Counterbalance jig?

[Lars Stole]

Not too long ago I experimented with a Stuart-Batty-style winged offset bowl and got my first taste of the force and vibration involved in turning a "light" off-balance piece. Last week's AAW sessions renewed my interest in multi-axis/eccentric turning. Given that I want to experiment with some more moderate sized pieces (e.g., 12-14" diameter platters and 12"x6" vases), I am looking into building a counterbalancing jig like the Kelton Balancer (www.kelton.co.nz/balancer.html). The Kelton Balancer retails for around $450, so I would like a cheaper solution for now. In Graeme Priddle's demo he mentioned he had heard of people attaching lead diver's weights as counterbalance, but that he didn't need to do this himself because he has a massive lathe bolted to 2 tons of concrete.

Has anyone had any success with making some sort of safe, configurable balancer like the Kelton Balancer? My current idea is to securely bolt two lead diver weights to the back side of a set of thick "cole" jaws in the unused holes; these could then be adjusted in/out/around to obtain a crude balance. I would also definitely screw the work piece to the plates rather than using the rubber stoppers -- this would avoid having a flying piece of wood at the same time as a newly unbalanced lathe. And I would make certain to never be in the line of fire of the weights. Altogether this strikes me as an inelegant and time-consuming solution compared to the Kelton. Perhaps it is also unsafe in a way I have not yet imagined. Comments? Other ideas?

 

[Bill Boehme]

The trouble with this idea is that while it is easy to statically balance something, it is far more difficult to dynamically balance it. On top of that, once you commence turning away wood, the object will no longer be dynamically balanced. If the piece of wood is flexing, even dynamic balancing isn't feasible (not that it ever was for woodturning). Overwhelming stiffness and mass of the lathe is a very practical solution. Static balancing will help to a significant degree in most situations. The Kelton system is for statically balancing a load. Another approach is to add a lot of balanced mass to the rotating load. This helps to decrease what is known to engineers who worry about that sort of stuff as the cross products of inertia.

I would think that your idea for balancing is too coarse. You need something that will allow for much finer tweaking. Check with the manufacturer of the Cole jaws to see how much load can be applied to the aluminum plates. If the weights are large and placed very far out on the plate, there will be a considerable shearing force on the two screws that bolt the plate to the chuck when running at high speeds. If I am not mistaken there is also a fairly restrictive maximum speed when using the Cole jaws which may not work well with off axis turning.

 

[John Lawson]

I did a quick back-of-envelope calculation, and if the weights were mounted 4 inches from the center and came loose, they would be going about 60 mph. I would find that prospect with something that heavy to be completely distracting. I calculated the kinetic energy for a one-pound weight, and I would be concerned for the integrity of my Cole jaws.

 

[wnnelson]

At the 1995 symposium at Davis Jerry Glaser had a rotation where he talked about a balancing system. I don't remember the name of it but it was a well know engineering solution to vibration in large equipment. It basically consisted of a steel arm extending out horizontally from a location close to the head stock ( mine was in the bed gap of a Powermatic 90). Mounted to the arm was a flexible steel shaft with a weight on the top. By adjusting the amount of weight or the height of the weight you could eliminate and I do mean eliminate any vibration. The limitation is it was only good for one set RPM. If you balanced it for 1000 RPM you could have a massively out of balance lump turning at that RPM and you could rest a water glass on the bed and not worry about the water splashing out. It worked amazingly great. I always considered how I could tie the height of the weight with my variable speed so it would work at multiple RPMs but never got the system off the napkin stage. Maybe some type of servo to turn a screw to raise and lower the weight.

 

[John Lawson]

I found this link in a thread from 2008 on this forum.

http://www3.sympatico.ca/3jdw8/antivibration.htm

 

[Gynia]

I did a quick back-of-envelope calculation, and if the weights were mounted 4 inches from the center and came loose, they would be going about 60 mph. I would find that prospect with something that heavy to be completely distracting. I calculated the kinetic energy for a one-pound weight, and I would be concerned for the integrity of my Cole jaws.

60 MPH? The RPM would be something like 2400 rpm. Why would the lathe be spinning that fast. You might want to check your envelope.

A 1 pound weight moving at 10 MPH is certainly a force to be reckoned with. Which I guess is the whole purpose of the balancer.

 

[John Lawson]

Ahh! I see what I did wrong. Still, I'm not volunteering to get hit.

