On belts and tension

Hardware settings, adjustments and fixes and other hardware discussion. This includes the "doHICky" Laser Power measurement system by Russ.
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Abraham Saenz
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On belts and tension

Post by Abraham Saenz » Mon Oct 17, 2016 11:07 am

During my fun struggles with my Acctek AKJ6040 laser cutter/engraver, one of the aspects that has a a mayor impact on cuts and engraving quality has been belt tension.

I've discussed the cutting quality issues I had with my machine in previous posts, but the biggest one has been striations when cutting horizontal and diagonal lines due to excessive stepper motor vibration.

On my troubleshooting I got to experiment with a number of things. One of them was belt tension, my machine came with extremely tense belts from factory, I do not have a belt tension gauge nor I've any experience with tensioning belts, they just seem rather tense to me. After relaxing the belts I experienced about 10% - 15% improvement, mostly because less noise was been transmitted to the laser head.

After researching a bit on the topic I got to learn three things.

1. Excessive belt tension can cause premature bearing failure increase noise and resonance.
2. Optimal belt tension can actually be used in your favor to help reduce the transmission of stepper motor resonance and noise.
3. Sub optimal belt tension can produce much undesired backlash.

My belt tension at the moment is done with out any scientific measurement. I'm mostly just doing trial and error. Have any of your guys experimented with belts on your machines? have to even considered upgrading your belts at some point?

Keep lasing
Acctek AKJ6040+Clearpath Servos+90W EFR laser tube, 1.5 inch lens, polyurethane belts, Boeshield T-9 Lub :)

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sebastien laforet
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Re: On belts and tension

Post by sebastien laforet » Mon Oct 17, 2016 1:21 pm

not sure if this is relevant, but for some bikes with belts (this is rare), you can control the belt tension with a weight than you suspend to the belt in the middle beetween the gears, and mesure how much the weight goes downward... obviously a standard bike user has no speciality tool to mesure that sort of tension correctly, so the manufacturer has to provide some way of measuring easily enough.

probably not very accurate, but is you happen to find a good setting of the tension by trial and mistakes, you can at least measure the good value. you don't know the tension (in term of newton or kg force), but you know that by applying for example 300g of lest, your belt has to go down 1.5cm.

if you happen to have your belt loosening, you can re-tighten to the value measured.
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Abraham Saenz
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Re: On belts and tension

Post by Abraham Saenz » Mon Oct 17, 2016 1:53 pm

schlaf wrote:not sure if this is relevant, but for some bikes with belts (this is rare), you can control the belt tension with a weight than you suspend to the belt in the middle beetween the gears, and mesure how much the weight goes downward... obviously a standard bike user has no speciality tool to mesure that sort of tension correctly, so the manufacturer has to provide some way of measuring easily enough.

probably not very accurate, but is you happen to find a good setting of the tension by trial and mistakes, you can at least measure the good value. you don't know the tension (in term of newton or kg force), but you know that by applying for example 300g of lest, your belt has to go down 1.5cm.

if you happen to have your belt loosening, you can re-tighten to the value measured.

Thanks for your input. Yes, indeed that is one way to adjust the tension. I'm currently not having issues with tension (as far as I can see), my post was more on the observational side as I think the topic of belts and tension seems a bit underrated. And it should not be, because having the proper tension gives you better cut quality as well as better longevity on both, your stepper motor and lose pulleys bearings.

I'm thinking on upgrading my machine from stepper motors to servos. As I expect much faster response from the motors and a lot more violent accelarations I'm thinking on investing to polyurethane/steel belts. My machine is fitted with rubber/glass fiber belts currently.
Acctek AKJ6040+Clearpath Servos+90W EFR laser tube, 1.5 inch lens, polyurethane belts, Boeshield T-9 Lub :)

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Gene Uselman
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Re: On belts and tension

Post by Gene Uselman » Mon Oct 17, 2016 2:12 pm

I googled this on belt tension- their machines range from 100 to 200 grams at .5 inch deflection. If you look at their tension tool is is a simple spring pull gauge (which I have a couple of)- I would guess that the range of different machines takes into account the length of the belt on that machine. Gene

http://www.engraversnetwork.com/support ... -tensions/

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Preben Hovedskou
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Re: On belts and tension

Post by Preben Hovedskou » Mon Oct 17, 2016 3:58 pm

Interesting subject.. ;-)

For many years I worked with industrial machines equipped with a lot of toothed belts.
To adjust the belts we used electronic belt-tension-testers. These testers was in fact just a frequency-analyzer with a microphone.
They worked by tapping or picking the belt with a finger(like you pick a string on a guitar) and let the device listen to the frequency made by the belt.
Then we had some forms from the factory, showing the frequencys for a correct tension of the belts.

