DIY Large Thread Tap

[old martParticipant @oldmart]

Any chance of being able to see the other end of the brass pipe? That might give an idea whether it is securely fixed in place.

[John HaineParticipant @johnhaine32865]

Would be good if the OP could respond to some of the points raised?

[Speedy Builder5Participant @speedybuilder5]

Do you need the full bore of 1 1/2″ bsp, would an 1 1/4BSP pipe be passed through the hole and lock nuts and seals either side , then an 1 1/4 to 1 1/2 adaptor ??

[Nigel Graham 2Participant @nigelgraham2]

I agree, John, particularly to explain what he’s really trying to achieve.

His original question implies the brass tube carried a fitting such as a pipe connection or a valve, and goes through a substantial thickness of wall; so it would be helpful to know why, indeed if, the thread needs be any deeper? And if the bore is critical?

[Phillip AllenParticipant @phillipallen34597]

Gentlemen, (and ladies, if present), thank you for the bountiful replies. There are so many, I will address things generically rather than individually.

My apologies for not answering until now but Saturday and Sunday were not my own! We were out visiting open gardens in the glorious sunshine, being summer in Australia.

I’ll address some points raised by several people. The brass tube is better described as pipe in terms of wall thickness. AFAIK it is a casting with external lugs, embedded in concrete, so I think it is well able to withstand the forces of tapping through.

As I mentioned, the concrete is a tank (for water) and the brass pipe was originally an overflow outlet. I need it to be the delivery inlet. To control the electric water pump at the other end, a float valve will shut off the flow when the tank is full and the rise in pressure will trigger a switch to turn off power to the pump. To reduce friction, the delivery pipe is 2”. At the tank, it will have to reduce back down to 1.5” for the float valve, which has a 1-1/2” BSP male thread, perfect for screwing into the brass pipe, if only the thread went all the way through!

There are other ways to provide this facility:

1.      Try Clive’s idea of using an 11 TPI Whitworth chaser (die box cutters) and a suitable holder to through-tap the thread.

2.      Try DC31k’s and Speedy Builder5’s idea of reducing from 2” to 1-1/4” through the brass pipe and step back to 1-1/2” for the float valve. It looks like 32mm O.D. PVC pipe would fit through the brass pipe with I.D. of 44.8mm. This, of course, introduces a slight restriction to the flow.

3.      Turn my own brass fitting to press-fit into the inside thread-less brass pipe. This would be simple to achieve as a threaded rod and nuts could be used to pull it into place. I would need to ensure sufficient wall thickness for strength. This option has less flow restriction than option 2.

4.      Go over the top of the tank wall with a 2” elbow and a short length of pipe, a 2” elbow, a short length of pipe, and another elbow reducing back down to 1-1/2” for the valve. This introduces the requirement to anchor down the float valve end to resist the bending forces on the pipe from the float. It also complicates the tank roof structure.

5.      Buy or hire a 2” diamond hole saw to cut a new hole in the concrete and fit a new inlet pipe fitting with the thread all the way through or at each end at least. I just found such a beast for A$62 plus freight; the saw is A$70. There is a possibility of paying a concrete tank manufacturer to get their delivery driver to do an extra job on his way home, as he will have a saw and powerful drill to do the job.

So, my thinking has always been to go with the neatest, most convenient solution: viz, use what is there. I have not found a tap as cheap as GBP22. I found some reasonably priced ones overseas (India, China) and second-hand ones from the US, but with freight, even those are expensive. If only there were still some old-school plumbers still around with BSP tools!

So, in summary, you have convinced me to not make my own tap. I will continue looking for a cheap tap or the chance of borrowing one. I am leaning towards options 3 and 5 and will scope these further.

 

Many thanks to all responders.

[Phillip Allen]

On Phillip Allen Said:

My apologies for not answering until now…

Do not feel obliged to answer at all. Anyone above who has posted just because they want acknowledgement is missing the point of the forum.

