The original pulley is sloppy when I grabbed it and it can be tilted left and right, so the fit has gone loose. Replacement is faster and more durable and more tight fitting, I don't think that lighter alu by itself helps with vibrations.
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How to reduce the vibration of a bench lathe ( Emco Compact 8 )
- Thread starter compact8
- Start date
It's the virbation that bothers me but the video cannot capture it. It may do harm to the machine in the long run I think
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- May 27, 2016
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If it is a spring vibrating, you can stop it doing so by damping. The "just right" size of rubber tube pushed up it can work, or a cut piece of plastic foam packing. Better is to identify where the vibration that excites it into resonance comes from.
Mechanic's stethoscope can let you hear all sorts of noises, but it takes some usage to get used to what is "normal", and no problem. A quick shortcut is to get a long large screwdriver, carefully press the tip on the end of the shaft by a suspect gear, or on the outside of a bearing cover.
Then get the handle end onto your ear lobe, and gently press to block your ear.
BE CAREFUL - DO NOT SLIP !!
You will hear things like bearing running badly, or cyclic throbbing that leads you to noise sources.
I am one who might get a mechanic's stethoscope, just because I am curious!
Mechanic's stethoscope can let you hear all sorts of noises, but it takes some usage to get used to what is "normal", and no problem. A quick shortcut is to get a long large screwdriver, carefully press the tip on the end of the shaft by a suspect gear, or on the outside of a bearing cover.
Then get the handle end onto your ear lobe, and gently press to block your ear.
BE CAREFUL - DO NOT SLIP !!
You will hear things like bearing running badly, or cyclic throbbing that leads you to noise sources.
I am one who might get a mechanic's stethoscope, just because I am curious!
There are many sources of vibration that you will need to systematically go through to reduce your problem. You can’t eliminate vibration entirely, but finding the source can significantly reduce it. Possible sources are lack of proper preload, bad bearings, worn pulley/shaft fit, motor unbalance, and bad belts. There are probably others, but that is off the top of my head having a similar lathe a number of years ago.
First step is to look for anything loose. If any bolts have come loose, that could cause a vibration problem.
Since it runs fine at other speeds, it is likely not in the motor, but can’t hurt to check the vibration. Check the motor by removing the belts and see if you have the same vibration.
If that is ok, check preload on your spindle and adjust as necessary. If that is ok, see if there a problem with your belt. Belts have a natural frequency and if they are going bad, or too loose, it could change the speed at which they vibrate. If the belt looks questionable, replace it.
See if the pulleys are loose on the shafts, or pulleys with bearings/bushings are loose. They should not have any play.
Check the bearings as explained above, if they are wearing out, you can experience vibration at certain speeds you didn’t see before.
There is a lever which engages the drive system, if the spring is broken or weak, it could cause a vibration problem. Check this by engaging the drive with the machine powered down, and see if the belt feels loose. If you can easily move the belt with vey little force, the spring is likely bad. There should be some resistance to deflecting it.
The last thing is you need more mass for your stand to reduce vibration. Everything has a natural frequency at which it vibrates and by adding more mass, or stiffness, you change the natural frequency. If everything above is ok, you might just need to make your stand heavier or more rigid.
First step is to look for anything loose. If any bolts have come loose, that could cause a vibration problem.
Since it runs fine at other speeds, it is likely not in the motor, but can’t hurt to check the vibration. Check the motor by removing the belts and see if you have the same vibration.
If that is ok, check preload on your spindle and adjust as necessary. If that is ok, see if there a problem with your belt. Belts have a natural frequency and if they are going bad, or too loose, it could change the speed at which they vibrate. If the belt looks questionable, replace it.
See if the pulleys are loose on the shafts, or pulleys with bearings/bushings are loose. They should not have any play.
Check the bearings as explained above, if they are wearing out, you can experience vibration at certain speeds you didn’t see before.
There is a lever which engages the drive system, if the spring is broken or weak, it could cause a vibration problem. Check this by engaging the drive with the machine powered down, and see if the belt feels loose. If you can easily move the belt with vey little force, the spring is likely bad. There should be some resistance to deflecting it.
The last thing is you need more mass for your stand to reduce vibration. Everything has a natural frequency at which it vibrates and by adding more mass, or stiffness, you change the natural frequency. If everything above is ok, you might just need to make your stand heavier or more rigid.
I have replaced the original steel pulley that runs on a brone bushing with one made of 6061 aluminium running on ball bearings. Now there is zero play between the pulley and the shaft but disappointingly the vibration is not reduced by even a bit.
This video shows that the excitation clearly comes from the belt. As the pulley is gradually lowered hence the tension and resonating frequency of the belt increased, the belt would vibrate strongly at some points. The last occurrence is so strong that the image stabilization mechanism of the camera ( an iphone 11 pro ) was somehow affected causing it to join the dance. The camera was mounted on a tripod which is not touching the bench or the lathe. I believe the strong vibration is the result of the belt and the spring resonating together.
I have tried to dampen the vibration by holding the lower half of the spring as tightly as I could with my hand but it didn't help at all so I doubt if attempting to dampen the vibration is the way to go. Now I guess I will have to live with it or avoid using this speed ( 850 rpm ) ? Too bad that this rpm should be optimal for turning steel stocks of the diameter range that I work on mostly.
This video shows that the excitation clearly comes from the belt. As the pulley is gradually lowered hence the tension and resonating frequency of the belt increased, the belt would vibrate strongly at some points. The last occurrence is so strong that the image stabilization mechanism of the camera ( an iphone 11 pro ) was somehow affected causing it to join the dance. The camera was mounted on a tripod which is not touching the bench or the lathe. I believe the strong vibration is the result of the belt and the spring resonating together.
