Spindle motor replacement options, ac/dc servo brushless...

[Mwmx54]

I think my original 110v motor that came with my Bolton zx45 mill is starting to get tired, it’s bogging down in areas that it did not used to, which is causing all sorts of problems when it happens during a cnc program. I have read and searched this forum, and found a few people using the 3hp bldc that kelling/automation tech used to sell, maybe they still do, but at $650 it seems a lot of people have problems with them, bogging down, same as what I have now.
So what other options do I have, I’d like to get it connected to Mach4 with speed control, so 3 phase with a vfd? I work about 50/50 steel/aluminum, so keeping the gearbox would be nice, but finding a little bit faster motor would be good, I can test out what the original gearbox can handle.

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[Al_The_Man]

Sounds like time for a 3phase motor and VFD?
Al.

[joeavaerage]

Hi,
another alternative is a servo. Modern servos produce a great deal of torque for their size, even more than a 3 phase induction motor.
A servo and matching drive are likely t be expensive though, I would guess at least double what you might expect to pay for an
induction motor and VFD.

I bought a 1.8kW Allen Bradley and drive off EBay cheaply for a spindle motor and it has served me well, still not as cheap as an
induction motor probably.

Craig

[Mwmx54]

Hi,
another alternative is a servo. Modern servos produce a great deal of torque for their size, even more than a 3 phase induction motor.
A servo and matching drive are likely t be expensive though, I would guess at least double what you might expect to pay for an
induction motor and VFD.

I bought a 1.8kW Allen Bradley and drive off EBay cheaply for a spindle motor and it has served me well, still not as cheap as an
induction motor probably.

Craig

Is a 1.8kw motor enough power, what is that about 1hp? I’m guessing different types of motors have different tourque curves, thus being able to run less power more effectively... are you running an ac servo? I’ve spent a little time looking at used ones on eBay, but then I have to find a matching drive, as well as finding one small enough, as most are made for full size commercial machines.

[joeavaerage]

Hi,
1.8kW is equivalent to 2.3Hp. My experience is that AC servos have very generous overload ratings, and while they cannot be operated in overload
continuously, they behave as if they have much more power than the rating plate would suggest.

My mini-mill has cast iron beds with 15mm square rails/cars and 20mm ground ballscrews. It weighs 400lb despite having travels of only 180mm x 180mm x 180mm.
I built it with the intention to mill steel and stainless, and this it does, but it starts flexing when I try to use all the power of my spindle.

I have two spindles, a 750W 24000pm asynchronous for engraving and easy metals like brass and aluminum, and my 1.8kW 3500rpm 6.2Nm spindle for
steel. The rigidity of my mini-mill is very adequate for the smaller high speed spindle but marginal for the slower high torque spindle, despite the efforts
I made to make it a rigid as possible.

I am building a new mill. I had the axis beds cast in iron, 115kg each. The frame would ideally have been cast in SG iron, but my budget has nearly run out so
am constructing a C frame in 32mm steel plate.

I have 32mm C5 double nut ground ballscrews, 20mm heavy duty THK linear rails and cars. The servos are 750 B2 series Delta (160,000cpr), one braked.
The travels are 350mm x 350mm x 350mm.

When complete the total weight including the table and enclosure will be close to 1000kg.

I did this not just to make it heavy........I did it to make it as rigid as I possibly can. It does not matter what spindle you put on the machine if it has more
torque and power than the frame and axes can contain the result will be abysmal. This is a lesson I gained from experience....and I will not be mislead
or over optimistic again.

Craig

[Mwmx54]

Hi,
1.8kW is equivalent to 2.3Hp. My experience is that AC servos have very generous overload ratings, and while they cannot be operated in overload
continuously, they behave as if they have much more power than the rating plate would suggest.

My mini-mill has cast iron beds with 15mm square rails/cars and 20mm ground ballscrews. It weighs 400lb despite having travels of only 180mm x 180mm x 180mm.
I built it with the intention to mill steel and stainless, and this it does, but it starts flexing when I try to use all the power of my spindle.

I have two spindles, a 750W 24000pm asynchronous for engraving and easy metals like brass and aluminum, and my 1.8kW 3500rpm 6.2Nm spindle for
steel. The rigidity of my mini-mill is very adequate for the smaller high speed spindle but marginal for the slower high torque spindle, despite the efforts
I made to make it a rigid as possible.

I am building a new mill. I had the axis beds cast in iron, 115kg each. The frame would ideally have been cast in SG iron, but my budget has nearly run out so
am constructing a C frame in 32mm steel plate.

I have 32mm C5 double nut ground ballscrews, 20mm heavy duty THK linear rails and cars. The servos are 750 B2 series Delta (160,000cpr), one braked.
The travels are 350mm x 350mm x 350mm.

When complete the total weight including the table and enclosure will be close to 1000kg.

I did this not just to make it heavy........I did it to make it as rigid as I possibly can. It does not matter what spindle you put on the machine if it has more
torque and power than the frame and axes can contain the result will be abysmal. This is a lesson I gained from experience....and I will not be mislead
or over optimistic again.

Craig

That sounds like it will be a hell of a machine, I have been wanting to build one myself, in a similar fashion as yours, just as rigid as possible, this conversion has been a fun project, and I learned a lot about what a cnc needs vs a manual machine that you can work around the areas that it falls short, cnc is a little more involved, it really shows you where it needs upgrading, usually by breaking something.
I also thought about bolting a second cheaper import high speed spindle to the head. But at the moment, the simplest thing to do would be installing a slightly higher speed and variable speed motor that has enough torque to cut steel. Cause if I can’t get it to that, then there’s no point in taking the machine any further.
Where did you go to get your iron castings? Sounds like an expensive endeavor.

[joeavaerage]

Hi,
my existing mii-mill I made a little over ix years ago. I machined the beds out of cast iron elevator weights I got from the scrap yard.
They worked out OK, but really the cast was pretty poor quality, the occasional inclusions and a hard rime on the outside. I should not have
been surprised, after all an elevator weight only has to be heavy.

I decided then that if I ever built a new machine I would get proper castings made, and that is what I've done. Yes they are expensive, about $3500NZD.
But worse was to come when I needed to machine them on a top quality large mill........nearly $5000NZD. I've got what I wanted and the accuracy of the machining
is superb but it was expensive. If I had known just how expensive it would be its dubious I would have pursued it.

CNC in general, and making first my mini-mill and more recently my new build mill, has been a great learning curve. I often argue that 'the value of a hobby
is the learning you do to fulfill it'. and the learning I've had to do over the last few years would suggest that CNC is a great hobby!

There is quite a bit I could do with my existing mini-mill to improve it, and given that it is now in regular use in my line of work, will probably do so.
I had the budget and the inclination to make a new machine without the shortcomings of my first attempt....ergo my new build mill.

Craig