Originally Posted by
joeavaerage
Hi,
I made my own mini-mill about seven years ago. It was not entirely dissimilar in size to what you have.
I fitted a 800W 24000rpm ER16 Mechatron spindle and VFD....its been brilliant. I don't know how many thousands of hours use I have had but lots and lots.
It works great on circuit boards, my main use, but also on plastics, aluminum and brass.
What it will not do is mill steel or at least very well. Steel, in fact all ferrous metals, require a spindle of much higher torque but much lower speed so about the same power, just
much much slower.
In order to do steel I made a second spindle using a secondhand 1.8kW 3500rpm 6Nm (cont) Allen Bradley AC servo, a Rego-fix cylindrical ER25 toolholder and P4 angular
contact bearings. It too has been great. The only real problem is that it has enough torque to cause my mini-mill to flex...so I have to take it easy to
accommodate the modest rigidity of my mini-mill.
Over the last few weeks I have commissioned my new build mill. It has 115 kg cast iron axis beds, twin "L" 32mm med-tensile steel frame, 32mm doublenut C5 THK ballscrews
and THK HSR 20mm linear rails and cars. All-in-all a much MUCH bigger and more rigid machine. My 1.8kW Allen Bradley based spindle has now come into its own,
it's a much better match than my mini-mill.
The important point here is that the spindle must match the machine. Having a high torque slow revving spindle is great for steel but what's the bet it will twist your little
machine into a pretzel. I personally have found that the low torque high rpm spindle to be much more useful. Addmittedly its not much good on steel but on everything else it
has been fine.
May I suggest that a 1.5kW 24000rpm spindle would be a good match. I would recommend water cooling as it means you can use the VFD to slow the spindle
to 6000-9000 rpm without huge risk of overheating it. An air-cooled spindle would very likely overheat by comparison.
My experience is that such a spindle will give you lots of service and will make lots of small to medium parts for you, and in short you'll have a lot of fun.
Having a BT30 toolholder would be nice, but you pay one hell of a premium for an ATC type spindle. A straight manual ER20 or ER25 spindle is less convenient to use
but likely 1/3-1/2 the price.
Having said that my next spindle will be ATC, BT30 probably. I have a second hand remanufactured 3kW 3000rpm (rated) 12Nm (cont) AC servo from circa '95. I want
to use it for another high(er) torque low speed spindle, again for steel and stainless.
Craig