I started putting a small layout together a year and three months ago. I’ve now installed over 20 standard (no sound) decoders in new and used analogue diesel locomotives I’ve bought from eBay and others. I admit I fried several decoders [:$] along the way but I’ve gotten better … I hope. I’m now wondering if there are any companies or individuals who do milling for the speakers if I were to get some sound decoders for my Kato N scale E8/9’s. I don’t think Aztec does that anymore.
I do have a Dremel tool (cordless) and some cutting wheels, etc. but would be reluctant to ruin a frame.
[#welcome] to the forum, your posts are delayed in moderation for a while.
When I lived in Maryland, I had a friend with a milling machine. He showed me how to use it and milling was simple. I wouldn’t want to do it with a Dremel but if you go that route, wear eye protection.
There are people, who I will call extreme hobbyists, like my friend the motorcycle nut, car nuts, machine shops and some gunsmiths who have the tools and might be willing to tackle a small job.
You can also trying contacting small machine shops around your area. A few might be looking for work and wouldn’t mind doing a one or two-off project during off-times.
I would first figure out what speaker/baffle you want to install. Next figure out where you want to install the speaker on the frame then draw up a quick but fairly accurate drawing (with tolerances) to give to the machine shop. I would also give them the speaker baffle to use for checking fit.
The key is to remove as little of the frame as possible - i.e. just enough to get the speaker to fit so that the shell snaps on; retaining as much of the frame weight as you can so that your locomotive will be able to pull a good length of rolling stock behind it.