Tap sizes

[PeterDRG]

I´m almost ashamed to ask this, as I should know !

I bought some taps (sets of three -TSP) from the local tool shop. The M6 were very cheap, worked OK but were Chinese. I went back for M4 and M5 and they were twice the price, albeit still cheap, but were German.
On using the M4s, I came to the conclusion that there were infinitesimal difference in size between the taper and plug that worked to my advantage. I had always thought that the difference between taper, second and plug lay in the grinding and the lead in taper. These seem to also give incremental differences when cutting the thread, involving definitely using all three for a full thread. This seems a good thing with small thread sizes as it puts less strain on the taps. Is this usual ?

 

[Jasonb]

Not usual unless you bought serial taps which don't cut to full depth until the last one.

 

[PeterDRG]

Thanks Jason. It sounds like they must be serial taps then. I had never come across them before. They are nicely made HSS taps. At a fiver for a set they are a bargain. I will return for a couple more sizes on Monday !

 

[Richard Hed]

I´m almost ashamed to ask this, as I should know !

I bought some taps (sets of three -TSP) from the local tool shop. The M6 were very cheap, worked OK but were Chinese. I went back for M4 and M5 and they were twice the price, albeit still cheap, but were German.
On using the M4s, I came to the conclusion that there were infinitesimal difference in size between the taper and plug that worked to my advantage. I had always thought that the difference between taper, second and plug lay in the grinding and the lead in taper. These seem to also give incremental differences when cutting the thread, involving definitely using all three for a full thread. This seems a good thing with small thread sizes as it puts less strain on the taps. Is this usual ?

I never heard them called serial taps before, but often they will come in a set of three: taper, plug and bottom. If you have a blind hole you definitely need the bottom. the three work very well together -- break less taps too, but stil have to be careful. I woul;d say that is usual.

 

[deverett]

Peter
You may have already realised, but with serial taps the first tap have 1 ring ground on the shank, the second tap will have 2 rings ground on the shank and the full depth tap will have nothing on the shank. That's the usual, but no doubt there could be different methods of identification.

Dave
The Emerald Isle

 

[Charles Lamont]

I never heard them called serial taps before, but often they will come in a set of three: taper, plug and bottom. If you have a blind hole you definitely need the bottom. the three work very well together -- break less taps too, but stil have to be careful. I woul;d say that is usual.

These taps are different from taper, 2nd, and bottom. I think they are common in Germany. As Dave says, the taps are often distingushed by ring grooves on the shank, and cut an increasing proportion of the full thread depth, as well as having a reducing length of tapered lead.

 

[rutzen]

Beware, taps aren't always the right size. I have a 3/8 x 40 plug tap [UK made] that is definitely undersize. I recently bought another set of 3 taps of this size and they are all slightly different overall diameter. To get a thread near enough the correct size I had to grind down the second tap to make a plug. The plug tap is smaller diameter.

 

[Jasonb]

I never heard them called serial taps before, but often they will come in a set of three: taper, plug and bottom. If you have a blind hole you definitely need the bottom. the three work very well together -- break less taps too, but stil have to be careful. I woul;d say that is usual.

As Charles says these are different to just a set of three with different end tapers. You need to use them all even on through holes if you are to cut the correct depth of thread. Look at the images on this page and you can see that the taper is flat crested as it does not cut to full depth, The Second is a bit deeper and only the finisher or No3 full depth
https://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Threading/Serial-Hand-Taps-Metric-Fine

 

[Richard Hed]

As Charles says these are different to just a set of three with different end tapers. You need to use them all even on through holes if you are to cut the correct depth of thread. Look at the images on this page and you can see that the taper is flat crested as it does not cut to full depth, The Second is a bit deeper and only the finisher or No3 full depth
https://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Threading/Serial-Hand-Taps-Metric-Fine

Thank you for that. I never knew any of this before.

 

[PeterDRG]

Thank you ! I´d never come across this before. They do, indeed, have the rings on them. Never too old to learn something !
I´ll get some 8mm and 10mm in the morning. The 4mm and 5mm were under a fiver each set. Arc Euro only seem to have 9mm and they are discontinuing them. I wonder why ?.

 

[Jasonb]

They were not good sellers. They now keep spiral flute and spiral point which I much prefer to the usual parallel flute T,2nd & P. Plus you only need one spiral flute instead of three old style.

 

[Richard Hed]

They were not good sellers. They now keep spiral flute and spiral point which I much prefer to the usual parallel flute T,2nd & P. Plus you only need one spiral flute instead of three old style.

I have been hesitant to bu;y those spiral flutes as I thot they broke easier. So . . . you recommend them?

 

[Jasonb]

Yes, all my commonly use ones are now spiral flute and I've yet to bust one even when power tapping. I do have a few spiral point ones too but don't use them so much

 

[awake]

Taps also come with different specifications for fit. Perhaps one of the taps is H3 and the other is H1, or something like that. (Likely I have gotten those codes wrong ...)

Spiral flute taps look relatively flimsy, but oh, my, are they nice to use, because they pull the chips up and out; since they don't pack up with chips, I think they are less likely to break even though seemingly less sturdy. Spiral point taps also clear chips well if you have a through hole, since they push the chips ahead of themselves. I do use them in blind holes, but one has to stop and clear out the chips that get packed into the end of the hole!

 

[Badhippie]

Yes spiral flute taps are made for blind holes
And the reason for this is because they bring the chips up out of the hole

 

[Badhippie]

Forgot something.
I use spiral flute taps about 98% of the time and have never broke a tap. In my honest the only reason a tap breaks is so to operator error.

 

[GrahamJTaylor49]

I did my apprenticeship as an aircraft toolmaker and I've never come across "Serial Taps". That does'n mean that they don't exist, but I don't know where I would use them. Spiral Flute taps are brilliant as are Spiral Point taps. I've sets of taps from 10 BA up to 2" BSF and 50mm x 2mm metric. God alone knows just what I'm going to use them for. Just keep model engineering and stay safe everyone. Now back to work, pressure vessel examinations in Chichester, U.K.

 

[Shopgeezer]

As Charles says these are different to just a set of three with different end tapers. You need to use them all even on through holes if you are to cut the correct depth of thread. Look at the images on this page and you can see that the taper is flat crested as it does not cut to full depth, The Second is a bit deeper and only the finisher or No3 full depth

These must be different animals than the usual tap sets. I have never heard of taps cutting different depths of thread. Of course I know little about it. The usual tap sets seem to cut equally. The tap and die sets we all buy have a course and fine tap for each size. These are universally plug taps and have to be full size since you only have one tap to use.

 

[methuselah1]

Re- the above photograph... God bless America, but they do manage to get engineering nomenclature wrong! For everywhere else in the world (from bottom to top) it's taper, second, plug. Bottoming and plug are interchangeable terms for the same tap, over here.

*sigh*

-Andrew UK

 

[Shopgeezer]

Explains why the term “plug tap” confuses me in these forums since it seems to be used for different things. I guess we should all go to spirals to avoid confusion. I will have to buy one to try.