Driving Small Taps

I am wondering what the generally accepted method of tapping small holes is. IE, what do you use to drive the 2.5mm square shank and keep everything straight. I know there are tools for the larger taps that you can put in a drill press to keep them square, but these tiny taps are another challenge.

thanks Dave

I hold the small taps in a pin vice with the handle of the vice lightly held in the drill press chuck to keep it aligned with the hole. Then turn the pin vice by hand.

Paul.

Dave, if I can get the workpiece under the chuck of my bench drill I put the tap directly in the chuck and just turn the tap into the drilled hole by hand, being careful, if using an ordinary hand tap that sends the chips upwards, to reverse direction regularly in brief spurts to prevent clogging.

When using the drill chuck this way to tap into blind holes with small taps you must be cautious when approaching the bottom of the hole because that is when you are most likely to break a small tap. In nearly all cases when using this method, I consciously hold off from the bottom of the hole with the first tap (or first two if I use two) and only go right to the bottom with the last tap when using it freehand (the workpiece being held in a vice) with the tap held in the smallest Eclipse tap holder. That way I can feel my way to the base of the hole much more sensitively than I could do if I was turning the tap in my drill chuck.

Edited By Bill Phinn on 16/01/2020 02:25:32

I do all my tapping powered by hand. Virtually all of the threads I tap are M6 or under. My "go to" tap holders are Starrett "T" holders, there are two, a small one which does everything under M4 and a large one which does everything over that. If the thread is over M6 (unusual for me) a conventional bar type tap holder is used. Some sort of centre is ALWAYS used to ensure that the tap stays lined up. If an array of holes is being tapped, the centres are marked out wherever possible using a height gauge, then into the (Sieg X2) mill, an optical centring scope lines everything up, spotting drill provides a starting point, pilot drill, tapping drill, countersink the hole to slightly over thread size; tap 1, using tapping fluid, clean swarf from hole; tap 2 using tapping fluid, clean swarf from hole; tap 3 using tapping fluid, clean swarf from hole. Then I move on to the next hole, starting with the centring scope...Sometimes only taps 2 and 3 are used. I must try spiral flute taps!!

I am about half way through tapping 16 x M3 x 0.5 in al. alloy, so far all the threads are good, to depth, they are blind, all point in about the same direction and (tempting fate here!) no broken taps. Yes, it does take a bit longer, but then I'm not on piecework!

cheers

Bill

Edited By Bill Pudney on 16/01/2020 05:16:58

Hi Dave, ,

What I have done in the past is turn up a button on the lathe bored at crest diameter, with a small countersink at each end, then use this to align the tap until well started then you can remove the button and continue tapping as required.

Keep this button in a container with your tapping drill etc.

Regards ,

Neil

Not so much keeping everything straight - more like starting straight. It is paramount that the first few threads cut are perfectly aligned with the tapping hole; as tapping proceeds after that, the tap will follow those initial threads. If they are off-line, the tap will progressively attempt to cut its way into the side of the tapping hole, increasing the load and eventually breaking (if the hole was deep enough!)

I always try to tap directly after drilling the tapping hole, without moving the machine position setting. The tap will fit the same chuck as for the tapping drill. Gentle downward pressure is maintained, to avoid stripping those first threads. A spring loaded tapping device is useful, if you are not confident, but that alignment is the most important bit - start right and it will end right.

Actual method depends on thread pitch and material, as well as machine. Like it must be a spring loaded quill unless a tapping tool is used. Hand tapping, as per Nimble, if off-machine. It has to be straight and if the hole is not vertical in the first place, tapping vertically will break the tap, given enough depth for the tap to dig in the side of the hole.

Small threads just need more care with alignment and careful progression, although any sized tap, not started aligned with the hole, will eventually break if tapping a very deep hole in tough material - that or stall you!

I use a tapping block, similar to the idea of Nimble above. Mine's just a piece of bright mild steel about 20mm thick. I drill a hole through it the diameter of the tap. Place it over the job to be tapped and poke the tap down through it into the hole to be tapped. It holds the tap square as I wind the tap with a small T tap wrench. Block can be removed once tap is started and stable, after a few turns.

Made a nice small tap wrench out of a tiny drill chuck for a Dremel etc that came with a spindle mounted on it. Just made T handle to fit and Loctited it in position. Left enough of the spindle sticking out it can be held in the lathe tailstock chuck loosely for alignment when tapping tiny holes in the lathe.

I built and use the GHT pillar tool. Fantastic bit of kit and superb design.does anything from 12ba taps

I like to tap at the same position that I drilled the hole so things are lined up 100%. For small taps grip by the shank with a small tap wrench and then use a simple bit of rod pointed at one end ctr drilled at the other which will engage the end of the tap be it male or female centred then apply light quill pressure as you wind it in.

