Not that I can think of at the time being. I wouldn’t lose sleep about it, but you can double-check and see if your motor shaft and lead screw line up ok just in case.
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I just had the same shaft break again after only 2 “ish” months of use. Already put in a request for help, and will check the alignment when I eventually get the new motor. I have noticed some whip on the threaded rod, up and down, but everything checks out as before. The whip or wobble has been going on since the beginning, but it is very slight and I didn’t think much of it. Noticable as the z gantry moves right to left or left to right on the x axis. Will try to get a video when I get the new motor.
A small amount of wobble in the long lead screws is normal. It’s odd that the shafts are breaking because the stepper motors don’t have enough strength to snap the shaft, at least under normal conditions. You can drive the X and Y axis to their end where the lead screws can’t turn any more and they don’t break the shafts. Do they snap in the same spot? Any specific relation to the position of the coupler or coupler screws? If the stepper shaft, coupler and lead screw aren’t all in alignment then maybe the stepper shaft is flexing slightly. This could cause work hardening of a portion of the shaft which would make it weaker/brittle. Just some thoughts.
Yes, it broke in the same spot, right at the base where the shaft is flattened from round inside the motor.
As far as the couplers and alignment, I am not sure - I installed everything as indicated in the directions. I can look when I get the next motor to see if the shaft and screw are aligned.
I was told there are new couplers, but not sure if I actually have the new coupler, or if there are newer ones than the couplers on the website.
The only difference this time from the last time the shaft broke (other than it took 6 1/2 months as compared to 2 months this time) is that I have been using the laser quite a bit, so there are more short movements in the x-axis direction than what would normally happen in a CNC job. Those movements can be more intense due to what is being lasered.
Still, I think it is more of an alignment problem, but there is not too much that can be misaligned as everything pretty much self-aligns during construction. Unless even the slightest misalignment is the culprit.
Interesting that there have been several people now with the same issue - even though it is a small percentage of the total.
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I have just encountered the X-Axis Stepper motor issue. It took me a little while to figure out the shaft had broken since the lead screw was still turning when the X-Axis was commanded to move. Even though the motor shaft had snapped, the friction and/or shape of the break was enough to allow the lead screw to still turn. After I discovered the problem, I contacted the guys at Sienci Labs and they were able to get me a new motor within a couple days. (Thanks to the Sienci Labs staff for excellent customer service) While I was waiting for the motor I tried to determine the cause and to the best of my knowledge I believe the issue is with the solid couplings. (As a Side note, I’ve been designing and building large multi ton machine tools for the past 30 years). In a typical servo connection you would pilot fit the motor to the screw with a housing and place a flexible torsionally rigid servo coupling between the two. In the case of the Sienci mill the motor is located off a non machine surface with non precision spacers. There is no way to true the shafts (using a dial indicator) to one another right out of the box. Which mean the shafts may not be parallel or angularly aligned within the tolerance of the bearings in the motor and the lead screw. Since the bearing are placed so close together, they can over constrain the coupling. This forces the weakest link, the shaft to flex and over time the shaft will weaken at the stress point created by the necking down of the shaft where it looks like your motor shaft snapped as well. Going forward, I purchased flexible beam couplings and replaced the solid coupling on all the axes. The results we immediately noticeable. All the axes are now running smoother and whisper quiet. Time will tell if this issue is solved, but I’m pretty confident that I won’t break another motor shaft.
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@Gassman69 Jason: Can you provide a link to the couplings that you bought?
I have no expertise in this area at all, so excuse the ignorant question. If the coupler can flex, why is the accuracy of the machine not affected?
This is the description of the couplings I purchased. There are many like them on Amazon. Just make sure you get the right bore sizes if you choose a different brand.
Rannb CNC MotorJaw Shaft Coupler Flexible Shaft Couplings 6.35mm/0.25" to 8mm/0.31" - Pack of 2. Approximately $9
To your question and it’s not ignorant. The couplings are designed to flex angularly but remain tortionally rigid so you don’t have a lose of motion when rotating force is turned into linear force. If you type in beam coupling or servo coupling in Google you’ll see many different styles of flexible couplings meant for precision axes. This solution is still not perfect. For that you would have to invest a lot more money, but it should lessen the fatigue the motors are seeing and not effect the precision of the machine for what most of us are doing with our CNC routers.
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@Gassman69 Tks much, Jason.
Just an FYI, on Amazon Canada, they are $47.42 for two, for exactly the same ones. They are not currently available on Amazon.com.
For a time sienci shipped machines with Lovejoy couplings. They didn’t last too long, though.
Found these on Amazon Ca
uxcell 6.35mm to 8mm Aluminum Alloy Shaft Coupling Flexible Coupler Motor Connector Joint L25xD19 Silver,2pcs.
More expensive than what I bought, but still affordable. Lead time is a bit long.
That’s weird. Amazon says They are available and I can have them by Tuesday. This is the direct link
@Gassman69 I looked at the page more closely. The reason that I get the “unavailable” page is that my shipping address is in Canada. When I change my address to the US shipping address that I have, I can order them. Of course, given Covid restrictions, I cannot drive to my US address to pick them up, but that’s another issue. 
Thanks for educating me on flexible connectors.
@Gassman69 Thanks for the information on why this had happened. I have had two shafts break on me, both in the same spot - and same thing - the lead screw still turned because it was an angled break, just not correctly or consistently. It is apparently not a widespread issue as I have seen other posts about this from Sienci being “minor”. Not sure what makes a few break and others not break, unless it has something to do with the lead screw not being true and moving “wildly” through the bearing.
Sorry it happened to you, but glad you could figure out what to get by understanding the physics behind the stress on the shaft. I will probably be ordering the couplers in your link when I get back up and running.