Topic: Cross Drilling Rotors

[anubiscycle]

Cross drilling your rotors. I am doing this article/thread because there appears to be an overwhelming interest in this. There maybe a step I goofed on or omitted so feel free to add if you know of some other tips and tricks in this. Also this is going on the assumption that you have a clean known good rotor that has had the “glaze” removed form the rotor surface. This is also done assuming that you want a 3/2 cross drill pattern.

Good solid planning is best in this and if possible use an expendable rotor to use for the first one you do. Normally we all ready have a pattern for cross drilling so we just use a transfer punch for each of the holes according to their size, but this is how it is done if there is no pattern.

You will need to have a heavy duty drill press with an index-able table (table that you can spin on center). If you use a small drill press it will take quite some time to complete this and will probably beat up your press.

For Honda rotors we used a upper neck bearing cup and a rear axle with a tapered head to give us an acceptable center.

Once we were sure that we had a reliable center we drilled and tapped the table so we could use the 12 mm bolts from the handle bar mounts to bolt it to the table.

When we set up a new rotor we use all of these parts again. Using the cap and axle allows us to get our center. There is some gap between the bolts and the rotor holes so finding center each time is important.

Using a cam shaft degree wheel we map out the vent runs. For simplicity we will only cover the straight vent runs here. Staggered vent runs are difficult to map and keep accurate, do yourself a favor and do not try one of these first.

This is figured on 18 vent runs.

I map out the first 9 based on the spokes of the rotor. Using a marker and a straight edge I draw the lines where the first set of vents will be orientated.

Now double check using a caliper to make sure the spacing will be even all the way around. Now half your measurement and start making your second run of vent lines.

Now that you have all of your lines drawn make a measurement across the surface of the rotor from the spokes to the edge. Divide this by three and make reference marks on one line at the thirds.

Now put your marking in the drill chuck and lock it in place. Put the table back under the drill chuck and line up the tip to your first reference mark on the vent line and lock the swing on the table and make sure the rotate is loose.

Going around the rotor lower the marker to make your cross reference marks at every other line. Don’t just spin the table as this will make you other reference marks confusing latter. When you are done you should have a bunch of crosses at you reference points for the vents. Use this same technique for the other marks.

There are literally hundreds of different ways of mapping out this rotor this way. You could skip the marker process and chuck up a spring loaded center punch instead so that each time you bring the drill head down it makes the center punch mark saving you a step.

At this point you can center punch all of your intended holes. I usually do not but this may help you with another level of accuracy.

Because you are dying to: Let’s get drilling….

You need to know what you are after before you start drilling. Do you want them all one size? Or maybe alternating between 2 sizes. It is always best to select them a little small when starting out. You can always drill it bigger for visual effect and performance later.

I usually start out with a 5/16 bit. If all my drill spots are pre-mapped I leave the rotate table and swing loose clamp loose. This lets me jump around the surface of the rotor faster and get it completed faster. I have done many of these so this just comes natural.

FOR THE OTHER HOLES:

At this point you can use the same pattern as you did before or you can find center between any two in the same string of the three hole pattern. And this will be the location for the 2 hole part of the pattern.

[dusterdude]

groovy

[kghost]

groovy

Hope not he said GOOD rotors 

Cobalt drill bit while a littel more expensive last longer and drill better on rotors.

It takes a while and more then one with steel bits (even titanium ones)

[anubiscycle]

groovy

Hope not he said GOOD rotors 

Cobalt drill bit while a littel more expensive last longer and drill better on rotors.

It takes a while and more then one with steel bits (even titanium ones)

That was a part I missed. Yes Cobalts are about $10 each but worth evey penny. Don't let them overheat, because they are junk in no time flat. I will revise this thread with pictures later so it makes more sense.

[nickjtc]

How much surface uneveness can you take out, before starting the drilling, Tom?

[anubiscycle]

How much surface uneveness can you take out, before starting the drilling, Tom?

