DIY "mini" Mill for cutting up to stainless questions.

[axefxpwner]

Hello, I'm building a mini mill to machine various lighter metals, but also the odd stainless product.

Looking for recommended specs/experiences with lower end spindles in this kind of situation, also
wondering if a 12x9x12 workspace will be a large enough machine to accommodate this size spindle.

I plan to do what I can to make it as rigid as possible, linear rails, ballscrews, epoxy granite, and have decided to go the
stepper motor route. Would nema 23's provide enough torque? I don't need a crazy feed rate

Thanks in advance!

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[QuinnSjoblom]

With steel you're pretty much required to have a geared down motor driving a separate spindle to get low enough rpm. I built my machine specifically for milling aluminum and the Chinese 2.2kw spindle is excellent for that, but with an rpm range of 6000 to 24000, sfm is too high for steel unless running tiny endmills.
Not sure what your budget is, but I've been dreaming about a servo driven spindle. Huge capability there. Full torque down to 0 rpm, will do any synchronized operations like rigid tapping, hobbing gears, etc. Dmm servos seem to be very popular and pretty affordable. I think about 500 bucks for the 750 watt servo/drive kit, 700 for the 1.8kw kit. For the size you're building, 750watt is probably plenty. Throw it next to something like a taig mill headstock/spindle, or a tormach bt30 spindle cartrige but that's getting a bit bigger. Not that you need a servo to drive your spindle. Just seems really cool to me to have the capabilities it adds for not a ton more money. Can also just drive it with a motor.
If you can give up cutting steel with anything larger than a 1/8 endmill, the Chinese spindles are really convenient and relatively cheap. For smaller spindles at low enough rpm for steel, I'm not really sure what options there are other than something like the headstock on the taig, but im curious if anyone knows of any

[axefxpwner]

Thanks for your response!

All of that was very good input, to which I'm going to do some more research into Servo driven spindles.

I may end up just driving the spindle with a motor, but the Dmm servo is very intriguing and the price point isnt bad.

[QuinnSjoblom]

Thanks for your response!

All of that was very good input, to which I'm going to do some more research into Servo driven spindles.

I may end up just driving the spindle with a motor, but the Dmm servo is very intriguing and the price point isnt bad.

The servo drive was kind of getting a bit off subject, but I figured I would mention it since it opens up a lot of capability in a small package. Probably first on your list is finding a spindle to drive. I went down that path before and the options are pretty limited for something small and affordable.

[QuinnSjoblom]

Did a bit of searching of my own. Glockcnc makes an upgraded headstock for the taig. Pretty beefy and small. They have an r8 version and a tts version (tormach tooling) which you could add an air drawbar to and have quick tool changes with programmed height offsets, or even build a full auto tool changer. Pair that with a dmm 750 watt servo and you would have a pretty sweet robust spindle setup for a mini mill. 1hp milling in a wide rpm range which gives pretty respectable mrr's.

[axefxpwner]

Thank you for that link, there really isn't much out there in the realm of 3rd party headstocks! I had been searching as well with little luck.

I've decided to go the dmm route, just trying to decide if I want to step into their 1+kw models.

As far as spindles go, I work as a programmer and have access to emco turn and mill 155's, and I'm very much contemplating making my own ATC spindle with them and buying some bearings.

[QuinnSjoblom]

I would go the same route if I had the machinery available. Headstock isn't such a big deal, but i imagine a precision ground spindle is a bit harder.
If you can handle the weight and size of the 1kw-1.8kw dmm, I would go that route. Not much more money, also you don't need a dc power supply for those, just ac input, so that offsets more of the cost. They are just gonna be a bit harder to manage on a small mill since they are 130mm square and over 20 pounds, but if you're building a nice beefy epoxy granite mill, it shouldn't be a problem. I Would also consider maybe going slightly larger footprint unless space is the issue. If you're using nice stuff like ball screws, linear rails, etc., going slightly bigger isn't gonna increase cost significantly. Rails and screws are probably gonna be your largest cost depending on what level of quality you go. You can get a full set of Chinese hiwin clone ballscrews and rails for cheap, like 500 bucks total, but the quality is a bit hit and miss. That's what i did and im reasonably pleased for what i paid. Some of the bearing carriages had a bit of play, no preload, but they swapped them out and they are pretty decent. The ball screws are good aside from a few issues. Consistency of motion and backlash were actually really good, but the bearing journals on the screws had some run out and the screws themselves have some bow. In my case the screws are longer than my travel so the ballnut doesn't travel all the way to the ends. Because of this, the runout was manageable. If I needed the full travel of the screw, the runout would probably cause some binding. I probably could have asked them to replace them and they would have, but who knows if the replacements would have been better. With the machinery you have available, you could probably address the journal runout if needed. Turn it true and use a sleeve or smaller id bearing. Problem is, if you get brand name stuff, even hiwin, you'll probably pay 4 times as much for slightly higher quality. All depends what your budget is and what type of quality you want. You could spend 3-4k building an ok machine, or spend 6k and build a really nice machine, much more capable than something like a tormach for example. Even the 3k machine using clone screws and rails will run circles around a tormach though. Linear bearings and ballscrews will allow 3 times the rapids, better accuracy, consistency, maintenance free, even when sticking with steppers.