The finished jig holding a piece of of 3/4in brass. The actual work-pieces will be shorter.
Purpose:
This is an engraving jig I plan to use for fabricating wax stamps, and wood brands. At the time of writing, I have completed the left side of the jig, which will be used for making stamps, and have left the right side of the jig unfinished so that I can add the proper geometry once I have finalized a brand design.
Design:
The design in it’s current form has two critical elements. The first is a large central pocket for use as a height reference. It is sized to fit our tool analog tool setter, and should make setting heights relative to the bottom of the part easy. The second critical feature is the actual part pocket. The brass hexagon is mounted on an eccentric socket head cap-screw such that it can press work pieces against jig as shown.
Precisely locating the part in this fashion takes a lot of the pain out of using round work pieces by allowing us to reference off of the included z floor, and x/y slots to get the part zero. Since the jig is rectangular, it can then be removed and returned to the vise without losing those zeros with the help of a workstop.
Note: This system works okay, but it required some tight tolerance machining and is a bit fiddly to set up. If I were making this part again I would locate the cylinder on a V, and mill a small V or ID radius into the Mitee Bite where it interfaces with the workpiece.
The piece immediately after the first operation, with the profile and lower surface cut.
Fabrication:
The part itself is composed of 7068 aluminum, and was machined in two setups. First, the bottom was faced and the outer profile of the part was milled. Neither of these operations is critical to the final performance of the part.
Second, the pockets, tapped hole, corner relief slot, xy references and engraving were milled according to the following order. It was important that all of these features be added in one setup so that their relative positions would be as precise as possible.
Using a 0.4in gauge block to get the x axis offset. I have found this method of reaching under the “hat” to be repeatable to half a thou or so in practice.
The part was faced with a 1/2in endmill. This does not provide a critical surface.
The pocket was first roughed with a 1/2in endmill using an adaptive strategy and then finished with a conventional pocketing strategy using the same endmill.
Next, the critical pocket edges and two reference edges were cut with a 1/2in endmill using a profile strategy.
The corner relief slot was milled with an 1/8 in endmill using a slotting strategy.
A 10 thou chamfer was put on all upper edges in to break the burr.
The MiteeBbite hole was then spotted, drilled, and tapped to 1/4-20 x .5
Finally my makers mark, and the writing was engraved on with a 20thou engraving ball.
The preceding operations ended up resulting in some warping towards the height block pocket, so I then cleaned up the underside of the part on a manual mill, and debured the remaining edges with a 600grit moldstone.