Drilling and tapping 200+ 3/8" holes in 3/4" aluminum

That's a good idea. Would you say, with a proper tin coated tap like this, and using a letter S drill, the 3/8" holes can be tapped consistently on my CNC mill?

i

Mike, did you use that head on a CNC mill?

I don't agree with Richard's analysis. His method assumes the probabilty of a broken tap is the same on every hole. In fact, once you've set up proper conditions and selected a top quality tap the probablity of breaking goes with wear. Taps used in machines last FAR longer than hand taps.

I use OSG brand taps. Gun flute on thru hole, spiral flute on blind hole. I forget, you aren't set up for rigid tapping??

Both your tension/compression tap holder and the procunier can be set up in your CNC. But, its tricky. You've got to match feeds and speeds to where the tap wants to be.

Karl

OK, good to hear.

I understand, yes. If I run the spindle at, say, 200-300 RPM, then it would take me about 0.2 seconds to stop the spindle, so about one revolution. The floating tap holder should be able to take care of that. You think ER16 collets would hold a tap well enough?

i

I wrote a G-code subroutine to do it. To run safely, it MUST have a floating tap holder that can take up the slack of the tap that moves off position, while the spindle is reversed.

(Tap a hole with a floating holder) O sub # = #1 (Hole Depth) # = #2 (Threads per Inch) # = #3 (RPM of the spindle, EXACTLY MEASURED) # = #4 (Safe Height)

# = [# / #]

M3 (Forward) G1 Z# F# M4 (Reverse) G1 Z# F# M3 (Forward again)

O endsub M2

So, make threaded inserts of steel, for oversized holes (stepped would be good) with a bit of loctite. The accuracy of a screw position isn't critical, I trust.

Of course, to churn out inserts might require a CNC lathe... or a turret lathe.

Ah. Thanks. I sit in an office and fly a desk, while right outside my door are a couple of machinists and weldors - on one side of the shop, we take big pieces of metal and turn them into little pieces of metal, and on the other side, we take small pieces of metal and turn them into big pieces of metal. :-)

On break, the only people I have to talk to, other than the boss and his secretary, are the machinists - When I'm chatting someone up, I like to be able to speak the same language as they. :-)

I do know what "spot-facing" is, however. ;-)

Thanks! Rich

Do people use the terms "drill" and "drill bit" almost interchangeably?

To me, the "drill" is the part with the motor, that turns the "bit."

Am I wrong?

Thanks, Rich

Once, after hours, I found some really spiffy pieces of aluminum out in back next to the bandsaw. I wanted to make a trinket, and the resident machinist taught me how to use a mill - I was astonished how much metal he could hog off that aluminum block; Previously, as a hobbyist, I had used about a quarter the feed rate this guy was getting away with.

I once got tasked to drill a couple of 1/2" holes in a 3/16" plate of

304SS. I din't even know you _could_ drill 304SS with an ordinary twist drill, but again, my coach(es) said, "GO FOR IT!" I really bore down on that handle thingie that extends the quill, and the stainless just gave way. I heard that sound that you hear when one mongo chip is being produced, and it felt almost like the drill was pulling itself into the work - I was through 3/16 of metal in a matter of seconds, almost effortlessly!

So, I guess I'd have to admit, when I'm playing with metal, I should be more aggressive with my cuts. :-)

I once saw a guy deburr a steel part with an ordinary pocket knife. Does that dull the knife?

How can steel cut steel? Howcome the part doesn't cut the bit?

Thanks, Rich

Well, this all SOUNDS good, but in fact, there is NO connection, at all, between the spindle and the Z feed. You'd have to do the first test holes carefully to make sure you get the desired depth of tapping. The spindle is running at whatever speed it is, and the Z infeed goes at the programmed rate. But, at the end, it is only the Z depth that determines when to reverse. NOT, the number of turns the tap has fed into the work.

Still, this is likely to work, assuming the springs on the tap holder are strong enough to start the tap into the work promptly.

And, you won't believe what a MESS this will make, if you ever mess up and have the spindle running at the wrong speed for the calculated feedrate. been there, done that!

Jon

Thanks; I was just curious, but it sounds like a fascinating opportunity for a geek like me (microprocessor programmer) who dabbles in mechanical stuff...

Thanks! Rich

You use an entirely different drill size (much larger) for a thread forming tap. The workpiece is pushed out of the peaks to form the valleys. The tap manufacturer should be able to recommend the correct drill size.

Jon

The only connection is that I measure the speed of the spindle with a handheld tachometer, and then calculate the feed.

Absolutely.

What will happen, it will tear the tap out of the collet?

Anyway, obviously rigid tapping, optionally with the floating holder, is the way to go.

i

Yep.

I will buy a form tap today at mcmaster, they say use letter S drill.

i

And never ease off the pressure until you are at depth or through the other side. Many steels will work-harden in an instant if you let the drill spin and not cut.

There's hard steel, and there's soft steel. The hard steel cuts the soft steel.

As a rule, no. Most people either always use the terms correctly, or always incorrectly. Very few use them interchangeably. ;-)

If you're in a machine shop, you're wrong. If you're in a hardware store, sort of wrong. If you're in a Wal-Mart, well... as long as the guy knows what you mean... ;-)

I think, with the proper coolant/lubricant, good gun (spiral point) taps, and the consistency of the CNC, he might be able to do this with no problems -- with a high quality tap and a good hard aluminum alloy. I would either use a TapMagic for aluminum, or just use WD-40 in aluminum.

Even better for the task would be a TapMatic tap head (which would eliminate the problem of feeding in reverse as you back the tap out). The thing with at least some models of TapMatic heads is a friction clutch, which you set up with a brand new tap so is just barely does not slip when cutting with the proper lubricant. Then, once the tap starts getting dull, it will slip and you can change out the tap

*before* it breaks.

I've used this setup in a drill press with 1/4-20 HSS gun taps with 1/4" steel (making an apron for an old DiAcro sheet metal shear).

Hmm ... the code which that website has which wants to know where I live is a pain. I can't find the right things to turn on to get it to accept my data (cookies and JavaScript on, and it still refuses to admit that I've given it a value and keeps asking. It probably wants flash, which I refuse to turn on.

So -- I had to start over and click the [dismiss] button to get anywhere since it would not let me back out to the original starting point.

Enjoy, DoN.

[ ... ] [ ... ]

That is a good idea. However -- be sure to look up the right drill size for a thread forming tap. It *has* to be larger than the normal thread cutting tap's tap drill. You say 3/8" holes, but don't say which thread pitch, so I can't look up the drill size. It can be found in _Machinery's Handbook_.

The nearest to perfect size for a 1/4-20 tap happens to be a metric size -- 5.7mm -- another argument for having drills of all kinds.

The proper size for 10-32 thread forming taps is a #17 -- from your recently acquired number sized drill set.

Good Luck, DoN.