What did I do wrong drilling these holes?

[CalG]

I did do this. One difficulty is that to do this you need an accurate hole location. Depending on the part geometry this can be pretty challenging for those of us who aren't professional machinists. In my case, because I had drilled a pilot hole, and because my part was flat on both sides with the hole perpendicular to the faces, it was easy. But, then, the pilot hole had caused other problems. Perhaps a very small pilot hole would be the best of both worlds. No bigger than the bit web, and maybe smaller. That might even provide a way to get cutting fluid flowing through the hole and around the cutting edges of the bit the whole time or at least every time we pause the feed pressure.

Just because this came to my notification box....

On thicker material, After drilling the pilot to just shy of penetration through the far side, I like to fill the hole with cutting WAX or sulfur based cutting oil or canola oil if the work is steel.

The pilot hole holds just enough to be useful and not wasteful. Plus, it is where it needs to be.

If I forget, and push the pilot through the work, the wax comes in handy to make a dam for cutting oils, or just on it's own.

Hole making is the most frequent task in any machine shop. at least it was when I was in it.

 

[Mike1955]

Just because this came to my notification box....

On thicker material, After drilling the pilot to just shy of penetration through the far side, I like to fill the hole with cutting WAX or sulfur based cutting oil or canola oil if the work is steel.

The pilot hole holds just enough to be useful and not wasteful. Plus, it is where it needs to be.

If I forget, and push the pilot through the work, the wax comes in handy to make a dam for cutting oils, or just on it's own.

Hole making is the most frequent task in any machine shop. at least it was when I was in it.

These are some awsome posts on drills, speed and lubricant. Thanks for the info

 

[NoTrespassing]

There is great searchable information at the link below:

popularmetallurgist.com - Just another WordPress site

Just another WordPress site

popularmetallurgist.com

 

[ray66v]

I have been using the Mibro cobalt drill bits for TSC, and they seem to be really good for the money.

Use oil, go slow, and do not press harder than you need to, to keep it cutting.

 

[Mike1955]

I have been using the Mibro cobalt drill bits for TSC, and they seem to be really good for the money.

Use oil, go slow, and do not press harder than you need to, to keep it cutting.

That sounds like a good technique

 

[SmallChange]

I am still enjoying this thread, and really appreciate all the contributions. My infrequent drilling is consistently working better than it once did.

There are a number of posts that are easy to follow, for example not using pilot holes below 1/2", or using Tap Magic. No question how to do those things.

But there are also posts that I think are good advice but I don't know exactly how to follow. "Read the chip" is a good example. It makes sense that the characteristics of the chip are going to be strong indicators of how well the drilling process is working. But, other than accumulating a great deal of personal experience, how do you know what characteristics to read and how to read them? It's very useful to understand that blue coloration means the metal is getting way too hot, so you should reduce RPMs or feed force or get a sharper bit. Beyond that, how do you read them? What does continuous versus broken up versus splintery dust tell you? How about shininess? I think we had suggestions both that stringiness is good and bad. Of course it depends on the work; aluminum and cast iron produce very different chips, so how do we take that into account. It would be VERY useful to find more researched information on this.

Also, it makes me realize I'd really appreciate a force gage built into the drill press. So often I hear you're to do things by feel, but who knows how each of us gets that feel? For an example from a different subject, we all know tightening threaded fasteners involves judging whether it's tight enough not to rattle apart versus whether it's so tight the threads may become damaged. I used to work with a Navy-trained electronics technician who carefully tightened fasteners so gently that I could take them apart holding just the shaft of the tool (hex key or screwdriver) and twirling it. His "by feel" was WAY different than mine. It almost makes me want to experiment with a torque wrench deliberately stripping a bunch of sample fasteners.

 

[UncleW]

I have an oxy acetylene torch and I try to use it for everything except making coffee. If the hole got blue work hardened, could you just anneal it? Not sure a MAPP torch would get thick stuff hot enuf, though

 

[ray66v]

That sounds like a good technique

I can get a lot more life out of the bits that way.

As soon as you start pushing hard, it starts requiring more and more force as you go, then they don't cut anymore.

That's why I cringe when someone grabs my drill bits. I know whats going to happen.

 

[jaxs]

I have an oxy acetylene torch and I try to use it for everything except making coffee. If the hole got blue work hardened, could you just anneal it? Not sure a MAPP torch would get thick stuff hot enuf, though

Some times it works for me and other times I'm not so sure. If I'm not in a rush I hit the hole with a large tip so it gets hot before heating surrounding metal more than i can prevent. Put soft fire brick on front and back then let it cool. As for lubricant, I've found keeping bit from overheating helps more than special lub. To accomplish that I periodically raise bit and dip in a 1/2 oz cup of transmission fluid. I get what they say about hot rolled steel not having carbon to make it harden but experience tells me different. I don't own expensive Brinell and Rockwell test equipment like some of these guys but I can make the point. Rapidly bend a wire or strip of sheet metal back and forth until it burns your fingers,lay it aside to cool then you can't bend it in the same place again.

 

[Mike1955]

I can get a lot more life out of the bits that way.

As soon as you start pushing hard, it starts requiring more and more force as you go, then they don't cut anymore.

That's why I cringe when someone grabs my drill bits. I know whats going to happen.

I agree. If you loan a bit be prepared to sharpen it when and if you get it back. Yuk