WAYS AND MEANS.
Page 67
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Useful Contributions From Our Driver and Mechanic Readers. ,
A Useful Loc.knut for Brake Turnbuckles, etc. TIIE locknut seems to have been one of the most favourable fields for the activities of the inventive mind, and ono would almost imagine that the whole gamut of possible variations of locking devices must by now have been covered.
A very practical correspondent, "J.P.M.," of Luton, however, sends us the following:— Much trouble was experienced with a turnbuckle which, in spite of loeknuts, would not keep tight. I overcame the difficulty in the following manner :— The ends of the turnbuckle were turned to:a slight taper and four saw cuts.made
2 2
to a depth of abqut in. A nut was then bored as shown, the depth of the boring and its diameter being such that the caned part of the turnbuckle did not "bottom."
On locking with this nut the cone had the effect of closing in the shank of the turnbuckle, effectually locking it on to the thread.
Since then pairs of nuts (nut and locknut) have been made on the same princ:ple, and when tightened up it is absolutely impossible to move the nut without first undoing the locknut.
This method is particularly useful when a nut is used as a stop and not pulled up against a face.
Testing Plugs and Magnetos Under Pressure.
A DEVICE, the details of which are sent by " J.F.M.," of Luton, is claimed by him to be of the greatest use, particularly to users of fleets of vehicles, for testing sparking plugs and magnetos. It is well known that magnetos and plugs will often function quite well.in atmospheric pressure, but owing to the increased resistance due to compression of the gases will not spark in the cylinder.
The testing device consists of a small container, cylindrical in shape, with a flange at one end. This flange is fitted with two studs passing through another similar flange, and held between these two flanges is a small piece of plateglass on rubber washers so as to provide a transparent and airtight cover to the container.
The other end of the container is tapped out to take the sparking plug, whilst the side of the container is provided with an ordinary bicycle-type tyre valve and a pressure gauge.
The plug to be tested, is screwed into its place and air is pumped in until the pressure, as shown on the gauge, registers about 50 lb. per sq. in. The plug is connected to the h.-t. distributor of a magneto which is known to be in good order, and the body of the plug, or container, is connected to the body
of the magneto. The magneto is then turned at about the cranking speed of the engine, say, at 120 r.p.m. A good spark should then jump the points and will be visible through the glass. If the plug be faulty the spark will be seen to occur across the surface of the insulating material.
By substituting a plug which is definitely known to be satisfactory, an unknown magneto may be tested. Starting at, say, 25 lb. pressure and cranking at a fairly slow speed, the pressure should be gradually increased. A magneto in first-class condition should spark up to a pressure of about 90 lb. per sq. in.
If the spark be extinguished at as low a pressure as 45 lb. then the magneto is not fit for service.
How a Bent Foden Front Axle Can be Dealt With.
ACCIDENTS sometimes occur to the
front axles of Peden wagons, so " F.W.," of Stoke Newington, tells us.. Out of a fleet of 15 vehicles he has had five suffer in this manner, and he explains how he got over the trouble in a quick and inexpensive way.
When such an axle meets with an accident and becomes bent, the bend usually occurs where the bearing part joins the main axle. The effect of this on the bush is usually to allow oil to 'escape and to damage the bah, so the sooner matters are put right the better, otherwise replacements may be required.
Our correspondent tells us that he heats the axle in a forge, after trying it in a lathe and marking the position of the bend, then, when at a red heat, he lays it on an anvil and gives it the required blows with a hammer to straighten it, then replaaes it in the lathe and repeats the straightening until it is true, or nearly so, as it is very difficult to produce a perfectly straight journal—a point which will be realized by those who have attempted the feat.
When approximately true he allows the axle to cool down, then places it in a lathe and turns the journal down to 2f ins., its original diameter being
ins. He then procures a piece of steel tube 2i ins, outside and 2i ins. inside and, leaving the axle journal slightly larger than the bore of the tube, he heats the latter, and when hot slides it on, so that when cool it becomes a tight fit. He then puts the axle in the lathe and turns the journal to fit the bush. He states that should the bush have become damaged by the bent axle it is better to fit a new one.
Care should be taken to note the position of the hole for the pin which goes through the collet, so that a new hole can be drilled through the tube.
A very common error in shrinking operations is to leave far too much difference between the bore of the sleeve and the part on which it has to be
shrunk. If too much be left it often results in the sleeve bursting on cooling. In the making of large guns a few thousandths of an inch is considered sufficient for the shrinkage ; our correspondent suggests'1-64th, but even less would be all that is necessary.
In the matter of straightening such an axle it is often very difficult to confine the heat to the exact spot where it is required, and in many cases, instead of correcting the bend, new bends are made where they are not wanted. A good plan is to heat the axle as near the required spot as possible, then cool down by pouring water on the parts where no heat is wanted, by this means the hot place can be located precisely. We would suggest that, instead of hammering, a long tube used as a lever w:11 in many eases be found best, provided a sufficiently strong vice can be Sound to bold the axle while being straightened.
If any cooling down be done, core must be taken that such parts are annealed, as when cooled quickly they are hardened and rendered brittle.