This overclamp knurler requires a quarter of the force in the tensioning screw required by scissors type knurlers. I really have to be very sensitive - only medium force is required on the T-handle to complete a knurl.
It knurls as close as 8mm from the chuck jaws, and is held off the chuck quite securely by its own angle bracket.
I can start the knurl by tensioning, or by traversing the saddle with some tension on the screw.
Moving the arms to accept different stock diameters, or interchanging the wheel, takes only minutes, as a result of making sure that all pivot bolts are a nice working fit in their respective holes.
I am astounded that I do not see more examples of this design. The only weld was to attach the vertical with the arm pivots to the horizontal tool bar - everything else is tapped and countersunk holes, and nuts and custom made setscrews.
|The parts out of the box for this overclamp knurler. The large angle bracket bolts to the cross slide and the knurler arms slide on it to prevent z-axis movement with comparatively lightweight contruction. I have a choice of springs to fit around the tensioner screw to hold the arms off the work when the tension is released. The support arm for the pivot is designed to fit in a Dickson QCTP.|
|Details of the construction. The through bolts for the knurler wheels have shallow heads These are recessed to allow close approach to the chuck, and locked by sinking a thin rod centred on the edge of the head. The lower snap shows a view of the knurler from above. The space between the arms accommodates the wider of the knurlers I have, and I shim out narrower wheels with washers.|
|The view from the chuck end. There are four holes to choose from for each of the arms, so for larger stock the arms are lengthened and the pivots get separated. The hand screw is very sensitive and needs only a quarter of the force that a scissors model does. Every scissors model I have used seemed to be straining itself. This knurler makes it a breeze.|
|The knurler set up to work on four inch stock - the geometry of the tool adjusts to this size easily. Thicker stock means I have to change the upper and lower arm pivots, and I have to fit a longer piece of allscrew for the actuation, and longer springs to match.|
|The knurler laid out in its cardboard box ready for use. It only takes a couple of minutes to change the pivot points for a larger or smaller diameter.|
|The knurler set up on my Colchester Bantam ready to knurl what looks like 1 1/2 inch stock with three holes in it. The root bar of the knurler mounts in any of my standard height QCTP holders. You can see how the angle bracket constrains the arms or the knurler in the Z-axis, making for high precision work. I can see that a small change in the construction of the bracket would allow the lower arm to drop below the level of the cross slide.
You can see the small clamp at the back. I fit this between two springs for wide stock to help force both arms off the work when the tension is released.
|A close up of the results from the above knurl. Each arm is two steel strips with spacers, all screwed together. The screwed construction allowed me to make late changes to the design, and would also allow treating the inner surfaces of the arms should they wear.|