rabidMunkee
New Member
Vid is self explanatory, but basically using a drill press and rotary table to give a consistent finish to the sanding
interesting vid on resurfacing brake discs
- Thread starter rabidMunkee
- Start date
Vid is self explanatory, but basically using a drill press and rotary table to give a consistent finish to the sanding
Interesting video. This looks boarder-line machinists territory but if you have a drill press and a pile of rotors …why not?
40 grit seems pretty harsh for a sanding disc. I thought maybe a 100 grit would work.
Mounting the rotor correctly might be tricky at first but the rotation could show a slight wobble also that could be repaired. Some of us might have the measuring tools (micrometers) to help keep things within tolerances. Looks like a good way to resurface or repair a rotor …if you have the tools/time/patience.
40 grit seems pretty harsh for a sanding disc. I thought maybe a 100 grit would work.
Mounting the rotor correctly might be tricky at first but the rotation could show a slight wobble also that could be repaired. Some of us might have the measuring tools (micrometers) to help keep things within tolerances. Looks like a good way to resurface or repair a rotor …if you have the tools/time/patience.
I’ve had a few friends experiment with different brake pad compounds. IMO using a good pad material for the type of typical ride you do is important. Resurfacing a rotor may be necessary when you change brake pads or brake pad compounds. Then bedding in those new pads becomes important.
Sometimes heat dissipation is important for long descents. A rotor with better heat dissipation might be useful, but those are a bit more expensive or slightly heavier. (My rear brakes failed once because of heat…was not a happy ending.)
Sometimes heat dissipation is important for long descents. A rotor with better heat dissipation might be useful, but those are a bit more expensive or slightly heavier. (My rear brakes failed once because of heat…was not a happy ending.)
I admire the bloke's ingenuity in performing a task using limited resources. It's a fun exercise, and prepares you for more complicated machine operations. He clearly states that he's not removing a lot of material and the primary benefit is cosmetic. He's spiffying up rotors that haven't seen much use. That's fine--everyone likes spiffy rotors.
Years ago when I got my first mountain bike with disc brakes, I had a similar idea. After all, automotive rotors develop grooves and need to be machined, right? I fabricated a tool post grinder for my lathe, and mounted the rotor to my faceplate. I was able to remove the grooves, and the results were satisfactory.
After running disc brakes for a while, I learned that small grooves don't negatively affect performance. When the grooves become substantial, the rotor is probably approaching minimum thickness and should be retired. Resurfacing was a waste, in my case.
Plummet
Flash Git
ahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahahaha.
That guy has too much spare time.
Ride ya bike more mate.......
That guy has too much spare time.
Ride ya bike more mate.......
Rod B.
Well-known member
It's not a good practice to machine your mountain bike rotors. Automotive Yes, mountain bike No.
All brake rotors have a "Minimum" thickness. As an example, the Shimano brake rotor seen being machined in the video is 1.8mm thick when it is new. Shimano recommends a "Minimum" wear thickness of 1.5mm and should be replaced once it reaches minimum thickness.
1.8mm new and 1.5mm worn out.....that's not a lot of meat on the bone if you know what I mean. Even a light sand with a drill press will remove too much material.
I would also like to point out that the man's rotor in the video is trash. The surface of the rotor has multiple high and low areas which will cause uneven brake pad wear, squealing and poor braking performance. This type of wear is often caused by several things including hard spots in a brake pad's compound (Metallic compounds), or an uneven stamping of the brake rotor when it was made.
Brake pad streaking indicating a rotor with high and low wear areas.
Hard spots in the brake pad compound, i.e. metallic compounds, can with time, wear grooves into the surface of the rotor. Additionally, when a brake rotor has been stamped out incorrectly during the manufacturing process, this can cause "High" and "Low" warping on the rotor's braking surface. I've found this to be especially so in lower grade Shimano brake rotors and much less so in higher grade rotors such as XT.
Unfortunately, a rotor with high and low areas will damage the brake pads. The warped rotor metal eats into the brake pad and will be indicated by a streaking wear pattern on the rotor and or brake pads. When a rotor and brake pads begin to develop high and low areas, it will cause a chronic squealing noise when braking, i.e. fingernail on a chalkboard.
Braking performance will also be poor due to the brake pad is not making full contact with the rotor's braking surface. The areas of the brake pad compound that do make contact will overheat from friction and develop brake fade on hard downhill braking applications. Unfortunately, no amount of cleaning or brake pad resurfacing will make the noise go away. The only remedy is to replace the brake rotor.
Because Shimano brake rotor's only have a finite amount of material thickness, .3mm, it's most likely not possible to successfully sand/machine a brake rotor flat with a drill press and still be above minimum rotor thickness.
Rotor manufacturers specify minimum rotor thickness due to several reasons. The first being that if a rotor wears too thin, it can overheat and tear apart under hard braking.
A brake rotor that is too thin quickly overheats and this can lead to brake fade....nasty business, I hate brake fade. Lastly, brake levers have a finite amount of fluid volume per stroke in which to activate the brake caliper pistons. When a rotor is too thin, especially when coupled with worn brake pads, the brake lever stroke cannot produce a sufficient amount of fluid volume to fully extend out the caliper pistons and apply sufficient braking pressure. Typically you'll need to do multiple quick pumps of the brake lever to engage the brakes. Obviously this is not good in a critical braking situation.
