Charlie G, Zander H, and Chad M. machined a bulkhead from 6061-T6 aluminum. We've determined that this is serial number 3, after the two bulkheads made for Hermes 2. It is a fit-check article, intended to support piston tests.

Creating Blank

Waterjet stock

Payload Bulkhead Stock Rev2.DXF is attached. This is the file that was used to waterjet the octagon blanks.

Preparing CAM

Used HSMworks

Facing op for nice top finish

Bore operation for nice ID surface finish

Pocket op to prepare for filet

2D contour to add in 1/16 in fillet

Milling

The part was set up in the mill, a small section was machined to allow tools to be touched to set the z-height for the tool table

Machining started with a .5in end mill. The initial z-plunge rate was high enough that the machine didn't have enough horsepower to keep up, stalling the spindle and breaking the tool.

The Z-plunge rate was lowered to a 50 thou step-down. This worked pretty well

Not all the operations were selected when the g-code was exported so, the remaining operations were posted, exported, and uploaded to the machine

At some point in time the 1/8in ball end mill z-offset became incorrect. It was re-zeroed and the final CNC mill op completed

A drill feature chart was prepared and a lot of holes were drilled

Turning

The bulkhead does not fit on the lathe chuck jaws in either orientation of the jaws, so a mandrel was turned.

The mandrel uses the bolt circle for the piston

The mandrel was chucked up, the bulkhead was bolted on, and the bulkhead was indicated in.

The OD of the bulkhead was turned to size.

Radial Indexing

First the radial indexer was checked for parallelism with the table using a precision ground rod.

Using the same custom mandrel as used with the lathe, the Payload Bulkhead was set up on the radial indexer. 

The part zero was found using an edge finder and the starting angle was found by using a dial indicator and pins in the main face holes.

Holes were center drilled, drilled to 0.159" dia, and tapped to 10-32 at increments of 45 deg.

Deburring, of course.

Manufacturing Defects

The ID surface finish is not very good, either the F/S were wrong or the tool was dull, or it need a contour finish pass. The rough surface finish made indicating it in on the lathe difficult.

The fillet op plunged a little too deep (2 thou) this was due to the tool table trouble

The stock started a little thick (12 thou), and the roughing pass plunged a little too deep (8 thou). These helpfully offset each other. Also a FoS of 6 makes it a non-issue.

The antenna pass-through is a little undersized (20 thou) because the right drill was not available.

Suggested manufacturing improvements

Clear ID stock with an adaptive clear using radial stock to leave, then finish with a light 2D contour finishing pass to clean up ID.

If we're okay with a larger fillet, we could machine the whole thing with a bull nose end mill, eliminating a tool change.

Leave a center hole to help locate the part on the lathe.

Start with a smaller blank, and give it more sides (12 or 16) so turning is easier and we can use smaller stock.

Design Improvements

We're already milling the heck out of it, doing the lightening pockets would not be much extra work.

Replace the antenna passthrough with SMA bulkhead pass throughs, easier to integrate, more professional, less chance of damage to avionics or antennas. Also stress relieves antenna cables. Easy change, just a different hole size.

Would integration be easier if the payload stack interface pattern were tapped holes with jam nuts on top?