DIY CNC machine for steel?

[Boyan Silyavski]

Hi Luke,

I see you have been impressed by other peoples videos where they cut steel on their routers. So lets cut the crap- the answer is:

If you want to properly cut metal- buy or make a proper metal cutting machine.



Detailed, i write this down for the benefit of others in the future that drop here with similar questions:

-with the machine you have drawn would be next to impossible. Forget aluminum, all need be steel, all needs to be braced in all directions, the thicker and the heavier-the better. You could use aluminum, but must be reinforced with steel.

-The spindle.
There is cutting, there is what we call scratching. This spindleis NOT made for cutting steel. Means bearings will fail at one moment. These bearings have 1 year life if machine working 8h a day. Thats what Chinese manufacturer states. And that routing wood. Many people, including myself have used them much more and on materials like aluminum.

The ideal spindle for a small machine to cut metal is the BT30, coupled with pneumatic release for tool change and belt driven by servo motor. Thats about 2000$ from China. If you weld and have a machine shop you coul dput together a frame. They /China/ sell a very nice VMC frame for that setup but is expensive. Thats one of the reasons you will not see many DIY mills in forums. Cause its cheaper and better to buy and retrofit old mill.

-the power needed
One thing worth noting is that yes, if you have very sturdy setup, use small bits, have rigid table, proper cooling and calculate properly speeds and feeds you could machine mild steel. I dont see how thats to happen if you dont use some software like HSMAdvisor or Gwizard to finely calculate what exactly you are doing. From there you will see the forces involved and the power needed to do that.

I myself use HSMAdvisor, inside there is an profile of 3kw 18k rpm spindle, use that to see what happens. I highly recommend getting the 3kw versus 2.2kw for metal.
Have in mind that most spindles use all ceramic bearings or partly. There are dedicated high speed spindles for metal that cost more and they say with better bearings. I have no info if thats reality or Chinese tricks.


-the machine design
So yes, if you go that way, its better to have the gantry fixed. Do your research and see build section in forum. There are discussed machines exactly made for what you say.

-me personally
i would buy me a small mill or retrofit big one. I in fact am just finishing a very sturdy build that could definitely do that what you want, but dont plan to f__k my spindle cutting steel

Hope that helps

PS. below a snip from HSMAdvisor, As you see spindle power is not the limiting factor. it would be the stiffness. sliders are adjusted for standard stiff machine/ mill/

[Sven]

You can also opt for building in epoxy concrete (often called epoxy granite).
And yes, you can use a chinese spindle but the bearings have to be ok.

A guy close to me built an epoxy concrete machine with a chinese spindle (I think 2200 watts but up to 18000 rpm) and can easily mill steel, to about 200s of a mm.
He used old servos but you can get simmilar results with closed loop steppers.

Have a look over here in a dutch thread (maybe use google translate):
http://cnczone.nl/viewtopic.php?f=8&t=8410&hilit=epoxy&start=406

Here it is
Here it is in action, steel 12000rpm, 4500mm/min feed, 15mm doc, 0.5mm, at long life settings:


He says he can also do 20000rpm en 9500mm/min but that is no good for tool life.

[lukeleb2010]

Thank you both for your responses.

After further research, I agree that the easiest way forward for me is to buy a small, cheap manual mill and convert it to a cnc machine.

I found this on Ebay:

http://www.ebay.co.uk/itm/Proxxon-MF...YAAOSwHjNV-BT2

And here's a conversion:

https://www.youtube.com/watch?v=iVYIXzO6UtI

Couple of questions:

Firstly, does this look like a rig that could cut steel to any degree of success?

Secondly, I know that manual mill can have quite larger backlashs. Will this be an issue in a CNC conversion and how can it be overcome?

Many thanks,

Luke Blades

[Davek0974]

Here is picture of a mill, it's a Bridgeport - the most common mill ever made i think, I have one just like it. It's 1100kg of solid cast iron and has a proper 2Hp motor on it.

It is capable of milling steel, but will only take relatively light cuts due in most part to it's versatile nature - the head can swivel, rotate and tilt, these are great features but make it weaker when it comes to real milling.

Steel needs lower speeds and more power, yes it can be done with high speeds but you can expect short cutter life and you will only be scratching away the metal.



That being said, I am building a gantry style CNC machine and fully hope to be able to do fine milling in aluminium but nothing tougher, i am looking at cutters of around 2 - 5mm diameter.

I really would look closely at what you need to achieve but steel milling is going to be a tough nut to crack.

Conversions can be done, plenty of Bridgeports have been CNC'd - ball screws are a must and a good machine as a foundation is a big help as lot of them have had a hard life.