Musing about movers and shakers: quieting them with harmony

I have turned a bunch of stuff off center that made my lathe shake, even though it's bolted to 20,000 lbs of concrete, and did something like what JRJohnson did. I have a bunch of lead diving weights that I melted down and use to balance the load, however I first try to balance by bolting to my waste block. I would caution against using the tailstock if you can avoid it only to reduce the dynamic load on the headstock bearings.

Even if it's statically balanced, there will be a large load on the two headstock bearings in opposite directions if the headstock and tailstock have opposite but perfectly balanced loads. It might not amount to much turning at low speeds, but 2x speed is 4x the load, and just think: You're increasing the load on the bearings and the housings and bolts that hold them in place when balancing on opposite ends of the headstock, rather than eliminating the dynamic load by static balancing at the same end of the spindle.

I did a quick calculation on a theoretical lathe with 12" between bearings and 20" between head and tailstock (= 4" bearing to weights): the dynamic cyclic bearing loads with 60 lbs unbalanced (equivalent to about 18 lbs@8" from center at 240 RPM and increases proportional to the SQUARE of the spindle speed) are 20 and 80 lbs, and this increases to 100 lbs on each bearing if you balance at the tailstock. Having bearings farther apart from each other makes it a little nicer: unbalanced bearing loads if the bearings are 24" apart (same 4" between bearings and weights) is 10 and 70 lbs, static balancing at the tailstock would make it more like 80 lbs steady cyclic load on both bearings.

So it doesn't double the bearing load, but it does increase it significantly. Anything that can make the whole lathe move on the ground, I don't want that much load constantly going through my bearings and the bearing races & housings. It's going to fatigue and break them eventually.

If you balance on the same end of the spindle by putting weights on the wood, the unbalanced loads on the bearings will disappear (excepting the weight of the wood&metal due to gravity, which will not change with spindle speed).

"professional plate-spinners" [1]

[1] The Modern Conjurer, C. Lang Neil, 1947 This book includes a section on the technique.

Arch

I just found this website, and this was the article I was referring to before, something one could try out if needed.

Have fun and take care Leo Van Der Loo

Arch wrote:

(Try this again), I just found this website, it has the article I was referring to, something easily made if you have a need for it.

Arch wrote:

Thanks Leo. I may have to try something like this with the Shopsmith. Do you know if the effect is linear, eg 5X mass for 3" height?

Lobby If you try it, you tell us, then we all know, , no I don't have a clue how well this works, and the amount of stilling swaying forces by increasing the distance away from the rotating center, what I do know is that pipes will bend and bolds shear off etc, if you go past their limit.

Have fun and take care Leo Van Der Loo

Lobby Dosser wrote:

Basic lever calculation. One lifts four at four to one.

Cute idea, but misguided. Easy to calculate a static solution, but this is supposed to counter an off-balance dynamic load, which is a bit different. When the stand and components are rigid, solution is simple.

It's where the load comes past 12:00 where the additional acceleration begins. At 9:00 it has maximum leverage, but eight is probably best combined for leverage and acceleration (squared, remember). Putting a weight straight up in the air is not going to be as effective as hanging it at 3:00.

Imbalance wants to lift the rear legs off the ground. That's where you secure things by putting weight low and behind or screwing to the floor, otherwise known as the big weight. You take the thrust forward by extending the footprint beyond the swing.

Friend of mine was having problems with vibration on a mustard monster. I suggested he wedge a touch under the front legs to shift the CG aft. Oddly enough, it helped. Same principles.

As soon as you have a point of elastic transfer, your calculation must shift and do a whole new set of vectors.

This is not a lever. The author is misunderstanding his system. To be a lever the pole must have a fulcrum. There is no fulcrum, just a load at both ends of a pipe. What I believe is happening here is the length of the pipe and the mass are acting as a mass spring damping system, and the action of the weight is not multiplied as you move out along the pipe. the length of pipe simply acts as a damping spring to reduce vibration. The unbalanced loads on his lathe and bearing are still there and things will still vibrate loose and fatigue and break.

