Belt tension numbers not even close to accurate?  

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Viced Rhino
(@viced-rhino)
Active Member

Hello,

I recently had my x-axis disassembled for some maintenance.  On putting it back together, the belt tension number was measured to be around 180 - according to all the documentation, this would basically amount to the belt being way too tight, but it felt about the same as the y-axis belt, which was measuring 277.  I loosened the x-axis, and sure enough, the number increased - I got it to 209...but at 209, it was so loose that there was a good few centimeters of visible sag on the bottom part of the belt, so no question that it was way too loose, despite the number indicating that it is still too tight.

So, I tightened the x-axis belt until it is as close as I can get it by feel (and pitch when plucked) to the y-axis belt, and I am currently printing a benchy that seems to be turning out ok (though it's still too early in the print to know for sure), so I'm not overly concerned about the belt tension - but could the inaccurate number be an indication of something else that is wrong with the printer, or is it something I should just not worry about too much?

Posted : 31/12/2020 8:39 pm
jimmy
(@jimmy-3)
Active Member

maybe your bearings are not moving smooth. i use dry bearings on my extruder. i also get 210 because they are dry bearings but it is printing fine and very quiet. loosen the belt and try to move the extruder by hand and notice of you are getting much resistance.

Posted : 01/01/2021 6:40 pm
jsw
 jsw
(@jsw)
Noble Member

I don't trust those belt numbers.  Yes, I know that some do, but I don't.

I consider a much better test to be to hold the associated motor shaft still with pliers and try to move the associated carriage.  If there's any significant 'slop' or 'play', things are too loose.

A while back somebody posted a belt tension guide to the Prints section.  I printed it out, but have not needed to try it yet.

Posted : 01/01/2021 9:57 pm
Viced Rhino
(@viced-rhino)
Active Member
Posted by: @jimmy-3

maybe your bearings are not moving smooth. i use dry bearings on my extruder. i also get 210 because they are dry bearings but it is printing fine and very quiet. loosen the belt and try to move the extruder by hand and notice of you are getting much resistance.

I'll give that a go, just to see, but I doubt it - I didn't make any changes to those bearings that would account for such a sudden and drastic change.

This post was modified 2 months ago 2 times by Viced Rhino
Posted : 01/01/2021 10:24 pm
Viced Rhino
(@viced-rhino)
Active Member
Posted by: @jsw

I don't trust those belt numbers.  Yes, I know that some do, but I don't.

I consider a much better test to be to hold the associated motor shaft still with pliers and try to move the associated carriage.  If there's any significant 'slop' or 'play', things are too loose.

A while back somebody posted a belt tension guide to the Prints section.  I printed it out, but have not needed to try it yet.

I am aware of the general skepticism in the community about these numbers, which is why I'm not overly fussed about it, was just wondering if it might be an indicator for another problem. I'll definitely check the bearings as per the previous post, will also look for the tension guide and see how it works out.

Posted : 01/01/2021 10:26 pm
jsw
 jsw
(@jsw)
Noble Member

Here's a question for you regarding bearings.  Do you semi-regularly lubricate the smooth rods, either using light machine oil as recommended by Prusa, or with something like Superlube, as some on the forum have suggested?

Posted : 02/01/2021 12:17 am
Baklin
(@baklin)
Estimable Member

I don't find the belt tension numbers very useful. They show the resistance for the total axis, not just the belts. Prusa should have named it differently.

 

When the bearings are not running freely the numbers go down and that has nothing to do with the belts.

 

A little tool that can be useful it THIS. With that tool you can easlily check the belts, even if it is only as a sanity check when you doubt the belts or bearings.

Posted : 02/01/2021 11:11 am
dimprov liked
jsw
 jsw
(@jsw)
Noble Member
Posted by: @baklin

A little tool that can be useful it THIS. With that tool you can easlily check the belts, even if it is only as a sanity check when you doubt the belts or bearings.

That is the device I referred to earlier in this thread.

