If it's in the cards, I'd rather you do a GFM for a new Robust AB, instead! 😱
-----odie-----
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Lathe vibration detector ideas please!
- Thread starter Odie
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If it's in the cards, I'd rather you do a GFM for a new Robust AB, instead! 😱
-----odie-----
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If you have a second nickel, I'l be looking at the Robust at the symposium. Just bring it with you.
Odie
I understand what you are trying to do, but don't expect that eliminating vibration at the headstock will always mean less vibration at the workpiece. Headstock vibration at a speed might be the workpiece, but could also be bearings, drive belt, etc. In some instances you can reduce the headstock vibration, but it might increase the workpiece vibration. Load does factor in vibration that is seen.
I understand what you are trying to do, but don't expect that eliminating vibration at the headstock will always mean less vibration at the workpiece. Headstock vibration at a speed might be the workpiece, but could also be bearings, drive belt, etc. In some instances you can reduce the headstock vibration, but it might increase the workpiece vibration. Load does factor in vibration that is seen.
Mark Hepburn
Artist & Chef
"I'll buy that for a dollar" (Bixby Snyder, Robocop I)
Yes, I think you are absolutely right William.......😀
I am not aware of any method (within my capabilities and financial reach) that can measure vibration at the actual workpiece......so, I am limited to an attempt to measure it at the closest place.....the headstock. As you indicate, other factors could interfere with an exact measurement. I have been reading the vibrations through the lamp and my fingers for a number of years, though......and, I'm convinced that minor vibrations detected by these less-than-perfect methods, are a positive input to my overall "equation" in determining the best circumstances leading to the best, cleanest, most perfect cut. It is without question that major vibrations (from the actual workpiece) are definitely detected at the headstock, and elsewhere on the lathe, so the debate is likely whether minor vibrations detected at the headstock are a reliable source of the desired information. 😀
-----odie-----
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Leave your work piece chucked up and remove the chuck and work piece together and take it down to your local tire shop and have them rotate and balance the assembly on their tire balancer. You can remove the weights after you are done finishing the work piece on the lathe.
Five years ago, I started this thread, and built my own "vibrometer", thanks to the input here. I'm still using it every day, and on every bowl I put on my lathe. I consider it to supply me with valuable information for finding the best possible rpm for any given piece of spinning cross-grain wood on the lathe. This is a great help in finding the ultimate cut.....a cut that requires the least amount of sanding that is possible. When that objective is met, then the least amount of deflection from a perfect geometry is possible. This is not withstanding that each piece of wood will have natural warping during the course of turning it into a bowl. Depending on the species and grain pattern, this can be minimal, as well as major. This can't be avoided, but the changing of shape, due to aggressive sanding certainly can be minimized!....and, this is the focus of this thread.
Even though no fixed rpm is perfect, because the act of applying a tool to wood where the resistance to the cut fluctuates, it does get me to the best rpm that can be had. Other sources of detection.....fingers on the bedways, lamps on the headstock, etc., help in determining this ultimate rpm.
I envision an automatic variable speed lathe that is controlled by the detection of vibrations emanating from the cut of the tool while in progress. It would seem such an automatic speed adjustemt, according to the detected vibration might be possible in this age of computerized electronics.
-o-
(Note: The "ultimate cut" is not determined by the best possible rpm alone......although it definitely is an essential element. There are a number of other factors involved in finding it. These include a sharp tool, best tool for the cut, presentation, technique....etc,etc,etc.... 🙂)
Even though no fixed rpm is perfect, because the act of applying a tool to wood where the resistance to the cut fluctuates, it does get me to the best rpm that can be had. Other sources of detection.....fingers on the bedways, lamps on the headstock, etc., help in determining this ultimate rpm.
I envision an automatic variable speed lathe that is controlled by the detection of vibrations emanating from the cut of the tool while in progress. It would seem such an automatic speed adjustemt, according to the detected vibration might be possible in this age of computerized electronics.
-o-
(Note: The "ultimate cut" is not determined by the best possible rpm alone......although it definitely is an essential element. There are a number of other factors involved in finding it. These include a sharp tool, best tool for the cut, presentation, technique....etc,etc,etc.... 🙂)
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Your tool feed depends on the rpm, if the lathe slows down so should the feed controlled by you. This can be controlled by a cnc machine if you want that. What you propose is the first step in a cnc lathe design. Is this what you want? Stick with a human controlled lathe if you don't. I do not want to rain on your idea but this is what I think this idea could possibly lead to. Personally I would like to remain in the loop as I am sure you also do. That's what makes it personnel. Good luck on your quest for the best vibration detector.
