Beechnut Auto Repair of Houston

Lateral runout, thickness variation and brake pedal pulsation

The rotunda pro-cut is designed to eliminate customer concerns due to brake pedal pulsation. The customer concerns will be that upon application of the brakes, a shaking or pulsation can be felt in the pedal, in the steering wheel, or in the entire vehicle.

This pulsation is most often the result of thickness variation in the brake rotor. New rotors are uniformly thick, and stop the vehicle smoothly. But thickness variation can develop over time, eventually leading to a pulsation concern. Why does thickness variation develop?

The answer is lateral runout in the face of the rotor. A rotor like this one with lateral runout will not wear evenly. As the vehicle drives, without the brakes applied, the rotor will contact each pad once per revolution, at the "high point" of the runout as shown.

The rotor will wear faster in these two spots, leading to two thin spots on the rotor. As the brakes are applied, the pads move in at the thin spots and back out at wider spots. This pushes the brake fluid up and down the brake lines, all the way back to the pedal.

In order to prevent the wear that leads to thickness variation, the rotor must turn on the hub without significant lateral runout. Since vehicle hubs often have lateral runout due to stacked component tolerances, even a new rotor will often have excessive lateral runout.

The rotunda pro-cut will allow you to leave every rotor "matched" to the hub on which it turns. Since you adjust the machine before the cut, and measure the lateral runout after the cut, you will guarantee that the rotor is within 0.002" every time.

So, the overall goal in adjusting the lathe is to align the lathe axis to the hub axis. If you do this, there will be almost no runout in the machined surface.

Vehicle Preparation

Before lifting the vehicle, the front wheels should be straight, the parking brake off, and the transmission in neutral.

Raise the vehicle according to the lift manufacturer's instructions. Raise until the wheel hub is about belt level.

If any other wheel service is required, it should be performed before machining the rotors.

Remove the wheels. Remove the brake calipers and suspend them out of the way of moving parts such as half shafts and CV joints.

If the rotor is free on the hub, mark and remove it in order to assess the mating surface. Use a scotch-brite-type wheel on the die grinder to remove rust or debris. Clean all material from the mounting area.

The rotor on the side of the vehicle that is not to be machined yet should be marked and removed if it is free on the hub. Marking rotors to match a certain alignment on the hub is very important.

Mounting the Lathe

Mount the adapter

The first step is to choose the proper adapter. Passenger cars use either the four (201-00052) or five lug (201-00053) Direct Fit(r) adapter. For most trucks and vans, you will use the larger adapter with many holes. This fits 5, 6, 7 and 8 lug vehicles (201-00050). it allows for the large hubs on these vehicles.

Many 4 wheel drive vehicles will require that you remove the cap from the locking hub. Some will also require the use of a spacer (201-R0087). If the adapter doesn't fit flush and square, use the spacer. Sometimes the holes in the spacer are not needed as the entire bolt pattern will fit in the center of the spacer.

Once you've selected the correct adapter try each bolt pattern until you find the one that fits the vehicle evenly. Do not use the vehicle's lug nuts to secure the adapter. Use the nuts provided with the machine.

The adapters are made of cast iron, not aluminum or steel like wheels. They are NOT designed to withstand the use of impact tools. DO NOT USE IMPACT GUNS TO ATTACH THESE ADAPTERS. 20-30 ft-lbs is plenty to secure the adapter to the vehicle.

Note: Always use the nut and bolt kit supplied with the lathe to attach the adapter. An exception to this is on the 1997+F150/250 and 1998+f250/350 vehicles that have hub piloted wheels and two piece flanged nuts.

REMINDER: DO NOT USE IMPACT WRENCHES TO TIGHTEN LUG NUTS. TORQUE LUG NUTS BY HAND. EXCESS TORQUE APPLIED WITH AN IMPACT WRENCH WILL DAMAGE THE ADAPTERS. ADAPTERS ARE NOT WARRANTED AGAINST MISUSE.

