Bandsaw vibration - how much is normal?
- Thread starter GraemeD
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GraemeD
Established Member
Good thinking.....I really must try and eliminate other matters before assuming the worst. The blade was new (and a DureEdge), but you never know.....
Graeme
Graeme
9fingers
Established Member
Graeme, when you are investigating this try and estimate the frequency of the vibration.
Not so much numerically but is it
once per revolution of the wheel - suggests wheel im balance,
once per revolution of the blade - possible weld problem,
many times per revolution - bearing brinnelling, motor vibration etc.
None of these - resonance in the frame??
regards
Bob
Not so much numerically but is it
once per revolution of the wheel - suggests wheel im balance,
once per revolution of the blade - possible weld problem,
many times per revolution - bearing brinnelling, motor vibration etc.
None of these - resonance in the frame??
regards
Bob
GraemeD
Established Member
Well I had a long play with it last night, and to be honest I'm more baffled than ever now! I did the following;
1). Took off the blade and ran the motor, so only the bottom wheel was turning. No vibration. So, the bottom wheel and the motor are not issues.
2). Spun up the top wheel by hand as fast as I could. No noticeable vibration....but I really couldn't get it to go very fast, even using a long cord wrapped round the hub and pulled hard, so I don't think this is conclusive. Also of course, the top wheel is not under blade tension, so if the bearings were the issue, they may not behave the same without the blade fitted. Is this fair to say?
3). Tried fitting a different blade. Vibrations exactly as before.....so it probably isn't the blade.
As far as I can tell, the vibrations are wheel speed related (although the blade revolves once per two wheel revs roughly, so it is hard to be sure!).
One clue perhaps is that the vibrations cycle every 15 or so seconds, getting larger and then smaller and larger again over that kind of period. What the heck could be causing that?! Do the bearings cycle internally at some rate lower than the wheels revolve??
Graeme
1). Took off the blade and ran the motor, so only the bottom wheel was turning. No vibration. So, the bottom wheel and the motor are not issues.
2). Spun up the top wheel by hand as fast as I could. No noticeable vibration....but I really couldn't get it to go very fast, even using a long cord wrapped round the hub and pulled hard, so I don't think this is conclusive. Also of course, the top wheel is not under blade tension, so if the bearings were the issue, they may not behave the same without the blade fitted. Is this fair to say?
3). Tried fitting a different blade. Vibrations exactly as before.....so it probably isn't the blade.
As far as I can tell, the vibrations are wheel speed related (although the blade revolves once per two wheel revs roughly, so it is hard to be sure!).
One clue perhaps is that the vibrations cycle every 15 or so seconds, getting larger and then smaller and larger again over that kind of period. What the heck could be causing that?! Do the bearings cycle internally at some rate lower than the wheels revolve??
Graeme
9fingers
Established Member
You are right that load can be an issue but difficult to simulate in the sort of tests you are doing.
The coming and going of vibration is not untypical. This can be caused by one resonant structure (the frame i suspect) being excited by the cause of the vibration but the excitation frequency is slightly different from the resonant (tuned) frequency of the frame. The result is the building up of oscillations in the frame and then dying away due to the frequency difference.
The different or beat frequency is the once per 15 seconds you observe.
Think of as the way a piano tuner does his job by listening for the difference between the tuning fork and the note from the string as the tension is changed.
All a bit of a distraction to what you are doing but I think it points towards the top wheel having some sort of problem.
How much play is there at the edge of the wheel when static?
Try pushing the edge of the wheel at a specific point, pressing along the axis of rotation whilst rotating the wheel with that finger. Can you feel any hint of lumpiness?
Bob
The coming and going of vibration is not untypical. This can be caused by one resonant structure (the frame i suspect) being excited by the cause of the vibration but the excitation frequency is slightly different from the resonant (tuned) frequency of the frame. The result is the building up of oscillations in the frame and then dying away due to the frequency difference.
The different or beat frequency is the once per 15 seconds you observe.
Think of as the way a piano tuner does his job by listening for the difference between the tuning fork and the note from the string as the tension is changed.
All a bit of a distraction to what you are doing but I think it points towards the top wheel having some sort of problem.
How much play is there at the edge of the wheel when static?
Try pushing the edge of the wheel at a specific point, pressing along the axis of rotation whilst rotating the wheel with that finger. Can you feel any hint of lumpiness?
Bob
GraemeD
Established Member
Makes total sense, Bob.....I guess we just need to isolate the source of the vibration energy being put into the system.
The tension/tracking adjustment on the top wheel is rattly and loose when there is no blade tension applied, so it's tricky to determine how much play in in the bearings.....but last time I had it all out on the bench, there was none discernible.
When I replaced the bears, there had been none discernible either, but I wanted to put a spacer behind the wheel to get its geometry right, so I removed the old ones to do this. They were obviously loose when you played with them by hand, hence I replaced them. I guess since there are two ballraces in there, any sloppiness (in one?) is kind of masked by the other....but that would not stop it from vibrating.