You can find tons of apps for your smartphone that can do exactly the same thing. (just google it for your type of phone)
F.ex this one..:
https://play.google.com/store/apps/deta ... equenSeeHD

Of cause we don't know exactly what frequency is optimal for our small belts,
BUT with an app like that, you are able to set all your belts to an EQUAL tension, whitch is also very important.
So try it out... your machine will for sure benefit from equaly adjusted belts on the Y-axis..!

Maybe I will make a "How To" about this issue later.. ;-)

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Abraham Saenz
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Re: On belts and tension

Post by Abraham Saenz » Mon Oct 17, 2016 4:50 pm

Pepsi wrote:Interesting subject.. ;-)

For many years I worked with industrial machines equipped with a lot of toothed belts.
To adjust the belts we used electronic belt-tension-testers. These testers was in fact just a frequency-analyzer with a microphone.
They worked by tapping or picking the belt with a finger(like you pick a string on a guitar) and let the device listen to the frequency made by the belt.
Then we had some forms from the factory, showing the frequencys for a correct tension of the belts.

You can find tons of apps for your smartphone that can do exactly the same thing. (just google it for your type of phone)
F.ex this one..:
https://play.google.com/store/apps/deta ... equenSeeHD

Of cause we don't know exactly what frequency is optimal for our small belts,
BUT with an app like that, you are able to set all your belts to an EQUAL tension, whitch is also very important.
So try it out... your machine will for sure benefit from equaly adjusted belts on the Y-axis..!

Maybe I will make a "How To" about this issue later.. ;-)

-Pepsi-

Thanks for the tip, I will be experimenting with one of the Apps.
Acctek AKJ6040+Clearpath Servos+90W EFR laser tube, 1.5 inch lens, polyurethane belts, Boeshield T-9 Lub :)

Chris Berry
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Re: On belts and tension

Post by Chris Berry » Mon Jan 02, 2017 3:51 pm

Preben Hovedskou wrote:Interesting subject.. ;-)

For many years I worked with industrial machines equipped with a lot of toothed belts.
To adjust the belts we used electronic belt-tension-testers. These testers was in fact just a frequency-analyzer with a microphone.
They worked by tapping or picking the belt with a finger(like you pick a string on a guitar) and let the device listen to the frequency made by the belt.
Then we had some forms from the factory, showing the frequencys for a correct tension of the belts.

You can find tons of apps for your smartphone that can do exactly the same thing. (just google it for your type of phone)
F.ex this one..:
https://play.google.com/store/apps/deta ... equenSeeHD

Of cause we don't know exactly what frequency is optimal for our small belts,
BUT with an app like that, you are able to set all your belts to an EQUAL tension, whitch is also very important.
So try it out... your machine will for sure benefit from equaly adjusted belts on the Y-axis..!

Maybe I will make a "How To" about this issue later.. ;-)

-Pepsi-
The main problem with trying to hear the frequencies of the belts is that there's no resonant cavity and the frequencies of the longer belts would be in the bass - hence very hard to hear at the energy levels.
I was thinking of using a paper clip clipped to the belt and an old guitar pickup wired up to a smartphone as there are lots of sympathetic vibrations in the machine and the belt is nearly inaudible. - this could also be rigged up to a phono input on an amplifier. The mass of the paperclip would lower the frequency somewhat negligibly but by the same amount on two identical belts.
A permanent magnet and a coil would do pretty much the same - although shielding may be an issue. Cheap guitar pickups can be had for a song (we're not interested in the tone so anyone's pickup rejects would do!)
--------
Chris
--------

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Mike Audleman
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Re: On belts and tension

Post by Mike Audleman » Wed Apr 26, 2017 1:31 pm

And the fact that every length of belt would resonate at a different frequency. I kinda think a fish scale is a better tool. Same problem remains though, what is the RIGHT tension.

My gut says tight enough so that any acceleration of the head/gantry has zero affect on the belt. What I mean is if the belt is loose, the stepper has to retrieve the tension from the belt before the head/gantry move. This should exhibit itself in direction reversals (ie, scanning). I should think you could use a scan to test if the belt is too loose. Should exhibit itself in the line's stop and start points not being lined up. Adding tension should fix that.

Y will be harder as the whole gantry moves and we rarely scan that direction. But you could just to test direction reversal. And there are 2 belts to work with usually on the Y axis.
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Martín Lázaro
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Re: On belts and tension

Post by Martín Lázaro » Wed Apr 26, 2017 2:05 pm

And some idea like this (stolen from 3d printer) ? (not to measure, obviously, just to maintain a better values)
Attachments
tension.jpg
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fred ungewitter
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Re: On belts and tension

Post by fred ungewitter » Wed Apr 26, 2017 5:24 pm

it's generally considered a poor solution to belt tensioning in the 3D printer world to use a "clothespin" type spring. Those designs often have "ringing" or other artifacts in the print, depending on the orientation of specific portions of the model being printed. The better designs all have solid fixed means to tension the belt.
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