Drilling Discs

What type of drill bit would you use to drill holes in a USED disc. Does the disc work harden with use & make it more difficult to drill than a new disc?
What size holes in the brake pad area?
What pattern arrangement for the holes? I believe you have to chamfer the holes for stress relief?
What size bigger holes for the none brake pad area near the mounting flange? I assume the disc will need to be mounted on a dividing head & drilled on a milling machine.

I have drilled a bunch of disks. There is nothing special about it. They are Iron, so any HSS drill bit will work. I used a Unibit on mine in a drill press. I used layout dye and made my pattern then center punched all the holes and went to town. I deburred each hole. As for the pattern, there are poeple who sell templates or you can create your own.

Now there will be arguments for and against drilling after I post my message. Since the disk is Iron there is a good chance it will crack at some point and drilling will provide no benefit. BUt many bikes have come from the factory drilled, and drilled rotors are a performance type option, so make the decision for your self.

On the plus side weight is reduced. Remember it's YOUR bike you can do what you want with it.

bwolfie said:

BUt many bikes have come from the factory drilled,

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Have many Nortons come from the factory drilled? I think drilling disks would be great if it was safe. Maybe some people with extensive experience running Norton disks in AHRMA could tell us if any drilled disks have ever come apart and caused problems.

And then of course it is who is doing it. There is certainly some engineering that can be done. Drilling whatever holes and pattern looks pretty is not going to have much to do with performance or safety.

Yes, it is your bike, do what you want with it. But there are at least three smart people here by my count that might be able to give you some really good advice and I would wait to see if they show up.

Drilling disks is taboo.
Here is mine.







Here is the template I made based on OldBritts pattern. 7/8" for the big hole, and 5/16 for the small ones,
The disk is, of course, cast iron and very easy to drill. I layed the pattern over the central hub, taped it in place and punched it all around. A small drill press will do fine. I think the because of the ease of drilling and the minimal depth, one could do it by laying it on wood and drilling it through.

Start with a smaller drill to start. Use a counter sink to deburr and a light sanding.

IIRC Ms Peel's was done by Hans Kulger. Its got kidney bean cut outs and 128 air holes
and I practice trying to stay in seat on pull downs with more negative G's than I can pull on poor stoppie prone dual 320 mm dual brake moderns pashaw. Cyrogenic tempering does have a benefit in our cast iron rotors if you are really concerned to have the best you can in real Norton components.

one & one half lb less spinning and unsprung mass can definitely be felt.

while you are at it , make it a floater
133 holes does keep you busy for a while
i do NOT champher mine as this reduses response in the wet ( try to figure out why....)
yes i know they should point the other way , but i never felt the difference and am too lazy to swap them round

Thereis plenty of fore's and plenty of againsts, I wont quote any...but google the subject, then it's make your mind up time. :roll: personaly i carnt see a problem providing its done properly.

13,000 miles on this but only 3/4lb saved compared to Hobots! 80 x 7mm and 40 x 7/16" holes all carefully chamfered and just redone.

My Brembo. Factory drill, no brainer.

ok, gotta ask....

Where did you get the disc and basket? Are you using this disc with a stock caliper?

JD

Skyguyz said:

My Brembo. Factory drill, no brainer.

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"jeffdavison" ok, gotta ask....

Where did you get the disc and basket? Are you using this disc with a stock caliper?

JD

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CNW

http://www.coloradonortonworks.com/catalog/brakes.asp

No fair jumping fence away from Norton factory items. This one shaves
5 lb off factory 6.5 lb rotor and floats to boot! For Peel of course. I'm sticking with the factory art deco caliper even if it cost a 1/4 lb on forks so help tame wheelies.

john robert bould said:

Thereis plenty of fore's and plenty of againsts, I wont quote any...but google the subject, then it's make your mind up time. :roll: personaly i carnt see a problem providing its done properly.

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It looks good when they are drilled. I bought mine drilled from somebody like Brit Bike Connection. But since doing that, I have learned that it is something that was done in the past to help cool the disk but is now considered not the best thing to do because it can develop hairline cracks on the holes (not common with normal usage) and today it is thought best to shallow groove the disk in order to increase the surface area and aid in cooling but not be subject to the hairline crack issue.

Disk drilling is a standard practice now...think of a single manufacturer that does not drill disks from factory. In all the years Ive drilled my discs and run discs. i have never heard of a disc cracking or exploding (on street bikes) I have run into a few problems with warped rotors...but cannot link it directly with the drilled rotor.
One benefit you will first notice, when riding in rain, and your hitting the brake for the first time, drilled rotors wipe away the water more effectivly and quickly. ( Iride every day rain or shine, and I can attest to this personally. )

When drilling the rotor, it is important to drill "clean". another words, high drill speed with moderate pressure, and most importantly, drill lubricant (Bolube)the Idea is to keep the inside bore of the hole free of ridges (places for cracks to start). making sure the rotor is clamped to drillpress firmly while drilling will help.

Another benifit to the drilled rotor is the "scraping effect" each hole has on the pads. each hold is another small edge biting into the pad (of sorts) wich allows a clean uncontaminated surface between rotor and pad. Notice how all the new bikes come with the "wave" rotors, there is a point to it, and its not just for appearance, it really does increase the braking effect for the same amount of pressure applied. Of course pad life is shorted...ever so slightly. But the newer bikes rotors are so thin, the huge holes and "waves" help dissapate heat quicker

The front rotor on my Norton has a rusty patch and I was going to have the disc resurfaced at a local shop to ensure even brake performance. Depending on price, I might go ahead and have the rotor drilled as well based upon what I've read.

How not to improve braking distance by turning down to new surface finish
http://www.oeqf.com/techinfo/scratching ... ing_lg.htm

http://s814.photobucket.com/albums/zz67 ... on%20Disc/

It's hard to see the cracks but they are there, every single hole along the center run of drillings was cracked. Chamfering was slight. Maybe a polishing of the interiors of he holes would have prevented the cracks. The disc had been in other hands and used before on another bike without cracking. I got a hold of it, put some good pads to it, and got it good and hot.

This is what happened to one of my Norvil discs
The other one went dish shaped, the photo was difficult to take to show this.

I am a little reluctant to drill expensive Norvil discs if the above happens to undrilled ones.

Whoa - ya fractured a race rotor - that's impressive level of use!

I had Peel's factory rotor cryo'd prior to the drilling, just in case. Peel's new Wave rotor has no counter sink to its waves and slot edges as they advertise the edges encountered has more friction effect than just flat surface area.

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One of the characteristics with “gray iron” is that it expands with heat and contracts when cold—some of the basic facts of physics. Repeated cycles over time produces gasses and internal oxidation, which causes internal cracking. In some instances, the rotor may look serviceable; however, internally cracks are developing. These cracks, once they reach the surface, will no longer allow the friction material to contact the rotor smoothly and will cause premature wear. A rotor in this condition can become a ticking time bomb if heated to extreme temperatures, say during a pursuit, and is then rapidly cooled by being partially or fully submerged in a puddle of water.

Cryogenic treatment has been around since the 1930’s, which was first documented when cryogenics was used on Jumo aircraft engine applications for Junkers airplanes,>>>
http://www.cryo-ice.net/pdf/police_fleet.pdf
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Pads too are reported to respond as well.