# 8mm taps needed



## Beau (14 Jun 2018)

Got a little job where I need to put some 8mm threads into steel. My 8mm taps from a set are tired so any recommends for replacements? 

Been on ebay and seen Groz, Volkel and Rotagrip. Any of these good or any other suggestions welcome.


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## deema (14 Jun 2018)

I tend to use Dormer if it’s for an industrial type application or Presto if it’s for my home shop. I’ve found Presto to be as good as Dormer but not as expensive.


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## Beau (14 Jun 2018)

Done. Presto were not much more than the others I listed.


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## AES (14 Jun 2018)

If it's only for a one off I can put 1 (or more) in the post to you as a loaner (no rush for return). Do you need 1st, 2nd taper, or plug; and do you want ISO standard coarse 8mm (the most common) or ISO standard fine?

Just for info I also find Presto pretty good for "general work, but recently I got given (given mind, lucky boy!) some Swiss brand taps called "DC". No idea if they're available in UK, nor what they cost, but they are really nice quality to use - "expensive" I guess!

Sorry but the above offer is for loan only, I'm not selling or giving any away, but a loan IS fine.


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## Beau (14 Jun 2018)

AES":2shtfwug said:


> If it's only for a one off I can put 1 (or more) in the post to you as a loaner (no rush for return). Do you need 1st, 2nd taper, or plug; and do you want ISO standard coarse 8mm (the most common) or ISO standard fine?
> 
> Just for info I also find Presto pretty good for "general work, but recently I got given (given mind, lucky boy!) some Swiss brand taps called "DC". No idea if they're available in UK, nor what they cost, but they are really nice quality to use - "expensive" I guess!
> 
> Sorry but the above offer is for loan only, I'm not selling or giving any away, but a loan IS fine.



Thanks but the Presto set of 3 are in the post to me. They will see plenty more action in due course. I only dabble with metal working so can you explain the following ? 

"Do you need 1st, 2nd taper, or plug; and do you want ISO standard coarse 8mm (the most common) or ISO standard fine?"


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## deema (14 Jun 2018)

The first and second taps have a length at the front that’s tapered to help start the tap. The first is more tapered. A plug tap has no taper and is used for blind holes.

For through holes use just the first tap with the longest taper. For blind holes, use the first, then second then plug.

The normal thread pitch is 1.25mm but you can get fine (1mm) and extra fine (0.75mm) bolts.


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## AES (14 Jun 2018)

OK,all understood.

"1st taper" taps are used to start ALL threads (and from the name you'll guess they have the biggest taper, starting with a much small dia at the bottom and gradually tapering to max at the top). This makes it easier to start the tapping, especially if tapping by hand.

"2nd taper" taps are not used so frequently, and have rather less taper - i.e. more full-ish dia - than 1st taper taps do. And "plug" taps have very little or almost no taper. You normally only use the plug taps when you want to tap into a blind hole (i.e. a hole than doesn't go all the way through the work piece, but you still want to screw into the full depth of the hole).

From that you'll probably guess (correctly) that a lot depends on the thickness of the work piece as to which of the 1st and/or 2nd taper taps you'll need. If tapping into thin-ish sheet or thin plate, and if the hole goes all the way through, then you can probably get away with just 1st taper, though when the job is thicker, and/or you need a better thread with more full screw thread engagement, and/or if it's harder material (harder than MS), then 1st followed by 2nd is the "proper" way. And plug is, as above, normally only used for tapping blind holes.

For all metric screw threads there are 3 separate ISO "norms" (standards). "Coarse", "Fine", and "Extra Fine". By far and away the most common you'll come across every day is the Coarse - they're so common that often the screw/bolt, and even the tap is NOT marked Coarse (but on the taps, the "pitch" (see below) IS usually marked.

The Fine threads are much finer (!!) - in both cases this means the length you move along the thread with 1 revolution. For example, 8mm Coarse (the everyday jobbies) have a pitch (commonly, but incorrectly often called "TPI") of 1.25 mm, whereas the 8mm Fine have a pitch of 1.00. What this means in everyday language is that on the 8mm coarse, 1 rotation of a "nut" on that bolt/screw will move the "nut" along the bolt/screw by 1.25mm. On the 8mm fine, 1 rotation will give you a lengthways movement of only 1.00 mm.

As said, the coarse is the everyday thread, but on electrical and electronics goods, computers, etc, fine and extra fine are more common (because the parent metal that the bolt/screw screws into is very often pretty thin sheet metal formed into a chassis or something). Extra fine has a pitch of 0.75mm. 

Sorry it's long but hope it's clear and that it helps you (as my good lady always says "Nobody fell down from the stork knowing it all!").


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## AES (14 Jun 2018)

Thanks deema - our posts crossed, but yours is more succinct!!


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## Beau (14 Jun 2018)

AES":2ldcc0mo said:


> OK,all understood.
> 
> "1st taper" taps are used to start ALL threads (and from the name you'll guess they have the biggest taper, starting with a much small dia at the bottom and gradually tapering to max at the top). This makes it easier to start the tapping, especially if tapping by hand.
> 
> ...



Must admit I didn't realise they were supposed to be used like that. I thought I had to work through them all with each one taking off a bit more than the last. I have been doing blind holes. Bungled my way through with the old ones I have but they dont have much cut left  

Only ever use course threads no confusion for me there presuming I have ordered the right taps


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## Farmer Giles (15 Jun 2018)

Tracy tools is my go to place for taps and dies.

I have acquired a large array over the years, mostly old second hand and good quality but if I'm missing a size, especially if its an unusual size then they are the place I go. 

Cheers
Andy


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## AES (15 Jun 2018)

Don't worry too much about that Beau. If (when?) you break a 1st or 2nd taper tap, you can always grind the taper off completely (go SLOWLY, do NOT let the tap go blue), which leaves you with an "emergency" plug tap, albeit a bit shorter than usual. DAMHIKT! Although 8mm is a fairly meaty tap, so if (when?) it happens, it's more likely to happen with smaller taps, 3 mm and smaller.

And as said the metric coarse taps are the "everyday" pitch taps, so unless you specified otherwise you'll most likely get the coarse automatically.


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## DTR (15 Jun 2018)

Beau":3rf6zenc said:


> Must admit I didn't realise they were supposed to be used like that. I thought I had to work through them all with each one taking off a bit more than the last.



Some taps do work that way, they're called sequential taps (IIRC?). They're not very common though. Sequential taps are said to work better but I've not had much success with them.


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## chaoticbob (15 Jun 2018)

Personally I have rarely found it neccessary to use 1st or 2nd taps - perhaps that's because most of the time I tap with the work in the same machine I drilled the hole with, so no alignment isues. Plug (aka bottoming) taps seem to work fine for both blind and through holes.
The thing about needing to do it in several stages to progessively remove metal is a common and understandable misconception, due to the confusing names given to taps I suspect - given 1st, 2nd, 3rd taps (which they are sometimes called), it's a logical conclusion.
The things DTR refers to (which do actually work like that) are called serial taps in my experience, but maybe there are other names for them!
Robin


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## t8hants (16 Jun 2018)

A lot of the very cheap chiwanese sets use a no2 as the first tap and then the plug. They are often ground abysmally leaving the amateur struggling and wondering if his technique is all wrong. I suspect cheap tap and die sets have done more to ruin the reputation of home threading as a possibility than any amount of bumble-fisted practice


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## DTR (16 Jun 2018)

chaoticbob":3a5thfgp said:


> The things DTR refers to (which do actually work like that) are called serial taps in my experience, but maybe there are other names for them!
> Robin



Right you are, they are called serial taps, not sequential. Sorry about that


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