD information is a bit sketchy, not due to omission, but rather to ambiguity! Having worked that part out, I am happy with the finished article and am slowly incorporating the electronics into my system control.

The only modification I did make to the spindle was to earth the casing, which I thought was a sensible precaution with the voltages being used.

The package of spindle and VFD came in at just over £200, which I thought was reasonable. I opted for one of the suppliers that holds stock in one of the UK ports and 'imports' it on demand, rather than wait for it to arrive from China.

I have only been using it for 40-50 hours so far, but it has performed faultlessly so far.

Rob

A few points:

1. Water cooling seems an over-complication with no advantage

2. The Chinese CNC spindle I had a look at on Ebay had a runout of 0.02mm; might be ok for a router, but hopeless for cutting metal with small cutters

3. Do you really need high speeds? Certainly they are an advantage for aluminium with small cutters (less than 6mm), but not for plastic. The key to machining plastic is lowish speed and high feedrates, or you just end up with a molten mess.

Andrew

I have one, the air cooled version, and the 8 deg inner taper for the ER collet needs to be corrected.

It has 2 problems, 1st the taper is not as close to the 8 deg as it could be, and it is not concentric to the bearings.I plan on setting it up and correcting this when I get time.

Neil

Thanks for the thoughts people ....

Andrew, you raise an interesting point about accuracy - I've seen them much better than .02mm TIR, but the one that I had considered is still only .01mm which is probably not brilliant either with small cutters, especially with Neil's comment. I think I'll do some more looking before jumping.

Neil, is there an ebay seller that I should avoid ?

Interesting comment about water cooling. The machine has a chiller for the original spindle, which is why I just assumed the cooling would be better. I guess that they would run cooler than air which probably helps the accurate spindles, but if the Chinese spindles are miles out anyway, this would be pointless. I'll do a bit more research on this as well, thanks.

The high speed is because that's what the machine was originally built for, it's was a true high speed milling machine which is designed for very light cuts at a very high feed rate with small cutters. It's a heavy old thing, but the slideways are built around recirculating ball slides and leadscrews and therefore the rigidity is totally different to a manual mill.

I don't have direct experience of milling plastic with very high speed machines (yet ), but I think Firstcut use high speed HAAS machines and produce superb components in most plastics, so I'll stick with plan A on this.

Cheers - Will

Taking into account that 0.01mm is less than four tenths of a thou, exactly how accurate do these spindles need to be?, or am I missing something? All educational replies are most welcome. I love to live and learn. Thank you.

Rick

Check out AliExpress when you are looking for these. Many of the Chinese ebay suppliers also have AliExpress stores but not many of the AliExpress suppliers have ebay shops. You may well get a better selection if you go (more) direct in this way and you still get some degree of buyer protection. The prices often include shipping and sometimes you can get stuff delivered within a week or so.

I've bought a range of stuff from there and so far I haven't had a bad experience. Obviously it helps if you find out about what's on offer and research other people's experience.

Some people seem to have fitted a water cooling system from a PC. Given that most of these spindle drives seem to be water cooled, that's probably not a bad solution. The cooling power rating is probably very similar and the cost (and quality!) not astronomic.

Consider the following, taking as an example the spindle I found on Ebay with a TIR of 0.02mm:

1. Presumably the quoted TIR is for the spindle taper. The ER collet itself also has a runout, which may be additive. A standard ER20 collet from Rego-fix (the inventors of the ER collet system) is listed as having a maximum TIR of 0.01mm, so who knows what the runout of a no brand name collet may be. But let's go with a value of 0.01mm, so the total TIR is 0.03mm.

2. With a total TIR of 0.03mm, and assuming everything is perfect, that means that the surface of the work will undulate by up to 0.03mm. Not the greatest of finishes.

3. For small cutters the chip load per tooth is small, although running at high rpm means that the feedrate can be large. Here are some practical numbers I used when machining 4mm deep slots, 2mm wide, in 6082 for a liquid cooled heatsink. The cutter was 2 flute carbide, running at 4000rpm with a feedrate of 150mm/min, full 2mm width of cut, and each pass was 1mm deep. The figures equate to a chip load of 0.01875mm. But the runout is ±0.015mm, so the chip load could vary from 0.00375mm to 0.03375mm. That's around an order of magnitude variation per revolution of the cutter. Would one feel happy running a normal endmill under such conditions? Even if the cutter survives it is likely to prone to wear and chatter, leading to a poor finish.

4. If the spindle is turning at 20000rpm, say, and the runout implies an imbalance, that may mean vibration which in turn directly affects the surface finish.

That's why I think a small runout is important, especially with small cutters at high speeds.

Regards,

Andrew

Ah! Lesson learned and food for thought provided. Aspirations to improve accuracy of Chester 626 mill spindle given a boost. Many thanks.

Rick

I am not aware of any particular seller of these spindles to avoid. I have not heard any bad sellers. The person I got this spindle from, was offered a replacement, but decided to get another brand of spindle at a considerable cost increase. The runout is about 0.02mm or so , maybe .03mm not a lot but it is on small cutters.What I like about the ER series of collets, is they are easy to make at home. An important and often over looked is the thread on the spindle for the nut ,must run concentric and true to the spindle taper.

There are different series of precision collets. Big from Japan ,make some of the most accurate ER holders and collets available. They have a series that they claim 1um at the spindle nose of the collet with a test piece.

They make a modified version that has more of the 8 deg taper engaged compared to the standard er system, and a much improved clamping nut design. Their precision collets only have a 0.5mm range, instead of the usual 1mm size clamp range. Some really good info in their PDF to download.

http://www.bigkaiser.com/hsk-er-grip.php

Here is the link to their site and their info.