I have tried to dampen the vibration by holding the lower half of the spring as tightly as I could with my hand but it didn't help at all so I doubt if attempting to dampen the vibration is the way to go. Now I guess I will have to live with it or avoid using this speed ( 850 rpm ) ? Too bad that this rpm should be optimal for turning steel stocks of the diameter range that I work on mostly.
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- Joined
- Dec 6, 2021
- Messages
- 224
I'm sure it's just a video/shutter thing, but on my end it looks like the belt is running true at the point of greatest vibration. Have you done the same test using the phone's slow motion setting? I'm not doubting your assessment that this is a belt issue, just pulling at straws. Other than changing belts, you're following the same diagnostic steps I would.
Are there other belt options available? I've had great results with linked belts on my machines, but I have no idea if they are available in a size that small. I went down this rabbit hole a few months ago and found there's a lot more variety than I'd ever seen. Here are a few related links I found...
www.rainbowprecisionproducts.com
Also quite a few pulley options at McMaster if the road leads to a different belt type...
www.mcmaster.com
Thanks for detailing your diagnosis. I've got a motor upgrade in the works for my mini lathe and haven't yet settled on a drive system. I'm learning a lot from this about things to consider.
Are there other belt options available? I've had great results with linked belts on my machines, but I have no idea if they are available in a size that small. I went down this rabbit hole a few months ago and found there's a lot more variety than I'd ever seen. Here are a few related links I found...
Accu-Link® Adjustable Link V-Belt
Also quite a few pulley options at McMaster if the road leads to a different belt type...
McMaster-Carr
McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.
Thanks for detailing your diagnosis. I've got a motor upgrade in the works for my mini lathe and haven't yet settled on a drive system. I'm learning a lot from this about things to consider.
Your video shows the belt on a different groove on the sheave than your photo earlier in this post. Do you get vibration on both grooves with the sheave mounted to the motor? If you are getting the vibration on both groove speeds, then it could be a motor problem being transmitted to the belts. Going through the slip clutch might be dampening the vibration enough that you are not getting it when using those speed settings.
Check the alignment of the two sheaves to each other, the grooves need to be in line to prevent rubbing along the side of the groove. If they are not aligned, it can cause an excitation of the belt natural frequency since the belt gets plucked like a guitar string as it rubs and releases when it rotates. You’ll also want to check the grooves for excessive wear, that can cause belt vibration problems too.
Did you try doing this test without a chuck mounted? If there is an imbalance, or something causing it to be eccentric, it could induce a vibration in the belt if it is at the same natural frequency of the belt. If removing the chuck eliminates or significantly reduces the vibration in the belt, then your problem is likely in the chuck and/or mounting.
I don’t recall reading if this was an old belt or if it has been replaced. If it is an old belt, you might try replacing with a new one. V-belts have a natural frequency and what you show in the video looks like it is running at the natural frequency, or something is exciting the natural frequency. Older belts weaken over time, or strands break, so their natural frequency can change, a new belt might run better at that speed.
If none of this solves your problem, the easy solution is not running at that speed, the more expensive solution would be to install new sheaves with different groove diameters to move the speed up or down a bit to get away from that speed, or installing a three phase motor with a VFD and operate at a speed where it doesn’t vibrate.
Check the alignment of the two sheaves to each other, the grooves need to be in line to prevent rubbing along the side of the groove. If they are not aligned, it can cause an excitation of the belt natural frequency since the belt gets plucked like a guitar string as it rubs and releases when it rotates. You’ll also want to check the grooves for excessive wear, that can cause belt vibration problems too.
Did you try doing this test without a chuck mounted? If there is an imbalance, or something causing it to be eccentric, it could induce a vibration in the belt if it is at the same natural frequency of the belt. If removing the chuck eliminates or significantly reduces the vibration in the belt, then your problem is likely in the chuck and/or mounting.
I don’t recall reading if this was an old belt or if it has been replaced. If it is an old belt, you might try replacing with a new one. V-belts have a natural frequency and what you show in the video looks like it is running at the natural frequency, or something is exciting the natural frequency. Older belts weaken over time, or strands break, so their natural frequency can change, a new belt might run better at that speed.
If none of this solves your problem, the easy solution is not running at that speed, the more expensive solution would be to install new sheaves with different groove diameters to move the speed up or down a bit to get away from that speed, or installing a three phase motor with a VFD and operate at a speed where it doesn’t vibrate.
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- Apr 16, 2019
- Messages
- 745
Just a thought , they do make hydraulic belt dampeners , our old dryer had one . Might be something you could try hydraulic damper for belt tensioner Think a shock absorber attached to your tension pulley. Edit, I thought my link posted but it didn’t,I’ll try again https://www.diycarserviceparts.co.uk/blog/2020/06/05/what-are-tensioners-idlers-and-dampers/
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Thanks again for all the detailed replies. I didn't mention it but I did have tried to replace the belt with a new one ( made by Gates USA ) but the result is the same. Then I took off the chuck as suggested by Ischgl99 and the vibration immediately subsided by a LOT. There are now two possibilities I can think of :
1) The original Emco 3-jaw chuck is unbalanced. Not sure if it indicates anything but I have tried mouting a four-jaw chuck with all the jaws touching each other at the center and the result is the same.
2) The additional mass of the chuck changes the resonating frequency of the whole structure causing it to resonate at 850 rpm.
What would be the sensible next step under such circumstance ?
1) The original Emco 3-jaw chuck is unbalanced. Not sure if it indicates anything but I have tried mouting a four-jaw chuck with all the jaws touching each other at the center and the result is the same.
2) The additional mass of the chuck changes the resonating frequency of the whole structure causing it to resonate at 850 rpm.
What would be the sensible next step under such circumstance ?
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