Posted : 02/01/2021 1:42 pm
Viced Rhino
(@viced-rhino)
Active Member
Posted by: @jsw

Here's a question for you regarding bearings.  Do you semi-regularly lubricate the smooth rods, either using light machine oil as recommended by Prusa, or with something like Superlube, as some on the forum have suggested?

I use Superlube on the smooth rods, and all my bearings were degreased before having Superlube applied inside them with an applicator similar to this one.

I will print off that tool to check the tension, and disassemble and re-lubricate the bearings if the belt turns out to actually be the right tension.

Posted : 02/01/2021 2:53 pm
dimprov
(@dimprov)
Noble Member

@viced-rhino

Is the need to degrease and re-lube something new?  I don't remember the build instructions making any recommendation to do it when I assembled my printer two years ago.  Has there been a change in the parts/supplier since then that make it now advisable?  Or has it been learned through collective experience that it's better off to do it even if it isn't official Prusa policy?  Actually, since I went off-line for two years, I should ask: is it now the official Prusa recommendation?

Posted : 05/01/2021 2:14 am
jsw
 jsw
(@jsw)
Noble Member
Posted by: @dimprov

@viced-rhino

Is the need to degrease and re-lube something new?  I don't remember the build instructions making any recommendation to do it when I assembled my printer two years ago.  Has there been a change in the parts/supplier since then that make it now advisable?  Or has it been learned through collective experience that it's better off to do it even if it isn't official Prusa policy?  Actually, since I went off-line for two years, I should ask: is it now the official Prusa recommendation?

I'm respectfully questioning the so-called need to clean out the supplied lube and re-lube the bearings.  I followed the instructions from Prusa and just installed the bearings, and I periodically lube them via the rods.

I figure that the Prusa folks know their machines better than anyone, and they have hundreds to over a thousand of them running in their 'farm' close to 24*7.  I figure that if the bearings were wearing out or falling apart, they would have noticed it and would have updated their instructions.

My conclusion is that Prusa considers the supplied lube to be adequate for the intended purpose for the expected life of the machine, with the usual recommended periodic lubrication, of course.

Posted : 05/01/2021 2:31 am
dimprov
(@dimprov)
Noble Member
Posted by: @jsw
Posted by: @dimprov

@viced-rhino

Is the need to degrease and re-lube something new?  I don't remember the build instructions making any recommendation to do it when I assembled my printer two years ago.  Has there been a change in the parts/supplier since then that make it now advisable?  Or has it been learned through collective experience that it's better off to do it even if it isn't official Prusa policy?  Actually, since I went off-line for two years, I should ask: is it now the official Prusa recommendation?

I'm respectfully questioning the so-called need to clean out the supplied lube and re-lube the bearings.  I followed the instructions from Prusa and just installed the bearings, and I periodically lube them via the rods.

I figure that the Prusa folks know their machines better than anyone, and they have hundreds to over a thousand of them running in their 'farm' close to 24*7.  I figure that if the bearings were wearing out or falling apart, they would have noticed it and would have updated their instructions.

My conclusion is that Prusa considers the supplied lube to be adequate for the intended purpose for the expected life of the machine, with the usual recommended periodic lubrication, of course.

Yes, you said it more artfully than me, but that's why I asked the question.  Since Prusa uses its own printers at a large scale, you'd think they'd have more than ample data to issue guidance on whether to clean-relube or not.

Posted : 05/01/2021 3:21 am
dimprov
(@dimprov)
Noble Member

OK, well looking at Prusa's 800 hour maintenance, it does say:

If you feel the heatbed or the extruder is not moving smoothly when pushing it by hand, you can dismount the Y or X-axis, remove the bearings from their smooth rods, and lubricate them on the inside. Be careful not to damage the bearings when inserting the smooth rod back.

Even then though it doesn't suggest cleaning them first.  Perhaps it was an oversight of the technical writer?  Who knows.  I guess if there's no downside to doing it, then it would be a good time to consider doing it if you're ever going to.

This post was modified 2 months ago by dimprov
Posted : 05/01/2021 3:34 am
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