rmclaughlin
XS650 Enthusiast
Hey all. 79 XS650 Special. Was wondering if I can resurface or turn the discs on my bike or should I get new ones.
Thanks
Rob
Thanks
Rob
-
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Turn or resurface Disc Brakes
- Thread starter rmclaughlin
- Start date
jd750ace
Front Toward Enemy
Use an orbital sander with 120 grit on it to smooth them out. Works great. Eats a bit of paper though. The disc is stainless.
Hi Rob,
like ace sez, an orbital sander will work. I tried a lathe but the material is too tough to machine to a good surface.
What you can also do is drill the disks full of holes. That takes a drill press, cobalt steel drill bits, slow speed, heavy tool pressure and lotsa coolant.
I was told, and I noticed it myself on my disks, is that a drilled disk will improve it's own surface finish with use.
like ace sez, an orbital sander will work. I tried a lathe but the material is too tough to machine to a good surface.
What you can also do is drill the disks full of holes. That takes a drill press, cobalt steel drill bits, slow speed, heavy tool pressure and lotsa coolant.
I was told, and I noticed it myself on my disks, is that a drilled disk will improve it's own surface finish with use.
jd750ace
Front Toward Enemy
I drilled mine, then worked the surface with the orbital sander. It works great. The surface grinder probably works great too, but I did not need a lot of correction. Mine only had 4-5 thousanths variations in them.
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rmclaughlin
XS650 Enthusiast
Thanks all. What size bit did u use to drill them. How many holes too.
rahndo
XS650 Addict
ridgerunner1965
XS650 Addict
you mite look on ebay for what is called a cup hone. you chuck it in a drill and go round and round on your rotor till you get the finish you desire. i just did a rear rotor on a 1975 harley that was smooth as glass. it turned out nice.
i think i paid about 40 bucks for it. it should do dozens of rotors. i mainly purchased for doing car rotors which i do a lot of. oh and its also nice for flywheels as well.
i have used the orbital sander trick and it works well also but not as good as the cup hone.
i think i paid about 40 bucks for it. it should do dozens of rotors. i mainly purchased for doing car rotors which i do a lot of. oh and its also nice for flywheels as well.
i have used the orbital sander trick and it works well also but not as good as the cup hone.
rmclaughlin
XS650 Enthusiast
I think i saw one online. Thanks!
The hole size when drilling should not exceed the rotor thickness. Holes up to the thickness increase surface area, this increases cooling, going larger than thickness decreases surface area, this decreases cooling.
Holes In one row should overlap holes in the next row. This insures the whole swept area of the pads has holes.
The purpose of the holes besides looking racy is to improve braking. They do this by cooling, cleaning, as the brakes wear the bits of metal of the rotor get imbedded in the pads. The sharp edge on the holes cleans these imbedded bits off. As the brakes are used the heat build up causes the pads to out gas, this gas can build up and lift the pads off the rotors.
Most people drill way to many holes. It doesn't take many. I use the rotors with slots. Look good and serve the intended purposes.
Leo
Holes In one row should overlap holes in the next row. This insures the whole swept area of the pads has holes.
The purpose of the holes besides looking racy is to improve braking. They do this by cooling, cleaning, as the brakes wear the bits of metal of the rotor get imbedded in the pads. The sharp edge on the holes cleans these imbedded bits off. As the brakes are used the heat build up causes the pads to out gas, this gas can build up and lift the pads off the rotors.
Most people drill way to many holes. It doesn't take many. I use the rotors with slots. Look good and serve the intended purposes.
Leo
Hi Leo,
According to my mathbox, the break-even diameter for a 6.5mm thick plate is 13mm.
So you are a little ahead even with 1/2" holes.
And yeah, slotted rotors are great but there's very few XS11 donor bikes out there compared to the number of XS650s that need the slotted rotors, even if one XS11 can supply two (or even three if you get clever) XS650s
That or have a "Bro with milling machine."
rmclaughlin
XS650 Enthusiast
Thanks Leo
jd750ace
Front Toward Enemy
You have to balance that surface area for cooling against the area for braking. Not sure how you got to 1/2" holes but about 90 percent of us use 1/4 drill size for this. There's been a couple of Swiss cheese jobs posted on here with 5/16 and 3/8 holes. They look WRONG! Just putting it out there. 6 mm is around .240 diameter. 1/4" (.250) just a tad beyond, but looks good, and works good.
The other balance is surface area to thermal mass. By removing metal, the braking heat going in there will produce a higher temperature. The greater surface area can dissipate that and hopefully keep the temperature rise in check...
Hi ace,
you are absolutely right, braking area gets less as holes or slots are added.
I was calculating the gain in surface area from the sides of the drilled holes vs the loss of surface area from their ends.
1/4" holes gain you twice the area on their cylindrical surface than you lose on their ends.
On 1/2" holes you break even.
And I can't go with 2many's thoughts on a brake disk's effectiveness as a thermal sink neither.
Sure, it is one, but that's far outweighed by how effectively it throws heat away into the air.
Check out modern brake disks, they look like effin' fretwork and got frilly edges on them, all to throw the heat away.
Yep, gettin' rid of that heat is important. However, beyond a certain temperature, brake fade sets in. The point here is the relations of heat, thermal mass and temperature. That's why disc and drum resurfacing has posted limits.
To get an idea of heat dissipation versus temperature, you could look up the Stefan-Boltzmann law...
