Power tapping

[Gordon WParticipant @gordonw]

A simple question, I hope. I need to tap a lot of M6 threads in 1/2" black plate. I have heard of people doing this with a battery drill but never tried it. What is the best type of tap to use ? Thanks in anticipation, having just done a dozen by hand using taper and finish taps.

[Gordon WParticipant @gordonw]

[davidsuffolkParticipant @davidsuffolk]

Personally I wouldn't. I snapped a couple of taps trying that (and either the last or most important one!). I found that unless you could be certain of the drill being upright etc the torque and leverage of a large drill made it easy to break a tap plus even with a sensitive trigger they can just go too fast..

A pillar drill tapping head on the other hand may be just what you need?

Edited By davidsuffolk on 14/09/2015 12:26:10

[pgk pgkParticipant @pgkpgk17461]

I believe it's possible to get combination drill and taps – save even more time?

[Anonymous]

If the holes in the plate are all the way through then use a taper tap, or even better a spiral point tap (aka gun tap). If the holes are blind then use a spiral flute tap. If you are using a quality taper tap, and you can get the tapered portion clear of the bottom of the thread, there is no point running the bottoming tap through as well.

I can't help with the battery powered drill. I've power tapped thousands of holes on the vertical mill, but I use industrial auto-reversing tapping heads. They're much quicker at tapping than drilling the hole in the first place.

Andrew

[egaParticipant @ega]

Small fine thread taps in thin material are OK with a hand drill where the sensitivity should help to avoid breakage. In your 1/2" plate you might try the combined drill/taps which come with a hex shank in combination with the clutch feature on the drill; Axminster do a set which might be suitable.

[John HaineParticipant @johnhaine32865]

I've drilled a lot of tapped holes in 3 mm Ali with an M3 tap in my Bosch drill without a problem, and have also tapped M6 on my mill using the inverter drive at very low speed (need to set up the jog function to make this easier). Spiral flute taps probably better, and you will need to have a guide to keep the tap upright. Use the screwdriver setting if your drill has one, and start at low torque and work up. Also probably best have a larger than normal tapping hole, as Tubal Cain advises. 5.3 mm gives 65% thread engagement for M6, with very little thread weakening, and you could perhaps go even bigger, say 5.4, depending on how much loading gets applied to the finished product. But I can easily imagine that breaking a tap could be easy! Good luck!

[Bob Brown 1Participant @bobbrown1]

There are different taps some designed for hand tapping and others for machine tapping, I tend to use machine taps when tapping multi holes be it in the lathe or milling machine with an auto reverse tapping head.

[Gordon WParticipant @gordonw]

Thanks for all the advice, just ordered a combined drill/spiral flute tap at a reasonable price off ebay, so not a great loss if it breaks. I was drilling 5.2mm, the taper tap was tight so had to put the 2nd thru' ( stubs tap) Should have said I was tapping thru'. Could also drill 6mm clearance part way thru', should help.

[Clive HartlandParticipant @clivehartland94829]

The 'K' factor for Metric tapping drills is 0.8. That is multiply the thread by 0.8 and the answer is the tapping drill size.

So, M6 x 0.8 = 4.8 tapping drill. I have used this method for years and have had no problems.

Yes, there are tables of tapping drill sizes but this calculation you do mentally.

Clive

[Bob Brown 1Participant @bobbrown1]

Clive,

To me that does not seem right even for M6 course as the pitch is 1mm so drill 5mm, M6 fine pitch 0.75 drill 5.25mm

Bob

[Keith LongParticipant @keithlong89920]

According to my Zeus tables, for metric the magic formula is o.d minus pitch = tapping drill dia. That seems to apply for fine from 8 to 30 mm (above they knock off an extra 0.25mm) but applies from 1.6mm through to 68mm in coarse.

[Gordon WParticipant @gordonw]

Always used thread dia. x pitch for tapping drill, plus a bit or two depending on material and usage. As a maybe useful addition- After ordering the tap/drill I have found a box of self-drilling roofing screws that just happen to be M6 ! These drill and tap into steel angle purlins, doubt they will do many holes before getting blunt but will try them. PS- a bit is a gnat's wotsit.

[Paul TomlinParticipant @paultomlin90922]

Page 443/444 of the latest ME has a brief description by Jacques Maurel of what appears to be a very handy tapping attachment for a pillar drill. I for one will be trying to figure out if reproducing the described item is within my abilities.

[KWILParticipant @kwil]

I doubt somehow that the dimensional accuracy of single use self drilling roofing screws will be good enough for tapping holes for other bolts and screws. You can always try of course!

[Clive HartlandParticipant @clivehartland94829]

I assume the 'K' factor is for standard threads, any finer or coarser threads were calculated on the fly. as we had many varying threads in use. on Instruments.

Clive

[FatgadgiParticipant @fatgadgi]

Hi Gordon

I'm one of those idiots – I do nearly all my tapping using a power drill in low speed with a clutch, have done for years.

It works very well, but 12mm steel would mean that you would need to be very accurate with the drill angle. So personally I may do one or two carefully with the drill, but for any quantity I would use a tapping head in the drill press. One of those arms sold for tapping that keep the head parallel would work I guess.

But for what it's worth, I set the clutch to a low setting, just enough to not ratchet out, so if there's a problem it stops. I power out in reverse as well.

I always put oil or tapping fluid on the tap.

I try to put the work vertically in the vice so that I can brace my elbows or forearms on a bench or the front of the vice and I make sure that the tap is perpendicular by eye by looking down, then from the side then down again and go. Wherever possible I use the right hand side of my vice so that if it kicks it's supported and doesn't swing upwards towards teeth and I find that I can position my arms best that way.

Sounds complicated, but believe me it's fast and surprisingly accurate once you get the hang of it and obviously the trick is getting the alignment right especially with thick material.

Anything up to 5 or 6mm with an M6 should be straight forward. But there isn't much margin for error in 12mm steel !!!!

Cheers = Will

[John HaineParticipant @johnhaine32865]

Regarding metric tapping sizes, this is covered extremely well in Tubal Cain's Drills Taps & Dies in the Workshop Practice series. He points out that there is very little reduction in holding strength in using a larger tapping drill than given by the theoretical "diameter – pitch" diameter, but a huge reduction in tapping torque and danger of tap breakage, and the book includes tables of drill sizes, threads (not just metric) and engagement. For M6 5.2 mm gives 75% and 5.3 65%. I always use these recommendations for tapping sizes, and whether related or not have never broken a tap since.

[Enough!Participant @enough]

Posted by Clive Hartland on 14/09/2015 14:49:00:

So, M6 x 0.8 = 4.8 tapping drill.

Seems pretty (well, very actually) tight. The core dia for an M6 x 1 thread (which I believe is what you are referring to) is 4.78mm.

I prefer the dia – pitch version (with Tubal Cain adjustments as needed.

[Gordon WParticipant @gordonw]

Thanks Will, glad of the reassurance. Problem is the job is heavy and awkward shape ( agricultural bit ) I think I will drill about half-way thru' clearance size first and leave about 6mm for tapping, still hard work tho'.

[JonParticipant @jon]

Posted by Clive Hartland on 14/09/2015 14:49:00:

So, M6 x 0.8 = 4.8 tapping drill. I have used this method for years and have had no problems. Clive

Careful how that's written, could be deemed 0.8mm pitch, recommended 5.2mm drill hole.

Spot on Will couldn't have put it better. Its the torque that counts setting the clutch and getting a feel for whats happening, I do it all the time with a Dewalt 18V.

In the mill I would be hesitant going below M5, M6 2nd should be ok if decent tap from reputable brand.

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