She is down again but I'm guessing why

[LEADNAV]

Anyone wanna take a guess?

Have not been honestly running it much this past month and she started failing consistently after one successful print. Now we are on print number 4 with three different chambers failing shortly after the preheat and initial printing.

It is “sink holing” again around the perimeter of the chambers and under dosing from the Left to Right pass of the doser.

It is doing this with a +5 doser offset.

This would be totally confusing to me…if I literally did not just go through this a few months ago with the same exact thing happening.

Last time I saw this, it was totally confusing as I had thought all three chambers went bad at once from all the leaking powder…

Anyone wanna take bets that when I pull the entire back off the printer… that we are going to see a loose coupler on the Recoater motor?

This was the culprit last time. That simple coupler gear broke loose on the motor shaft making the Recoater roller cause all these same things.

Bout to let it cool down before I rip it apart to confirm.

If this replacement Recoater motor and coupler are broken loose again…my next question is why?

I probably have had only a few dozen prints done since the last time this happened and it was replaced…

Posting this because this took a solid month to troubleshoot the first time it happened with a Formlabs rep here on scene checking and troubleshooting all the chambers before figuring out a simple loose coupler on the doser motor caused all these issues.

The actual fist thing Formlabs support suggested when I sent the reports were to tear the back off the printer and check the doser motor coupler… so I assume this happens a lot and wanted to check with other Fuse users out there.

For those that have not experienced this, hopefully this saves you some time if you see these failures and under dosing/sink holes.

[CARobertM]

I really appreciate you sharing this. The more we talk to each other about these issue, the more we can help each other and depend on FL less.

[LEADNAV]

I have definitely solved the majority of our issues via my own troubleshooting and/or other customers on this forum… so no problem

[jmasterson]

What a frustrating issue. This seems to be the way Fuse repairs go in my experience; problem occurs, you fix it, run a couple successful prints, and then it’s back again.

Which coupler is breaking on you?

[LEADNAV]

Confirmed

The “recoater” motor coupler broke free again on the new replacement motor after 2-3 dozen prints.

Jmasterson : Sorry for the confusion this is the Recoater motor coupler. breaks free and wiggles which I guess is enough to mess with the roller and cause all these issues.

Very tough to diagnose without ripping the back off the printer and pulling the motor and if you did not know any better…you’d be like me thinking it was your chambers leaking. Inside the printer the roller feels and looks like it’s functioning smoothly. No indication when looking at all that inside the printer. However, that slight slop in that coupler I guess is enough…

and here is the Formlabs manual to access it
https://drive.google.com/file/d/1RaElXug2lNuCXqiaxGDDz0FQmfs_3QJo/view

[LEADNAV]

Here is a better video of the motor and coupler and how something this small can cause all these problems

VIDEO
https://youtube.com/shorts/LkiAVgiGzaI

[jmasterson]

What a poorly designed coupler. It looks like it’s pivoting around that pin, is that correct? I feel like there should be an additional pin in the perpendicular direction if the shaft fit tolerances can’t be controlled well enough.

I’d like to see what the mating end under that coupler looks like. If it wasn’t rocking before, I’d think some material must have worn away because I don’t see any other means to prevent movement in that direction.

Hard to say why that would be failing repeatedly but, in my mind, it seems unlikely to be a manufacturing defect on the motor side since you’ve had 2 fail on you. At first, I was thinking your recoater roller could be getting bound up on that front rail, but I think that would fail in a different way. Maybe the printer-side mating end is not aligned and over time causing that motor shaft to wear down and loosen up the coupler?

[CARobertM]

a roll pin for a coupling connection where 1/32" of slop bricks the machine?

[LEADNAV]

Well a few months ago when I was trying to figure all this out the first time… I pointed out that the actual recoater roller shaft was slight bent. I literally put my CNC run out gauge on it and spun it to show them. They said that’s totally acceptable…even though I can literally hear the full rotation of the recoater on one side. If I can find my video of that I will post it. Don’t think this would wear that coupler throughout that assembly but at the same time that coupler slop is obviously enough to cause all these issues on the other end so…

And correct… the coupler has total slop on one axis opposite that pin but also on the pin axis slightly. You can look down it and see the weak design in the shaft to coupler. I still have the old motor and obviously this one I can dissect whenever the replacement shows

[CARobertM]

worth pouring some epoxy in there to stop the wobble? Or just make a shim?
I wonder how many of these motor replacement they have to send before it cost more than the cost savings of a roller pin over other options.