Accessory: dual rear wheel adapter (201-00051)

The low profile dualie adapter allows you to machine vehicles one ton and under with dual rear wheels. Will not machine vehicles with a Dana-70 axle or vehicles with other axles over one ton.

Mount the Lathe to the Adapter

Disengage the feed knob by pulling out the feed engage plunger (6). Turn the knob to move the cutting bits (11) away from the middle of the lathe. This allows the tools to clear the rotor when the lathe is being attached to the hub.

Before using the machine, notice the four screws (15) on the face of the mount flange (5). These are called RUNOUT screws. When they are tightened, they protrude beyond the face of the mounting flange. Be sure that these screws are back out so they do not protrude.

Roll the machine into place and attach it to the adapter. The trolley is spring loaded, and the lathe can move up and down 10:. The adapter has a dowel pin which must line up with one of two holes in the mounting flange (5).

Once the flange is flush to the adapter, the shaft of the machine bolts onto the adapter by turning the large mounting machine bolts onto the adapter by turning the large mounting knob (4). Be careful not to bump the cutting head against either the rotor or the fender as the machine is rolled in.

Once the machine is snug on the adapter, you should make sure the trolley handle (7) is loose. Rotate the machine so that the cutting head is in position where there is enough room to cut the rotor, typically the brake caliper area. lock the mahine in place by tightening the trolley handle. This will keep the lathe from rotating.

Shown here is the lathe fully assembled onto the vehicle:

This shows the lathe in the 'right side up' position. Notice that the opening in the dust shield is on the right of the hub. Depending on which vehicle you are servicing, this opening will either be on the left or the right. You will always want to begin with the lathe shown as it is here. Also note the position of the dial indicator.

POSITION CUTTING HEAD & SET SHUTOFF CAM:

Notice that there are five mounting holes in the slide plate that can be used to lock the cutting head. Use the T-handle 6mm Allen wrench to remove the securing screw and center the head so the cutting arms will straddle the rotor.

The cutting head assembly can be secured into any one of the five holes. It is a good idea to clean out these holes as well as the dovetail and plate surfaces when you change cutting head position, as they can easily fill up with metal chips.

It is absolutely critical that you pull the tool holder plate back into the dovetail so that it is square before you tighten the securing screw. You can use your left hand to push the cutting head firmly back into the dovetail as you tighten the set screw with your right hand.

If the tool holder is not squarely and firmly pressed into the dovetail, a poor surface finish will result.

Different vehicles have different offsets, so the head must be moved in or out for each vehicle. On large trucks, the head will actually be mounted as far out as it can possibly go. Even though the head hangs over the edge of the base plate, the lathe will cut smoothly provided the head is squarely pressed into the dovetail.

When you proceed to the other side of this vehicle, the lathe will be mounted in the upside down position. The offset of the cutting head for this vehicle will already be set, with the cutting head firmly in the dovetail. This is why we always begin a brake job with the machine right-side up.

DO NOT ATTEMPT TO MOVE THE CUTTING HEAD LATERALLY WITH THE LATHE UPSIDE DOWN.

Adjustment for Lateral Runout

The point of adjusting for lateral runout is to align the lathe's axis with the hub's axis. You will measure this misalignment with a dial indicator and use the two of the four runout screws to align the lathe to the hub. When the dial indicator reads less than 0.003", proceed with your cut.

Set up the indicator and measure the runout

Attach the Vise grip/Gooseneck to the vehicle hub and position the dial indicator tip against a flat surface on the cutting head. Whatever surface you choose, it should be parallel to the rotor surface, smooth and not curved. Be sure the vise grip end is attached to something firm and cannot move. The plunger on the dial indicator should point towards the vehicle centerline.

Disengage the feed by pulling out the feed knob. Pull the knob until you feel it click. This will stop the cutting head from feeding when the motor is turned on.

Turn on the lathe, and observe the movement in the dial indicator. You may wish to turn the face of the indicator so that zero is at the low (furthest counter clockwise) point.

