Stay away from stepper motors if at all possible. You can loose steps, they are noisy and i just dont feel comfortable personally going the cheap route on something that needs to make me money. I put Clearpath servo drives on mine. Worst case if it wouldn't have worked, I could use the servo motors elsewhere. The entire retro was less than $3k. The Masso controller needs some help but it does what I tell it to...
I wasn't planning on cutting from the chuck back so when I made my acme nut, the threads were cut so they were 95% thread and the nut is about 3" long so as to reduce the chance of backlash. Granted it will eventually happen. I have zero issues starting and repeating my Z location if I cut one way only. I didn't want to spend a lot of $$ for a proof of concept machine kinda thing. To be honest, I make a lot of hydraulic parts on this machine. 4140 ht, 410 ss, 416 ss, 304 ss, and 1018. It cuts it all. Finishes seem to vary from material to material. Hence why I want to get it set up with a vfd. For doing the 1 off type of part, I tend to walk away from it but if I have 2 or more parts to make, then I start looking into running it on that machine. For a 1977ish machine, it cuts beautiful with the retro. I don't use this thing as a manual machine anymore. Strictly cnc.
Now cutting with HSS tooling, your RPMs will be low. I would have to look at my chart but if my memory serves me correctly, your looking at around 150 sfm for 1018. Aluminum is 300 sfm. Plastic, well let's just say you probably can't get your spindle fast enough for the sfm (600-1000 sfm or higher). I would look at your application and what your plans are for the machine. Make money, play with a cnc, or learn something new? I built mine for both proof of concept and to make money on the parts I didn't have tight tolerances for. Well turns out I can make parts and hold .0005" and make money on it at $45 an hour too. This machine has morphed from nothing to my go-to tool room cnc lathe.
Just my $.02
Chips
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