Did they break off when they just got started, and the break was flush with the top? I mean, is there nothing sticking through on the bottom side? No chance at all of getting a needle-nose vice grip in there?
The first one broke very early on. The second one broke with quite a bit of tap in there; I think the threads are fully and successfully tapped. But it got to a point where it started "creaking" going both forward and backward.
There's absolutely no chance of grabbing onto anything. There was some sticking out, so I tried latching onto it with a drill and drilling it out. It wouldn't grab, though. And then I tried using pliers, but just grabbing on the tap broke it so that there's nothing to grab onto anymore.
Use the proper size drill bit. If you used an oversize bit that would make it easier to tap but your threads will have less engagement and with a #2 screw there is not much engagement to begin with. You could strip the threads when you go to tighten the clip down.
I don't have a whole lot of experience, but it seems to work very well for the one screw that got in there. I can only imagine that the tapping process would be more difficult with a tighter drill bit.
When you are starting the tap, alignment is critical. Any misalignment will cause the tap to bend, and taps are hardened like untempered knives- they will just snap rather than bend. To help get the alignment right, set it up carefully and use a proper T-handle for the tap. I would remove the liner completely from the knife assembly and lay it flat on a peice of wood. Beforehand I would drill a hole in the wood large enough to clear the tap (1/8" would probably work- you don't want it too large). Line the hole you're tapping over the hole in the wood and clamp both the wood and the liner together to the table top. Now you have both hands free to manipulate the tap, and the liner won't flex on you.
I was doing everything in a drill press. I had the tap in a drill press, and I was turning it manually. The liner was held down with a C-clamp, so it wasn't going anywhere.
And it didn't feel like flexing was the problem, or anything to do with the angle. The taps just got locked up in both directions, and torque is what destroyed them.
If alignment is that critical, I can't imagine what a nightmare this would be using a T-handle by hand
Use lubricant. They make a special tap cutting oil but something like transmission fluid works ok for tapping steel.
I used Hoppe's 9 gun oil. I have a hard time believing that using transmission fluid instead would make the difference between a successful tap and a broken one, but I don't know for sure...
The first couple of revolutions with the tap are critical. Set the tap on the hole and eyeball it from several directions to confirm it's perpedicular to the liner. Very gently start rotating the tap. You don't need to push down on the tap, the weight of it will suffice. Once it starts cutting you will feel it get hard to turn. Now you need to clear the chips by rotating counterclockwise for maybe half a turn. Rotate clockwise for a turn, then counterclockwise for half a turn. It's basically a two-steps-forward-one-step-back process. If you don't clear the chips it will get so hard to turn that you'll break the tap. With such a tiny tap I would err on the side of caution and do tiny increments like 1/4 turn foward, 1/8 turn back, at least to start. Pay very close attention to the amount of torque required to spin the tap, if it gets tight don't push it! Back the thing all the way out and re-start it if you have to.[/quote]
I did exactly this in the drill press! I did go forward and reverse very frequently, and I felt the need to back all of the way out several times. But the last time I tried to back out, the tap was locked up in every direction...
BTW, these are tapered taps, correct? If you got plug taps they are going to be extremely difficult to start.
They were tapered, yes. Would a plug tap be stronger and less likely to break, especially in the beginning?
Also, would a HSS tap do better in a situation like this?
If you have a drill press I have had good luck using one to hold the tap and start the threads.
Too bad I've had bad luck with this :grumpy:
The hard part now is getting the broken tap out. Think you can post a picture? If the tap is sticking out both sides and you can't grab on to it, you might be able to put it in a vise and shatter the tap. Probably wouldn't work on a bigger tap but might on one that small. Your last option will probably be drilling it out with a bigger bit and going to a larger screw. You would most likely need a drill press and a vise that will keep the liner from moving. If you don't have that it might be best to send it to someone.
I'll try to get a picture, but the taps are about the thickness of the liner. I think I'll have to either shatter them or use some sort of chemical to dissolve them, hopefully without ruining the liner in the process...
