A Cracker locomotive

[arnoldb]

Shop time has been limited and slow the last couple of weeks, and I suffer from an overload of projects as well...

A while ago, I finished the basic layout for my "garden railway" - well, to give it a better name, it is a stoep (porch) track.  Absolutely MASSIVE  :


When I got the tracks last year, there were no joiners; the supplier in South Africa I ordered the track from excluded the joiners even though I specifically asked for them  , and I ended up making a crude handful using M2 screws:


For now I have the track loop loosely laid and joined together - except for the points and siding which I will make at a later date.
I gave Fred the loco a run around the track, and soon learnt that plastic track ties and his spirit fired pot boiler does not mix well 

So I started on a Cracker locomotive that is a simple build - normally - and have been making a tiny bit of inroads on it.

First up were the gears.  I used the rack "hob" method, and was going to do a full how-to write-up, but things didn't quite work as planned, so for now the how-to is on hold.  I know where the problems raised their heads, and the next time around making gears should be a lot better - and then I can hopefully do a write-up.  I did end with a serviceable set of gears though.  The toolbit to cut the hob, the hob and the gears:


Yesterday I started off on the frames and footplate for the loco - just bits of steel plate sawn from an old UPS cover that I had to introduce to the blowtorch to get rid of the powder coating, then a wire wheel in the drill press to remove the gunk that was left, and finally drilled and filed to size.  I could have used the mill to trim them to size, but setting up and holding thinnish plate (1.6mm) takes a lot of effort and time, so the files were quicker, and besides, it is terribly cold here and there's nothing like a stint of filing to warm one up    So this is where things stand for now:

The plates are nice and straight; it's camera lens aberration that makes them look curved 

This build might be a bit slow; some work projects look like interfering with my hobby time - and I can't stand the cold in the shop...

 , Arnold

[andyf]

What gauge is the track, Arnold?

And how cold is it, really? If no ice on the inside of the windows, it's just a bit on the cool side of temperate.

Andy

[DaveH]

Andy,

It's not really cold, wuzies in Namibia
( Don't tell Arnold)
 
DaveH

[Rob.Wilson]

It's not really cold, wuzies in Namibia

DaveH

Tart,, is the word i would use  Dave 


Nice going Arnold ,,,,,,,,,,, i have never tried cutting gears that way   


Rob

[arnoldb]

  - aye; us Namibians are scared of the cold; must be partly cold-blooded, as I can't work at 10C or less 

Seriously though, last week for a couple of days it dropped down to -3C by 5pm and one night down to -13C - Really not used to that!

Andy, it's 0 gauge (32mm) track.  I wish I could have 2.5" so I could build a real loco to drive, but my yard is too sloped for that.

Rob, cheers mate; I need to refine a few things for the gearcutting still.

 , Arnold

[narrowgauger]

Good morning Arnold,

sure remember it being very cold in Windhoek.  When developing Van Eck Power station and Tsumeb & Okahanja depots there were some nights down to -12.  But always followed by glorious days.

by the way do you also make Kudo biltong?

have fun with your loco

Bernard

[arnoldb]

Hi Bernard

  I have fond memories of Van Eck from my apprentice days at SWAWEK - had to crawl in amongst the generator control circuits to get at circuit boards quite a bit.  We used to joke you could walk through the plant with your hands in your pockets and still come out with them dirty. 
And yes, I do make a bit of biltong; though I'm partial to Gemsbok.  In fact, weekend before last I lost shop time to a bit of butchering, but now the freezer is stocked for months to come.

 , Arnold

[arnoldb]

Well, finally a bit of an update...

Today was a nice and mild day, so I decided I didn't need warming up by filing and milled the cut-outs in the footplate:


The buffer beams and axle bushes followed.  The axle bushes was just a simple turning job in brass.  I made the buffer beams from some 60x10mm aluminium bar; unfortunately it was rather soft extruded bar, so it was a bit of a challenge tapping all the M2 threads in them, especially the ones on the ends, as I could not even use the tapping guide for those...:


My one concern up to this point was whether the pinion gear spacing would work; I couldn't resist checking:

  Works a treat; just a hint of free play but that's fine.

