Belt Tensioner is NOT repair friendly
After a week of happy printing I was checking the tension on my belts and the dreaded nut was spinning, munching on the PCCF belt tensioner.
After several hours of cursing, disassembling the printer, and eventually bolt cutters, I managed to get the old part out. The nut was askew on the bolt, not square, and it was impossible to turn even with a wrench and vice grips. The nut was effectively welded to the bolt. My guess is the belt tension causes a twisting moment on the nut and it "slipped" a thread. The nut cross-threaded itself!
I've printed a replacement part which uses a heatset insert instead of the M3NS nut. Fingers crossed this is more resitant to slipping than the M3NS nut. But the whole belt tensioner is difficult to repair. You need to disassemble the printer just to get to the tensioner and if the nut is cross-threaded you have to destroy the PCCF parts to get it out.
https://www.printables.com/model/1360563-core-one-belt-tensioner-pulley-to-take-a-threaded/
RE: Belt Tensioner is NOT repair friendly
I'm thinking @Chris_Hill's replacement set will be one of the first things to print after this and other similar feedback here. I have PETG-CF on the shelf, so hoping that will do the job. Even if just as a stopgap.
RE: Belt Tensioner is NOT repair friendly
I'm thinking @Chris_Hill's replacement set will be one of the first things to print after this and other similar feedback here. I have PETG-CF on the shelf, so hoping that will do the job. Even if just as a stopgap.
The insert is 5.7mm long so that's a lot more threads in contact with the bolt. It should resist twisting far better than the M3NS nut. I think it's a must-have upgrade.
I also put some grease on the tensioner, and some grease on the bolt and insert, so everything slides effortlessly now. I am not pulling this apart again!
RE: Belt Tensioner is NOT repair friendly
galling
noun: a type of wear caused by friction between metal surfaces, often leading to parts sticking or seizing.
Example: "Galling can lead to a nut and bolt binding under high pressure."
adjective: extremely irritating or frustrating, vexing.
Example: "It was galling to tear down half the machine just to reach that one seized nut and bolt."
— From some exasperated mechanic’s dictionary, probably.
I'll get my coat.
RE: Belt Tensioner is NOT repair friendly
This is my reason for holding of any new firmware or adjustments, in particular belts, before replacing the pulley with Chris design, I want to make the replacement before it breaks and the assembly freeze up, I am just waiting for brass replacement bolts to arrive. I a thinking brass bolts in brass threads will not freeze up easily and make a better combo for adjustments.
/Anders
RE: Belt Tensioner is NOT repair friendly
I'm no expert, but I understand that galling is less likely when the two materials are different. Brass is a little self-lubricating, so brass-on-brass is probably ok in this respect, but I suspect a stainless bolt into a brass insert is better. Happy to hear from anyone who knows for sure though.
RE: Belt Tensioner is NOT repair friendly
When you use a fastener of a different material than the base (metals here) you use anti-seize. Metal fasteners should never be assembled dry if you want to disassemble them at any point. Many folks assume that threads should be clean and dry, this is 100% wrong. Folks also assume that lubricating threads will cause a fastener to loosen over time. This is also wrong. You put anti-seize on the lug nuts of your car (if you want to remove them) and torque to spec. Dunno about anyone else, but mine hold over time and I check.
I've learned quite a lot doing repair on large manufacturing tooling. We did a lot of interference fit shafts in the 6-12" dia range, and the ones that galled during removal always had been assembled dry. Galling occurs as friction between the surfaces causes the high spots to smear off and roll like a snowball, gaining size, and wedging itself further between the surfaces. When you pull a shaft from a bore you can see the tracks left by the snowball, as well as the snowball itself sometimes. Similar in threads.
Short answer is lube all threads. Also brass on brass isn't going to help anything.
RE: Belt Tensioner is NOT repair friendly
When you use a fastener of a different material than the base (metals here) you use anti-seize. Metal fasteners should never be assembled dry if you want to disassemble them at any point. Many folks assume that threads should be clean and dry, this is 100% wrong. Folks also assume that lubricating threads will cause a fastener to loosen over time. This is also wrong. You put anti-seize on the lug nuts of your car (if you want to remove them) and torque to spec. Dunno about anyone else, but mine hold over time and I check.
I've learned quite a lot doing repair on large manufacturing tooling. We did a lot of interference fit shafts in the 6-12" dia range, and the ones that galled during removal always had been assembled dry. Galling occurs as friction between the surfaces causes the high spots to smear off and roll like a snowball, gaining size, and wedging itself further between the surfaces. When you pull a shaft from a bore you can see the tracks left by the snowball, as well as the snowball itself sometimes. Similar in threads.
Short answer is lube all threads. Also brass on brass isn't going to help anything.
Any advice which lube to typically use for this? The Prusa supplied lube or is typical sewing machine oil also fine (or too thin?).
RE: Belt Tensioner is NOT repair friendly
Best is as said anti-seize. Just good stuff to have around. Loctite-504469-Silver-Grade-Anti-Seize is but one example. There are more liquid ones in jars with brushes that will also work fine. Avoid "lubricants" like wd-40 which is a water displacement and not meant to hold a film under pressure. Something is better than nothing, but you want something with a bit of tack. Prusa lube would be ok, but not great for that purpose.
RE: Belt Tensioner is NOT repair friendly
My in
Any advice which lube to typically use for this? The Prusa supplied lube or is typical sewing machine oil also fine (or too thin?).
My intention was to use an anti-seize grease during assembly to give the stock component a fighting chance
RE: Belt Tensioner is NOT repair friendly
Would a ceramic anti-seize paste be a good option? I was thinking maybe it's a good idea it's not metal based...
I've recently built a C1 but managed to destroy one of the belt tensioners in the belt tension adjustment step. So I'm trying to figure out how to try to prevent this when I get the replacement tensioner.
RE: Belt Tensioner is NOT repair friendly
From my experience stainless threads are sharp and easily cut into softer materials causing all kinds of problems. This is probably more of a personal preference that a scientific argument, I figure while fixing this thing I will try to do this once and get rid of the stainless bolt I simply don’t want in there. There is probably no reason for anyone to follow my path until there is a track record of these stainless bolts sticking in brass heat inserts, which is unlikely.
/Anders
RE: Belt Tensioner is NOT repair friendly
galling
noun: a type of wear caused by friction between metal surfaces, often leading to parts sticking or seizing.
Example: "Galling can lead to a nut and bolt binding under high pressure."
adjective: extremely irritating or frustrating, vexing.
Example: "It was galling to tear down half the machine just to reach that one seized nut and bolt."
— From some exasperated mechanic’s dictionary, probably.
I'll get my coat.
I regret not doing more machining courses at school. I studied the theory of engineering - which has been good for my career - but the machining side is still a mystery to me after all these decades.
These days I watch youtubers like Marius Hornberger and This Old Tony hoping to learn their skills via osmosis. Galling is the appropriate word both for the belt tensioner problem and my lack of knowledge!