Running a job

The basic workflow for running a job is covered pretty well in Carbide3D's docs/tutorials, the intent of this section is to provide background information and various tips about the different steps.

The ordering of these steps can vary based on personal preference and software being used. For example, I like to have the machine turned off while I change the cutter, but many find it more convenient to have it turned on to be able to jog the router automatically to the front.

Installing the cutter

A few things to watch out for when installing a tool in the collet :

  • make sure the collet matches the endmill diameter. This may sound silly, but once you start having a collection of various imperial and metric tools and collets, inadvertently using a 6mm endmill in a 1/4" (6.35mm) collet is a (remote) possibility, and not paying attention to this will result in serious trouble during the cut.

  • the collet and collet taper must be clean of any debris/dust. Those might introduce runout.

  • stickout: it should be

    • as low as possible to minimize tool deflection

    • but still be compatible with the max cutting depth for this job

    • short enough that the shank is engaged over the full height of the collet

    • but not pushed so far back that the flutes are inside the collet

  • runout: if it matters for the job at hand (high-precision and/or micro-machining), now is the time to check it and tune it.

  • the saying goes that the collet should be "monkey tight, but not gorilla tight". It should not be a baby monkey either, or the endmill might slip in the collet.

Moving manually

Whenever the machine is turned off, it is possible to move it manually, with just one constraint: do it slowly. When the machine is turned off and moved manually, the stepper motors behave as alternators, they generate current, enough current in fact to back-power the electronics (you might see the LED on the controller board come to life...). Moving slowly ensures that the generated current stays low enough to not damage the stepper electronics.

Homing

That "clonk" sound when the machine is turned on is just the stepper motors locking in place, nothing to be concerned about.

The reason for homing was introduced in the CNC workflow section: the only way the Shapeoko can tell for sure where it is, is when it contacts the three limit switches. Without homing, each time the machine is power cycled it would be unable to go back to any specific coordinates with precision.

You could argue that homing is useless since you are going to manually jog to the Zero point and set it to be the reference anyway. For a job that can be done in a single run / with a single tool, that could work. But the power of homing is that it will allow returning with great precision to Zero point defined last (which happens to be stored in the non-volatile memory of the controller by the GRBL software).

If you turn off the machine to change tools, this will be needed. But even if you don't, you may still want to home between runs: if for some reason the steppers or belts skipped a few steps during the previous run, returning to Zero without homing first may bring the machine to a subtly different point, a few steps away.

The notable exception is 2-sided jobs: depending on the precision of your limit switches, you may find that it is better to NOT re-home between the two sides to have minimal offset error.

Setting & checking RPM

Unless you have installed a spindle or a PID controller (see HW upgrades), you need to adjust RPM manually using the knob on the trim router. The Anatomy of a Shapeoko section has a reminder about the mapping between knob values and RPMs, but the actual RPM can be slightly different than advertised, and on my router the knob did not even have a reference point on the casing, so I added a visual cue with a marker to at least have a repeatable setting:

But it's not easy to interpolate between knob settings to use intermediate RPM values, so I found it much easier to buy a laser tachometer (about 20$), turn the router on, and adjust the knob to get the desired value:

All it takes is a small patch of white/reflective tape on the collet nut:

Zeroing (manually)

After jogging to the vertical of the intended X/Y zero point on the stock surface, lower Z gradually then use fine steps to touch off on e.g. a piece of paper placed between the tool and the stock, stopping as soon as the paper cannot be moved freely under the tool anymore, and then tell the G-code sender to reset X0/Y0/Z0. Yes, it does mean that you will zero a tiny bit above the real stock surface, but the average thickness of a piece of paper is around 0.004" / 0.1mm, and chances are that you are already compressing the paper since it cannot move anymore, so you will actually be very, very close to the stock surface.

Miscellaneous tips:

  • double-check your Z jog step before doing the final steps to touch off. It is very easy to hit the "down" arrow one time too many by mistake, and if the step is still say 0.1", this might bury your tool into the stock, or more likely break it if it is a small endmill.

  • touching off with a very pointy V-bit can be tricky, it's easy to go too far down without noticing, so you should use even finer jog steps and/or extra caution.

  • for jobs involving multiple tools, consider the fact that you will have to re-zero after tool change: it is more convenient to zero on a part of the surface that will...still be there after the first tool has done its job.

The main limitation of manual zeroing is that you need to eyeball the X/Y location, which for some jobs is not precise enough. And of course, the manual careful jogging to touch off is somewhat time consuming.

