josh harrignton gill
If you don't do this often then I would advise that you use a coping saw as it is cheap and fairly easy to use. however if you have a lot of scribes then I would suggest investing in a jig saw. for the miter cuts. You're cheapest option is getting a miter box, this will guide the hand saw so you can achieve a 95 degreee angle. if you have a lot to do it might be woth investing in a chop saw which you can pick up a basic one for around £100. hope this helps.