Thanks to Leo we now know of someone with personal experience with this approach to vibration. I've invited John to discuss what he has learned _using_ his device and to offer any advice and further discussion he wishes, including general woodturning topics. Maybe Leo can use his charm to persuade a fellow Canadian Immigrant. I know he would be a welcome and appreciated addition to rcw.

Thanks Mark, for suggesting another way to look at the problem. I had dimly seen an analogy to resistance in a resonant LC circuit, but hadn't thought of a damped spring mass system. My knowledge re the physics of damped spring mass systems (or any other) is too limited to follow up on this classic physics example. I hope you will explain a bit more. What are the actual physical characteristics of our lathe's annoying & dangerous vibrations. I know mine shakes and that's about all I really understand. except as with the wood drying problem, I think there must be different ways to skin a cat. (sorry Ecnerwal) :)

Turn to Safety, Arch Fortiter

Hello Arch,

I've just placed the article that Lyn wrote on the "Glaser Tunable Vibration Absorber for Lathes" on Lyn's page at my domain site. This is the one that you remembered, I'm sure.

Fred Holder

I was asked to enter the fray as it were about lathe balancing and on my site I have a balancing system for a homemade lathe. These things change and I no longer have the CTC lathe so do not use a weight mounted high. Instead I use electronic speed control and find that this is better for turning out of balance wood. (For wood that will remain out of balance I use counterweights to balance the mass on the lathe.) The electronic speed control allows the turner to start at zero RPM, thus large pieces can be mounted and turned and once they have their high spots turned off the speed can be increased to allow faster turning. I do still use my outside lathe but quite frankly the speed control is so much more convenient that I only use the outside lathe for relatively small faceplate turning. The counterweights mounted high above the spindle do work, but they are dependent upon the base being firmly anchored to the ground too and on the tightness of the bearings. (Sloppy bearings are the worst thing for turning as the wood will move as the tool is placed against it, causing all kinds of problems) I actually found that the base of the lathe was wobbling back and forth while the massive weights I have mounted high up are sitting relatively still with a out of round piece turning in the lathe. There is additional stress on the bearings and I find that I have to tighten the bearing races on the pillow blocks every now and again. Fortunately the pillow blocks have this option as some do not.

Many thanks, John. Please continue to participate, but I guess we can put this idea to bed and let it sleep for a while. :)

Turn to Safety, Arch Fortiter

JD, I gotta stop by your shop someday and see you turning at zero rpm. Isn't that called 'carving?' LOL!

Dan

Hi Dan

Come to think of it, I always seem to START at 0 rpm, it just ramps up fast after that. :>))

Have fun and take care Leo Van Der Loo

Dan Boll> > The electronic speed control allows the turner to start at

It does the job safely. I cut blanks with the chainsaw, but not after I bring them in from the woodpile. After that it's round on the bandsaw and nibble for balance.

All this talk, and no one has mentioned flywheels? Less weight applied at a greater distance will static balance, and the mass of a flywheel smoothes a lot of things out.

Hi John

I just did the same thing, I had a piece of cherry, cut from the side of a log, it was the base of a larger branch, had been sitting in the shop for at least a year, and started to show signs of splitting, so it was either use it or chuck it :>)) (pun intended), but the shape made it so that band sawing was not an option, so after measuring I drilled it for the wood worm screw and put it on my lathe. After having it swinging around and trying to cut the dry end grain, I thought sawing a lot of the one sided lump off was a good idea, locked the lathe and cut most of the lump off, sure made a lot of difference, I just finished turning it, leaving the bark on partially on the bottom side and having a nice oval top made for a real beauty IMO. Of course as always you got to be careful and know what you're doing, when working with power tools and things that cut.

Have fun and take care Leo Van Der Loo

JD wrote: