Mechanical Failure

pyronaught · Post by **pyronaught** » Wed Dec 16, 2015 8:56 pm

Well it took a year, but my M2 finally had a mechanical failure during a print. Somehow one of the leveling screws on the build platform had worked its way completely loose and dropped out, progressively tilting the platform out of level until the hot end started colliding with the part, which then cause the print head to lose a lot of steps. By the time I saw it the print head was so disoriented it was banging against the right side where there happens to be no limit switch. I don't know how long that was going on but it can't be good for the motor-- there really should be a limit switch on both sides just like on any other CNC machine. That would have stopped things as soon as they started going bad.

I noticed one of the other platform leveling bolts was continually moving out of position on each print, to the point where I had to adjust it on every print to get it level again. The spring tension seems to have stopped working as a method of keeping the screws from turning. Perhaps over the course of a year of adjusting the level that the adjustments had managed to bring all the screws too far out, reducing the spring compression to the point were it was no longer strong enough to keep the screws from moving.

Hopefully nothing got damaged.

Bratag · Post by **Bratag** » Wed Dec 16, 2015 9:23 pm

pyronaught wrote:Well it took a year, but my M2 finally had a mechanical failure during a print. Somehow one of the leveling screws on the build platform had worked its way completely loose and dropped out, progressively tilting the platform out of level until the hot end started colliding with the part, which then cause the print head to lose a lot of steps. By the time I saw it the print head was so disoriented it was banging against the right side where there happens to be no limit switch. I don't know how long that was going on but it can't be good for the motor-- there really should be a limit switch on both sides just like on any other CNC machine. That would have stopped things as soon as they started going bad.

I noticed one of the other platform leveling bolts was continually moving out of position on each print, to the point where I had to adjust it on every print to get it level again. The spring tension seems to have stopped working as a method of keeping the screws from turning. Perhaps over the course of a year of adjusting the level that the adjustments had managed to bring all the screws too far out, reducing the spring compression to the point were it was no longer strong enough to keep the screws from moving.

Hopefully nothing got damaged.

This kind of thing is why when I level my bed I tighten all my screws as far as they can go and then loosen as needed to level. It means I start all screws at a set point and never over loosen. I do agree a micro switch on both sides would have helped but I cant recall any printer I have seen having one

pyronaught · Post by **pyronaught** » Wed Dec 16, 2015 9:28 pm

Bratag wrote:
This kind of thing is why when I level my bed I tighten all my screws as far as they can go and then loosen as needed to level. It means I start all screws at a set point and never over loosen. I do agree a micro switch on both sides would have helped but I cant recall any printer I have seen having one

That's how I'll be doing it now, or at least taking a closer look at the gap above the spacer block to see how far the spring is extended.

Does the switch on the left side even act as a limit switch or does it only function as a homing switch? I wonder if the control board has an empty slot for adding a limit switch on the right side. I could just add one myself.

Jules · Post by **Jules** » Wed Dec 16, 2015 9:31 pm

Sux.

(Doubt it damaged the motor tho....these machines seem to survive the worst of abuse.)

One of the guys at some point had recommended using loctite on the screws to keep them from working their way out. Once you get everything squared away and cleaned up and re-leveled, you might try that on the screws to keep them from pulling that trick again. (Don't remember which one it was - the one i tried was not the right one - it just made a mess.)

If nothing else, a tiny bit of that teflon thread tape wrapped around the screw will keep it from moving.....damned if i can remember the name of it......plumber's tape? Pipe tape?

ednisley · Post by **ednisley** » Wed Dec 16, 2015 9:34 pm

pyronaught wrote:it can't be good for the motor

Stalling doesn't bother a stepper motor in the least. It sound terrible and looks awful, but there's no mechanical collision going on inside and nothing will break. The driver isn't applying any more current to the windings than usual, so the rotor magnets aren't in any danger.

"Real" CNC machines with extremely powerful motors + mechanical drive trains definitely can cause damage and will have safety cutouts, but piddly little 3D printers survive without such complexications.

It's tough to look cool when that sort of thing happens to your printer during a demo, though...

jsc · Post by **jsc** » Wed Dec 16, 2015 10:04 pm

Also, the homing switch does not act as a limit switch during normal printing. I've had the carriage lose steps against the left stop with a dual setup when trying to print a little too close to the left edge with the right extruder, and it just keeps going.

pyronaught · Post by **pyronaught** » Thu Dec 17, 2015 12:04 am

The leveling screws were definitely extended out way to far. Now that I've reset them to being all the way in it takes much more effort to turn them. They were very easy to adjust prior to the failure. I don't think loc-tight or Teflon tape is required, you just have to keep the springs compressed by not letting the screws drift too far out of their holes. It is kind of amazing that a bunch of random adjustments wound up moving them all in the same direction over time. My leveling procedure must involve always turning them counter clockwise or something.

It's all working again now, no damage.

It's funny (well, not really), at the same time my M2 was melting down, I was in the shop swearing at another CNC machine that had just taken two hours worth of work and cut it in half at the VERY END of a long sequence. I mean, for a brief moment, the 100% completed work was sitting there, then I accidentally bumped the machine as it was heading over to make the final cut, which racked the gantry, which caused it to lose a bunch of steps, which kept it from getting to the end of the work and it made the final cut right in the middle-- instantly wasting two hours of my time and 50 linear feet of film. So then I come inside to escape that aggravation and my M2 is in shambles. Not a good day.

ednisley · Post by **ednisley** » Thu Dec 17, 2015 12:29 am

pyronaught wrote:and it made the final cut right in the middle

Like those Youtube videos of CNC crashes where the cutter gnaws a trench through the vise: that's gotta leave a scorch on your job performance record!

pyronaught · Post by **pyronaught** » Thu Dec 17, 2015 1:09 am

ednisley wrote:
pyronaught wrote:and it made the final cut right in the middle
Like those Youtube videos of CNC crashes where the cutter gnaws a trench through the vise: that's gotta leave a scorch on your job performance record!

Yep, except I'm cutting thin sheets of film at 600 inches per second, so the machine can instantly wreck the job before you even have a chance of hitting the emergency stop button. Material and damaged tool cost is nowhere near what the metal working guys risk though. The main damage is lost time.

JeremyV · Post by **JeremyV** » Tue Jan 05, 2016 7:12 am

I worked at a cnc shop and we had one part that we machined in two pices press fit then sent out to get welded then machined again was some kind of mixer motor mount thing and had to be balanced perfect and everything they were all made of stainless steel. idk how many hours we had in them but I know they sold for like $800 to the manufacturer. not a good day when you forget to put the mill in the right gear and it thinks the spindle is going one direction really slow when in fact its going backwards at 2500rpms. friction welded the endmill to the part. I feel your pain.

Mechanical Failure

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