A good rule is if the rotor has a pulsation, then it is junk. If you are talking about grooves, this depends how close the rotor is to minimum spec already.

[anubiscycle]

How much surface uneveness can you take out, before starting the drilling, Tom?

A good rule is if the rotor has a pulsation, then it is junk.

That is usually why the rotors would need to be turned down in the first place.

Look wise ass, I have had about enough of you and your bull#$%*. Find another hobby besides me, like making money. I am trying to better this forum by contributing. My guess is everyone (not here) has the same opinion of you as I do.

Specs for cb 750 rotors are such that it does not allow for a whole lot of machining. Besides there are so many available out there I can not believe that you are willing to ride around on THIN CRAP rotors.

[cafehonda]

Hey, dgfischer, what's your beef with Tom here? He seems to be trying to help while you just seem to follow his posts and punch him in the dick. The primary reason one would surface a disk is to remove the scratches and grooves carved by errant pieces of debris lodged in the leading edge of the pad. To elaborate on Tom's point, he just suggested that if you have pulsing in the disk, its warped and probably not a good candidate to cross-drill. Another thing to consider is that if the holes you drill are too large, you begin to lose braking power because of insufficient surface area. The brake pads can't get much grip on a hole, see. I've seen guys with giant 5/8" holes in their disks, looking like swiss cheese. In my humble opinion, and I think the opinion of most manufacturers, 3/16" - 5/16" holes are optimum. Problem is, you've got to drill a lot more little holes than a few giant ones. You really should never remove more than 20% of a disk's surface area. For what it's worth, I have helped prepare a club-level 750 racer and we took the disks down to 4.5 mm with a 1.25mm radius @ .250" from the edge of the carrier recess. They held up just fine, but race braking is different from most daily driving (shorter, more intense heat cycles). As an aside; Tom, although I don't know you personally, may I offer this advice: Just don't respond to this little man's posts anymore. It's not worth it and makes you look like a crabby #$%*, which, based on the sense of humor you have displayed in hundreds of other posts, seems not to be true.

[anubiscycle]

Hey, dgfischer, what's your beef with Tom here? He seems to be trying to help while you just seem to follow his posts and punch him in the dick. The primary reason one would surface a disk is to remove the scratches and grooves carved by errant pieces of debris lodged in the leading edge of the pad. To elaborate on Tom's point, he just suggested that if you have pulsing in the disk, its warped and probably not a good candidate to cross-drill. Another thing to consider is that if the holes you drill are too large, you begin to lose braking power because of insufficient surface area. The brake pads can't get much grip on a hole, see. I've seen guys with giant 5/8" holes in their disks, looking like swiss cheese. In my humble opinion, and I think the opinion of most manufacturers, 3/16" - 5/16" holes are optimum. Problem is, you've got to drill a lot more little holes than a few giant ones. You really should never remove more than 20% of a disk's surface area. For what it's worth, I have helped prepare a club-level 750 racer and we took the disks down to 4.5 mm with a 1.25mm radius @ .250" from the edge of the carrier recess. They held up just fine, but race braking is different from most daily driving (shorter, more intense heat cycles). As an aside; Tom, although I don't know you personally, may I offer this advice: Just don't respond to this little man's posts anymore. It's not worth it and makes you look like a crabby #$%*, which, based on the sense of humor you have displayed in hundreds of other posts, seems not to be true.

Point taken.. thanks

[CBGBs]

dgfischer- Please stop. You are ruining the board. You may think Tom is solicitous and thats fine....whatever, but keep your angry jealous posting to yourself.
 I don't want to pick a fight here, and I don't want to see the fight you guys have ruining this site.
I'm glad that your both posting.

I've seen options on simillar boards where you can ignore a persons posts. I have used this in the past and it works pretty well. The two of you can just omit the others posts and you'll just have to wonder what the other is posting.
 

