Tag Archives: lathe work

Relief Vales and Drain Cocks

An experiment – Steam Operated Combined Drains & Relief

Much earlier in the process I baulked at drilling the cylinder castings for the cylinder drain cocks because they looked hard to drill with out risking damage to some rather expensive castings. Moreover, previous experience with manual cylinder drain cocks on the loco had been poor (leaky, difficult linkages etc.) and on the steam launch most people seem to opt for 4 manually operated cocks which involves a deal of “faffing” in use. Continue reading

The &^*$! reversing gear…

Well, if you’re building this engine then I hope the valve gear goes more smoothly for you than me!

The Draglinks

The Drag Link Bearings

Drag Link Bearing Blanks

A handfull of work, drag link bearing blanks ready for drilling boring, fitting and oil-hole drilling

I cannot believe just how long it has taken to complete the reversing gear on the engine – and it’s still not done.

The multitude of little blocks (drag-link bearings) take an age to make – if you had some 7/16″ sq Ph Bronze bar to hand then it might be OK, but I didn’t so decided to hack the blanks out of a piece of 2-inch square bar I had. However, I discovered that my trusty Warco bandsaw did not cut as straight as I hoped, and half of the resulting blocks were undersize. So then you spend a while silver soldering extra bits back on, to bring them to size, and then (literally) DAYS on the shaper, transforming a set of rough cut rhomboids into little cuboid shapes.

Drag Link Pins

Meanwhile a relatively simple turning and pressing job produces the pins for the lifting arms and eccentric pivots.

Drag Link bearing pins pressed into lifting arms and allen-screwed into expansion links.

Drag Link bearing pins pressed into lifting arms and allen-screwed into expansion links.

I happened to have some EN1A on the shelf that these got cut from – this is lovely free-cutting (leaded) mild steel, but I must confess I worry that this is so “soft” that it might not last well in service.

BTW – Midway thru the gear building I ran short of 1/4MS bar. So I went off to Metal Super Markets in Southampton (metalsupermarkets.com) and stocked up on a variety of bar and plate, that my “stores” were running short of; (these really are great people, and very helpful and economic – I would recommend them to anyone, over the counter service with a smile, for even small quantities) – But they only had EN3B, and when it came to turning and screw-cutting this stuff you really miss the free-cutting EN1A!!!

The only issue with the manufacture of these pins, is that one of the errors in the drawings means these pins need to be longer than drawn, to clear the bolts and lock nuts securing the Expansion Links and Die Blocks. There’s not a lot of space, so take care – I extended mine to 1.5″ overall (I think).

Drilling and Boring Drag-Link Bearings

drilling the bearingsThe next job was to drill the bearing halves for the rods. I did this by clamping them into a small jig (with tool-makers clamps). My normal approach to this would be to soft solder (“sweat”) the bearing halves together and then drill and bore them as one, separating them at the end. But this was not what the ME articles said – so I followed them… The plan was to create a small jig, drill half the blocks 2BA clearance and the other half 2BA tapping – then tap these and use temporary screws to assemble them into pairs while they are bored, and then open out both sides to clearance for the long rods to be fitted.

Jig Drilling DragLink Bearings

Jig Drilling DragLink Bearings

I think this approach was slower.  A better plan would have been to solder them into pairs while they were all still oversize, drill, bore, finish to size and then separate.

As it was I then discovered that despite machining all the blocks to size, the journals on the pins were too tight (only a few thou, but enough to stop them fitting, so yet more fettling was needed)- At this point I discovered that the relevant reamer has gone missing, so more careful hand work on pins and bores (scrapers and emery tape) was needed to get a good fit….

The Valve Rods

This is about to start sounding like the blog of a complete idiot, but at least it’s improving my patience.

