[joeavaerage]

Hi peteeng,
Diamond or DLC or PVD tools are hopeless in steel.

You may well be correct that coatings may well offer surface speed advantage is aluminums and/or composites, but they don't offer a huge amount in steel.

Carbon is highly soluble in hot iron, thus a diamond or diamond coating is literally going to dissolve when cutting ferrous metals. At some very particular point where
the chip is being formed and the deformation is large and rapid, the chip will get hot and ergo the carbon of the diamond will dissolve. If you were to hugely flood cool the cutting zone
and proceed slowly enough such that the rate of 'doing work' on the chips is low enough that you don't get the red heat....then you might get away with diamond tooling.
It's a very good way to wreck expensive diamond tools.

Ceramic tooling or CBN tooling is used on ferrous metals when you need something harder than carbide. CBN is eye wateringly expensive. The manufacturers recommend in the range of 100m/min to 200 m/min.
You can be ABSOLUTELY sure if I ever buy a 3mm CBN ball nose endmill for $475USD I will NOT EXCEED the recommended surface speed. In most case the manufacturers don't recommend
flood cooling for CBN either, siting thermal shock. There is another school of thought amongst users of CBN that use cooling and HUGE AMOUNTS OFT IT such that the tool never experiences thermal shock.
I would guess that I am in that camp. Flood cooling is the night and day improvement to my CNCing, and just about every material.

Craig

[peteeng]

Hi Craig - So we don't hijack this thread lets move the machining discussion to the Milli thread. Happy to talk about it there. I looked at the diamond coatings and they don't use it on steel as you say. I'm not super keen to cut steel on my router. But happy to experiment. I wanted to get aluminium dialed in so I can make laminated AL parts. I think I'm there so I'll do some more research on steel and see where that ends up. Peter

[joeavaerage]

Hi peteeng,
you are correct, we are rather drifting away from the core subject. Recall that we started on this track because OP was hoping to cut steel with a 2.2kW 24000rpm spindle.
Such spindles are poor in steel because they spin just too fast and with so little torque. They can and do cut steel but in limited circumstances. I would like to summarize what those
circumstances are.

Firstly: High speed spindles can and do run at part speeds but they don't like it. Air cooled spindles are particularly prone to overheating at half speed and less. Water cooled spindles are better
and offer more certainty at half speed, but could at need be run at quarter speed provided the applied load is small. It is a risky endeavor to run a spindle at quarter speed.

Secondly: There is a distinct upper limit on the rotational speed that will work with steel. Depending on your source of information the limiting surface speed in mild steel, free cutting steels etc,
with an uncoated carbide tool is 80m/min to 100m/min. I myself use 100m/min as a rule of thumb. Common coatings like TiN, AlTiN, and CAlTiN and various combinations thereof lift the surface speed limit
to 125m/min to 150m/min. The Sutton catalogue shows some coatings that I've never heard of, and most certainly never before seen on sale, and that document claimed another increase in usable surface speed.
This summary is what I've have learned over time, I choose not to comment on these coatings as I have no experience of them. As a rule of thumb I use a maximum of 150m/min for quality coated carbide tools.

If you are cutting tougher steels, say 4140 or hardened and tempered 4340 then the above limits (100m/min uncoated, 150m/min coated) reduce by 50%. Any moderate stainless, say 300 series reduce by 25%.
For tough stainless reduce by 50% to 75%.

Diamond or diamond coatings are not for use in any ferrous metal. CBN is good in hard steels, but still limited in surface speed.100m/min to 200m/min. If OP can afford CBN then why is he wasting his time
building a machine, just buy a DMG Mori or Okuma and be done with it!

HSM will not come to your rescue if you spin the tool too fast. The limiting surface speed is in effect a thermal limit, and the toolpath does not play a role in that.

I've never had success cutting steel with air blast. Air blast is good for removing chips form the cut zone and is especially useful and beneficial for plastics and aluminum, but for steel cooling is paramount
with lubricity and chip evacuation a distant second. For that purpose, fluid cooling is by far and away preferred. I use flood cooling, very modest pressure and flow rates, but provided the flow is well
directed it works well. Either way OP will have to consider very carefully what solution he uses for cooling the tool. Failure to cool the tool will result in it getting red hot and destroying itself.

Thirdly: We come now to combining the understanding of the first two considerations. If you have a 24000 rpm spindle then half speed, the recommended minimum is 12000rpm.
Quarter speed, only at greatest need and with extreme caution is 6000rpm.

1/8th tool (3mm equiv) at 12000rpm is a surface speed of 118m/min
1/8th tool at 6000rpm surface speed is 59m/min

1/4 tool (6mm equiv) at 6000rpm is a surface speed of 118m/min.