I must second this method, Only difference is that my Eclipse pin vice is held lightly in the chuck of my X2 mill - At the same table setting that was used to drill the initial hole.

* Danny M *

If I've had to reacquire the position setting between drilling and tapping, I've sometimes put the tapping drill in the chuck backwards, and felt for non-contact (or as near as I can get it!) insertion with tiny table movements and very gentle quill pressure. Then swap the drill for tap (or tap and pin vice) and rotate by hand gently.

+1; mine's in frequent use for tapping. Much more convenient than any other method of starting a tap

If, for whatever reason, it is impractical to use any system of alignment ...

When working ‘freehand’ with a small tap, I clamp the plain shank of the tap in the pin-vice, instead of using the square: This provides some ‘safety’ by slipping before the tap breaks.

MichaelG.

I think a lot will also depend on the part being tapped. A GHT may be a convenient method for starting a tap in a small regular shaped part but what if you have just spent 20mins setting up a large casting at an angle on the mill to machine a face and want to drill and tap a hole perpendicular to that face. Do you strip down the setup and then redo it on the GHT if it will even fit or just slip a tapping guide into the mill and tap it there knowing that everything will be perfectly lined up.

Would anyone want to move this setup onto a GHT to tap the bearing cap holes after machining the mating face and then set it back up in the mill again to mill the sides of the top and bottom halves flush?

The other factor is how you go about drilling the tapping hole. Back in the distant past GHT would no doubt have carefully marked out the holes position, dot punched, checked position and then ctr punched before setting up on the drill press, lathe or pillar tool to drill. Move on 50years and the methods have changed (at least for some of us) pop the part in the mill vice and locate edges or ctr and use the DRO to position the spot drill followed by moving round again for tapping drill and it makes sense to then go round again using the mill to guide the tap. When I say tap that's just a single spiral flute or spiral point not T,2nd & P

Edited By JasonB on 16/01/2020 09:46:57

Certainly down to M3 I almost always tap in the mill under power, if possible at the same setting just used to drill the hole with the tap in the chuck. Set the VFD frequency to just under 10 Hz-ish, use the quill lever feed to bring the point of the tap down to nestling in the hole keeping it under light pressure throughout, switch the drive to fwd so the tap cuts the thread, once it has threaded through switch to reverse to withdraw the tap. If it's a blind hole I just start the tap this was, then stop, lock quill, loosen chuck leaving the tap in the work, raise quill, finish off using a tee bar tap holder. Touch wood, I haven't broken a tap yet this way.

What tends to break taps, apart from failing to clear the swarf, is bending. So supporting with a centre, spring loaded or dead, is good practice, in a drilling or milling machine.

As an alternative, a tapping tool such the GHT Pillar Tool is good method. I use a converted drill stand with a small Jacobs chuck on a sliding spindle. Not very pretty, but it saves broken taps. If things get tight, the chuck slips.

The tommy bar is a short length of 6 mm fuel injection pipe, centrally positioned across the spindle, so that I am less likely to apply excessive torque.

HTH

Howard

After breaking several 10 BA taps I decided I needed something to guide the taps, or face bankruptcy.

The design here has the advantage that the collet can be set to allow the tap to spin if the tap meets an obstacle while the driven part, the larger knurled ring carries on rotating. The slider part of the design has a spring loaded clutch which stops the tap dropping when traversing from hole to hole.

The design in full was described in HSM a short while ago.

Regards

Gray,

Graham's point about about the tap being able to spin if anything sticks, is absolutely correct.

For the lathe, I use ER collets. It is surprising how tight they have to be to drive the tap, but they will slip (since the drive is on the plain OD and not the square ). The holder is a loose fit on the arbor in the tailstock, allowing the tap to self align, reducing the risk of bending,and imposes minimum stress on the thread being cut in advancing into the work. A 40 tpi ME thread, being shallow, is likely to strip in pulling a Tailstock along the bed, but will pull a light holder or small drill chuck along an arbor without damage.

Howard

I had to tap 1000 holes M3. They were for a grubscrew and were through a 4mm wall. I decided to buy 3 sets (of 3 taps) as I was bound to break some. I used a battery drill to drive them and needless to say didn't break a tap.

I should point out that whilst accuracy was not of concern, I was surprised at how easily a taper tap aligned itself. As I recall there were no rejects.

Regards.

David.

In this kind of job the combined drill/tap is very useful and of course today's drills can be quickly reversed to withdraw the tool.