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Lyn J. Mangiameli
 
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Default Kelton Balancer Review Draft--long

This is a near final draft of the Kelton Balancer Review that will be
published soon in Fred Holder's periodical More Woodturning. The print
version will include a photo and be better formatted, but otherwise
pretty much the same.

Kelton Balancer

Woodturners who choose to make medium or larger bowls and hollow forms,
regularly must deal with out of balance turning blanks. Frequently the
imbalance occurs because the initial turning blank is out of round
because it would have been awkward or impossible to true the blank fully
by means of chainsaw or bandsaw prior to mounting. Even with a perfectly
round blank, there is sometimes unbalanced mass. This most often happens
when the blank contains wood of widely different density, such as when
light sap wood is on one side of the turning while the remainder is
composed of denser, heavier heartwood. It can also occur when voids or
spalted areas result in uneven distribution of mass within a turning.
Finally, there are times when woodturners deliberately mount otherwise
balanced wood off center, to achieve eccentric shapes.

A while back Don Watland provided a good description (see Watland,
4/24/02 in the archives of rec.crafts.woodturning) of what occurs when a
turner mounts a good-sized, unbalanced chunk of a log on a lathe. In
Don’s example, he used an unbalanced log big enough to turn a 14" bowl,
specified the unbalanced portion of the log to weigh 5 pounds, with the
weight distributed on one side somewhere near of the outside edge of the
log, and set up the situation such that the log would be rotating at 500
rpm. Put more abstractly, his example was equivalent to a balanced
cylinder, to which was added an additional 5 pounds of weight located 7
inches away from the center of the spindle. Putting the 5 pounds of
mass, rotating at 500 rpm (the equivalent of a rotational speed of 52
radians/sec), at a radius of .58 feet into the equation for the
acceleration of an oscillating system, gives an acceleration of 1,577
ft/sec2.

To quote Don directly, “This circular motion means that hunk of mass
moves back and forth in a horizontal plane, while going up and down in a
vertical plane, at a clip of 8 1/3 times per second. It must stop moving
one way (back, away from the turner), and rapidly accelerate the other
way (forward, towards the turner), twice for each of the revolutions at
that rate I just mentioned. For comparison's sake, I'll add that the
acceleration due to gravity of a falling object is 32 ft/sec2. Since
force is equal to mass times acceleration, the oscillating motion of
that 5 pound chuck of unbalanced wood, sitting 7" off-center, while
spinning at 500 rpm, will become a reciprocating horizontal force equal
to the weight of 250 pound person (first backwards, then forwards,
vibrating at a rate of 8 1/3 times each second).”

Imbalances in this range are not uncommon when working with larger
turnings, thus it is of little surprise that most turners have been
forced to deal, in one manner or another, with significant vibration due
to such translational forces (this being but one of several different
sources of vibration). Of course the magnitude of the translational
forces is reduced by lowering the rotation speed, which is why we often
begin roughing out a blank at some of the lowest speeds our lathe makes
available. Yet, as every turner knows, this is only effective to a
point, for if the imbalance is great, even the lowest practical speeds
still result in considerable vibrational force, not to mention that low
speeds pose other, different problems of their own.

The other common approach to dealing with large vibrational forces is to
increase the mass against which they operate. In practical terms, a way
to keep one’s lathe from dancing about the floor is to either make the
lathe (and its attached stand) much heavier than the forces that can be
generated by imbalance—which is no mean feat when you consider how the
combination of even modest imbalances and speeds can result in
substantial forces—or to couple one’s lathe solidly to a substantial
floor through a rigid stand (in essence coupling these forces to the
ultimate available mass, the Earth itself). These traditional approaches
can be quite effective when it comes to constraining lathe movement, but
they really do nothing to reduce the vibrational forces which arise from
the imbalance and are then imposed on the lathe (e.g, the spindle shaft
and bearings, headstock casting, stand) and attachment devices (i.e.,
chuck jaws and slides, faceplate screws, live center, etc.).
-
There are additional valid ways of dealing with a large out of balance
piece of wood. Perhaps the most effective of those, though one less
commonly utilized by woodturners, is to redistribute the center of mass
of the turning blank so that it coincides with the rotational center of
the lathe (i.e, the spindle), thereby bringing the turning blank into
balance. If it wasn’t that one is trying to turn (cut) the surface of
the mounted wood blank, a turner could just screw some weights opposite
to, and of equal mass to the “heavy side” side of the blank, thus
removing the imbalance. This would be somewhat similar to how a motor
vehicle tire is balanced. For turners, though, applying such
counterbalancing weight is not nearly so simple. Even if there was not
the issue of the weights getting in the way as wood is being cut, there
would be such troublesome issues as making sure the weights would be
solidly secured (the last thing one would want is to have a chunk of
lead or other weight come loose and become a projectile), the depth of
penetration into the potential usable surface of the blank by the
attachment device, and being able to readjust the amount of
counterweight as the roughing out progresses and likely reduces the
original imbalance.

