Sent: Thursday, November 08, 2007 11:28 PM
Subject: A new WTC, The 2" SubDriver, Part-4
Attachments: DSCN0130.JPG; DSCN0134.JPG; DSCN0138.JPG; DSCN0120.JPG; DSCN0144.JPG
A new WTC, The 2" SubDriver, Part-4
A Report to the Cabal:
It's late, I've been working all day without a nap, Rose has gifted me her cold (THANKS, Rose!), my puncture wound is festering, and the frig'n Writer's over in Hollyweird have managed to get 24 off the air for the duration. Union scum! Overpaid, under worked, formula puking, Liberal, Hack's!
Anyway .... were was I?
Oh yeah: I finished producing the single, two-piece, multi-cavity tool that will form all the resin pieces needed to build a KILO SubDriver unit. Now to show how I cast the parts, with an emphasis on how I encapsulated watertight seals within two of the bulkheads as well as within the 1/16" pushrod seal bodies (which are later inserted into the motor bulkhead and after ballast tank bulkhead).
The casting resin of choice is Alumilite's RC-3 (they say it has a 3-minute pot-life, but don't you believe it, it kicks off sooner than that!). The rubber tool halves are clamped hard together between two wooden strongbacks secured with rubber bands. An electronic scale permits easy measuring, by weight, of the resin and hardener. Water thin, this stuff has no problem finding every nook and cranny within a properly gated tool. Two smaller 'ready service' dispensing bottles are used to pour the liquids into a common mixing bowel.
Once A and B are mixed you have to work quickly to fill the tool, get it into the pressure chamber, button down the lid, and slam one-atmosphere's worth of pressure in there. As a practical matter, you have less than 2-minutes to get it done!
I have four of these pressure chambers on hand under the work table. I have huge pots in the corner of the shop for bigger jobs, those custom made to my specifications. A pot like this you can buy from Harbor Freight for less than forty-bucks! You'll need a high CFM compressor or a big volume tank to top the pot off with pressure in time to beat the resin -- you want to have pressure in there before the resin 'kicks' i.e., make the state change from liquid to solid.
A bunch of cast parts, ready to be snipped away from their sprue and vent channels. I guessed right on the amount of oversize to crank into the masters -- all bulkheads fit right into a test sample of the 2" Lexan tube I have, without need of machining. I caught a break there, I've eliminates a machining step for each bulkhead. Great!
You can easily see the two 3/16" diameter brass mandrels projecting from the two ballast bulkhead parts. These brass rods each hold an O-ring or quad-seal in place during the casting operation. When a mandrels are removed from a cast part it leaves a seal in place girdling the bore formed by the mandrel. The rubber packing, being elastic, springs out a bit into the bore where it will make contact with the slid in place conduit tube, effecting a watertight seal between it and the bulkhead. Pretty neat ... huh, kids?
I sacrificed one of the bulkheads to cut it away here to demonstrate how a quad-seal (I'll use O-rings when those things run out) is suspended within the casting. Note how that seal projects enough into the bore left by the mandrel to make contact with the outside of the conduit tube. Also seen here is a cut-away of a 1/16" pushrod seal, showing how its little O-ring is situated within the seal body.
I'm repeating this shot from the last Cabal Report to again point out how the 3/16" diameter mandrel works to suspend an O-ring or quad-seal half-way within a bulkhead cavity within the tool. Atop are five 1/16" diameter mandrels supporting O-rings within the cavities that will give form to the pushrod seal bodies.
A close-up of how the quad-seal and O-ring type packing are encapsulated within a bulkhead and seal body.
Ah, nuts to all this ... I'm going to bed!