Building a Hunslet 'Jack' in 7/8ths Scale

[Steve Cook]

I've been a big fan of the 18" gauge loco 'Jack' built by the Hunslet Engine Company for many years and have long harboured a wish to own a model of one. I got as far as purchasing some parts from Roundhouse a couple of years ago and started to research the build but as ever, my interests moved around and it got consigned to the back burner. A kick up the posterior arrived this year with the serialisation of Brian Wilsons build in Garden Rail magazine (noted here) but the more I looked, the more I wasn't happy with the compromises made.

Having mulled it over some more, I've decided to go back to scratch building my version, but using the Roundhouse cylinders and valve gear, along with the really useful parts made to support the Garden Rail build. I had planned to start with the frames but after further consideration, I figured I would be best building the known components first (smokebox, cylinders etc) and design the frames around those 'fixed' parts.

I've spent a bit of time sorting out my lathe recently and with a few tools as Christmas presents, the smokebox has been the first thing to be constructed. The basic kit parts are supplied by Model Engineers Laser for £22.50 and save a whole load of marking out, especially the smokebox curves.



From left too right we have the smokebox front, front inner wrapper support, rear inner wrapper support, smokebox rear and smokebox ring. The wrapper is below but will not be used as anything other than a test piece - its supplied drilled for 1/16 rivets and I will be using 3/64 rivets at a different spacing and on both edges to represent Jack as built.

The smokebox ring was covered with permanent marker and the centre line scribed around, before four marks were made at 90 degree intervals. The ring was clamped to the smokebox rear so the fixing holes could be drilled through both components.



Countersinks were added to both components ready for riveting.



Rivets were added through each hole and bashed into place with a ball pein hammer (rear ones fully formed, front ones waiting for the hammer bows).



The smokebox door keep was next. The fixing holes were drilled into the smokebox front and the position of these transferred to a length of 5mm square brass bar.



As before, both components are countersunk to give something for the rivets to form into



Lots more gentle blows with the hammer and a quick dress with a file saw the front completed.



The heads of the rivets were then hammered into the rear of the door keep, then filed flat.



A set of spacers were turned up from 1/4" brass bar stock.



The smokebox was then loosely assembled to check alignment.



Its a bit nerve racking, swinging a large hammer when there isn't much room for error - fortunately I only caught the smokebox ring the once It takes a while to gently start compressing the brass into the countersinks on the outside of the smokebox - its definitely a job not worth rushing.



A bit more bashing, quite a lot of filing using different grades of file, then a finish off with 600 grit wet and dry and its come out OK.





A new smokebox wrapper was cut out next from 1.45mm mild steel sheet.

 

[Dikitriki]

I'm impressed with the riveting, especially the flush finish. Was it still absolutely square when you'd finished.....not that I'm doubting your abilities, it's what I would be concerned about

Richard

 

[Steve Cook]

I was just about to use the original wrapper as a test piece for trying out the 1/64 rivets when I realised I didn't have a rivet snap to protect the rivet heads when hammering the rear of them down. No chance of buying one at this time on New Years Eve so a piece of silver steel was chucked in a collet and a stub turned down to the same outside diameter as the rivet heads (2.06mm). I gently hand filed a curve on the end with the lathe running at a slow speed.



A quick back to back with a rivet loosely held in the tailstock chuck showed I was in the right ballpark shape wise.



The collet was transferred to a mounting block and held in the clamp in my mini milling machine.



Very light cuts were made to remove half of the stub, then the milled surface was flattened with a stone to create a sharp cutting edge and voila, a D shaped cutter (its D shaped if you look end on).



It was then heated until the tip was a bright red



before being quenched in oil. You know it was hot enough when you get a scale formed on the outside of the material



The scale was cleaned off, the tool polished and then heated again until the tip was a light straw colour. The last two operations harden, then temper the tool meaning it should now be strong enough, without being brittle, to be used to drill a short hole.

