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jd750ace
Front Toward Enemy
You can blast it without masking it. I did, then went over the swept area with an orbital sander and 180 grit to give it that random but dressed finish that new pads work best on.
LuckyLeprechaun
XS650 Enthusiast
I also used an orbital sander. I stuck my rotor on a lazy suzan so I could hold the sander still and turn the rotor under it. I used a garnet sandpaper, I read somewhere that the garnet will not imbed any contaminants in your rotor or something like that. I forget what grit I used, but I think it was 100
maynard911
old guy who likes bikes
I have blasted rotors with medium glass beads and used them with no further finishing. It leaves a very nice matt surface that breaks in quickly. If a sharper more aggressive media is used then sanding would be advised.
2eightcustoms
XS650 Addict
I do this to all the time to remove glazing, I use a 60/40 mediaequivilant to like a 240grit finish I also do the same thing to the brake drum (if drum brakes)
maynard911
old guy who likes bikes
I think that you would be ok, but if it was me, I would sand the pad swept surface with some 180 or less sand paper to knock off the sharp points and keep the pad break in from being too aggressive. Black diamond type abrasives leave a sharp edged surface that would cut your new pads pretty fast. That might be a good thing if you are looking for instant break in.
Hi FrkyMnky,
nice photo but there's something missing.
Where's the holes?
If you drill that thing full of 3/8"(ish) holes the brake pads self-clean and shed water better in the rain, the disk weighs less and the disk's braking surfaces tend to smooth themselves out over time.
jd750ace
Front Toward Enemy
Don't go to 3/8" the hole size should not exceed the thickness of the disc. I did .220" diameter holes. Something like 84 holes. Lost almost 4 ounces of weight. Worthwhile for the reasons listed above, and keeps your pads cleaner too.
Hi ace,
I did say 3/8"-ish and sure, .220" will work too.
I went to 3/8" because it's the nearest common drill size to meeting the "do not remove more cooling area from the surface than you create on the hole circumference" requirement.
Using .220 holes adds cooling surface by a ratio of ~ 2 to 1, way more than my rule sez, so your alternative "should not exceed the disc thickness" requirement must have a different basis, do you care to share it?
jd750ace
Front Toward Enemy
No true basis other than I read it here, and have otherwise read that no more than 1/3 of the swept area of the pad (radially) should be drilled away, but slotted discs bypass all these "rules" we throw around. The thickness of the disc rule makes good sense from a standpoint of balance between rigidity and increased surface area. Specifically for rigidity, which is an important feature of a non floating disc.
LuckyLeprechaun
XS650 Enthusiast
Fredintoon: The reason I've heard for not drilling holes a bigger diameter than the thickness of the rotor is surface area for cooling. When you drill holes you lose brake surface area, but if your holes are equal to or less than the thickness of the rotor you actually gain total surface area(the "walls" of the hole you just drilled) which promotes cooling. If you drill your holes too big, you lose more brake surface area and total surface area as well which hinders cooling(less thermal mass and less surface area). Most people drill as close to the thickness of the rotor as possible because you remove the most weight while still increasing surface area for cooling.
I drilled my holes 6.5mm which is the minimum recommended thickness for our rotors as stated by Yamaha.
I drilled my holes 6.5mm which is the minimum recommended thickness for our rotors as stated by Yamaha.
maynard911
old guy who likes bikes
I'd say drill the size holes that look good to you. There is almost no chance that a rotor will overheat in normal usage. Racing is a different story. I've not heard of any rotor overheating problems on these bikes.
HH pads, Teflon lines, and a properly sized master cylinder will way more than make up for any lost area.
My Ducati Brembo's are 5mm thick and have 8mm holes.
HH pads, Teflon lines, and a properly sized master cylinder will way more than make up for any lost area.
My Ducati Brembo's are 5mm thick and have 8mm holes.
I think I am going to try running them as is. I can barely feel the ridges left by sandblasting when compared to the ridges already in the rotor from the caliper. Should also help break in the pads as well. If I don't like it, well I have a DA handy and it shouldn't take too long. Then I can drill some holes in them at the same time.
LuckyLeprechaun
XS650 Enthusiast
If/when you decide to drill it, remember to use a slow cutting speed(I think I did mine at around 350-400rpm, somewhere in that range) and a mid-weight lube(I used engine oil).
Hi LuckyLeprechaun,
FWIW, my 10mm holes lose 157sq.mm on the braking surfaces and gain 204sq.mm on the bore of the hole.
your 6.5mm holes are at 66/133 and jd750ace's .22" (5.59mm) holes are at 49/105.
As to the loss in braking surface, depends how many holes you drill, dunnit?
And on the drilling technique, yes, slow as the drill can go and flood with oil (cutting oil is best but engine oil works too).
Also, reef down real hard on the feed arm and use cobalt steel drill bits.
FWIW, my 10mm holes lose 157sq.mm on the braking surfaces and gain 204sq.mm on the bore of the hole.
your 6.5mm holes are at 66/133 and jd750ace's .22" (5.59mm) holes are at 49/105.
As to the loss in braking surface, depends how many holes you drill, dunnit?
And on the drilling technique, yes, slow as the drill can go and flood with oil (cutting oil is best but engine oil works too).
Also, reef down real hard on the feed arm and use cobalt steel drill bits.
LuckyLeprechaun
XS650 Enthusiast
Based on those calculations then, I would have to say that all I can think of is maybe the smaller holes give a better loss of braking area to gain of total surface area ratio?
And you are correct, as for loss of braking surface, it would matter how many holes you drill, I think I drilled 84.
I just used HSS(high speed steel) drill bits when I did mine, key is that they're sharp and you go slow. I think I applied medium steady pressure. The rotors are actually a hardenable stainless steel, so if you heat up the area you're drilling too much you can harden the hole you're drilling and then you have to drill hardend steel.
And you are correct, as for loss of braking surface, it would matter how many holes you drill, I think I drilled 84.
I just used HSS(high speed steel) drill bits when I did mine, key is that they're sharp and you go slow. I think I applied medium steady pressure. The rotors are actually a hardenable stainless steel, so if you heat up the area you're drilling too much you can harden the hole you're drilling and then you have to drill hardend steel.
