After the trammel platform is complete, the next part to start working on is the trammel arm. This arm consists of a router carriage and two pivot blocks connected by threaded rods, see Fig. 13. The carriage supports the router, the pivot blocks determine the shape of the oval. I started on the carriage.
carriage. When routing an oval frame with a detailed profile, router bits need to be changed frequently. To make this a quick process, the carriage is designed so that it can be tilted up—making it a lot easier to get to the collet
The carriage is actually a frame with a tilting base to hold the router. To build the frame, start by cutting two ends (E) and two sides (F) from W'-thick stock, see Fig. 9.
Next to accept the threaded rods, drill W holes near the ends of each frame end (E). Also drill countersunk holes for the wood-screws that hold the frame together.
tilting base. After the frame is screwed together, a tilting base plate (G) can be cut from V4"-thick Masonite, see Fig. 10.
To support the base plate within the frame, cut two tilting base ends (H) to size, see Fig. 10. Then drill a W'-dia. hole for a threaded rod near one end of each piece. (Note: The hole is located V&" up from the bottom of the base end — it's not centered on the thickness.)
There's one more step before the base ends can be glued to the plate. To keep the bottom of the plate flush with the bottom of the carriage frame, rout a V&"-deep rabbet along two edges of the plate, see Fig. 10. Then glue the base ends to the plate.
bit& mounting holes. Now remove the plastic base from your router, and use it as a template to locate the bit and screw holes for mounting your router to the jig, see Fig. 11.
notch the base. After the holes are drilled in the base plate, there's one last step on the tilting base before it's complete. To allow it to sit down on the threaded rod (see Fig. 13), notches have to be cut at one end of the base ends (H).
To do this, I cut a rabbet on the edge opposite the W' holes, see Fig. 12. (Note: YouU remove some of the Masonite base plate when doing this. That's okay.)
pivot blocks. The last parts to make for the trammel arm are the pivot blocks (I), see Figs. 9 and 13.
After cutting the blocks to size, drill a W-dia. hole in the center and two holes through the sides of both blocks, see Fig. 9. Note: The holes in the sides must align with the holes in the frame ends (E).
assembly. Finally, assemble all the wood parts, hardware, and threaded rod for the trammel arm, see Fig. 13. Once the arm is completely assembled, attach the pivot blocks to the guide blocks with washers and lock nuts.
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