How not to break a 16BA Tap?

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Julian Roberts
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How not to break a 16BA Tap?

Postby Julian Roberts » Sun May 13, 2018 7:10 am

I wonder if anyone has any thoughts?

Bought one of these for £20. Broken within 15 minutes. I could see it was delicate so I oiled it and the brass tube I wanted to tap, was screwing it in by hand, unscrewing it every time it got sticky to clean off the swarf.
I wonder if another time (if I buy another one) I'll drill it out to 0.7mm. I had drilled it to 0.65. The intended use has no mechanical strain, it will be merely for retaining one bit fixed to another.

Obviously I'm not very savvy with all aspects of workshop practice, though I've successfully used a 10BA tap previously, but hey that's what the Forum's for...?!

So what I'm wondering is, what is the proper technique for using one of these things?

Any ideas I'd be most grateful. Working till later so I won't be able to respond till then.

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John Bateson
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Re: How not to break a 16BA Tap?

Postby John Bateson » Sun May 13, 2018 8:14 am

Wow - it lasted 15 minutes. My first two tries were a lot shorter than that. I bought a couple more but am too scared to use them - they will go into the rogues gallery I think.
I don't think there is anything wrong with the technique, the only change I was taught was to screw in 1 full turn, then 1/4 turn back, but I guess that removing the tap and cleaning it would have the same effect.

Oil as a lubricant is probably not the best thing, turps or white spirit would be better, brass is a rather messy metal.

Any lateral strain at all seems to break these things, whether it is NiSi layered or 3D printed FUD plastic. In the end I cheated and went to 14BA for my particular job.

John

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Guy Rixon
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Re: How not to break a 16BA Tap?

Postby Guy Rixon » Sun May 13, 2018 8:38 am

Use a pin chuck rather than a T-handle tap wrench. That reduces the tendency to bend the tap over. Works for me down to 12BA and I've never tried smaller taps.

Consider using a machine tool, turned by hand rather than under power, to keep the tap aligned with the work. A lathe is obviously good for this, but perhaps also a pillar drill feeding the tap into work held in a machine vice? Not tried this.

Being a mechanical coward, I'd dodge the whole process. Drill out the tube to clearance, decapitate the screw and solder it in as a stud.

GraemeJ
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Re: How not to break a 16BA Tap?

Postby GraemeJ » Sun May 13, 2018 9:28 am

With due respect to John, I would say that the technique of 1 full turn and a quarter turn back is asking for trouble especially with such a small tap.
I always tap with a quarter turn forward and then at least a half turn back, no harm in going further back particularly in deep holes. When the tap is advanced again to the point where cutting will start again it should do freely. When the point of resistance is felt, repeat the process.
With regard to lubricants, I would always advocate a cutting compound. It will prolong the life of the tool, as well as ease the cutting process.

Graeme

John Palmer
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Re: How not to break a 16BA Tap?

Postby John Palmer » Sun May 13, 2018 10:32 am

Little to add to what's been said above. For a tap as small as 16 BA I agree with Guy about avoidance of a T bar tap wrench, as you should be able to apply sufficient cutting force by rotation of the tap holder between the finger and thumb of one hand whilst using the other hand to steady the holder on the axis of the hole being tapped. With taps 12 BA size and larger I find that the extra leverage of a T bar wrench is required for a hole of any significant depth.

For lubricant I use tallow. I also find this a useful lubricant/rust inhibitor on woodscrews.

Perhaps the most significant consideration of all: do you really need a fixing that utilises a 16 BA thread? I would spend at least the fifteen minute lifespan of your tap thinking about whether I could re-design the job in such a way as to avoid the need for such a fixing. To date my 16 BA tap remains intact. And unused!

Philip Hall
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Re: How not to break a 16BA Tap?

