Tapping my first thread into Cast Iron

[Steve RowbothamParticipant @steverowbotham77083]

I am seeking advice on tapping a 1/4" 32TPI thread into cast iron. I have just completed my first engine, a Stuart Oscillator, for which I tapped the same thread into the Brass standard using a set of HSS taps purchased from Tracey Tools for the task, and achieved a good result. I have now embarked on a Stuart 10V and have just drilled the cylinder for the exhaust and now need to tap the 1/4 32 TPI thread. I have not moved the cylinder since drilling and plan to fit the taps into the drill chuck and turn by hand whilst applying pressure via the quill. I have not drilled CI before, and now have a lot of holes to drill and tap down to 8BA and am nervous about stripping the threads. The 1/4 32 TPI taps are nice and sharp having been used once only into Brass. My questions are a) is using the drill chuck to hold the taps a sensible approach or would I be better off by hand, and b) should I use cutting fluid – there seems to be mixed views on this matter on the web. Any advice gratefully received before I press on.

[Steve RowbothamParticipant @steverowbotham77083]

[Andrew TinsleyParticipant @andrewtinsley63637]

Using the drill to hold the tap is a wise move. Tapping by hand usually gets a slanting tap and then a broken tap. I still tap by hand once in a while, even though I have built a tapping stand. Using a drill chuck to again hold the tap.

I never use a lubricant or cutting fluid tapping cast iron. The free carbon is a self lubricating system!

The only caveat is that on rare occasions (hopefully!) you can sometimes hit a hard spot which can cause trouble or even a broken tap. I have been lucky so far and have not yet come across the problem, but I know others have.

Andrew.

[Jon LawesParticipant @jonlawes51698]

If this is the Stuart castings then there is a very high likelyhood of hard spots. Make sure you listen to the drill.

[JasonBModerator @jasonb]

If using the drill chuck I tend to leave it slightly loose on the tap and drive the tap with the wrench part way down the round shank. Trying to turn the whole spindle by hand will not give much feel on small taps.

The alternative is to make up a simple guide which can just be a short bit of 1/4" or 6mm steel with a point turned on one end and deeply ctr drilled at the other. This can be held in the chuck or collet and brought down with light quill pressure as the tap is turned again with the tap on the round shank.

having the tap on the round part acts a bit like a slipper clutch as the wrench will hopefully slip before the tap brakes if it bottoms out or jams.

Edited By JasonB on 14/08/2022 18:11:56

[old martParticipant @oldmart]

I would use the chuck to keep the tap straight for about three turns and then finish by hand. Cast iron is tapped dry, and with a small workpiece you can get some of the dust out by simply inverting the work with the tap still in. Otherwise clean out the hole as soon as you detect tightening of the tap.

Keep any bits of spare cast iron to practice tapping on.

Edited By old mart on 14/08/2022 18:37:43

[Steve RowbothamParticipant @steverowbotham77083]

Thank you all for your very helpful responses, I will put your advice to use in the morning. The lack of sensitivity via the chuck was what originally worried me, I have practiced on other materials but don't presently have any bits of CI to practice on. I love the slipping clutch suggestion.

[Ramon WilsonParticipant @ramonwilson3]

I don't like the internal support cone centre for one reason – you need three hands particularly to keep the contact with the tap as it drives forwards.

I much prefer to hold the tap very loosely in the chuck and use the method Jason shows but always grind a small flat on the side of the tap for a positive drive even on small taps down to 10/12BA. Tap shanks are not always a standard size but if a brass tube can be drilled or found to fit and held in the chuck as a guide even better

I don't think these small Eclipse tap wrenches ae available any more but are ideal for this. This is tapping 8BA – 48 holes on two cylinder blocks without a hitch. For the smaller 10 BA and below taps I use a circular tap wrench – just a slice of 3/4 dia knurled MS with a grub screw in it to drive the tap – again on a flat on the shank. The tap is turned between finger and thumb – very sensitive feed back from the tap

I don't know how many small (5BA down) holes there were in total on the above build but all were put, without breakage, in this way or by gently gripping in the drill chuck, turning the drill on then off and as the spindle runs down use the residual motion to drive the tap in four or five threads until the drill stops. Release the tap, remove and finish by hand.