A piece of bar was chucked up, centre marked and a very short hole started with a 2.1mm drill bit. The D cutter was then plunged into the hole with plenty of cutting fluid. It creates a very fine swarf, but without flutes its worth regular withdrawal and cleaning to preserve its life. The test bore came out like this.



It all gets a bit out of phase here as I ended up making two rivet snaps - the large diameter one got so far along the process before I wanted to change the tip detail. Alas, it had been hardened and tempered by then and even a bastard file just skidded off the surface. I decided to try and anneal it by heating to cherry red and leaving it to cool down naturally - in the time available I decided to make another tool as a back up. The same process as above was followed, then the tool tip was tapered down to a narrower diameter. The tip was machined away until the base of the rivet was just sticking out when the head was inserted



A test riveting session showed that it was very easy to mark the sheet material with the rivet snap, especially if one misses with the hammer.



The tip of the rivet snap was then radiused off using a file



That turned out to be a success so the snap was hardened and tempered and I got back to the wrapper. I marked out where I wanted the rivets to sit in relation to the edges (1.8mm), then the centre line so I can put in a pilot hole for the chimney. There are no rivets on the centreline as they will be covered by the chimney base.



The rivets are set at a 6mm spacing and I found it a lot easier to get everything in a straight line using an optical centre punch.



Its a great tool for accurate marking out, you can use either perspex view finder - one is marked with a cross and the other with a dot. You just place the tool over the scribed lines and adjust the position until the marker of your choice sits over where you want to put the centre punch. When using the cross its normally aligned with the scribed lines but for showing up in the photo I've rotated it 45 degrees.



The dot is nice and simple but despite my best efforts, I couldn't get a decent photo with it sat on some scribed lines, sorry!



When you have the base in the right position, as indicated by your choice of marker, the perspex view finder is removed and replaced with the centre punch. This is then given a light tap and if all is well, a small mark ends up exactly where you want it. Or pretty close anyway The perspex bits can survive the odd smack with a hammer too - its all to easy to concentrate on not moving the base and forgetting to swap in the punch

The routine I used was to mark out the holes on either side of the centre line down one side of the wrapper, centre punch, then mark the next hole location using a pair of sharpened calipers. Rinse and repeat and you end up with something ready for drilling



Steve

 

[Steve Cook]

I'm impressed with the riveting, especially the flush finish. Was it still absolutely square when you'd finished.....not that I'm doubting your abilities, it's what I would be concerned about

I hear you, buts its spot on When I made the spacers, the brass 'rivets' on each end were made a very tight fit inside the holes in the sheet metal parts, which combined with the square shoulders resulting from being turned up in the lathe meant there is nowhere for anything to move out of alignment. The spacers were gently hammered all the way round, then on the other side so that everything pulled up gently together - and it seems to have worked! I was impressed at how well the riveting worked - the book / articles make it seem so easy and whilst there is a bit of a learning curve its actually not too bad at all. Time consuming though...
Steve

 

[JohnFla]

Great skills you have there Steve, Boy do you like a project I must be following about 4 I think.

 

[Steve Cook]

Thanks John, I do bounce around a bit project-wise

Just a quick workshop job this morning before heading out for the day, drilling the wrapper. I had started to very lightly countersink the holes on the top surface (front left corner), but the rivets fit nicely through the holes without them so I stopped. There are larger countersinks on the rear ready for more hammer action, hopefully this evening.



Steve

 

[SteadyRed]

Excellent engineering @Steve Cook.

Wish I had space to do this type of model engineering, unfortunately my location (first floor flat) prevents riveting or space for a lathe or other machine tools. Neighbours wouldn't be too please if I started rivet bashing!

Despite being brought up in an an engineering environment, don't think I would have thought about making my own rivet set.

Dave

 

[mickoo]

Kewl, I have the interest, but not the skills to do anything anywhere as good as this patience is not my strong point

I'm struggling to grasp the physical size of this, there's little in the photos to judge the actual size in your hand, I know 7/8ths is pretty big but, well it's the wrapper that's has me flumuxed, at 1.45 mm thick that's got to be near the thickness of the real engine, does it really need to be that thick, you must have a big set of rollers to bend that sort of material

Finally, appreciate riveting the parts of the smoke box front and rear but would it not have been easier to silver solder them.