I cut the axles as well and assembled the frame.  All the bits done so far:


I started looking at the engine, and realised I have a wee bit of a problem...  The only pipe I have to make the boiler from is 42mm in diameter rather than the plans' 35mm - which leaves no room for the engine sticky-outy-bits  - So I have to re-think the engine mounting a bit; might have to offset it from the frames by about 5mm to get the necessary clearance...

 , Arnold

[DaveH]

Arnold,

Looking good

I am a bit concerned about that banana shapped steel rule you have there

 

DaveH

[arnoldb]

  Cheers Dave  - I use the curved steel rule to check that things are straight and in-line...  If I used a normal straight-edged one, nothing I make would ever work 

I'm still pondering the engine...  I assigned one brain cell to that problem, and forced my other one to multi-task between all the other day-to-day life issues.
Like turning wheels...

Turning up these small loco wheels is actually a tricky little chore, so I tried a different method to what I've used in the past.
First I turned a bit of cruddy HRS down to the outer diameter needed, and put some parting grooves in it to a mm or two below the tire diameter - using convenient readings on the leadscrew dial to index them across:


Then I removed most of the excess stock off the rim sections, leaving them about 0.2mm over-size:


A couple of minutes at the bench grinder with a new 8mm HSS square tool blank, and I had a good form tool to turn the wheel profiles in one go.  Using the same indexing from the leadscrew, I used the top slide combined with the cross slide  to get the first wheel done to size, noted the reading on the cross slide, locked the top slide and just repeated to the same infeed depth on the cross slide at each index point off the leadscrew.  Easy-peasy  :


After a quick 9.8mm drill and 10mm reamer through the whole lot, I faced and parted off each wheel in turn.  Then I turned up and parted sections off some 12mm hex brass for a light press fit for the wheel hubs (just 0.01mm/0.0005" over size), drilled and tapped for m3 grub screws, and ended up with this lot:


Pressed each wheel and hub together with a dab of green retainer for a little extra security, and the wheels were done.  A trial fit in the frames:

The gears mesh beautifully; much better than I expected from this home-brew lot, so I'm a happy chappy   
I do need to replenish my stock of short M3 grub screws though; had to use some long ones here... 

It's always gratifying to see it up on rails  :


, Arnold

[cfellows]

Looking good, Arnold.  So, here's a question... How come the tires on the wheels are tapered?  I would think they should be flat???

Chuck

[DaveH]

Arnold,

Coming along nicely, must be warm in Namibia
You got two brain cells, have you had a sneaky brain cell transplant.
There again I would think unused brain cells in Namibia are quite common.
Looking good Arnold.

 

DaveH

[spuddevans]

Looking good, Arnold.  So, here's a question... How come the tires on the wheels are tapered?  I would think they should be flat???

Chuck

I cant remember all the reasons why, but it is something to do with helping stability when encountering any sort of non-straight tracks, the camber on the wheels really help staying on the rails in the corners.


Tim

[Bernd]

Reason for the taper is that a solid axle on a locomotive has no differential like a car for going around corners. When going around a curve the outer wheel will ride higher on the taper giving it a faster speed than the inner wheel. I hope this makes sense.

Bernd

[Dean W]

It's looking great, Arnold.  They are a neat little loco.

Dean

[Stilldrillin]

Arnold.
I don't do locos/ railways. Don't know what a Cracker is........  

What you've done so far, is looking good.  

Quietly watching it develop. I'm sure it will be a "cracker", when finished......  



Bernd.
That makes sense to me!  

(I thought it was for the centralising, diabolo effect)..... 

David D

[allanchrister]

Nice build Arnold - any chance of a pic of what it will look like when finished??  Drawings perhaps?

BTW - introduced my wife to Africa last December, and after a sot introduction in Cape Town and Stellenbosch, next trip was a tour around Namibia.  I'd experienced your beautiful country on numerous visits about 10 years ago when resurfacing Hardap Dam, and promised her a visit.  had a fantastic time, and enjoyed the very high standard of some of the game lodges, but driving around Windhoek, Swakop, Uis, and Etosha was incredible.  I can categorically state that it was a vacation of a lifetime.  People are fantastic, warm, welcoming, and distinctly practical (try getting a 'bakkie' tire on a Corolla -  successful), and everyone seems to know one another - let me guess to see if you know Dudley Biggs....

best,  Allan

[arnoldb]

Chuck, Thanks for checking in  - Like Bernd said, it's mostly used for the speed differential in cornering.  On real trains, in a straight line, it also helps to keep the engine and rail cars from snaking around thus saving wear on the wheel flanges and track insides, as well as providing a more comfortable ride for passengers (think "horizontal" sea-sickness).  In the model world, we don't care about the passengers, but it does help to eliminate some running friction - something my first loco with flat wheels suffers from quite a bit.