Zeroing (with a Probe)

Enter the touch probe, to automate the zeroing process. The Shapeoko controller has a dedicated "Probe" input, that works like the other limit switches. It detects whether there is continuity between the two pins:

For zeroing Z only, a probe can boil down to a piece of (conductive) metal sheet (of known thickness), for zeroing X, Y and Z, it needs to be 3-dimensional but the principle is the same. X/Y/Z probes typically have a recessed face on the bottom side, so that they can be placed on a corner of the stock top surface:

Probes come in two types: passive and active. Passive is just what was described above, i.e. a glorified metal cube. Active probes have internal electronics to support features such as an embedded test LED that lights up when contact is made, which is useful for checking that the probe chain is working fine before initiating the probing cycle

The probing goes like this:

  • the probing cycle starts with the tool raised above the probe. It could be anywhere above, but there is usually a target area above which to (coarsely) position the tool, to facilitate the rest of the sequence.

  • the tool is lowered along Z, until it makes contact. When it does, the software can just read the current Z and subtract the thickness of the probe (PZ in the sketch above) to get Z0. This Z touch off sequence can be repeated to average out values and improve precision

  • if the probing cycle is configured to also probe X and Y, it retracts the tool and proceeds to move away from probe, lowers the tool and then comes back towards it until it detects contact, then repeats that operation for the other side. It can then determine X0 and Y0 by reading the X or Y values at contact, add PX or PY, and add half the (preconfigured) diameter D of the tool itself.

If the stock shape does not have a straigtht corner, the probe can also sit on top of the stock surface and be used for Z probing only (the software will know that when Z probing only is selected, it should compensate for the total height of the probe, not just the PZ step).

One problem remains: the X0/Y0 computations depend on (half the) diameter of the tool, so the geometry of the tool must have been configured beforehand, and this manual operation is error prone. Also, the actual precise diameter of the tool is often not quite the advertised value, so this will introduce a slight error in X0/Y0, which will result in a shift between runs with different tools. One more probing trick can be useful: if the probe has a hole, one can lower the tool into the hole and then probe its sides: probe left and memorize current X value, then probe right and memory current X value: the average (middle) of these two values is at the X center of the hole. Repeating this operation by probing on the front/back side of the hole will locate the Y center of the hole. Since the location of the center of the hole is at a known distance from the inner corner of the probe, this gives X0 and Y0. Z-probing can then be done normally elsewhere on the top surface. The beauty of this method is that it is independent of the tool diameter !

@neilferreri on the forum came up with a wonderful probing macro for CNCjs, that does just this, go check it out.

Running the job

This is straightforward, nothing special to be said here so I'll just share my own habits:

  • if your G-code sender allows, raise the tool after zeroing. It is normally not necessary, but depending on your CAM post-processor's settings, the G-code may or may not contain an opening statement to do it, so this will give you a (little bit) of time to react if something unexpected happens. It is also required anyway in case your dust shoe model cannot be installed if the tool is lowered (and since zeroing with the dust shoe in place is not fun)

  • double-check that the dust shoe is lowered at stock surface level and won't crash into anything during the job.

  • turn on the dust collection (and air jet/lubricant mister if applicable)

  • put on your safety goggles and/or close the enclosure window.

  • turn on the router.

  • hit start...with your hand/mouse over the pause/stop button.

At least the first time I run a new project, I like to watch & listen throughout the cut, looking for hints of incorrect cutting parameters (chatter, bad looking chips), debris build-up, or anything I might have done wrong in the CAD/CAM, or could optimize.

Tool change

  • some people like to bring the router to the front using a predefined position in the G-code sender, to have easier access.

  • I guess most people do not turn off the machine, but I do it for a variety of reasons:

    • paranoia: I don't like to have my hands in the work area while the machine is powered. Too much software and hardware to trust.

    • re-zeroing will be required anyway after the tool change: I might as well re-home too.

    • it feels a bit weird to me to tighten the collet nut with the steppers locked.

  • safety: if you are using a router or spindle that is externally controlled, I would recommend actually cutting its power source (wherever this is done in the chain). Do you really trust your PID/VFD that much? If you are manually turning the router on and off, this is less of a risk but I choose to be extra cautious (paranoid?), and also kill the router power source (in my case, flipping a switch on a control panel)

  • remove the tool and collet and make sure the collet taper is free from any debris/dust that could create runout for the next tool

If the collet is stuck in the taper, you may try moving the endmill gently left and right in the collet to get it out.

  • install new tool, monkey-tight nut, etc...

  • re-zero Z

    • yes, this is obvious, but if you are anything like me, one day you will be in a rush and forget to do it.

    • be careful of the "return to Z0 + xxx mm" command. It is very convenient, until one day the second tool sticks out by more than xxx mm compared to the previous one...