Non-Directional Finish

Non-Directional Finish

Non-directional finish is a process to help mechanics ensure a quality rotor job is done. When a non-direction finish is not applied, it is not uncommon for a customer to experience poor stopping power or brake noise after leaving the shop. In fact, many times the rotors friction surface isn’t correct. As a result, poor contact is made with the brake pads. Likewise, the customer is likely to experience less stopping power and more brake noise.

Poor surface contact reduces the surface area available for creating friction. As a result, the brake pedal has to be pushed harder in order to stop the vehicle. Additionally, the poor surface contact can also cause the pads to vibrate while stopping, which causes the brake noise.

Non-Directional Finish: An Insurance Policy

Before beginning, it is important to note that performing a rotor service consists of more than a non-directional finish. In effect, non-directional finishes should be looked upon as an insurance policy. For example, it should enhance the rotor’s finish, NOT try and fix it. The following steps will go over the process of completing the rotors finish:

1. Resurface the Rotor

If you are resurfacing the rotor(s), use the proper machining techniques and make sure that the lathe is in good working condition. On hub-less rotors, make sure to clean the mating surfaces with the appropriate tool. Next, scratch cut the rotor(s) to ensure an accurate setup. Always use sharp bits and a vibration damper when machining.

2. Non-Directional Finish

After machining, apply a non-directional finish by using 120 grit drywall sandpaper on a rubber sanding block for 60 seconds per side. Apply the finish by applying moderate pressure. At the same time, use a slight rocking motion. (See Figure 31.1)

Hand holding sand paper on a rotor

3. Clean the Rotor

Finally, clean the rotor before installing it onto the vehicle. This is done in order to prevent machining dust from contaminating the brake pads. To begin, using a mild soap and water solution, wash both friction surfaces and wipe everything dry with a clean, lint free rag. Likewise, if using brake cleaner, us more than usual and wipe the surface down with a clean lint free rag or paper towels while still wet. In contrast, never use petroleum based cleaners as they will leave a residue.

More Information

There are many theories and opinions about non-directional finish. Typically, they center around the reasons and methods of completing the process. In this case, if we start by defining what is meant, we can clarify the two areas. For example, most lathes produce a directional finish. In this case, directional means that the finish has a pattern to it. Usually, the pattern produced is a spiral similar to an old vinyl record. If too pronounced this spiral could cause brake noise or even a loss of stopping power.

On the other hand, a finish that is non-directional will not have a pattern or “direction” to it. One common myth is that the finish must be a swirl finish. This myth is born from some new rotors coming out of the box with a pronounced swirl finish. In reality, you don’t have to see the finish for it to be effective.

Non-directional finishing should be viewed as an "insurance policy". It represents a simple step to help ensure the best possible surface to finish.

Non-Directional Finish Improves Results

With this understanding we can now discuss why and how to perform a non-directional finish. First, it is important to know that by correctly applying a finish with no direction the surface finish can be improved by up to 20%! As a result, the improved surface will provide a better mating surface for the friction material resulting in less chances for brake noise and reduced stopping power. And the best part? It only takes 2 minutes! That being said, it should be mentioned that most quality brake lathes produce a surface finish that falls well within acceptable limits. So, why bother applying a non-directional one? As stated above, performing this process may not always be necessary, but it is an insurance policy that only takes a few minutes to perform.

Figure 31.2 - Rotor

To Help, Not To Fix

At this point, it is important to emphasize that this process will not correct a poor surface finish. For example, if the base finish is substandard, you will gain little by applying a bit of sandpaper. In fact, proper surface finish is accomplished by a combination of a well maintained lathe, sharp cutting tips, and having the correct setup. Only after a quality base finish is obtained can the benefits of a non-directional finish be realized.

Don't Use an Angle Grinder

Contrary to popular belief, the angle grinder is not the best tool for the job. In fact, it is not even an acceptable method! Not one friction or rotor manufacturer, or any of the OEM’s endorse the use of an angle grinder as a method of applying non-directional finishes. This is because there are too many variables involved with angle grinders to perform the process correctly. Because the speed, type of disc, disc condition, time spent, and angle of the tool can be changed, results will always be inconsistent when using an angle grinder.

In figure 31.2 a rotor is shown that had an angle grinder used on it. The surface finish was measured before and after the application of the finish. Believe it or not, the surface finish was actually rougher after the finish was applied! For example, the smoothness of a rotor is measured in what is referred to as its RA factor. The lower the number, the better. The typical specification range is 15 to 80. On the rotor depicted above the RA started at 42, and ended at 45!

