Topic: Disk brake won't drill!

[tanman855]

I'm trying to drill holes in my disk brake but it is extremely difficult for some reason, I'm drilling a pilot hole just fine but the bits are getting burnt up. Any advice on drill speeds and ideas about what kind of bit to use would be helpful thanks.

[Elan]

i'm sure more experienced people will chime in, but You want to keep it cool with cutting fluid, and at least titanium or colbalt bits. thats a lot of stainless your going through!

[brandEn]

Use a Kobalt bit and oil, should cut right through.

[Xjbear]

Or what they call 'titanium' bits, drill press, oil, slowest speed... Buy several 3/32 or 1/8" bits and do all of the holes, then open em up to 1/4" anything bigger than that looks funky

[hockeyteeth]

You want to keep the RPMs as low as possible so you don't overheat the bit. Also, apply a good bit of pressure to the bit to help it bite into the material. And definitely a bit of cutting oil.

[754]

 First off, most regular drill presses are pretty high speed some too fast for drilling metal.
 Second you need a fairly good drill , not cheapo "got a nice set at HF or Crappy Tire and they have gold coating"variety..
 And the big one.. once you experience difficulty, it has probably work-hardened, and now will be muuch harder to continue.. sorta a pita for  someone with the right tools/knowledge.. and  very high on the difficulty scale for someone that has never done it..
 Once a drill bit starts to "go away", it will only make things worse till it gets changed or sharpened.
 You may have to send it out.. if your drill press does not have speeds below 200 rpm.. gonna be tough to fix it...

[-CB-Jamie-]

I only drilled my disk about three weeks ago for my 400f and had no problems with it. I used a middle speed on my drill press which I think was about 1000-1200 rpm. I got a loan of a drill bit from work called a ''centre bit'' to make a small pilot hole and sunk it about 2-3mm into the disk just so the bigger bit wouldn't wander around when trying to start it. I then used a 6mm(1/4'') cobalt drill bit and went straight through taking it nice and easy with moderate pressure and using a cutting lubrication spray, oil will do the exact same thing or I've even heard washing up liquid being suggested for this if you don't have any oil.

I had 48 holes to do in mine and I think it took me about 75 mins total for the actual drilling part. Here's a few pics I took while doing it.

Hope this helps,
Jamie

[Xnavylfr]

Good looking job!! You need to see if you can find a COUNTERSINK  or maybe even a small ball rotary file and go back and deburr each hole. Every hole will have a sharp edge around the top and bottom of the hole and this will eat up your pads real quick. all you need to do is chuck it back up in the drill press and just lightly touch each hole top and bottom to remove the burr!!

Xnavylfr(CHUCK)

[-CB-Jamie-]

Hey chuck thanks,

Forgot to mention I did actually deburr the holes using an oil stone and some oil as lubrication by just rubbing it flat over the disk. I checked every now and then by rubbing a stanley blade at a very shallow angle to see if it was catching up on the burr on the holes and kept going til the blade wasn't catching up when I rubbed it over the holes. You are not supposed to countersink brake disks at all as far as I know, something to do with heat build up I think and if you think about it have you ever seen a factory drilled brake disk on more modern bikes with countersunk holes?

Jamie

[70CB750]

Titanium - gold looking - bits are only coated.  You want cobalt, the wrap will say for stainless steel. HD or Lowes or Sears have them. If you buy whole set it is cheaper per bit and they are handy at times.

And slow steady drilling, dont let it heat up.

[754]

 Centre drills are crap for this job for a few reasons, Spotting drills are easier on the drills that follow them. I prefer stub drills with a split point. You didnt really drill that without clamping did you? If you mount a centre plug on the table that the disc can turn on, they will stay VERY concentric...

[mitch500]

Does anyone have a template available to download and print off? So I can place it over my rotor and have evenly spaced holes??

Thanks.

[-CB-Jamie-]

Centre drills are crap for this job for a few reasons, Spotting drills are easier on the drills that follow them. I prefer stub drills with a split point. You didnt really drill that without clamping did you? If you mount a centre plug on the table that the disc can turn on, they will stay VERY concentric...

