Bloody Mary in 1/8 scale scratch build

[Jo NZ]

I have finally sat down and learned a CAD program (this is my fourth - Euclid 3d, Autocad, Bentley 3D and now Fusion 360.) I couldn't figure out how to make the Armstrong lever arm dampers on the front suspension, so they are being drawn and printed. Here's the first effort...

[MODEL A MODEL]

Beautiful rendering. (Don't over-torque your screws, just to get them to line up!)

[Jo NZ]

I'd like them to be at different angles but haven't worked out how to do that yet....

[JunkGTZ]

Seems to be a trend of making miniature versions of Bloody Mary. This one is rather ....dare I say it.....cute!

[Jo NZ]

Having thought that I'd mastered at least the rudiments of Fusion, I thought I'd try the gearbox. It's a 1930s(?) Sturmey Archer four speed motorcycle gearbox. I have loads of photos of these boxes but nothing that quite matches up to the one on BM, so this has been drawn from dealer information, photos and a very flexible scale ruler. Here's a couple of pictures of the box:



The vee that sticks out is the clutch cable support, you can see that the clutch operating arm pushes a rod through the middle of the output shaft...



All the brackets and linkages hiding most of the top of the box are the positive stop control, to return the gear lever to its original position after the change. An early version of a sequential gearbox?

Here's where I am so far....



If anyone knows any better, please let me know!

[MODEL A MODEL]

You must either really know your subject, or you are very brave! Your second photo would scare most modelers! What a confusing mess!

[Jo NZ]

It scared me, too, until I realised I'd downloaded the positive stop control information. I'd originally discounted it , but it makes perfect sense, if a little work...

[xken]

Your work is looking great! Another way to cut cylinder fins is using round saw blades in a mill and the cylinder stock or shape to be cut set up in a rotary table. Saw blades come in various thicknesses and I have used .010"; .015 and .020" for cutting fins. Here are some for a Stearman engine. This was was first attempt and the challenge is getting the spacing even. The cylinder head is a separate part.

[Jo NZ]

Thanks Ken. I may well have a go at that - I have plenty of slitting saws. I had thought about mounting several on a mandrel to get the correct spacing (and do it quicker). As I've fitted a digitised read out to my mill I should be able to get the spacing to look OK. From memory, when I used saws to put the fins on the Bentley oil cooler, a minimum fin width of 0.75mm was as far as I could go.

[Jo NZ]

Nearly there with the gearbox - just the clutch actuator to add.

The complex bit on the top is the Positive Stop Control - I'll quote "The principle of this control is a step by step change, the control lever always returning to a central or normal position. The travel of the lever is regulated by a stop in either direction and the movement is such that only one gear-change can be made at a time."... "It has been developed to provide a quick and positive gear change for racing machines, thus enabling the the rider to keep both hands on the handlebars, giving better control of the machine."

[Banditclone]

Very meticulous and impressive work. I been scrounging parts for years to build a small scale cnc. Raspberry pi powered. Got 90% of the stuff or one of my old arduino's. Love your progress.

[Jo NZ]

And on to the carburettors.... There are 4 SUs, pre 1935 so not even the first"H" type, and information is very sparse. The only identifier is a stamped number on the side"1530". I had a few pictures of period carbs so started with the choke size (1 1/8") and estimated my way around the drawing.
I drew one using a picture from the car, and then realised that they are all different.
As the front engine is canted over, and the carbs need to remain upright, the manifold flanges are angled. The float chambers are fitted to either side, depending on the position of the carb, and the float chamber tops are also handed where the fuel union enters....and the float chambers appear to be bigger than standard, presumably because BM ran on Methanol. Here's a picture of one in situ. It illustrates the relationship between the carb and manifold quite well as it's more exposed than the others.



Here's my version

[MODEL A MODEL]

Wow! Such density! There are so many parts to just as many sub-assemblies!

[Jo NZ]

In 1/8 scale the whole lot is 1" long. It should look better when I print it in 1/4 scale for a standalone display model...

[Jo NZ]

There is a raised script on top of the SU float chamber - It says "S.U. Adderley Park Birmingham" and it's curved to fit the top.
Like this



Fusion 360 has recently been upgraded to easily etch or raise lettering on curved surfaces. Unfortunately only on single curves, and the float chamber lid is part of a sphere. I tried a 2d engrave of the lettering but it didn't look right. I was discussing this with the guy who gave me the original 3d model and he offered to do it for me! Said - it's my job, I do this sort of thing every day. I sent off the 3d model of the lid and it came back with the script on it - marvellous! Then I discovered that there are two different lids - they are handed with fuel inlet being effectively mirror imaged. That isn't a problem, however the script won't mirror...
I solved it by taking a spherical cut of the lid, leaving only the script, and then joined it to the mirrored lid. It seems to work - and - it is just readable in 1/8 scale.



I have been printing parts as I go along, and because I've got big fingers and the parts in 1/8 scale are small, I've printed them in 1/4 scale as well. It's much easier to see where any fit problems are, and also how to split the parts for assembly and painting.

I've started to model the rocker gear, but I have a feeling I'm going to be making four different rockers...

The model so far - this a test piece, so I've only painted it for a quick look....

Drive side



Timing side



Carbs and inlet manifold (a deep breath when I fitted the manifolds - there is a gap between them - just).



And the first valve rocker. The whole thing is split into 3 components so that it can be assembled. I still have no idea how the full size ones are fitted....





As you can see, there are castellated nuts! I had no idea they were standard in Fusion so I started to make my own - see the timing gear on the back of the crankcase. Then I did a search and found them - and in Imperial sizes too.

Jo


PS - looking at the pictures I realise that I have the SU script upside down. Ho hum....