LP Valve Rod

Firstly, while assembling and testing the valve gear (prior to first run on air) I found that the LP valve was fouling something and could not accommodate the full travel of the eccentrics, over a couple of hours of assembly, disassembly, reassembly (repeat as needed) I came to the conclusion that the tailrod was too long and clouting the end of the tailrod guide… there being no opportunity to lengthen the guide, I decided to shorten the tail rod – carefully sawed 1/4″ off, and reassembled again, only to find it STILL DOES NOT FIT!!!!!

Further inspection determined that the valve buckle was actually fouling the nut holding the tail-rod guide – and actually the shortened tail-rod was now falling out of the guide at the lower extent of the valve travel!!! So, it now needs lengthening – more work yet to be completed…

HP Valve Rod

The HP valve rod has a “joggle” on the bottom to line up the valve rod with the eccentrics. I decided to make this as a separate part and screw it to the rod proper. This joggle also serves to further widen the already widened drag-link pins resulting from the error in the drawings. I did measure this and allow for it in the longer pins – but I forgot to take account of the lock-nut on the die-block pin….AAAARRRGGG!!!

I concluded I could shave enough off the joggle to accommodate all this, but the amount of metal left for the thread holding the actual valve-rod into the joggle was going to be a bit thin, so I decided to braze the rod into the joggle – this I did (with no distortion), and decided to use the Linisher (belt sander) to just clean the flux and oxide off the joggle…. What I failed to see as I did the final side was that I was holding the assembly slightly out of square and ground a nice 20thou depression in the bally valve rod – thus rendering the whole shooting match scrap! 😐

Either way it provided me the opportunity to screw-cut the 3″ long 3/8″x26 thread on the new rod, using the off-set compound slide method often recommended (but never tried by me) mechanism – and it does a much nicer job (even on the nasty EN3B!), so I conosoled myself that the extra 3 hours work, had resulted in a nicer job (displays a fixed grin)!

BTW, In this process I again reminded myself that under conditions where you need to take fine cuts on tough material a carefully sharpened carbide or carbon steel tool will outperform a indexable tipped tool – as if you check the specs these are not typically made to make a cut of less than 5thou !

The Result….

Jig Boring the holes in the lifting arms for the weighshaft and drag-link pins

Jig Boring the holes in the lifting arms for the weighshaft and drag-link pins

Overall these 16 half bearings and eight rods and 4 pins took more than a 10 days of effort (probably about 30 hours! not including the remaking of the vale rod) – a slog…. assembling the whole sh-bang produced something that worked but was too stiff, so more fettling and adjusting needed!

I am really hoping I can bring this all to a good end – sometimes I wonder!

Chucking out the Chucks?

I realised the other day that I have almost stopped using chucks and vices. When I first got the milling machine (20+ years ago) I spent a lot of time looking for and building milling vices, and similarly on the lathe kept looking for nicer/larger chucks.

But in the last few years nearly all the milling/shaping is done by clamping work pieces directly to the table (either using clamps or stop-pins) , and when you do this you tend to wind up with more solid set-ups, with fewer errors from things slipping, and much more accuracy, and you are not plagued by lifting jaws putting things out of true etc.

Similarly on the lathe I seem to be doing more between-centres work, which I used to view as old fashioned, but I now realise it tends to be more accurate, and you can take a job off the lathe and put it back, and its in the same place!!!

That and the purchase of the ER25 collects and chuck have almost made use of the 3 and 4 jaw chucks a rarity.

I guess if I had had a proper apprenticeship or teachers watching, I would have learnt all this earlier – but none-the-less I am enjoying my improved productivity and accuracy as a result of this change.

Connecting Rods & Big Ends

The connection rods were a nice between-centers turning job, and then a selection of milling set ups.

Rather than write a lot, I will put some pictures below – the main thing to note was that almost all of the milling and boring was done with the partially machined big-ends attached to the partially complete rod – in order to ensure a good level of concentricity….

Straigtening a bent crank

The previous posts discussed the manufacture of the webs and journals, and I felt very confident of the approach. Half the joints were to be shrunk together (very cold journals, warm webs, and a press (large vice)) and the others were to be loctited in place.

