Centre of a cylinder casting.

Hi Guys,

I am looking at building a 3 1/2 inch gauge Fowler 4F. I have bought the drawings from Reeves. One thing that confuses me is how to find the centre of the bores of the locomotive cylinder casting. Reading the articles that people have written it says plug the casting end with a piece of wood and mark out the centre. As the castings are rough how do I measure and mark out the correct position for each bore? Where do I measure from?

Cheers,

George

You need to do it so hat the appearance is OK - i.e. any unmachined parts of the casting will be placed correctly in relation to the bore, but also make sure you allow sufficient machining allowance for things like the valve face.

One way of doing this could be copy the end profile of the cylinder onto a card template and offer this up to the end of the casting, then mark through it onto the wooden plugs.

Neil

Thanks Neil. The card Template sounds a good idea.

George,

Start by cleaning up the outer surfaces of the castings using a file etc. to get rid of any flash or "knobbles" etc. Then plug the hole with wood just short of each end of the cylinder. Finishing the ends of the wood with car body filler which is then smoothed down flush with the cylinder ends. Then use a scribing block and rule (or better still the centre finding head of a combination set) to find the center and mark it on each end. It is best to do this very lightly with a sharp pencil to begin with. Once you are happy that you have found the centers then mark them more heavily. As Neil says it is important to get the outside i.e. visible parts looking right and so work from them and not the cast-in hole which may be well out of center. The wooden plug and thin layer of body filler can be knocked out carefully once the casting has been set up for machining.

Eric

Once you have found the ctr of teh bore check all the other surfaces in relation to it to make sure you have sufficient material to clean up all the faces and that any cast in bosses etc will be where you want them. If not you may have to shift the ctr of the bore to give the best of both worlds.

I'll often set the casting on the surface plate and use feeler gauges to shim it up so it sits level and then run over it with a height gauge, square etc checking the above mentioned items. I then transfer the casting with the same packing to the mill an machine a face which other features can then be set out from.

One of the biggest problems for beginners!

Some (not all) casting suppliers have very little extra meat on the vital parts. The finished dimensions should show the dimension between the bore center and some other part, such as the port face. Normally you can file or otherwise grind away any "knobs and excrecances" as LBSC used to say, to get a reasonably flat surface to work from as a datum point. If you have a vertical marking gauge then lay the port face on the table and measure up the cylinder face to find the correct bore center and scribe a line across the end face. Rotate the casting through 90-degrees and repeat for the other tramline. Now you have the casting scribed set it up in the four jaw chuck and then scribe a circle on the end that is concentric with the cylinder bore.

Often you have to work with what you have got, the core hole might be a a bit off the correct position but you can compensate as long as you don't cut into the port face or the cylinder circular end faces. At the end of the day you are only making one off items so if the bore comes out slightly out from the correct place it can be worked into the other parts by adjusting the dimensions to fit. Rather make the bore concentric with the end faces than offset it. If it comes out a bit higher or lower it is not a train-smash.

Thanks Lambton, JasonB & John for your answers. As John has written one of the biggest problems for beginners. I just could not see how to do it but at least I now know that it cannot be done perfectly but more of find the best solution you can based on the factors explained above and work from there.

Cheers,

George

Good morning George,

I think most people have given good advice, what I would say it is essential to work from a datum and I make that the port face, Put a rule all over the casting to determine roughly how much is to be taken off each face, I then carefully set the casting up in a 4 jaw to run as true as possible and face off what will become your port face, that is then your datum for marking off all the other dimensions. What you will need also is a small supply of say 13 gauge annealed copper sheet, cut just smaller than the finished faces, this will protect those newly machined faces from any damage from chuck jaws etc. As for marking out the bores then a couple of pieces off a broom handle forced in the bores, I will pin a couple of odd pieces of brass or copper sheet on the end of the wood plug as it is easier to mark out than the wood.

Having built three of the Don Young designed 4Fs I can safely say it's an excellent design, if you can get hold of the words and music, read it and read it again, you'll find it a great project.

If you need any advice on their construction etc then drop me an e-mail.

Regards,

Bob

Thanks for the advice Bob. Once I get started I will take you up on your offer of advice.

Hi DMB, I expect to have plenty of offcuts when I make the boiler, I have not silver soldered anything yet although my wife bought me the Sievert gear for Christmas. Making the boiler will be VERY interesting!!!!

Good afternoon George,

When you're ready to get started on your boiler let me know and I can send you a series of photographs how I construct mine also some words and music that'll make the job that much easier to achieve. Are you a member of a club? It is always helpful as there is always advice.

Regards,

Bob

Hi Bob,

Thanks for your offer I will definitely take you up on that. I have
not joined a club yet but I will when I start construction. I have a choice
of 3 near me Sale, Urmston and Rochdale. At the moment I am constructing
a gauge 1 4F to get some experience on an easier project as I am new to
this. I am looking forward to silver soldering next once the drier
and warmer weather arrives as I will be doing that in the garden.

Thanks again,

George