Can I offer a late No. 6? Buy a 1 1/2″ threaded flange and bolt it to the inside of the tank concentric with the incoming pipe. Rubber gasket or silicone to make it liquid tight. If it is a curved tank, 3D print a washer to make the transition from curved to flat.

For example this:

https://www.plasticpipeshop.co.uk/1-12-Threaded-BSP-PVC-Full-Face-Flange-PN1016_p_884.html

You might have to screw the float into it first to see its clock position when the thread is snug and then locate the securing holes, and adaptor holes, accordingly (visions of fixing the flange on, screwing in the float and it goes tight upside down).

[John HaineParticipant @johnhaine32865]

Phillip, thanks for your response, good to know the application background. I hope at least some of the suggestions are useful.

Regarding option 3, you could consider loctite or jb weld to fix the adapter rather than a press fit. The latter particularly would give you plenty of fitting time.

[Charles LamontParticipant @charleslamont71117]

Just throwing in a daft idea: ditch the float valve altogether and use a float switch to control the pump. You would not need to tap the fitting and could have a full bore entry. Might need a non-return valve though.

[noel shelleyParticipant @noelshelley55608]

PLAN X = drop down to 1.25″ Nom bore pipe, this with may be just a bit of fitting will go through your 1.5″ nom bore brass fitting and can then be bushed back up to 1.5″ for your fittings, valve Etc.  BSP is used the world over for pipe work and no serious attempt has been made to change a system that works, even in the home of metric it is widely used not withstanding that it is British and Imperial.   Noel.

[JasonBModerator @jasonb]

As you say you could not find the £22 tap. Try searching for G-1-1/2 rather than BSP as the Australian sites may not call it BSP.

[Martin ConnellyParticipant @martinconnelly55370]

I’ve also seen it referred to as Rp for internal threads and G for external. So a tap might be 1½” Rp

Martin  C

[Phillip Allen]

On Phillip Allen Said:

………..

So, my thinking has always been to go with the neatest, most convenient solution: viz, use what is there. I have not found a tap as cheap as GBP22. I found some reasonably priced ones overseas (India, China) and second-hand ones from the US, but with freight, even those are expensive. If only there were still some old-school plumbers still around with BSP tools!

……..

I found one on AliExpress for AU$35, plus taxes/shipping. Obviously I can’t speak for quality or reliability of the seller.
There’s likely to be others too.
They claim to ship to Australia; I selected Queensland, though obviously you may be somewhere else.
Bill

[JasonBModerator @jasonb]

That is the same one I showed Bill.

[Nicholas FarrParticipant @nicholasfarr14254]

Deleted.

 

[JasonB]

On JasonB Said:

That is the same one I showed Bill.

Yes I know, but Phillip failed to find it.
Bill

[duncan webster 1Participant @duncanwebster1]

Float switch instead of float valve and pressure switch sounds much easier to me. If syphoning  back is an issue fit a vacuum breaker, but if discharge is above water level not an issue

[duncan webster 1]

On duncan webster 1 Said:

Float switch instead of float valve and pressure switch sounds much easier to me. If syphoning  back is an issue fit a vacuum breaker, but if discharge is above water level not an issue

Agreed.  Also, there will be need for another outlet – as an overflow from the tank.  I expect that large bore pipe was considerably larger than required for filling – so the tank would not overflow with a small head at maximum in-feed.

[old martParticipant @oldmart]

Drilling a new hole in the concrete would be a good solution, but check first for steel reinforcing and avoid hitting that if possible.

If you have an SDS hammer drill, you may find that the carbide tipped hole borers are cheaper and easier to get hold of.

[duncan webster 1Participant @duncanwebster1]

If you’re worried about the float switch failing and overfilling the tank fit 2 and duplicate everything else ( contactor) so that a single component  failure won’t let the pump run on. Make sure that any wire dropping off or getting cut stops the job.