Determine the total needle sweep between the high (furthest clockwise) and low (furthest counterclockwise) reading by counting the number of lines on the dial indicator.

WARNING!

YOUR LATHE IS FITTED WITH A KNOB ON THE BACK OF THE MOTOR. DO NOT TOUCH THE KNOB WHEN THE MOTOR IS TURNING OR REMOVE THE SAFETY COVER.

Compensate for Run-Out

Stop the lathe so that the needle reaches the extreme high end (furthest clockwise) of its sweep. You may have to bump the start button to reach one of these points, or you can use the motor crank knob.

Once you have stopped the lathe at the high point, look for the two runout screws opposite the dial indicator. They are on the side nearest the lathe motor. Imagine a line between the center shaft of the lathe and the tip of the dial indicator. Now look for the lateral runout screw (remember the runout screws are on the mount flange) nearest this imaginary line on the motor side. Remember which number it is. You will adjust ONLY this screw and one adjacent to it.

Use a 6mm open end wrench (not 1/4"-it will round the screw heads) to begin turning the screw closest to you imaginary line. Remember, you are turning two screws on the motor side of the lathe. Turn the first screw until the needle moves about halfway of its sweep. If the screw is exactly on your imaginary line turn it until you are at exactly half the sweep. If your imaginary line is exactly between the two screws, turn your first screw until the needle moves about 3/8 of the way back towards the low end.

Turn the lathe on and note the new runout. If runout is still above 0.003", repeat the above process. If your original two screws are not on the motor end of the lathe when you stop at the high point you will have to LOOSEN one of the two you first adjusted. Do not tighten one of the screws on the motor side in this case, as it will only work against the one you first adjusted.

For example, if you have turned screw #3, you will never adjust screw #1.

If your imaginary line between the dial indicator and lathe spindle is the 9:00-3:00 line, the two screws you would adjust would be numbers 1 and 2.

When your dial indicator shows less than 0.003" you may begin cutting. Since the dial indicator is much farther out than the rotor you will be machining, you get an exaggerated reading. By ensuring less than 0.003" on the indicator, you will guarantee less than 0.002" on the cut rotor.

(Note: you may notice the circular motion in the lathe body parallel to the vehicle centerline. This 'scrubbing' motion up and down is not harmful in any way.) If you notice that the dial indicator does not make an even back and forth motion like a windshield wiper, this may be an indication of another problem. There may be foreign matter behind the rotor, causing a wobble, or there may even be a driveline part that has been damaged. You will not be able to totally eliminate the runout if it is not an even once per revolution sweep.

Causes from lathe setup can include:

.loose dial indicator or gooseneck.
.dial indicator tip is on an uneven surface or edge
.loose dial indicator tip
.vise-grip attached to a loose part on the vehicle
.the lathe is not fully engaged to the adapter
.the adapter is not fully seated.
.run-out screws were not backed off before you began.

Uneven motion can indicate other vehicle problems and warrants further investigation if one of the issues listed above is not the problem.

Making the Cut

Loosen the clamp knob on top of the cutting head

Next you will set the shutoff cam. Crank the feed knob until the bits clear the outside edge of the rotor. Loosen the cam screw and slide the cam back until it contacts the automatic shutoff switch plunger. Tighten the cam screw. This cam will press the shutoff switch when the bits clear the rotor. This allows for unattended operation.

Turn cut depth knobs counter clockwise until the bits can clear both sides of the rotor. Turn on the lathe. Crank the cutting head in to the middle of the braking surface of the rotor.

Start with the inside (behind the rotor) tool arm. Turn the depth knob clockwise (tighten) until the tool bit just barely makes contact with the rotor surface. You can listen for the contact. Next move the outside tool arm in until it also makes contact.

Now advance the cutting head in towards the center of the rotor.

