How to drill a blind hole?

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A drill press at 600 RPM? For your 40 TPI holes your tap will bottom out after 5 revolutions. 600 RPM equals 10 Revolutions per Second and 5 revolutions will take only a half second. How can you turn it on, start tapping with it, go in for HALF A SECOND, and then almost instantly stop it. There will be momentum. You are going to have to hit the STOP button before the tap hits bottom. You may even have to hit it before it even starts cutting the thread. I doubt that you have that kind of reflexes: I KNOW I DON"T.

So the tap hits the bottom and jams. Or it becomes a drill and just hollows out the few threads it just cut. You are little better off with your larger hole. 600 RPM is just too fast for this.

That's why tapping heads were invented. They sense the resistance on the tap and when it reaches a certain value they stop the forward motion and usually reverse it. Or they go in a fixed distance and then reverse. They can also be reversed manually.

If you are going to do this in the drill press, without a tapping head, you are going to have to go a lot slower. Something more like 60 RPM or 1 Revolution per Second comes to mind. And then, a standard drill press does not reverse. So how are you going to back the tap out? That is the second thing a tapping head does; it reverses so the tap comes out even faster than it went in.

My mill does have low speeds and does reverse so they advertise that you can tap with it. I haven't tried it yet and I guarantee I will not make the first such effort with a #4-40 tap. And not with a blind hole.

I have tapped hundreds, probably thousands of holes with a hand held drill. It can work quickly. And small guide block will ensure the threads are square. Reread what I posted about that above.

Or look for a used tapping head.

CTV47 said:

I don't use a plug tap, just one step with a bottoming tap. The blind holes are actually done with a little grizzly hand tapping tool. It comes with what amounts too a hollow tube with a belled end that holds the taping wrench straight. Surprisingly effective. I don't think I would save much time by getting a tapping head for this operation. Though it would be nice to know that over eager hands can't break anything.


I can slow my drill press down to 600 RPM. It's a single phase 120v model. Think that will do the trick?I'll look into the possibility of getting a tapping head. It sounds like I may end up doing quite a few of these in the long run.

Thank you very much for the feed back so far folks. It's much appreciated.

Yes I am aware, they're only holding some LED parts to an aluminum bar. Don't need much in this instance. A tiny bit of locktight will stop anything from wiggling lose from vibration or thermal expansion.I don't use a plug tap, just one step with a bottoming tap. The blind holes are actually done with a little grizzly hand tapping tool. It comes with what amounts too a hollow tube with a belled end that holds the taping wrench straight. Surprisingly effective. I don't think I would save much time by getting a tapping head for this operation. Though it would be nice to know that over eager hands can't break anything.I can slow my drill press down to 600 RPM. It's a single phase 120v model. Think that will do the trick?I'll look into the possibility of getting a tapping head. It sounds like I may end up doing quite a few of these in the long run.Thank you very much for the feed back so far folks. It's much appreciated.

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OK, you don't need much holding strength. AND, you won't have much. So be it.A drill press at 600 RPM? For your 40 TPI holes your tap will bottom out after 5 revolutions. 600 RPM equals 10 Revolutions per Second and 5 revolutions will take only a half second. How can you turn it on, start tapping with it, go in for HALF A SECOND, and then almost instantly stop it. There will be momentum. You are going to have to hit the STOP button before the tap hits bottom. You may even have to hit it before it even starts cutting the thread. I doubt that you have that kind of reflexes: I KNOW I DON"T.So the tap hits the bottom and jams. Or it becomes a drill and just hollows out the few threads it just cut. You are little better off with your larger hole. 600 RPM is just too fast for this.That's why tapping heads were invented. They sense the resistance on the tap and when it reaches a certain value they stop the forward motion and usually reverse it. Or they go in a fixed distance and then reverse. They can also be reversed manually.If you are going to do this in the drill press, without a tapping head, you are going to have to go a lot slower. Something more like 60 RPM or 1 Revolution per Second comes to mind. And then, a standard drill press does not reverse. So how are you going to back the tap out? That is the second thing a tapping head does; it reverses so the tap comes out even faster than it went in.My mill does have low speeds and does reverse so they advertise that you can tap with it. I haven't tried it yet and I guarantee I will not make the first such effort with a #4-40 tap. And not with a blind hole.I have tapped hundreds, probably thousands of holes with a hand held drill. It can work quickly. And small guide block will ensure the threads are square. Reread what I posted about that above.Or look for a used tapping head.

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