I have run the wheels (with and without a blade fitted) using a finger too, and I must say it all seemed smooth with no hint of lumpiness. With the blade fitted (but all the guides retracted and the wheel brush removed) there was some slight "frictional" noise from the top wheel which I couldn't identify, and I even checked the blade path to see if it was rubbing somewhere....but it wasn't. I concluded it must be the blade on the tyre....kind of like road noise in a car....but I guess it could have been from the bearings. Maybe I need a stethoscope!
Graeme
The tension/tracking adjustment on the top wheel is rattly and loose when there is no blade tension applied, so it's tricky to determine how much play in in the bearings.....but last time I had it all out on the bench, there was none discernible.
When I replaced the bears, there had been none discernible either, but I wanted to put a spacer behind the wheel to get its geometry right, so I removed the old ones to do this. They were obviously loose when you played with them by hand, hence I replaced them. I guess since there are two ballraces in there, any sloppiness (in one?) is kind of masked by the other....but that would not stop it from vibrating.
I have run the wheels (with and without a blade fitted) using a finger too, and I must say it all seemed smooth with no hint of lumpiness. With the blade fitted (but all the guides retracted and the wheel brush removed) there was some slight "frictional" noise from the top wheel which I couldn't identify, and I even checked the blade path to see if it was rubbing somewhere....but it wasn't. I concluded it must be the blade on the tyre....kind of like road noise in a car....but I guess it could have been from the bearings. Maybe I need a stethoscope!
Graeme
9fingers
Established Member
Hi Graeme,
I've been having a google around to find a picture of the machine.
I found the Mini-max website and looked at a few manuals and all seem to have a belt drive to the lower wheel and I think you said yours was direct drive so i guess I'm looking at the wrong machines.
I also found the forum for Minimax owners here
http://finance.groups.yahoo.com/group/MiniMax-USA/
you will have to register and maybe get a Yahoo ID - which does not hurt at all and I've not experienced much spam as a result over quite a few years.
Posting there might help but many readers will be 'merkins' many of whom do seem to speak a different language. Sweeping statement I know but I have had some pretty confusing circular discussions with folks from the other side of the pond.
I did wonder about the tensioning mechanism. If it is loose and incorporates a spring there is a perfect oscillation source. There is no needs for slackness especially with the tension forces involved in a band saw so this could be very well worth attention to remove all free play.
hth
Bob
I've been having a google around to find a picture of the machine.
I found the Mini-max website and looked at a few manuals and all seem to have a belt drive to the lower wheel and I think you said yours was direct drive so i guess I'm looking at the wrong machines.
I also found the forum for Minimax owners here
http://finance.groups.yahoo.com/group/MiniMax-USA/
you will have to register and maybe get a Yahoo ID - which does not hurt at all and I've not experienced much spam as a result over quite a few years.
Posting there might help but many readers will be 'merkins' many of whom do seem to speak a different language. Sweeping statement I know but I have had some pretty confusing circular discussions with folks from the other side of the pond.
I did wonder about the tensioning mechanism. If it is loose and incorporates a spring there is a perfect oscillation source. There is no needs for slackness especially with the tension forces involved in a band saw so this could be very well worth attention to remove all free play.
hth
Bob
GraemeD
Established Member
Hi Bob,
Well I appreciate your support and time. The Professional 32 is a fairly rare machine.....when I bought it I did a lot of searching and found almost nothing on it, certainly no pics. I guess it comes from a "pre-internet" age, and MiniMax have not put any older material on the web.
I wasn't aware of the MiniMax forum, so I will gladly give that a try. I used to have a Yahoo ID, so I'll have to see if it still works! In terms of dealing with our colonial cousins, I have to work with them on a daily basis, so they don't scare me! That said I know exactly what you mean.....our cultures are similar but on a slightly different plane......
The tensioning mechanism is an interesting area to look at....I had more or less ignored that so far. When no blade is fitted, it is quote loose and rattly, though it seems that way by design. Of course I could easily have reassembled it incorrectly somehow.....I will take another look tonight.
One can of worms I have not opened yet is the question of blade tension. Could I be under or over tensioning the blade? I've tried applying less or more tension and the vibration definitely changes (though not dramatically). Could this be an issue?
Graeme
Well I appreciate your support and time. The Professional 32 is a fairly rare machine.....when I bought it I did a lot of searching and found almost nothing on it, certainly no pics. I guess it comes from a "pre-internet" age, and MiniMax have not put any older material on the web.
I wasn't aware of the MiniMax forum, so I will gladly give that a try. I used to have a Yahoo ID, so I'll have to see if it still works! In terms of dealing with our colonial cousins, I have to work with them on a daily basis, so they don't scare me! That said I know exactly what you mean.....our cultures are similar but on a slightly different plane......
The tensioning mechanism is an interesting area to look at....I had more or less ignored that so far. When no blade is fitted, it is quote loose and rattly, though it seems that way by design. Of course I could easily have reassembled it incorrectly somehow.....I will take another look tonight.
One can of worms I have not opened yet is the question of blade tension. Could I be under or over tensioning the blade? I've tried applying less or more tension and the vibration definitely changes (though not dramatically). Could this be an issue?