Well I'm far from an expert at this kind of stuff but I'm very happy with how it turned out considering it was my first time ever drilling SS. I used the centre bit on the advice of a metal fabricator in work who I presume would have pretty good experience. What are the reasons that they would be no good here? And what are spotting drills? everyday is a learning experience so I'm all ears lol 

Yes I did drill it without clamping it, I just kept a good firm hand on it as I drilled and the holes have turned out perfectly concentric as far as I can see anyway and I'm normally not a person to half ass something, I normally have to have something absolutely perfect or it's not acceptable to me.

[-CB-Jamie-]

Does anyone have a template available to download and print off? So I can place it over my rotor and have evenly spaced holes??

Thanks.

This is where I got mine, Thanks to 'Goon 1492'
http://forums.sohc4.net/index.php?topic=45389.0

[754]

 Eventually a centre drill will wear and they are tricky to sharpen..wait till you have to reverse layout a disc to try to save it and the hole to drill the broken c-drill from the backside.. 
 Mainly what I dont like about c-drills,, breakage and the angle pasr the point its 60 degrees. Most drills have an included angle of 118 degrees...when that hits the hole started with 60 degrees, its tough on drill edges. Spotting drills are very short and 118 degrees.. very rigid and easier to sharpen than C-drills. Way harder to find... but far kinder to the drill following it.

[AbbyRider]

I just drilled mine the other day. Used a 1/4" cobalt bit that was about $10. Tried lubricating but actually found drilling dry was easier. Ran the drill press at 600 rpm. Used a center punch and then purposefully did not clamp. That way the bit finds the punch mark and the rotor centers itself. Biggest challenge were the red hot sharp spirals of metal spinning around the bit. And as far as the holes, I've read that they should not be countersunk. Something about the holes acting as a way of "cleaning" the pads.

[lucky]

i'm sure more experienced people will chime in, but You want to keep it cool with cutting fluid, and at least titanium or colbalt bits. thats a lot of stainless your going through!

You have to use a cobalt bit in that 400 series stainless.
Keep the drill bit speed down! If you told us the drill bit diameter I could give you the correct speed. 750RPM maximum !!!!

IF you go too fast the stainless becomes work hardened and then you will have a hard time drilling it. You will have to start with a new bit. But do not use the NEW bit on a work hardened hole. Use it a couple times THEN drill the work hardened hole.
See drill bits must be broken in or they can chip.

Cobalt is a thin layer of cobalt over M42 steel base.
the Titanium bits are not as hard and it is a very thin coating of Titanium.

Many people do not know WHAT those pulleys in the top of their drill press are for.
And a wood drill press has speeds that are too fast.

[Elan]

I bet that $40 dollar rotor drilling service on here is sounding not too bad now haha

[754]

 I am pretty sure cobalt is an alloyed component, but the Tin is a coating..

[70CB750]

I am pretty sure cobalt is an alloyed component, but the Tin is a coating..

And you are right. Cobalt lathe bits are ground to shape all the time - it must be an alloy.
I wrote my thesis on PVD and CVD processes back in the day with experiment on end mills life span with different coatings. In some case the titan coating had amazing positive effect.

[tanman855]

WOW thanks for all of the info, I finally got it! I got some fancy drill bits donated to my highschool from a tech college nearby they did the trick. But the bit jumped over a little and scuffed the disk. Should I get it re-surfaced?

[Big Bob]

Yes, absolutely get it resurfaced.

I did a pair for one of my CB750's a few years ago.  Lots of hours at the drill press.

Then I found a guy who would do batches of 10 in a CNC machine.  Did that a few times, sold off the ones I didn't need.

Godfrey's Garage sells a very nice thinned and lightened rotor for $80 or so with exchange.  Not positive on the price, ask him.  Totally worth it.  My guy looked at one and said "I can't compete with this."

I've now got the Godfrey rotors on two different race bikes that I've built and there's going to be one on my street bike soon.

[Godffery]

Thanks for the endorsement Bob; it means allot coming from someone with so much track time on these bikes!

If anyone is interested, here is a link to my modified Rotors & other Brake components.
http://www.vinmoto.org/gallery/v/VinMoto-Garage/album03/Godfferys-Garage-123/album185/
I could also offer a deal to SOHC members for thinning or exchanging Rotors that have been drilled .