Hope that's of interest too

Tug

 

Just realised I had these images too – shows the smaller wrench n use

 

 

Edited By Ramon Wilson on 14/08/2022 20:02:11

Edited By Ramon Wilson on 14/08/2022 20:09:37

[Clive Brown 1Participant @clivebrown1]

What you really need is a Geo. Thomas Universal Pillar Tool. Invauable gadget. here

[Ramon WilsonParticipant @ramonwilson3]

The main castings for which have sat under my bench for years Clive – just never got round to it as the above has proved more than adequate when required.

I do agree though – it's a lovely bit of of very useful kit if you have time or desire to make one.

[Nigel Graham 2Participant @nigelgraham2]

When tapping a blind hole it is worth putting a pair of lock-nuts of the tap as a depth-stop: the thread is not usually needed to be the same length as the tool.

Where I do need a deep thread I measure the tap's threaded length, or to the shank diameter, from its very tip, then measure the amount protruding to assess the cut depth.

If the tapping hole depth is not important, e.g. in the end of a stretcher, I drill well over depth.

One important tip is to withdraw the tap at intervals to brush it clear, and to clean the chips from the hole.

.

I've invested in a spring tap-guide – yes I know making them is among the exercises in the primer books but this was one where I felt buying it justified.

It has proved very useful, in the lathe, drilling-machine and bench-drill. (My mill's quill is so stiff that it cannot used with any real sensitivity.)

For bigger taps I sometimes used the drill rather as a pillar-tool by – unplugging its mains lead, slipping the belt off and turning the chuck by hand, the other hand applying gentle starting pressure with the feed-lever.

Ramon –

I do like your circular tap-holder. I don't remember seeing this device elsewhere. It must give a lot more control with very small taps, than does a conventional, arm-type tap-wrench.

[Steve RowbothamParticipant @steverowbotham77083]

Thank you for sharing the above wisdom which is all complementary and absolutely addresses my concerns of achieving perpendicular threads, some into blind holes, whilst also minimising the risks of stripping and tap breakage. I will definitely be making a circular tap holder for small taps, and am giving very serious consideration to making a UPT as a starter project, it does look like a very useful piece of kit. I have established availability of UPT castings from Hemmingway, but if anyone has unwanted castings I would be happy to purchase them. I have now asked several questions on this forum as a novice and been overwhelmed by the knowledge of forum members. There is a wealth of knowledge in the above thread alone, and there will likely be further contributions. Just a thought, but has anyone thought of collating the responses to beginners questions, which are in the main based on practical problems, into a publication of some form and so capturing the massive knowledge of forum members?

[Ramon WilsonParticipant @ramonwilson3]

You are more than welcome to what castings I have Steve – no charge but help with the postage would be appreciated. I'll have a look what's there this morning then send you a PM later.

With regard to drilling and tapping very small holes in cast for such things as lagging bolts things can be eased slightly by using a slightly larger tapping drill but a much safer way (safety as in looking after the tap) is to drill and tap small brass inserts on the lathe and Loctite them into pre drilled holes in the casting.

If you are unfortunate enough to break the tap then at least it's not in the casting.

Best – Tug

[JasonBModerator @jasonb]

I feel things have moved on since the UPT was published in the 70s. back then very few would have had a mill so drilling could have been done with a tailstock pad, on the vertical slide or with a basic bench drill. None of these are ideal as tapping guides.

Move on 50years and the number of hobby workshops with a mill has increased considerably, many of these also have a DRO added to them.

