Lots of dif ways of doing inletting. I never inlet a lock with a chisel. I know allot of guys do & that is fine, but I don't.
I cut the line I want with a Exacto knife with a heavy blade, then go inside the inlet & cut half a V to that first cut & lift out the sliver. I go all the way around the lock inlet like this.
Then I go back over all the initial cuts & do it all again. Then I take a chisel or carving tool & remove the inside area, trying to keep the inlet area flat.
Then I blacken the edges of the lockplate with Inletting Black (just a little will do it) and I lay it on the inlet & lightly tap it & remove the lockplate.
Then I make the cuts to adjust to where I am off.
DO this til the lockplate will start in by tapping it lightly with a plastic mallet.
Then remove the lockplate & do it all over again, til I get the lockplate down to where I want it to be.
It is important to make your cuts straight down, be it with a knife or a chisel. You will have a tendency to go IN & this as you get the lock panel worked down & the excess wood removed from the top, you end up with gaps in the lock inlet, thus it looks poorly inlet.
When I get the lockplate down in the inlet ? 1/8" or so, I look at how much more I have to go to make it fit up to the barrel at the bolster. If it is allot, then I take a wood rasp & take off about 1/16" of the top of the lock panel & I inlet down again. Repeat.
One the last inlet to where I have it flush to the barrel, I don't take that top wood off the lock panel now. I leave it there while I do other parts of the build. I can take that last bit off any time.
The reason I leave it is if I bump the lockpanel on the vice or whatever & ding it, I have protection there, as I have left this wood. If I take it all the way down, I have an issue to deal with & much easier to take wood off later, than to try to swell a ding out.
Keith Lisle
PS: I suggest a 5/16" vent liner. This way if you screw up, you can go to a larger size. If you screw up the 3/8" one, you really have a problem......