Testing An Inexpensive CNC Spindle

The old saying “you get what you pay for” is a cautionary cliché, but is directly contrary to several other common sayings. In the case of [Spikee]’s planned CNC machine build, he took the more adventurous idiom of “no risk, no reward” to heart when he purchased these spindles for the machine from AliExpress. While the delivered product seemed fine, there were some problems that needed investigations.

Upon delivery of the spindle, everything seemed to work correctly out-of-the-box. Even the variable frequency drive, which was programmed at the factory, was working properly. But at around 8000 rpm the machine would begin shaking. The suspected part causing the vibration was the tool holder, so after checking the machine’s runout and also using a specialized vibration sensor this was confirmed to be the case.

Luckily [Spikee] was able to get a refund on the tool holders since they were out of spec, but still has a quite capable spindle on his hands for an excellent price. Without some skills in troubleshooting he might have returned the entire machine unnecessarily. If you are looking for some other ideas in setting up an inexpensive CNC machine, you might also like to look at BLDC motors from a remote control vehicle.

22 thoughts on “Testing An Inexpensive CNC Spindle

  1. Congrats for going through the missing quality check himself, learning things on the way, adjusting / correcting (and getting refund) some parts, which results in a good quality tool for a fraction of the cost.

    For sure he could have “buy american” and maybe get the exact same spindle but rebranded, QC checked, with a warranty but for a hefty price tag.

    1. Indeed. All commercial systems I know use a (multi stage) pneumatic cylinder to compress a stack of belleville washer springs.

      One of the reasons these spindels are relatively expensive is because of these washers. They have a relatively big diameter, and this necessitates big bearings. And big bearings that can run at 24000rpm are expensive.

      An alternative is to use the old fashioned pull thread instead of a stack of belleville washers. If you want to make an auto tool changer, this would also need some kind of locking system and a motor to tighten and loosen the thread.

    1. Spikee here (OP) ; Bottom of the barrel 2 pole spindles go for about 200$; With some better bearings, 4P motor etc ~500$ . These are all manual tool-change ones. If you go to automatic tool-change you are looking at 3-8K for EU/US one’s. So 1k is (relatively) cheap for such a capable spindle motor.

    2. Wanted to say this too. It’s inexpensive for what it is. But man, what it is is way more than what I’m buying. :)

      $200 gets you a nice water-cooled 2.2 kW ER20 spindle motor these days. The one that came as an upgrade to my reasonable CNC router is well balanced and runs fine up to max RPM. Runout is unmeasurable with my el cheapo dial gauge. It’s honestly a _lot_ better than I had expected. It’s not the weakest link.

      (Sold by RATTM, but I don’t know anything more about them, so don’t necessarily take this as an endorsement.)

      But I can also attest that at the very bottom of the price range, you get junk.

      1. Meh, got a cheap as chips CNC3018. Spindle must be super cheap, definitely doesn’t reach the claimed speed. But provided you set it up true, surprisingly good.

        The weakest link was crappy cutters. With some good quality solid carbide cutters surplus from a local very high-precision engineering firm (a “these have been used once so might be out of spec, not worth the risk” type place), it runs a lot better. Obviously not a big machine, but definitely not junk.

        Even set up roughly and with the stock cutters, it paid for itself very quickly.

      2. (op here) if you read the post on my website I go a bit into what makes this spindle more special and thus more expensive. You can’t compare the bearing quality, available power and torque etc that such a spindle provides vs a bottom-of-the-barrel retail 200$ spindle (which sells in china for 60$ FYI and gets built for ~30$).

  2. Atc is extremely important and they are quite well made boys of equipment. The dimensional accuracy is really high. Good to hear things worked out

    I need to buy one myself but I need higher rpm. I will have to buy the so called dental or pcb spindle from someone on Alibaba. Ali express doesn’t have them. They grab the tool directly, no tool holders, and typically go to 60k rpm. And yes there are downsides to this, eventually the clamp thing wears out, but it should last a couple years and then I’m. Hoping I can replace just that part.

    The problem with bt tool holders is lower rpm which is too low to get the right surface speed with small diameter tools, and secondly the tool holders take up a lot of space so there isn’t much space for very many tools on a small machine like a 3040 that I have.

    I seriously wish there was more stuff in the community about atc though. Also the price difference of 200 vs >1000 for no ATC vs at is baffling. Atc spindles aren’t that much more complex. Maybe, hopefully, they are better made in other ways, but absent clear specs that day that I would not be so generous to assume that. Sheer profit is a more likely explanation.

    People don’t understand how important atc is. It allows you to make a much wider range of geometries and work at higher speed because you can use rest milling. Also it reduces end mill cost because you can use different end mills for roughing and finishing and still get good tolerances and long tool life.

    It’s a major factor in quality, economical milling, and it’s useful and improves economics no matter what your are making, usually.

    1. Are you sure AliExpress doesn’t have dental spindles? I’ve seen plenty. Maybe your search term is wrong, try dental handpiece etc. Same for PCB or nail drills that are used in cosmetics.

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