Neil

I'm a bit puzzled how on a hobby CNc you make the jump to a big dai Showa toolholder

on an ISO spindle for a good CNc like the Mazak or DMG we use the taper is made to a certain standard up to the gauge line from there up you look at contact this is your first area runout issues can start an er system is not really in the same league with low contact in the taper it will deflect an er32 collet which has low stiffness also you see this when cutting materials like en36 or d2 where the runout causes tool wear on one flute only it's about as usefull as using a side lock which is stiffer but has higher runout ,a better result is sometimes achieved however because your using a stiffer holder

a cutter holder like a big dai Showa will indeed give 1 micron runout if your ISO taper will have a much bigger contact taper to taper ours are at worst 4 micron at 6xd of tool

A 2mm cutter in aluminium should be spinning at somewhere near 30k even a commodity machine like a haas Vf would struggle at 5mm as the spindle tops out at around 12k which then you up the flute count to only find you need to increase feed rate

so you actually improve surface finish through the higher rpm as with a single flute cutter for aluminium CNc machines did fine with spindles that only did 4k for 20 years but then you run HSS or cobalt Carbide is really just with most small lathes pointless

we now use constant tool engagement angle to keep metal removal rates up and not worry about chip loads but I'm actually surprised anyone would bother using a 1mm doc at 2mm wide you could bastard file the job out quicker

Thanks for the feedback Neil, I feel better for that.

Interesting info on the site - I can only dream of 1 micron run out and it took me a couple of attempts to count the zeros !!!! But, actually, I found the specification of the original spindle and it was less than 2 microns run out. Problem is it uses balanced BT10 collet chucks and they are only available through a couple of specialist companies at upwards of £350 per chuck.

(Anyone got any used BT10 collet chucks they want to sell at a reasonable price ???? )

Mike - what is "constant tool engagement angle". I'm familiar with chip load, but is this is a more up to date way of calculating speed/feeds ?

Cheers - Will

Thanks for the comments people - so I've done it, I've ordered a cheap Chinese spindle .........

It's watercooled, has best "adopt Japan imported bearings" and has a TIR of 0.005mm (yes, the decimal points are correct and yes, of course I believe it all )

I went for an 80mm diameter case which theoretically could be a better choice than the smaller diameter ones for air gap tolerances and torque reasons.

Might be surprised one way or the other, so I'll post the experiences in a few weeks time when it arrives and I try it.

Cheers Will

That's due to a lack of knowledge on your part regarding the item I was machining.

Andrew

BT10 i a standard and 350 quid however is what you will routinely pay for bt40 big dai showa shunk in fact any of the sub micron runout holders, collets then run around 60 quid a go but do actual push runout to whole new levels

Constant tool engagement keeps the tool in the material with constant chip thickness and thats the key keeping it in the material, ONE THING YOU NEED A CAM PACKAGE TO TAKE ADVANTAGE OF THESE MODERN WONDERMENTS

a lot of people dub it as trochoidal milling which it isn't it has significant differences but heres an example tool breakage even in toolsteels is very rare

https://www.youtube.com/watch?v=CORSb2NtV0Q

its most useful for little underpowered machines where the choice of hogging material off is not an option but lots of fast cuts are as in hobby sized machines with high rpm low torque spindles its also very beneficial for tiny cutters where plodding around taking tiny cuts just rubs the mill to death and causes premature breakage

Edited By mike mcdermid on 21/06/2014 11:15:23

Thanks Mike - clever stuff and that video's mesmerising.

So if I grasp this correctly, trochoidal milling is normally for milling slots in a sort of D shaped circular motion using a smaller cutter than the slot width but cutting it widthwise in one pass. And it requires very clever maths by the CAM program to accomplish it.

Can't wait to get the spindle up and running !!

Cheers Will

The Adaptive Clearing technique used in CAM applications like Mastercam, Solidcam, HSMworks etc isn't ensuring a constant chip thickness at all, it is targeting a more constant tool load which is quite different. If you haven't grasped the difference, there's a great introduction to the basics on the Solidcam website (possibly even a bit laboured) although the same principles seem to be used in the other applications, give or take.

I'm no expert on the matter but it looks as if the "Adaptive Clearing" concept was conceived by a couple of Brits (blog here). The approach sounds pretty simple on the face of it but once you start to dive it it becomes clear this is a pretty involved matter. When you cut into a corner with an end mill using "simple offset" contours, you will find that the cutting surface suddenly wants to extend to perhaps 1/2 of the circumference or more, depending on the stepover. This could be a problem, yet if you reduce the overall speeds and feeds for the whole operation just to make this one situation safe, you end up taking longer than necessary for the rest of the machining. With Adaptive Clearing, the solution is to continuously vary the stepover and feed rate (and spindle speed) to even out the tool loading.

If you have Solidworks, the HSMXpress add-on is free for 2.5D use and includes this functionality. I'm looking forward to trying it out for myself soon. There are a lot more features in these CAM applications than just Adaptive Clearing of course and I am sure there are many patents and PhDs still to be written in the field! Fascinating stuff.

Murray

(Double post deleted)

Edited By Muzzer on 25/06/2014 05:50:33

Spindle arrived from China today. Only 10 days delivery time, which I think is good.

Forget the 0.02mm TIR on spindle run out .......... It's actually so small I can hardly pick up any error at all on the collet taper on the inside of the spindle. Guess that puts it at a micron or less.

With the supplied collet fitted and a 6mm cutter, the runout on the cutter is just under 0.005mm.

Pleasantly surprised so far, but it'll be a few weeks now before I will get the chance to try it in the machine and report again.

Cheers - Will

Will, any chance of a link to one of these spindles, I am curious as to what you get.

Thanks.