Sanjay's Banjo Engine

[Jasonb]

Sanjay (Redhouseluv) posted some images of a small unknown engine in this thread at the beginning of April. It will now always be known as "Sanjay's Banjo Engine".

https://www.modelenginemaker.com/index.php/topic,12258.0.html





I was quite taken with its looks and although I had made a pump with the banjo type arrangement in the past I had not done an engine with the crankshaft in this form which is not unlike his recent Trapizoidal engine. A couple of evenings on and off with Alibre making use of "trace" to pick sizes off of a screen shot of the laid out parts and I had something that looked the part and while designing it gave some thought as to how I would go about making it. As usual I did the design in metric and it has a bore and stroke of 13mm x 13mm.





It was a toss up between using iron or bronze for the cylinder but in the end a piece of bronze bar won the day. After facing the end I turned a 2mm length to the diameter of the top flange before drilling and finally boring to the final 13mm diameter. it was then reversed in the chuck and the bore clocked true before facing to final length and forming a similar flange diameter as the other end.



I roughly squared up 3 faces of the mid section so it was easier to hold and then took the port face to it's final height.



The end cover screw holes were drilled and tapped M2 and two 1.5mm holes drilled down to where the inlet ports would be, doing the holes first meant that the drill would not break out into the side of the port and risk snatching or worse. Repeat for the other end as well as milling a notch so the end cover spigots do not restrict steam/air flow.



Over to the CNC which made a relaxing job of cutting the three ports slots. The outer ones are 1.5 x 4mm and the middle is 2 x 4mm. Back on the manual mill and the valve chest stud holes were drilled and tapped M1.6



A quick hole in the side to link up to the central exhaust port tapped m4 x 0.5 was the final drilling operation. I then supported the cylinder on a 12mm ground bar resting across the tops of the vice jaws and using a 10mm R1 corner radius cutter machined the mid secton down to it's final shape and finished by blending out the resulting facets with a fit of filing.



The two end covers were fairly straight forward, if small turning jobs from some offcuts of cast iron bar. held in a 5C collet block to drill the screw hole son their PCD.

[redhouseluv]

Well fame (and fortune) have eluded me in my life thus far, but I guess this must be my 15 minutes of fame

I never noticed/realised the similarities between this tiny engine and the Trapezium engine, but, yes, I see it now. One thing that fascinates me with this little engine is that dependent on which way you rotate the flywheel by hand, the eccentric arm pivots left or right, however, which way it stays when running depends on how the timing has been set

Thanks Jason, I've got an enormous amount of  lined up for this one.

[PaulR]

... by blending out the resulting facets with a fit of filing.

I often have those as well 

What's the cross hole for in that block at the top above the cylinder? The reflection in the 3D CAD images males it look like the curving bar is passing through the block M C Escher style!

[redhouseluv]

I think that's the hole for the banjo pivot pin (see pic). I never managed to disassemble that part and didn't fancy drilling it out. As you can see I slightly butchered the end with a pair of pliers! 

[PaulR]

Ah yes, silly me, I didn't look at the bottom of the 3D model to see it needs to pivot at the top 

[Jasonb]

Yes the banjo needs to move from side to side so there is a pin that goes in the hole to allow it to pivot in the piston rod end.

Having got the first tunes out of it yesterday the link on mine also moves to one side

[redhouseluv]

Having got the first tunes out of it yesterday the link on mine also moves to one side

Already! Wow, super fast, I don't why that side movement fascinates me so much 

[Jasonb]

The piston, it's rod, the rod end and pin were all farly straight forward turning jobs. I used aluminium for the piston, 2.5mm stainless 303 for the rod and some Colphos 90 for the end, silver steel for the pin..



Being quite small the valve chest and cover allowed me to use up some off cuts of cast iron which were squared up and the two ends of the valve chest turned.



Small offcuts also got used up for the valve and nut. Not sure if going for the usual threaded nut was the best choice as it does have a tendency to want to unscrew at high speed as the valve rod needs to be a loose fit in the top link. The original just had a reduced diameter to the rod which allowed it to fit a narrow vertical slot in the valve.



The base plate was from 2mm thick steel, I drilled the 4 mounting holes on the manual mill and then used those to hold the plate down while the profile and important holes for cylinder and bearings were done on the CNC



The two crank shaft bearings/supports were CNC cut on the ends of a piece of bronze bar before being sawn off, milled to final thickness and two 2mm fixing holes added



Coming together now. The coil is approx 7/8" or 22mm diameter

[redhouseluv]

This build intrigues me; everytime you make new pieces I pull the engine down off the shelf to take a look, I also have the pictures from when I first got it and dismantled it.

The engine came from an auction in a box of random bits 'n' bobs including a poorly semi-machined Stuart 10h none of which interested me apart from this little 'un!

Fantastic work, I can't wait to see it completed and running

[Jasonb]

The eccentric was next, first turning to overall diameter and cutting the 1mm x 1mm groove for the end of the rod to locate into. I then held it in a collet block to drill and ream the crankshaft hole followed by laying the collet block on its side to drill & tap for a grub screw. Back to the lathe and using the grub screw to hold it to a piece of 4mm rod the spigot was turned down to size.

For the strap I started by boring a  hole in the end of a piece of bar then used the CNC to cut the lollypop shape which was parted off and a M1.6 hole tapped for the rod



A piece of stainless steel rod completed that group of parts



Finally the part that gives the engine the other half of its name. Two discs were machined to suit the internal radii of the banjo halves and these were screwed to some scrap angle iron at the correct ctr distance and offsets and some 2mm dia steel rod bent around them.



The top and bottom blocks were fairly straightforward milling and drilling. I used another bit of scrap bar as a jig to hold them in place while I soft soldered the two halves of the banjo into place and that completed the build. Well I did make a few screws and a couple of pivot pins as well.



A bit of orange paint and time to play test the engine.

<a href="https://www.youtube.com/watch?v=9Eif8JrYpXE" target="_blank">http://www.youtube.com/watch?v=9Eif8JrYpXE</a>

[PaulR]

Very nice  How hot did you get the 2mm rod to make the Sanjay banjo - red hot or is that too much?

[redhouseluv]

Absolutely perfect! When its running fast it looks very strange, just like the original, you can see the banjo at the top and bottom of its rotation at the same time

I wonder how fast that's turning, sounds and looks like its going at a fair old pace! Maybe one day someone will discover the origins of the little engine, who made it, for what and when.

I have the same question for you .............what's next? 

[Jasonb]

I just bent the rod cold, it went round quite easily.

I did not get the Tacho out on that one but as you asked will see what it can do over the weekend and report back

I mentioned on ME Forum that I thought the banjo design had been used to keep the height as low as possible, either to get it below decks or to keep the ctr of gravity low or a bit of both. This is it stood end to end with my 12 x 12 Bassett Lowke replica by way of comparrison.



Next is a hot air engine, looks like a Raab but I don't think the one I'm basing mine on is actually a Raab. The other three hot air engines that I have done have all been water cooled so this aircooled one will be a bit of a change.

[crueby]

Thats a neat motion, runs great!

[redhouseluv]

Next is a hot air engine, looks like a Raab but I don't think the one I'm basing mine on is actually a Raab. The other three hot air engines that I have done have all been water cooled so this aircooled one will be a bit of a change.

I've been sitting here debating 'what's next' and that's just swung the vote in favour of................. see other thread