Postby Philip Hall » Sun May 13, 2018 1:24 pm

I would not entirely trust that the 0.65mm drill you have actually drills a precise 0.65mm hole. In my experience it is likely to be a little less. So a 0.7mm tapping hole may be a good plan. If you are tapping a tube then much more of the tap is going to be engaged than if it were merely a hole through (say) 1mm material, so tapping only until a little resistance is felt and then backing off is helpful. In a tube I would take the tap fully out, clearing off and then restarting. A pain and time consuming, but...

Philip
Last edited by Philip Hall on Sun May 13, 2018 3:47 pm, edited 1 time in total.

Edward45
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Re: How not to break a 16BA Tap?

Postby Edward45 » Sun May 13, 2018 1:42 pm

If I were tapping into tube I would use my Unimat by disengaging the drive and turning by hand. Whilst not 16BA I have used this technique for tapping 14BA into steel when making up crankpin parts. Using the lathe ensures that any lateral pressure is minimised, and so far I haven't broken a tap. I'm sure I will be sorry stating the obvious, but always buy HSS taps.

Enigma
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Re: How not to break a 16BA Tap?

Postby Enigma » Sun May 13, 2018 2:28 pm

Are there different types of 16BA tap ie taper and plug? They are so small that the difference may not be noticable! If a taper tap is used there should be a 'feed' for the tap into the hole and the initial 'force' required to start the thread cutting may be less then if a plug tap is used.

I use a pinchuck for general tapping (8 to 14BA) and as soon as any resistance is felt I remove the tap and clean it. I tend to use a bit of spit as a lube, probably not recommended by the experts! ;)

David Knight
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Re: How not to break a 16BA Tap?

Postby David Knight » Sun May 13, 2018 2:58 pm

I would concur with most of the advice given so far in as much as using a pin chuck and frequent backing off is concerned. Where I would respectfully differ is the matter of a lubricant, I was taught that cutting in brass of any sort was best done dry. 16BA is very small so if anything a lubricant would cause things to gum up worse.FWIW, I suspect the tap used is a HSS tap given the price of £20, if you are only using this size for brass, a carbon steel one would work just as well and cause less grief if it happened to break.

Cheers,

David

Julian Roberts
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Re: How not to break a 16BA Tap?

Postby Julian Roberts » Sun May 13, 2018 9:08 pm

Very many thanks all. Food for thought. I'm relieved to see I'm not the only one to find this challenging!

Yes certainly reviewing the need John! Whatever I come up with will be on my Crab build.

The tap is a taper, carbon steel, BTW

Terry Bendall
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Re: How not to break a 16BA Tap?

Postby Terry Bendall » Mon May 14, 2018 7:46 am

Normally lubrication is not needed when threading brass regardless of the size. Removal and cleaning may be useful. Certainly using a pin chuck is a very good idea and I have done the same with small sizes. There should be a difference between the taper and plug taps but ti will not be easy to see. The use of a lathe to guide the tap in square is a good tip but the ide is more difficult using a pillar drill. And yes I have broken that size of tap as well! :(

Terry Bendall

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Colin Parks
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Re: How not to break a 16BA Tap?

Postby Colin Parks » Mon May 14, 2018 9:27 pm

Hello Julian,

There are types of brass which are better for machining or tapping holes.

CZ121 is probably the best and is self-lubricating: https://www.smithmetal.com/pdf/copper-b ... /cz121.pdf

From personal experience, most brass sold for hobbies is not of that grade, it being very hard to machine to a good finish and it will cause taps to bind. So the answer to the question 'How not to break a 16BA Tap?' is to use CZ121 brass, which would probably not be the grade available in small sizes of tubing. Also, and from what I remember about hole sizes for tapping, there are choices as far as percentages of thread goes, so it might be worth experimenting with a drill slightly larger than has been used so far - as Phillip Hall suggests.

The CLAG website has a table of drill sizes for BA tapping and clearance holes, which at 0.6 mm for tapping 16 BA, is even tighter than the 0.65 mm drill size that you have used. A quick search through other websites showed that they all quote 0.6 mm for tapping.

