ME taps and dies : HSS, carbon steel or tungsten steel ?

[brian777999]

I need to buy a set of taps and dies for model engineering. The only sizes I need at this stage are 1/8-40, 3/16-40, 1/4-40 so I will buy them separately rather then in a set.   

 

1. From my research I have found that HSS is the strongest but some people have said that if you break one then it can be very difficult to remove it. Does anybody have any opinions on this ? I will be working with steel, brass, copper, bronze and aluminium.

 

2. Why do ME taps and dies have 40 TPI ? It is not a thread count which is readily available.

 

3. Is the intermediate tap really necessary or can you go from the taper tap to the bottom tap ?

[Peter Beckett]

Hi Brian,

1. HSS is the best.

2. 40 TPI is ideal for tapping thinner materials as you get more threads. 32 or less means you might be getting only 1 thread being able to be used which may not be enough to hold the fitting.

3. If you are tapping softer materials such as copper or aluminium then you can omit the No2 or intermediate but make sure you are using a lubricant and only take small bites at the thread (hope that makes sense)

 

As to broken taps(which are usually caused by hurrying, trying to tap to much in one go), unless you have the right extractors, all 3 types can be tricky to remove.   

The other hint I can offer is to buy a good brand with a heavy shank as you get a firmer grip when using them (especially taps) also make sure you have good quality stocks and tap wrenches. I find a small T wrench very handy for 1/8 taps as you get better control of it and less breakages

 

Cheers

 

Peter

[Debs.]

Hello Brian,

If you haven`t seen it previously, you may find that this chart is useful in selecting the correct tapping drill for use with specific thread-forms.

 

 

 

 

[talyllyn1]

Having worked in the cutting tool industry for over 35 years, I feel I can offer a little bit of advice here.

For hand tapping the materials you mention, carbon steel taps are perfectly good enough (as indeed are carbon steel drills and reamers). HSS and carbide cutting tools were developed for machine cutting of harder materials (cast iron and steel, hardened steel, etc.), or to provide a longer life (i.e.bigger component batches between tool changes).

The only proviso with carbon steel taps is that there are some poor quality tools on the market (particularly these days) - mostly of far eastern origin. This also applies to HSS and carbide to a lesser extent. As a rough guide, you need to look for taps (and drills) with ground flutes rather than rolled flutes. It would be a wise precaution to drill and tap a piece of scrap first and check the thread when using any tap that is from an unknown source.

 

HSS is not necessarily the "strongest" or the "best" (not sure how you would quantify these terms!).  Carbide are the hardest, followed by HSS then carbon. This means they retain their cutting edge for longer, but they are more brittle, so more prone to breaking. For normal hand tapping of the occasional thread you are not likely to see any advantage in the extra cost of HSS and carbide. This also applies, incidentally, to the various Ti-n and Tic-n coatings - they were developed to reduce tool wear in machine applications.

 

When hand tapping, breakage usually occurs for the following reasons:-

1) wrong tapping size used (i.e. too small)

2) bottoming out in a blind hole.

3) incorrect tool use - cutting more than one complete rotation at a time without reversing for at least one rotation to clear the swarf. This is particularly important if the depth of the threaded hole being cut is greater than twice the diameter. This problem is overcome in machine tapping by using spiral pointed taps for through holes and spiral fluted taps for blind holes. Neither are applicable to hand tapping applications.

4) Incorrect or no lubricant.

 

You can omit using a second tap, except for blind holes, where the difference between the cutting edges on the taper and bottoming taps will be too great to cut a full thread near the bottom of the hole, resulting in possible jamming of the bottoming tap. It can be done, but plenty of lubricant and a gentle touch are needed, along with frequent reversal of the tap to clear the swarf.

 

It's been a few years since I was involved, and although I became aware of some very obscure thread forms (mainly aerospace) I was never asked about ME. All my reference books were disposed of with the last house move, so I can't help with that one I'm afraid.

 

Hope this helps

Dave

[PenrithBeacon]

Agree with post #2, but I think the use of a tap wrench in smaller sizes is unwise. This is because you are likely to 'put in' a sideways force while using it on smaller size taps which will then break. Use a pin vice instead and just spin the vice in the fingers.

 

It's a moot point whether to use carbon or HSS. Carbon doesn't last as long, but how often does a hobbyist use a tap?

