Member postings for Bob Wild

I said that I was a novice ! Made a lovely hardwood former to shape the lower tapered part of the boiler. Sawed off the excess overlap after bending and silver soldered the join after a fashion. Drilled two sets of 36 rivet holes at a 6 degree angle by tilting the head. Being a novice I completely forgot that the burrs from the drilled holes would dig into the wood. No amount of (gentle) tapping or prising would persuade the ring to separate from the former !!!

So as a last resort I decided to (hack) machine away as much wood from the former as I could to expose one set of rivet holes

The former is actually made from two pieces of 25 mm beach screwed together. So I figured that if I drilled four clearance holes in one piece and bashed four screws it was worth giving it a try to separate the two pieces to improve my chance of getting the ring off the other piece of wood.

And bingo, it worked. And finally the ring came off the former in one piece. Got to fettle it up and figure a way of riveting it to its mounting plate. That will be in a while since SWMBO wants to go off in our caravan for a while.

But it gives me an opportunity to think about how to fix those rivets. My inclination is to glue the lower ones in place since they are purely cosmetic and don’t hold anything. Especially as the annealed copper scratches even when you look at it.

When it comes to the upper mounting plate I thought about tapping the end of the rivet and bolting the ring to its mounting plate. The rivets are 3/32 dia which is only a nat’s whisker over 8ba. So a little skim on the end of the rivet would make this possible which would avoid any bashing to form a proper rivet. Any thoughts from you experts would be most appreciated.

Bob

At last. Can start to get moving on from that blooming engine. So started on the boiler. Some new techniques for me on this part, but very pleased with the result:

Thanks Werner - I’ve added more oil to the valve chamber.
Noel - done some tests at low pressure. Giving a nudge at dead centre I notice that it goes with a much bigger thump at the top compared with the bottom. That suggests to me that the slide valve is slightly offset and needs centralising. I’ll try and improve this, not sure how. Unfortunately not for a while since Mrs W wants me to take her for a break in our caravan. Grrrrr

Bob

Edited By Bob Wild on 27/06/2021 22:55:01

Edited By Bob Wild on 27/06/2021 23:01:27

Good fun to watch too 👍

Found this on my travels, but a bit older than mine:

Hi Werner. Thanks for your reply - it’s always interesting to hear of other people’s experiences. As I mentioned it took me ages to get everything lined up. I did make all the clearance holes wherever I could to be much larger than they should have been and I tightened them up progressively to get the smoothest fit. So, I am going to have another go at prefabricating the crankshaft and will hope for the best. Anyway, I will have a little time to ponder as my dear wife wants me to take her in our caravan for a few weeks on one of our rare visits to the south of England!!!!

Bob

Edited By Bob Wild on 23/05/2021 23:07:19

Still struggling on. Finally got the engine assembled and after ages finding the tight spots (I now have a new meaning to the term “Quantitative Easing) it now turned over relatively smoothly. First run on air would not rotate, but there was a significant downward thrust at times. I had followed the dimensions in the book for the valve mechanism, which occurred to me was a metric conversion from the original imperial drawings. Upon reflection it occurred to me that there may be minor differences. So I reduced the width of the slide valve by ten thou each side. After a lot of fiddling with the timing - bingo, it run. It needed twenty psi to get it started, but it ran like the clappers and nearly shook itself off the bench! And then disaster. The crankshaft had come loose. I had prefabricated it, cross pinned it and loctited it, but two of the joints had come loose. So off to make another. I don’t think I can retrieve it so it’s a matter of staring from scratch. I’m wondering whether to persevere with loctite or to try and silver solder it or even soft solder it. I’m a bit concerned that if I use solder that it will distort. Help please, this is driving me mad!!!!!

Bob

Can thoroughly recommend Derek Harper Foundries in Bradford (UK). They cast non-ferrous metals. I gave them a couple of patterns for my Fire King, and they were ready in three days. Quality looks fine; no apparent blowholes or inclusions. Reasonable price (to me) and a most helpful guy, who even replied to my email on a Sunday afternoon. Very impressed.!

Bob

Thanks chaps for all your useful comments, and sorry about the delay in replying. SWMBO insisted on using the relaxing of lockdown to use the opportunity to go off in our caravan for a much needed break. Anyway, I have made a strategic decision which may not meet with the approval of some. This model will only run on air. Firstly, it makes the construction simpler and secondly, it means that I can show it in my display cabinet along with my other models. As I said earlier, if it was good enough for Cherry Hill then it’s good enough for me.

Bob

Here's a drawing of the modified boiler, taking account the various suggestions I've received. The changes are :

1. I have done away with the outer conical section and extended the boiler outer shell to the bottom of the boiler.
2. The twelve curved fire tubes have been replaced by 2 pairs of straight tubes fitted directly across the firebox, each pair being at 90 deg to the other.
3. The firebox inner skirt now meets the outer shell so it may be soldered directly to it.
4. All the rivets have been replaced by dome headed screws fastened to three new rings. These are labelled Top, Middle and Lower Ring. These new rings can be soldered directly to the outer shell, so there will be no holes into the boiler.
5. Question: What about doing away with the top ring and screwing the Boiler Outer Shell and Top Dome directly? There is no water or steam in this region only the exhaust gases.