This to me is the perfect tapping guide as after drilling you can go back round an position the spindle exactly over the hole and then tap using some of the suggested guide methods mentioned above. If odd shaped castings have taken a while to set up at an angle they will still be at that angle without having to transfer the setup to a UPT. If it's a hefty casting or block of stock then will a 10BA or M1.6 tap really pull 1kg of iron exactly below the spindle?

You also have the option to power tap if you mill can do that, though best for through holes. Add in modern spiral point or spiral flute taps and you also eliminate the backing off needed to break the swarf which is cleared from the hole by the tap. Yes they will even lift CI swarf up out the hole.

£150 cost of castings, materials and a chuck would go a long way towards the cost of a small mill.

[Ramon WilsonParticipant @ramonwilson3]

Whilst I cannot disagree with any of that thinking Jason, after all that's exactly why the castings I have have languished for so long I was attempting to show there are simple alternatives.

I have the means to power tap – TapMatic head – but rarely, if ever, bother to use it. I use my bench drill to power tap the initial threads as said and finish by hand. Most beginners will not have much else and (small) taps can be expensive items if you start breaking them. Power tapping in and out does require a means for the tap to move vertically within it's drive on coming out particularly on the smaller taps

I concur – control is all important – but that cylinder shown previously was a weighty beast compared to an 8 BA tap and it's floating as such on the mill table but as you can see it has a back stop in the angle plate and the magnet is used to keep it there on each repositioning. As always though – the constant worry of breaking the tap was ever present.

Taps are another matter – I still have (most) of the original (carbon) BA, ME32 &40 and brass taps bought from Tracy tools near 50 years ago and though most are still working well for most needs there are some that aren't.

Recent purchase to replace a worn 7BA in HSS was a bit of an eye opener for sure. I wonder what such a spiral flute type at that size would set you back let alone spiral point.

Best – R

 

Edited By Ramon Wilson on 15/08/2022 08:26:05

[HopperParticipant @hopper]

Ramon — Now that's a darn cunning trick with the brass inserts Loctited into a larger drilled hole.

Steve R — another simple tapping aid is a tapping block: a piece of square BMS or key steel of suitable size with a hole drilled through it in the drill press just the right size for the tap to slide through. Place the block on the job over the hole held by finger pressure and put the tap down through the hole and gently tap your thread in the usual manner. Once the tap has started and gone in a certain way, you can dispense with the the block and the tap with stay straight. I have a block with various sized holes drilled in it that I use for different sized taps.

[DMBParticipant @dmb]

Ramon, I also have those flat tap wrenches in 2 different sizes and really like using them. Last time a few weeks ago with M2 in BMS, with thin oil concoction. I have made a couple of your knurled disc type holders, but from a Joe Piezincski video on YouTube. Am thinking what a good idea of yours, pre – threaded brass inserts and why didn't I think of that! Just one fly in the ointment, quoting LBSC, will the Loctite withstand the hot steam? Is it a special heat resistant type? I have further suggestions, always use thin oil rather than any form of paste/gease jollop for small taps in say BMS. It's easy to wash out oil and swarf with paraffin, My thin oil concoction for small taps is what Guy Lautard recommended in one of his books, 3 parts Olive oil + 2 parts White Spirit + 1 part Genuine Turpentine. I found it works a treat and smells pleasant! I use a tall narrow bottle with a strip of paper with the graduations stuck on the side, to mix up. Oh and one further suggestion from a fellow club member who was teaching school metalwork some while ago, always use the very next larger diameter drill than the one advised in tapping drill tables. Just remembered that I have copied a table from an old SMEE Journal, which is useful but only covers a few thread systems.

John

 

Edited By DMB on 15/08/2022 09:30:00

[HopperParticipant @hopper]

Posted by DMB on 15/08/2022 09:22:19:

…Just one fly in the ointment, quoting LBSC, will the Loctite withstand the hot steam? Is it a special heat resistant type?