Sanding Block

The image below shows a rotor having a finished applied via a sanding block with 120 grit. Similar to the above rotor, this one was also measured. In fact, before the finish was applied it had an RA factor of 42. After sanding the rotor, the measurement dropped down to 33. As a result, the RA changed by 9, or roughly 21%. The non-directional finish is applied by using a full contact rocking motion while applying moderate pressure to the sanding block.

Non-directional finish using a 120 grit sanding block

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Measuring Hub Runout

Measuring Hub Runout

Excessive installed runout on hub-less rotors can be a problem. Because of this, we’ve prepared this article in order to help you diagnose and fix the issue. By following this guide, you can rest easy knowing that the job was completed efficiently and accurately. 

Solving Hub Runout

To determine if the hub is the cause of excessive runout, measure the hub runout. To do this, perform runout measurement and an indexing procedure as described here. If indexing determines that the hub is the cause of runout, hub runout should then be measured. The hub’s design will determine how the measurement should be performed. Figures 30.1 and 30.2 show two different hub flanges. First, figure 30.1 has a flat surface area outside the wheel studs while the hub in figure 30.2 has little to no flat surface outside the wheel studs. For your example, use the procedures below to measure hub runout.

Rotor illustration
Rotor illustration 2

Shouldered Hub

1. Setup the dial indicator as shown in the image below.

2. Position indicator plunger at a slight angle near the outside edge of the hub flange. Additionally, make sure that the dial indicator will not contact the wheel studs.

3. Next, using the appropriate size socket, rotate the hub in the direction that the dial indicator plunger is pointing. (in figure 30.3 the correct direction would be clockwise)

4. Note the difference between the lowest number and highest number obtained. This is the amount of hub runout. Most manufacturers do not provide a specification for hub runout. Generally speaking hub runout should be .001″ or less. Remember that the rotor runout caused by hub runout will be multiplied by the rotor’s larger diameter.

Dial indicator illustration

Non Shouldered Hub

1. Begin by setting up the dial indicator as shown in the image below.

2. Position the indicator plunger so that it is perpendicular to the hub’s mounting surface, evenly spaced between 2 wheel studs so that it contacts within a 1/4″ of the outside diameter of the hub flange as shown in figure 30.4


Dial indicator 2 illustration

3. Next, position the dial indicator scale so that the needle is aligned with the “0”. Gently pull the indicator plunger 1/4″ away from the flange surface, then bring it back to rest on the flange surface. The needle should return to “0”. If the needle is at “0” proceed to step 4. On the other hand, if the needle is not on “0” then repeat steps 1-2 making sure the vise grips are tight, the flexible mount is rigid when the lever is turned, and the dial indicator clamp is snug.]

4. Pull the plunger out and rotate the hub so that the indicator plunger is located midway between the next 2 wheel studs. Now, gently bring the plunger back to the hub flange. Continue by noting the indicator reading.


5. Repeat step 4 for the remaining wheel studs making sure to note the indicator reading until the hub has been rotated a full 360 degrees. Recheck the indicator reading at the starting point to make sure that the needle is at “0”. If the needle is not on “0” then start the process over. This will be caused by the indicator mounting having shifted.

6. Note the difference between the lowest and highest number obtained. This is the amount of hub runout. Most manufacturers don’t provide a specification for this. Generally, the runout should be .001″ or less. Remember that the rotor runout caused by hub runout will be multiplied by the rotor’s larger diameter.


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Rotor Indexing

Rotor Indexing

When you run into runout problems, there can be a few different culprits. Because of this, it is important to determine the correct source in order to fix the issue. One of the best ways to do this, is by rotor indexing. By performing an index not only will you find the problem, but often times, you’ll fix it as well. Typically, installed runout can be caused by any combination of the following:


  • Rotor has runout
  • Hub has runout
  • Hub to motor mating surface is not clean
This article will go over a process known as “indexing” in order to help you identify and correct any installed runout you may come across.

Rotor to Hub Index

The following steps will go over the indexing process. Following these steps will help you find the issue and, in most cases, fix it as well. To get started, follow the steps below to index the rotor to the hub.

