I needed to make slots in the grilles that cover the actual speakers in my Melodium Restoration project. Since the pieces are small, about 4" x 4" (102mm x 102mm) and I needed four slots spaced 1/4" (6mm) apart, I decided a jig or template of some kind would make the job easier.
A 1/2" bit and a guide bushing with a template could give me a consistent slot, but what about the 1/4" spacing and working on such small pieces? The easy solution would be a template with four 5/8" slots. But I don't have a 5/8" bit to make that easily.
My solution was a step-and-repeat jig that only required a template with one slot and allowed the template to be moved in increments that yielded 1/2" slots on 3/4" centers with 1/4" between them. The slot in the template was made by drilling two holes with a forstner bit and cutting the slot with a jig saw.
The base (photo 1) has a two template supports (marked A and B in the photo). Side (A) has 1/4" spacing holes drilled on 3/4" centers. The pieces to be slotted will be pin-nailed in place between the supports.
Photo 2 shows the template on top of the supports and a 1/4" bolt used as a pin for registration. On the opposite side of the pins is a cleat attached to the template so it can stay square and slide along the left edge of the base.
Photo 3 shows the end result after routing. Both pieces were stacked and routed at the same time so they would match. The final photo show the grille in place on the Melodium.
1. I attached the cleat to the template before attaching support A to the base. I had to put a pin thru the template registration hole and into A to line everything up. I pushed the cleat flush along the left edge of the base while trying to space support A properly using the registration pin in the top hole. When in position, A was pin-nailed to the base.
It was a mistake because I did not succeed in getting Support A square to the base. The result was that as I moved to the other holes the cleat was no longer tight against the left edge and I had a little bit of wiggle. You can see that my bottom slots are sloppy on the left end. Annoying but not worth redoing for this project.
2. I should have attached support A to the base first, making sure it was square. Then used the pin to register the template making sure it was square to the base and finally aligning the cleat along the left edge of the base and attaching it to the template using pin nails.
In any event, the jig worked as planned. As usual, it took longer to think about and build the jig than it did to cut the slots.