If you want to mill an angle on a metal plate when the milling machine does not have a tilting head. A sine plate can be used, but it takes up a fair bit of vertical room and requires a set of gauge blocks to prop it up with, you also need to know how the sine function works and make use of it. How to mill angles or how to cut angles on a mill? Instead of using a sine bar, you can figure out the vertical deviation over a known distance and set up with a plunge indicator or those fin angles, probably don’t need to be at a perfect set angle, just eyeball it on a standard bevel protractor. If your bevel protractor is small enough, you can set it on the bottom of the vise and rest your workpiece right on the blade. Do not adjust the protractor and do the same to flip the part to the other side.

Here is a video from Youtube shows the technique for how to set a super accurate angle without expensive sine bar or gauge blocks, it is precise than you would get using a protractor and a scribe. Suitable for cutting an angle on a part in a mill and do not have angle gauges.