Hello Stu......The "vibrometer" photo I posted in post #88 does work, and quite well for finding the best static rpm, and that is very important information. Whether a CNC controlled rpm, according to vibration detection is possible, or useful.....well, that is yet to be determined.
As far as feed rate determined by the human element, that is something that remains unchanged. Keep in mind that the feed rate one uses is also determined by the distance to the centerline of the spindle. The closer you get to the center, independent of the rpm, the feed rate changes, due to the circumference measurement that changes according to the radius distance to the centerline.
-o-
Quite possible. The things to determine would be if you want the lathe to speed up or slow down when the vibration threshold is detected, what the threshold is and how much you want the speed to change.
- I would think rather than using a fixed number for a vibration level you would to use a rate of change, how much the vibration increases in a short period of time.
- First thought is you want the speed to slow down to go back to a previous lower level of vibration, but if the vibration is from a resonance you may actually want to pass through it to get smoother. Resonance requires at least a 10% speed change, so is/when is this tolerable?
- If not a resonance, is the simpler solution of a 10% speed change up or down always tolerable? If not, what would be preferred?
At this you are stepping beyond a bare bones VFD to one that ties to a PLC (programmable logic controller) or you computer to take care of the logic. The drive will also need to accept an input for the PLC to communicate back and tell it what to do.
As mentioned, there are production machines already doing this. A simpler solution could be similar to what you already have, a vibration transducer that provides a readout so you can see the increase and adjust the speed yourself.
- I would think rather than using a fixed number for a vibration level you would to use a rate of change, how much the vibration increases in a short period of time.
- First thought is you want the speed to slow down to go back to a previous lower level of vibration, but if the vibration is from a resonance you may actually want to pass through it to get smoother. Resonance requires at least a 10% speed change, so is/when is this tolerable?
- If not a resonance, is the simpler solution of a 10% speed change up or down always tolerable? If not, what would be preferred?
At this you are stepping beyond a bare bones VFD to one that ties to a PLC (programmable logic controller) or you computer to take care of the logic. The drive will also need to accept an input for the PLC to communicate back and tell it what to do.
As mentioned, there are production machines already doing this. A simpler solution could be similar to what you already have, a vibration transducer that provides a readout so you can see the increase and adjust the speed yourself.
Five years ago??? Always amazes me how time flies. I'm still using the first MK1 Mod2 shown here.
www.aawforum.org
Changed the rubber bands a few times but haven't come up with any improvements.
Maybe a new color for 2024, or a gluten free option.
Or change the name to See-n-See Vibrometer?
odie, I am glad to hear you still find it useful, I really enjoy following your quest.
Lathe vibration detector ideas please!
I am looking for ideas for devices, or inventions for detecting minor vibrations on the lathe. The purpose is to adjust the rpm to where the least possible vibrations are present. Right now, I use my fingertips on the lathe bed, plus there is one long neck spot lamp that consistently gives me...
Maybe a new color for 2024, or a gluten free option.
Or change the name to See-n-See Vibrometer?
odie, I am glad to hear you still find it useful, I really enjoy following your quest.
Hey, me too, Clifton. I changed out the rubber bands to lighter duty bands that are a bit more sensitive to the fine vibrations I'm attempting to zeroing in on.
The photo I posted is the same one I used earlier in this thread, but it's the same vibrometer I made up back then....only difference is the bands are smaller, and it's now showing some wear from continual use.
-o-
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Is lathe vibration the biggest concern or is the tool deflecting away from the work twice in every revolution of a flat grain workpiece a bigger problem? My theory is the action of this turning against the grain deflects the tool resulting in micro tear outs in the workpiece. I wonder if using weighted tools in the 50 to 100 pound range might result in dampening the tool deflection resulting in better quality turnings. Of course, you'd have to eat your spinach to get arms like Popeye.
I've noticed tool rigidity in CNC and automatic lathes (and even OT machines) give far better quality turnings than hand held tools. Better quality turnings mean less sanding.
I've noticed tool rigidity in CNC and automatic lathes (and even OT machines) give far better quality turnings than hand held tools. Better quality turnings mean less sanding.
May well be available in the cnc arena. Conceptually not difficult - a 2 axis accelerometer tied into an existing electronic speed control. Software for calibration of signals and sensor to speed control function, signal conditioning parts, etc.