Tip: Using this procedure will either correct the runout problem or tell you whether the problem is related to the hub or rotor

1. Measure rotor runout

2. If runout is greater than the allowable specification (usually no more than .002″) then proceed to the next step.

3. Index the rotor to a wheel stud.

4. Rotate rotor until the dial indicator reading is at its highest value. Use a magic marker to mark this point on the rotor and hub flange as shown in the image below:

Rust buildup

5. Next, remove the rotor. Check the hub and rotor mating surface for dislodged rust or anything else that could cause the runout. If the mating surface is good install the rotor by rotating it 2 lug positions from its original position.

6. Finally, Measure the runout. If it is now within the specifications, proceed to the next wheel. If not, rotate the rotor until the dial indicator reading is at its highest value. Continue by checking the position of the marks on the rotor and hub in relation to the high spot. If the high spot aligns with the rotor, the rotor is the source of the runout. If the high spot aligns with the mark on the hub, then the hub has runout.

Indicator Dial

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Rust and Runout

Rust and Runout

One possible cause for high speed pulsation is happens when rust builds up. This article will go over how rust causes this problem and the necessary steps to resolving the problem.


The problem occurs when one or more of the rotors installed have excessive runout. Generic specification being used by domestic OEMs is .002″. Excessive runout causes disc thickness variation (DTV) over time. The average for most vehicles is 3,000 to 6,000 miles. This number can vary up or down based on the variables involved.

Rust buildup in jacking

Rust on hub’s mating surface is a leading cause of runout. The rust can from to a point where it actually pushes the rotor away from the hub even with the wheel bolted on (See image above). This process has been termed “jacking”. It works much the same way as a tree root under a side walk. There are tremendous forces involved as the rust “grows” between the rotor and hub.


Cleaning of the rotor and hub’s mating surfaces is a critical part of the brake job. The hub to rotor mating surface must be free of rust or runout induced DTV can occur shortly after the brake job. As little as .001″ of rust at the outside edge of the hub will result in .002″ to .004″ of runout.

The method used to clean the hub depends on the severity of the rust buildup. The hub’s mating surface can be a difficult surface to clean due to the wheel studs. The area between the wheel stud and hub centering flange is the most difficult area to gain access to. Here are the best methods to clean the hub’s mating surface.

Method 1 - Mild Rust Build Up

1. Use an angle grinder equipped with a Scotch Brite disc to clean the majority of the surface area. Get as close to the studs as possible and change the disc when needed.

2. Finish the process by using the tool shown in the first image below to clean the area around the studs. This tool fits over the wheel stud to allow easy cleaning of the hard to reach area of the hub. The second image shown the finished result.

OTC Tool

Method 2 - Severe Rust Buildup

The hub shown in the first image below will not be able to be cleaned effectively using the steps outlined above. The end result would look something like the second image below. The OTC tool does NOT work on mild to heavy rust. It has a tendency to polish the rust instead of removing it. The most effective method is to use the following steps.

Rust Hub
Polished Rust

1. Abrasive blasting is the most effective method for rust removal. There is a specialized blast cabinet available that allows cleaning of the hub while it is still on the vehicle. The tool uses a drawstring boot to allow the unit to be used on the vehicle as shown in the image below.

Rust Buster

2. The following image show what the final product should look like. This is the same hub as shown above. This hub will not be the source of rust induced runout. While there are other methods that can be used to clean rusty hubs the method described above the most effective. Other methods can be time consuming, yield a lower quality job and may not result in all of the rust being removed.

Finished Product

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How to Verify Accuracy of Setup on Bench Lathe

How to Verify Accuracy of Setup on Bench Lathe

Bench lathe induced runout is one of the leading cause of runout induced DTV pulsation comebacks. Typically, there are three main reasons for bench lathe induced runout:

1. Arbor runout

2. Adapter condition

3. Not verifying accuracy of setup

This article will cover a process called “Scratch Cut” which is used to verify accuracy of setup.


All rotors and drums machined on a bench lathe should be scratch cut before machining. This is necessary to verify the accuracy of the lathe setup. Skipping this step can lead to machining runout into the rotor. The process of verifying the setup is commonly referred to as “scratch cut”. The list below shows each step of the process:

1. Position the bits away from the outside edge of the rotor.

2. Bring the outside bit in until it barely touches the rotor. While holding the outer knob, place the inner dial on zero. On lathes without this feature, take note of the dial reading.

3. Back the cutting tip away from the rotor a small distance and turn the lathe off.

4. Observe the scratch cut. If the scratch cut is at least 50% around the rotor proceed with the machining process. (first image) If the scratch cut is less than 50% then the setup needs to be verified. (second image)

Scratch on rotor more than 50 percent around
Rotor with a scratch less than 50 percent

Steps 5-10

5. Two things will cause a scratch cut less than 50%. The first is that the rotor has runout and needs to be machined.

6. The second is a problem in the setup. Adapter cleanliness, arbor runout and tightening of the arbor nut are the main causes of setup problems.

