7.25 inch gauge Milner Hunslet

[terrier060]

Well gentlemen and ladies - it had to happen! I have owned my Myford Super Seven lathe for 50 years and used it most days without doing any damage to it other than wear and tear. Then yesterday I was happily machining the parts for my regulator and came to cutting the 32 TPI thread on the regulator spindle. Normally I would be holding the work in the Burnerd Griptrue chuck (one I got as long ago as my apprenticeship there in Winchester), but for accuracy I was using a collet in the mandrel and quite forgot how close I was working to the headstock. There was an almighty crunch (back gear engaged) and the whole machine locked up and I had to 'persuade' the saddle to disengage from the leadscrew. Luckily the Tufnol gear in the reversing tumbler took the full force and the teeth stripped thus saving the cast-iron teeth and other parts.

Myford came to the rescue with a new tumbler gear, which should arrive soon. There is no clear method described as to how to fit the new tumbler, as the spigot is a press-fit in the casting. A Myford engineer said it was the larger bush seen in the photo that has to be pressed out, not the smaller piece in the centre. I gather there is an oil hole which has to line up with the outer bush that should not be disturbed. I any of you have had to replace a tumbler gear, your experiences would be appreciated.

Meanwhile the regulator is waiting for its stainless spring.

Myford Tumbler Reverse by ed cloutman, on Flickr

[terrier060]

Still waiting for the new tumbler gear to arrive (tomorrow!). I made a jig for the PTFE washer where the regulator fits into the backhead as suggested by Roger. The jig was made in the Tormach and is very accurate - great for positioning the holes. The front piece was parted off in the lathe and the faces machined flat. Three of the holes were then tapped to take the three securing bolts. Once sandwiched, the PTFE was very easy to machine.

PTFE washer by ed cloutman, on Flickr

[terrier060]

Lathe all back together now. To replace the tumbler gear you have to push out the spigot (pin) which is the larger piece you can see in the previous images directly in contact with the casting. You need to make or find a suitable punch - I used an old piece of bronze that I was going to make a bearing out of (see insert). I put the broken wheel on open vice jaws and drove the pin out. Make sure the punch does not hit the protruding centre part if the pin. It comes out quite easily with minimum force.

The new wheel is then placed on the pin and the pin pushed back keeping it square with the casting and leaving a small amount of end float on the wheel.

NOTE! The two tumbler wheels are different! One has 30 teeth, the other 28. Make sure you count the teeth and replace the correct one.

My lathe must be 50 years old, and other than losing a bit of it's grey paint in places it is still in pretty good shape. I must say I never liked the green colour scheme or the cheap saddle handwheel that replaced the cast one.

Tumbler wheel replacement by ed cloutman, on Flickr

[mbrown]

You certainly keep your lathe in good condition!

Malcolm

[terrier060]

Thanks Malcolm - yes Myford did a very good job with the paintwork - you have to be really rough to crack it. They seem to have built up the base with something like gesso? It really has been used pretty well every day, certainly since 1995 when I left West Dean College as a qualified antiquarian horologist, and took up antique clock restoration full time. The bed is a little worn, but it can still turn out accurate work - you just have to adapt to it's foibles! I am also fortunate in that my workshop is centrally heated, and I think that makes a great difference with no condensation to contend with.

You will notice the damaged paintwork on the casting a few images above. That is where the pin which locks the mandrel to assist the removal of chucks etc bangs against the casting when it is pulled out! Shame on Myford for not limiting it's travel!

[terrier060]

Having got the lathe working again I was able to machine the 32 pitch thread on the regulator spindle. The final assembly is shown above and the internal parts below.

As there is no means of oiling the disc, and if the friction is high and the regulator becomes stiff to move, I may consider putting a PTFE face on the moving part.

The final test will be when I get steam up. Fingers crossed!

Regulator assembly by ed cloutman, on Flickr

[terrier060]

Machining the 5/16x32TPI thread on the stainless regulator spindle, using the Myford with it's new Tufnol tumbler gear wheel. The regulator is now installed in the loco, but the tank and pipework need connecting before testing on Saturday!

Machining the 32TPI thread by ed cloutman, on Flickr

[Cro]

Hi Ed,

Sorry I have just caught up on this and seen your PTFE Washer - I had looked at doing something similar on the 9f regulator but when chatting to a friend who had already tried this he advised it doesn't work as a washer due to its expansion and contraction over time the sealing joint essentially becomes loose. Would it be possible to make your washer thicker in bronze with a large ID and fit an O-ring between the bore of regulator and ID of washer. The washer can then be just thick enough to allow compression of the O-ring when you have metal to metal contact.

Just a thought,
Adam

[Roger]

Dec 10, 2021 7:50:56 GMT Cro said:

Hi Ed,

Sorry I have just caught up on this and seen your PTFE Washer - I had looked at doing something similar on the 9f regulator but when chatting to a friend who had already tried this he advised it doesn't work as a washer due to its expansion and contraction over time the sealing joint essentially becomes loose. Would it be possible to make your washer thicker in bronze with a large ID and fit an O-ring between the bore of regulator and ID of washer. The washer can then be just thick enough to allow compression of the O-ring when you have metal to metal contact.

Just a thought,
Adam

Hi Adam,
I'm curious to know the design that your friend used. I've got three large pins that engage with the thick valve 'washer', and was wondering if the issue was with the amount of drive area that was being used to move the valve.

[Cro]

I don't know, it was when I showed him a simple washed I made up for the wet header on the 9f and he pointed it out to me after his experience. This was sandwiched between two faces when done up tight but if it was a valve face driven with a spring holding the faces together it won't be a problem as the spring will account for the changing thickness during expansion/contraction.

