It all depends if you want to do a concentric hole or an excentered one.
For a concentric, you can use router bits with a bearing that will follow the existing hole but adding around 1.2 cm each turn. You can change the bearing for further adjustment. The last turn has to be done with an other bit, still with bearing but bearing of the same diameter than the tool, so it will finish flat (sorry I ignore the english terminology for this). That's easy job.
For an excentered hole, then it's with your jasper jigs. You have to create a pivot support, a piece of wood with another one to compensate the level. The difficulty is to screw it from the inside if the speaker box is not very big. It can be easier and radical to screw it from the outside and when done, fill the screw holes.
Using a new baffle as said just above can be the easiest way finally.
For a concentric, you can use router bits with a bearing that will follow the existing hole but adding around 1.2 cm each turn. You can change the bearing for further adjustment. The last turn has to be done with an other bit, still with bearing but bearing of the same diameter than the tool, so it will finish flat (sorry I ignore the english terminology for this). That's easy job.
For an excentered hole, then it's with your jasper jigs. You have to create a pivot support, a piece of wood with another one to compensate the level. The difficulty is to screw it from the inside if the speaker box is not very big. It can be easier and radical to screw it from the outside and when done, fill the screw holes.
Using a new baffle as said just above can be the easiest way finally.
The best way I have found is to 1st cut a piece of 1/2" MDF that fits tightly into the front of the speaker (assuming speaker front surface is recessed) or is the same size as front of speaker if front is flush. Locate the larger hole center you want to cut in the right spot on the MDF and use the Jasper jig to cut the new larger hole in the MDF. Then clamp the MDF to the speaker and use a flush trimming bit with a ball bearing pilot behind the cutter to copy the hole into the speaker. The trick is that you will need to shim the MDF out for the 1st couple passes enough that the bearing depth is inside the MDF hole. Then drop the shims once you are far enough into the cut that the bearing will remain in the MDF and finish the cut.
It will be easier to start over with MDF (medium density fiberboard.)
I don't know where you are in the world but in the US both Lowes and Home Depot have 3/4" MDF. If that is the same or thicker than your current baffles, you are good to go. They also will give you 2 cuts for free and the next few are really cheap.
Measure your baffle carefully (maybe use a metal ruler.) Most rulers have a very fine scale for the first inch. This seems stupid but first line up the ruler to the nearest inch on the OTHER end. Then you can get really good (1/32) measurement if you look straight down on the ruler/edge on both sides.
Think about whether the tallest inches x 2 will be less than 50 inches. MDF is usually 50 inches wide. If this is true you will only need 3 cuts: 1. slice off the short dimension from the end. 2. set the saw for the "tall" dimension and cut two pieces.
I use the jigs you have with a "regular" 1/4" cutter to do both the countersinking and the hole cutting.
Let me know where you are in doing.
Paul
Depending on whether the existing cutouts are rebated and how deadly accurate you need to be, I'd use a rabbeting router and stepped bearing set
An externally hosted image should be here but it was not working when we last tested it.
mind you if you don't have such tooling handy, and the baffle is not already installed, it might well be cheaper to simply redo
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