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"

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

Stew