 

Regards

[Enterprisingwestern]

Engineers avert your gaze.

 

"Generally" we only tap softer metals, so I run a steel screw through the workpiece.

 

Mike.

[talyllyn1]

Engineers avert your gaze.

 

"Generally" we only tap softer metals, so I run a steel screw through the workpiece.

 

Mike.

Not as "non-engineering" as you might think!

Very soft materials (such as aluminium) are often "tapped" by roll-forming, using a fluteless tap. This type of tap is generally only used in machine-threading applications (with lots of lubricant), and the tapping drill sizes are different to fluted taps. Obviously the tap is made to different tolerances, so it is a bit different to the screw that will go into the thread. A bit more sophisticated than just forcing a screw in, but the same idea!

 As the material is deformed outwards around the edge of the hole a countersinking operation is carried out before the tap is used - a little refinement you might want to consider.  

Cheers

Dave

[Enterprisingwestern]

 a little refinement you might want to consider.  

 

As many people will testify, I don't do refinement!!

 

Mike.

[brian777999]

   

The other hint I can offer is to buy a good brand with a heavy shank as you get a firmer grip when using them (especially taps) also make sure you have good quality stocks and tap wrenches.

 

1. Could you name some good brands of taps and dies ?

 

2. Can machine oil be used as cutting fluid or does it have to be the correct cutting fluid ? Is this the same cutting fluid as used on a lathe ?

[meil]

personally I would only use BA threads or Metric fine as they are easily obtainable and reasonably cheep. They are also finer than ME threads. A 3mm tap has 72 TPI (0,35mm pitch).

[talyllyn1]

My experience was mainly with machine tapping, so I was more familiar with HSS and carbide brands than carbon steel.

Also, the "globalisation" of engineering (read "disappearance" in the UK) means that many of the long-established cutting tool manufacturers have gone. Some of the old brands still exist, but the sources of manufacture are now questionable.

This is perhaps more of a concern when buying the more usual thread forms (e.g. Metric Coarse & Fine, UNC & UNF, BSW & BSF and BA), but less so with ME. The market for ME would be too small for someone to manufacture cheap and dubious tools. You might therefore only be able to find HSS?

 

The sets that you can buy from general tool suppliers aren't necessarily bad, it's just that they are usually unbranded, or the brand is not a mainstream one. With these, a recommendation from someone who's used them is probably the only way to assess the quality - but be aware that "own-branded" products often get switched from one supplier to another!

 

The type of lubricant used when hand tapping isn't critical. Almost any oil would be suitable - even water is better than nothing!

 

Cheers

Dave

[pointstaken]

Failing the availability of oil, a quick squint to ensure SWMBO is out of sight, and a cocktail stick dipped in the butter dish and transferred to the tap is effective.

Do not send me your personal injury claim if you are caught red handed.

Dennis

[raymw]

One advantage of the ME threads, is that when cutting them in the lathe, no need to mess with changing the pitch. For many applications, pipework, and steam fittings, hand held dies would not be used. Also, of course, you don't need to have charts for tapping drills, since the thread depth is constant for all sizes. Fwiw, I've a drill/tap chart at http://yertiz.com/cnc/tapchart.pdf print it out on a couple of sheets of a4, as many copies as you like, laminate it if you want. Also a couple of other useful items http://yertiz.com/cnc/millchart.pdf and and http://yertiz.com/cnc/convert.htm

 

Best wishes,

 

Ray

[flubrush]

2. Can machine oil be used as cutting fluid or does it have to be the correct cutting fluid ? Is this the same cutting fluid as used on a lathe ?

 

A good tapping lubricant is Trefolex.  It's a paste so sticks to the tap and the hole and doesn't get all over the workpiece.  The only problem is that the smallest can available is 500 grams and that is overkill for our modelling use.  I was given a small pill box sized container filled from a large tin in the mechanical workshop at work in the 1970s and I haven't finished it yet. :-)  So begging a small amount from any source you can find is probably the best bet. :-)

 

Jim.

[brian777999]

The other hint I can offer is to buy a good brand with a heavy shank as you get a firmer grip when using them (especially taps) also make sure you have good quality stocks and tap wrenches. I find a small T wrench very handy for 1/8 taps as you get better control of it and less breakages

 

 

1. I am using a T wrench at the moment to clean out some threads which were not properly drilled. Should the tap only be inserted into the T wrench as far as the square shank ? I have been pushing it in further so the wrench is gripping the round part of the tap like a drill chuck.

