Adapter to fit a Record Power SC1 chuck directly on UNC 3/4" x 10 tpi. (as on Oneway Live Center)

I sometimes want to mount my bowl or vase on the lathe in reverse direction for sanding or light finishing touch-up but I want to keep the alignment of the chuck that is still mounted. 

I then drive the bowl with a soft prop chuck and mount the SC1 chuck on the live center. 

I want to keep the load on the bearings of the live center as small as practicable, so I preferably use a small light chuck like the Record Power SC1. There are two problems though: First the original steel adapters to mount the SC1 on a UNC3/4x10 tpi are no longer produced and, second, they are heavy. Stacking 2 adapters (Oneway's UNC3/4x10 to M33 and RP's M33 to Record Power 40 mm) is even more heavy, and also it increases the length, so putting the weight further away from the center of the bearings.   

I therefore made this small light adapter that features a direct mount. Also it is as short as practicable. 

The model, including the external ‘Record Power’ thread, was made by myself in OpenSCAD. For the internal UNC ¾ × 10 thread I used elements of the UNC library by Gilles Bouissac/agentscad. 

The hexagon on the LiveCenter side of the adapte was designed to fit the 43 mm spanner delivered with the KS lathes. I needed to grind a little off the hexagon on my print to make it fit in the spanner.

I printed my copy in Prusament PETG, standard settings, 0.4 nozzle, on MK4. 

I use it only for the purpose I designed it for: Alignment and Very LIGHT WORK at AT LOW RPM with the workpiece SECURED BETWEEN CENTERS. I consider it DEFINITELY NOT A REPLACEMENT FOR OR EQUIVALENT OF THE ORIGINAL PARTS. 

I use it only for light workpieces and before I do I make sure the headstock and tailstock are perfectly aligned. I usually drive the workpiece via some flexible connection, like a sanding pad or soft rubber pad.  If I do not do this I would very quickly ruin the bearings in my Live Center. 

Anyone deciding to print this and use it for the purpose I use it for, or for any other purpose does so on his own risk and liability.    

Note: for accuracy I designed the model to have a tight fit at room temperature. Plastics do have a much higher coefficient of thermal expansion than steel has, so fit may be less good if your workshed is very hot or very cold. If, in winter condition dismounting the adapter from the live center proves difficult it may help to keep the assembly in a warmer place, under your clothes if must, for a while to warm it. Do not try to force.   

Where, in theory this adapter could be used to align an SC4 chuck, this is not recommended because of the weight of that chuck and the size of workpieces it is used to hold.