[anubiscycle]

I do believe this says alot, Solicitous? No dig meant at CBGB's

 It looks as the SOHC gods are shining their happiness down on all of you, on this, your lucky day. It just so happens, I have an Aluminum Front wheel off a GL 1000 on Ebay right now.
    Heres the link.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=017&sspagename=STRK%3AMESE%3AIT&viewitem=&item=270041152762&rd=1,1

  Lets all watch this and in a weeks time when it ends, we will all know the answer to that nagging question we all have in the backs of our mind “
 What can I get for an ALUMINUM GL 1000 19 INCH FRONT WHEEL?”

Really I am so done. And he was #$%*ing about my "Wares"  Apparently not much $$....

[cben750f0]

ok ok ok..... this is a good thread, have done the hole cross drillin thing my self.... but the rest of this thread needs pissin off, quit it guys, it makes it hard to look at an thread with your names attatched, wondering weather it just gonna be another sh#t fight.... i dont care who is right or wrong, just dont bring it here...

end of rant

peace

[eldar]

I am with Ben. Dg, christ man, get over it already. Your method is not better than Tom's. It is just YOUR preferred way. A drill press works fine and is just as good. You just have to take the time to line things up correctly, as you do with ANY job.

[cben750f0]

thanks for the back up... NEway here the disks i got done.... they are a modified CBR pattern. the holes cover eack other slightly, and they also cover the complete pad area, if any one wants the CAD drawing of the set let me know....

 peace

[Roach Carver]

thanks for the back up... NEway here the disks i got done.... they are a modified CBR pattern. the holes cover eack other slightly, and they also cover the complete pad area, if any one wants the CAD drawing of the set let me know....

 peace

yes please! THANKS

[Hockers Choppers]

I just finished my rotors after around 6 hours of work ( my arm is still sore from pressing on the drill press handle )!! Used one 3/16 bit to pilot all the holes in three rotors, 180 holes. Snap-on thunder bits ( cobalt ). I'd post pics but don't need any crap from dgfouker . Anyway what pads are you guys running, my bike has some metallic pads that seem to gouge the hell out of the rotors. Do I need to find some different pads? 78 cb750f. Thanks for any ADVICE.

[TheGenuineThing]

O.E. pads usually work best.  No experience with sintered pads in with the cross-drilled rotor.

[cafehonda]

EBC Kevlar offer great braking power but squeal like hell on undrilled rotors. Once they are drilled, squealing is almost non existant.

[ieism]

I'm thinking of drilling my rotors myself, but i'm not sure if I have the right machine for it. I have a machine that looks similar to this at work:
.
But it doesn't spin that fast, maybe it's a machine for wood. What RPM is likely to work?

Somebody have a pattern they want to send me?           ivar.eisma@euronet.nl

[dusterdude]

you dont want it to be too fast,so that may work for you.

[Hockers Choppers]

That looks nicer than the one I used for mine! Use the slowest speed with a cobalt bit.

[Jinxracing]

Definitely run at slow speed, and some cutting fluid too...Tap Magic's a good choice, though any cutting fluid will do. Also not a bad idea to use one of these to start the holes and give them a nice chamfered edge:

http://www.use-enco.com/CGI/INSRIT?PARTPG=INSRAR2&PMAKA=369-1850&PMPXNO=16770033

[Hockers Choppers]

Only use cobalt bits!! carbides will not even touch the stainless steel rotors. Regular high speed steel bits will drill 2 to 3 holes at best. COBALT COBALT COBALT!!!!!! at slow speed with some oil, don't let them get hot. You can't go wrong ( hell, I did it ).

[Jinxracing]

Only use cobalt bits!! carbides will not even touch the stainless steel rotors.

Thought the stock rotors were cast iron...am I mistaken?

[hopterfixer]

Stainless steel, which explains why it is not rusty .  I used one 3/8" cobalt bit to drill my 48 holes out on a Harbor Frieght drill press in about 35 minutes.  Slow speed, firm feed, let the big dog eat.  I used a little oil, but the bit stayed cool enough to touch after each hole.  I used pattern from someone on this site and modified it a little.  I think I am going drill a few more offset holes this winter, who knows. 
Good Luck