[Phillip AllenParticipant @phillipallen34597]

Once again, thank you all for the overnight replies.

Option 6, proposed by DC31k is an idea with promise. The main concern would be its ability to hold pressure. I think Option 3 will provide a better seal, especially if Loctite or JB Weld is used, and easier to execute. One issue with 3 that I have thought of is the possibility of the fitting turning whilst tightening the float switch. If I start with a fitting with a hex, I can hold it while fitting the float.

I tried searching for a G-1-1/2 rather than BSP like JasonB suggested, but this only came up with even more expensive taps! Then I saw peak4’s find on AliExpress – AU$34.59 + $27.47 freight. Claims to be HSS and certainly looks the part. I could handle that, but need to trust the seller and hopefully be able to pay with PayPal. Has anyone used AliExpress?

Duncan webster 1 suggested an electrical float switch: that would be the ideal solution if only I knew I needed it 20 years ago when I had major cabling work done. To do so now means trenching 600mm in shale and going underneath ½ cubic metre concrete blocks in a retaining wall! This is why I am going the mechanical route. Also, back siphoning is not an issue; similarly overflowing the tank is not an issue.

Also, thank you Duncan for the fail-safe idea of duplication. I have considered a tank-level reader with a Wi-Fi connection, to enable monitoring – tells me if the tank is empty as well as overfull.

Old mart, cannot a diamond saw cut through steel reo?

Well gentlemen, I think we have nutted through some good ideas for the first part of the overall problem of getting water into the tank. If you are collectively game, I’ll toss you a really curly one, but it will require some considerable effort to put it down in words. I’m game if you are. Not all of it pertains to engineering; I have spent countless nights awake, thinking through ideas and solutions. Some keywords, to spike your interest: river, frequent water-level changes, floods, debris (logs, rubbish), 3-phase bore pump, special pump housing, launch and recovery thereof, and serviceability.

To finish off, I will look into AliExpress, diamond saws and a brass fitting to be adapted to press-fit into the tank inlet pipe.

Cheers.

[Phillip AllenParticipant @phillipallen34597]

I have noticed that the tap at http://www.aliexpress.com/item/32299173148.html is more like a bottom-tap. How will it go cutting threads through 50mm of pipe (not considering quality)?

Thx.

[JasonBModerator @jasonb]

If you find it hard going it would not be hard to freehand grind some more taper along the flutes, as you already have some thread you won’t have to worry about it starting square if the tapers are not all exactly the same.

[duncan webster 1Participant @duncanwebster1]

Assuming the pump is one end of the trench and tank the other, you could have a solar panel and battery to power the level switch and a radio link back to the power stuff at the pump end. We had a similar set up at work.

[old martParticipant @oldmart]

A diamond saw will cut through any steel embedded in concrete if you only have one hole to cut, but any iron will wear out diamond chemically so try to keep the boring well cooled with water. Also keep speed down as much as possible. Do you have any tool hire firms within easy distance?

[Phillip AllenParticipant @phillipallen34597]

JasonB, yes, I could grind a taper and then dress the teeth with a stone afterwards.

Duncan, your idea has merit and I would be keen to know what electronics was used. The float switch can be either open or closed circuit to indicate full (and v-v when empty); the circuit somehow must transmit a wireless signal to the pump controller, therefore a receiver and antenna there. More info appreciated, please. A float switch gives me a lot of adjustment between switch-on (low water-level) and switch-off (tank full). Idea, farmers probably have that technology already – further investigation required.

old mart, good information re using a diamond saw. I have a small drill press and it would not be too hard to weld up an adapter mounted from the existing 1.5″ pipe bore. That would enable slow feed, but it would operate at the slow speed setting of my old Desoutter drill – powerful (it comes with an extra handle and breastplate) it has no speed control at the trigger switch. I’m not sure if my Makita 18V drill will have enough power.

 

Thank you.

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