 

2. Most of the ME boxed sets sold in the UK omit the second tap. Is it worth buying the second taps at all ? The boxed sets are the cheapest way to buy taps and dies.

[Adrian]

A good tapping lubricant is Trefolex.  It's a paste so sticks to the tap and the hole and doesn't get all over the workpiece.  The only problem is that the smallest can available is 500 grams and that is overkill for our modelling use.  I was given a small pill box sized container filled from a large tin in the mechanical workshop at work in the 1970s and I haven't finished it yet. :-)  So begging a small amount from any source you can find is probably the best bet. :-)

 

Jim.

 

That's the stuff I use as well - I've got a small film canister sized pot of the stuff which Iooks like a sales sample, but can't remember where I got it from though!!!

[brian777999]

Now I have found out that the UK and the US are different (55 and 60 degrees) so I have to decide which way to go ? Nothing is ever easy is it ?  It may be better just buying what I need as I need them although buying a whole set appears to be quite economical.

[raymw]

Hi Brian,

 

60 deg is some euro bastardisation - http://www.britishfasteners.com/threads/ME.html  or are you talking of the abomination that is standard iso metric?

 

The old imperial threads (Whitworth) were in the main derived empirically, metric weren't, but BA was a sort of mix of both.

 

Best wishes,

 

Ray

[brian777999]

 

60 deg is some euro bastardisation - http://www.britishfasteners.com/threads/ME.html  or are you talking of the abomination that is standard iso metric?

 

 

No, Model Engineering threads are different in the UK and US. The taps, dies, bolts, nuts etc. are not interchangable ! This is what I am reading on the internet ; please correct me if I am wrong.

[raymw]

Hi Brian,

 

It may be that some folk are trying to promote the metric system, but the Model Engineer thread is 32 or 40tpi and to the Whitworth thread form. If it is something other than that, then it is not ME thread.

 

However, since most ME threads will be machined in the lathe, then I expect a 60deg cutter is more available for folk who can't be bothered to do it right    

 

Perhaps you should look into the history as to how the various thread forms originated, and the benefits of each, it may or may not be interesting (sort of 'unseen rivet counting', if you like   ).

 

Best wishes,

 

Ray

[Mike Boucher]

My comments:

1) If you're planning on using this tap/die more than once, get HSS.  Carbon loses its edge way too quickly IMHO.  Carbon is cheaper, but you'll have to buy them more often!

 

2) If you're worried about breakage, build yourself one of these:

http://www.spaco.org/Blacksmithing/TapDrillBlock.htm

 

The one I have was a Christmas present from my father, who was a toolmaker for 30+ years before he retired.  The one I have is rectangular, and only has the holes for the taps themselves (i.e it doesn't have the holes to guide the tap drills) but I've never broken a tap when using it.  its also been hardened.

 

3) As for UK vs US, I see you're in Australia, so take your pick.  If you're using BA taps/dies elsewhere in your projects. go Brit.  If youre using USF taps/dies, go US.  If metric, flip a coin  or buy whichever one is cheaper including shipping.

 

(Also note that after March 31st, the cost of international shipping from the UK is going up considerably for packages over 500 grams, so order soon if you're getting it from the UK!)

[Mike Boucher]

1. I am using a T wrench at the moment to clean out some threads which were not properly drilled. Should the tap only be inserted into the T wrench as far as the square shank ? I have been pushing it in further so the wrench is gripping the round part of the tap like a drill chuck.

 

2. Most of the ME boxed sets sold in the UK omit the second tap. Is it worth buying the second taps at all ? The boxed sets are the cheapest way to buy taps and dies.

 

1) The tap wrench should grip the square at the end of the shank.

 

2) I've never used the 2nd tap.  Use the tapered tap as deep as you can, then switch to a bottoming tap if necessary.  (I've also never bought a bottom tap, just used my bench grinder to grind the tapered section off a older, slightly worn tap)

 

Also, To follow up on my last post, here's a photo of my tapping block.  The smallest hole is appropriately sized for the shank of taps between 1-72 and 6-32, IIRC.

 

 

and what it would look like in use with a 4-40 tap  (Imagine 1 hand holding the block steady, and the other on the tap wrench)