IT IS EXTREMELY IMPORTANT NOT TO TOUCH THE HAT OF THE ROTOR WITH THE LEFT TOOL BIT. THIS WILL DAMAGE OR BREAK THE TOOL HOLDER PLATE. THIS TYPE OF DAMAGE IS NOT COVERED BY THE WARRANTY.

When you are at the inside edge of the pad contact surface, you may adjust for depth. Each line on the knob moves the cutting bit 0.002". Each number on the knob is two lines from the previous number. By turning the knob is two lines from the previous number. By turning the knob from 1 to 2, you have moved the tip 0.004". Cut at least 0.004" on each side with each pass. The maximum depth is 0.008" on each side.

Now that you have adjusted for depth, tighten the clamp knob (over the cutting arms). This must be tight to minimize vibration. Place the chip deflector/silencer over the cutting bits. This silencer is very important, and it should be used on every rotor to prevent vibration.

Press the feed engage crank handle in to engage the automatic feed. The machine will shut off when the cut is finished. The cut will take two to three minutes depending on the size of the rotor.

Note: If the rotor is severely worn, it may be necessary to machine away the ridges on the inside and outside of the pad contact area before machining the pad contact surface.

The Rotunda Pro-Cut leaves a uniform, glazed-looking surface. At times the metal structure of the cut rotor will appear to have an 'orange peel' surface. This is normal and it is a smooth, uniform braking surface.

When you are finished cutting, loosen all runout adjustment screws. Loosen the mounting knob and remove the lathe from the adapter. Be careful not to bump either the rotor or the wheel well with the brake lathe. As you remove the machine, take special care not to bump the bits into the rotor. This can fracture the bits.

Before removing the adapter, measure and record the lateral runout on the rotor 5mm [0.196"] from the OD edge of the rotor while turning the rotor by hand. Also measure and record the thickness to ensure that it is above 'machine to' specification. When you have finished your measurements, be sure to clear the hub area of any brake chips, dust or debris.

Careful cleaning of the adapter prior to removal is particularly important on vehicles with exposed bearings.

If the rotor is loose on the hub, be certain that it is match marked to the hub before removing the adapter.

Clean any dust or debris from the finished rotor with 150 grit sand paper and then damp rag. Cast iron dust left on the rotor can cause brake squeal.

Machining the Opposite Side

To prepare the lathe for the other side of the vehicle, you need to remove the chip tray, loosen the trolley handle, and rotate the machine into the upside down position.

The procedure for cutting in the upside down position is the same, but the cutting head has already been moved to the proper position so it will not need to be set. The lathe mounts in the same manner. Often, the shutoff switch will still be depressed from the previous cut, so the machine will not turn on until you move the head. The cutting arms will also still be advanced in from the last cut, so be sure to loosen the clamp knob and spread the arms before advancing the head. Measuring and adjusting for runout is exactly the same as in the upright position. The entire cutting process is also the same, right down to the silencer clip which mounts upside down in the exact same position.

Advancing the cutting head towards the hat of the rotor requires even more care in the upright position. DO NOT BUMP THE HAT OF THE ROTOR.

Reassembly

When machining on both sides is complete, all surfaces should be cleaned of chips and dust. Special care should be used in making sure that ABS sensors are free of debris. Once everything has been cleaned, apply Nickel anti-seize to the rotor/hub contact surface before re-assembling the brakes.

If these procedures are followed properly on each brake job, the Rotunda Pro-Cut will operate quickly and efficiently. The machine also requires simple routine maintenance on a weekly basis.

Maintenance

The best way to ensure smooth operation of the Rotunda Pro-Cut is to keep all parts as clean as possible. The machine also requires simple maintenance on a weekly basis.

DAILY

• Check tool bit edges. If there are chips or dings index or replace the bit. be sure they are right side up so that the groove is visible. Each bit has three cutting points. When worn out, replace them (Rotunda part #201-R0086). When indexing or changing tool bits, clean the threads and put a spot vaseline (or thick grease) in the bottom of the screw hole before tightening the tool bit screw. The Vaseline will stop chips from accumulating in the hole and rusting place. If chips do rust in place they can often be dislodged by poking a needle through the hole.
• Clean the tool holder plate (50-499), taking special care that there are no chips or dirt wedged in the dovetail.
• Check the electrical connections and cord for cuts in insulation or wear.

