Brake Lathe Basics

Brake Lathe Basics

Resurfacing drums and rotors is a machining process with its own specific guidelines.

There was a time when our brake lathes never stopped, humming their metallic tune almost all day long. If rotors or drums could be turned, that’s what we did, but it’s a rare occurrence today. We almost always replace them. Most shops still have their lathe because it’s valuable equipment, and while it’s silent most of the time, when you need it, you need it.

Resurfacing drums or rotors is a machining process with its own specific guidelines to follow. So, the next time you need to blow the dust off the machine, here’s a refresher on some brake lathe basics to make sure your lathe is humming in the right key. If you’re new to the process, that’s more than just a bad joke. You can always tell when your cut is going well by the sound. If it changes, so is the quality of the cut.

The basic operation of a lathe consists of mounting a drum or rotor onto a spindle. The spindle shaft is turned by a motor, which rotates the mounted component. When a cutting bit contacts the turning component, metal is removed.

There are two different feeds on a brake lathe: spindle feed (the distance the spindle moves per revolution) and cross feed (the distance that the cutting tool moves per revolution of the spindle). Spindle feed is used for brake drums, and when engaged, the spindle moves to the left, which moves the surface of the drum across the fixed cutting tool. Spindle feed rate is adjustable on most lathes.

Cross feed is used when turning brake rotors. In this case, the rotor is turning but the spindle remains fixed, and cross feed pulls the cutting bits across the rotor. Cross feed speed has a fine and course adjustment. The key to successful resurfacing is based upon the combination of spindle rotation speed, spindle feed or cross feed speed, correct component mounting and vibration elimination.

Mounting hubbed drums or rotors is accomplished by using tapered cone adapters. Choose the sizes that are closest to contacting the middle of the bearing races.

Mounting hubless drums utilizes hubless adapters, along with a spring and cone to center the drum. Hubless rotors also utilize a cone and spring to center the rotor, but a different style of adapters. Be sure all mounting surfaces are free of rust or debris. Use spacers as necessary to reach the arbor nut, and always be sure to use the self-aligning spacer next to the nut to prevent diagonal thrust on the adapters.

When turning a drum, first install the drum silencer band, making sure it is wrapped up to the right-hand edge. Position the boring bar so it is close to the drum and tighten it. Turn the drum by hand to make sure everything is clear, then start the lathe. Using the cross-feed handwheel, bring the cutting bit toward the drum until it just contacts it and makes an initial scratch cut.

Back the bit away from the drum, turn the lathe off, then loosen the arbor nut and rotate the drum 180 degrees and retighten the nut. Start the lathe once again, rotate the spindle feed handwheel a ½ turn, the bring the cutting bit toward the drum once again to make another scratch cut. Turn the lathe off and look at the scratch cuts. If they are on opposite sides of the drum, you most likely have dirt or a burr on a mounting surface. If they are side-by side, the drum is properly mounted and you can proceed with resurfacing.

As a general rule, rough cuts for a drum should be no deeper than 0.020”, and finish cuts no shallower than 0.004” (adjusted using the cross-feed handwheel). The spindle feed for cutting a drum should be 0.006” to 0.020” (adjusted with the spindle feed dial while the lathe is running).

brake lathe

When turning a rotor, the twin cutter is used to cut both sides of the rotor at one time. Install the rotor silencer band, then center the twin cutter around the rotor. You can use the spindle handwheel to help position the rotor but be sure to lock the spindle position afterward. Here’s a step many people miss: Adjust the spindle speed to match the rotor size.

On the most common lathes, this is done by moving the spindle drive belt between grooves. The outer pully groove is for most passenger car and light truck rotors; the inner grooves for larger and solid rotors. The important point is, you are changing the speed based on the size of rotor, slowing it down for larger rotors.

As with the brake drum, rotate the rotor by hand to make sure everything is clear, then start the lathe. Cutting bits are adjusted by using the knurled knobs. Use the cross-feed handwheel to position the bits midway on the rotor surface and make a scratch cut. These are almost always an incomplete circle, but it can be caused by rotor runout or by incorrect mounting. Similar to the procedure with a drum, turn the lathe off, loosen the arbor nut and rotate the rotor 180 degrees.

Make a second scratch cut. If they are side by side, the runout is caused by the rotor, but if they are opposite each other, there is most likely a burr, rust or debris on the mounting surfaces. Once you have confirmed the rotor is mounted correctly, you can proceed with resurfacing.

