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rpbidgood

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Hi everyone. This is my first post and my first build, I hope I get both right. I bought a lathe a few years ago, but employed it largely making pieces for my other main hobby - model boats. I made several cannons, drive couplings, bushes etc., but nothing that actually "worked". I have been "lurking"on this site for some time now, but the postings for Cracker; Nina; Idris have inspired me to try and make something that really does something. I have been working on a scaled up (45mm) Cracker (and the house) for about 4 weeks and have become so absorbed that I even bought a milling machine last week - what a wonderful machine! I wish I'd had it at the start, my side frames would have been much better (I'm not very good at filing). The wheels are made from some sort of duralumin type alloy that was lying around my shed. It's has a sort of greasy feel when being turned and produces long bits of curly swarf. The wheel bosses are large because I was worried that the soft alloy would strip if I screwed the wheels to the axles too tightly. I have since acquired a chunk of 'meehanite'? and have turned one wheel with a smaller boss as an exercise
Anyway, a month and a large rubble sack of swarf later I have reached the position shown in the photographs. Next I have to make the cylinder and piston, an exciting but slightly daunting prospect.


Questions:
(i) If I use a template to drill the exhaust and inlet holes on the standard, what angle before or after TDC should I go for. Common sense seems to suggest that the steam should be admitted almost immediately after TDC and the exhaust just after the bottom of the piston stroke, but could last for the whole upward stroke (I don't need reverse on this) - but common sense has let me down before.

(ii) I was trying to apply a nice surface finish on the standard with a fly cutter, but ended up with something that resembled a ploughed field -the brass seemed almost melted. I wasn't taking a deep cut, was the speed too high? the fly cutter is new, so should be sharp. I managed to redeem the piece with some judicious sanding, but it doesn't bode well for the piston.

I attach some pictures of the progress to date.



Standard.jpg


Meehanite wheel.jpg


Cracker buffers.jpg


Cracker 4.jpg
 

GordTopps

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Hi rpbidgood & wEc1 to our forum.

No doubt some knowlegable folk will chirp in with your questions

Regards from Sunny ( and wet) Spain
 

Tin Falcon

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First of all welcome to the board. and thanks for tel us a bit about yourself and interest in this hobby.
I have built several Oscillators that all run well I have always layed out the hole according to print.
Also perfect alignment is not needed the design is pretty forgiving. as for how to make a drill jig /template.
IIRC A couple of the Elmers engines plans explain a jig as does the KN Harris book .
I will try to get you a specific link or reference when I have time. Or someone else may help.
Tin
 

zeeprogrammer

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Welcome to the forum rpbidgood.
I can't help with the questions (I've just started out).
There's been a Cracker or two on the forum and I'm sure someone will pop in.
I have an interested in locos too so I'm looking forward to seeing your progress.
Have fun!
 

kustomkb

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Welcome, and very nice work!

Does your fly cutter look something like this?



You say it was new, does that mean it is a brazed carbide tip? If it is a high speed steel, (or carbide), relief angles will have a lot to do with its performance. Did it squeal while you were cutting? Also a thin piece will tend to chatter.
 

shred

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The Cracker motor is a simple oscillator-- I built mine to the plans and stuck the holes at the 'end' of the cylinder travel (actually I missed with the exhaust hole-- I had to enlarge it so they'd line up). Might not be the very best use of steam, but hey, it's a Cracker, not a super-heated piston-valve multi-cylinder jobbie :D

 

rpbidgood

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Kevin,

Thanks for your interest.

The cutter is very similar to the one in the picture - I think it's hss. (I attach a pic.) It didn't make too much noise, but the brass seemed to have 'melted" (exaggeration) and formed a 1/8" lip over the edges. Strangely enough, I used it again to form the final, flat surfaces on the cylinder and it behaved impeccably. Perhaps my technique is improving?

If truth were told, I was a little nervous about the boring operation, and it did look a bit agricultural initially, but after playing around with some different tools I managed to get it pleasantly smooth. Big sigh of relief. I'll have to hone it next.

If it is of any interest, I attach a picture of a wiggler (or is it a wobbler?) that I made to centre the cylinder. It uses a swivel joint from a model car track rod end. The spring maintains pressure on the job and the neoprene (fuel) tubing keeps everything in place.

Wasn't the 'Wiggler' Batman's arch enemy. Even I wouldn't be frightened of the 'Wobbler!'



FlyCutter.jpg


CylinderBrass.jpg


WigglerC:up.jpg
 

xo18thfa

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Alright, a Cracker. It's a great machine. Yours is coming along nice.
 

GWRdriver

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rpbidgood said:
. . . employed it largely making pieces for my other main hobby - model boats.
Welcome rpbidgood,
What kind of model boats? I also have an interest in model boats, specifically wooden boats that will need a steam power plant. Also, I would ask you where you are located as it's eventually helpful to know where one is loacted, but the "bits of curly swarf" told me what I need to know.
 

rpbidgood

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Hi GWRdriver,

The last boat was a civil war (American) paddle steamer - Coeur de Lion, but I have a varied interest. I have an unstarted 'kit' of the Disney Nautilus which will probably be my next project, once I finish this Cracker.

I always wanted to use steam power in my boats, but was put off by the price, and I didn't think I was capable of making the steam plant myself. This site has given inspiration. Who knows now?