WEEKLY

• Lubricate the cut depth adjustment wedge threads with a thin coat of light machine oil.
• Check the tool holder plate for damage. Slide a 0.003" feeler gage between the tool holder plate and the base plate (50-499). If it can be inserted freely your tool holder plate may be damaged. A damaged tool holder plate will often cause a vibration during the cut. This will leave a characteristic herringbone pattern on the rotor.
• Check the tool holder for lateral play. Lateral play often causes ridges and matching grooves when a rotor is resurfaced. To check for lateral play, grab the tool arm assembly and try and rotate it diagonally. There should be no motion. If there is motion, you will need to adjust the gib.

To adjust the gib, first loosen all four set screws by freeing the 7mm lock nut and loosening the Allen set screw.

Then remove the plate and gib completely, and clean the contact surfaces. Use steel wool or a sharp tool if buildup is difficult to remove. Once these surfaces are clean, slide the plate back on and perform the adjustment. The procedure is to locate the plate in the middle of the rail, and then tighten each Allen set screw individually until you feel it snug against the gib. Lock the screw down with the 7 mm lock nut. After tightening each nut, slide the plate to make sure you have not over-tightened the screw. If you have, then the plate will be seized and you will not be able to force it to move. When the gib is adjusted properly, the plate will have some resistance as it slides. There will be no lateral movement possible.

To re-attach the feed block, position the slide plate as far in as it can travel, and wind the feed block in using the feeder wheel.

This ensures that the feed block will mount squarely. Wind the head back out and the machine is ready to go.

COMMON CAUSES OF POOR SURFACE FINISH

The Rotunda Pro-Cut on-car brake lathe should provide a smooth surface finish on every cut. There should be no chatter, tone or roughness in the finish. This quick reference should serve as a guide in case your machine is nor providing an adequate surface finish. if problems exist, often the "chattery" or rough finish will show up only on certain rotors. Regardless, you need to find the problem. Here are some common sources of poor surface finish.

CUTTING BITS: The cutting bits must be right side up. The grooved and ridged side must face up. The cutting bits may not have chips or dings on the point in use. If the bits become too worn, a rough surface will appear on the machined rotor.

CUTTING HEAD NOT SNUG: On each brake job, the technician must center the cutting head for that particular vehicle, using one of the 5 holes on the slide plate. Once the head is centered, it is VITAL that the technician use the left hand TO PUSH THE HEAD FIRMLY AND SQUARELY BACK INTO THE DOVETAIL on the slide plate while using the right hand to tighten the Allen colt that secures the head. Failure to do this will result in chatter.

TOOL HOLDER PLATE IS BENT: the tool holder plate is the plate that the cutting arms are bolted onto. It will bend or break if the technician accidently runs the cutting head into the hub of the rotor while the rotor is turning. It will also bend if a cut deeper than 0.020" is taken. ONCE IT IS BENT THE LATHE WILL NOT CUT PROPERLY until it is replaced. To diagnose whether or not your plate is bent try and slide a 0.003" feeler gauge between it and the slide plate. If the feeler gauge between it and the slide plate. If the feeler gauge can be inserted freely, the tool holder plate is bent.

LOOSE GIB (50-464): As wear occurs between the slide plate and the box it rides on the fir becomes looser. You must take up this slack periodically. To tighten the gib (50-464) follow these directions:

(See Illustrations Above)

a. Remover the two feed block screws from the feed block.
b. Move the slide plate forward and clean the dovetails. Lubricate with graphite.
c. Tighten all four Allen set screws until the slide plate can just barely be moved by hand from end to end.
d. Slide the plate (50-499) forward until the back edge lines up with the rear bearing. Crank the feed knob until the feed block abuts the slide plate.
e. Reconnect the Allen bolts from feedblock to slide plate.
f. Tighten the four Allen set screws approximately 1/8th turn more. Lock in place with the 7mm lock nuts.

