How much porting could be done on the mill with the right setup and guy. CNC as required. Mild next step stuff. Have too many iron heads to quit now.
With even just the Mill you can get the valve bowl Throat size diameter set which will save a ton of work when you dealing with stock Throat percentages of under 85 and need to go up 90 or better. Here are some shots of a seat cutter being used to enlarge the bowl. Cutting in this way also provides a great indication of how much core shift your may be dealing with which tell you that going above a certain increase in Throat size and the needed size of the rest of the port will be a issue !
The Ostridge! Is a seat cutter the best tool to use? Any feed and speed recommendation's for the cast iron heads? Is there a thread with mild iron head porting basics? Stevem, Are you machining on the valve guide axis in the photos above? Is it primarily the intakes?
To answer your question a lot can be done even with just a Mill if you have one at home , or access to one, the question now becomes do you know where to Mill and how much to Mill?
I am pretty sure Chris Skaling was working on a CnC porting program for the stage 3 heads. I could be wrong...
The Throat rework must always be centered off of the valve inclination angle, yes. All ports shapes and sizes are based on direct geometric principles and then these ideal shapes and sizes are modified/ comprised to fit within a given motors layout and engine compartment space. These geometric principles start off with the size of the valve you are using for a given air flow target. Knowing how to analyze a port in regards to reworking it is paramount to getting increased flow numbers in the average lift range you are thinking about using. For instance a 2.0o" valve needs a minimum of a 85 % Throat to even begin to make good use of that 2.00" valve , this percentage can go up to 91% if we are talking about a exh valve. The size of the Throat used will now determine the minimum short turn height we need. Here's a shot of a short turn template guide made for use with a 1.77" Throat, the template is the OD of a 1.77" Throat ,or .885" radius. This head started off with a 1.60" Throat and flowing 208 cfm to now with a 1.77" Throat and flowing 280 cfm.
So for the sake of discussion...In theory it would be best if a 1.77 diameter ball could fit though the path, for a 2.00" valve? What exactly is the Throat?
You could interpolate some bowl work below the throat cut, keeping the top of the profile conservative and allowing a tiny bit of hand blending into said throat cut when finished. You'd still have to do the short turn by hand and depending how deep you want to go around the guides, determine if you want to use a 5th axis or hard fixturing to reach everything. You could easily set the part at an angle on your roll over fixture and negate the 5th axis. We had a few old 4th axis deals that required a manual button push after an M00 program stop for angle change and to move the parts to the other side of the table to catch a different feature (for those unfamiliar with production machining) If you became more brave you could use a reduced shank inserted ball mill and catch much of the short turn in the machine. Only need two profiles (one for each, I and E) if you set each valve as a work location and flip the program for the mirrored port. Not sure if your CNC or computer allows you to do that, but that would simplify the programming time. Indicate the guides vertical on each end of the head and edge find the rest for work offsets, of course. Most heads I've checked caliper close enough to blueprint locations that a quick check would be all that was needed. That said, stabbing the bowl with a manual machine is going to be quicker if all you are doing is mild bowl work. The program is easier than you think.
I started a porting basics (aka porting for dummies) Word document. Why?.... because I'm middle aged now and my memory isn't getting any better. It's based on what I've read on this forum. Would anyone be interested in seeing and commenting on it? It would be great to get some expert opinions and maybe make it a sticky. Also, can the throat easily be opened by hand?