Well both Jason And Dave have the right idea but its not quite how I did it.
The next step was to attack the castings with an angle grinder to remove any lumps and bumps, the final finish will be corrected with filler and paint towards the end.
I thought it might be an idea to get under the skin in the critical areas with a roughing cut, the last thing I needed on the finishing cuts was to hit a hard spot and blunt the cutter before all the segments were finished.
Here is the first cut holding them in a normal vice.
Agian the vice was used to hold them for the second face to be cut, I uded my digital angle gauge to get them positioned somewhere near flat.
This was where I nearly spoilt my one spare casting, as soon as the cutter bit into the metal it just dragged the casting over in the vice, apart from a couple of unwanted cutter marks on a face that was going to be re-machined anyway that was all that happened.
It just shows how easy it is for something to move in a vice though.
So after a bit of thought I jury rigged a back stop and approached the part from the opposite side to ensure the cut was pushing the part against the stop.
Dave mentioned a "sine bar", well I dont have a sine bar big enough, but I do have a sine table.
This is a lovely bit of kit that I normally use with a pair of centres on it for measuring tapered shafts etc.
In this case I need an angle of exactly 22.5° so I can tip the milling machine table to that angle as Jason suggested earlier.
Once I had the sine table set to the correct angle, I clamped it to the table making sure it was square to the tee slots. The mill table is then tipped up until until the top of the sine table is dead level again.
This is done by using a verdict indicator on the "Y" axis slide, I took a great deal of time over this, as any error here would be multiplied by eight when all the segments are bolted together.
Jason had the right idea about flipping the fixture round but I did not use the vice, I chose to use the rotary table to ensure repeatability.
I have drawn out the profile on Solidworks 3D, so I know what some of the key dimensions need to be. But in reality it does not matter too much if the finished size is slightly out. The most important thing is that each segment is identical.
So having machined the casting that had the least amount of spare metal first, I settled on the final cut depths and zeroed the DRO for both "Y" & "Z" axis.
This is one cut.
And this is the other.
After spinning the job 180° the same two cuts were done at the opposite end with same DRO readings, thus ensuring that relationship between the angled faces were all the same.
Jo mentioned the grub screws in the base of the fixture, these were individually adjusted to make sure there was no "rock" and that one of the machined side faces was square to the top of the rotary table.
I did use the same fixture for one other job, and that was bringing the flange thicknesses down to the correct size.
My next challenge was how to get all the holes in the correct place, there are four holes for the bolts that pull the segments together, and two in each end for the bolts that holds the spoke flanged end so that it spans the joint.
I wondered about using the same fixture and the DRO on the mill, but eventually chose a different approach.
More later.
Phil