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Drilling Front Discs

  • Thread starter Thread starter Suzuki_Don
  • Start date Start date
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Suzuki_Don

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Hi there guys. I need some advice on drilling the front disc rotor on my GS550, '77 model. I have access to a pedestal drill. Will normal drills bits cut the disc material OK. Do I use a pilot drill first. What size should the finished hole size be. What pattern should I use. Do I chamfer the holes when they are finished so they dont rip the pads on application. Any other useful tips that I should be aware of. Thanks in anticipation of some good info from people who have done this or have more machining experience than me.

Cheers
 
The rotors are made of some extremely hard metal & are a b***h to drill. I couldn't make a dent using my hand drill & titanium bits. I had to go to a machine shop & even they couldn't believe how hard the metal was. They didn't chamfer the holes either. I didn't notice any change in braking & it cost me about $50.

Paul
 
Be careful that stress cracks don't appear around the edges of those holes.
 
Suzuki_Don said:
Hi there guys. I need some advice on drilling the front disc rotor on my GS550, '77 model. I have access to a pedestal drill. Will normal drills bits cut the disc material OK. Do I use a pilot drill first. What size should the finished hole size be. What pattern should I use. Do I chamfer the holes when they are finished so they dont rip the pads on application. Any other useful tips that I should be aware of. Thanks in anticipation of some good info from people who have done this or have more machining experience than me.

Cheers
Click to expand...

First, the rotors are stainless steel. Yes, it is difficult to work. It is not hard, really, but it work hardens extremely well and this is what causes the trouble. Be prepared to be shocked at how much tougher it is than carbon steel.

HSS (high speed steel) drill bits are fine, you need to use SHARP bits, high feed pressure and low speeds. I believe that you don't want coolant or cutting fluid, but an old machinist with stainless experience would know better than me on that one. You will likely have to stop and sharpen the bit once in the middle of the job.

No pilot hole should be necessary.

If you make the hole diameter twice the rotor thickness or smaller, you gain surface area for cooling. Usually, the hole diameter is about equal to the rotor thickness from what I have seen.

Do not chamfer the holes, you want the sharp edge to wipe the pad clean. Do remove any burrs you get.

Your hole pattern should be such that the holes will sweep across the entire surface of the pads, with no area of the pads left unswept. Other than that, you can be as artistic as you want.

Mark
 
Cobalt bits ONLY or you risk over-heating and warping the rotor.
DO NOT chamfer the edges. That would greatly hinder self cleaning action and you'll easily gall the rotors if you pick up any decent sized burr/crud.
Main benefit of drilling besides looking cool is water is shed much quicker and (for a time at least) any squealing should stop or be greatly reduced, and sharp edged holes greatly minimize galling (grooving of the rotor).
My opinion is a 1/4" hole is good. I don't recommend going larger.
Don't drill too many. Mine are drilled in sets of 5 in a sweeping arc so the entire pad is effected. Each set of 5 holes is spaced so that the very outer edges of the outer holes is a total of 3 1/4". There is approx' 1" of space with no holes between all rows. My pattern used is actually called a "2/3" pattern and if you saw a pic you'd see what I mean. I don't have a pic at this time though you could zoom up on some recent pics of my bike around here and probably see it well enough.
 
Best I could do.

uploadedmay4178.jpg
 
Thanks Keith and everyone. Some good advice given and is much appreciated.
Cheers
 
Lots of good information on this thread. I just have some slightly different experiences.

I haven't done any on Zuks but did do all of my 3 Yammies. What i found is that the disks are a bit harder than carbon steel but I don't think they are stainless. I could well be wrong. I was able to cut them very easily with decent quality Titanium bits in 1/4 inch on a drill press set at lowest speed with cutting oil.

The first ones I did, I made a template, center punched them, drilled a starter hole (1/8 inch) then ran the 1/4" through.

By the 3 rd bike I was eyeballing. Laid out the pattern 2-3-2 and marked with a permanent marker. Lined up and drilled. Done in 20 minutes.

For a first time, I would lay out the pattern and center punch all spots. Fix the disk to the table with a c-clamp and take time introducing the bit to ensure it doesn't skip. Take your time, it is tedious but worth it.Once you get the hang of it, you can loosely hold the disk with the clamp and one of your hands which will allow you to move fairly quickly from one hole to the next.

As mentioned don't champher just clean up any burrs. You might also want to go with fresh pads and I heartily recommend Ferrodo Platinum for fantastic bite.

This is a good winter day project and I think you will find its worth doing performance wise.

Let us know how it turns out for you.

Cheers,
Spyug
 
Thanks, Keith, for all of the info! On some old bikes I have had, I always wanted to drill the rotors, but never did. I was afraid of making them brittle.
 
Ferodo Platinum 1983 gs1100ED

Ferodo Platinum 1983 gs1100ED

Any ideas for a US or North A. supplier? Or other options for pads?
TIA
Posplayr

Edited: I did a GSresources search and found this:
http://www.vintagebrake.com/
 
Last edited:
Looks like you might find a supplier off their web site

http://www.federal-mogul.com/

Federal-Mogul Corporation Montebello, Aftermarket

Aftermarket

Address: 2100 Yates Ave.


City: Montebello State/Province Country Sub: California Country: United States Zip/Postal Code: 90040
 
I work at the machine shop at my college and I asked a fellow technician what he thought about this. He used to work at a bike shop, took one look at my SS rotors, and shook his head. They're tricky to drill, be careful.
 
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