Member postings for Robert Smith 24

To clarify, the steel was purchased from a supplier on E Bay.

Many thanks for the responses. It does seem I have purchased a length which is just within tolerances so it will have to be consigned to the stockpile. I will order some 5/8 inch stock and machine it down.

The supplier by the way was the Bay of Evil.

I recently ordered a length of 1/2 inch diameter round steel bar, EN16T to make a new small end pin for a model steam engine. On checking the dimensions when it arrived, I was surprised to note that the diameter was 4 thou under the nominal size. Is this usual? Is there a source of accurately sized stock?

Thank you all for your excellent replies. I am giving the matter further thought.

Thank you for a very comprehensive reply. Looking at the respective yield strengths, do you consider high tensile steel viable in my circumstances? I'm thinking I could turn down a suitable high tensile bolt and use the pin without heat treatment.

I appreciate that the pump pin is not in tension so maybe shear strength is more important?

Edited By Robert Smith 24 on 05/10/2021 11:36:37

Thanks Duncan. The pump ram is 5/8 inch, boiler pressure 120 psi, pin diameter is 1/4 inch and the bearing length is 3/16 inch.

I have no knowledge of calculating the stresses so please advise. TIA

Following from the above, as I need to replace the pin which articulates the eccentric rod with the pump piston, I am considering replacing it with a case hardened mild steel version. The original was hardened and tempered silver steel and that of course broke.

I am doubtful that I could hold a precise tempering temperature long enough to achieve the correct temper all through. Could I please solicit opinions as to whether case hardened mild steel is suitable?

Finally bottomed it. I refitted the old broken rod after it had been welded to check alignment etc. The topside of the rod had been contacting the the bottom edge of the horn block in a kind of "stroking" motion hence no warning knocks. The contact point on the block was directly over the fracture point and bears the scars, fortunately not visible when the second shaft is installed.

I will mill a new rod with a tad more clearance and "move" the removed area to the opposite side of the rod where there is ample clearance. This way the rod strength is preserved.

My only problem then will be remembering how it all goes back together!

Clack valve already checked and pipes blown through and no isolation valves present. Thank you for your post though and all help is much appreciated.

The sharp transition from minor to major diameter of the pin will be addressed when I machine up a new one.

Nigel, thank you for your response. In my post on 24 September, I described the fracture as being "not like mild steel at all". The fractured area, whilst not dead hard, is not easily filed unlikely to be MS.

The rod broke on a straight length about half an inch from the welded on piece which bolts to the eccentric. As I did not build the engine I have no idead as to the steel used but as I will be making the new rod I want to ensure no repeat. It took me a full day just to remove the second shaft!

The first thing I checked was the ram clearance and there is no way it contacted the end of the barrell as it had a good half inch of further travel.

The pin was hard and fractured at the shoulder of the 2BA thread and 1/4" pin. The tempering colour is still visible on part of the pin.

The rod failed half an inch from the eccentric strap where the flange is welded to the rod itself. The break was very crytalline in appearance, not like mild steel at all. I suspect that after welding it was quenched too soon and that has caused a hard spot.

The pin attaching the rod to the pump ram also fractured. That pin was very hard and not possible to file so I suspect it was made from silver steel hardened and tempered. I intend to replace that with case hardened mild steel.

Thanks Mick. I have some 3/16 x 3 inch mild steel plate so rather than stress the steel by bending I'll mill from the plate.

Thanks Harry and Chris. No hydraulic lock so I am puzzled as to the cause. I certainly don't want it to recur as it is a major job to replace it. Rear wheel, gear guard, gear change levers (3 speed) 2nd shaft bearings and 2nd shaft itself all have to come off.

Not looking good. Connection timed out just now.

My three inch scale traction engine has broken the boiler pump rod between the eccentric and the pump ram and I need to make another. The rod is rectangular section 11mm x 4mm but has two 45 degree opposite bends in to clear the second shaft. The working pressure is 120psi so the rod is subject to a fair bit of stress. Could anyone please recommend a suitable grade of steel?

After removing the fiddly connector box screws on the fron of the dynamo, hanging upside down under the canonpy to disconnect the concealed voltage regulator, removing the countless tiny nuts and bolts from the canopy supports, then removing all but inaccessible dynamo hold down nuts and then removing the dynamo base from the smoke box extension, hand filing the slots (I have no milling machine) the replacing all the above and finally re-touching the paintwork inevitably chipped during removal.

I reckon a new belt is a bargain

Thanks to all who replied. I already had a belt but it was too tight and risked cream crackering the dynamo bearings. I eventually found the maker of the original belt and have ordered from him.

Could anyone suggest a supplier of flat belting made to measure suitable for my three inch scale showman's engine please?

Hi Nigel,

Thank you, yes I did find it where suggested over the foundation ring on the backhead. An absolute pain to find and read. I never knew I could bend my neck in such a shape!

It seems to be an odd place to stamp the number when boiler inspectors are expected to check it. The obvious place for most traction engines must surely be over the foundation ring on the throatplate. Maybe there is a reason?