 

[Charlie Knighton]

John, that counter balancing above headstock is very interesting

i had acquired some metal weights i was going to bolt to a mdf mounting board to counter balance multi axis outboard turning, even 50 rpm is scary if centered, not centered i find other things i need to turn. good thread and very timely Lars. thanks

 

[MichaelMouse]

Idea of the high counter is that it's starting right as the heavy side (center of mass) transits 12:00 going left. Reverse happens at 6:00. Keeping such a beast in "tune" would be a chore and a half. Fortunately, a close static balance and low rpm are able to take care of most problems as long as the lathe is rigid and firm to the ground.

Limit on my Cole jaws is 600, which was about what Ol' Blue could do at his lowest. Between a few bores to lighten where there was to be air and a few lead counters bolted on, it would do when I used it.

 

[GLENN ROBERTS]

Lars, be very careful with anything you design. Anyone who has turned these types of work soon realize that you need many things to be correct. Such as a very large lathe that is secured to the floor and has variable speed that can be slowed, sometimes to a snail pace. The securing of all the components must be suitable. Do you think the small screws that hold a cole jaw in place are suitable?? Also the securing of the piece.
And then you have the problem of poor cutting because your piece is turning slowly.
I mention this, for your own safety. Please take everything into consideration if you are thinking of off- center work.

 

[Bill Boehme]

I did a quick back-of-envelope calculation, and if the weights were mounted 4 inches from the center and came loose, they would be going about 60 mph. I would find that prospect with something that heavy to be completely distracting. I calculated the kinetic energy for a one-pound weight, and I would be concerned for the integrity of my Cole jaws.

60 MPH? The RPM would be something like 2400 rpm. Why would the lathe be spinning that fast. You might want to check your envelope.

A 1 pound weight moving at 10 MPH is certainly a force to be reckoned with. Which I guess is the whole purpose of the balancer.

I checked John's envelope and it is just fine. Using 4" radius and 2400 RPM, I get just over 57 MPH and 60 MPH is certainly close enough for back of envelope work. Your 10 MPH number seems rather suspect to me. Even so, a 10 MPH whach in the head with a 1 pound chunk of lead or any other hard stuff is dangerous.

 

[Don Geiger]

Counter balancing off center turnings

Dear fellow woodturners:

I've turned several pieces off center and up to 90 degrees off-axis. I've used everything from faceplates to 6 lb lead weights bolted through a back plate as counterweights. I've also turned several pieces off center and off axis without counterbalancing. One of the photos attached shows a piece I turned in 72 poistions and several were up to 90 degrees off axis. When doing this, I limit the speed and make a very diligent effort to stay out of the line of fire.

This is extremely dangerous work and in most cases is probably not worth the risks. You have to really think through the potential problems and check everything numerous times before turning on the lathe. I do not encourage venturing into this unless you have significant knowledge of physics and mechanical engineering. Even then, it is dangerous at best.


Don Geiger

 

[Bill Boehme]

60 MPH? The RPM would be something like 2400 rpm. Why would the lathe be spinning that fast. You might want to check your envelope.

A 1 pound weight moving at 10 MPH is certainly a force to be reckoned with. Which I guess is the whole purpose of the balancer.

I think that I might have misinterpreted what you were trying to say. I was assuming that you said that the spindle speed needs to be 2400 RPM. After further reading through everything again, I now think that you are really saying that in order to have a tangential velocity of 60 MPH, the RPM would need to be 2400 RPM.

In any event, I would heed the advice of Don Geiger and others about exercising extreme caution.

 

[Joe Greiner]

Within my vast repertoire of how to do things wrong, about 50 years ago I toyed with the idea of encasing liquid mercury in a donut for a self-adjusting dynamic balancer. A crude approximation, using fishing weights on strings, proved to exacerbate the problem, and I considered it invalid.

However, a recent search of the patent office database indicates that some folks have found success by similar methods:

Results of Search in US Patent Collection db for:
(((TTL/dynamic AND TTL/balanc$) AND self) AND centrifugal): 26 patents.

{the $ is a wild card suffix}

I examined only a few, but most of them seem to be devoted to computer disk drives, with very slight imbalance and low overall mass. Upgrading to the scale needed here would be several orders of magnitude, and involve lots of money - probably much more than the cost of the lathe; assuming you survive the experiments.

 

[hockenbery]

12-14 inch platters you can do quite nicely on an 8" or 10" steel faceplate.
turning some of the rim mass away before going off center will help. The mass of faceplate will reduce the vibration a lot. Go off center about an inch for the first one.


I think this under the category --- Don't try this at home.

Christian Buchard used to do massive sculptural turnings by mounting work to a ply wood disk.

he used screws and steel banding to attach the piece to the plywood and screwed small face plates onto the plywood disc for counter weights.