Any thoughts about these changes? One immediate benefit that I can see is that I only need one casting. Although the foundry I found quoted quite a reasonable price and fairly quick delivery. Apparently he gets quite a few similar requests from model locomotive builders. I am thinking that I may need to use different melting point solders and build it in stages. Any advice would be most appreciated.

By the way the boiler is 4in dia and overall height is 10 in.

Bob

Edited By Bob Wild on 08/04/2021 17:10:37

Brilliant, I'll be watching your progress avidly.

Bob

Thanks Nigel. More good ideas.
Bob

Thanks Jason, this is all getting very interesting. I like the idea of a separate ring to take the rivets. In fact I have some round headed ba screws with no slot. I could use these and they would look just like rivets.

I can certainly increase the height of the shell to increase the separation of the top dome and smokebox ring.

I am considering doing away with the cone shape on the outer lower ring which would mean I could just extend the whole outer shell down to the bottom of the boiler. And as you suggest I could use an L shaped ring to hold some dummy rivets.

If I increase the angle of the inner cone I can make it butt join directly with the outer shell. I don't mind not having any rivets at the base since this is right at the bottom of the boiler and right out of sight.

I can get rid of the 12 bent fire tubes and replace them with a couple of pairs horizontally across the top of the fire box.

Not sure if Cherry Hill would approve of all these changes, but what the heck. I am starting to draw this out (slowly).

Incidentally I have spoken with Gégé and he tells me he did use a gas burner in the end. I presume this also will give a higher heat output than the spirit version. He also said he made the conical parts by wrapping a sheet round a former and the soldering the seam. I would have preferred to use a tube the same diameter as the small end, and then try and swage it up a former. Any thoughts?

Bob

Chaps, thanks for so many constructive and detailed points. I think the general consensus is that it could be simplified' I have had a few thoughts about this and will post a sketch shortly. I do have a few specific queries:

Nigel - what is a fire hole tube? The design shows a spirit burner mounted directly below the boiler. A bit more iinfo on the spear point would help.

Jason - How do you fasten dummy rivets to the copper tube. I like this idea.

Keith - I looked up "Keith Hale" on Amazon books,

I have been in touch with Gege in France who has bee most helpful, and also Werner in Germany.

Having read up about the Fire King it seems that the boiler was not lagged. Another interesting fact is that the total time for working pressure to get underway was about 6 minutes!

Bob

Edited By JasonB on 31/03/2021 07:08:35

Nearly finished the engine, and started to think about the boiler. So I posted this thread to aim at a wider audience, asking for advice on what, to me, looks like a daunting part of the build:

https://www.model-engineer.co.uk/forums/postings.asp?th=172017

Looking for any helpful advice.

Bob

Edited By Bob Wild on 28/03/2021 23:14:22

Here is an assembly drawing for my boiler:

There are many features which frighten me:

1. All the various rings are supposed to be rivetted. Surely I must solder all the parts to make them steam tight?
2. The rings are supposed to be copper, but I can't find any supplier of solid material that size (approx 4in dia). But I have found a foundry that can cast them in brass. Would that material be OK, if the price is right?
3. What is the best way to make the conical inner part. Should I start with a piece of tube with the same diameter as the smaller section and bash it up a former. Or should I start with a tube the same as the larger diameter and try to spin it down? Or should I even prefabricate it from sheet wrapped round a former and soldered at the seam?
4. There is a pipe in the centre called the "Steam Supply Pipe" (is this a superheater pipe?) which has a 180 deg bend. This pipe is 6mm OD with a 4mm inside radius. How on earth can you bend this?
5. Finally, and this is the scary bit, how am I going to solder it all together? Do I need different melting point silver solder, and in what order should I try to assemble it?
6. I've just read a biography of Cherry Hill in which it explains that all her beautiful models were built to run on air only. If that was good enough for her, then it could be for me as well. In which case I could leave out most of the internal parts and simplify things enormously, let alone worry about making it steam tight.

Any advice from those more experienced than me would be most appreciated.

Bob

Finally got all the parts for the engine finished. First the crossheads:

and with the pistons and crankshaft:

and to show my new toy milling machine, working on the eccentric rods:

and finally the valve chest and other bits:

Spent ages lining everything up and getting things to move almost freely. I've got a way of mounting the assembly on the lathe so I can then try and run it in and get it rotating smoothly.

Thanks chaps for all your helpful and interesting comments. They certainly have given me something to think about.
I understand that the purpose of lubrication is to reduce friction and reduce wear, which is why I wondered if running in oil had some extra ingredient. Perhaps I should have included a bit more info in my original post. I am most concerned about the three crankshaft bearings. After some considerable effort lining them up I got them to the state where you could rotate the crank by hand, but it would not spin freely. I left it running at about 500 rpm for 4 hours but that didn’t make any significant difference. Perhaps I am asking too much. I do have some grinding paste and was wondering about lapping in the bearings with a dummy shaft. Any thoughts?

Bob

Slowly getting to the point of finishing the engine for my Merryweather Fire King. I have read that it needs running in with a special running-in oil. I cursory search reveals that such products do exist, but they seam to be aimed at cars, and come in 5 litre containers. So, what is this oil, and can I get just a cupful ?

Bob