Like the optical punch, I could use one of them, are there any preferred outlets to source one from please?

Looking forward to watching this unfold

 

[Ian@StEnochs]

Nice work there Steve. I like the way you made the rivet sets which I had never thought of.
I had a similar problem when I was building a large scale, 1/4 size, Traction engine. The commercial sets available did not match the rivets I had. So I had to make one. However I made mine with a bit more brute strength and less of the machining you did. I used high carbon steel, what we used to call chisel steel, and faced a bit of hex bar in the lathe and drilled a hole, same size as the rivet head part way in. I obtained some ball bearings same size as the rivet head, fixed one on the anvil with a bit of putty, then heated the end of my blank to red heat and gave one powerful blow with a hammer. The bearing shaped the recess to exactly half sphere and matched the rivet. After hardening and tempering the sets are still in use some 20 years on.
This was not an original idea of mine but culled from an article in Model Engineer.
Ian

 

[Steve Cook]

Thanks Dave - I'd agree that living in a flat isn't ideal when it comes to riveting - fortunately for me (and my neighbours), my garage is standalone which means I can make a fair bit of noise without disrupting everybody else

Kewl, I have the interest, but not the skills to do anything anywhere as good as this patience is not my strong point

I would have thought with your ability to sit down, research, draw and archive research material you are both patient and thorough enough to be very good at the engineering side of things Mickoo As for the skills, well I didn't know I could do any of it until I started - without wanting to sound big headed about it I've just rolled up my sleeves, got stuck in, looked at youtube videos when I get to something I don't understand and been willing to use the scrap bin And boy, have I used the latter!

I'm struggling to grasp the physical size of this, there's little in the photos to judge the actual size in your hand, I know 7/8ths is pretty big but, well it's the wrapper that's has me flumuxed, at 1.45 mm thick that's got to be near the thickness of the real engine, does it really need to be that thick, you must have a big set of rollers to bend that sort of material

Sorry, I could have made the size thing a bit clearer - for reference the smokebox is 58mm tall, 78mm wide and 29mm deep. As to whether you consider that large or not depends on your perspective I suppose



The wrapper thickness is probably a bit over the top I'd agree, but the laser cut components were designed with that thickness in mind to create the right steps / offsets. According to the instructions, I shall be able to bend the wrapper over a wooden former with my bare hands...I'll let you know how I get on with that! As an aside, I've no idea how thick the real smokebox would have been, but given the corrosive nature of coal burning I would have thought that 1.5mm thick steel would be quite short term in life expectancy in the real world.

Finally, appreciate riveting the parts of the smoke box front and rear but would it not have been easier to silver solder them.

Yes...and they still may be, I'm undecided. You would still need to hold all the parts physically together to silver solder though so that task has been removed. To be fair to the designer, he designed the smoke box to be assembled without silver soldering gear and it has proved to be an interesting lesson. I think I would prefer the wrapper to be fully sealed around its perimeter - one additional option could be to go old school and use putty instead...

Like the optical punch, I could use one of them, are there any preferred outlets to source one from please?

Mine came from Chronos but it appears to have been superseded by the looks of things. Similar are available on Axminster and ebay, prices vary wildly as expected

Looking forward to watching this unfold

Thanks, I'm rather hoping the smokebox doesn't unfold

Thanks Ian, the method was driven by necessity and its only because I made a spot facing cutter out of silver steel the other week that I thought it was worth a bash. I like the method you posted though, thats another great (and dare I say it, simpler) way to make a set of rivet snaps. I think you've just proved that adage that in engineering terms, there are many ways to skin the proverbial cat. As for a 3" traction engine, I salute you - I'm reading about a chap who built one and its a long way up the engineering ladder from where I am today. Perhaps we should set up an engineering corner for things like that...

Steve

 

[unklian]

Enjoying this Steve, good work there . One advantage of the thickness of your wrapper will be the extra meat to attach the chimney to. I added an extra bit inside the smokebox I last made as my wrapper was only 1mm brass. I will be interested to see how you go about fixing your chimney too.

