Hi, I would consider myself to be only a very basic apprentice, so take the following as un-expert opinion, but I do happen to have a what I believe is a Proxxon Mill, it was marketed as the JewelMaster NC, and also a Taig Mill for comparison. Both are CNC, and I have used both on aluminum and wood. The proxon mill was very economical, but I do have some concerns over the durability of the mill for computer controlled applications. For the version I have, the Nema 17 steppers were fastened with C-channel aluminum, machined into a mount, and coupled with some cast aluminum couples with set screws. After a few hours of operation, the set screws on one of the stepper to screw couples on the y axis failed, requiring repair and ruining the piece I was working on. Also, the alignment of some of the steppers and screws was off a bit, resulting in a noticable movement of the stepper up and down as the X-axis screw rotates. These issues may not apply, depending on who does the conversion, how it is done, or what mill you have. The gib is thin, and slides on the aluminum table, which appears to me to be an extrusion. I have concerns over how the machine will wear over time. I found the spindle on the Proxxon to perform well for what light work I was doing, although it sounds to me similar to a Dremel. I have not tried to cut any steel on it, and I'm not sure if it has the power to take much of a cut in steel anyway, although light engraving with a suitable engraving bit would probably not be much of a strain for it.
In comparison, the Taig has thick adjustable brass gibs on the X and Y. It feels to my unexpert eye to be more sturdy and smoother. It is however more costly.
In summary, most stuff I Make on a micro-mill, I make on the Taig, while the Proxxon sits idle. I do think it is an inexpensive mill to learn the basics of NC on however. If I were relying on it for small scale production, or serious work, I would go with a heavier and sturdier mill.
I don't know if any of this will assist you, but that is my opinion on it anyway, Rich
for as far as my experience goes proxxon and steel shouldn.t be mentioned within one breath.
though i must mention the very diverse offering by proxxon making it impossible for a man to be sure it will/won't fit your needs.my experience ends at the dremel a-like multi-tools.wich by the way operated fine for handwork but i cant imagine what would happen to it on a cnc job