John Palmer
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Re: How not to break a 16BA Tap?

Postby John Palmer » Tue May 15, 2018 1:01 am

I too am accustomed to thread forming with the aid of my Unimat's tailstock. I have found it perfectly satisfactory to hold a tap in a Jacobs chuck and allow the entire tailstock to be drawn towards the job as the tap advances into the hole. For male threads, I made a die holder with a threaded rear extension onto which I could screw an extension bored to be a running fit on the tailstock ram. In this case the tailstock can be locked with ram extended, and the die holder plus extension can then advance along the ram towards the workpiece as the die forms the thread. It occurs to me that a similar principle might be applied to small taps held in a pin chuck: a journal that is a close running fit in the bore of the pin chuck will keep the tap aligned on the axis of the hole being threaded and inhibit the application of that deadly lateral pressure. Such a journal could equally well be mounted in the tailstock of a lathe or in the chuck of a pillar drill. The advantage of such an arrangement would be avoidance of the need to lower the drill chuck towards the job as the tap cuts its thread, and you would be better able to feel the amount of resistance the tap is encountering – a factor I find important with small taps in particular.

CornCrake
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Re: How not to break a 16BA Tap?

Postby CornCrake » Tue May 15, 2018 6:31 am

Would it help to anneal the brass tube first?

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Colin Parks
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Re: How not to break a 16BA Tap?

Postby Colin Parks » Tue May 15, 2018 8:14 am

CornCrake wrote:Would it help to anneal the brass tube first?


No! Ideally, the brass should be hard but free cutting. Exactly the opposite of most of the stuff for retail sale. I think the grade I mentioned before was also called 'clock brass', as used by horologists.

All the best,

Colin

Julian Roberts
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Re: How not to break a 16BA Tap?

Postby Julian Roberts » Wed May 16, 2018 8:15 am

All, thank you for your further thoughts.

I should have said I don't have a lathe. But those of you who have described how a lathe might be used will I'm sure be helping others who may refer to this.

I realize from this that my best chance is to minimize the thickness of material I am trying to tap. I've just measured the thickness of a 16BA nut, it's somewhere around 0.7mm. For my application where almost no mechanical force will exist I guess quite a bit less than that thickness is all that will be needed. I will drop the idea of tapping into a tube.

I now have to admit that the other material I was considering tapping is solder! Is that a shockingly hopeless idea? I have a nickel silver item, probably 0.6 - ish thick with a hole in it that is already 0.8 diameter. Seems to me an option is to drill that out to say 1mm, fill it with solder, then drill say 0.7 and then tap. Easy to refill with solder if the screw is then too loose and try a smaller drill.

What about nickel silver itself as a material? The other option would be to plug the hole with NS (or brass) wire, smooth off to the same thickness as the rest, and drill and tap into that.

Just to add that the 16BA bolt is just the perfectly elegant way of achieving what I want to achieve, that's why I haven't given up yet.

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Simon_S
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Re: How not to break a 16BA Tap?

Postby Simon_S » Wed May 16, 2018 8:21 am

Can you drill a recess then solder a nut inside?

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David B
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Re: How not to break a 16BA Tap?

Postby David B » Wed May 16, 2018 9:50 am

Simon_S wrote:Can you drill a recess then solder a nut inside?


A thinned down nut could work quite well. You can solder the nut on with your RSU! See S4News No.207.

Philip Hall
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Re: How not to break a 16BA Tap?

Postby Philip Hall » Wed May 16, 2018 8:09 pm

I don’t think that tapping solder is a workable idea, because solder is so soft that it would be so easy to overtighten the screw and strip the thread in the solder. Drilling out the hole and plugging with brass or nickel silver and redrilling/tapping might be better, or use a thinned down nut or half nut. If half nuts are still available that is.

Philip

Terry Bendall
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Re: How not to break a 16BA Tap?