 

[mickoo]

Steve cheers,

Optical punch, I think the price is usually reflective of the quality from what I've just read today, I've a nice Soba (seem to recall they are a good make) book marked on E-bay at £44 and Warco (unbranded) do one at £33, I've also seen them at £11.99, you pays your money.....

Engineering I do for a job and yes I did/have/do a lot of hands on work, but if someone asked me to file a perfect square hole it in sheet metal it wouldn't happen, that's why I etch, which to be fair is only copying lines from a drawing onto a screen
Mind I am currently vexing on how to produce my next set of proposed frames, which in G1 are 3 mm thick and a lot of holes in them, bespoke laser cut or three layers of laminated 1 mm NS and tedious cusp filing.

Going back to the wrapper, I checked a few sources and the GA for the Coronation class smoke box gives a wrapper thickness of 3/8" which if my math is correct would be scaled to 0.67 mm in 7/8 th scale, so yes, 1.45 mm is a bit chunky but, if the model is designed around that and it works then that's what you have to use.

Having said that, the Coronation class and pretty much most steam engines I believe, have a sacrificial plate inside the bottom third of the smoke box where the ash accumulates.

Obviously work in progress but having drilled the wrapper I do not see a suitable flange to attach it to, I'm sure that'll come shortly....told you I was impatient LOL

 

[Steve Cook]

Enjoying this Steve, good work there . One advantage of the thickness of your wrapper will be the extra meat to attach the chimney to. I added an extra bit inside the smokebox I last made as my wrapper was only 1mm brass. I will be interested to see how you go about fixing your chimney too.

Cheers Ian The design allows for a couple of options - either thread the bottom of the chimney and the top of the smokebox, or make the chimney a friction fit in the smokebox hole and use some high temperature Loctite for added security. As the smokebox isn't used to create a draft due to being gas fired, I'm toying with the idea of creating a shaped washer to sit inside the top of the smokebox wrapper to give me a flat surface against which a nut threaded onto the chimney could be tightened. Could be a bit of faceplate machining coming up

No worries Mickoo - my optical punch is a Soba too and it seems OK in my hands / under the hammer...
I couldn't file a square hole either, I keep trying but its beyond me at the moment! Thanks for the wrapper thickness on the Coronation, thats a lot thinner than I thought it would be. As for the wrapper fixing, you'll just have to wait and see

Speaking of the wrapper, I put the first rivet in and bruised the bloomin' wrapper The one thing I was trying to avoid and I did it straight off...

To try and minimise the number of times I'd repeat the same feat a small spacer block was made up from wood and an offcut of ali - the top surface of this being slightly higher than the rivet snap when that was held vertical in the vice.



If you look from the side, you can see that the wrapper is now held off the rivet snap, so short of miss hitting with the hammer, it should make it much more difficult to ding the wrapper (the rivet tail is chopped down to around 3mm before riveting).



It didn't all go according to plan, the shape in the rivet snap is slightly different to the rivet meaning the head gets ever so slightly reshaped which results in a tiny flat appearing around the outside. However, it doesn't look too bd and it will all be getting a good coat of high temperature paint which should hide a few sins...(might even mask some of the wobbly rivet lines ).



There is some work left on the smokebox front, I want to bring the radius down a bit as it looks like it was made fractionally oversize to be filed down to meet the wrapper - fine for a welded / flush fit but not ideal for a riveted look. That should keep me quiet for a bit - I can always get on with the former for bending the wrapper, a suitable piece of wood having been found in the 'useful one day offcut' stash

Steve

 

[JohnFla]

Doesn't look too bad Steve? It looks the mutts nutts to me.

 

[Steve Cook]

Thanks John

The wooden former for making the wrapper was made according to the drawings in Garden Rail - the main radius is slightly smaller than required to take into account the spring in the steel.



