Holes in High Tensile Steel

Hello,

Any suggestions for cutting #10 holes in steel?

I've cut 11 other holes using my drill press in what I thought was regular grade steel sprockets (the drills went fairly well). On the

12th I've done nothing but polish a dent. I've tried several other bits of varying sizes with no results.

So I tried to cut other holes in some of the other sprockets with the same dissappointing results. I find it strange that the first 11 went so well and then nothing but dents after that. (I'm making holes in bicycle small sprockets.)

All of my bits are metal grade bits (some Bosch Titanium's) and I have

3-in-1 oil.

Is the sprocket's metal soft in some areas and hard in others?

Should I try to heat the sprocket, say with a blow torch, before I try to drill the holes?

Any help is appreciated.

Thanks.

Reply to
b_t_k
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Do you need them hard after the holes are done? If so, you might be able to soften them with a flame and all...

#10 holes? Running 1000 RPM would be a good start with oil. Motor oil would be better. Cutting oil would be best.

Are the bits true HSS or the Titanium ones really TINcoated?

Could be a bunch of stuff... Or it could be different grade sprockets...

Reply to
Joe AutoDrill

Sounds like you work-hardened the steel and then it dulled your bit.

Get some new bits, and always lean into the drill as long as it's cutting. Don't ever let the drill just idle in the hole not cutting. You always want the cutting edge bringing up fresh meat. If you need to stop mid-hole, pull the drill out smartly.

Pilot holes will help as well. If you have to choose between keeping the pressure on during the cut and putting in lubricant, keep the pressure on.

Bosch is a consumer tool company. If you want industrial quality, buy US-made drills from an industrial supplier.

Yes, after you work-harden it by letting the drill bit spin in the hole without cutting.

I wouldn't. I'd get new drills, pilot and #10 and try again.

Reply to
Jim Stewart

Wow! Thx for the fast responses.

Here's the dirt on the bits I used (looks like coated bits):

the new Bosch titanium drill bit line is the industry's toughest. By coating each bit with high-speed steel-titanium nitride, Bosch not only made the surface of the bit harder, in excess of 80 HRC(Hardness Rockwell),

As for which US bits I should have in my kit what are some recommendations and I'll head out to get them shortly.

Thanks again.

Reply to
b_t_k

You might want to spend a few dollars and purchase some carbide center drills for drilling pilot holes, it will save your drills and give you a much better hole. . You can sharpen your drills by hand just by gently touching them on a fine grinding wheel. Just look at the geometry carefully first. Once a drill loses it's edge, it goes downhill very quickly. Also, those drills are made with kind of an all purpose rake, but they can be ground by hand to give some web relief, however. It helps a lot.

Reply to
Eli_S

I would guess that your drill got dull drilling the 11th hole and when you started the 12th hole the rubbing finished the job and left you with a superhard surface where the drill was rubbing. Heavy pressure and low speed with a new drill will break through the hard surface but then change drills again and finish the hole or you will repeat the hardening of the metal and burning up the drill.

John

Reply to
John

3-in-1 ISN'T cutting oil, barely suffices for lubrication. If you have no industrial supply house, go to the hardware store and pick up some dark, sulphurized pipe threading oil out of the plumbing department, the stinky stuff. This is sort of thing needed for drilling harder steels. Lard oil works, too, but you probably won't find that at a normal hardware store. I'm assuming this is NOT stainless, if it is, it opens a whole other can of worms.

If it's off a peg at a big box, it's not the best drill that can be had by a large margin, I don't care how much you paid for it or who's name is on it. TiN can be coated onto just about anything ferrous, the famous HF untwisting twist drills are a prime example. Surface treatments have very little to do with a bit's ability to hold an edge, I think you've found that out. If you're doing a lot of this sort of thing, go get some decent bits from the likes of MSC, Chicago- Latrobe is one good make, get some cobalt in them while you're at it. They won't be TiN coated, they'll either be black oxide or bright finish, good bits don't need gold-plating to sell.

Stan

Reply to
stans4

Some things to consider. Titanium coating on drill bits does not make them "tougher", sharper, or much else for your application. The advantage is in production runs where the coating prevents the chips from sticking to the bit and building up heat.

Go to a machine shop supply house (If you live in an area with industry) and look for stub drills. These are a little bit cheaper than jobbers length and you are drilling thin stuff.

Consider if you need the #10 drill. This is .1969 inches. A 3/16 is only a little bit smaller (About the thickness of two sheets of 20# paper. They should be cheaper.

A technique would also be to drill them with the fractional bit, and then punch them to size with the #10.

Reply to
Roger Shoaf

Also try running your drill press about 650 RPM, firm pressure lots of oil.

Reply to
Roger Shoaf

I just got a carbide 3/16" bit (stubby little thing) from the industrial supply shop that I'm hoping will do the trick. You can tell this bit is different than anything I purchased before so I have high hopes.

Looks like a good bit so I'll try it tonight now that I've geared the press down to 570 rpm.

Thanks.

Reply to
b_t_k

Actually the carbide runs faster than HSS. Also with the carbide it is much more fragile so go easy on the pressure, not to say let it rub, but they don't flex well.

Reply to
Roger Shoaf

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