von Paul Vos
Forging threads with Lennart Hoffmann
A nice presentation how to forge threads by Lennart Hoffmann. After the last presentation in May and a holiday now behind us, we are back to work.
The Treff once started by explaining how to make forged utensils with the materials and techniques used. With the discussed topic, we are completely back to the roots.
Screw thread forging is a challenge. Because how do you do something like that. Especially if it needs to be extra strong for use in a leg vise. After deep thinking for a long time, Lennart found a way to forge a threaded end for his workpieces -leg vices- by means of open die forging.
Open die forging is the process of deforming a piece of metal between multiple dies that do not completely enclose the material. The metal is altered as the dies “hammer” or “stamp” the material through a series of movements until the desired shape is achieved.
However, for screw thread forging, the dies must closely enclose the workpiece. After all, it is a workpiece that must be dimensionally stable for the vice to function properly.
The method devised by Lennart gives an astonishing result. See his presentation!
For the length of the metric thread, the size of the dies isn't that important because you're essentially screwing the bar between the dies while working on the power hammer.
A method of making the inside thread (like in a nut) is to copy it from a threaded rod by heating a close-fitting pipe/sleeve and squeezing it several times around an existing thread between the press or power hammer and a V-block. This method requires extra alertness during forging because there is a chance that the sleeve will shrink around the thread and then never come loose again.
He recommends the steel grades C45 for the thread and C60 for vices nut. It is important to properly lubricate the workpiece with graphite during the forging processes.
For this Lennart made a simple mixture consisting of hammer scale, graphite and animal fat.
Lennart also forged wood screws as an experiment. It is difficult to get the imprint to the mold. After the initial impression from the wood screw, one has to deepen the impression with fullers and chisels
Lennart found 10 very engaged listeners from 7 countries, with whom he shared his experiences and answered questions.
We will make another post, when the recording is published.
The next Treff is on September 11.
Start: 19.00 CEST
Room Open: 18.40 CEST