Graeme
9fingers
Established Member
Hi Graeme,
I'm not surprised that blade tension makes a difference as it is another tuneable resonant structure but I doubt that it is the source of the problem.
Good luck
Bob
I'm not surprised that blade tension makes a difference as it is another tuneable resonant structure but I doubt that it is the source of the problem.
Good luck
Bob
GraemeD
Established Member
Cracking idea, Pete....I'll give it a go tonight!
G
G
jonny boy
Established Member
I use a minimax SC3 at work and while you would say the machine runs smoothly, if you look really close, there is a noticable vibration. Not enough to cause any problems while cutting though. I'm almost certain it's down to the weld in the blade, not that there's a problem with it, just that as the blade go's round and curves around the wheel, the weld as it just touches and leaves the wheels, is showing a slight difference in smoothness of rotation.
jon.
jon.
GraemeD
Established Member
Well, I did some more investigating after recent suggestions.....my theory has now changed, but I'm keen for any thoughts you guys might have!
I listened to the bearings using the long screwdriver method, and they seemed ok.....just a gentle whooshing sound, with no indication of rumble or vibration. Not conclusive, but a good start.
I then looked at all the moving parts in a bright light, with and without the blade fitted. It looks to me like the tyre on the upper wheel is not exactly round. The blade rises and falls slightly looking across the top of the wheel whilst in motion.....not be much, but I'm convinced it is visible.
This in turn would put an oscillation into the blade, which might excite a vibration in the frame. My current theory at least.
I tried to measure the irregularity of the tyre with a dial test indicator, but failed dismally, so unfortunately I can't put a figure on it. But it is visible....a fraction of a millimeter for sure, but visible.
Anyone have any thoughts on this? Moreover, anyone have any tips on tyre replacement? These are rubber bonded on ones, so does that mean a professional refit job?
All the best
Graeme
I listened to the bearings using the long screwdriver method, and they seemed ok.....just a gentle whooshing sound, with no indication of rumble or vibration. Not conclusive, but a good start.
I then looked at all the moving parts in a bright light, with and without the blade fitted. It looks to me like the tyre on the upper wheel is not exactly round. The blade rises and falls slightly looking across the top of the wheel whilst in motion.....not be much, but I'm convinced it is visible.
This in turn would put an oscillation into the blade, which might excite a vibration in the frame. My current theory at least.
I tried to measure the irregularity of the tyre with a dial test indicator, but failed dismally, so unfortunately I can't put a figure on it. But it is visible....a fraction of a millimeter for sure, but visible.
Anyone have any thoughts on this? Moreover, anyone have any tips on tyre replacement? These are rubber bonded on ones, so does that mean a professional refit job?
All the best
Graeme
That'll do it right enough.
A tyre replacement is not necessarily the answer, on some machines I've used, after the tyres were renewed it was standard practice to dress them to ensure even running. It is also, or was, a standard procedure after extended running had worn the tyres.
Roy.
A tyre replacement is not necessarily the answer, on some machines I've used, after the tyres were renewed it was standard practice to dress them to ensure even running. It is also, or was, a standard procedure after extended running had worn the tyres.
Roy.
GraemeD
Established Member
I hear what you say....in my case the tyres are quite thin (only about a millimetre or so at the end, slightly crowned in the middle). I don't know if they were much thicker when new, or if they were always like this, but I'm guessing that dressing them to make the wheel circular again is not an option. What do you think?
Graeme
Graeme
Till the teeth show that they might actually pass through the tyre it might be worth a try.
The other point is that with a tyre that thin replacement will be needed soon, so this might be a good time to dress the tyre and see if it cures your problem. It would be useful to you in the future to know.
Roy.
The other point is that with a tyre that thin replacement will be needed soon, so this might be a good time to dress the tyre and see if it cures your problem. It would be useful to you in the future to know.
Roy.
GraemeD
Established Member
Fair point....might as well give it a try. So, the burning question....how do I dress it? I have scrubbed the tyres previously with abrasive paper, but that won't true it. Presumably I need to hold the abrasive in some kind of fixed means, to true the wheel?
Graeme
Graeme
That's correct. What I do is glue a piece of glass paper to a piece of wood, but as you say, you will have to find a spot where you can brace one end of the wood against.
Can't help on that, you'll simply have find a suitable spot.
For the bottom wheel simply remove the band and run the motor.
Now here's where I get the 'slings and arrows' thrown at me, to do the top wheel the safety types will tell you to leave the band off, then duck telling you how to spin the wheel without it.
I leave the band on and work on the centre of the rim at the bottom. The tyre needs to be 'crowned' to have the band track correctly.
Roy.
Can't help on that, you'll simply have find a suitable spot.
For the bottom wheel simply remove the band and run the motor.
Now here's where I get the 'slings and arrows' thrown at me, to do the top wheel the safety types will tell you to leave the band off, then duck telling you how to spin the wheel without it.
I leave the band on and work on the centre of the rim at the bottom. The tyre needs to be 'crowned' to have the band track correctly.
Roy.
