Bo, from experience JB Quick sets up in 15-30 minutes, there is a point when it's like a plastic, when it's about half dry. Then can be cut/shaped with a sharp knife. After it's dry it can be smoothed with fine sandpaper, easier control w/ a piece of sandpaper by hand then a Dremel sanding roll by my experience. I learned to slightly over-fill with JB quick, and cut/file or sand it down after it's set. I agree w/ you on filling in a Groove to do over, I'd use water to cool bit in that case instead of oil to avoid contamination of epoxy.
I've never painted a throttle blade, but I have outlined a finished Groove w/ black felt pen for visual contrast. Ron told us it's OK to have scuff marks on the blade, happens to me every time. In the pics I posted above, the plate is shiny, 'cause I did plate shaping to it, removing the bit scuffs.
Unfortunately I wrongly thought you were using some type of cut down cutter bit to do your Groove job the bit looked wrong to me in the first pic. There is a good chance your first Groove could have worked. But you're becoming familiar w/ metal epoxies and different techniques. I use different things to apply epoxy to give me pinpoint control where I put it-an old flat blade screwdriver, a narrow popsicle wooden stick, whatever. In becoming a Gadgetman you learn to improvise and figure stuff out. I learned to closely look at whatever TB I'm going to Groove. Some of the details of Grooving are in the training DVD, the rest you learn as you go.
You can continue on w/ this TB, or just find another and start again.
I see there is an Idle Air Control (IAC) bypass channel in this TB. See the big wide black trench below the Groove area, and the square ridge just above the upstream center of throttle plate. Notice that square ridge has a hole in it. I so far don't see the Idle Air Control valve itself in your pics, it may be off of this TB. Anyhow, look at this square ridge/hole, see if/how it has a tunnel going to that big trench under the Groove. That's an IAC system, the IAC valve would mount to TB, and control bypass air through this hole and trench. Next- see the 2 square openings in the bottom trench, these openings are where IAC idle air dumps into the inlet air stream. How much air the IAC valve allows through this top square hole, bypassing the closed throttle at idle, and dumping in below the closed throttle blade, determines engine idle speed (RPM). The engine needs air to run-but the throttle plate is closed at idle. The IAC valve and air passages let the needed air in for the engine to run at idle. The IAC valve, opens up more at cold start, to give a higher idle speed, then starts to close off the airflow through the passages as engine warms up. The more IAC is open, the higher the idle RPM is, the computer controls this. It also can open more when you run the air conditioning (if the car has it) to support engine idle load when A/C is on at idle. This is normal and OK.
I'm going to talk of a slightly "advanced Gadgetman technique" next. Bo, you can apply this to this TB, now or later, if you want.
In our case, you have to look at a TB and think of how the airflow is, air behaves as a fluid. I see a problem w/ the upstream raised square ridge around the hole, and w/ the right side square opening in the bottom trench. Ron taught us that in many cases the IAC valve, NEVER completely closes. This means- some air is entering the engine, and it's NOT going in through the Groove, instead the IAC airflow, whenever the IAC is open, goes AROUND and bypasses the throttle plate. We are trying to enhance manifold vacuum, remember, in the training DVD? But this IAC flow is adding in air much like a vacuum leak. Plus, see that square opening at right side of bottom trench--see how it's downstream from right side of the Groove? IAC air is going to dump in there, and disrupt part of the Groove's "waveform". The left side trench opening, it's just about under the throttle shaft, pretty much out of the way of the Groove's "waveform" so it's probably OK to leave the left side opening alone.
That square ridge in the casting, around the IAC entry hole above the closed plate, well that ridge is going to disrupt the boundary air, the air going in that sticks to the TB casting's bore wall, and is crucial to building the smaller tighter rotating air vortex in the Groove. I would use the sanding roll on your Dremel, and carefully smooth down that square ridge, just get that ridge gone and keep the existing round shape of the bore wall. I might smooth it down w/ fine sandpaper after the sanding roll.
For that right side bottom trench opening--Bo, if you can use spray carb. clean or brakeclean, or whatever, get the black crud out of that trench, and shoot a pic or two of that trench so we can see it good. I'll give details of what I'd do to it after I can see inside that trench clearly. I'll probably recommend some epoxy work in that area. By the way, I learned, to first completely clean all crud and carbon from a TB, before I do anything else. This way there's no solvents interfering w/ any epoxy work! Also Bo, with any IAC valve, I ALWAYS completely clean off all crud/carbon from the round pintle end, the actual valve that opens/closes to control air in the IAC passages. A dirty IAC valve can stick open, and cause sudden un-controlled dangerous high idle RPM. That can cause a traffic accident!
Bo, we're glad you're here, and thanks for posting so many pics of your work, you are learning a lot now! Plus these posts, will help other Gadgetmen learn as well! You're doing well!
Tracy G