Belt Tensioners "Frozen"  

RE: Belt Tensioners "Frozen"

After peeling away the pulley off the tensioner with a heat gun, it LOOKS like the nut ended up binding, then stripping the recess for it in the pulley part. The screw and the nut barely turn on their own, and when I peeled away the plastic, the nut was rotated about 45 deg along the screw axis  from where it was originally seated.

So, needs better quality hardware and possible reinforcement in the pulley around that nut.

Or am I wrong?

RE: Belt Tensioners "Frozen"

You’re not wrong - this is a known issue with the Core One. The screw and nut can seize up due to galling. The build instructions have since been updated to recommend adding a bit of lubrication to help prevent it, but that doesn’t help you after the fact.

The general consensus seems to be to print new pulleys with threaded inserts instead: https://www.printables.com/model/1360563-core-one-belt-tensioner-pulley-to-take-a-threaded

For anyone else reading this: if you’re re-tuning your belts and still have the original parts intact, take a moment to remove the screw completely, lubricate it, and reinstall before something breaks.

RE: Belt Tensioners "Frozen"

That solution makes sense, though I would expect the galling to occur between different materials. My Core ONE was one of the first delivered, so there was no assembly, and these parts were clearly never lubricated. Once I get it up and running again, I will defo try the threaded insert route along with some Moly-Di lubricant to prevent that galling.

RE: Belt Tensioners "Frozen"

Galling under heavier loads is a common problem with the thin nut. Not enough threads to spread the load in my opinion. I have one of the first Core Ones that came assembled. Mine did not have a problem, but my past experiences with the thin nuts led me to use the thread insert mod. More threads and the brass does not tend to gaul. I used Prusament PCCF.
The screw in insert looks a lot easier than the heat I used. It wasn't available when I did it.
Getting the heat based insert to full depth may be a problem if your heating tool tip is not long enough with this mod from my experience.

RE: Belt Tensioners "Frozen"

PCCF ain't cheap (cheaper than PACF, though), but can I assume it has the same requirements for exhaust/filtering because of the CF?

RE:

Posted by: @cyrusjk

PCCF ain't cheap (cheaper than PACF, though), but can I assume it has the same requirements for exhaust/filtering because of the CF?

Prusa PC-CF is constantly out of stock. You could probably get away with using ASA. Would stay away from Nylon unless you anneal it before using the part. Best would be to ask support what they would recommend (if any) as a substitute. 

RE: Belt Tensioners "Frozen"

Hi all,

I’ve been struggling to maintain alignment since I built the printer and have had to adjust belt tension / xy alignment every 7-8 prints.  Now, I’m I seem to have been struck by this very issue on my left (top belt) tensioner.  The tensioner was frozen, I applied a little pressure to free it, and now nothing.  It feels slightly chunky when I turn the tensioner.  It’s very annoying and slightly disappointing.  That said, couple of questions:

1. Does the replacement pulley also come with the square nut and the the m3 - 30 screw? Or do I need to source those separately?  It is unclear from the item description.

2. Is it common to have to re-tension the belt that often?  I believe I read somewhere that adjusting belt tension should only need to be done every 200 hours or so.

3. Does replacement of the pulley require me to completely rebuild the core XY top end or is there a trick to replacing the pulley in line without removing the belts? I am thinking I might be able to assemble pulley around the belt and the pull it into the tensioner using the tensioner screw.  That said, it might be a moot point because I am not sure how I get the old pulley off, but thought some of you might have tips on how to do with out completely re-rigging the whole top end of the printer.

thanks in advance for your thoughts.

RE: Belt Tensioners "Frozen"

To answer question 3, I have removed both tensioners and pulleys with minimal disassembly. It's all tedious, but it has worked so far. I removed the top and side plexi panels, then unscrewed the right pulley wheel, freeing up the pulley from the belt, and then removed the three tensioner screws and the whole right tensioner and pulley mount. Then I unscrewed the left tensioner, and then the door switch. After that I again unscrewed the pulley wheel freeing up that belt as well.

Per question 1, my replacement parts are yet to arrive, but I did order new square M3 nuts (5.1mm x 2mm) as well as inserts. I am not the notification for when the PCCF is back in stock, so hopefully I'll get to make those pulleys even better.

I do not think I'll reinstall the door switch. I know it had to be there for safety, but I already set it to disabled, and it makes dis/assembly in that tight space a pain in the ass.

For question 2, this was my first time attempting to adjust the tension since I got the unit with the first round of deliveries. I was hoping to reduce the banging at the start of the print and see if the VFA fixes worked, but there was no other compelling reason for the exercise.

RE: Belt Tensioners "Frozen"

Posted by: @cyrusjk

...

I do not think I'll reinstall the door switch. I know it had to be there for safety, but I already set it to disabled, and it makes dis/assembly in that tight space a pain in the ass.

...

Just a note of caution, do not unplug the door switch from the Buddy board.  The presence of this switch is the signal to the board that it is installed in a Core One printer.  The printer will not function correctly without it present.  I know of at least one other poster who removed the switch from the gantry but left it attached and coiled in the back enclosure.

Regards,

Steve

RE: Belt Tensioners "Frozen"

Thanks!