[LEADNAV]

Thought about it but my concern is making sure it’s straight and that maybe their design was to add a fail point in the pin versus anything past that if something jams etc… a shear pin.

However, I can’t imagine that coupler pin would easily break before anything past that point in the recoater so not sure on the design choice.

I imagine they get the motors stock and the best thing they came up with was just drilling a hole through the motor shaft and putting a pin in their coupler…

I could easily design and machine out something better in a coupler and attachment method but again not sure if that is an intentional fail point in the design in case things jam.

[leonhart88]

Is this just a coupler with a set screw in it? Does the set screw have picture thread locker on it? If not I would at least use some blue thread locker when you re assemble it.

I’ve had instances of couplers coming loose over time because of vibrations etc. or they weren’t torqued appropriately. Thread locker always helps!

[LEADNAV]

Well… if it was a set screw that would make too much sense and I wouldn’t be complaining about it…

No… this is a press pin and not adjustable. The first thing Formlabs does when this comes loose…is send you another entire motor. Pretty sure if it was as simple as fighting a set screw and adding lock tight this would be obvious…

It’s literally just a through press fit pin to stop the coupler from spinning and offers no tensioning on the shaft.

And yes… I tried to press it out but assuming all they do it slap some sort of glue in there that obviously breaks free on the sloppy coupler/shaft mating surfaces.

And again… this came loose a second time on a brand new motor they sent within 2-3 dozen print jobs

[leonhart88]

Ah I see. I should have watched your video, it’s obvious now

Pretty wild.

You could try drilling through the coupler and shaft and pressing in your own pin…or drilling through the coupler and tapping it for a set screw.

But neither of those would answer your question on whether these are designed to shear at a specific load.

They don’t really look like standard shear pins though…hard to tell from the picture but it just looks like a roll pin or a coiled spring pin.

[LEADNAV]

Since I have two motors now and waiting on Formlabs for a third… that is what I was thinking. I was planning to drill one of these pins out, remove the coupler and see if it is truly just a round shaft with a pin through it. If so… I may design and CNC machine a new coupler with tight tolerances to the shaft with an actual set screw.

It seems like they found a stock motor and a stock coupler and slapped the two together with glue… with the coupler they found being super sloppy on the shaft…when that glue wears out it obviously just flops around.

[leonhart88]

The only potentially non trivial thing with making your own coupler is that square mating end to the other side. Not sure if that needs very tight tolerances or if it needs to be broached.

You might be able to find some OTS couplers that could work - good luck!

[CARobertM]

I don’t think it’s a shear pin. That’s a stepper motor. They don’t have enough torque

[SMute]

What exactly is the failure mode here? The coupler begins to wobble a bit and that causes the recoater to fail advancing powder fully across the print bed? I’m struggling to understand how this can be. (I’m not denying its happening, just want to understand).

[LEADNAV]

It’s definetly happening…I can promise you that. Not sure exactly the mechanics of it as the coupler turns the chain gear to the Recoater roller but whenever that coupler breaks loose from the glue they have keeping it stiff…all goes to hell.

Immediately you will get sink holes forming around the chamber walls, under dosing… only thing I can imagine is its throwing the roller askew enough to vibrate or push powder through the thermal break of chamber on the prime/pre print.

This is why…this was the most difficult troubleshooting I’ve ever had to deal with on this system. If it was not for having three build chambers that all did the same thing all at once… I would think it was a bad chamber.

You start seeing this immediately (I had 5 failures in a row on three chambers)

Then you swap that motor with a stiff coupler and you’re instantly back in business. Just swapped the motor and here is my current print

Formlabs is aware of this as they will instantly ask you to check that motor coupler. On this trouble support ticket…they did not ask anything else but to check that motor. They overnighted a new motor and said they made some improvements to it as this is the second time this year we had this loose coupler issue on two different motors…but looking at this new motor I see no difference in the coupler. So maybe they “improved the type of glue” that is holding the coupler stiff..

[SMute]

That’s very interesting. I wonder if you may be on to something with the vibration theory. Does it make any unusual sounds when its in the process of failing?