Rough cuts should be taken with the cross feed speed lever in the fast position; finish cuts in slow. Rough cuts should be 0.006” to 0.010” per side, and finish cuts should be 0.004” to 0.006”. Cuts shallower than 0.004 tend to reduce the life of the cutting bit, because the heat generated isn’t transferred to the rotor. Enjoy the music! TS

You May Also Like

Embracing Cutting-Edge Solutions the Industry has to Offer

Embracing cutting-edge solutions is strategic and imperative for technicians navigating the constantly changing landscape of automotive maintenance and repair.

Nadine Battah

Remember last month how I said 2024 was your year to be the technicians you always wanted to be? Remaining stagnant as a technician is simply not an option anymore if you want to be successful in the automotive industry. You must proactively seek out opportunities to embrace new tools, techniques and solutions that promise to enhance efficiency, accuracy and customer satisfaction.Embracing what’s new is strategic and imperative for technicians navigating the constantly changing landscape of automotive maintenance and repair.One of the top reasons I can give you for embracing new technology is the potential for improved diagnostic accuracy and efficiency. With the arrival of advanced diagnostic tools, like the Bosch ADS 625X, the Autel IA900, or the Hunter ADASLink, technicians can pinpoint issues with precision, reducing guesswork and minimizing the risk of a comeback. Whether it’s sophisticated tools or cutting-edge software solutions, the ability to leverage these new tools should empower you to deliver next-level service and drive positive repair experiences for your customers.Another thing to keep in mind is that embracing new technology and equipment opens doors to expanded service offerings. From state-of-the-art lifts and alignment systems, to specialized tools designed for specific makes and models, investing in the latest equipment enables you and other technicians to tackle a larger range of repairs and maintenance with confidence and precision. As the technology in cars continue to evolve, so too must the tools and equipment that technicians rely on to get the job done.Embracing new technology and equipment can also lead to improved productivity in the shop. By leveraging high-quality products that are specifically designed for today’s vehicles, you can streamline workflow, minimize downtime and deliver exceptional results for your customers.At TechShop, we understand the importance of embracing new technology, equipment and products in the automotive repair industry. That’s why we’re excited to announce the debut of our all-new “Tool Time” video podcast series, where guests from brands like Ingersoll Rand, Clore Automotive, SATA Spray Equipment and many more will sit down and join Eric Garbe and myself to discuss education and training on the latest products our industry has to offer.Join us as we embrace the future of automotive tool supply and equipment advancements together. And, be sure to subscribe to the TechShop newsletter to stay tuned!

Refrigerant Oil Has to Be Right

Oil type is just as important as oil capacity.

Three bottles of refrigerant oil
Top 5 Tools: Steve Coffell, Auto World, Hazelwood, MO

Steve Coffell, a technician at Auto World in Hazelwood, MO, says his Top 5 Favorite Tools are:   OTC Genisys Touch – Quick scan, bidirectional control Snap-on VANTAGE Pro – Easy-to-use waveform views. Power Probe IV – Power and ground control PicoScope – Live wave viewer OTC – Low Amp Probe   WHAT ARE YOUR TOP 5

Wheel Bearing Adjustment Tools & Equipment

A wheel bearing that’s out of adjustment can reduce bearing life and can affect more than just the bearing. It’s important to adjust the wheel bearing endplay to the proper specifications. If the bearing set is adjusted too loose or too tight, it can cause the bearing to fail prematurely. There are a few types of assemblies, so using correct procedures and tools will ensure a comeback-free wheel bearing installation.

What R-1234yf Means for Service, Equipment, Safety

For shops, R-1234yf means several new procedures, a certification and new equipment in order to properly handle these new systems. Why the difference in handling and servicing R-1234yf systems versus R-134a? Flammability.

Other Posts
Fuel Your Summer Fun with Federated

Enter on Facebook for a chance to win.

Fuel Your Summer Fun with Federated Auto Parts
ASE xEV Certification Program

Testing and certification is a great addition to high voltage safety training.

Bosch Auto Service Franchise Program Expands Workshop Management Solutions for Service Shops

Bosch Auto Service Franchisees will receive exclusive access to Tekmetric’s software suite and customized training for seamless integration.

LTI Tools Introduces New Socket Set

Seven-Piece Half-Inch Drive Flip Socket Set covers the most common lug nut sizes.