I'd rather be lucky than good

[thebuildist]

So I got started on machining my fancy new Dual Isolated-Port Pressure Relief Valve with Integrated Tee.

I started by face milling all the sides that need to be flat. Nice clean surfaces on the 4 edges, so the o-rings won't have any trouble sealing later on.

Then I set it up and started drilling the pressure relief passage with a 3/16 bit. I planned to drill it about 2.5" deep, to get well into the opposing chamber that will be drilled from the other side. The bit was about 2" deep, running pretty high rpm, and using a pecking method: bite in for about a 1/4", then back the bit fully out to allow chips to clear, then take another bite.

And then everything went straight in the toilet.

Because around that time, with the bit about 2" deep into the steel, it bound up on something and INSTANTLY snapped. It apparently broke off somewhere down deep, and since I was applying pressure at the time, the broken stub in the drill chuck ground into the walls of the hole and the remains of the broken bit and generally packed the little 3/16" hole full to the top of packed in, wedged in metal chips.

My heart sank. This kind of thing is really hard to clear, particularly with a small bit. The stuck bit is crispy-hard steel, and you can't drill it out. If it weren't for the fact that this is my only piece of steel this size, I would have just scrapped it and started overr right then.

But I didn't have much choice, so I started working at it with a little pick and occasionally punching at it with the tip of an automatic centerpunch. I got the first 1/4" to clear out fairly easily, and saw that a broken off sliver was wedged so hard into the wall of the hole that the softer steel was visibly deformed. So I put a dentist's carbide end mill in my dremel and started cutting away at that crispy hard wedge piece. After about 10 minutes of grinding and picking and centerpunching at it, that wedge finally fell out. Once it came out, I thought I was home free, as the remaining shank of the bit was clearly moveable. I picked at that shank, blasted with an air gun, and turned it upside down and hit it with a hammer, and it finally fell out. All 1/2" long of it.

Well, crud. So now I was looking 3/4" down into this little bitty hole where I could just see the tip of the remaining drillbit stub. It was deep enough that I could barely see it and couldn't manipulate it at all.

So I put it back in the mill/drill and went ahead and drilled down to it with the 25/64 drillbit that the hole was eventually going to be drilled out to. (Tap drill for a 7/16 fine thread) I was able to drill down about 5/8" or so before I hit the nub of the stuck drillbit. Not very far, but at least now I could see in there to fiddle with it.

So I picked and centerpunched at it for another 10 or 15 minutes, and though I got the hole cleaned out nicely so that it wasn't so pack-wedged in there, the broken nub wouldn't twist at all. But as I worked at it I did realize that the visible nub could now very clearly be wiggled back and forth in the hole. That confirmed that the top end was clearly not stuck, now it was simply stuck down deep on whatever had bound up in the beginning.

So that left only one option: I put it back in the vise, this time upside down, and carefully centered up on the opposite end, in the spot where the bit would have come out the other side. Of course, the steel is 4 inches thick through here, and drillbits pretty much always wander at least a little bit whenever you drill deeper than about an inch or so. So my hole from the other side had presumably wandered, and my hole from this side would presumably wander, and it's only a 3/16" hole to begin with, so my chances of drilling in from this side and cleanly hitting the tip of that stuck bit were not great.

But it was either that or throw it away and order a new piece of steel. So I drilled.

This time I pecked a lot more, after every 1/8" of progress. And I slowed down the spindle a bit, just to try to give myself at least a hint of warning before the bit snapped off.

And as I drilled down about 1 1/4" deep, the sound changed, I felt the spindle chatter a little bit, and then the resistance vanished. For a second I thought I'd snapped ANOTHER bit. But no. It had apparently drilled through and was pushing the old bit backward toward the other side.

I took it out of the vise, rammed a piece of stiff wire through there and the broken bit fell right out on the floor. I blew it out with the blowgun, and it looked clean as whistle inside. Unbelievable.

So there went a solid hour just to get a single hole drilled. At least it worked out in the end. And these things happen, right?

Bob

[Eugen]

Wow Bob! Quite an adventure. Glad it worked out in the end. I think we've all had some similar experiences. Me most often when fixing the car. Like the saying, the broken bolt that makes that 2 hour job a whole weekend.

I am curious, do you not normally use any cooling/drilling liquid?

[thebuildist]

Yes, I just use regular sulfur tapping oil for something like this. As you get deeper with a small bit, it can be tricky: if you use oil, the cutting edges of your bit tend to stay sharper longer. But the metal dust/chips tend to form an oily sludge that seems like it doesn't clear the hole as well as if you were drilling dry.

Since it had been drilling so effortlessly and clearing chips so well, I hadn't oiled it up to that point.

But then I decided, based on the result I got, that oil was a good idea, so I used just a hint of oil after that.

Bob

[Eugen]

Good idea!

[Harry]

Thanks for the great story Bob. Sorry to hear it was a PITA. Some projects are like that. One step forward and two steps back.

Keep the Peace
Harry

[DavidBarkey]

Yes, I just use regular sulfur tapping oil for something like this. As you get deeper with a small bit, it can be tricky: if you use oil, the cutting edges of your bit tend to stay sharper longer. But the metal dust/chips tend to form an oily sludge that seems like it doesn't clear the hole as well as if you were drilling dry.

Since it had been drilling so effortlessly and clearing chips so well, I hadn't oiled it up to that point.

But then I decided, based on the result I got, that oil was a good idea, so I used just a hint of oil after that.

Bob

I have found the same issue Bob . I switch to WD 40 when getting deeper or aluminum. In a pinch sulfur oil thinned with diesel fuel works as well . But no matter what you do unless you have these

chips get stuck and $hit happens .

[thebuildist]

You can rest assured, I cannot afford to run any of those!

Bob

[DavidBarkey]

You can rest assured, I cannot afford to run any of those!

Bob

Ya , me too . I can't even afford to pay attention .