If you listen to the end, it's revealed that there is now generous funding available which allows people to do this kind of open-source development as a full time job, which is what he is now doing. For that reason, I think there's a good chance he will complete his project within the allowed 6 months., and so by the deadline it will likely be nicely polished.

Both have active forums on discord. Comparing the two, MillkCR8 is focused on a desktop machine about the size of a milk crate (hence the name), whereas PrintNC is scalable in size, leveraging a parametric design to generate plans that will make it any size you like (from small to jumbo extra large) to encompass any cutting volume you might want. MilkCR8 relies on a wooden box frame, which doubles as an enclosure (notionally similar to a Nomad CNC), whereas PrintNC has a standalone steel frame that you bolt together, with an enclosure being both separate and optional. Because the goal is stiffness, neither project makes use of extruded aluminum, so in that respect they are very different from Chinese CNC kits.

Thinking about it now, two known points are required when nothing is pinned because that's how many points are needed to re-establish the origin as well as correct for any rotation that may have occurred after the board is flipped over. So, presumably, first a new origin needs to be established, and then all of the g-code for the second side needs to be amended after-the-fact to account for any rotation that may have happened when the board was flipped.

pro machines with auto tool change do benefit from auto probing, but that is a total different story.

• for PCB milling this spring loaded stuff simply does not work, as the whole area should be mapped.
• for non-PCB Z zeroing it could be good, however in such case (imho) this is just an over complicated/engineered method for a simple probing.

when you need a single z touch levelling then better to have a rock solid solution rather then have additional moving parts and potential other vectors for a failure. even with a slow feed rate, a single probe can be done in an acceptable time period, so why should you risk your result?
I can imagine that this spring stuff can help you when you approaching with quite high feed rate for first, but in such case I would be afraid of the "wearing" of the probe surface over time and the inaccuracy it may cause later on.

btw, the "double probing" with fast then a slower feed rate is used by other sw/firmware, e.g. marlin does the same (in certain configurations) for 3d printers.

It's notionally the same as the probes you listed, but it includes a spring to compensate for any overshoot. Of course, if you're moving the z-axis extremely slowly in the first place, then I guess the spring wouldn't be needed. I presume the "double touch" that candle does is to speed things up: find approximately the right height at high speed, then back-up just a little then and find it again at a much slower speed. For the Candle approach, maybe this thingiverse spring-loaded touch plate would be better than just a rigid touch plate that has no spring to it. I suppose it depends on whether the spring loaded touch plate can repeatably reach exactly the same height again and again, or not.

Speaking of repeatability, and measurements thereof, I just today receive this electronic dial indicator gauge:
https://www.amazon.com/gp/product/B07888LX1R/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
When combined with a matching data cable, it can help to automatically collect repeatability data and log it into a spreadsheet on an attached PC. I have the data cable (actually, a specialized RS232 to USB converter) on order. From what I've read, it can be triggered either by pressing a button or by an external contact closure, which is what I hope to use to automate the button pushing.

This is necessary even for the PCB milling. After the levelling is done, a single touch probe is needed somewhere in the working are to set the Z0 and to make it as a reference point for the bed levelling mesh.
At least this is how it is done in bCNC.
After the isolation routing is done, I make a single Z touch probe for each drill bits to set the correct Z0 for the given bit. This is done in the same way as in case for the PCB probing.
Note that as the drilling on Z axis does not require high precision (basically if your drilling depth is slightly bigger than the PCB thickness, then even if your Z is just roughly adjusted to the PCB top, it will do the job).

As I currently work with PCBs only, no other touch probe was necessary, however for woodworking (or for other non conductive materials) one can use a dedicated "touch probe".

There are nice solutions form a simple PCB:
https://www.youtube.com/watch?v=l9o6ZUjb3k0&ab_channel=NikodemBartnik

or
https://www.youtube.com/watch?v=58m1v-fHFjU&ab_channel=CosmoChannel

or you can buy a cheap touch probe as well:
https://www.aliexpress.com/item/4001010640247.html

or you can go for nicer and more expensive professional touch probes :)

I made two mistakes:

• as I was in hurry, I did not use enough measurement points for the levelling. A small extra copper remained at two places, hopefully it won't need too much work to get rid of it. The time saved on the levelling will be spent twice on the post-processing... lesson learned... again...
• I made an unintended short during the levelling and had to reset the controller. Working coordinates were re-defined manually, causing a small shift between the two sides. Once I'll have my new controller ready, this should not happen again.

