The heart of the cross head.

I decided to fabricate the cross heads (avoiding castings....) and weld them up from 40 x 25 steel - the slide bar material - and 10mm side plates. The piston rod is threaded M22, and so the first job was to accurately mount the 'nut' in the lathe, all nicely centred, and drill it out for tapping. Some years ago I bought a set of reduced shank blacksmiths drills from Tracy Tools - a set going from 9/16ths up to one inch. This set has been worth its weight in gold, and are well used....
I opened the hole out to 3/4", started a 13/16ths drill in there to help the tap, and introduced the tap whilst still in the lathe - very important to get the thread absolutely square. Of course I couldn't get the shank of the tap into the tailstock chuck, and so I was forced to use a large tap-wrench - and I was delighted to seethat the tap had a centre drilling in the back of the shaft for exactly this purpose. By putting a centre in the tailstock and keeping the pressure on the tap, I was able to pull the chuck round by hand, and got a reliable square thread on both 'nuts'.

How the crosshead will go together

The lower slide face is welded to the plate (hence the 'V' prepping on some of the corners) and the upper block will be through-bolted for removal.
The holes for the gudgeon pin are drilled and then bored to exactly the right size. Normally, the pin would be expected to sit in a taper, having been introduced from the back, with a nut on the front. However, I'm not that lucky.....
The way No 2 is proportioned, there is no way a gudgeon pin has the clearance to withdraw backwards, and so I'm forced to have front entry, with no room for a nut behind either.....
The pin will be held in from the front, aided by a boss 15mm thick to help give it support.

Half made bosses for the gudgeon pins - bored accurately, two tack welded together for cutting and finishing.

The assembly will be welded and bolted together after I've finished the gudgeon pins, as I need them to ensure the side plates are exactly square. After the two slide blocks are welded and bolted, the crosshead will be fitted, the slide bars accurately lined up parallel with the piston rod, and then the 'nut' will be welded in - thus ensuring that everything is lined up accurately.

That's the theory. Incidentally, I have a steel cross head running on a steel slide bar. I have thought about wear, but I was reassured by Dave Wiseman (who built the magnificent 'Duchess') who has done exactly that for years with no problem. Obviously, lubrication is required.......
The gudgeon pins will be drilled and cross-drilled, and fitted with grease nipples to lubricate the roller bearing little ends.
I will make M22 lock nuts to tighten the cross head to the piston rod.

JUST TO DEMONSTRATE THIS IS A WARTS-AND-ALL STORY...
Having completed the first crosshead, set up the 'nut' ready for welding, and finally welded it, I found that the M22 thread I had so carefully cut is in fact slightly drunken - which is no good at all......
I decided to re-work it all properly (rather than any sort of bodge...) and have taken the piston rods back out, and machined a three degree taper (with an M16 locking nut on the end) and made new bosses at the same cross-slide setting, which fit into clearance holes I've bored where the M22 thread was.....
They are now welded in - having checked alignments very carefully.
This has gone very well, and the finished cross-heads are nice and square - and indeed a better job than it otherwise would have been....

Cross-head shown prior to welding the boss in

The job went absolutely fine - much better than mark 1.... and once the con rods were fitted it felt like another stage forward.

The Priest' sat at Ally Pally, on the 10 1/4" Society stand, where a lot of people were surprised at the size of the thing, but most were interested in the simplicity of construction.

The next jobs are valves, valve spindles and glands, and valve gear - which I intend to laser cut as much as I can....

10th May 07

I've been pottering on with valve spindle glands as I've had the chance (not a lot...), and the general technique is as follows:
cut chunk of 40mm dia bright steel bar to approximate length, put it in the lathe, face off both ends, and chamfer both ends (one end to look pretty, and the other to form a groove for welding).
Chop suitable piece of 6mm plate, and weld part A to part B. This then gets put back in the lathe and cleaned up, and the flat plate faced off square again (after the welding...).

This then needs drilling and boring, ready to have a chunk of gunmetal or similar silver soldered in.

Like this....

(the black is entirely from heating for silver soldering)

The gunmetal insert then gets bored to take the vavle spindle (in this case 1/2" dia), and then it gets bolted on like this....

I've already done the back end in a similar fashion. Note the gland is made with a gunmetal bearing sleeve, and a brass (for economy) bolting flange.

28th May 07

I've now had a chance to make the valves. These are quite large blocks of cast iron, of which I first roughed out the exhaust cavity, and then carefully and accurately milled the working edge of the valve and the corresponding edge of the exhaust cavity (to make sure that inner and outer end of the valve was the right dimension, and parallel), I then milled the other end, to get the whole valve to exactly the right length, finally going back and milling the remaining inner face of the exhaust cavity to match. I'm not describing it very well, but the inportant thing is to get everything to the right dims, and parallel (obviously.........)

I then turned the valve over (now that all the critical edges are done) and milled the slot for the valve rod, and the recess for the actuating block (since we don't have a buckle...). This was all easy, but time consuming. Me being pretty inexperienced, each valve took about six hours of machining - though I'm quite sure I could have worked the Herbert much harder, I didn't want to take risks....

The really easy job was chopping off all the excess 'meat' with the band saw.

The finished valve

The valve with block and rod

In situ...

The exhaust 'T' has been on my list for some time - and as I was passing a 'Pipe Centre' branch, I popped in to get some bits and pieces.
The exhaust is in 1 1/4" BSP, and comprises of the following:
Twin Elbow (not twin bend) Male / Female Union, 3 Barrel Nipples (those double ended thread things.....)

The trick is to assemble the whole thing with PTFE in the Vise, making sure everything's properly tight - and then trim the ends to fit in the gap (between the cylinders), Line the unit up by fair means or foul, and tack weld one end.
Needless to say, one must ensure that the exhaust is properly centred in the frames. One cylinder was then removed with the exhaust tee tacked to it, whereupon it was fully welded.
The assembly was then refitted, and the exhuast tee tacked to the other cylinder (doing it this way means you don't get trouble with contraction from the welding....), the second cylinder with exhaust was then taken off and welded - and job's done!

I recently bought a surface grinder on e-bay for £60, so whilst the cylinders were off, I thought I'd grind the valve faces for practice (I've never used one of these before...). The machine is only just big enough to cope - but it does. I was also re-assured that the fly-cutting I had done wasn't too bad - but non-the-less, I was pleased with the improvement of finish.