Is it good practice to nut up taper pin?

[GreensandsParticipant @greensands]

<p style=”text-align: left;”>I have a potential problem with ensuring the security of a taper pin used in the the reversing mechanism of a 5″ gauge model locomotive. As far as I am aware the pin fitting is satisfactory but, belt and braces, I have been considering nutting up the tapered end with an 8BA nut. I am sure that this is not considered good practice but I would be interested in hearing the views of others.</p>

[OldironParticipant @oldiron]

If it is a safety concern I can see no problems with it. Bicycle pedal crank were held on with tapered pin with a nut for many years. Not exactly the same thing but similar.

[Speedy Builder5Participant @speedybuilder5]

Its getting a bit small, but you sometimes see a split on the small end which can be set over to prevent it working loose.

[Nigel Graham 2Participant @nigelgraham2]

It might be unusual but is not “bad” practice in the sense of untoward results.

Tapered, rectangular-section cotters arranged to adjust and secure split brasses on components like connecting-rod ends were commonly provided with a nut on a spigot turned on the end. To give the nut something to work against the cotter slid against a glut extended to a small bracket drilled to accept the spigot.

That is a cylindrical-section spigot though, like that on the bicycle cotter Oldiron suggests. Making a successful thread on a taper-pin is perhaps not really feasible unless you can turn the projecting part of the pin to be cylindrical of the right diameter.

I would experiment on a spare pin before trying it “for real”.

[john fletcher 1Participant @johnfletcher1]

When I worked for BR and when the train actually ran and mostly on time, all the side rods were were secured by a big nut and a split taper pin. Opened them up with a hammer and chisel. As others have said bicycle have been doing it without any problems.

[Harry WilkesParticipant @harrywilkes58467]

I did it on my 3″ Burrell after loosing the taper pin from the cross head I put a thread on the end and a small nut.

H

[bernard towersParticipant @bernardtowers37738]

Surely a bicycle crank is fitted with an angled cotter against a flat on the shaft where a taper pin fits into a tapered hole making the two parts as one, there isn’t the same action on the taper pin it is in double shear where the bicycle crank flat can push. The pin out if fitted the wrong way round hence the nut, and maintenance.

[SillyOldDufferModerator @sillyoldduffer]

Better practice to use something more positive than just a nut, such as a split-pin.

One of my old aircraft books is downright rude about spring-washers, and refuses to recommend lock-nuts, or nuts with vertical or horizontal set-screws, considering them all likely to vibrate loose.   Even stop-plates are considered iffy, unless the plates are securely fixed themselves.

These days thread-lockers do a good job, and possibly have the advantage that the fastener isn’t weakened by having a hole drilled through it for a split-pin.   Never seen any comparative figures though, and I don’t know if thread-locking compounds are allowed in a modern piston engined aircraft.

Dave

[Nigel Graham 2Participant @nigelgraham2]

The split-pin hole does not weaken the fastener if installed correctly: above the load-bearing area of the stud and nut, which is usually of castellated form. This is used on, for example, car stub-axles. The split pin is simply to stop the nut from rotating.

[Michael GilliganParticipant @michaelgilligan61133]

I’m a little surprised that no-one has yet suggested wire-locking.

The problem with a nut is that it is quite plausibly likely to work-loose under the same conditions that might loosen the pin.

A simple cross-drilling and wire-locking provides a true ‘belt & braces’ safety mechanism, specifically because they are different !

MichaelG.

.

As is so often the case, Wikipedia provides a good introduction:

https://en.wikipedia.org/wiki/Safety_wire

[GreensandsParticipant @greensands]

I think my objection to using wire locking on it’s own would be the need to ensure that the cross hole is precisely located to maintain the tight friction fit.

If on the other hand the pin is nutted and then cross drilled for wire locking the operation becomes less critical, the down side being the pin is getting progressively narrower the further you move away from the head. Just my musings as I have not put the ideas into practice

[Paul LousickParticipant @paullousick59116]

The crankshaft journal on my engine has a screw for adjusting and locking a tapered pin.

 

The taper pin on the cross-head has a series of holes and a split pin to secure it in position.

[duncan webster 1Participant @duncanwebster1]

I think there is confusion twixt taper pins, which are round and tapered cotters which aren’t. You shouldn’t need a nut on a taper pin, but I can’t see it doing any harm. If a taper cotter is used for adjustment then it needs a nut, and probably some means of locking the nut. If it is driven in tight then some means of stopping it falling out completely is usual, see split pin above.

 

[duncan webster 1Participant @duncanwebster1]

For wire locking bolts the fitters where I briefly worjed had a tool like a cross between locking pliers and a Yankee screwdriver for twisting the ends of the wire.

[Howard LewisParticipant @howardlewis46836]

Ideally, a taper pin will be an exact fit in the taper hole.

We all know how much force is required to break a morse taper, and they have an angle of 2 -3 degrees

On many of the full size locos that I  have ssen the nut is locked by a taper pin hammered through the nut and pin.

In my experience, a taper pin, well hammered home, will take a lot to remove it.

A properly fitted split pin is a very effective way of preventing nuts coming loose.

Personally, I do like wire locking, but time consuming to do, and is reaslly intended to prevent threadeds fasteners fron unscrewing. Very popular in aircraft practice (Excepting Boeing doors!)

Howard

[duncan webster 1]

On duncan webster 1 Said:

For wire locking bolts the fitters where I briefly worjed had a tool like a cross between locking pliers and a Yankee screwdriver for twisting the ends of the wire.

Still part of the aircraft mechanics toolkit:

I bought mine in a surplus store in Rushden many years ago. The proprietor didn’t know what they were and was removing the innards and selling them as pliers for £1. We said we’d save him the trouble of removing the innards and offered 50p each, which he accepted.

Generally wirelocking on aircraft is not used to secure nuts. Nuts are either castellated with a split pin, or are a variety of locknut. Wirelocking is used on bolts/studs that fit into fixed threads. The classic example is bolts holding on a propeller. The bolt heads are drilled for the wire. The bolts are wirelocked in pairs and the skill is in orienting the wirelocking such that both bolts cannot loosen against the wire. Wirelocking also used to be very common on turnbuckles used to adjust tension in control runs using steel cable. Another use is restraining, and sealing, pipes on pneumatic instruments. Although that has largely been replaced by large O-rings normally used for castrating sheep.

Andrew

[JAParticipant @ja]

A chief designer or a design standards manual would condsider any of the above suggestions for tapered and cotter pins bad practise. However they are acceptable bodges to keep something running until a proper repair can be made. My feeling is that they should be avoided when making a model but since you are the designer or constructor you can make your own rules.

One comment about the above cotter pin pictures, I cannot see the matching tapered pad for the pin. If there is not one the pin will work itself free quite rapidly.

No one has mentioned Loctite, yet.

JA

The proper repair could be years or thousands of miles away.

[Nigel McBurney 1Participant @nigelmcburney1]

In My auto jumble hunting I have come across taper pins which have a split in the end as another post has mentioned,my thought was the split is nearly invisible,I have wondered how they got such a fine split and then managed to machine the  whole pin tapered, possibly machined by centreless grinding,but how did they get such a fine split, I remember after the 1987 hurricane I bought a Poulan chainsaw to cut up the largeamount of firewood that became available,it worked well for a small saw though it had a habit of vibrating some of the nuts loose so I made some long sleeve nuts,drilled small holes across the top of the nut and fitted locking wire that solved the problem, never had that problem with Stihl saws though nowadays they dont shake loose as you cannot easily start them with on this rubbish modern green petrol.

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