[u]Cracker update[/u]

Tried drilling/tapping the cylinder to take the trunnion pin. I had grave reservations about my ability to drill/tap an accurate hole just a couple of mm deep. I failed dismally. How do you drill a 3 mm hole perhaps 0.1" deep and put a thread on it? (sorry about the mix of imperial and metric).

Hours of work down the drain (I am new to this and a slow worker). I'm going up the shed (workshop) to try plan B.
 

rpbidgood

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Commitments have prevented me working on this for a few months, but I have now managed to progress a little. Last week I finished the engine and attached it to my airbrush compressor. More in hope than expectation I flicked the flywheel and the little beauty started running! I've made boats, planes, helicopters, and all give a sense of satisfaction when they do what they're supposed to, but I don't think any of those compares to pleasure I got when my engine started puttering away by itself. Wife bemused by my smug expression. It needed about 15 psi initially, but soon was ticking over around 2 psi (if the gauge is accurate). Next step was to connect the drive chain - This worried me a little - I have used no gears and have a direct chain dive to both axles (14:18 tooth or 1:1.3 approx.) and it's been a long time since I "played" with meccano. Would there be too much friction? - but no, the wheels turned nicely, and after a few minutes the stiffness left and the engine ticked over again about 2psi - I can just about keep it going for a few seconds on breath power - wife impressed (I think).
I don't want to appear sycophantic, but it is the wonderful models/articles/ideas on this site that inspired me to have a go.

Cracker drive chain.jpg
 

rpbidgood

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Inspired by the progress on the engine I decided to tackle the boiler. The end plates were screwed to a wooden block and turned in a 4 jaw chuck - the method described by Bob Sorenson in the excellent account of his building of "Nina". The attached photo shows the unsoldered boiler so far - I will have to summon up the sinews before I start silver soldering.
ps. I don't think I'm going to paint this loco, so I'm not sure I can live with that shiny smoke box door.
Attached is the safety valve - it seems to work well on compressed air, but looks a little small to me. I think I'll make a bigger one, but first the funnel/stack. I wanted a tall pipe on a "tailored" base. I found an old piece of brass and milled the curvy bit on the bottom, again pinching Bob"s idea. Popped it on the boiler - it's too big. It looks silly. And since I have bored it out I can't turn it down any smaller. The milling took a long time. Misery. Back to the drawing board.
Question I am thinking ahead, but what sort of flame do we aim for on the burner? The hotter, blue flame or the gentler, but dirtier luminous flame?

Keith.


Safety valve.jpg


Boiler:Smokebox Door.jpg


Funnel.jpg
 

compspecial

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Congratulations RP! and what's wrong with a "cracker anyway?" ;)Welcome RP
stew
 

shred

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We're nowhere near the Cracker-limit ;)

Looks great. Running on 2 PSI is very good-- should be relatively easy to get going on steam then.

I think I have a bit on making the stack flanges for mine-- I used a boring head on the mill to cut the curvature on the end which wasn't so bad.

For flames, you want the roaring blue blowtorch one. My burner will only do that inside the flue-- outside it's quite a bit less active.


 

Peter.

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That is an interesting-looking measuring tool in the 'safety valve' pic Keith. Does it have a specific purpose?
 

BMyers

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There is always room for more crackers. I enjoy seeing how everyone's version is different and interesting. Maybe it should be mandatory that all members build a cracker.
 

rpbidgood

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Hi Peter.
It is a sort of neolithic, vernier callipers.The 'front' side is just a simple ruler, but the reverse side, pictured, has a vernier scale and shows the readings given on this instrument and on a digital callipers. The modern instrument is obviously easier to use, but the older one fits nicely in a pocket and its use amazes youngsters who've never heard of a vernier scale. It is a beautifully made instrument, and even though it is probably at least 50 years old, the brass slider has little or no free play but still moves easily.
I also attach a picture of the Mark II funnel.


Vernier.jpg


Funnel.jpg
 

Gedeon Spilett

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Hi,
Nice work with your cracker!
I have just finished three of them, and after unsuccessful attempts to drill holes under 0.2 mm for the burner's jet, I finally choose to install a burner saved from those cheap lighter-style small butane torch with success. Although it takes ages to get the water boiling, once hot, the loco runs for 25 minutes pulling two coaches at a lively pace. If you take the larger burner from a pencil torch, she runs now fiercely with many coaches behind (I have tested up to 8). in the boiler tube, both type of burner are not roaring as usual but whistling at very high pitch while burning, and this is useful to know if everything is going right, contrary to silent types of burner.
I have to give them a coat of paint, not my favourite task.
There is always room for many more crackers!
Zephyrin
 

bearcar1

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RP, that is some very clean looking work you have been doing. I too have one of those 'antiquated' brass caliper arrangements and use it some times just for the nostalgic bit of it. It was my Grandfather's and I cherish it, and by putting it to work once in a while, I feel like I am paying him tribute. Anyway, I notice in that last shot, you seem to have a silver colored smoke box door affixed to the front of the boiler in lieu of the usual copper cap arrangement. Can you elaborate a bit on it please. It seems to have a pleasant convex shape to it and I'm curious as to how it will finally be held in place. Keep up the good work and thanks for sharing.

BC1
Jim
 
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