drilling into sprockets

[greencactus3]

we have these HEAVY sprockets we would like to drill holes into to lose weight. they are the black ones. im assuming hardened steel. we've tried carbide bits, cobalt bits, and regular bits and each one burns up with one hole or less. we have been applying oil generously but they still die on us. what are we doing wrong? we drilled lots of holes in the same sprocket with one bit with no problems before. and we barely had to use oil then.. we arent sure which bit we used back then but we know it was a 1/2 in bit. same as what we are using now. why can we not drill a 1/2 in hole into our sprockets without killing them? or we know we can take off the hubs. can a bandsaw cut them off? (we are not allowed to use a lathe... this is for OCCRA. which lathes are not allowed.)
well, any other way we can drop weight from these sprockets? (we are not allowed to use smaller sprockets/chains.)

[sanddrag]

are they Martin sprockets? if so they shouldn't be hardened, or maybe only surface hardened. Some sharp regular HSS or TiN coated bits should go through them just fine with a good amount of oil (making lots of smoke in the process). Are you using a hand drill or a drill press? What rpm? Use a d illpress if you can. From what you describe, try using more oil (most anything works, even motor oil) , a much slower speed, and a slightly heavier feed. I've drilled through many sprockets in my time and the black carbon steel ones never gave me any problems.

[greencactus3]

i actually have no idea what brand they are. but they are harder than regular steel. our carbide and cobalt bits were brand new. so they hsould've been nice and sharp. and we are using a drill press. i dont remember what rpm but we tried a variety of speeds. and we were using motor oil. and we were basically drenching the bit/sprocket continuously while drilling. and we are supposed to go slower rpms? thats what i thought but the guy someone talked to from the hardware store said spin it as fast as you can. darn. knew that meant more friction...

[Greg Perkins]

harder the material=slower the rpms
harder the material=TONS OF MACHINE OIL/LUBE (NOT MOTOR OIL)
the more oil=better cut=longer tool life

regardless to the amount of smoke that you make, the smoke should be minimal with proper rpms....if you hog into the peice and your oil instantly burns up, turn the rpms down and add more oil....

One more thing, is drill smaller holes into hard material first...that means less for the big drill to remove (big drills have less of a angle that enters the material first, thus making it much harder to get in.)

hope this helps

[Tristan Lall]

Originally Posted by greencactus3

we have these HEAVY sprockets we would like to drill holes into to lose weight. they are the black ones. im assuming hardened steel. we've tried carbide bits, cobalt bits, and regular bits and each one burns up with one hole or less. we have been applying oil generously but they still die on us. what are we doing wrong? we drilled lots of holes in the same sprocket with one bit with no problems before. and we barely had to use oil then.. we arent sure which bit we used back then but we know it was a 1/2 in bit. same as what we are using now. why can we not drill a 1/2 in hole into our sprockets without killing them? or we know we can take off the hubs. can a bandsaw cut them off? (we are not allowed to use a lathe... this is for OCCRA. which lathes are not allowed.)
well, any other way we can drop weight from these sprockets? (we are not allowed to use smaller sprockets/chains.)

First of all, if you used to drill these without issue, and now there's more effort required, maybe your drill press spindle is wobbling a bit? Or maybe the workpiece isn't secured quite right?

If that's not the case, try centredrilling, then starting with a smaller bit (3/16" or something), and going up in increments.

If you want to get rid of the hub, grind it off with a surface grinder (if the rules permit it). If the hub is welded on, cut the welds off with an angle grinder, then try to split it with a chisel.

[Andrew Blair]

Mmmm, I hate to even bring this up, but are you drilling in the correct direction for your bits? I know occasionally you'll accidently pick up a left handed bit, or not check the direction. We burned up a hole saw two years ago, and I've broken a couple bits myself in this way.

[Rickertsen2]

I'm no machining expert, but my guess would be that you are using a spindle speed that is way too high. As a general rule, use faster spindle speeds for aluminum and VERY slow ones for metals like steel. In addition, the bigger the bit you are using the slower the speed should be. Also, it might be a good idea to work your way up to 1/2" rather than tackling it in one step.

[greencactus3]

thanks everyone. yea. thats what i thought..... $@#$@#$@#$@# hardware-store-guy-that acts-like-he-knows-but-doesnt-really... ill try spinning it slower. and yes these are right handed drill bits. only lefthanded ones ive ever seen are tiny screw removing ones. and well.. thanks again. ill let you guys know if nothing works.. and then we can wonder how our steel sprocket turned to diamond overnight lol.

[NoodleKnight]

Originally Posted by Tristan Lall

If that's not the case, try centredrilling, then starting with a smaller bit (3/16" or something), and going up in increments.

I'll second that, I remember drilling through the large kit sprockets (2004 KoP I think). It wasn't extremely difficult once you got the drill through the surface layer.

[team222badbrad]

What ever you do, just make sure this does not happen in the process.

[Rickertsen2]

Originally Posted by team222badbrad

What ever you do, just make sure this does not happen in the process.

How did you manage that? Metal can break in funny ways. I remember one year a piece(made of extremely hardened steel) falling off the table and shattering into two very sharp pieces.

[team222badbrad]

I'm not exactly sure, but the metal the sprocket was made out of was junk.

I think the bit may have caught on a burr and from there it just shattered in half. It could have also been that it was clamped in the vice to hard.

This was in 2004, I was in the shop at the time, but I wasn't machining it.

[billbo911]

Originally Posted by team222badbrad

I'm not exactly sure....... It could have also been that it was clamped in the vice to hard.

I think you answered the question quite well. I photoshop'd the image as best I could. Looks like it must have been clamped in the vice by the hub, compressing across the central axis. Even if the sprocket didn't break, you might have had one incredibly rough time putting it on a shaft.
Suggestion; next time, put it in compression along it's central axis. That way, you won't risk deforming the hub, and, much less chance of it breaking.

[evelyn1503]

I think I know the sprockets that you are talking about and they are a pain to drill. I think what we have done is the t we have 2or 3 drill bits and when one wore down then we grabbed another and so on... then you have some one sharpening the dull one it sounds like a pain but I found that it was a good way to do it the you have a sharp drill bit.

[Doug G]

If you are trying to lose the weight of an attached hub, get a portable bandsaw or borrow one from a plumber type, they use them for cutting metal pipe in the field, Milwakee makes a great one. Use the portable band saw to hack most of the hub off. We did this in 2003, with a bunch of donated gears and sprockets and saved several pounds of weight. Last year we tried to use a lathe to turned down a sprocket hub and it sucked, found out later that the spocket has Stainless which is more difficult to machine. My advice is to use a portable band saw.