He used a 1/4 scraping bit in a massive handle to shape the wood. A catch with a big off center mass would be catastrophic.

I suggest you work with small pieces and go up in size as you gain confidence in your abilities. A large piece of wood can hurt you baldy. you have to have all the variables under control before putting a large out of balance piece lathe.

Be safe.
Al

 

[john lucas]

Terry Scott uses the plywood disc with webbing screwed over the work quite successfully. He screws all sorts of things to the plywood disc as counter balance weights.
I have only tried this a few times but had great success. I did have one failure. I didn't screw a weight down well enough and they come off at high velocity. Fortunately I was standing out of the line of fire and do so as much a as possible. I highly recommend you follow this procedure for any at risk work.

 

[Don O. Jr.]

As John said Terry Scott is the current master (in my opinion) of large off center turning. I don't remember his website but google search will find him. You might even want to contact him and discuss the issues he deals with on his larger pieces.

As always- SAFETY FIRST!!!

 

[john lucas]

I got interrupted earlier as I was posting. I meant to tell you that they had an extensive review and discussion on Fred Holder's More Woodturning newspaper about the headstock vibration reduction attachment. It was very enlightening. It's been a while but in a nutshell, you had to continually adjust the weight on the arm to compensate for mass removed from your turning. Several people tried run of the mill all-thread rod to make adjusting the weight easier but found that the vibrations and stress would cause the rod to break. I think a special threaded rod was called for but don't remember the details. You may be able to find back issues on Fred's site.

 

[Richard Lukes]

John, you are correct as to threaded rod not being used -at least in the first
device of this type which I remember seeing. Jerry Glaser demonstrated a device of this type at one of the Southern California Woodturning conferences which were held in Claremont,CA in 1986, 87,88 and 1989.
We had a rotation for new inventions and woodturning devices (I believe in
1989) at which Jerry showed a prototype. A very large piece of out of balance wood was on the lathe and the lathe didn't move at all when it was
turned on.

Jerry would not divulge details of the device at the time, but later made a drawing and showed me how it was made. He had a large cylinder-somewhat
like an upside down can-with a rod projecting from the bottom attached to
a rectangular bar which was probably 18 to 24" long and which in turn was bolted to the lathe bed next to the headstock. He used his son's weight lifting weights which were mounted on the top of the rod. The rod was some
kind of higher grade alloy (not threaded rod). The weights had to equal the
weight of the lathe. I believe the rod was heat-treated. The "can" was perhaps just a few inches above the horizontal rectangular bar.

My best recollection was that no one turned the wood at that time--the
object was just to show how Jerry's device worked. I believe the device would work regardless of how much wood was removed. I'm sorry I can't recall for sure whether wood was turned --I was nervous as I was demonstrating the Stabilax device for the first time.

Hope this is of some help to you.

AAW Member #: 1213

 

[Pascal Oudet]

Hello,

I have used counterweights many times in the past. they are usually directly screwed into the piece itself.
One idea I proposed many years ago to a chuck manufacturer, but he didn't really caught the ball so here it is for everybody to use:
on the back of your chuck, drill and tape 4 holes into the "crown" (this works for vicmarc, you need to remove the indexing plate, and proceeed slowly during taping because the body steel is really hard)
cut a thick plywood disk (12"), remove the center to that you can fit it over you chuck "nose", drill 4 holes and screw this "backplate" onto the chuck. now you can securely screw counterweights on this backplate. but as has been said, this is not dynamic balancing. it will just help you increase a little bit the speed (within safe limits) and have less vibrations, and you will need to readjust this many times as you remove more wood.
I have used this a lot, and it works very well, you don't have screw holes in your piece, it also works for spindle turning (multi axis heavy spindles) where the drive center is held in the chuck

Pascal

 

[GLENN ROBERTS]

As John said Terry Scott is the current master (in my opinion) of large off center turning. I don't remember his website but google search will find him. You might even want to contact him and discuss the issues he deals with on his larger pieces.

As always- SAFETY FIRST!!!

Don, I could not help but mention that without a doubt Alain Mailland has always been one of the masters of this work. Terry and perhaps others have just used the idea, after seeing how Alain works.
Another person worth investigating is John Wooller of Australia
www.johnwooller.com/index.html his turned work begs belief!!

 

[john lucas]

The first person I saw do this was Stoney Lamar. I read about his work about 25 years ago. Now where he got the idea who knows. He had been doing it for a good while then. I'm sure the idea of adding some sort of counter balance started a long time ago. Someone probably had a cobbled together angle iron lathe and was simply trying to tame it. Who knows. It is fun to re-invent things.

