How to identify M2 first, second and third tap

I have some M2 serial taps and these are easy to indentify : tap 1 has one circle, tap 2 has two circles and the tap 3 has no circles.

But I also have a set of ordinary taps which I keep as spares and these are not marked with circles. In the larger sizes it is quite easy to identify the first second and third taps by the amount of thread that has been filed off the tip but with this smaller M2 size I am having difficulty working out which is which. Any tips ?

I have also broken a few serial taps. The correct tap drill is 1.6mm...what about going up to 1.7mm ?

It is a good idea to use a magnifier to look at items like this. With regard to drill size I tend to use charts as a guide only and usually increase the size for small taps which are prone to snap. I often conduct a quick test on a scrap of the same metal to see what size will then tap easily. For non critical applications it is often surprising how large the tapping drill can be and still provide a decent thread.

Doug

Brian, drill/ream a 1.60mm diameter hole in a piece of 1mm thick plate to use as a gauge, the Taper tap will pass the most through the hole, the plug will pass less if any at all.

Emgee

I rarely use serial taps having gone over to Spiral Flute and Spiral Point, so much easier even at M2.

I can't imagine you'd need serial taps for M2, the thread depth is pretty small anyway? Ordinary taper, second and bottom taps would be fine. In fact taper only is fine unless the tapped hole is blind. It should be straightforward to identify the taps by the length of the lead in, although a magnifying glass would help, for me at least!

No way I'd be drilling 1.6mm for M2, I use 1.7mm upwards. I normally aim for a thread engagement of about 60%, may be a bit more in aluminium, and less in stainless steel. Some years ago I did an experiment with M4 tapped holes in aluminium. With a thread engagement of 50% a high tensile (12.9) SHCS broke before the thread stripped.

Plus one with KWIL for spiral flute and spiral point taps. They're great for power tapping, but work equally well when hand tapping.

Andrew

Okay, I will try the 1.7mm drill bit tomorrow.

What is the difference between spiral flute and spiral point taps and why are they less prone to breakage ? Where can I buy them in the UK ?

I am still looking for my magnifying glass !

Spiral point taps are designed to be used in CNC milling/drilling/tapping machines. One tap does all jobs and they are stronger than hand taps. Great for holes which pass right through the material, but not so good for blind bottomed holes. For this you need to provide extra hole depth and stop the tap at the required depth of thread, easy to program on a production line.

Spiral flute taps are like a twist drill and have a helix type groove. Typically that are needed for tapping threads in aluminium extrusions where the cored hole isn't a full circle. A normal straight fluted tap would hang up on the slot in the hole and snap. Again they are designed to be driven by a machine, although they often have a square tang to take a normal tap wrench as well. Production spiral point taps are a parallel shank with no square on the end. Designed to be held in collets. Some special machine taps have the pilot drill and tap combined as a way to speed up production. But you are unlikely to find these in a normal tool merchants stock. This type is widely used in the mazak casting manufactured items like carburettors etc in the older days.

Here's a picture of some M8 taps:

The top tap is M8 taper, next one down is M8 bottoming. I don't bother buying 2nd taps as I never use them. The third tap from the top is M8 spiral flute - should be obvious why! The tap at the bottom is M8 spiral point (known in the US as a gun tap).

The spiral flute tap is intended for blind holes, it usually taps within a couple of thread pitches of the bottom of the hole. The spiral flutes push the swarf upwards and out of the hole. In ductile materials you get three continuous ribbons of swarf exiting the hole.

The spiral point tap is intended for through holes. The cutting edge is angled such that it pushes the swarf down and away from the tap, and out of the bottom of the hole.

Although spiral flute and spiral point taps are intended for machine tapping they work perfectly well when used by hand. They have better swarf clearance so may be slightly less prone to breakage than hand taps. However, you still need to take care over the size of the tapping hole or they will jam and break. Generally I buy spiral flute taps as one tap then does everything.

I don't know if ME suppliers deal with spiral flute and spiral point taps, but any commercial/industrial tool merchant will stock them. In the UK I use Drill Service for mail order.

Andrew

Brian, Rotagrip do standard, spiral point and spiral flute taps and also sell via e-bay as "Fordeight" I find the Volkel set of 3 work fine.