Beside these issues, the result still looks amazing.
Here are some pictures for reference:

isolation:
https://youtu.be/7kZHOMzWgUI

drilling:
https://youtu.be/kUqxxttMfyc

Conclusion: CNC2030T is an affordable CNC machine which can be easily used for precise PCB prototyping.
Btw, this was my conclusion for my previous CNC2418 as well. Both of them proved their capabilities. CNC3020T is just better, more robust and good for more stuff.

To be honest, if one buys a CNC from the super cheap 2418 category and the main goals is PCB milling/drilling, then I do not see any reason to spend money and time on upgrades, as the base machine is good for the job.

I've bought it via ebay from an European reseller, faster shipping and no taxes di*king around.

By "tuning" the endmill I mean: take out the collet/nut, blow the dust out, insert the endmill untill the chamfered edge passes through the collet. Insert collet/nut/endmill as it is in the spindle and tighten LIGHTLY!!! Do NOT overtighten! Start spindle, turn to max rpm, if it's noisy stop! take out whole collet/nut/endmill from spindle and rotate the endmill in the collet like 30-45 degrees, reinstall and run test again. If patient enough you can get to 60k rpm without much vibration.
Lately I'm not going over 35-40k rpm, the VFD shows the speed from 0 to 1000 and I stick around 700-750. For drills I run even lower, like 550-600 and don't bother tuning at all.
You can find the sweet spot as I said earlier, turn up the rpm, then slowly decrease until silent. You will find there are rpm ranges where vibration is high and ranges where is low, just use the lowest vibration one while still having a good rpm (find the vibration function poles).

Imagine the in the picture rightmost is 60k rpm, the blue line is the noise/vibration level, as you go to the left (lower rpm).

which is 75v, still single phase, water cooled, but it has a recognizable ER8 on it. Costs around $175, delivered.

I'd probably opt to pay more, though, to get something with less runout, like maybe this:
https://www.aliexpress.com/item/4000812286377.html?spm=a2g0o.detail.1000060.2.97ea29d2lqjJXu&gps-id=pcDetailBottomMoreThisSeller&scm=1007.13339.169870.0&scm_id=1007.13339.169870.0&scm-url=1007.13339.169870.0&pvid=dafeb530-8e0e-478a-8fdf-1fa3b2193609&_t=gps-id:pcDetailBottomMoreThisSeller,scm-url:1007.13339.169870.0,pvid:dafeb530-8e0e-478a-8fdf-1fa3b2193609,tpp_buckets:668%230%23131923%2328_668%23808%233772%23437_668%23888%233325%2317_668%234328%2319940%23948_668%232846%238115%23852_668%232717%237563%23559_668%231000022185%231000066059%230_668%233468%2315607%2336

which claims a runout of just 0.004mm, because whatever spindle runout there is will get amplified at the tip of any bit that gets inserted. I just have no way of knowing by how much it will get amplified, so for that reason I'd lean toward minimal spindle runout. They also claim to be the spindle manufacturer, so in theory they should know what they're talking about. Since the spindle itself is rated for only 75v, hopefully I could find a VFD somewhere that runs from 110v input voltage, which here is a lot more convenient, without having to wire for 220v or step 110v up to 220v just to meet the more typical Aliexpress VFD input requirement of 220v.

The collet itself looks a bit mysterious.

If I "tune" the position of a new endmill I can reach 60k rpm without any vibration at all, so I get almost no runout.

How do you tune the position of a new endmill? Are you referring to how far into the collet you are inserting it?

BTW, thank you very much for your posting. It was extremely helpful. I didn't know anyone was using ER8, but from your positive experience, it sounds like ER8 may be the way to go. All else being equal, it makes sense that a narrower ER8 assembly would be prone to less runout, as an imbalance on a wider ER11 assembly would obviously be amplified more at higher RPM's than an equivalent imbalance on an ER8 assembly.

If you don't mind my asking, which manufacturer and model ER8 60,000 RPM spindle do you have, and from where did you source it?

Contrary to my 3D printing and PCB/component experience, where I do okay with cheap/counterfeit parts, the tolerances and high cost of mistakes in my CNC experience are leading me to pay the premium for quality parts.