Lathe Preparation

Check bits

Before mounting the lathe check the cutting bits and make sure they are ready for use. The cutting bits are one of the most critical components of the machine. It is vital that they be Rotunda cutting bits in good condition and properly mounted. Each butting bit has three corners, or bits, which may be used. This correctly installed bit has a groove facing up. An improperly installed bit has no groove facing up, and from the side you can clearly see that it does not fit correctly.

You should get at least 7 cuts per corner. However, bit life is affected by variables such as rust or ridges. In order to determine when to rotate bits, monitor rotor finish. If the rotor finish befins to look inconsistent or feels rough to the touch, bits should be rotated. Bits that are chipped or cracked should never be used.

Be sure that the pocket the bit rides in is clean before positioning the bit. Any foreign material pinched under the bit will cause problems and may even break the bit when you tighten the screw.

Use only Rotunda bits. Although other bits will fit the machine, no other bits are made of the proper material. Rotunda bits have been specially engineered in tandem with the Rotunda lathe. Non-Rotunda bits will complicate use of the lathe and may result in poor rotor surface finish.

Again, cutting bits are an essential part of the Rotunda Pro-Cut lathe.

TO REVIEW:
.USE ONLY ROTUNDA BITS (201-R0086)
.NO OTHER BITS ARE MADE OF CORRECT MATERIAL
.OTHER BITS COMPROMISE PERFORMANCE OF THE LATHE
.OTHER BITS MAY RESULR IN POOR SURFACE FINISH

Where to Start - Driver or passenger side?

It is important to start on the proper side.

The Rotunda Pro-Cut mounts directly to the hub of the vehicle, at the center flange. When the lathe is right side up, the cutting head is to the right of the hub. You will want to befin with the lathe right side up. The lathe will be set up to cut where the caliper normally rides, because that's where you have clearance.

On a vehicle where the calipers ride in front of the hub we will always start on the passenger side. If the caliper rides to the rear of the hub, you begin on the driver's side.

It is important to note that the Rotunda Pro-Cut machines both front and rear rotors. The lathe's operations do not change at all in the rear of the vehicle.

Note: The lathe has a powerful 3/4 hp motor. This requires 20 amp service. All extension cords must be at least 12 guage and less than 25 feet; drop light cords are not recommended.

Setting Up the New Lathe

Assemble the trolley

Open the trolley box, check the contents against the parts diagram and proceed with the assembly. If you are missing any parts, call ProCut at 18005436618 immediately. Follow the assembly instructions that are packaged in the trollley box.

Mount the lathe to the trolley

Once the trolley is assembled you will need to mount the lathe to the trolley. The easiest way to do this is to remove the mount arm from the trolley and assemble it onto the lathe body. Remove the trolley handle (37-456) and thrust washer (37-251) and slide the support arm (50-533) out from the L-tube (50-509).

Slide the thick spacer (50-537) over the vetical post ont he srupport arm (50-533) and place one of the rubber washers (37-519) over the spacer.

Remove the lathe body from the shipping pallet and turn it upside down. Slide the support arm (complete with spacer and rubber washer) vertical post through the hole in the main lathe body. Position the support arm so that the slot on the flat portion rests over the mounting lug on the bottom of the lathe body. Place the other rubber washer (37-518) through the support arm and into the mounting lug.

Turn the lathe back over and secure the top of the support arm vertical post with the female trolley knob (37-517).

Position the serrated lock washer (37-620) over the horizontal stud on the support arm. Using proper back protection and lifting procedure, lift the support arm and lathe and fit them into the L-tube (50-509). Slide the thrust washer over the threaded portion of the support arm and re-attach the trolley handle (37-456).