Yes. Loctite 620 is good for 230C so good for most model steam use. O

In LSBC's day there was not such a wide range available. The original Loctite was basically a sugar solution. You could taste it. And anyone who has worked in a sugar mill or refinery knows what a universal threadlocker sugar is. Oxy torch is the order of the day for undoing bolts and nuts on process pipework there.

Edited By Hopper on 15/08/2022 09:33:59

[JasonBModerator @jasonb]

Ramon, it certainly is not the best option for all jobs and one I rarely use on a model but do on jigs and fixtures. Smallest I have power tapped is M3 and largest M12 all through holes not blind. My main mill is the X3 which does not have the tapping function so probably why I don't do it so much but the SX2.7 has it and it works quite well, if I had a DRO on that machine then I expect it would see more use. The standard quill spring provides all the lift needed Quite a few of the Hobby benchtop mills will have this tapping function so they have the means.

 

Yes most of my imperial stuff is still traditional straight flute taps though I have a couple of BSP spirals. That brings us onto costs. I think Tracy double the price for spiral flute but that is for what are now lesser used BA threads. Again moving on Metric would bring the price down, that M6 tap in the video is £5.10, a M2.5 which is close to 8BA £4.64. I use that brand for general work but on the Models I use a slightly better YG-! range which would be a couple of quid more. I rarely seem to use BA these days and even ME is getting used less as I have Metric fine in the common sizes found on our sort of models

 

But that is only half the story, with spiral flute you only need the one tap not three so you are actually paying LESS and a spiral flute will work just as well in through hole so a single spiral flute will do for all your tapping needs. This is why I bought the Spiral flute BSP taps as I was tapping a hole that was quite shallow and blind and the taper of the taper tap hardly did a thing and 2nd was not going in.

 

M£ about 3mins 20 into this video as well as M5, 1/4BSP and M12. Green buttons on teh quill levers reverse the spindle

 

 

Edited By JasonB on 15/08/2022 09:45:38

[DMBParticipant @dmb]

I usually drill tapping size+ then change to tap in the drill chuck and get it started then move work to next position and repeat. No alignment problems. I recently did 4 off M3 in the edge of a 5mm thick plate of BMS for the swivel base part 31 in Harold Halls tool and cutter grinding jig. Done on a knee type mill, carefully hand winding the vertical spindle and gently raising the table. Still possess the unbroken tap! Lucky or what? Having completed it, realised that I had put said holes in wrong side of plate!! Now what? Take safest way out and re-tap the row of 6 off M6 holes on the 50mm wide side in the opposite side, 15mm from that edge which would make the original error very obvious or re – do the riskier M3 holes again on the opposite edge. I now had the confidence to go for the latter. So, 8 small blind tapped holes in total, punishment for not reading the drawing properly, ha, ha.

[Ramon WilsonParticipant @ramonwilson3]

Hi Jason,

Well I'm not saying anything is the best option (did I actually imply that?) but that as always, one has to bear in mind what kit someone has at their disposal. Whilst I have the means to reverse on both mills that I have both have to be switched at the control panel which unlike your button control makes things a bit fraught. Besides, on one, the Linley, the quill is not lever driven so it would mean trying to wind out at the same rate as the tap comes out. Fine if you are careful on the way in for a few initial threads but a most definite no no on retraction. If the tap was in some kind of sliding spindle of course that would be a different matter. On the other, Amadeal, mill the quill is just too heavy to feel small taps under say 2BA without a real degree of caution. Even then the same issue of control applies – lever on the right, control on the left

As you implied previously if DRO is available then that is a good and much better way to go too. In fact I've just done the flange holes in the Marine Compound in exactly that manner

As I approach my eighties however buying new kit, unless a required direct replacement, is not really viable as I intend to dispose of it all in a couple of years or so. Though I do use metric threads from time to time, moving over to metric threads as opposed to BA, though certainly less expensive, is not something I'm keen to do at this time in life. I have sufficient stocks of BA fasteners (still readily available of course).

