This is where making from bar stock is more preferable for a beginner than making from castings. You can easily get a datum face with stock, rather difficult with a casting.
But that doesn't solve your problem. Finding a datum face to work to.
Without a datum, you will be working totally blind and stabbing at it, hoping everything will line up afterwards. I will tell you now, that way just doesn't work.
Not having the castings to handle, it is difficult to imagine the best way to machine them, but by looking at the picture I can only suggest a way to go.
Looking at the main bottle casting, I personally would go for one of two ways.
The first one is the rim around the top.
Holding the square base in the four jaw, get the casting running as true as possible, you can see how it wobbles about when run up. By eye, get the main bottle shape running as true as possible by moving the jaws and tapping with a soft hammer, and hope that it is nearly symetrical. Then using super fine cuts, turn the end rim on it's outside edge until it has just cleaned up all round (do not take it down to size, that can come later), followed by a very fine skim across the end face. These first two operations have to be carried out very tenderly, as any heavy handling will knock it off centre. Once that is done, you will have a good datum.
If you have soft jaws you would bore them out until you can fit the datum into the recess, but if you don't, put your outside jaws into the 3 jaw self centring chuck, and mount the newly cut datum part of the casting into those. By gently tapping and seating the casting into the back of the jaws, the bottle shape should run true, or very close. Now another very fine cutting exercise, face off across the bottom of the base.
That was the first way.
The second way goes like this.
Using outside jaws, mount the casting by holding the rim in the nipped up jaws, and tap the casting until it is running true by looking at the bottle shape of the casting. Fully tighten up the jaws and recheck it is still running true. Very gently tap to straighten it up. You might need to shim the rim to get the neck part running true as well.
The better you can get it trued up, all following machining operations become easier.
Machine very gently across the casting foot. This will ensure that at least the casting is looking upright when sitting on the foot.
Mount the casting onto your faceplate using the now datum foot, and tap everything straight, bottle shape running true. Now you can machine the rim and it's face, plus maybe the hole in the end as well.
If you can get those two datum faces made, you will most probably find you can mount it onto a faceplate using the base datum, and a mandrel to go into the end hole for mounting the other way.
There is another way, by making a mandrel and fitting it into the core hole in the end, but it all depends on how accurately that core has been placed prior to casting.
Castings have to be machined initially by eye, to get your datum faces. Only then can other machining be carried out.
I hope this has helped a little and not confused you too much.
John
