Brass plug

Alan,

Right on all counts!

And Russell, he also said four wheel brakes weren't dangerous (not his uncoupled variety at any rate) because people would be so busy trying to steer as not to have a hand free to put the front ones on at the same time as the back!

Martyn

Alan,

I must admit to driving a bit like a hooligan when I had my Frazer Nash which had been fitted with big Humber hydraulic brakes

Russell.

Purely for the record, British Standard Brass threads are 26 tpi, Whit form (55 degree)

Cycle Threads are 26 tpi, but 60 degree form.

Couldn't understand why there were two sorts of 26tpi threads, so went and found what the difference was.

As to a Cap removal tool; how about turning a recess to fit snugly around the cap and then cross drill at the appropriate distance and fit a silver steel pin of the same size as the slot in the cap? To be really precise, make and fit a square or rectangular section pin of a size to fit the screw driver slot.

The rest of the tool can have a hexagon for driving with a socket, or be cross drilled for a tommy bar drive, whilst you press down to stop it jumping out of the slot.

Hope that this is some help, or starts a train of thought.

Howard

Edited By Howard Lewis on 10/07/2015 12:42:45

Another option is to make a proper screw driver as they can't be bought as far as I am aware. We had some wooden furniture delivered that cam in 4 parts fixed together with a few brass slot screws. The people who did it had to get some one to make screw drivers for them. The key is hollow ground with a temper not far off one suitable for a cold chisel - dark straw at the most. A cold chisel can rough out mild steel pretty quickly.

All sorts of older things may be fixed with slotted screws even lathe chucks and the right sort of screw driver is likely to be needed to undo them. Chances are similar screw drivers would be used to fit these plugs and the people who did were probably rather strong - professional muscle usually is.

As it happens I made a fitters screw driver as part of training. Something like 3/8 square tool steel should make a decent one. Square so that a spanner can also be used. Get the end red hot and forge it to shape. Allow to cool slowly so that it can finally be shaped with a file. Blade width from memory 3/8 wide at the tip widening upwards and about 1/16 thick a the tip - best check some slots. Turn the other end round for an inch or so. Make a nice large mild steel handle of the right size to grip firmly slot the end to take the 3/8 square and drill and ream to take the round part, Knurl it leaving bare metal at each end. It can be hollow to get a balance to prevent it being handle heavy. Chamfer the end fairly heavily as sometimes they have to be placed in a slot and given a hefty whack with hammer. Grub screw in handle onto the round part of the blade to hold in place. The slot was finally filed to ensure a tight fit. Might be easier to roll pin or dowel it. Harden and temper the blade. As I have seen the square rounded over via use of spanners it might be worth hardening and tempering part or all of the shaft as well.

The blade end after filing should be dead square and dead parallel to close limits. The side of the blade is then placed on the edge of a grinding wheel at an angle to cause the tip to neck in by a few thou. This means that if a line from the tangent to the wheel is drawn to it's centre the tip will be some fraction of an inch above it - probably 1/4 in or so. Each side of the blade can be felt onto the wheel so that the blade remains parallel.

Silver steel could also be used for a blade but bang goes the spanner.

Well at least people now know why these sort of things may be extremely tight. It's no good trying to do the same thing with a modern screw driver. Might help but all are made of air hardening toffee these days.

John

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Edited By John W1 on 10/07/2015 15:24:12

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John,

Although your description of making a screwdriver is exemplary ... May I just mention that the item pictured earlier has a "coin slot" recess, so the blade end of a special screwdriver would need to be made to the matching arc.

MichaelG.

Howard et al

Thank you for that interesting train of thought for which I am very grateful. I do think we must not now apply rocket science to this! It did occur to me that a collar might be the answer which is a sort of variation on your theme. It leaves the fundamental problem of determining the thread, that as far as I can calculate is about 19/20 tpi on a diameter of about 6/10’’. But once the type is established one could insert the collar and then fit a new plug to it threaded to a size of one’s choice. The snag is, there has to be enough room for the king pin to be extracted upwards and there’s not going to be much metal to carry a male (for the boss) and female (for the new plug) thread. Your idea is simpler (i.e. better) and more elegant.

Another advantage with your recess scheme is one could easily get the plug flush with the top of the boss. This is important, because the nut securing the pivot for the brake shoes (the pivot passes through the back of the stub axle base) is directly above the plug and close to it which, I guess, is why the cap is so thin in the first place.

To be honest, I don’t think special tools or hand crafted screw-drivers are necessary here. The plug’s slot is very shallow with no practical means (remember, it’s flush with the top of the boss) of deepening it. Also it’s usually so brutally butchered that if it is at all tight a device created by Sir Henry Royce himself would be unlikely to shift it. Drilling, drifting and/or a chisel are, in my experience, the unfortunate but only way of extracting something that is already ruined.

