Drilling/Tapping small blind holes in aluminum, quite a few questions.

Alright so I'll keep this short and sweet. I am taking on a project where I have to drill and tap 675, #4-40, 1/8" deep, blind holes in 6061 aluminum. Since I can't afford a proper CNC mill I am making do with my 1/2hp drill press and grizzly hand tapping tool. I'm not a professional by any means but I do hope to get there eventually .

My questions are namely in regards to the best type of drill bit and tap for this job, and how long I can reasonably expect my tools tools to last.

1: What is the best type of drill bit to use for my application? Thus far I have been using #43, TiN coated drill bits.

2: What would be the best style and finish tap to use for 1/8" deep holes by hand?

For a long while I was using bright finish thread forming taps(with appropriate size drill bit) in aluminum. I switched over too using a TiN coated, spiral fluted tap midway through my last project to great results. Much easier cutting and clears chips remarkably well. WD-40 was used for lubrication.

3: Is there a good way to calculate the useful lifespan of my cutting tools like the drill and tap?

Thank you very much for your time and expertise, it is very much appreciated.

I like Titex then Guhring for drills and chromed bottoming form taps for aluminum. For the drill size I would shoot for 50% thread, which depends on the H limit to some extent. Tool life generally is when you break it, they really shouldn't wear much. I have never used WD-40 as a lubricant so no help there, but if it works and what you like why change. If you are not having any problems with what you are using then I don't see any reason to change.

Is there any way to leave material on and use a plug tap then follow up with the bottoming tap, then cut to height/length?

Circuit board drills like what DScott mentioned are good.

Reverse spiral taps would be my choice for such a shallow depth regardless if you leave material on.

A Procunier Tapping head would be worth the investment if you have a ton of tapped holes to do.

Life span on tools, when they break, replace them.


Tom

And use some appropriate cutting fluid for drilling and tapping,Alum. galls real easy.

A small tapping head with a flat bottom spiral tap is gonna be the answer you need. The clutch in the tapping head will be a tap saver.

JH

Right so I have another question for you folks. Something more pressing that I forgot about when making the original post. I also have to drill and tap 50, 1/4", 6061 plates for a 1/2" NPT hole.

Last time I did this task it was a chore. I've used black oxide and S&D finished drill bits. The black oxide bits did not hold up, and seemed to wear out quickly. The S&D drill bits seemed to work OK. An appropriately sized pilot hole was used both times.

The tap was started in the drill press. Then finished freehand in a vice using a T-handled ratcheting wrench. I had moderate success but a few holes came out less than perfect. I'm definitely going to get a coated, spiral flute, tap for this. However is there an easier way to go about this? Would a 1/2 hp drill press be able to do this task with an appropriately sized tapping?

I was looking at the rather inexpensive pneumatic tapping arms. However I'm not sure if I'd be violating rules by bringing them up.

Thanks for the help so far!

For through holes, I would use spiral point rather than spiral flute. They're easier to turn (they have more unfinished threads, so cut more gradually) and easier to keep streight.

I've tapped a bunch of big holes (M20) on a bridgeport. I held the tap in a collet, set the RPM to the lowest setting, and used lots of Rapid Tap. For that part, I actually had the through holes waterjet to size. The tolerance for an M20 was loose enough that my waterjet vendor could hit it going slow. The only machining required was running a tap through the holes.

If you look through my threads, you'll find we did a similar project of 1/2" NPT in 1/4" 304 plate on a 1 HP Bridgeport. Had to do 600 holes. Used a single $100 spiral point tap for the job. Many here said it couldn't be done on the BP, but with the proper hole, taper ream, moly-dee, and the BP set at 80 RPM, it worked. My point is just that the NPT shouldn't be a problem in 6061.

In aluminum, I have had good luck with a skip tooth pipe tap and moly-dee. Again, I would recommend a tapping head.

JH

I've tapped 10s of thousands of blind 4-40 holes 0.25" deep in 6061-T6. I used a Balax form tap in a Procunier 1E tapping head with Relton A9 fluid. This setup works well if hand tapping in a drill press or in a CNC mill. I first use a 90* spot drill then a #37 drill before tapping with the Balax 4-40 form tap. That way there is no extrusion from the form tap and the tapped hole is slightly countersunk.The Procunier works extremely well with blind holes because of the cushioned double cone clutch and the fact that it stops within 1/3 revolution. The Balax taps last a very long time in 6061-T6 with Relton A9 fluid.

4-40 blind holes, 1/8" deep in aluminum. 1/8" deep equals only five threads at 40 TPI and you will lose 1.5 of them at the bottom with a bottoming tap and probably another half at the top with the chamfer. So you are going to have only three threads left. Are you aware of that?

Anyway, yes, do use a 50% tap drill. You will not lose much strength but that will make it easier to tap.

I use WD-40 to turn and mill aluminum, but prefer TapMagic Aluminum for tapping aluminum. It makes the job a lot easier.

Starting a tap in the drill press and finishing with a hand tap wrench is OK, but time consuming. I have done large batches of small, tapped holes with a battery powered, hand held drill. I used a shop made guide (steel disk with a close, clearance hole for the tap) to start them straight. With blind holes, DO set the clutch at the lowest setting and increase it ONLY enough to drive the tap: perhaps one step more, but that's it. At 1/8" depth, you could easily finish the holes with the guide still in position so it should go fast.