In order to bring the outside radius of the smokebox front down I cut a strip of brass to the wrapper dimensions



Used the former to create the right shape



And then clamped it into position before scribing around the outside. This gave me a reference line to file down to and should result in the wrapper standing 0.5mm proud of the smokebox front which is what I'm after.



With the filing done, the main wrapper was formed over the former - it wasn't actually a difficult job to do by hand, although getting a good fit to the rest of the smokebox required a bit of tweaking and manipulation.



The mounting holes were marked at both ends of the wrapper and drilled through. The wrapper was then clamped in position and these holes transferred to the brass spacers ready for them to be drilled and tapped 6BA.



The suggested method of assembly is use 8BA countersink bolts and countersink the wrapper so the bolt heads are flush or below the wrapper surface. I tried a couple of test pieces on some scrap and figured I could use 6BA instead, and by hand countersinking create a rough enough shape for me to effectively rivet the bolt heads in position. In order to do that though, I needed to be able to support the inside of the brass spacer whilst I hammered the bolts on the outside. A rummage through my metal odds and sods box turned up something that was quickly adapted to suit - as anvils go its a fairly strange shape...



It does allow the smokebox to be supported in the right place though



A set of 6BA bolts were cut down so that around 1mm or so protruded through the brass spacer on the inside of the smokebox - these bits would rest on the anvil and would therefore, as the other side of the rivet, end up being squashed into place to stop any chance of the bolts unscrewing on their threads. Just to be doubly sure, the bolts were loctited in position with a high temp loctite. The rivets on the wrapper were covered with strips of cardboard to reduce the impact of any wayward hammer blows.



The bolt heads were then hammered into the rough countersink marks, the depth of the countersink being such that the slotted section of the bolt head remained proud of the wrapper.



With a lot of careful filing, the end result



And a quick compare against the suggested method to prove the extra effort was worthwhile.



Having gone a bit photo heavy above, its now time for a 'camera-lite' episode. Having done the wrapper, I thought it made sense to start on the chimney fixing, well, that and I don't have any steel yet to turn the door from Having tried to set things up on a faceplate I wasn't happy with the way things were fixed so I changed tact and decided to radius the base of the chimney saddle by making a boring bar to fit between chuck and tailstock. That whole process was rather eventful, but I got there in the end - theres no photos as its a length of bar with another bar crossing through it at right angles. The most interesting job was getting the brass for the chimney base at the centre height of the lathe - I used a fixed centre and a ruler to get it right (by moving the brass up and down, the ruler changes angle as the point on the centre moves above and below the centreline - when the ruler is vertical, the centre is aligned with the brass centre).



With the boring bar in action.



And the end result



The saddle could do with being machined at a slightly smaller radius, you can see gaps to the left and right but hopefully that won't be too bad a job - at least I know all the kit works now

Sat at the front is the small brass spacer that fits under the chimney, but on the inside of the smokebox - that gives me a flat surface to screw against. It has just occurred to me though, that I ought to check just how far into the smokebox the boiler is going to protrude, I fear a little light machining is going to be required....
Steve

 

[ceejaydee]

Fantastic work Steve and some good tips/techniques in there too
I like the method for centering a bar in the vertical slide which may come in handy when I have a go at milling in my lathe.

From the pic I'm guessing you have an ML10?

 

[mickoo]

Not only is your steel work perfect but the wooden former is a work of art, I bet it's square and true too

Like the vertical slide, I can see a use for one of them to perhaps use my lathe as a Neanderthal milling machine, also like the scribe, looks sharp, mine just will not hold it's tip, must invest in some new decent tools I fear.

Rather then filing the front and rear of the smoke box down, could you just not have left the brass wrapper inside and laid the steel one over the top, granted the wrapper would be a slightly larger dia, but it would of saved an awful lot of filing

 

[Steve Cook]

I like the method for centering a bar in the vertical slide which may come in handy when I have a go at milling in my lathe.

It works well when using a pillar drill too - makes it a lot easier to find the centre of round brass stock when drilling in from the side.

From the pic I'm guessing you have an ML10?

Well spotted Its far more capable than I am, but the learning is good fun!

