have 16 plate America seen on another forum about drilling out rear baffle have tried but weld very hard anyone else done this gone through three hole cutters already lol !
Yes, it's not easy! You using a wooden plug to help keep everything straight and true ? You might need to get a good brand of hole saw.
I am in Australia so I'm not sure what brands are available in Blighty and Oz ? I went to the Plumbing section bought hole saw kit there, hope that helps. You need to get guide drill centered, as otherwise you will be drilling along/down one side of the tubing.
Best hole saws are Starrett. Make sure the arbor isnt bigger that the hole saw if you need to drill something thicker. Most electrical wholesalers stock them ie City Electrical, Newey and Wilts etc.... https://www.starrett.co.uk/shop/power_tool_accessories/holesaws/?gclid=CKCA-aiE5c8CFYydGwodEhoKOw Or like Mr Orange says get some short Tors or by the time you've spent £50 on hole saws, buy a set of these for just over £100. http://www.classicbikeshop.co.uk/tulip-u-s-customs-36mm-44mm.html
I went for "Forans" short slash cuts, have a removable baffle, so can be louder or quieter ( comparatively speaking lol ). Runs. Sounds. Awesome....