So…how about this? Pop the cap in the post to Tracey Tools (or equivalent) and ask them to categorically identify the thread and send it back with a die. Then, with a lathe and piece of brass bar one could make as many as one liked and give them to the similarly afflicted. Simples?

Thanks again Howard for a bit of ‘out of the box’ thinking.

Martyn

In return Michael might I mention that from the look of the plug the blade I described would fit it perfectly but each may do what ever they wish. Real coin slots are few and far between but if they are in this case the slot would need to be rather large to get a sensible sized coin in it. Some how I can't imagine a garage mechanic reaching into their pocket for one.

John

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John,

I deliberately put "coin slot" in quotes, because it describes the shape, rather than the precise usage.

... but I suspect that you knew that.

MichaelG.

Hollow ground screwdriver blades don't jump out of the slot. That's the whole idea of them. Instead of thickening from the tip they narrow slightly and actually dig in so little downward force is needed as well, just a sensible amount. They still need to be kept square. The pressures are so high that they will literally dig in hence the need for heat treatment to cutting tool levels.

Mine was stolen along with a number of tools from the boot of a car I was working on otherwise I would be able to be sure of a blade thickness. One thing I had noticed is that if the screw was of a suitable size for the width of the head or the screw head was larger it fitted well which suggests that there was some sort of convention in this area.

A method I used to remove a gearbox oil filler plug with a stupidly thin hex head that some one had rounded trying to get it out was to drill 2 holes across the diameter and tap in silver steel pins, carefully tightened an adjustable spanner of the King Dick type on them. Then found I needed 2ft of leverage to even loosen it. I suppose an alternative would be to make a spanner with pins on it instead but it that case I would most definitely taper and harden them. The trouble with the knocked in pins is that if the spanner isn't hard up against the surface being rotated they will probably just pop out and leave a bit of a mess behind them.

John

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Edited By John W1 on 10/07/2015 23:22:03

John,

I don't want to labour this, but; you previously linked a picture of the plug:

[quote] Image here **LINK** [/quote]

If using a straight-ended blade; what width would you use?

... The broader the blade, the higher it sits in the recess, and the more likely it is to damage the top edge.

... The narrower the blade, the deeper it can sit in the recess, but the more likely it is to damage the central area.

Surely it would be safer, and more effective, to radius the end of the blade to match the recess.

MichaelG.

Speaking of Austin Sevens, a local couple just drove their 1928 model to the northern tip of Australia, about 1400 miles of dirt (ie mud) roads and river crossings. I'm not sure how to post a link on this steam-age site so yarn and pic are copied below.

RATTLING back into Cairns in a 1928 Austin 7, Lang and Bev Kidby had recreated history when they returned from a trip to Cape York Peninsula.

The Brisbane couple travelled to the tip of Queensland in the same vehicle New Zealand pioneers Hector Macquarie and Dick Matthews used when they became the first to make the journey in an automobile, in the same year the Austin 7 was manufactured.

Mr and Mrs Kidby, both 68, are passionate about historical journeys.

Together, they’ve retraced the Peking to Paris motor race of 1907 and crossed the Sahara Desert in a 1922 Citroën Kegresse half-track, as André Citroën did in 1922.

Two weeks of creek crossings and corrugated gravel roads took their toll on the Kidbys’ poor Austin, nicknamed “Daisy”.

“But it was great to share history and for the kids to realise that you don’t need a 4WD and winches packed to the roof to do a trip like that,” Bev Kidby said.

Just for some context, this is what the road they travelled on is like for most of that 1400 miles.

No mention of what they use to tighten their brass plug with!

Edited By Hopper on 11/07/2015 02:36:56

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Alan ... I give up !!

My original suggestion of making a properly-shaped tool was to fit the new plug properly, and thus avoid future difficulty.

Obviously; removal of an old [damaged by abuse] plug would require the use of "whatever" tools & techniques 

MichaelG.

Edited By Michael Gilligan on 11/07/2015 05:35:37

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Alan,

The hours I keep, and the reasons why, are frankly none of your concern.

MichaelG.

Michael

You are so right about 'talking this one to death'. Or, don't let's tear the arse out of it!

Most of the posts have been so helpful and I can now definitely come up with a solution.

There's no need for elaborate special tools to get the darn thing out and I'm gratified that Austin Seven expert, Alan, does it exactly as I do. Hammer, drift, drill, chisel!

Thanks to everyone who has helped me here. Much appreciated.

Martyn

'Ere I resemble that remark.😉