Member postings for Martin Johnson 1

Duncan, I know you will know this but for the benefit of others who might be looking at gas firing in the larger scales there are a few obstacles to overcome:

1. You don't get the full benefit of the "calorific value". That is because CV is based on cooling all the products to ambient, which would condense out the water vapour and reclaim the latent heat. Gases like propane and butane have roughly 3 times more hydrogen by weight than "coal", so that loss of CV becomes a lot more important. That is why we all have condensing boilers at home. (Actually I have a heat pump, but thats another story)
2. Burning a nice blue flame is efficient combustion, but it doesn't radiate so the firebox surfaces are not working as they would with nice bright flames and a yellow hot bed of carbon. That is quite a loss in heat transfer.
3. Tubes in coal burning models are actually sized to prevent blockage with ash etc. (No I don't believe Jim Ewins or Keiller when it comes to boiler tubes!) So for an optimum gas fired boiler you would really want smaller tubes and more of them.
4. Coal is very forgiving of air control, whereas with gas or oil you need more active control of the air. I think a bank of Marty burners are likely to be running with significant excess air drawn up between the burners, which is dropping the combustion gas temperature and making for poor heat transfer again. Those of us with silver hair remember the fun and games the Festiniog had when changing to oil firing. So some experimentation with dampers and ashpans is likely to be the order of the day.

That is not to say it won't work and can't be done, but as Harry Wilkes' post shows, it can give performance problems. So I would not want to set too low a design target knowing some of the problems that lay ahead. 40 lbs/sqft/hour is pretty much mid range of IMLECS that I have analysed for 5" gauge engines.

Martin

"Fitting things which are essentially round shapes into a rectangular framework is possibly not the best, Noel's suggestion of a longitudinal tube with transverse slits might well work better. I'm off to ring my tame plumber to get him to recover a central heating burner when he next does a boiler swap."

Thinking back to LBSC's designs for parafin firing, after a venturi it was a longitudinal tube with transverse slits. Substitute gas for vaporised parafjn and thè job is done.

BTW, Duncan I think you are a bit light with 25 lbs/sqft/hr for 5" gauge. 40 would be a better design value based on my analysis of IMLECS.

Martin

Conversely, I saw somebody overturn a trolley load of fizzy drinks cans onto the tarmac outside a supermarket. A whole load of them burst, which was a most impressive, but short lived fountain.

Coclusion - the design safety margin is pretty small.

Martin

This web page shows it has been done, with detail on burner design:

http://ibls.org/mediawiki/index.php?title=Marty_Burners.

Martin

Thanks for all the replies.

To Paul L and Dalboy for links to the UNO lookalike as Circlip notes. Like Circlip I remember the UNO from Drawing Office days and have a fair selection of them in the back of the drawer still. I have tried them on paint and the results were not great, probably need more clearance to function on paint. To be fair, they weren't great on ink either - the Rotring was like waking from a nightmare!

Anyway, the real problem is that I need to do 1/4" lines and while twin lines with a UNO and fill in the gap with a brush is possible it is very slow. Some of my 4" Burrell was done that way with a draughtsman's pen rather than a UNO.

Thanks to KWIL and Paul R for the experience on lining tapes. I might go that route as I do have some curves to do.

I went down the scrap mine last night to see if a Dave Fenner pen might appear and I have found some scrapium that might be suitable.

However, there is a more interesting possibility as a result of this thread, which I will tell you about if it comes to fruition.

Thanks to everybody, an excellent forum as ever,

Martin

Just found it Issue 155 by Dave Fenner.

Still interested to know if anybody other than Dave has made one and how you got on lining.

Martin

Long ago there was an article on making a Beugler pinstripe lookalike published in MEW.

If anybody knows which issue it would save a lot of looking through on my part.

More importantly, has anybody made one and did it work and was it worth the effort?

Failing that has anybody got any foolproof methods of putting 1/4" lines on a stlightly over half size steam lorry. I have been fooling around with a lining brush for a while and we just don't seem to be getting along. It's not her it's me.

Thanks in advance,

Martin

I faced a similar problem at the start of my steam lorry project. Design in the main building blocks as far as you can on paper. Then make a full size cab area mock up in wood and junk. That allows you to sort out seating and get a stab at ergonomics. One observation is that controls like levers and pedals take up more space than you think thay will.

Rest of the design was done by overlaying the design on Fowler origial drawings, scanned to jpeg and scaled to model size.

Hope that helps,

Martin

Thank you, I have learned something today. A very neat solution, beautifully executed.

Martin

The wee jobbers with a ball on each end are just like metal equivalents used by pattern makers for rubbing down leather fillet, or smoothing polyester filler for making fillets. I have a coupleof home made ones for that purpose. I am still pre 3D printing.

Martin

Dell,

Clamp the knurling wheels on to the so they contact at points 7 and 11 o'clock looking from the tailstock. I appreciate your hand problem, so now you feed in on the cross slide. The force from the cross slide is greatly multiplied as the knurl wheels ride up toward the 6 and 12 o'clock points.

Gary,

I just have to ask what nicely knurled widget in photo 3 is for?

Martin

Gritblasting will leave a dull matt grey. If it is display only some thinned rust colour paint would give it that rusty silver sheen of the real thing.

Martin

Edited By Martin Johnson 1 on 10/03/2023 13:00:46

Here is my set up for a steering box screw on a Tom Senior M1 and the usual Taiwan 6" rotary table:

https://www.flickr.com/photos/140734312@N06/37334008234/in/album-72157669955074511/

Sorry dont know how to do a hyperlink.

Martin

Edited By JasonB on 08/03/2023 13:13:53

Lob it in a bucket of diesel. Go on holiday for a fortnight. Try again.

Martin

Well yes but if the design had specified a bit of angle instead of half round, the OP would probably be running the engine in by now. Easy for me to say after 40 years in engineering design, not so easy for a beginner to see.

Martin

Hats off to Jason B for ILLUSTRATING the full chapter and verse.

That said the standard of design on so many "beginner" designs is very poor and turns the project into anything but beginners work. Add to that castings that hardly ever include chucking or clamping pieces or sit down pieces and you have a supply industry doing it's level best to strangle our hobby. It makes me so annoyed.

I think JasonB might feel the same way given his re-working of old designs that are designed to be MADE.

Martin

I bought a Thor No2 for the job and find it a bit too big for most model engineering work. So I agree with Robert that a No1 would suit most folk. Copper / hide heads are the way to go.

Martin

Try a hair dryer to soften the glue a bit, then peel it off slowly pulling the tape back on itself i.e a 180 bend at the peel point.

Martin

A good starting point is 1 diameter in from the edge, so for M10 bolts scribe lines 10 mm from the edges and there you are. A bit more say 1.1 D looks better if washers are used. Basically don't let the corner of a hexagon head be hanging over the edge.

Martin

Ps And how many model designs do you see where the above rule is ignored?

I think you miss my point, Neil. Continuous cast iron bar is cast iron. It is not "less brittle". The data sheet in your second link shows a tensile of 250 which is a good quality iron, but still cast iron. Typical foundry fodder would be around 170.

The reference in your blog to heat treatment for a prolonged period fell out of use a long time ago. True you can get over hard spots to some degree with heat treat, but you wont improve ductility. For that you need SNG.

Martin