morticed nut blocks

I have read that many, perhaps even most Central European crossbows had their nut-blocks reinforced with horn and set into a mortice.  My question is, when did this become the norm? Was there a point where it was usual to carve the socket for the nut directly into the stock and then add a reinforcing wedge of horn?   For those of us with the correct tool-kit, is it quicker/easier/better to cut the socket directly into the tiller or go with a morticed block?

Mortised/horn-bone reinforced nut sockets: The easiest way to do this is cut two blocks of bone or horn, about 1 inch by 1/2 inch, and as long as the stock is wide.  Cut two slots into the top of the stock and glue the blocks in place.  Then cut the nut socket with a forstner bit... preferably on a drill press, to get it really straight.  That will get you a good reinforced socket. 
Down side of the above system:  It leaves the sides of the nut socket pretty weak. Strong bows may tend to break out the spacer, and you'll spend a fair mount of time fixing the problem. 
Second way: cut a block of wood, make the same bone slugs, inlet them in the block, and then drill thru between the blocks.  Now you have a nut-socket without a stock. Cut the pre-made socket to the size you want, mortise a corresponding hole in the top of your stock and install the pre-made socket.  This gives you a much stronger stock thru the sides, but it's a lot of trouble to do if you don't have a mortise machine or a mortise attachment for your drill press.  Can be done with hand tools, but it will take time. Does that make sense?  That's how we do it in my shop anyhow.  Geezer.

I recently used the 2nd method Geezer mentions (both antler blocks attached to a base plate, drilled from the side, slotted from below for the trigger, then inletted into the top surface of the tiller). It worked well, and made a very tough, low-friction socket for the nut.

In earlier builds I didn't use reinforcing blocks, and did see a bit of damage and cracking to the edges of the socket from use. I think blocks are a good addition to any bow, and probably absolutely necessary with bows over a certain power level.

Pic shows the set of blocks and nut, ready to install:

Yes-yes: exactly right.  You do very nice work.
These days I bone-reinforce the socket on every bow I make over @ 100 lb. draw.  Geezer.

Just a quick one, I know I should know, but what sort of radius should the nut be, and, anyone able to supply one? I'm fairly confident i can carve one, but...

Roller nut size:  I have seen them as small as one inch (25.4 mm) diameter and about the same in width... on the slender Padre Island bows, and as large as something over 2 inches in the big wall bow on display in the Kunsthistorisches Museum (Vienna)  On the average, most nuts I have seen on extant bows (tending toward later sporting bows) run 1 and 3/8 to 1 and 1/4 diameter and about 1 inch to and inch and a quarter wide.  (again the roller on the siege bow was closer to 2 inches wide) Figures I have seen in archaeological texts tend to agree.  25-30 mm wide, @ 35 mm diameter.  Remember, the smaller you make the nut-diameter, the more critical the fit between nut and socket.  So I would recommend using a fairly large diameter unless the entire stock is very skinny, like the Padre Island bow.  Geezer

Thanks Geezer

I've red an archeological study about diameters and most of them are between 25 and 45 mm diameters. the average diameter increase from about 30mm at years 1200-1300 to 35 and more at the end of Middle Ages. (maybe because of stronger draw weight).
there are also a very few models of "hammer shape" nuts that are longer than others.