Design spindle adaptor - A2-5 to D1-3

I bought a cast iron backplate for the Tree from ebay, as this was the only example I could find. My hope was that I'd be able to bodge it so that it would allow me to fit my collection of D1-3 "Camlock" chucks, faceplates etc to the Tree rather than have to fork out for a whole new set. It may turn out to be usable in some form but there's clearly not enough meat on it to be able to use it for an A2-5 to D1-3 adaptor as such. I'm going to have to make my own from barstock.

Let's dig out the spec for the A2-5 and D1-3 spindle noses. They are both specified in BS ISO 702 (parts 1 and 2). 

They are both conical couplings but the A series use bolts, while the D1 series use cams to hold the chuck in place. 

• A1-x series have 2 bolt circles
• A2-x series have one (outer) bolt circle.
• The second number denotes the size (diameter). 
• They all have 7.125 degree cone angle (1:4 taper, tangent 1/8)
• Mine is an "A2-5" ie one bolt circle and 133mm diameter.

As for the D1 series, the nose tapers and diameters are the same as the A series. So you could remove the cams from a Camlock chuck and it would fit an A series nose. In my case, I have size 3 Camlock chucks and a size 5 nose, so the cones are different diameters. Never mind.

A series:

Mine only has the outer bolt circle. Note the drive pin and the fact that there are 12 fixings, so it's possible to use either 3 or 4 bolts if preferred. If you have a 3 -jaw or 4-jaw chuck or a D1-3 adaptor, the fixings won't need to get in the way.

Here are the cams. The form on the LHS is the "size 3" used on the D1-3.

CAD modelling:

Let's create something to work with. To start with, the A2-5 spindle nose used on my machine. Note that in my case, I have 7/16" UNC threads, not M10. Other than that, the dimensions all seem to agree.

Now for the "standard" D1-3 spindle nose. This is what my chucks etc would expect to encounter eg on my Bantam.

Clearly when you mount the D1-3 nose on front of the A2-5 nose, more meat needs to be added to accommodate the taper nose of the A2-5. Also, the A2-5 fixing bolts would fall outside the D1-3 profile, so the diameter will need to be increased. At this point, it's no longer the "standard" spindle nose, so I have freedom to redesign as required. This also includes the cams, which need to be lengthened. And I can change / move the retaining screws.

Here we go - rear view:

Front view:

Front view, mated with A2-5 spindle nose:

And here's the modified cam:

Let's order some steel for the adaptor. I'll go for 4140 (aka EN19T). It needs to be 135mm diameter by 60mm long, so 140mm x 70mm it is - and 2 off in case I fuck up the first attempt.....