Alyn Foundry Nattie

[RayW]

I think I got one hard one and one not quite so bad. These two were machined using the same tool at the same speed.

[vtsteam]

You could try heating the offending web up to cherry red and then putting it into a bucket of wood ashes to cool overnight. This has worked for a number of chilled castings for me.

[RayW]

Thanks for the suggestion. I don't  have access to any wood ashes. Would sand serve the same purpose?

[vtsteam]

You could try it. It's not as good an insulator, and especially not good if damp. But bone dry sand might be sufficient. Ideally it should take several hours to cool a small piece of heated metal. The very slow cooling is what takes the hard chill out of cast iron.

If you know someone with a fireplace, they can save you some wood ashes. A bucket of them is handy to have in the shop for slow cooling anything that needs to be annealed.

I haven't tried this myself but it's possible vermiculite would also work, as long as it is bone dry. Worth a try if that is more available for you.

[RayW]

Thanks for that advice. I have a neighbour who has a wood burning stove, so may have to speak nicely to him. I think I may give up with these two castings though, and resort to steel as Jason did.

Jason, what stroke length did you manage to get? I was aiming for 2 inches, but for the webs to be long enough to bored at 1 inch centres they would foul on the rounded cutout at the back of the main casting. I suppose I could always lower and widen that a bit to clear the webs, or, alternatively, I could go for a shorter stroke of, say, 1 3/4".

[Jasonb]

Ray, if they are that local just ask if they can put the parts into the woodburner for the night.

40mm stroke on mine, you could probably get a bit more if the exhaust holes were drilled towards the head and flap valves secured nearer the crank.

[RayW]

Many thanks Jason. I think I could probably get 45mm or so and that would still give me enough room to shorten the webs sufficiently to clear the bed. Will have a word with my neighbour.

[RayW]

A night in the neighbour's wood burning stove seems to have done the trick and softened the hard spots on the webs, so I should be able to clean them up to finished size now without any further problems. In photo 2, the problem web is the one on the right. As you can see, the end which was glass hard now cuts easily with a file.
Thanks to all  for the advice.

[Alyn Foundry]

Well the gears arrived today but I fear they might be a tad too big for Nattie?

Glad you managed to anneal the crank webs ok Ray, we all just need the flywheels now….

   Graham.

[Jasonb]

Just need to double check but I think I went with MOD 0.5 15T which gives a PCD of 10.56mm and they come with a 3mm bore which is ideal for the side shaft.

https://ghw-modellbau.de/Schraubenrad-Stahl-Modul-05

EDIT Yes the 15T MOD 0.5were the ones that I used

[Alyn Foundry]

Thanks for the link Jason.   

Upon reflection I should have probably chosen a smaller Modulus, I went with MOD 1. I will try to cut one in half but I think the downside will be that the sideshaft ends up being too low at the cylinder head.

   Graham.

[RayW]

Unfortunately, the annealing of the webs did not prove as successful as first thought. Although a bit easier to machine, the outer ends of the offending web are still pretty hard. When turning the outer radii on the lathe with a carbide tipped tool, it cuts a bit better than before, but still leaves a very shiny surface with a poor finish and some brittle chips to the edge. With a lot of grinding, filing and sanding, I have finally got a reasonably satisfactory finish which I can live with.
There is, however, one final hurdle to oversome, namely drilling and reaming the crank pin holes, then reducing the overall length of the webs to clear the back of the bedplate. The bosses also need milling to length. I know, Graham, that you put the crankpin at the big end of the webs. Was this for a particular reason or should it really be at the small end?

That's really annoying about the gears. Does the centre line of the sideshaft need to be in line with the centre line of the shutter, or could the gate on the end of the shutter be longer?

[RayW]

One piece of goods new is that I have received a full refund from the eBay seller for the set of 6 carbide milling cutters, two of which I ruined trying the mill the glass hard crank web. So, I now have four free good ones left which I will try on some less challenging material in the future. Hopefully, I may also be able to touch up the 1/2" one to make it usable.

[Alyn Foundry]

I know, Graham, that you put the crankpin at the big end of the webs. Was this for a particular reason or should it really be at the small end?

That's really annoying about the gears. Does the centre line of the sideshaft need to be in line with the centre line of the shutter, or could the gate on the end of the shutter be longer?

Good morning Ray.

Pleased to read that you got a full refund.   

The main reason that the crankpin is running in the effective “ counterbalance “ area was because I had forgotten about the height of the raceway. I was trying to get as much stroke as possible but discovered, upon assembly that I had overdone it. To get it right the crankpin would have been in a half hole situation. Rather than start from scratch I decided to shorten the stroke by drilling the opposite end to get it running. We were, at that time under a little pressure to get the model finished in time for the event at the Anson.

Needless to say Nattie never ran as intended and, as you know was shelved for nearly 18 years. Had we have got a running engine, at the time a new pair of webs would have been fitted.

Regarding the sideshaft I’m not sure how the Scotch yoke would work if the yoke was offset to the slide? Normally they run through the natural centre line. I’d be inclined to suggest that you follow Jason’s link for the 0.5 MOD gears, recently posted. The ones I have bought, two pairs, were cheaper than a single gear! So no real financial loss.

   Graham.

[RayW]

Now I understand Graham. I am making a fully silver soldered crankshaft and will fit either a bronze or brass big end. I am placing the crank pin in the conventional  location opposite the counterweights.

Please let me know how much I owe you for the gears as one of the sets you ordered was for me and I don't expect you to be out of pocket. As I am using 1/4" silver steel for the crank, I will order Imperial ones to suit.