The smoke chamber is basically the same as one in a handout from Frank Turley's Blacksmithing School. I don't know if it's his design or someone else's, but it works very well. I have a removable visor which is rarely needed on the smoke chamber. The smoke chamber sits between and is bolted to the two angle irons bolted at the back of the forge. I have a 10 inch smoke pipe that is about 16 feet long, fitted with a chinaman's cap. It ends at about 2 feet above the peak of the shop roof. The smoke chamber draws very well and I have no problems with smoke in my shop unless a 10 x 12 foot door that is about 6 foot from my forge is open and a cross breeze blows across my fire.
A note about chimneys:

• Sufficient Fresh Air: For a chimney to draw properly, it is essential that enough fresh air is entering the building to replace the air consumed by the fire that goes up the chimney. I believe many smoke problems are caused by this lack of fresh air entering the building.
  
• Chimney Height: Generally speaking, the higher the chimney, the better the draw. A higher chimney contains a larger volume of gasses which are less dense than the surrounding air. This creates a larger pressure differential causing better draw.