Building a 31/2" Gauge Locomotive Engine

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sbwhart:

Options

1.   Bore out big and make oversize piston to suite.
2.   Bore out big and Sleeve back to size.
3.   Buy a new casting.
4.   Buy a chunk of Phosphor Bronze and machine this up.

A new casting would cost £ 85, a chunk of Phosphor Bronze would cost £ 35, I didn’t like the idea of going over size or sleeving the bore, as there was not much meat left in the wall of the cylinder. I bit the bullet and bought a block of phosphor bronze that had 1/8” machining allowance on it all round, the supplier (College Engineering Supplies) were prepared to cut the block to size with no additional charge. Going this way meant that some of the casting detail would be lost: however, this would be well hidden between the frames so was of no consequence.

Starting from scratch again:- this time squaring up the block was a lot easier, I simply held the block in my big four jaw chuck, got everything nice and square and brought it to size. As I was dealing with a solid chunk of material there was no need to plug the bores for marking out the hole centres.

Tip :- Mark the centre of the block and the bore centres clearly and extend the lines all the way round so you can pick up off these when you marking or machining other features, also scribe the diameter of the bores as a check that your machining is going OK.

The job was set up on a face/angle plate as before but this time clamping was easier because of the more uniform shape. A good big deep centre drill followed by progressively bigger drills, to get the meat out:- a job that was made much easier thanks to the modification to the tail stop suggested by John (Bogs) this stopped the drill spinning on the taper. Swapping over to the boring bar to bring the bore to size, this time everything went OK.

Machining out Steam Ports

First Job was to accurately mark out the position of the steam ports as I’d got the scrap casting I marked this out as well, as I planned to have a practice on this first. The steam inlet port is 1/8” and the exhaust port ¼” wide, I acquired some slot drills these diameters. As my machine is graduated in metric, I drew out the steam ports in autocad with the required table co-ordinates.

I use the old Fag Paper Trick (cigarette paper for you folk living in the colonies) to find the edge of the casting, but I don’t run the machine, instead I use a plain set piece that is dead on 6mm diameter, salvaged from on old Video player, advancing the table until I feel a pull on the paper, the machine is zeroed and the position set to the co-ordinates.

A quick check that all looks OK with the marking out, and you can start to cut metal.

When milling slots like these I’ve found it best with my machine to first drill two holes slightly smaller than the slot at the extremes ends, this prevents the cutter pulling into the corner and giving you a “hockey stick end”. With my machine also I put a cut on from the same end, putting a cut on from both ends gives a series of steps in the slots, as the cutter is first pulled one way and then the other resulting in a slot wider than the cutters, and I take small 1mm deep cuts. Tip:- Don’t forget to lock the table in position. It is quite a simple matter then to progress slowly and methodically to finish off the ports, it’s a job that I find satisfying.

Cutting steam ports I think is one of those jobs where it pays to have a practice on a piece of scrap first, to develop a method that best suits your kit and machine, you’ve nothing to lose, even if it means having two or three goes.

Drilling the steam ways into the valve ports was a matter of carfully marking out there position and transfering the line to the outside of the casting. The casting was then gripped in the machine vice, and getting it lined up with with the aid of a set square. As the drill has to go in on an angle it will run off if you don't start it with a good deep centre drill, filing a small flat will help, but even with this you will need to take it stead. These holes are on the deep side, and can run off if you don't take it easy and keep pulling the drill out to clear the chips.

Well that was the Job back on track a bit expensive, but I learnt one valuable leson:- you don't always need expensive castings

:D :D :) :)

Have fun
:wave:

Stew

bogstandard:
Stew,

That proves my brain is on the way out, I now remember you showing me that on my first visit to your shop.

A real nice rescue.

John

sbwhart:
Steam Chest

The steam chest is machined from a casting with the valve rod stuffing glands an integral part of the casting. First job was to clean up the casting and check it over with a ruler and look for blow holes. The casting was set up in the angle plate and squared up and the outside dimensions machined to size, it was then blued up and the inside features and stuffing gland position marked out.

The casting was set up in angle plate pushed up hard against a parallel so as to keep it square. The centre height gauge was used to locate the centr of one of the stuffing glands. A deep centre followed by a roughing drill followed by finishing drill all the way through, this was then drilled to depth with a 5/16*32 tapping drill and the hole tapped. The casting moved over and the second stuffing gland machined

Using a cranked turning tool the outside of the boss was then cleaned up.

The casting was set up in the machine vice on parallels and the inside cleaned up to the lines with a small end mill and the corners squared up with a hand file in the bench vice.

The clamping holes were marked out, the casting set up again in the machine vice and the clamping holes drilled. The steam chest was carefully positioned on the cylinder I used supper glue to fix it doesn’t set straight away so you’ve got a chance to get the position right, alternately you could use two way type. It was set up in the machine vice with a tool makers clamp keeping the chest in place, the hole positions were spotted through onto the cylinder, the steam chest removed and the clamping holes drilled a tapped in the cylinder, taking care not to go too deep.

Tip:- use the tapping drill first in the steam chest only open them out to the clearance drill when you’ve spotted through to the cylinder.

Ok that will do for a few days

Have :wave:

fun

Stew

Darren:
Please keep these coming Stew, I'm fascinated.... :thumbup:

Brass_Machine:
Nice Save Stew!

I am with Darren on this one. Keep em coming!

Eric

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