Fortunately for turners, Kelton Industries (the same company which bring
us the McNaughton Centre-Saver and Kelton Hollowers) offers a device
that conveniently, effectively and safely provides a means to apply
counterbalance immediately adjacent to the turning blank. Consistent
with its purpose, the device is simply called the Kelton Balancer. The
Kelton Balancer at first sight appears to be a large, heavy flywheel
mounted to the front headstock spindle and to which the log is then
mounted via a faceplate or chuck. [see photos] A closer look reveals the
Kelton Balancer has two massive movable weights located inside the rim
which allow one to redistribute the mass of the combined
Balancer/turning blank system so that rotational balance is achieved.

Detailed examination reveals the Balancer to be composed of essentially
four subsystems:
1. An internally threaded mounting block that bolts to the flywheel body
and allows the Balancer to be fitted to a variety of standard spindle
types (custom threadings are available by special order). This mounting
block can also be ordered with set screws to lock the Balancer to the
lathe spindle (standard for Oneway threading).
2. A 10 inch diameter, over 20 pound, cast steel flywheel body that has
channels to hold movable weights. The flywheel has indexing marks
provided at 30-degree intervals on the headstock side of the body to
assist in locating and recording weight positions.
3. Two circumferential-position, adjustable, 6 pound, mild steel
counterweights. These weights fit in an inner radius channel and are
retained in position by hex-key screws through their radial axis that,
when tightened, forces them against the outer retaining ring of the
flywheel body.
4. An externally threaded spindle that attaches in a recess on the front
side of the Balancer flywheel body with six bevel-countersunk hex-key
screws. This spindle can be chosen to replicate your lathe spindle size
and threading, or you can order a different (perhaps larger) size
spindle. M33x3.5 spindles (the standard Oneway size) come with a spindle
groove for a chuck or faceplate restraining set screw; a groove for
other spindle sizes is available by special order (and I recommend it).
Traditional faceplates and chucks, as well as specialty devices like the
Kelton Angleplate or an eccentric chuck (Kelton also makes an eccentric
plate that can combine directly with the Kelton Balancer and has its own
spindle).

As the Balancer is quite heavy, you are going to want to mount the
Balancer onto the lathe spindle first, then mount your turning blank to
the Balancer spindle. I generally use a four or six inch, cast iron
Oneway faceplate when working with a large imbalanced piece, and a three
inch steel faceplate or chuck for more modestly sized turning blanks—all
these work well to attach work to the Balancer.

It is a good idea to start with the counterweights directly opposite of
each other for an initial zero balance. Only this way can you
effectively judge just how much imbalance you are dealing with, and
where it is located in your turning blank. You can use the indexing
marks on the back of the body, but generally a quick eyeball is more
than sufficient to achieve adequate opposition. The balance weights are
unlocked for movement and later locked into position by loosening, then
re-tightening a hex-key screw whose head is conveniently located at the
outer periphery of each weight.

By locating the Balancer weights in their neutral opposition, and
releasing the lathe spindle to freely rotate, the out-of-balance (or off
center) side of the turning blank will rotate down due to gravity. The
greater the imbalance, the faster the turning blank will rotate its
heavy end to the bottom. One now unlocks and begins to shift the weights
in the back of the body upward, away from the heavy side. It is wise at
this early stage to try to underestimate the amount needed, rather than
overshoot the adjustment–after a few times using the Balancer, one gets
a good feel for how much movement is required. Lock the weights in
place, then let the turning freely rotate again. Unless you just
happened to achieve perfect balance from your first adjustment (an
unlikely event), a new heavy side will swing to the bottom, though
likely more slowly this time. Through a process of trial and error,
repeat this procedure, making smaller adjustments of the weights until
there is no tendency for one side of the rotating mass to rotate down.
After a little experience with the Balancer, it usually takes only a
couple of adjustments to achieve adequate balance (depending on how
perfectionistic you are about it). Once balance is achieved, snug down
the weight locking screws to prevent any movement and loss of balance
during turning. This is an important step, as any shifting of the
weights when the lathe is at speed could be most disconcerting, though
fortunately I have never had the experience.