Not sure about 4 wheel “cages”, but many motorcyles employ IMU’s (inertial measurement unit) for lean sensitive ABS, traction, and wheelie control. The IMU is connected to the ABS control for pressure modulation, and ECU (engine control unit) to close the throttle plates to reduce power - very sophisticated. 2 of the 3 axis of the sensor would be employed. Very doable, for the right person, and as mentioned may already exist in the cnc world.
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I have incorporated a 3-axis accelerometer into the the controller of the fully-remote control VFD integration I posted a while back. My idea was not to find the "sweet spot" but to detect any massive changes as a result of workpiece failure or operator error (turning on the lathe a full speed with an unbalanced load) and shut the lathe off. In theory, this could be used to find this sweet spot, but it would require much more carefully consideration of sampling rate, sensor positioning, etc. I found that the programming these things is definitely not totally straightforward!
Hi Odie, I'm intrigued by your vibrometer. Can you help me understand how to attach one, similar to yours, to my headstock? I agree with Clifton. #92 🙂
Howdy Larry.......I'm using strong magnets to hold the vibrometer to my headstock. That way, there are no modifications required, and it can be repositioned as desired. 🙂
-o-
Thanks for responding, Doug.....and bringing up several issues concerning the quest for the "perfect cut". 🙂
No, certainly not! ..... Finding, and then eliminating Inherent vibration due to rpm selection, is only one small piece of the total equation for finding the perfect cut.....but, it is an important consideration, nonetheless. Besides the best rpm, there are other components.....like tool selection, technique, proper presentation, sharpness, feed rate, and something that many other turners seem to not comprehend at all (and subsequently disregard).....and that very uniquely important component is called..... "spiritual turning". *
*(Spiritual turning is an element of human sensual perception, and thereby transforming that information into a reactive physical adjustment of things like presentation and feed rate of the turning tool. This is according to how your perceptive senses tell you the quality of the cut is responding to small in-progress adjustments.)
It would be interesting to find out if a 50-100# tool could/would result in an improvement in the quality of the cut. Personally, I've found cases where a bigger heavier "standard" tool will result in a better cut, so the assumption may have merit. As you suggested though: Tools that heavy are out of the question for us mere mortals! Another consideration is if the spinning wood itself is vibrating (even very slightly), there is nothing a heavier tool can do about that. I would think that (and there's room for speculation on this) the only thing a heavier tool can do better than a lighter tool, is to prevent oscillation due to fluctuations in resistance to the cut.
-o-
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Along the line of good turning practice I've favored rounding blanks on the bandsaw rather than turning from square to round. In metal turning that's considered an interrupted cut. Interrupted cuts are hard on metal cutting tools. You have a short cutting followed by a bang as the next corner hits the tool. I have no idea if an interrupted cut in wood is hard on woodturning gouges, possibly it prematurely dulls them? But I can't imagine it doesn't have an effect.
For sure turning from square to round creates far more dust and shavings than 4 band sawed off corners.
I suggested this a while ago with at least one poster saying bandsawing takes too much time compared to turning. My thought is it's kinda a macho thing like "I don't need no stinkin' bandsaw".
For sure turning from square to round creates far more dust and shavings than 4 band sawed off corners.
I suggested this a while ago with at least one poster saying bandsawing takes too much time compared to turning. My thought is it's kinda a macho thing like "I don't need no stinkin' bandsaw".
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In general a bandsaw’s product is a cut and sawdust. Most turnings produce shaving and a round surface.
With green wood there is virtually no dust. Dry wood some dust.
Interesting question!
A lot of my turning is interrupted cuts. Natural edge bowls, bowls from a 1/2 log, Spindles from square stock, multi-center turnings, multi axis turnings all have lots of interrupted cuts.
I’ve never noticed it dulling tool faster than uninterrupted cuts. I know the air part of the cut doesn’t dull the tool. Having extra entry cuts might.
Just seems inconsequential. Cutting dirty bark definitely dulls tools quickly.
Depends on the blank size and weight and the object.
Sawing corners off square spindle stock I never do. Sometimes you need the square as an element.
But 4 passes to cut the 45 degree corners is about 4 times longer than it takes to cut from square to round.
NE bowl from a 1/2 log. Small I don’t bandsaw big ones I do.
An 8” x 6” blank can be turned easily without band sawing
A 16x12 blank I cut the ends round on the bandsaw with a 16” round guide disc.
Or it's just what they find efficient.
never would have suspected that. Fascinating.
Odie, maybe you could find one of those old reed tachometers we used in the wayback to detect and isolate drive train vibrations. With a little bit of arithmetic, you can pinpoint the actual component responsible for the frequency of the vibration. The toughest ones are those that come-and-go with the phasing of two components!