  Dave, it is a bit warmer  .  Life was generous with me; I actually received 3 brain cells - but I didn't receive good looks, good luck or any of that stuff    2 Brain cells are used for day-to-day living; the third is reserved for matters related to the fairer sex; that one's not allowed in the shop at all  - it causes havoc and nothing gets done!  Besides, without the looks, luck and all of that, the 3'rd cell is permanently in overdrive on it's own mission 

  Thanks Dean.  I just hope it will work with my modifications... 

David, thanks    - when this one's done I'll take a note from your book and build a Stirling - well after making some tooling and possibly attempting a fairly unique engine build...

Thanks Allan  - There's quite a lot of Crackers on HMEM - Shred's is particularly nice and Tony Bird has built some very well-running variants of the Cracker.  The plans are available from John-Tom.  The basic Cracker plans are extremely simple and lends itself to the builder's imagination, but I wouldn't recommend the Cracker as a very first project - exactly because of that, as well as some construction and assembly details that are not clear from the plans. 
  Glad you like Namibia; I go to Hardap once or twice a year for a weekend fishing trip; nice big carp and really big catfish in there.  If you did Swakop/Uis/Etosha, did you go through Damaraland - Stunning over there.  Around Swakop a trip to the Moon Landscape and welwitchias is always a winner.  The Namib desert really gets under one's skin.
And  - I'm not surprised the people could make a bakkie tire fit a Corolla - over here bakkies and Corollas are pretty much the bread-and-butter transport...  Nope I don't know Dudley... Though I might have met him somewhere along the line in the local watering holes; I'm TERRIBLE at names!


Well, this morning my engine-building brain cell farted...  After waiting for the stink to clear, and using Charlie Docstader's Valve Gear program for checking things and running simulations with new dimensions, things looked to be on the up-and-up and good to go.
For the port block, the steam and exhaust ports needed to be moved lower to use available space around the boiler.  Seeing as I'd have to do some fairly deep-drilling in the port block to, I decided to make the engine a double-acting rather than the single acting oscillator the plans show.  The new design needs a thicker port block than the plans - preferably about 4m thick.  I don't have  4mm thick brass plate, but a while ago I bought a ~4mm thick and ~200mm diameter phosphor bronze "washer" from my local supplier at a whim (and good discount!). A bit sawn from it:


After more sawing, I had about a third of that section cut out - which was then milled to the engine port-block size and laid out.  Then I started drilling some port holes:

2mm drill for 3mm deep, then 1.6mm drill 20mm deep

All the port holes were drilled to intercept the steam passages; I made an oops on one and drilled right through the port block  - fortunately where a bit have to be soldered on.  The back of the port block, showing a lot of scars from over-vigorous de-burring (I forgot that PB will "grab" a drill bit - even if twirled manually - hence the scars around the big hole) - but more importantly the broken through port hole, a line to mark the center through it, and two groups of four punch-marks around the line:

  Not up to my normal standard - I'm actually feeling bad showing such a bad-looking part.  Mister's Moderator, can we please get an "Embarrassed" Smiley ?