 

[Joe Greiner]

John, you are correct as to threaded rod not being used -at least in the first
device of this type which I remember seeing. Jerry Glaser demonstrated a device of this type at one of the Southern California Woodturning conferences which were held in Claremont,CA in 1986, 87,88 and 1989.
We had a rotation for new inventions and woodturning devices (I believe in
1989) at which Jerry showed a prototype. A very large piece of out of balance wood was on the lathe and the lathe didn't move at all when it was
turned on.

Jerry would not divulge details of the device at the time, but later made a drawing and showed me how it was made. He had a large cylinder-somewhat
like an upside down can-with a rod projecting from the bottom attached to
a rectangular bar which was probably 18 to 24" long and which in turn was bolted to the lathe bed next to the headstock. He used his son's weight lifting weights which were mounted on the top of the rod. The rod was some
kind of higher grade alloy (not threaded rod). The weights had to equal the
weight of the lathe. I believe the rod was heat-treated. The "can" was perhaps just a few inches above the horizontal rectangular bar.

My best recollection was that no one turned the wood at that time--the
object was just to show how Jerry's device worked. I believe the device would work regardless of how much wood was removed. I'm sorry I can't recall for sure whether wood was turned --I was nervous as I was demonstrating the Stabilax device for the first time.

Hope this is of some help to you.

AAW Member #: 1213

Sounds like this: http://www.woodworkforums.com/f8/vibration-dampening-system-81850/

 

[wnnelson]

Glaser Attachment

THe attached PDF is a article on the Jerry Glaser attachment. This is exactly what I used on my Powermatic and it absolutely works perfectly.

 

[john lucas]

I just read the article by Lynn Mangiameli and I'm wondering if the bar that hold the weights could be square or rectangular. You could rig up some sort of quick release on the top and bottom to make adjusting the weights easier and you would do away with what Jerry calls Stress risers waiting to break, when referring to threaded rod.

 

[Bill Boehme]

Having a "large mass on the end of a stick" does indeed reduce the overall shaking from a lathe, but you can't fool Mother Nature very much. There are a couple things that folks ought to know regarding this approach. The first is that it "tunes" the overall system to have resonance nodes that basically decrease the damping. This is somewhat OK when the system is tuned to a null point, but because of the lower damping, it means that more frequent "fiddling" will be necessary to tune the system back to a null point as the wood mass moment of inertia changes while turning. The other shortcoming is that this approach actually increases the radial loads on the bearings considerably. Whether this is significant is very dependent upon the particular configuration, but as a ballpark figure, the bearing radial load would be approximately doubled.

 

[john lucas]

Bill I have been playing with my hand mirrors made out of one piece of wood. consequently you have that handle flying around creating vibration. That's one reason I'm looking at this counter balance. I need to turn at quite high speeds because you are only hitting the handle once per revolution which in itself creates some vibration. I think if I could reduce the overall vibration I could turn at higher speeds which might make turning the handle (which is just a 1 blade propeller) a little easier.
does the radial load you are talking about involve the mass of the wood? Big mass, large radial load, small mass, small load.

 

[Bill Boehme]

Bill I have been playing with my hand mirrors made out of one piece of wood. consequently you have that handle flying around creating vibration. That's one reason I'm looking at this counter balance. I need to turn at quite high speeds because you are only hitting the handle once per revolution which in itself creates some vibration. I think if I could reduce the overall vibration I could turn at higher speeds which might make turning the handle (which is just a 1 blade propeller) a little easier.
does the radial load you are talking about involve the mass of the wood? Big mass, large radial load, small mass, small load.

Basically, just the portion of the radial load that is due to mass imbalance will be increased by using this "mass on a stick" approach ... and the momentum of the out of balance portion of the load is more a function of the spindle RPM than the mass. The handle of a hand mirror is not a very large mass so it doesn't seem like it would be too much of a problem. Even so, I think that it would be a good idea to first use some sort of counterweight to roughly balance out the mass and then use the "mass on a stick" to take care of the residual vibration.

 

[Charlie Knighton]

seems like if i built a u-shaped box open at one end that rests/bolted on the ways behind the motor and rises above the spindle, filled with sand bags, it would bound to help with outboard turning

any suggestions, the mdf that i mount the blank on has been cut back somewhat, started out 4 x 4 and it is more 3 x 3 now

 

[Bill Boehme]

Charlie, it looks like the sheet material pictured is MDF. I would consider using something else because MDF is not very strong for any structural load other than compression.

 

[Charlie Knighton]

added sand, lowe's july 4 sale @ $2 bag