Not only is your steel work perfect but the wooden former is a work of art, I bet it's square and true too

Don't tell anyone, but its just down to a Proxxon Disc sander, takes all the effort out

... also like the scribe, looks sharp, mine just will not hold it's tip, must invest in some new decent tools I fear.

The scribe is a home made jobbie - I followed some instructions found on YouTube

The chap who did that video also does a range of videos as he works through building a clock. Now I'm not into clock making, but the videos are slick and informative, short enough to watch with a brew and leave me feeling like a trip to the workshop would be worthwhile. Highly recommended, just search out Clickspring.

Rather then filing the front and rear of the smoke box down, could you just not have left the brass wrapper inside and laid the steel one over the top, granted the wrapper would be a slightly larger dia, but it would of saved an awful lot of filing

Proxxon again Mickoo I sat the support at a slight angle to make sure there was no chance of me accidentally sanding the rear smokebox plates, then when the bulk material had been removed I just draw filed around the perimeter.


Funnily enough, it comes highly recommended too

Steve

 

[mickoo]

Steve,

I've actually got one of them and had completely forgotten I had , used it to form the wooden shapes for my aborted class 40 and Deltic in gauge 1 and frames for my 1:96 US warship hull. Some of it was ok, the theory was sound but as always it's the application, the armored chines were not straight enough and I gave up and got back into trains. It's still in the loft, still square and solid, thought it would of bowed by now, it could be cleaned up and made presentable, just a case of finding the time.




Thanks for the reminder of a excellent tool I forgot I had, and for the links to the tool maker videos, that'll save me a few bob as I was looking for a new one and while away a few hours on the lathe

Addendum, watched the video had a brain wave and came up with this, a pin vice with a pin in, works a treat, thank you, I can now scribe really neat sharp lines, the other scribe can revert back to the small dot punch it was more often used for, which probably explains why it's always so blunt

 

[Steve Cook]

Pleased to have been of assistance Mickoo

The brass bar for the chimney base had another couple of passes with the boring bar to improve the fit around the smokebox. The bar was then chucked up in the three jaw and covered in permanent marker into which reference lines were scribed for overall length, start of radius etc. The bulk of the material was removed with a parting off blade



The main body was then turned down to a few thou oversize and a chamfer put on to reduce the work the radius tool was going to have to do.



The radius tool was ground up from a HSS tool blank, a line was scribed around the bottom of a 9mm dia drill bit onto the blank to use as a guide. When the shape was right, the tool was gently relived on the vertical faces to give some extra clearance when turning. The cutting edge was then stoned to give me the best finish I could get. Its shown here mounted on the lathe and ready to go.



It does create some lovely wafer thin swarf, and lots of it too



The next job was to bore the hole through the centre. Brass can be very grabby when drilled and the technique is actually to put a small flat on the cutting edge, less than 0.5mm or so. If you don't, the drill tends to try and feed itself into the brass due the shape of the cutting edge which can lead to the chuck being pulled out of the tailstock. This can be overcome with well matched feed rate and turning speed but when dealing with fragile components, just putting the flat on works best in my opinion. It does mean I have a set of drills for brass and one for steel, but the ease at which I can drill brass means it is well worth the extra outlay.



The hole is spotted with a centre drill, then drilled in increasing sizes to the final diameter.



I left the chimney base in the chuck for the filing and sanding, it meant I could dress the top of the base down to its final diameter after the filing was done to get a good blend with the radius.



20 minutes later and a polish up with 600 grit wet and dry and its come out OK.



It was then parted off to length and placed on the smokebox to check the fit.



Whilst there was plenty of swarf around, another piece of brass was chucked up, faced off and turned to diameter before being drilled through to make the chimney cap. Another tool was ground up to @3.5mm radius using the same method as before and a set of reference lines lightly scribed to help with the machining.



The finished cap alongside the chimney base.



The chimney base should have 6 bolts around its perimeter, I'm not sure how I'm going to drill those and get them evenly spaced at the moment. I thinks its time to ask around and see if anybody local has a rotary table I can borrow for an evening

Steve