Now it is possible that the imbalance within the turning blank is so
great that the twelve pounds of weight provided by the Kelton Balancer
will be insufficient to achieve an adequate counterbalance. This will be
apparent when balance cannot be achieved (that is, one side of the work
will continue to rotate down) even when both the counterweights are
located fully opposite the heavy side. This will be a rare instance as
this represents an unusually large amount of imbalance, but it is
possible with very large turning blanks, or heavy turnings deliberately
mounted off center. Kelton suggests that when balance cannot be achieved
by the balancing weights that you do not operate the lathe. I don't
blame them for their conservative stance, but I find this unnecessarily
cautious. After all, we have been turning unbalanced wood for years. How
much imbalance you can get by with is a judgment call, but I would
suggest you accept about 50 percent less than you would have considered
had you not had the Balancer in the system. I suggest the reduction
because the imbalance is now located farther from the headstock, due to
the intervening Balancer.

During the course of turning, despite near perfect initial
counterweighting and resultant balance, imbalance can return as a result
of at least three different circumstances. The first is that during the
normal course of turning, the inherent imbalance in the wood blank is
reduced, and the initial settings of the counterweights now excessive.
Should such degradation of balance occur and vibration becomes
troublesome, it is quite easy to stop the lathe, shift the weights a
modest amount, check for balance, make any further readjustments, and
return to turning with a smoothly running work piece. This may need to
be repeated several times if the initial imbalance was great and the act
of turning will result in further removal of the wood causing the
imbalance (as is commonly the case with an on axis bowl or hollow form,
but usually not required more than once, if at all, for an eccentric
turning). Is this a minor hassle? Yes it is, but a welcome hassle if it
makes possible the smooth turning of a work piece that might otherwise
not have been feasible to turn. To insure particularly smooth running,
one can stop and check the work piece periodically for a heavy side and
rebalance even before any vibration is detected.

Two other possible ways for imbalance to develop are usually unforeseen
and sudden. In over a year of using the Kelton Balancer, I have never
encountered either, but they do represent potential problems. I already
made reference to the possibility of weights coming loose, shifting and
generating unexpected imbalance. The other situation is to have a work
piece which required major counterbalancing break free of its mounting
such as following a bad catch. This could result in a “naked” balancer
with up to twelve pounds of off-center weight whirling about at
relatively high speed. So make sure your adjustment locking screws are
tightened down and that your wood is securely mounted (a reason I tend
to prefer faceplates).

This brings us to the issue of speed. Kelton recommends the Balancer be
used with
lathes capable of near zero speed and capable of soft start and stop.
They also recommend that initial startup should be done from near zero
speed with speed gradually increased to insure that the work is safely
balanced and secured (basically the standard procedure for dealing with
any large turning blank, regardless of whether or not one is using a
balancer). Much of the reason for slowly increasing and decreasing speed
is that the rotational mass of the Balancer is considerable (it being
almost 40 pounds for the Balancer alone) not to mention the weight of
the work piece, thus the inertial load on one's lathe drive mechanism is
considerable.

I use the Kelton Balancer on a Nova DVR. With my older DVR, I can
program an extended ramp up in speed to occur over several seconds, but
am limited to a 250 rpm minimum speed (later DVR's go down to 100). I
have never had a problem with these settings, indeed, the Kelton
Balancer is particularly valuable when used with lathes like the DVR
where you can't reduce the rotational speed to the extremely low, below
100 rpm, levels desirable when turning out of balance pieces. Unlike
most lathes, my DVR is almost free wheeling when power is cut. On the
DVR, the combined mass of the Balancer and work piece can result in
quite a flywheel effect, and result in the work piece spinning on quite
some time after power is cut. Having a handwheel to help slow the work
piece is very desirable.

You can choose to utilize the Balancer until your turning is completed.
This will be standard procedure when deaing with off center forms, as
well as those where even in the nearly completed work piece, there
continue to be sapwood/hardwood differences in density that cause
lingering imbalance. Other times you may wish to remove the Balancer
from the system after the wood comes into natural balance after roughing
out. Removing the Balancer as soon as possible may be desirable with a
work piece that will be smaller at the mounting end and the 10 inch
diameter of the Balancer may get in the way; it is also helpful to
remove an un-needed Balancer when frequent stops and starts will be
required. Again, because of weight, it is best to remove the work piece
from the Balancer first, and then remove the Balancer alone from the lathe.