Thus OP can see that to cut steel effectively with any prospect of useful tool life it is necessary to slow the spindle down into a zone where it is not happy and some risk of damage is involved.

The last consideration is torque. A 2.2kW 24000rpm spindle has a rated torque of 0.9Nm.

0.9Nm should and will drive a 1/8th tool in steel up to the strength of the tool. Not so a 1/4 inch tool. You would have to take very light cuts so the cutting torque does not stall the spindle. If the spindle stalls
and the machine continues its programmed cutting path the tool will be snapped within milli seconds.....ask me how I know!

The important takeaway point for OP is that steel is tough and requires a great deal more torque to peel off chips than aluminum say. Your spindle needs a surfeit of torque or the spindle will stall.

OP might think I'm painting an extremely negative picture of high speed spindles, but that is not the case. The vast majority of my milling is done with such a spindle. Further, as I have posted I have just
bought another highspeed spindle, albeit very much more powerful than my current spindle. It will be a very useful and welcome increase in steel capacity, but primarily I bought is for its high rotational
speed and its ATC capability NOT its steel capacity.

On the basis of value for money I would recommend OP's approach, namely get a 2.2kW water cooled 24000rpm spindle. They are just so cheap and readily available. I would commend you consider
a quality VFD....but even the el-cheapo Chinse VFD's work well enough and are certainly well priced. OP needs to be aware of the limitations of the spindle with respect to steel, but unless steel is a make or break
capability then you'll have just so much fun with a 24000rpom spindle.

Craig

PS: tracking my spindle, its been to Guangzhou from Ho Chi Minh City, to Singapore. Its left Singapore, I think possibly as a backload on Santa's sleigh. I imagine it will be in Auckland or Christchurch by tomorrow.
We'll see then whether NZ Customs have got a hangover, if they are on their game, they should charge me GST of $450NZD in tax....but you never know sometimes they lets stuff in without collecting GST.

[peteeng]

Hi Sid - so if a high speed spindle is in order I suggest one with good build quality and bearings such as this. Peter

https://g-pennymachine.aliexpress.co...79055dafb8LlKg

I did find some coatings that go to 350m/min in steel dry. They are the alum chrome family. They have to be run fast. If babied they apparently fail. mainly used on hard tool steels. To be continued in the MIlli thread.

--------------
Link to Milli thread: https://www.cnczone.com/forums/cnc-d...ml#post2574232

[joeavaerage]

Hi,
little update, my spindle has arrived in Auckland and is going through Customs clearance as of a few hours ago. I'm pretty impressed, I bought this thing late morning, say 11am 22/12
at its come from Vietnam and is in Customs in New Zealand at 4am 27/12. If it had been delayed by the holiday rush, I would've said 'well, yes I can well believe that' and waited quite
happily. Fedex claimed they would deliver it by 28/12, which I thought very optimistic, but to give Fedex their due they are on schedule. If the package is delayed trough Customs, and
that is highly probable, I certainly could not fault Fedex.

Craig

[joeavaerage]

Hi,
yet another update.

You may recall me mentioning that I managed to wreck the servo of my high torque/low speed spindle that I built some years ago just for doing stainless and steel.
I had it lying in the bottom of my mill enclosure while I had my little high speed spindle installed. Coolant got inside the encoder housing and wrecked the optical encoder.
Very VERY silly of me.

About three weeks ago I found and bought a very rough looking Allen Bradley servo to replace it. It was pretty cheap, $170USD, reflecting its cosmetic state. The seller claimed that it
was operational so I took a gamble. It arrived a week or so prior to Christmas. Just this morning I have hooked it up, and lo and behold, it works!!! Great news. I was half expecting that it might
not work, and sending it back to California was going to cost more than I paid for it. If that were the case I was just going 'to take my lumps' and carry on.

All up it cost was $270NZD, the NZ dollar equivalent of the purchase, and another $251NZD being the shipping from the US and the GST (local tax). To say I'm glad it works
is an understatement. Might also suggest to OP that I mean what I say about a high torque/low speed spindle, you might say I voted with my wallet.

Craig

[Siddvo]

For now, I will use the 500W brushless spindle I currently have, but the upgrade will be soon.

Another question: I just got my 7I96s. Do I have to connect the frame GND to my 36V power supply GND or Earth from my outlet (the electronics enclosure I'm using is connected to Earth)? Also, I am using a separate power supply for 5V. Do I have to connect both GND terminals for the Mesa card to be able to communicate with the stepper drivers?

Thanks for all the advice. I'm very thankful for everyone replying to my questions. The feedback from my first topic is cool, and I'm just happy for every piece of information that I can get.