Re: drilling into sprockets
 

for future reference try also drilling a pilot hole and/or stepping up in size rather than going straight to the hole size you need...

Re: drilling into sprockets
 

If you want to learn how to drill out sprockets, try making Trophies out of them. I got the privilege of drilling out about a dozen sprockets to finally get the trophies for my teams off season even right.

Pretty much all the good advice has been noted, but I'll try to sum up my experience.

Because we had to make about 8-10 trophies, each a half of a sprocket, we had to drill out about 5 sprockets. And since we wanted them all to be about the same, we experimented with some hole patterns till we got one we liked. Once we had that figured out, we had the good fortune to be able to use an indexed vise that could be rotated a variable number of degrees. All we had to do was clamp the sprocket in the vise, and center mark all the hole points in a mill, and each one came out identical.

To actually drill out the holes, I used a drill press. Because of the volume and time constraints, I clamped the sprockets to the table with a few vise grips rather then struggle with a full vise. Then I picked a small bit, 1/8th I think, and pilot drilled all the holes. Then I would step up the hole size till I got to a full 1/2 or what ever size I was aiming for. I probably used 3 steps to get to 1/2. I used wd40 for the small bits and some generic cutting oil for the largest. It's not necessary to drench the bit, but to listen and feel carefully for when the oil has burned off. When that happens, back out the bit, add more and keep going. High speeds can be used for small bits, but you'll still be slow, perhaps 500 rpm? I used 300 rpm for the bigger bits.

Because each bit only had to remove a little bit of metal, each cut was clean and fast. I didn't have any noticeable loss in sharpness on the bits by the end of the marathon drilling session (spread over 3 days).

Also, most large bits can't start a hole at all. The very point of them are just blunt, and won't do anything but make a lot of noise if you try to force them into metal.

Re: drilling into sprockets
 

Last year we had trouble drilling into our sprockets. We had the guy at our sponsors machine shop help us. During I think the day before the shipdate the sprocket broke right in half... kind of like that picture a few posts back. Anyway we found out, it was due to the sprockets being cast steel rather than solid steel. I would stick to the solid steel, we ended up having to replace a lot of sprockets because of it.

Re: drilling into sprockets
 

You need to step up drill size to drill an accurate hole. Or even in some cases to get the drill to cut at all. If you have a drill bit and look at the cutting tip or the "Chisel Edge" you will notice that its not a point its flat. If you need to drill an accurate hole the drill bit you start with needs to have a chisel edge smaller than a punch mark. Then as you step up your drill bits you shouldnt have the chisel edge larger than the hole which you drilled before. As you get to larger drill bits the chisel edge is obviously large, the edge doesnt cut very well thats why if your starting off with a 1/2" drill bit you wont get a cut. This also explains why when your drilling your drill bit will "walk" as the drill moves around on the chisel edge.

You can see the chisel edge in the attached picture below taken from werko.de If your at a book store or library look and see if they have the machinery's handbook, it has a whole section on twist drills.