Member postings for Peter Brown 1

Just had an email from Richard Clarke of GLR KENNIONS, he has had the drawings for 7 1/4 TICH updated to correct the design and drawing errors and from the list of alterations this must have taken considerable effort so WELL DONE and I hope this will help those who are building at the moment and encourage those thinking of starting as it is a nice engine to have a go at as it is not such a watch making exercise as the 3 1/2 inch version with decent size parts to handle.

WELL DONE AND THANKS TO THOSE INVOLVED

That’s great Richard if they want to contact me I can give them some of my ideas. At the moment I am spacing the frames 3/16inch further apart to get rid of the axle float and then taking a 5 thousand inch skim off the back of the wheels to give a running clearance, by doing this it helps in the alignment of the connecting rod to the crosshead which I think can now be achieved by a slight modification to the big end bushing it also reduces the overlap of the crosshead and coupling rod but does not provide enough for them to clear so I am now considering ways to achieve this, With regard to the spring rods I think I will remove them completely and rearrange the springing as per the 31/2inch version with the springs on top of the axle boxes sitting in pockets which will then also act as oil reservoirs for the axles. At the moment the only casting this would affect is the centre pump stay with needs to be 3/16 longer but in my case I will just add spacers either end.

If I was starting again I would make the frames from 1/4 inch plate which would achieve the same increase in width but would leave the inside measurement at 6 inches but this might require the hornblock castings to be slightly thicker.

Peter

Edited By Peter Brown 1 on 29/02/2020 12:31:17

Yes I know many designs contain errors and some are better documented than others, Big Tich just happens to be the project at the moment but having a set of drawings which cost £50 I really don’t expect to the spend hours redrawing them I would rather be out in the workshop machining.

If I can get permission I will try to put together an article for the Model Engineer on the problems and my solutions and suggestions to produce a working version of what I hope will be a nice little “big” engine and encourage others to have a go building one.

What has really annoyed me with this is that there are fundamental design errors not just the odd drawing error. On sheet 4 of the drawings for the valve gear if you actually draw in the missing front wheel and complete the coupling and connecting rods it is clear that the crosshead will foul on the coupling Rod and not align with the connecting rod. Similarly on the drawing for the frames and wheels if you draw the outline of the wheel over the horn block and spring assembly it becomes clear that the spring rods extend below rail head. Yes we are an inventive lot and having invested a considerable amount of money in this I will find a way round it and will try to document my solutions as I go.

You are right, wheel radius 2 1/16th protrusion of spring pin 2 1/8th Also there is no drawing for the saddle. I have a professional made boiler so I won’t need to worry about the hollow stay.

I have completed a Rob Roy but that had drawing issues as well, no wonder there are so many part built locos on eBay it’s enough to make you want to give up and try something different.

I don’t know how anyone has managed to build a 7 1/4 Tich from the Kennion drawings. If you build the frames and axles to the drawing you end up with 3/16 inch end float on the axles, also the motion work fails to line up correctly the cross heads foul on the coupling rods on the front wheels also the cross heads fail to line up with the coupling rods. My drawings are old so I contacted GLRKennions to see if the drawings had been updated only to be told no, not only that but they know about the errors but have done nothing to correct them. Surely to sell an item that s not fit for purpose is wrong, if I had machined expensive castings to an incorrect drawing would I have any comeback? I have now spent several hours redrawing the motion to find a solution and am dismantling the frames to correct the end float whilst maintaining the correct gauge. Has anyone else come across this problem and if so what is their solution?

I've seen a neon used as a voltage regulator 180v if I remember correctly

As the graph in Neil's post shows once the junction reaches a certain point the voltage across it remains close to a constant but a slight increase in voltage produces a large increase in current. I agree that the design published will work I was simply pointing out that it isn't the best or safest way to use LEDs.

Apologies yes the leds are correct, my mistake I better go to spec savers.

The circuit for 3 leds in series which is on page 492 of the current edition has an error the left headlamp should be reversed.

However the method shown is very poor electronics, an led is a forward biased diode which should be supplied from a constant current source which will limit the current to the required amount in this case about 20mA for a voltage of 3v across each diode. A small increase in voltage of say 0.2 v would increase the current flow Considerably and would risk damaging the diodes. A new PP3 battery can give 9.6v I.e. 3.2v per led.

A better solution is to either supply the leds in series with a current limiting resistor using a higher voltage supply or wire the leds in parallel each one with its own resistor