Why not to use spring tensioners on timing belts? October 18, 2018 12:16AM |
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Re: Why not to use spring tensioners on timing belts? October 18, 2018 03:42AM |
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Re: Why not to use spring tensioners on timing belts? October 18, 2018 09:01AM |
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Re: Why not to use spring tensioners on timing belts? October 18, 2018 10:43AM |
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Re: Why not to use spring tensioners on timing belts? December 06, 2018 01:51AM |
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Re: Why not to use spring tensioners on timing belts? December 06, 2018 06:48AM |
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Tierod
Shock absorber might work if done correctly. Take an automotive timing belt for example, many use a hydraulic tensioner with an internal spring rated for a specific belt tension.
When vibrations try to push tensioner back it resists. It will move back but very slowly and with increased effort. If it could be made to apply the optimal pressure for any given belt,
There would be no need for adjustment and may also dampen vibrations. I like the idea. Anyone know what 6mm and 10mm gt2 rated for psi? Also, anyone know what belts are good, brand?, stiffness etc? Would that effect vibrations?
Rod
Re: Why not to use spring tensioners on timing belts? December 06, 2018 09:05PM |
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Re: Why not to use spring tensioners on timing belts? December 08, 2018 06:42AM |
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Re: Why not to use spring tensioners on timing belts? December 08, 2018 10:59AM |
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Ed3D
You can use springs to tension belts and it will have an effect on the vibration damping and many high-end machines (not printers) do. The spring can be used to easily apply a tension to the belt and maintain tension as belts stretch so less servicing is required. There are three key issues with the springs that clip around the belts though which are:
1. The spring rate is FAR too low, they are not nearly stiff enough so act to make print head positioning inaccurate at high accelerations.
2. There is often no preload. Springs should (almost) always be preloaded which the lack of will result in a very small tensioning force which means your belts are not actually anywhere near tensioned enough. So people think you put the spring on loose belts and it's sorted, which is not the case at all.
3. The loading from the torsional springs is kind of in the wrong direction. The inertia forces on the belt have a mechanical advantage over the spring which reduces effectiveness. Its much easer to pull a belt tight than to pinch it together with a lever arm which is effectively how those springs work.
Re: Why not to use spring tensioners on timing belts? December 08, 2018 12:52PM |
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Re: Why not to use spring tensioners on timing belts? December 08, 2018 01:23PM |
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Re: Why not to use spring tensioners on timing belts? December 08, 2018 02:02PM |
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MKSA
Quote
Ed3D
You can use springs to tension belts and it will have an effect on the vibration damping and many high-end machines (not printers) do. The spring can be used to easily apply a tension to the belt and maintain tension as belts stretch so less servicing is required. There are three key issues with the springs that clip around the belts though which are:
1. The spring rate is FAR too low, they are not nearly stiff enough so act to make print head positioning inaccurate at high accelerations.
2. There is often no preload. Springs should (almost) always be preloaded which the lack of will result in a very small tensioning force which means your belts are not actually anywhere near tensioned enough. So people think you put the spring on loose belts and it's sorted, which is not the case at all.
3. The loading from the torsional springs is kind of in the wrong direction. The inertia forces on the belt have a mechanical advantage over the spring which reduces effectiveness. Its much easer to pull a belt tight than to pinch it together with a lever arm which is effectively how those springs work.
So, to use or not to use ?
Re: Why not to use spring tensioners on timing belts? December 08, 2018 02:26PM |
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Re: Why not to use spring tensioners on timing belts? December 08, 2018 04:26PM |
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Re: Why not to use spring tensioners on timing belts? December 09, 2018 12:12AM |
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Re: Why not to use spring tensioners on timing belts? December 09, 2018 05:18AM |
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Re: Why not to use spring tensioners on timing belts? December 09, 2018 05:48AM |
Registered: 5 years ago Posts: 61 |
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MKSA
None of them in fact.
Explained in previous posts.
"careful design" ? Please show.
Re: Why not to use spring tensioners on timing belts? December 09, 2018 08:11AM |
Registered: 12 years ago Posts: 1,450 |
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Diggrr
........................................
I have no idea why 6mm belts are the standard. I use one to hold my bed wires up off of the limit switch, and that is it.
Re: Why not to use spring tensioners on timing belts? December 09, 2018 03:17PM |
Registered: 6 years ago Posts: 93 |
Re: Why not to use spring tensioners on timing belts? December 09, 2018 04:40PM |
Registered: 6 years ago Posts: 1,007 |
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Ed3D
Quote
MKSA
None of them in fact.
Explained in previous posts.
"careful design" ? Please show.
As I said in my previous post which it looks like you didn't actually read yes, springs are a viable option for tensioning a belt. In fact I can name 3 industrial machines right off the top of my head that use a spring to tension a GT2 belt and they are all capable of sub micron positioning at up to 1G acceleration with a head weighing close to 1 kg - so far more rigorous than what a 3D printer will ever experience. I'm not talking about the cheap spring you would find in a bic but something with a much higher spring rate that has been properly specced and thought through.
To be clear the way people use a spring currently is not the same and I agree that it will ruin your tensioning but properly designed and specced spring has several benefits over simply tensioning a screw. Those being:
- Ease of assembly - assembly lines will struggle to over tension or under tension drives.
- Reduced servicing - belt stretch is compensated for by the spring, yes it's not ideal but better to have a belt slack off a little bit than a huge amount.
- Reduced influence of thermal effects - as aluminium members expand / contract you limit the amount of undue stress applied to the belts.
- Vibration damping - the spring will help isolate some of the vibration from the drive transmitting into the machine which can often cause resonance.
- Belt life - due to the reduction in sharp stresses belt life can be greatly improved.
No offence but the benefits of a properly designed spring tension unit are fairly obvious but I know that no matter what I say you wont change your mind so that renders any kind of productive discussion here pointless as you "know best". Unfortunately in this case you're wrong and I think I'll chose to follow the lead of the professionals, who have engineered products far out performing the needs of a printer, and conducted rigorous testing on them on this occasion instead of someone on the internet with no credentials and nothing to back up anything he says.
Re: Why not to use spring tensioners on timing belts? December 10, 2018 05:34AM |
Registered: 6 years ago Posts: 1,007 |
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Tierod
Mksa, ok,ok, was late, bit tired,lol. Foot pounds it is. Ok, back to timing belt thing. I was using that example because of the type of damper used. It’s internally spring loaded and oil dampened which also acts as a strong resistance to backward movement only. Moves quickly the other way. Unfortunately weight would be an issue because the best placement would be the carriage. But some form of self adjusting self locking arrangement may help with belt vibrations. Anyone tried mounting adjustable weights on motors, etc to deal with harmonics/vibrations that way? I’ll try and find some time to do that with an accelerometer hooked up and see if it has any effect.
Cheers
Re: Why not to use spring tensioners on timing belts? December 20, 2018 08:26PM |
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Re: Why not to use spring tensioners on timing belts? December 20, 2018 08:38PM |
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