Here we see one part of the crank assembly, clamped in v-blocks while the loctite sets – guaranteed straightness (you would think!)

The theory being that the press/shrink fits are bound to be square (as the holes and journals already are, and there is no spare space for out-of-aligned-ness), and then the loctite joints are assembled with the journals fitted into V-blocks, thus ensuring everything was straight and true … how wrong can you be?

The press fits went together “OK”, but were too long to be pressed together in the bench vise so an Edwardian sash-cramp was “pressed” into service :-). Then loctite and v-blocks and Bingo!, it all comes out bent! 😦

Out with the engineer’s square and dial-gauge and we discover that the press fits are not square… Much head scratching, and a few tentative (and then very hard) clouts with rubber mallet prove that it’s all MUCH to solid to bounce back into shape.

(The current theory on how this happened, is that the sash-cramp was not really square, and the shoulders on the webs were too narrow and deformed under the stress of the shrink fit and pressing together. However it might have been that the webs were milled from oversized stock, and I have seen loco coupling rods bend like a banana from the retained internal stress which becomes unbalanced as material is removed – no matter what it was BENT!)

So I google “crank straightening” and discover “peening”. The idea being that by hammering (with ball-peen hammer (always wondered where the name came from)) the surface of the bent web you release surface stresses (as a result of stretching the surface with the hammering) and the web bends towards you.

A little peening to straighten the crank web – before it all went a bit Pete Tong

Well it almost worked, I cheated and used a pneumatic chisel with a domed tool in it, and as predicted the dial gauge confirmed that everything was coming back into shape. With a run-out of less than about 3 thou I was feeling very positive. I figured I would give it one more treatment and get it “bang-on”. But I seemed to over-cook it and it was bent the other way (quite a lot), so I set too on the other side, to bring it back, but it just seemed to get worse and worse (starting to feel stressed now!)… after a few more attempts I realised what had happened was that I had managed to break one of the loctite joints and the error I was trying to correct be peening web #1 was actually as a result of a joint on web #3 moving – by the time I realised this I was in a right two-and-eight!

Not looking good

It was now clear we were in serious trouble, so I heated the whole thing up until the Loctite let go, pull the pins from the webs, clean everything up and start again.

I really thought this time it would go better, but no, runnout on the journals when spun between centres was about 20-thou, and while you could get the crank into the bearings it was stiff to turn, and I figured it would just murder them over time, so it’s time to give up!

and the next post explains how we progressed… (let’s try that again)

Piston Valve

Over the last few weeks I have been progressing with the HP valve assembly – a greenly long-type piston valve (apparently).

Because the Harrison is showing it’s age (70) the wear on the bed sometimes leads to

starting on the HP valve liner

trouble you can’t manage… most notably tapers everywhere! The HP Valve chest had to be bored on the lathe, as it was too small/long to be done on the Vertical Mill – as a result it had a taper on the bore of about 3thou. The piston valve liner therefore needed to be similarly tapered, and it was not possible to try the chest on the liner while being constructed – so this just makes it harder.

Machining the Liner

The liner is meant to be a push fit into the valve chest, and my machinery handbook suggests that this meant there needed to be about a 1thou clearance – all a bit tight, but with carefull use of a set of inside micrometers my friend Juliet donated to me (her father’s) and a lot of carefull miking it all came good! The picture above shows the first facing cuts on the liner casting in progress.

The first stage is to cut a small part of the bore at each end, and press in a centre at one end – I happened to have a bit of cast iron bar which was a nice fit – and by the three-jaw (with inside jaws at the other) and then the outside of the liner can be machined. This was carefully made with a taper to match the liner, but you can’t check the fit till you finish, as dismounting it, or removing the centre, would disturb the allignment. Later when the outside was finished I was very pleased to find that it slid in with the last 1-2 inches needing a push.

