Stuart? MTB 1M

[Jasonb]

Thanks for following along.

The Lower half of the crankcase was machined in much the same way as the top. Starting out with an Adaptive roughing pass and then a parallel finish path as the Curve was fairly shallow which meant the horizontal stepovers were fairly constant along the circumference of the arc



Then turned the other way up to hollow it out. I nearly came a cropper as I selected the finishing path for the top half but heard the cutter taking heavier cuts than it should and stopped well before it cut right through.



After power tapping the various holes using the tapping feature of the manual mill the two halves were screwed together, drilled and then reamed 10mm. The original has the crank running in the iron castings but I made up some bronze bearings as I did not want to run the crank in this grade of aluminium (6062)



As I drilled and reamed from each end it was reasuring to have a 10mm ground HSS rod rotate freely within the two holes. You can also see a shallow recess in the top surface, this is to locate the lower camshaft support and there is a similar one in the top of the cylinders.



The two camshaft brackets were milled to size and screwed to their respective parts, the shaft position established and the lower one reamed 6mm for a bronze bush. I then fitted the cylinders and with the mill spindle still in the same location ream the top cast iron bracket 4mm as the shaft will run directly in the iron, there is a bit to come off the top.



The last bit of machining was to drill and tap M4 fine for the drain plug and filler spout, as this is angled at 10degrees in two directions, I set it at 10deg in the vice and then tilted the vice at 10deg. Started the hole with a 4mm milling cutter then drilled 3.5mm before tapping.



After a bit of hand work to remove any fine machining marks the two halves were bead blasted to give a nice even satin finish.

[redhouseluv]

That's looking really nice, the finish is superb!

Jumping ahead slightly are you going to be cutting the bevel gears? It's something I've never attempted and something I'd like to see how its done 

[Jasonb]

Not this time I'm affraid. I have done it in the past for governor gears which don't tend to run that fast but hoping to get a few thousand rpm out of this little beasty so bought them from GHW in Germany.

[PaulR]

Hang on, there's only one 'wedge' providing the 10 deg angle on top of the vice, is there a shorter one hidden from view or was that enough support? I don't understand where most of these parts fit in the scheme of things but it's fascinating to see how you make them!

[Jasonb]

The grip of the vice was really enough, I just left the loose wedge in place just in case and took it gently.

If you look back to the first post you should be able to spot where bits go on the two external views of the engine and I also posted a section a while later.

[PaulR]

If you look back to the first post you should be able to spot where bits go on the two external views of the engine and I also posted a section a while later.

OK I've stopped being lazy and had a good look, all pretty obvious now! Seems an odd choice to design the filler pipe like that rather than having it sticking out at some orthogonal angle with an elbow. I think it'll look better on your engine without the cladding and some space around it, with the cladding it looks a bit like it's a jammed in afterthought to me.

[Jasonb]

The photo of the old engien is a bit decieving as it has quite thick wood cladding which comes close to the filler tube. They originally had a thin steel sheet so that would have given a bit more clearance.

I was asked on ME Forum whether this would be a suitable subject for 3D printing, this was my reply which some here may find of interest:



3D printing would certainly be an option if you have an aversion to swarf or just don’t feel able to cut it from solid on manual machines. The parts could be simplified a bit for manual machining  eg just straight internal sides, etc.

I just roughly joined the two crankcase halves together with a couple of sprues and exported a STP file for pricing. The wall thicknesses could be reduced to bring the cost down and the holes omitted, a bit of machining allowance would need to be added.

Price for printing in aluminium is around the £75 mark with £10 postage. VAT included at source.

The top half could also be simplified for manual machining particularly if you clad the cylinders or even just made them an oval shape with some dummy screws and a seam line to look like cladding. Price for the cylinders, head and chest cover in stainless 316 was £62 but higher postage at £23.

So you could have all the major “castings" 3D printed for £170, similar if all done in stainless

That does not compare too badly with the slightly larger Stuart Sirius kit at £500 plus postage but is a bit more spendy than raw materials from M-Machine that work out at just £14 for aluminium and £15 for cast iron plus a bit of postage. Gears plus a few other bits of metal would be £30-40.
 

So £65 total materials cut from solid, just over £200 3D printed once you include the sundries and gears.

[Jasonb]

With the crankcase complete it was time to start filling it. The crankshaft started life as a piece of 10x30 hot rolled steel which after a pickle to remove the mill scale was reduced to 10x28 and the ends milled square so that three ctr drill holes could be added to each end. Doing each pin in turn I milled out most of the waste then used a parting tool to turn the pin to 0.1mm oversize. I then used a small boring bar with a CCMT 04 insert to machine the sides of the webs, first as shown then mounted upside down and with the lathe running in reverse to do the opposite side



The pin was then taken down to final size of 7mm dia with a parting tool moving side to side while gently feeding in, quick polish with emery cloth on a stick to complete.



Now that the outer two ctr drill holes were no longer needed the waste was sawn away so that the end of the shaft could be taken down to the required 7mm which was checked using the previously made bronze bearing.



Similar for the other end which also needed to be reduced to 4mm to suit the bevel gear.



Pistons were fairly straightforward turning and then milling the pocket for teh conrod, then drilling and reaming at right angles for the wrist pin.



Some 20mm dia 2014 aluminium was milled to a rectangular section to make the conrods from. First job was the shape one end and then drill and tap for the big end bolts



Then the caps were sawn off. Not sure what I did but the cut was a bit nearer the end than I intended. Wrist pins can also bee seen here and the tapped holes for 3mm grub screws to keep them from moving sideways and marking the bore.



Holes were then drilled and reamed



Before final shaping on the CNC

[Jasonb]

<a href="https://www.youtube.com/watch?v=4N4_aHff0PE" target="_blank">http://www.youtube.com/watch?v=4N4_aHff0PE</a>

[redhouseluv]

I remember that shaped crankshaft from my Stuart Sun build at the end of last year - it jumped out of the lathe and tried to get me!! 

The piston and bevel look familar too, I guess Stuart's kept building on that design for many decades to come, but for different models

[steam guy willy]

Hi Jason, looking good and very clean lines everywhere ...am quite busy at the allotment at the moment so not much WKSP time for me  !!!
Willy

[Dave Otto]

Coming along nicely Jason!

Dave

[Jasonb]

Thanks all for looking in

The crankshaft shape with its diagonal central web is quite common across the Stuart enclosed engines and also the compressor. And it was your couple of threads that got me thinking of making this engine. You can also take the blame for the next one too.

I uploaded a couple of videos in relation to another thread elsewhere but a sthey are of this engine may as well post here.

The first is the beginning of cutting the steam ports, this is one of the outer ports 1.5mm wide and 8mm long. 3-flute 1.5mm cutter going 4mm deep but I have shortened the video.

<a href="https://www.youtube.com/watch?v=Lt_swEAAZcI" target="_blank">http://www.youtube.com/watch?v=Lt_swEAAZcI</a>

And this one shows a 2mm dia 4-flute ball ended cutter producing the "X" shape on the valve chest cover after an initial bit of milling to bring the outer edge down to finished height as the detail stands proud of that  in the middle.

<a href="https://www.youtube.com/watch?v=_tN5hW36dAE" target="_blank">http://www.youtube.com/watch?v=_tN5hW36dAE</a>

[redhouseluv]

The crankshaft shape with its diagonal central web is quite common across the Stuart enclosed engines and also the compressor. And it was your couple of threads that got me thinking of making this engine. You can also take the blame for the next one too.

Under the bench I have an a set of Stuart Compressor castings .......hmmmm......that has me thinking! Anyway happy to take the blame if it results in such wonderful engines being made!