I lied...
Entry posted by Swede
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I still had a bit of work to do on the electronic hydraulic pressure gauge system, and the result, I think, is worth a blog entry. If you haven't read the background on this thing, read my entry on the 9th of April for the whole story.
Any gauge for hydraulic pressure is going to suck and be a pain to use if it is not convenient. With the transducer in its current disk-shaped form, it was going to be very difficult to utilize. I decided, then, to encase the transducer in two massive blocks of 7075-T6 aluminum, which is both harder and stronger than mild steel, yet machines beautifully. The sandwich and the transducer platform would form the base of the hydraulic press, and anything pressed on top of it will be indicated by the voltmeter on the amplifier.
Work starts with two blocks, 4" X 6' X 1.5" thick, roughly band-sawed from a larger plate. The first step, not shown, was to drill, tap, and countersink the two blocks so as to form a secure, bolted sandwich that would not flex or bend under extreme pressure. This called for no less than eight alloy bolts, 5/16-24 X 1.5" long, around the perimeter. Once sandwiched and held together by the bolts, I was able to clean up, and square, the exterior of the device.
The sandwich is held in a 6" Anglock mill vise, and a Lovejoy face mill does the honors. The Lovejoy cutter is one of the finest cutting tools I have ever used, and never fails to leave behind an outstanding finish. Note the black-painted and quite coarse surface being cleaned up by the mill:
All four edges were milled, and the sandwich became square and quite attractive.
The next step was to create the nest for the transducer on the bottom side of the top plate, which will allow the bottom of the transducer to rest on the intact lower plate. The transducer is 2.75" in diameter, and since there is no home shop that I am aware of that has a 2.75" drill, such a major hole is best started by a more modest drill like the 3/4" drill shown here, with a pilot hole already drilled, and then opened up with a boring head.
A boring head is a single-point cutting tool that cuts any sized hole by offsetting the tool radially. Two massive dovetailed steel blocks, adjusted by a precision threaded leadscrew, adjusts the size of the hole.
Probably 20 to 30 passes were needed to open the hole to 2.75". Having both the transducer to test-fit, and the use of telescoping bore gauges, I was able to cut the hole to maybe 2.755", leaving 0.005" for clearance, making it easy to install.
Almost done! The cable for the transducer needed an oddly-shaped channel milled into the aluminum. I used both normal end mills, and ball-nosed end-mills, to cut the channel as shown for the cord. This whole process, up to this point, created a HUGE amount of Al swarf. Once again, I was tempted to collect it, but it is far too coarse in general, even for go-getters or visual effects, much less using it for any form of burst. It all ended up in the trash.
Time for final assembly. The two blocks of aluminum are shown here, along with the transducer. Finger-pressure was all that was needed to seat the transducer upside down, in the upper plate, with the cord in the channel.
The very last thing I needed was a disk to set on top of the transducer, and oddly enough, this was one of the tricker pieces to make, as the lathe chuck jaws interfered with much of the cutting. The disk started out as a slice of 3.5" dia. Al round, and the recess for the nipple on the transducer was carefully machined. It was then turned down to 2.747" to fit into the recess smoothly, yet not bind.
Everything went together nicely. This thing is probably overkill, but again, I wanted a device that would last a lifetime, and hopefully this whole setup will do the trick. An additional benefit... it is portable between presses.
The end result is a nearly 3" diameter pressure-sensitive "work surface". Rocket tooling can be placed upon this disk as a base, and the pressing of rocket tubes, AND the corning of BP, will be a snap with this rig. I tested it in the press, and it works perfectly.
This is the last of the non-pyro blogs, hopefully! 
Time to get to work for the Fourth of July. Hopefully, this year will see a nice, moist fourth, and no burn-bans. It would suck to create a nice display, only to have to put it aside due to dry conditions.
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