At the same setting I cut the port grooves. (One of the really pleasant things about the Harrison is that it is so ridgid you can plunge a tipped parting tool in a near full speed without a jot of chatter or other pain). However, it was noticable that the finish I was able to get from the tool on this was no-where near as nice as I had achieved on the cylinders, some difference in the iron I imagine.

Ports

Once the outside was ready I transfered the liner to the mill and drilled the port holes using a rotary table and the DRO (to ensure perfect positioning)..

Because of the limited vertical clearance I was worried that I would not have room to get the drill bit in, and guessed that I would have to use a centre drill and then finish the job on drilling machine – but for once the gods smiled and I realised that two of the standard sized centre drills were the size I needed – so just drilled straight thru 🙂

Once this was done then milling the exhaust ports was a simple slot-drill excercise.

Boring the Inside

Now we are on the home stretch, a simple boring job – first make a plug gauge,  but again the dreaded  the tapers bite – and I discover the the inner end is about 4 thou larger!!!

The book suggested using the plug gauge to lap out any such problems, but of course it is now too damb small!! So I set to with my trusty sykes-pickavance cylinder hone (three wobbly slip-stones in a hand drill), and carefully reduced the error to about 2 thou, and decided that could be accomodated by a tapered valve and it’s rings… time will tell, but I am starting the “buy Malcolm a newer lathe fund!”.

(yes I know you can see the whitness marks from the chuck jaws, but this surface is the push fit into the liner (secured with Locktite Structural Adhesive) so I am guessing it will not be a problem, and you can also see the less-than-perfect bore, but the hone cleaned this up a lot).

The Valve

The casting was one of the few parts which had been machined, and I would guess was the point at which the builder threw in the hand towel, as the cored recesses were not well aligned with the outside, and I think they took a starting cut over the outside, aligning things at one end, not realising the recess at the other was so far out that they then had a “scrap” valve… however my inherent tightness and belief in shrink fits took charge! so I cleaned up the errent recess and srunk in a block of cast to provide the meat to effect a repair.

The rest of the job was a nice turning and parting excercise. The final sizing and ring groves being turned with the valve mounted on its spindle (as a mandrel) in the (newly made) collet chuck – buy yourself a set of ER collets NOW… I can’t believe how many years I delayed that purchase, and just how good they are (and mine were second hand of ebay!)

It’s a funny thing, throughout my life I have read constant warnings about breaking piston rings, and the man who started this engine had even got spares for the 6 on the piston valve – now I know I am going to regret saying this – but I have never broken one, not even the ones on the Edgar Westbury Seal I am making (5/8″ bore)…

Fitting the Liner

I used locktite structural adhesive (the yellow stuff) to fit this, I am not sure about it’s high-temperature performance, but the recommended Slow Areldite is much the same, so I am hoping. I had left the liner a few thou long to match the cylinder block, which will get a final skim over the top, and crossing my fingers, just pressed it home with the help of a G-clamp and a pair of plates – and it looks OK… Job Done!

Boring Bar Blues

preparing to bore the HP cylinder

preparing to bore the HP cylinder

It seems I am getting lax at downloading the pictures from the new Nokia N8 to update the blog, so here is a quick summary of the progress being made.
I have a couple of pictures here of boring the highpressure cylinder and pistonvalve chest – the problem with these two is that they are too small and long to allow me to get the boaring head in – and I have an inbuilt hatred of between centre booring bars – so thy had to be bored with a long boring tool… (here’s a video) This is right at the start of the boring process, and the cored hole in the casting is somewhat off centre, so at this point it all looks a bit wobbly and we have an interuppted cut in progress.

This approach to machining has resulted in the bores being a bit tapered (wear in the 60-year-old harrison’s bed 😦 ). It looks like they might be about 2thou off parallel, so I will need to pay some attention to this. For the piston valve I can probably make the liner match – for the cylinder perhaps some AGRESSIVE honing might help… we’ll see.