7. To verify the setup, loosen the arbor nut. While holding the inner and outer adapter rotate the rotor 180 degrees. Re-tighten the arbor nut. This process changes the relationship of the rotor and adapters.

8. Turn the lathe on and move the twin cutter in or out a small distance.

9. Make a second scratch cut by turning the dial to zero. On lathes without this feature, turn the dial into the same number as the first scratch cut. This process makes each scratch cut the same depth which makes comparing the cuts easier.

10. Back the cutting tip off a small distance and turn the lathe off. Compare the next two scratch cuts. If the problem is in the rotor, the cuts should be on top of one another. (See below)

11. A setup problem will cause the second cut to be in a different position from the first. (See first image below). If this is the case, disassemble everything and check for cleanliness, correct adapters and for nicks on the mating surface. (See second image below) Do not proceed with the machining process until the scratch cuts are in the same position. Doing so will include runout into the rotor.

Scratch Cut Not Matching
Clean Surfaces

Bonus Tip: EVERYTHING machined on a bench lathe should be scratch cut to verify accuracy. For additional info, see our article on bench lathe adapter service.

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Bench Lathe Adapter Service

Bench Lathe Adapter Service

When high speed pulsation occurs after 3,000-6,000 miles bench lathe induced runout is a likely culprit. This article will go over everything you need to do to fix this issue. Likewise, images are provided in order to help you visualize the steps necessary.

Bench Lathe Adapter Solution

Preventing the majority of bench lathe setup problems is a relatively easy process. For example, follow the following steps.

1. Arbor Shaft Runout

First, Measure the arbor runout and correct it if necessary. Typically, the specification for arbor runout near the end of the arbor is .002″. However, if the runout is outside of the specification, remove and clean the mating surfaces. If the problem persists, consult your bench lathe manual.

Arbor Shaft Runout

2. Arbor Face Runout

Second, measure the arbor face runout. Usually, the specification for this measurement is .0005″. If the measurement is off, a correction will have to be performed using the bench lathe manufacturer’s procedures.

Arbor Face Runout

3. Hubless Adapter Arbor Mating Surface

In some cases, you’ll come across adapters like the one pictured below. This adapter is typical in many shops. These kinds of adapters rly on the mating surface as well as the arbor face to be accurate and true. Because of the state of the one pictured, it would be impossible for an accurate setup with this adapter.

Dirty adapter face

4. Correcting Arbor Mating Surface

In order to fix a mating surface, it will have to be cleaned. To do so, place a piece of sandpaper on a flat surface and run the adapter’s small face up and down a few timers while applying even pressure. As a result, you’ll end up with something resembling the image below. Likewise, it is important not to worry about pits or indentations as these won’t effect the mating.

Clean Adapter Face

5. Indexing Adapter to Lathe:

(This step is optional if the arbor face runout was .0000″.) Next, if the arbor face runout was greater than zero, then the hubless adapters will have to be indexed to the lathe before continuing. This is important because some adapters have index marks cast into them while others don’t. As a result, if there is no index mark use a file to make an index mark on the edge of the small mating surface as shown in the image below.

Adapter Index Mark

6. Preparing Adapter for Machining

Next, install the adapter on the lathe and position the twin cutter to enable machining of the large mating surface as shown below. At times, it will be necessary to remove the opposite tool holder to achieve the proper clearance.

Twin cutter setup

7. Machining Large Mating Surface

Next, remove only as much material as is necessary to achieve a 360 degree cut. Typically, this only requires .002″ to .005″. Make a slow cut to machine the large mating surface. As a result, the mating surfaces becomes true to the lathe as shown below.

Finished product

8. Optional Adapters

Similarly, the same procedure can be used on the optional adapters available for most bench lathes such as the composite rotor adapter shown in the picture below.

Other adapters


The average bench lathe setup will take between 1 and 2 hours to preform. Once this procedure is performed it will become a simple matter of keeping the mating surfaces clean and free of nicks and burns. If the arbor face had runout and index marks were used then the adapter and arbor index marks should be aligned each time the adapters are used.

Even after this procedure has been completed, it is still necessary to check the setup. To do so, you’ll need to perform a scratch cut.

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Brake Job Done Well

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