Kinetic Precision
Kinetic Precision
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Balancing Rings

Balancing Rings

(You can buy KP Balancing Rings here.)

If you run a surface grinder, you need to true, dress, and balance your wheels for best results. For small grinders which typically use 7-inch wheels, the available options for wheel balancing are few. An extremely common adapter used with small grinders and 7-inch wheels is the Sopko Model 200. (It has a boss which has a nominal diameter of 1.26-inches and a height of 0.39-inches. The KP B-200 Balancing Ring will work with any adapter having a similar boss.)

This adapter provides no inherent means for balancing the wheel. Some much larger wheel adapters have balancers built in. There is a pervasive falsehood in the grinding world that “small wheels don’t need to be balanced”, and that “you can true the wheel to remove the effects of imbalance.” We think this is pernicious nonsense. For best results when surface grinding, wheels need to be balanced and trued - two distinct and required preparatory processes. Small machines have small-diameter spindles, and are likely MORE sensitive to wheel imbalance than large machines.

The very common Sopko adapter.

Another potential balancing solution is purchasing the Sopko balancing rings. You’ll need two, and they cost about $45, each. That’s $90 on top of the cost of your adapter, which is perhaps $65. They are more complex, and each have their own setscrew and a simple cylindrical hole to slip over the adapter’s boss. More on this later.

The KP Balancing Ring, Model B-200, is designed to work with the excellent Sopko Model 200 adapter.

The KP B-200 Balancing Ring mounted on the Sopko Model 200 adapter.

The KP B-200 balancing ring has some cool features. It easily attaches to the adapter with a single brass-tipped setscrew. It uses a 3-point mounting system, just like a three-jaw chuck on a lathe. This allows for variation in the diameter of the adapter’s boss. It also reduces distortion on the tapered bore induced by the setscrew. Imagine if the hole in the ring was a close-fit cylinder (just like our first internal version, and like the Sopko rings). When the ring is slipped over the boss, and the radial setscrew tightened, there would be a two-point “pinching” effect and distortion of the tapered bore. Only if the fit was PERFECT would the distortion be minimized. A little bigger and more distortion is possible. A little smaller and it will not even slide on (we found this out the hard way).

These are the reasons we introduced our two trademark 120-degree mounting “bumps” into the bore, such that the equal pressure from the setscrew and the two bumps are evenly spaced around the circumference. This feature is visible in the photos above and below.

Note the two “bumps” in the bore of the balancing ring.

With our trademark mounting bumps, there are three pressure points, and the distortion is greatly reduced. Also, a wide variation in the boss diameter is accommodated. That innovation alone is worth the cost.

If you do your homework, you’ll find a YouTube video from a respected US manufacturer of grinding tools and accessories which recommends balancing wheels by removing wheel material with a carbide drill bit. Let’s think this through. First, prior to mounting on an adapter, you are taught to “ring the wheel” by gently striking it with a tool to insure it is not cracked. A dull thud means the wheel is cracked and should be discarded. A nice ringing tone is what you want to hear. Second, when you mount your wheel you are admonished to make sure the blotter papers are intact so that you spread out the stresses induced by tightening the nut on your adapter which squeezes the wheel. Then, in order to balance your wheel, you are instructed to drill blind holes in the side of your wheel to balance it before spinning it up to 3000 RPM. What?!??! By increasing the probability that the wheel will shatter, and simultaneously reducing its useful life, you get a balanced wheel? No, thank you.

Another issue that is rarely addressed is the change in balance as the wheel is consumed. You will true a wheel many times as you use it up, and the balance WILL change due to non-uniform density of the wheel material. It’s just a fact of life. With the KP Balancing Ring and a good balancing stand (coming soon!), balancing will be as fast as dressing. It will be simple to KEEP the wheel balanced. Imagine balancing by drilling blind holes in your wheel. How many times do you want to do that??!?

The KP Balancing ring does not require any changes to the wheel. It minimizes bore distortion and accommodates variations in the adapter size. It does not increase risk of fracture. It is removable and replaceable. It makes balancing fast and easy. It uses balancing weights which are available in any catalog, and you may already have some in stock. Let’s see how…

From  A Handbook On Tool Room Grinding , Norton Abrasives, 1947

From A Handbook On Tool Room Grinding, Norton Abrasives, 1947

Balancing Wheels the KP Way

There are a thousand ways to make an omelet, all involve breaking a few eggs. Preparing a wheel for grinding is no different. One respected source suggests “Mount, true, balance, grind.” Based on the quality of his work, it’s hard to argue. The 1947 Norton Handbook On Tool Room Grinding states that wheels should be “rebalanced if necessary”, and proceeds to give no advice on accomplishing that. Our way is not the only way, but it’s a good place to start. You can modify it as you see fit.

First, you need to mount a wheel to an adapter.

Mounting a wheel to a Sopko 200 adapter with two Sopko wrenches. Note that blotter paper is present on both sides.

Second, you mount the wheel on your balancing stand arbor. I know, I know, you don’t have a good balancing stand yet. But, you can use two stacks of 1-2-3 blocks or 2-4-6 blocks on a leveled surface plate, and make an arbor (the taper is 3-inches per foot). Or you can cough up over $300 for a Sopko balancing stand WITHOUT the arbor. We recently saw advertised on MSC a Sopko balancing KIT, for $900, which comes with an arbor and stand. Ouch. I bet you know where we are going with this… yup, the KP balancing stand is coming SOON.

So, the first thing you do is let the wheel settle and identify the heavy side and the light side. When the wheel is settled down, mark the top side (the light side) with your ever-present Sharpie or pencil.