I like the spiral taps for this: plug and bottoming. I would do all the holes with the plug tap and then come back and use the bottoming one.

With the taps in a battery drill, you can have a toothbrush mounted nearby. After doing a hole, rev. the drill up to high speed and brush the tap against it to clean the chips off quickly. Then dip the tap in the tapping fluid and line up on the next hole. It can go quickly.

For your 1/2" NPT holes, I would use a drill press if you can slow it down enough. You will find the slower, the better. Again a brush to clear the chips and a small container of tapping fluid to bring to the tap to dip it. I find that faster than using a brush for the tapping fluid.

A tapping head would be ideal for both of these jobs, but they can be expensive.

EPAIII said:

4-40 blind holes, 1/8" deep in aluminum. 1/8" deep equals only five threads at 40 TPI and you will lose 1.5 of them at the bottom with a bottoming tap and probably another half at the top with the chamfer. So you are going to have only three threads left. Are you aware of that?

Anyway, yes, do use a 50% tap drill. You will not lose much strength but that will make it easier to tap.

I use WD-40 to turn and mill aluminum, but prefer TapMagic Aluminum for tapping aluminum. It makes the job a lot easier.

Starting a tap in the drill press and finishing with a hand tap wrench is OK, but time consuming. I have done large batches of small, tapped holes with a battery powered, hand held drill. I used a shop made guide (steel disk with a close, clearance hole for the tap) to start them straight. With blind holes, DO set the clutch at the lowest setting and increase it ONLY enough to drive the tap: perhaps one step more, but that's it. At 1/8" depth, you could easily finish the holes with the guide still in position so it should go fast.

I like the spiral taps for this: plug and bottoming. I would do all the holes with the plug tap and then come back and use the bottoming one.

With the taps in a battery drill, you can have a toothbrush mounted nearby. After doing a hole, rev. the drill up to high speed and brush the tap against it to clean the chips off quickly. Then dip the tap in the tapping fluid and line up on the next hole. It can go quickly.

For your 1/2" NPT holes, I would use a drill press if you can slow it down enough. You will find the slower, the better. Again a brush to clear the chips and a small container of tapping fluid to bring to the tap to dip it. I find that faster than using a brush for the tapping fluid.

A tapping head would be ideal for both of these jobs, but they can be expensive.

Click to expand...

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.

600 RPM?!?!?! WAAAY to fast unless you have a tapping head.

I'd use a variable speed cordless drill with a clutch, and aluminum Tap Magic. Sure, a tapping head would be nice, but you're looking at $300 for a used one on Ebay. That's almost $ .50 per hole. Unless you plan to do a bunch of these, I'd do it by hand.

"Last time I did this task it was a chore. I've used black oxide and S&D finished drill bits. The black oxide bits did not hold up, and seemed to wear out quickly. The S&D drill bits seemed to work OK. An appropriately sized pilot hole was used both times."

WHAT? Silver & Deming is not a finish. It is a drill with a reduced shank, usually to 1/2". And they are not "bits". They are drills.

You needed a pilot hole for a 1/2 inch drill? What are you turning it with, an eggbeater?

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.

CTV47 said:

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.

Click to expand...

EPAIII said:

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.

Click to expand...

I read your post again. I understand what the purpose of the tapping head is. I am not trying to attempt to tap the 4-40 holes in with my drill press. For the exact reasons you listed really. I have a hand tap with a guide that keeps the tap straight for the whole operation. Using a hand drill would be more or less the same thing only different from what I can see. A tapping head would be nice for this operation, especially to reduce the chance of breaking taps. However I wouldn't consider it pressing for tapping the small holes.

What I am more interested in knowing is if my drill press with a tapping head can handle doing the 1/2" NPT through holes. Those take considerably more effort to do by hand so I'm very interested in automating this task as much as possible(short of outsourcing). The tap wrench with the guide that I have isn't capable of holding the 1/2" NPT tap. My drill press isn't capable of reversing, so a tapping head would be necessary. Like I said though, I only have a 1/2 hp, 120v, belt driven drill press. I'm not sure that it would be up to the task.

In any case, thank you for your time. Sorry for my mistakes in terminology.

tdmidget said:

"Last time I did this task it was a chore. I've used black oxide and S&D finished drill bits. The black oxide bits did not hold up, and seemed to wear out quickly. The S&D drill bits seemed to work OK. An appropriately sized pilot hole was used both times."

WHAT? Silver & Deming is not a finish. It is a drill with a reduced shank, usually to 1/2". And they are not "bits". They are drills.

You needed a pilot hole for a 1/2 inch drill? What are you turning it with, an eggbeater?

Click to expand...

Sorry about that mistake. You are correct, they are Silver and Deming drills with a reduced shank. A 1/2-14 NPT calls for a 45/64 hole, so it's a bit over 1/2 inch.

Do you have an specific recommendations for tackling this portion of the job?

For hand tapping in a drill press, mill, or lathe this little gadget with a T handle tap wrench is hard to beat.
Fisher Machine Shop Pee Dee Wires and Tap Guide