Don't forget to clean up when finished cutting. I place all of the parts except the frames in zip lock bags to keep any flying debris away. IAfter cutting, vacuum all around and usually change my shirt to keep the particles out of the mechanism. A bath in soap and water scrubbing with an old toothbrush cleans the frames. A little compressed air speeds drying.
also VERY important is to totally strip the chassis before you start grinding. do not attempt any grinding or cutting with the motor and gear towers/bogies installed. better still is to take the chassis outsidce to do it so no little bits of metal can find their way into mechanisms. and also clean the frame well afterwards to make sure there are no stray bits of metal statically attatched.
Thanks mfm37 - the dremel tool (number 199 - if anyone is looking for one), worked just fine. It was quite a simple task to machine out the speaker shape with this tool. First I used my Bench Grinder to take out the bulk of the material, then I fine tuned the fitting with the Dremel #199. I hope that it is of use to others who want to shape the frame themselves, as it didn't take long (about an hour - all done). Anyone else who is contemplating this - just be carefull to only take our the depth (thickness of the speaker)required to fit the speaker in. If you take out to much hight in the frame you will weaken the bit on the other side of the frame that holds in the sprung copper contact strip.
Then your second best option would be asking a local machinist.He likely knows nothing about model trains but still,he's got the knowledge and proper tooling to do it.And it may not be so expensive after all.However,like David said,it's not a good idea to start with.
This is the high speed cutter I've used in my dremel:
http://www.dremel.com/en-us/Pop-ups/Pages/ProductImages.aspx?pid=199&tab=1
I've cut them with a Dremel and a rotary cutter blade. It looks like a small circular saw blade. Be careful. If you hang an edge the cutter will fly out and do serious damage to your fingers and hands. I've also used an end mill in my drill press which is a PITA to get set up.
Now I use Aztec. John's turn around is fast and his prices are very reasonable. He could cut a box full of frames for less than the doctor would charge to stitch a finger.
Has anyone had any success in grinding out a shape in the fuel tank part of the frame for mounting a DCC Sound decoder speaker? I read in the instructions to use a rotary tool. I tried with my rotary tool and it didn't even make a scratch! What are the frames made of (Atlas Dash-8) anyway? The are incredibly hard. Can I use a bench grinder or a hand grinder with a metal disk? Or will these destroy the frame? Has anyone successfully done it? I have been searching all over the net and can't find a web sight that will explain how to do it with what tools.