These pages are provided by HABA Members from notes they made at recent blacksmithing demonstrations conducted at monthly meetings. If you can provide a note to publish, please send content to your HABA webmaster. FORGE WELDING A KNOB ONTO A ROD
NOTES AND INTERPRETATION FROM THE HABA ROB LYON DEMONSTRATION
submitted by David Bailey
Welding a knob onto a rod is a useful and relatively easy forge welding process. It can be used for producing knobs of various shapes for handles, finials, bolt heads, and other applications requiring a mass on the end of a rod (see figure a). It involves forging a collar onto the rod and then forging the collar to the desired shape.
A collar formed of half-round stock (prepared on a swage) will produce a sphere and a collar formed of rectangular stock will produce a cylinder, a cube, or a bolt head (figure b).
For smaller stock, heat and scroll the end of the appropriate collar stock so that the inside diameter of the scroll is a tight fit on the receiving rod. Mark the collar stock with a chisel to the apparent length needed (at an angle so that the outside circumference will be larger than the inner), heat, and cut off on a one-bevel hardie (figure c).
Flux both pieces, drive the collar onto the end of the rod, and complete the bend around the rod. At this point, the collar should make a tight friction fit all around and there should be a gap between the ends of the collar. If there is no gap and you hit too hard as you weld, stretching the collar, you’ll be welding at one point and forcing the collar away at another. Flux again, bring to a welding heat, and weld using a light hammer and a half-round bottom swage. Forge into the desired shape.
Be careful in the final heat not to let the collar fall into the fire when removing the parts. Lift the end up rather than sliding it out. If the collar should slip down either in the fire or in preliminary welding, simply drop the rod into the pritchel hole or an equivalent after the initial weld and flatten the rod end, welding it to the ball (figure d).
For larger stock you need to calculate the collar length more closely. Make the length of the collar the diameter of the bar times 3 (not quite pi) plus the thickness of the collar stock. This will produce a collar not quite meeting when bent and slid over the rod. The gap allows for some stretching during the welding process. Cut the collar ends at an angle such that the outer and inner circumferences will be equidistant at the joint (figure e).
In shaping the knob, the spherical and rectilinear shapes are intuitive. The faceted cube involves forging a cylinder into a cube, placing a lower corner of the cube onto the anvil and hitting the opposite top corner, thereby flattening those two corners, rotating the cube to the next set of corners and repeating the process. Alternating this faceting with dressing of the original flats will produce a sophisticated, appealing shape. You may leave the corner facets smaller than the original faces or enlarge them to the size of the flats. Additional shapes could be achieved using swages or treadle hammer dies.
prepared Jan 28, 2003
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