The forces involved can cause the faceplate/chuck to become very firmly
seated on the Balancer, and the Balancer to be firmly seated on the
spindle. It is not very difficult to remove even a well tightened
Balancer from the lathe spindle because there is so much to grab on to
help with removal. However, it can be more awkward to get one’s
faceplate/chuck to come free from the Balancer without the Balancer
loosening from the lathe. Indeed, sometimes this has become a major
difficulty with my early version of the Kelton Balancer, as it is
difficult to restrain the Balancer and remove a stubbornly seated
faceplate at the same time. Later versions of the Balancer should now be
fitted with a couple of holes in the periphery that will allow use of a
Tommy bar to restrain the Balancer during work piece removal. One of the
advantages of using a Oneway faceplate is that it too comes with sockets
to take a Tommy bar. Leveraging both the Balancer and faceplate Tommy
bars against each other makes dismounting a workpiece a simple task,
even when the faceplate has become firmly tightened to the Balancer’s
spindle.

I've taken a lot of time with the above descriptions because balancers
of this nature are fairly unfamiliar to most woodturners (though they
are well known to many metal machinists). In actual use the Kelton
Balancer is actually uncomplicated to set up and use. I find it to be
very well engineered and robust. The Balancer just makes so much sense
by reducing the forces at the source, rather than having the lathe and
stand attempt to absorb them downstream. It will allow some turners to
turn wood pieces they otherwise would not have dared to, and to turn
other pieces at speeds higher than could otherwise have been safely
achieved. What makes it particularly appealing is the Balancer’s
combined ability to extend the range (and type) of possible work pieces
that can be fitted to your lathe, as well as ability for you to work
more smoothly and safely. I use mine quite frequently and would not care
to be without it when turning large pieces.

You can find out more on the Kelton Website.
http://www. kelton .co.nz./

The Wood-Tradesman is one of the few stocking dealers I am aware for it
in the US. http://www.thewoodtradesman.com


SIDE BAR
In the main review, several times I have referred to the main body of
the Kelton Balancer as a flywheel. Kelton doesn’t promote their balancer
as a flywheel (and it certainly is much more than a flywheel), but it
does function as one.

Leo Lichtman has discussed the significance of lathe mounted flywheels
in a past post on the rec.crafts.woodturning newsgroup, and I shall
provide an slightly edited version of his comments he
“The question about whether revolving weight on the spindle shaft
smoothes out vibration does not have a simple answer. Adding spinning
weight to the spindle shaft increases the rotational inertia–sometimes
this can carry the wood past a potential catch, and sometimes it can
make the disaster worse.

If there is some kind of pulsation or unevenness in the drive, the added
rotational inertia (called "moment of inertia"), helps smooth it out.
That is what flywheels do. I have never seen a lathe with a flywheel,
and I am sure this is because the kind of vibration we encounter is not
torsional. A spinning unbalanced load produces translational vibration.
Spinning mass has no greater effect in this regard than stationary
mass. If you make the headstock, or any other part of the lathe heavy
it is going to vibrate less–it is cheaper and simpler to increase the
mass of the stationary parts than the rotating parts.”

Thus a flywheel in and of itself does nothing to deal with the
translational forces of out of balance wood. A balanced rotating mass
(be it a faceplate, heavy motor, or separate flywheel plate) will
actually do very little to deal with imbalances in the turning blank,
other than the addition of added mass near the headstock (and in this
sense it doesn't make any difference whether the mass is fixed in place
or rotating). This is because the "flywheel" weight alone is dynamically
balanced and does nothing to diminish the source of those translational
forces described in the main review. It is the mounting of the movable
weights to a flywheel body that makes the Kelton device a balancer
rather than just a flywheel, and thus able to reduce or eliminate the
translational forces. Yet as Leo notes, what a flywheel may be able to
do is contribute to a smoother, more consistent speed of rotation by
increasing the rotational inertia. Thus the effect of motor fluctuations
in drive speed, elasticity in drive line components (belts, etc.), and
bogging due to application of cutting tools may be decreased at the
rotating wood’s surface. On some lathes this may contribute to an
increased consistency of cut and resultant smoother surface. Likely the
difference is subtle at best, but I have found it to be discernible with
some combinations of lathe and work load. Furthermore, with a lathe that
has speed control circuitry like the Nova DVR, a heavy flywheel may
help smooth out variations at low speeds and makes things easier for the
speed control circuitry at those speeds as well.

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