All of the buildings, all of those cars
were once just a dream
in somebody's head
Mercy Street - Peter Gabriel


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Pic 400

A new spindle for the CNC 3040

Another problem I encountered with my cheap CNC 3040 was the cheap spindle. First problem was that it started vibrating (a lot) at certain speeds. Another problem was the higher than expected run out (i.e. rotation inaccuracy which occurs when the tool is no longer aligned with the main axis).

The consequence of a higher than expected run out is that the traces you mill away from a PCB are much wider than expected and there will be less copper left (or even none) for the actual PCB track.

Measuring the run out (at the wrong place...).

The mounting head for the CNC 3040 is very inflexible and only accepts spindles with a diameter of 52 mm. I tried my luck by ordering another spindle from Aliexpress but that one was even worse…

Looking around for a decent spindle I stumbled upon the Teknomotor C2431-B) (link given to the web shop where I bought the spindle since the manufacturers website lacks detailed information). Which is certainly not expensive for its performance:

  • Easy to replace a KRESS spindle since it has a 43mm mount
  • Fbase at 18000RPM (RPM where max power is available)
  • 24000RPM motor at a low price level
  • 270W of power, suitable for engraving and 3D milling with small tools
  • Low noise level
  • Degree of protection: IP54
  • Ventilation: Shaft Driven Cooling
  • Balancing: executed according to ISO 1940: balancing grade 2.5
    • Guidance for balance quality grades for rotors in a constant (rigid) state
      • Compressors
      • Computer drives
      • Electric motors and generators (of at least 80 mm shaft height), of maximum rated speeds above 950 r/min
      • Gas turbines and steam turbines
      • Machine-tool drives
      • Textile machines

Since it has a standard 43mm KRESS neck I could easily reuse this spindle in case I would later upgrade to a more capable CNC mill (which often have a mount for such a spindle).

Drawback is that you need to add a 3 phase VFD controller to power this spindle. I did choose the VFD004E21T 1x230V->3x230V 0.4KW from the same shop I ordered the spindle from. For a modest fee, they can make the required cable and set up the VFD controller to work properly with this spindle as well. Which is recommend since setting up a VFD can be tricky if you have no experience with this and can destroy your spindle if you get it wrong.

How to fit a square peg in a round hole…

How to fit a square peg in a round hole...

Since it’s clear you can’t fit a square peg in a round hole I had to do some drastic modifications to the mount and be very careful in not making any mistake. You get only one chance in doing this right.

I hope that the following pictures can give you an idea how I tackled this problem.

First step, taking some measurements how wide and high the new mounting area could be:

80 mm wide.
50 mm high.

Removing the mount:

Disassembling the mount I.
Disassembling the mount II.

Cut away the front half of the mount. There is no way back now:

Cutting away the front part of the old mount.
After a bit of polishing.

Drilling plenty of holes and tapping M4 threads so that a new mounting plate can be attached. The thread tapping tools I bought at Lidl for less than 15 Euro’s:

Drilled 14 holes.
Tapping M4 threads I.
Tapping M4 threads II.

Now we need to make some kind of a mounting plate that can be fitted on what remains of the old mount and can mount the new spindle.

To achieve that, I used a sheet of 4 mm thick aluminium and made 4 smaller sheets out of it. 2 are intended to be mounted to the spindle. The other 2 will be mounted to the old mount. Since the sheets are so thick, the screws for the spindle and the old mount can be recessed. Then it’s a simple mater of screwing both parts securely together.

Those 4 sheets were made when the CNC mill was still in full functioning order of course.

Sloeber inspecting the machining work.
Sloeber clearly not happy he can't eat it.
Some holes have been enlarged here to fit the head of the screws.
The 2 sheets used to mount the spindle to.
Side view of the spindle mount.
Securing the other 2 sheets to the old mount.
Putting the old mount back to the CNC mill.
Attaching the spindle to the mount.
Verifying the Z axis is exactly 90 degrees to X and Y I.
Verifying the Z axis is exactly 90 degrees to X and Y II.

After a few hours of work, the new spindle was in place and it was time for a test drive. What a difference compared to cheap Chines spindle. Run out was well within spec. Even the ER11 collet that was part of this spindle had much less run out than the one provided with the Chinese spindle. No vibrations at all, no matter the speed you choose (up to 24.000 RPM!). But, to my ears, it’s definitely noisy at the higher RPM’s (> 12.000 RPM).

I made a quick test with a simple PCB design and the result was certainly a lot better and predictable now (in the past, I needed sometimes several retries before I got a somewhat satisfactory result).

Milling the traces.
Ready to cut the PCB edges.
Ready for use after tinning.

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