Unless you are using some way to guide the spiral flute taps they may not be the best option for hand tapping

Edited By JasonB on 11/03/2016 13:22:50

The sprials don't need to be reversed to break the chip but if your problem is really down to not aligning the tap with the hole they could easily make things worse.

It's also worth bearing in mind that a poor maximum length for thread engagement between the screw and the tapped hole is 2 diameters. The usual rule is if more than 1 1/2 cut the screw down. The deeper the tapped hole is the more likely alignment and other problems will break the tap.

John

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I have some M12 spiral flute taps and the short thread length on them makes hand tapping easier than with standard taps due to lower friction between tap and workpiece, initial alignment is important though as Jason pointed out. They work well in lathe tailstocks as well as vertical mills, I use them with a tapping box and as Andrew said you get continuous ribbons out of the flutes as the thread is cut.

On a slightly off topic point if you look at thread mills for M2 size the maximum depth of thread that can be cut is often stated as 3 diameters. This can be taken as a guide for any thread that is being cut, anything deeper is probably not needed for screw engagement.

Martin

It's interesting to look at the usual rule for tapping drills on metric just subtract the pitch.

If that is used m2 would be drilled 1.6mm. Above says the core diameter is 1.567mm. So a 1.6 drill give a bit over a thou clearance. Sounds great before both the drill and the tap are measured.. Drills usually under size, taps over plus brass effects - the drill tends to cut a hole much closer to it's size, The other aspect is those sharp corners usually shown in images like this. The actual tools are very unlikely to have them. Clearing any rads makes a big difference to the effort needed to tap a hole. It's extremely noticeable on BS threads.

I reckon all of the taps and dies I used during training must have been H6 and ground thread maybe even 5.

John

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I tested the non serial taps on a piece of 1.5mm thick brass. I had to drill a 1.9mm hole and just the tip of one tap passed through, the second one less so and the third one not at all. I actually did identify them correctly by eye before conducting this test ! I then marked them by putting the taps in the lathe chuck and gently making circles on them with a parting tool ; just enough to mark them with one, two and three circles similar to the serial taps.

I drilled some 1.7 and 1.8mm blind holes in some brass then tapped them using both the serial taps and the new taps. 1.7mm is okay but 1.8mm seemed a bit loose. I will use the 1.7mm drill bit as my standard tap drill for now.

I will also buy some M2 spiral flute taps ASAP.

If I was having problems with M2 Brian I would probably use a No50 drill in brass but would also measure the tap.

John

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Ajohnw : No. 50 is 1.778mm so do you think I should use a 1.8mm tap drill ?

I have successfully drilled and tapped the eight blind holes in the new power cylinder. I am thinking of using a brake hone on the bore of this one. I used a 1.7mm tap drill, some tap magic fluid (which I have not bothered to use before) and I was very careful ie. down two turns and back one turn. I drilled 10mm holes and cut 6mm threads on each one ; hopefully this lessens the chance of tap breakages.

1. Are serial taps more inclined to break then regular taps ?

2. How do you clean up the tap fluid and brass shaving mix from the holes ? Should I wash it out with something ?

3. After drilling and tapping holes, a slight burr is always left on the face of the work piece. Do you put it back in the lathe to shave a bit off with a facing cut or just clean up with some 2000 wet and dry ? I know what I do...but what do you do ?

Edited By Brian John on 13/03/2016 07:25:44

3 .You can use a deburring tool, twist a countersink bit in by hand, twist say a 6mm drill bit by hand all will take the burr off. Or if using spotting drills then use them to chamfer the edge before drilling and tapping the hole like these M2 tapped holes

Good idea with the spotting drill but why before drilling and not after drilling ?

Spotting drills are very stiff and if positioned slightly off centre will chamfer eccentricly, on a small hole this will show up visually. If you use the spotting drill first then it creates a lead in that the more flexible twist drill will follow concentrically. It is similar to using a centre drill in a lathe to start a hole on the spindle axis.

Martin

Why use the spoting drill twice. It is used instead of a ctr drill to form the dimple for the drill to locate in and at the same time the chamfer is done, saves going back around all the holes again. This is the way industry uses them as its one less operation not due to concentricity which is not an issue on CNC machines.

I also use a spoting drill on the lathe unless I specifically need a 60deg hole.

Edited By JasonB on 13/03/2016 08:09:09

A shallow cut with the clearance drill before tapping will ensure the tap does not throw up a burr.