Sorry can't be more useful.

Adam

[terrier060]

Hi Adam
There always was a PTFE washer on the backhead, though a much thinner one than the one I have just made. Not only did the original seal very well, when I came to remove the regulator the nuts were only pinched up and the regulator boss came away cleanly needing no persuasion, and leaving clean mating faces. It never leaked, running at 100 psi. The new washer is a lot thicker, so we shall have to see how it performs. I will keep you posted, as all being well I should have he loco back together tomorrow and may have time to steam it. I have not used PTFE on the valve face however. That is bronze to bronze, with a stainless spring holding the moving disc on to the fixed face until pressure builds up in the boiler.

Incidentally, during the replacement of the original ball valve regulator, I removed and replaced the regulator boss using the same PTFE washer and it still sealed perfectly.

My main reason for changing to a disc is that it is easier to remove, fixed much more securely than the original, which relied on the main steam pipe and the regulator rod to locate it and was not firmly held at all, and was very fierce and tended to be either fully on or off.  Hopefully the new ports should give much smoother operation - we shall see.

[Roger]

Seeing what you've done with the gasket, I'm wondering if I should bin my cylinder gaskets and make some PTFE ones

[terrier060]

I just contacted Royston, who put the original regulator in the boiler and he said it was 'Expanded' PTFE which is very expensive compared with the standard stuff. I think he said he thought it was 1.5mm and he did have to screw it down several times to keep it steamtight. I measured the washer when I took it out and it was 0.8mm so it has compressed quite a lot. However, it never leaked with me, even when I re-used it and I did not have to screw up the nuts very tightly. The great advantage of PTFE is that it comes away cleanly and the seal breaks without any hassle.

I have just had the regulator out again and I will try putting it back a third time and see if it is still steamtight!

[terrier060]

Stainless disc by ed cloutman, on Flickr

I promised an update on the Hunslet disc regulator. The first attempt it leaked past when shut and I found that the disc was too tight on the square on the valve rod so had to loosen it.

I lapped in the valves and it worked perfectly, with no leakage and very smooth operation - not at all fierce like the ball valve, or as stiff. I had a smile on my face and was just beginning to enjoy myself, but then after about half an hour it got stiffer to operate and finally started blowing past again when shut.

I phoned my guru when I got home and Roger said what materials did I use? And I replied - well I only had one piece of brass large enough. I should have known better and used two dissimilar metals. It is a basic no-no to use similar materials on parts that rub together - something my father taught me 60 years ago and I had forgotten in my old age!

So I machined a new disc on the Tormach in some free-cutting stainless I happened to have around. It took 11 hours, but the cutter stayed sharp and the finish is excellent as you can see. The Chinese PCB drills worked really well when I used them to pre-drill the small ends of the curved slots. I expected them to break and left the machine to itself and went off to watch a film on TV. To my surprise both holes were neatly drilled when I checked!


For those of you living near Cardiff, the stainless came from C G Rees near Gabalfa Roundabout, sadly no longer there. The bars used to be painted with yellow ends. What a treasure trove it was for model engineers, and although I think he used to get fed up with us, always asking for small pieces, I always found the place had a cheerful atmosphere and was always helpful, often cutting off small pieces if there was no suitable off-cut! I have a few pieces left. All my con rods, coupling rods and much of the valve gear are made of this stuff, which is so nice to machine and cleans up really well.

HAPPY CHRISTMAS TO ALL! And let's hope the New Year brings back normality!

[penybontshed]

Lets hope the next steaming is successful Ed, and we can all enjoy the New Year!

[terrier060]

Indeed I fully agree - the poor boiler has had quite a bashing - all that gasket making - though I swear by that Loctite liquid gasket. It is wonderful stuff, though expensive, when you have 16 studs to deal with! I have replaced the thick PTFE gasket with a conventional one made of car gasket material and coated each side with a very thin layer of white Teflon grease. It sealed perfectly. I have yet to take the regulator out and see if the gasket comes away easily.

[terrier060]

The regulator is out again, and the gaskets came away without damage and did not stick. The large dome liquid gasket also came away without trouble, but I was glad of the three flange releasing screws. I just tightened them down after I had loosened the 16 bolts and the dome cover came away cleanly. I recommend doing this with a large flange as it makes the job so easy without resorting to a chisel and mallet!

The disc valve was scored so I hope the stainless replacement will do the trick.

[terrier060]

New polished valve.

New Polished Valve by ed cloutman, on Flickr

[terrier060]

So far so good. It has had one three hour run with the new stainless valve and behaved well. I shall not be happy until it has run a few more times without fault.
Then I can get on and finish the tender.

[terrier060]

With a lot of help from Roger, I am having a go at adapting his design to my Hunslet using the same outer dimensions to fit the existing pipework. The design fits surprisingly well, but whether it will work is quite anothe matter. I do not have Roger's skill - this is watchmaking and I am a clockmaker! It is needlework, even on a Myford, and I think Roger's lathe is a lot larger.

So far I have made the flat valve that sits in the overflow. I used my rotary table under my mill and hand-drilled using a PCB drill to start and then a normal 1/16th inch drill to finish.  The viton rings allow the one-piece cone to be adjusted towards the steam cone by turning the delivery nut and squeezing the union against the end of the cone.  It remains to be seen whether it will leak underpressue, and if so I may have to fit a soft washer at the union joint.

Two Cone Injector 01 by ed cloutman, on Flickr



Injector valve by ed cloutman, on Flickr