PS. The best way to check for runout is the sound test, run the spindle empty, then with collet+nut, then with the endmill inserted. If I "tune" the position of a new endmill I can reach 60k rpm without any vibration at all, so I get almost no runout.

and an ER11:
https://www.aliexpress.com/item/32948530784.html?spm=a2g0o.cart.0.0.7a203c00aR74s0&mp=1

I tried to make it apples to apples. Prices are constantly fluctuating, so at the moment this particular ER11package seems priced lower than a lot of the other ER11 60,000 RPM packages, so that will contradict my earlier 2x statement (which is more of a running average across different vendors). At the moment, the price looks fairly attractive, if the quality is there. If the quality is poor, I'd probably be stuck with it, so there's a lot of risk in buying from sites that don't list the tolerances.

Marcos Reps suggests that buying used industrial equipment might be a safer path, because on his theory most industrial equipment gets replaced while it still has reasonable life left on it, and the quality tends to be high to begin with. But in his case, because of his vlogging, a manufacturer actually just gave him a high quality spindle, so he never really tested his theory.

Which 60,000 RPM spindle manufacturer is the best value? It may boil down to who makes it and what the tolerances are. That sort of info is often missing from the aliexpress listings. If the etchings on the spindle cases can be believed, then in this particular comparison the manufacturer is the same (namely, Changsheng).

Anyhow, Wegstr, for instance, seems to get great PCB results without relying on such massive spindles, so maybe I should be looking elsewhere.... But where, exactly?

Also, who makes the best VFD? I've read that certain brands are problematic, but I haven't kept a list (yet) of which ones to avoid.

These spindles are quite heavy, but maybe the extra weight would just amount to more preloading, which maybe (?) could be a good thing. I do like the portability of my CNC, which a Marco Reps style machine has clearly lost, despite its other advantages.

1. They advise that I can go up in voltage, no problem--all the way to 42v if I want. Even at 42v there's still some safety headroom leftover. However, they advise against increasing the current, unless absolutely needed to avoid stalling, as that may lead to overheating, unless active cooling (a fan) were to be added.
2. "10mm/revolution a 32 microstepping input will give you 0.0016mm resolution. " This is a good point. Actually, with the current lead screws I'm at 8mm/revolution, and if I switch to ballscrews it will be either 4 or 5mm/revolution, which would be even better. Hence, maybe even the current (default) 16 microstepping is good enough.

So, I guess once I get limit switches installed, then before I get fancier it'll be time to do some milling and see if I notice any improvement brought by just the uStepper drivers alone. Then I may upgrade to the 20,000 RPM motor to see what, if any, difference that makes.

I still have my eye on a 60,000 RPM spindle. They seem not much more expensive than the 36,000 RPM spindles. I've found ER8 60,000 RPM spindles for less than $200 delivered, but ER8 seems like it would be too tight a fit (?), especially for regular router bits like the ones with 1 inch diameter heads used to flatten spoilboard. For some reason, ER11 60,000 RPM spindles seem to cost around twice as much, though I have no idea as to why. Is it really that much harder to make an ER11 spindle than an ER8 spindle that's otherwise the same?

It appeared I was able to drive the y-axis at a nominal 10,000 mm/min, but going faster than that yielded wildly unpredictable results. Plugging in a 10a 24vdc power brick instead of the 6 amp power brick seemed (so far) to avoid the problem, so I'll be replacing the 6 amp power bricks with 10 amp power bricks for about 4x the cost. All this just to avoid dust incursion into a single, centralized, standard, high current, "open to the atmosphere" power supply. :face_with_rolling_eyes:

That said, I'm unsure how well even the 24vdc-10a power brick will hold up over time to the very spikey current demands of a CNC-driven stepper. That's the lingering doubt that accompanies going down the quick and dirty path with no datasheet. Given the unknowns that come with power bricks, maybe a fan-cooled , ordinary power supply isn't such a bad trade-off even if it sucks in a lot of dust... :rolling_on_the_floor_laughing: Or maybe a Redundant Array of Inexpensive Power Bricks is yet another alternative. Meh,....

Another, unrelated thing I'm noticing is that the Dupont and RJ45 connectors and barrel jack on the uStepper boards are a bit loosey-goosey. They may be conceptually neat and convenient but in reality they don't seem particularly good at handling vibration and/or physical strain without tending to wiggle loose from their connections. Not sure yet what, if anything, to do about that. Even if I were to solder the connections, it may still need some kind of additional physical anchoring to hold everything firmly in place and provide sufficient strain relief.

Unlike the original nema 17 steppers that came with the CNC kit, these higher torque nema 17 steppers don't work at all on just 12v. However, the good news is that the upgraded higher torque steppers are pretty snappy when running them at 24v.