Marking the “light” side. Note that this shows our not-released first-generation balancing ring.

Now you can attach your balancing ring with the mounting (radial) brass-tipped setscrew toward the “light side” mark. While you are at it, write your wheel information on the blotter so you can read it with the adapter on. One day, a wheel manufacturer will do this for us.

Write your wheel information on the blotter that is toward the operator.

Now, re-mount the wheel on the arbor of the balancing stand. It will again rock toward the heavy side. When the wheel is acting like a pendulum, it is indicating an imbalance. The higher the imbalance, the more quickly it will settle out. Very slow swings indicate small imbalances.

Put a weight, in the form of a 1/4-20 set screw into the hole on the “light” side, which is on top, if the wheel has settled. DO NOT OVER-TIGHTEN. The screw need only be lightly finger tight. We’ve never seen one back out from normal use. You can use nylon-patched screws if you are nervous about that, but it’s not necessary. Now, observe the balance again. If it is still heavy on the same side, you can add another screw. Repeat until it is balanced. If you can’t find a wheel position where the wheel wants to keep moving, you’ve reached the limit of your balancing stand’s sensitivity. You’re done.

To get finer resolution, you can use two screws in opposite spots (zero added balancing, or moment), and march them toward the light side symmetrically. Alternatively, you can substitute shorter screws for the 3/8-inch long screws, or even use the hollow screws that have the hex extending through. For really badly imbalanced wheels, you can start with a socket-head cap screws in place of the radial setscrew. Use a piece of copper wire or lead shot to protect the adapter if you do this. More importantly, think about getting better wheels. We’ve not yet encountered a wheel that would not balance using the procedures described herein.

Once you have your wheel perfectly balanced, you should put it on the grinder and run it. Feel the wheel housing. Chances are you won’t feel much of any vibration when it’s running. That’s the sign of a balanced wheel. As an experiment, you can remove the balancing wheel (leave your balancing “weights” where they are… isn’t that cool?) and run it again. You’re likely to feel a significant vibration without the balancing wheel, now.

At Kinetic Precision we had a visit from Mr. Tom Hoenig of GTI Spindle, Manchester NH. Tom used his cool sensors and software to evaluate the vibration of our Brown & Sharpe Micromaster 618 grinder with a wheel installed. He was amazed at the vanishingly small signal from the wheel. In fact, the bearing vibrations exceeded the wheel vibration significantly, and it was well within specifications. Changing the wheel balance by removing a weight was immediately observed on his instrument. Thank you, Tom!

After balancing, true your wheel as usual, with your single point diamond dresser. Also, TRUE THE SIDES OF YOUR WHEEL. Nobody seems to recommend this, but we think it’s critical to getting the best finishes, even if you are flat grinding. You need only true the sides to the maximum depth you think you will ever plunge, plus a margin. This will remove the change in load on the wheel with each revolution as it is cutting with cross-travel. In the photo below, a wheel gets it’s sides trued, and this uncovers how tilted the wheel is after mounting. This is after a 0.001” deep truing cut. As shown in the photo below, a simple 1x1x3-inch block was made to mount a single-point diamond dresser - it can be used for truing both the bottom and the sides of a wheel (Does this need to be a KP Product?).

After first pass of truing the side of a wheel. Note only about 30% of the circumference was contacting. The diamond in the yellow block was not in use. Yes, the surface of the chuck was a hot mess after an experiment with the wrong wheel type. Note the yellow paint marks for adapter-to-spindle alignment - just to remove another variable.

Now, take a pencil, paint marker or Sharpie, and mark the position of your adapter on your spindle. Remove the wheel from the spindle and balance it again. Yep, balance will change from the truing operation. Then, re-mount it on your spindle in the same orientation it was previously, and true it one more time, lightly, but evenly. NOW, you are ready for work.

If you picked the right wheel, balanced it properly, and trued and dressed properly, you’ll have a great grinding experience.


Summary

To summarize our recommended procedure:

  1. Mount the wheel on the adapter properly.

  2. On the balancing stand, find and mark the light side of the wheel.

  3. Position the KP Balancing Ring on the adapter with the logo away from the wheel, and the radial setscrew to the light side.

  4. Mount the wheel on the grinder spindle and true the sides and bottom of the wheel.

  5. Mark the position of the adapter on the arbor, remove the wheel and re-balance.

  6. Mount the wheel on the grinder spindle and true the sides and bottom of the wheel.

  7. Grind the work.

It’s a chicken vs. egg problem as to whether you finish with truing and dressing or balancing. But, two cycles should be enough either way. And trust your fingers… you can feel the vibrations going away as you balance!

Perfectly balanced wheels make for great results.


Just one more thing…

If you don’t own a pair of PFG Stones, you may miss some clues. Because they are like X-Ray Vision, and you can start to uncover variations in your grinding that are just not obvious. Here is the same chuck with and without treatment from PFG Stones.

A freshly ground magnetic chuck with and without treatment from PFG Stones.

PFG Stones reveal imperfections in your grinding that are very, very hard to see. In this case, those shiny spots (high spots) were not measurable with a tenths indicator. Yet, clearly, they are present. Was it a problem with wheel dress, wheel balance, bearings? … That’s a discussion for another day. But, it’s there, and it’s another level of perfection you can chase if you have the tools. Get yourself a pair of PFG Stones if you don’t own them already.

And, yes, our super skookum balancing stand is coming soon.

Order one balancing ring kit for each wheel you want to have at the ready.

(You can buy KP Balancing Rings here.)