Marc Brown hooked us up with a review on the Park tool DT-5.2 Disc Brake Mount Facing Set. Let's take a look at what he has to say.
I am an avid cyclist and mechanic and recently purchased the Park Tool DT-5.2 from Worldwide Cyclery to face the brake posts on a new Borealis Echo fat bike frame. I wanted to finish this build as soon as possible for an upcoming race and Worldwide Cyclery came to the rescue and shipped the DT-5.2 to me right away. Park Tool disc brake mount facing tools are really the only good option for brake mount facing. I would not recommend attempting to grind or sand down brake mounts by hand. The tolerances on many current disc brakes are very tight and precise. In the best case, trying to face brake mounts by hand will probably result in uneven pad wear and less than ideal stopping power; worst case, you may ruin your frame or fork.
The posts on this 197mm rear spaced carbon fat bike frame needed facing as they were not even close to perpendicular to the brake rotor. The posts were significantly angled down and in, making it impossible to install and adjust the caliper without the pads rubbing the rotor.
Park does not supply any written instructions with the tool, nor are written instructions available anywhere that I could find. Park does however, have video instructions available for the DT-5.2 available on their website and on YouTube. The DT-5.2 will face any brake mount, including; IS mount, post mount, and Shimano Flat Mount. The DT-5.2 comes with telescoping axle adapters for use with any open or thru-axle dropout (including Boost 110, Boost 148 and all fat bike axles). The DT-5.2 also comes with two facing cutters for IS mounts and post and flat mounts, and a hard case.
To begin the facing process, I selected the correct axle adapter and cutter for the job at hand, I watched the video several times to familiarize myself with the procedure. Once the DT-5.2 is set up, the process is fairly simple and straightforward. One thing that I did, that is not mentioned in the video, is I used a paint marker to paint the tops of the brake posts. Doing this allows you to see how much material you need to remove before the face of the post is completely flat, without removing any more material than is necessary. Simply, face the posts until all the paint is removed. Be sure to use cutting oil with this tool. Park does not supply cutting oil with the DT-5.2.
Once I started facing the posts, I soon realized that turning the tool by hand could take hours of facing in my case. There was a lot of material to be removed. Luckily, Park has machined an 8 mm hex opening into the top of the turning knob. This allowed me to use an 8 mm hex bit and a slow speed cordless drill to remove the material at a much quicker, although still slow rate. The cutter seemed to cut the carbon fiber slowly. Although, I have no doubt that this cutter would cut aluminum mounts at a much quicker rate. Also, be conscious of how hard you push down on the cutter while cutting. Even making sure the axle adapter is tightly installed, the tool can still rotate if you’re not careful. Once I completed facing the first post, I set the depth stop and faced the second post to the same height. After facing, I installed and adjusted my caliper and my problem was solved thanks to the Park Tool DT-5.2!
The Park Tool DT-5.2 is a must for any shop, frame builder, or anyone who builds a lot of bikes or has a lot of cyclist friends. I have several other bikes where the brake mounts could be more precise and will face those with the DT-5.2 as time allows.