Postby Terry Bendall » Thu May 17, 2018 8:55 am

Julian Roberts wrote:What about nickel silver itself as a material?


For those who want to find out more about non ferrous metals have a look at https://www.smithmetal.com/ This company is a major supplier of non ferrous metals to industry and has a very informative web site including downloadable data sheets. They list 12 different types of brass and 4 different types of nickel silver. Of course what we buy from our usual suppliers could be anything and it is difficult to identify the different types by eye.

Nickel silver is a bit harder than some types of brass but the same tools can be used. The difficulty here is in the very small size of the tap being used. Soldering a nut is place is a good idea but if the solder creeps into the thread a tap will be needed to clean it out. A good tip to avoid this is to cover the thread with grease but that is not easy in this size. Apart from the problem of stripped threads, trying to thread solder will cause the tap to get clogged up which will increase the risk of breakages.

Terry Bendall

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Will L
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Re: How not to break a 16BA Tap?

Postby Will L » Thu May 17, 2018 4:28 pm

Terry Bendall wrote:...Soldering a nut is place is a good idea but if the solder creeps into the thread a tap will be needed to clean it out. A good tip to avoid this is to cover the thread with grease but that is not easy in this size...


A better tip is to hold the nut in place with the point of a cocktail stick. You insure that both the nut stays where you want it and no solder gets in.

On Julian's basic problem, as a kitchen table modeller like him, I have tried tapping down the centre of a suitable sized bit of tube by hand in the past, and for lots of reasons this is just a lot more difficult to do (and thus more stressful on the tap) than tapping a hole in a plain bit of sheet brass. I don't usually break taps (mostly i go for 12BA or 14BA, 16BA is getting hard to see) but I did take the tip off a 12BA tap trying to do this. I wouldn't bother trying again.

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Le Corbusier
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Re: How not to break a 16BA Tap?

Postby Le Corbusier » Thu May 17, 2018 9:20 pm

Will L wrote:
A better tip is to hold the nut in place with the point of a cocktail stick. You insure that both the nut stays where you want it and no solder gets in.



I'm afraid Will you are just showing your high level of soldering competence. I have managed on many occasions to foul the thread on a nut whilst using a cocktail stick to hold it in place. Furthermore, in Tony Wright's right track kit building DVD he does the same and has to re tap ... so its not just me. Terry's grease tip sounds like a good insurance policy to me :thumb
Tim Lee

Julian Roberts
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Re: How not to break a 16BA Tap?

Postby Julian Roberts » Thu May 17, 2018 9:41 pm

So many thanks to everyone for all these good ideas! When I get some modelling time I'll do one of these options and describe on my Crab thread...maybe I'll end up trying them all!

PS 'Fraid I have no RSU David..!

Philip Hall
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Re: How not to break a 16BA Tap?

Postby Philip Hall » Thu May 17, 2018 10:39 pm

My favourite dodge for preventing solder from going where I don’t want it to go is to chemically blacken those parts. In the case of a nut I would blacken the thread inside the nut using an etch marker pen, or at least the threads you can get to, which should be enough. Another way is to blacken a steel screw and put that in the nut before you solder it to whatever it’s going to be attached to. If any solder does get inside, it’s fairly easy to undo the screw which will clean out the thread as you do so.

Philip

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David B
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Re: How not to break a 16BA Tap?

Postby David B » Fri May 18, 2018 7:52 am

Julian Roberts wrote: PS 'Fraid I have no RSU David..!


You could still try the same technique using a bigger bit on your iron. After all, whether you use an RSU or soldering iron, you are just applying heat.

Try tinning the nut, holding it in place and putting a big bit on top. Watch for the solder melting then remove the iron. The ceramic tipped tweezers I have shown elsewhere would be useful to hold the nut. Look for them on Ebay - cost about £3.50.

Quite lot of jobs can be done in a similar way with either the RSU or soldering iron. It's just that with the RSU the heat is applied more quickly and locally and you can hold the part in place throughout the process.


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