Brakes are "Mission Critical" and not something to experiment with or neglect. The parts are fairly cheap, long stays in the hospital are not. Why take the chance...?
Be safe,
Rod
Utah Rider
Well-known member
I thought everybody dressed up their rotors. Been doing that since around 2005. While the video is top notch, they can be resurfaced with a cheap die grinder and 3M wizzy pads. Without the drill press. A new rotor here is $60 US. Why waste your money on new. I've never had any issues. Cheers
While I agree it sounds like the OP likes to make his work look nice when he returns it to his customers/friends, once the pads are rebedded into his nicely polished rotors, they will loose that cool looking spiral pattern. Also, using 40 grit sanding discs would take off metal and reduce the thickness of the rotor like you mentioned. On the contrary, after a hard day or two of long and steep descents, I often notice my rear rotor turning black, which I was told was the metallic compound not being able to dissipate enough heat thru the 200mm Icetech rotor. To remedy this, I deglaze both my rotors and brake pads using 150 grit emery cloth until the black glaze is removed and rebed the pads into the rotors. I have used this method for many years and only worn out a couple of rotors. I use 220mm rotors and Maven brakes on the front without issue.
I would like to hear more about the story behind this picture. From what it looks like, the rotor got red hot (not much braking happening at that point) but I cant understand how it would snap off into pieces!
Rod B.
Well-known member
I'm going to make it up to Vancouver next year. I've heard the riding there is incredibly good and the scenery even better.
I think it's important to point out that all of us ride completely different areas of the world, with much different climates, terrain and braking needs. What works for one person might not work for another. I average about 3,000 miles a year of riding. My current bike is a Specialized Turbo Levo set up for Enduro and it's fairly heavy. I weight 195 lbs. and coupled with the bike's weight, I go through brake rotors rather quickly. I gravitate more towards Utah technical rock riding, i.e. Moab and Hurricane. In 2019, I literally destroyed my ankle so jumping and bike parks are mostly out. I'm 65 years old so that plays a factor also.
As for me and my riding, I'm currently running TRP DH-R EVO brakes with 2.3mm thick, 220mm rotors. The rotors are very thick and I find that because of their thickness, they don't warp or fade and the rotors wear evenly. I'm currently running TRP Semi-Metallic pads. Occasionally I will also use MTX Red Label Race pads. I've put about 2,000 miles on my TRP's in the last 10 months. I broke my arm on a ledge drop in May so I was off my bike for a few months. I've found that the EVO's have been incredibly reliable and very maintenance free, i.e. no sticking pistons.....SRAM.
I know there are many great brake systems out there. At this moment in time, I like TRP brakes, who knows it may change with something new and better.
I find that working on mountain bikes is a constantly evolving mechanical process towards betterment. I occasionally discover that what worked for me 20 years ago or even six months ago may not be as effective as I thought. As a bike mechanic, I've learned to keep an open mind. This often leads to new and better methods of doing things. Nothing is written in stone and it pays to have an open mind when it comes to mechanics. I do like the idea of the drill press resurfacing method, however I dislike any material loss on a rotor if it can be avoided.
I use to use a bit of emery cloth to do a bit of light sanding on my rotors to scuff and clean them. I no longer sand my rotors. It's been my experience that scuffing the rotor does not improve my braking performance. It causes rotor wear and I believe its no more effective than soaking a clean rag in Isopropyl alcohol and giving the rotor a vigourus scrubbing. I also like to give the brake pads an equally good scrubbing with alcohol.
I would be remiss in not pointing out that I also like to drink a beer, non IPA please, when working on bikes. The body needs an occasional scrubbing with alcohol....jus sayin. I realize it's hearesy to say I don't sand rotors. For my braking application, I find alcohol used as a rotor cleaner to be effective and no metal is removed from the rotor.
Regarding the broken rotor. I do not know the history of the photograph. If you look at the top of the rotor, you'll see severe scoring. This could be caused by running the rotor way past minimum thickness or the person ran his brake pads down to the metal backing plate. The rotor became so thin it sheared in half where the caliper clamped onto the rotor.
Shit happens,
Rod
All good points. As for alcohol vs emery to deglaze a rotor, I guess it was the machinist in me that went in that direction. I am most likely guilty of dragging my rear brake on the long descents we get in Whistler and when our steep loam trails turn into dust, we tend to do more rear brake skid steering which also doesnt help to stop the rotor glazing. I am reluctant to size up to 220mm rotors on the rear as I have quite a collection of 200mm but maybe that is the solution.
I also fractured my calcaneus bone into 9 pieces around 2018 (pedal slip off a drop) and have a titanium plate in my ankle but my other ankle slipped rearwards off a pedal doing another drop which tore tendons, which that gives me more grief. I just wear more braces and pads and keep on going at 62 years old.
I have ridden a Moab and Hurricane and other places in the US and prefer the slower technical descents as well. Whistler has its perks of lots time riding DH in a day but I am NOT that good/interested at the HUGE drops and high speed jumps that the kids seem to love (Dirt Merchant is HUGE but still not anything like a Rampage line!). It never ceases to amaze me that riders feel comfortable without wearing at least knee and elbow pads. I have recently started wearing a full face helmet on my non Bike Park rides (which are really just as sketchy if not worse in consequence). YMMV
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I found it too easy to drag the rear tire with a 220mm rotor. Both front and rear feel the same now and have similar modulation with a 220mm front and 200mm rear. I’ll keep that combo …unless I gain 100lbs
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