Topic: Drilling Rotors

[Greg]

Hey all!
Anyone have any advice on drilling the front and rear rotors for my 76 cb750f?
Is there a particular pattern I should emulate, should I bevel the edges of the drill holes, any other advice?
Thanks!
greg

[Terry in Australia]

G'Day Greg, well there's always a fair bit of "discussion" on this site (well on the old Lusenet site at least) about the value of drilling your discs, but regardless of the effectiveness, by drilling your discs your are reducing your unsprung weight and if done properly, improving the brake rotors appearance.

The best way to do it is to have an engineer drill them on a milling machine with a rotary table, that way he can dril the holes very precisely, ensuring that they stay balanced by having an even amount of material all over the rotor. Also it looks a lot neater if the pattern is even and uniform..

With a rotary table you do everything mathematically by degrees, so all you need to work out is what size holes, how many holes you want per row, and how many rows. The most common pattern is the old 2 holes, then 3 holes etc etc, but with a rotary table you can come up with all sorts of interesting patterns by just moving the ratary table by a set amount of degrees with each hole you drill.

The CB750 early K and F rotors were big slabs of stainless steel that weighed about 4 pounds each and are very hard, so the engineer may well charge you for a reasonable amount of labour and several drill bits may well get worn out in the process, but apart from the possibility that the perforations will actually assist in the braking performance, the reduction in unsprung weight and aesthetics alone is a good reason to do it.

Make sure each hole is slightly countersunk to remove the rough edge and give it a little insurance from cracking between the holes if you decide on a radical big hole (not recommended) pattern. Cheers, Terry. 

[cben750f0]

dude they should work better in the wet, and reduce dramatically the squeel due to self cleaning..check  the.... im proud ...post... i have drilled the discs on my bike... i have the drill patern on autocad 2002, and PM it to you if you like.... let me know...peace

here is a pic of my discs

[Steve F]

  Hey Greg, (and Terry). I drilled my rotors on my '76 750F cafe and used a milling machine. No rotary table either. Just clamped them down on a plate of aluminum, picked-up the center, and programmed the CNC to do the drilling. I used the 2-hole, 3-hole pattern with a short (screw machine length) 5/16 cobalt drill bit directly in the collet.  Drilled all 3 rotors with one bit.  Chamfered the holes .030 on both sides when done.  See the results here   http://home.mindspring.com/~highvoltage/www/ 

[cb650]

I just used a kz rotor that was already drilled as a guide and did it on a drill press. With SS you need to go slow and use oil. 



                     Terry

[MRieck]

Hey guys- using CNC is cheating.

[cben750f0]

i admit i got mine done at a machine shop on CNC... i did the picture on autocad 2002, its a copy of the cbr600/1000 pattern, but done with 12mm (1/2) holes... they just put it into the cnc and away they went.... love the fact that all 3 discs are the same size!!!...peace

[Terry in Australia]

Hey guys- using CNC is cheating.

Hey Mike, CNC IS cheating, but then again, I just bought a digital vernier caliper (about all the hi-tech engineering equipment I can afford at the moment) and I kinda like not having to tax my poor old brain too much, ha ha! Cheers, Terry.

[cben750f0]

your a crazy man. terry.... though if there is a will there is a way...

[heffay]

forgive the naive-ness... what is c.n.c.   

[cben750f0]

heffay... C.N.C=computor numerical control..... automated machineing...

[david 750f]

Drill away, I have done both and I think is more for looks than anything.. Never have noticed any increased braking quality. it does look good though.

I think that loosing 10 pounds would do more for performance than drilling the rotors.......

Cheers,

David

[MotoDave]

I've done this on my '70 CB750.  Fortunately, my bike came with its rotor already drilled and I was just match drilling another for a dual disc setup.  The bad news was that I found after an hour and a half of drilling that the second rotor was warped and unusable , that's another story however.  I have another rotor that's straight that's use next time.  See attached pic:

[eldar]

Does anyone have or able to make a template for drilling K rotors. I have a 750 K8 but size wise they should not be any different than the earlier Ks. I would like to drill to reduce squeal, improve braking, reduce weight, ect.

Anyone able to do this, would be good faq item.

[pmpski_1]

This is for a CB400F. I'm not sure if it'll work for the 750:
http://www.eaglescall.com/images%5Ccb400f_disc_template.pdf


Here's a how to article:
http://eindiancompanies.com/howto/howtorotor.htm

[Buffo]

that steel is HARD! unless you have  a real good drill press and REALLY GREAT bits you are going to be drlling forever...lots of fluid is needed when drilling them too.

you might want to have a machine shop do it

[Terry in Australia]

Contact CBen750F1 Eldy, he has a CAD template that he can email you. Cheers, Terry.

[Alan F.]

The stainless steel isn't that tough to drill through, just use a new decent quality bit and a drop of oil each time. A decent drill press and a fan are required too. I'll try to find the template that was e-mailed to me years ago.

[bike54]

i agree with buffo
try high speed steel drill bits and step drill them 1/8 inch 1/4 inch and so on takes longer but not so hard on the drill press plenty of oil to keep every thing cool and finally slightly counter sink each hole just to take any burs off
if the 400 rotor diagram is to small photo copy it at the right magnificaction will get you a working copy

merv   

[Alan F.]

there seems to be some controversy over whether or not to countersink the holes to deburr them or not, after drilling two rotors I wasn't about to step up to the drill press again, I just gave the rotors a nice surface with an orbital sander and some 150 grit paper....looked really nice.

[bike54]

good idea alanf not only will you get rid of the burrs but any crap on the disk

merv

[Terry in Australia]

I think I'd still slightly countersink them, it'd involve changing from your drill bit to your countersink bit as you do each hole, (unless you've set the discs up on a rotary table) but I doubt that rubbing a bit of sandpaper over them is gonna do much to remove the burrs sitting below the level of the disc.

I'm sure I've read somewhere that slight countersinking reduced the incidence of discs cracking, and the holes retaining water, which reduces braking effectiveness. I agree with Al that after drilling all those holes the last thing you want to do is spend any more time on the drill press, but if you've gone to all that trouble, then you may as well finish it off properly?

Honda discs had a "glazing" problem which reduced their effectiveness, so we would often break the glaze with some wet and dry sandpaper, which reduced the squeal, and helped them stop better, and some guys had cast iron discs fitted, which made an enormous difference. Cheers, Terry.  

[Bodi]

I was told not to countersink (after I had) because the sharp edge on the hole helps scrape off water. The main improvement with drilled rotors is rain performance; solid discs are frigging scary when wet, they have zero stopping power then rather suddenly recover... not what you want on a slippery rainy road. Drilled discs are a bit weak at first when wet but MUCH safer.
Anyway, I looked at several factory discs, drilled and slotted. They are all sharp edged, no countersink or chamfer. So maybe the guy that told me not to countersink knew something.
The countersunk holes still look nice and wet braking is better. I'm planning on drilling another disk and will not countersink it.
If you drill properly - stepped sizes, sharp drills, correct spindle speed, plenty of cutting fluid, and drill into something solid - you don't get burrs. If you're really anal you can clean the hole with a machine reamer a few thou larger than your final drill size and get a mirror finish inside the hole plus razor sharp clean edges.

[eldar]

Well I dont want to drill the rotors myself since I do not have the tools. So I want to get a template if someone has one, then I can have a shop do it and I can make sure it is right with the template.

[ProTeal55]

A template would be very good to have.

Anyone have one of these floating around ?