Today while I was machining some wood on my shapeoko 3 I experienced a few crashes. I’m working on a program that has 12 pockets to cut. At first everything was going fine but when the machine finished the 2nd or 3rd pocket it failed to fully retract to the safe height before moving to the next pocket. The machine plowed straight through 3/4 of oak. I stopped the machine and initialized everything. Adjusted the heights in my program to make sure they were more than enough to clear the material and tensioned the z belt to reduce a risk of skipping teeth on the belt. Nothing worked. I ran the program again and it crashed again during the transition from one pocket to the next.
When the machine is off and I manipulate the z by hand it seems to move pretty smooth as long as I go slow. However when I move the z up and down rapidly the travel gets really clunky and almost slams through it’s travel. I’m wondering if the motor can’t handle the speed and is somehow malfunctioning.
If the cut goes too deep, it’s typically (but not always…) one of these reasons:
the Z axis retracts high enough that it crashes at the top, and looses steps while doing so. It is unlikely in your case as the first pockets are fine, but I’m mentioning this just in case, especially since you said you increased retract height.
the endmill slips inside the collet, gets pulled out during a retract move, so you end up with extra stickout length and while plunging back down the tip of the cutter will be lower than expected. In your case, going through 3/4" of stock does not seem to match that possibility.
and then there is the Z axis pulley slipping on the motor shaft, because of a loose/improperly positioned set screw. It is possible that the pulley slips only in one direction (when Z moves up in your case). Can you tell if the Z retracts to the expected height when transitioning from the 2nd to the 3rd pocket ? If this is a likely possibility, you will want to check that one of the set screw is positioned against the motor shaft’s flat, and that both are tight.
During that second crash, was it also between the 2nd and 3d pocket ?
Also, it’s never a bad idea to double-check the G-code file itself, can you post it here for a quick look? (or use a G-code viewer to check it)
The problem seems to be that the machine is not fully retracting to the safe height. The machine starts retracting but the z carriage seems to jam slightly before reaching the safe height. Then the machine rapids to the next pocket while still below the top of the stock and begins plunging.
I don’t think the problem is in the code because I ran another program for finishing the pockets and the same thing happened. It did a few of them fine and then at random when transitioning from one pocket to the next the machine fails to retract all the way.
The problem seems to be in the z carriage somewhere. The z movement up and a down is very jittery when I move the machine while it’s powered off.
I would check the set screw first. If visual inspection is not showing anything suspicious, you should still draw a line across the pulley & shaft with a marker, like so:
so that at least next time the problem happens, you will be able to tell whether the pulley has slipped with respect to the motor shaft.
If it’s jittery when moved rapidly, but smooth when moved slowly, then this is normal: when you move it rapidly by hand, enough current is generated by the motor back to the controller to momentarily power it, at which point it (very momentarily) holds the motor, and it feels like a bump.
If you have a mean to upload a quick video of the carriage movement, we may be able to get better clues as to what is going on. But first, check those set screws.
That’s a link to a video I just put on YouTube because I couldn’t post it in this thread. Hope you can view it. It shows how clunky the Z is. When the crashes occurred it’s as if the motor got stuck part of the way through it’s retract and then plows into the stuck during the next rapid because the actual Z height and the machines perceived Z height are not the same.
does it do the same jittery sound/movement when jogged from Carbide Motion?
If you unplug the Z motor connector from the controller and do that same test, does it do the same?
Have you checked those set screws on the pulley ? It’s hard to tell from the video whether there is any slippage when moving upwards
In you have not done so already, you should probably contact support@carbide3d.com in parallel to this discussion, it might be more convenient if they have a phone or video chat with you to address this.
Maybe @WillAdams will have seen this before and could comment.
First, please don’t move the machine by hand with force thus, the stepper motors function as generators and it’s possible to generate sufficient current to damage the stepper drivers.
Second, this is usually caused by a missing or misplaced shim in the Z-axis — see if you can identify where things are hanging up — it might be a reversed pulley — get a photo of the mechanism to us at support@carbide3d.com and we’ll sort this out with you.
