Curious how other might go about this.
You have a blank door, 1-3/4″ thick wood veneered with a engineered core similar to strand board. You are tasked with cutting in a narrow lite. So you need to cut out a 6″x30″ rectangular opening that will later get flush trim so the cut edge is exposed for everyone to see. You have all the normal woodworking tools at your fingertips tablesaw, circular saw, routers, hand saws, chisels, etc. No CNC available. There is a woodcraft less than 10 miles away if you need a bit or something. Go.
Replies
Strand board core, left exposed at the end? I'd never leave that exposed. Covering it makes cutting out the opening easier as well.
I'm reading that the strandboard will be covered by a flush-fit window insert...
Make a hardboard template for use with a downcut spiral router bit using a PC guide collar. The smaller the bit is the less handwork you'll have to do. Tape and razor cut the line before you start routing. Tape the back also. Pre-finish if the tape might create fuzz when you pull it off.
Rout to a depth that will let you run an upcut bearing-guided bit against the ledge. Use anything you have to remove the waste inside of the routed groove as close to the outer edge of the lite as you can. A larger bearing and/or bit combo could work leaving the same template in place. Leaving less interior waste will make your finish cuts cleaner.
Go back to the downcut bit and do passes to remove the remaining waste as deep as you dare, then switch to an upcut top bearing flush cut bit. Pull off the template and use the routed lip to guide the rest of the cut. Finish up with hand tools to get your corners squared for the insert.
If you really want it to come out crisp, you are facing two problems: tear-out ahead of the cut, and router bit chatter.
First remove the bulk of the opening material with a saber saw.
To limit tear-out, I would make a rectangular jig that contains the router. Use a large diameter bit (7/8"-1&1/4") with of course a 1/2" shank. Measure from the router bit to the edge of your router's base (I would use a circular base.) Use that measurement to make your rectangle bigger than the desired hole. Once you have it made and securely clamped in place, tape a layer of thin veneer to all four sides, reducing the cut by the veneer's thickness. This makes your final cut on the door veneer very light. Light cut and large diameter bit reduces tear-out. Removing the bulk of the waste before removing the veneer also will reduce bit chatter. Remove waste most of the way through, but don't use a bit that is longer than necessary, as that will increase chatter. After the veneer is removed, again cut most of the way thru, but taking multiple shallow cuts rather than deep ones. The first one can be really shallow, just to cut the edge of the opening.
Put a layer of veneer on the inside of the opening, turn it over, and use the largest bearing guided trimmer bit you have to remove the last of the waste, remove the veneer, and trim again with shallow cuts. Trimming into the corners will be the most dangerous moments, as the bit is cutting larger areas.
For trimming the corners square, use a sharp chisel with a flat back. I made a jig by gluing two 4" straight narrow pieces together in a 90º angle, then gluing two guide blocks to the last 2" of the inside edges of the two legs, that will fit against the sides of the routed opening. Clamp the jig in place, and trim the corner. Only the first part of the trimming needs to be accurate, as that veneer edge is all that will show. Check the finished opening with a square or stick of wood to make sure that there are no lumps. Be forwarned that the composite interior may rapidly dull your chisel.
This is the way, except for a thin door a jigsaw is easier to control.
I think we are talking about the same tool. Not a "Sawsall" or bayonet saw used for demolition, but a hand held jigsaw or saber saw. And not a scroll saw, which is the stationary tool used for cutting veneers and thin stock. The terminology for these guys has always been a bit variable.