I needed a steam and exhaust connector to the port block, and all this faffing around was to get those down to a level where there would be space around the boiler to make those connections.  The original plans call for a connection soldered behind the top port faces - I don't have that space - so I moved it down.  A bit of 5mm hex brass was turned down and threaded M5 on each end, with a nice 90 degree countersink in the "steam" side (more on that later) and centre drilled at 2mm for about 12mm deep each end while on the lathe.  Now the reason for those punch marks...  The mentioned hex brass is to be soldered to the port block. Ordinary soft solder (electronics lead based type) could work, but I prefer silver solder (or hard solder or silver brazing) around steam bits.  The silver solder (and flux) needs a gap to wick through, and the punch marks raises some high spots to allow just for this.  A bit of soldering with a plumber's torch later:


After a quick pickle in warm citric acid (~10 minutes) and a rub-down with scotch-brite and another rub of the port face over some 800 emery, the block looked better and I could drill the bottom port holes through into the connector - this time without breaking through the back side  :

I love my camera; it shows all the bad detail - even on a reduced photo

And a final drill through from the port connector sides using a "wiggly wire" to feel when the drill bit comes through:


Finished port block - back side:


And piston side - dings and all; fortunately there are no dings where things matter  :


 , Arnold

[DaveH]

Arnold,

Looks really good, comming along nicely.
Nicely posted as well, a real pleasure to read your posts Arnold 

 
DaveH

[sbwhart]

Looking good Arnold  nice bit of soldering 

Stew

[Stilldrillin]

Nicely done Arnold. 

Like the idea of centre pops, to hold off for silver solder penetration...... 

David D

[arnoldb]

Dave, Stew & David - Thanks chaps  .  Today's soldering wasn't quite as neat though...

David - the centre pops trick I picked up from other modellers - but it's good to show little bits like that for those that have not seen it or are newer members.

A bout of 'flu has kept me from being my normal self for the past week - so I spent yesterday in bed and slept most of it off.
This morning I felt quite a bit better, so started on the cylinder from a bit of 10mm hex brass stock:


I wasn't in the mood to make up a reamer to ream the cylinder, and the hand reamers I have are no good for a blind cylinder, so I used an 8mm end mill to run in to final depth - with a very fine feed both in and out this makes a pretty good finish in the cylinder - as long as the lathe's tailstock is very well aligned with the headstock; which mine fortunately (well, after a lot of work adjusting in the past!) is:


For the cylinder port face I used a bit of the same 4mm bronze the port block is made from - just poked some holes in the correct places and gave it a shallow counter bore with an 8mm slot mill:


Flipped it end-over end, and ran a 10mm ball nose mill over the back side to match the cylinder outside diameter:


And made a flange from 1mm brass plate for a light press fit over the step I left on the cylinder end.  This will be used to bolt the cross head and piston gland to the cylinder.  I also milled a small corner off the port face block to accommodate the flange:


Then I fluxed things up and used bits 'n bobs to hold it in place on a fire brick:


With a snipped-off bit of 1.6mm silver solder embedded in the flux on the "other side as shown in the last photo" along the cylinder, I heated things with the blow torch from the viewpoint of the photo; not ideal, as the flux closest in view would get direct flame and burn off a bit (hence the reason for the large amount of flux applied!)  I also added a dab of solder to the top behind the flange when things were hot; unfortunately a bit too much  :

Not the neatest job I've done; but that's OK - my defence is "I'm still learning"  - this was the most complex job I've tried in such a relatively small size.

After a bit of clean-up it looks better; not good; but OK for now:


I forgot to include scale; the screw in the last picture is an M2 and the holes in the port face is 1.2mm (0.01")

This might seem like a lot of faffing around...  There's several reasons though.  I want the cylinder block to have as little metal as possible on it - with a small live steam engine, it's crucial to keep the amount of metal down to a minimum, so that it can heat up quickly, especially with a small boiler.  In fact, I'll be removing even more metal off both the cylinder and port block.
As to silver soldering the lot - ordinary electronics soft solder would have done for this job, but some of my future projects will require accurate and neat silver soldering on small complex parts, so I'm just practising!

I wanted to do a bit more today, but it started getting chilly again, so I went inside; hopefully I'll feel better during the week or next weekend.

Regards, Arnold

[ozzie46]

   Hang in there Arnold, Hope you feel better soon.

   Cracker's coming along nicely.   

  Ron

[DaveH]

Arnold,

Looks good to me, a bit of a clean and polish - perfect

Look after yourself mate, hope you feel better soon

 
DaveH

[Stilldrillin]

Arnold,
I love to see the adaptation of milling cutters. I do it a lot, when necessary.  

Don't be too hard on yourself with the outcome. Looks very good to me!  

Hope you are soon feeling 100% again...

David D