I've been tapping holes for few years now – other than the Tapmatic devices which really are good despite my previous statement of rarely using mine – the best system I've ever used was a set of three large drilling pillars mounted above one big table, Meddings or possibly Pollard I think. They had a foot control to knock them into reverse which was instantaneous – wonderful bit of kit but it would require a bigger space that most have available.

I know things have moved on but I believe it's as important to show that you don't have to have modern kit to be able to do a job just as well as it is to show what's available now. Many now think of CNC pretty early on – as you know I left that behind twenty odd years ago but I've often had the comment ''Are the crankcases made by CNC'' on my diesels.

I began my model engineering as a complete amateur – zero knowledge but full of enthusiasm. In my mid thirties that quickly lead to a change of career and proper training before spending so many happy hours in a machine shop environment for the rest of my working days – like I said, quite a few tapped holes in that time – not always done on the right bit of kit

Best – R

 

PS just realised I haven't responded to others – have to go out right now, Sue is standing by the door, chomping at the bit – you know how it is   so will come back later.

Edited By Ramon Wilson on 15/08/2022 10:39:17

[Steve RowbothamParticipant @steverowbotham77083]

I didn't realise what I was starting with this thread, but now have more information on tapping than I could ever have imagined, no doubt the above will be of great value to others starting out. Jason I appreciate your comments on progress since the UPT design was published, but it does seem a good learning project which will also produce a useful piece of kit. Ramon thank you for your very kind offer, will look out for your PM. Steve

[derek hall 1Participant @derekhall1]

+1 for the GHT designed pillar tool

One of the most used tools in my workshop. Essential for tapping square small holes and I would not be without it. However this is not the only reason for my positive review !

Making the thing gives you a lot of valuable experience in machining to close tolerances, working with different materials and making some ball handles which really sets it off ! Just follow the masters instructions and you will end up with a tool that with more accessories can be used for other functions, sensitive drilling attachment, staking, riveting and number punching and also an attachment that can convert the UPT to a clock bushing tool.

Yes I do have a vertical mill but I don't have the sensitivity or "feel" to tap confidently e.g. down to 10 BA with it (perhaps I should make something !)

Fully agree with Andrew – no need to use any cutting compound when tapping or machining cast iron

All the best

Derek

[Ramon WilsonParticipant @ramonwilson3]

Hopper – I don't know about 'cunning', just something I came up with as the inserts are 14 BA and I didn't fancy tapping the cast iron using the only tap I had – again. I had previously done so on another engine and, as mentioned previously, used as DMB suggests, a larger size drill. Whilst that certainly eases the tapping pressure on such small sizes it raises another issue of the thread engagement being marginal at best in such small sizes. It worked well so will be used again on the Marine Compound.

Loctite used would have been basic 638 – as said the temperatures involved on steam had no effect – the engine shown was run on steam under 'working' conditions powering a model boat

As a sugar lover Hopper I can't say I've noticed the similarity – when you do get to taste it inadvertently it's a bloody horrible flavour that's difficult to get rid of. Incidentally I found a long time back that the best thing to 'kill' any Loctite residue is methylated spirits. Lots of other solvents will work to varying degrees also but as with the 'Domestos' slogan meth's 'kills it 99% dead'. No good as a mouth wash though.

As said Derek, I never did get round to making a pillar tool but a good friend did and another bought it when he passed on. One did, and the other now does, praise it's usefulness.

Tug

Edited By Ramon Wilson on 15/08/2022 14:40:40

[Steve RowbothamParticipant @steverowbotham77083]

Having tapped the few threads in the Oscillator 'freehand', with slightly questionable results in terms of perpendicularity (though it does run very well!), I was a bit daunted by the number of threads on the 10V. Using the advice given in this thread, and a direct message from Thor, I have now tapped the exhaust port mentioned at the start of this thread and am delighted with the result, and now feel ready to tap the remaining 20 threads in the cylinder. Thanks once again, till my next question, Steve

Edited By JasonB on 15/08/2022 15:41:15

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