Building a 31/2" Gauge Locomotive Engine

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sbwhart:

--- Quote from: bogstandard on June 27, 2009, 02:55:27 AM ---
My suggestion would be to do a bit of manual hacksawing thru a 6" bar of cast steel, that just might knock that damned smile off your face. :lol:

Bogs

--- End quote ---

Why would I do that when I know a man with a powered haxsaw :lol:

Thanks for your kind comments gents much appreciated.

Stew

sbwhart:
Been busey this week fitting the slide bars to the cylinder.

I was unable to spend as much time as I hoped what with work demands and my old Dad strugling with the heat, and needing a little bit more looking after than normal.

Any way this is what I've been up to.

Cut the cylinder head studs off to length using Johns tip of putting two washers under the nut, cutting the stud off to this, cleaning the cut end off, and removing one washer, this leaves all the studs standing out all the same length, all very neat, the cylinder heads at the other end are held down with 7BA countersunk sloted screws a bit more easy to deal with, but still very fiddly.

I also made the slide bars from 1/8" thick gauge plate, quite a simple little job, sorry no pics.

The next job was one that's been troubling me for some time:- the slide bars are held onto the end of the cylinder heads with 7BA screws, for this the covers have a 3/4" across the width flats, that need to be concentric with the centre line of the cylinder.

When you read old Curley's instruction: he makes this sound deceptivly simple, he basicaly recomends making up what is in effect a filing button, 3/4" wide that you centre up on the bores and file the flat working to this, describing the fit as a nice slide. This is where I have problems what's one mans nice slide fit is anothers tight fit, its very dificult describing touch fits to another person, in industry we get around this by very well specified limits, fits and tolerances, but in a home maching environment you can't do this, it very much depends on the individuals skill and experience.

To make this even worse there is no easy datum to work off, so I decided that I would have to create my own Datum.

I fixed the cylinder complete with pistons and covers in my vice, and with my height gauge did some carfull measuring.

I then did some calculation and work out a setting height that I made up with slip gauges (I convert the answer to imperial as my slips are imperial so don't be confused)

I then brought the cutter down (no power) to touch on this pile of slip and zeroed the DRO.

I then milled the flats on one side down to the DRO zero:- flipped the cylinder over repeated the measurements and calculation for this side and machined down to the zero.

I was very pleased with the result the flat was 0.756:- .006 big but I can compensate for this with the mating part but I still don't know if its simetrical arround the centre line, to do this I need to fit the slide bars.

Drilling the tapping size for 7BA this was done on the centre line of the cylinder picked up from the piston rod.

Tapping 7BA on tapping stand nice a square

Now fitting the slide bars I was able to check symetry by measuring the gap each side between the piston rod and the bar, it was within 0.003"

:nrocks: :nrocks:

:D :D :D :D

I think I can live with that

This is the slide bars with the motion frame which they will be fastend to eventualy with a 3/4" slip gauge which moves up and down the gap lovely.

Next job is the cross head (big end) I'm going to try and do this using the RT so it should prove interesting.

Cheers

:beer:

Stew

sbwhart:
My Boss because of the hot weather hasn't slept too well, beging very restless, this in turn has agrivated her bad back, as a consequence she's spent the best part of today resting, so that I don't disturb her I've spent a fair bit of time in the shop:- well thats my excuse any way :lol:

So got a fair bit done on the cross head.

This it

In the build instructions Curly calls for it to be made from mild steel section, machined in the lathe four jaw and the vertical milling slide. Most of Curley's designs were done between 1920 to 1960, so he was writing for a very different bunch of medel engineers than today, they'd give their right arm for some of the kit we've got. So it seemed OK to me, to take advantage of some of my kit and try to make it, to my way of thinking :scratch: , a more accurate and easyer method:- so what I'm going to do is use the Rotary Table.

Starting off with a bit of 30mm diameter mild steel bar, turn it down to a diameter eaqual to the hypotenuse (Mr Pythagorus again) with a groove to give datum points for each Cross head.

Drill full length roughing drill I'll finish drill when I've done with the milling

Transfer the bar in the chuck over too the RT set up Horizontaly in the mill.

Note use of centre support.

Check for squareness sideways

Check the other way, Note stylus on DTI you can do this on this type

Rough mill out one side (1/2 mm from size)

I'll drill and mill the cross holes whilst it still got plenty of meat on the underside.

Slot drill out the 12mm steped holes:- my little mill grumbled at this but it copped.

Check on depth with home made depth gauge as I couldn't get in with the vernier.

So thats it for know so far so good we'll see how the rest goes another time.

:beer:

Stew

Darren:
Stew you are really motoring on with this aren't you..looks like a very "engineered" bit of work there.
As always following with keen interest..... :thumbup:

Stilldrillin:

--- Quote from: Darren on July 04, 2009, 01:16:26 PM ---Stew you are really motoring on with this aren't you..looks like a very "engineered" bit of work there.
As always following with keen interest..... :thumbup:

--- End quote ---

Me too!
Just like what he said....... :wave:

I was going to say "professional". :thumbup:

David D

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