Put a Ring on It

With the propane locker well underway, I turned my attention to the lid.  The rules are pretty clear that it must be top loading, and the lid must not require any fancy tools to open in order to access the required manual shutoff valve.  After working through a multitude of lid options, I settled on the elegance of a round Beckson-style access port, or what is often referred to as a PYHI ("Pie-Eye").  

Several brands make them, and they all follow the same basic design at first blush.  My original plan was formulated around a terribly heavy 5# Worthington bottle, and it's diameter required a 10"cutout.  This led me to the only obvious option that fit, which is produced by Sea Choice.  I unboxed the new lid the same night it arrived from our friend Bezos, and was left with feeling pretty discouraged.  The thing worked, yes, but it was unsightly with its plastic alligator skin texture, and obviously huge.

At the same time that I was facing disappointment about the new lid, I was facing an even more daunting dilemma.  No matter how I positioned the new locker in the boat, I was having an extremely difficult time getting the floor of the locker high enough to create a drain that actually flowed properly downhill to exit above the waterline.  It was agonizingly close, but not really happening.  It hurt my brain to re-direct, but I needed to take the plan in a new direction.  With that, I decided to nix the Worthington, and go with 4 Flame King bottles instead.  The benefits of this move are as follows:

• Safety-  The biggest possible leak would be 1# of gas.
• Flexibility- The ability to take just one bottle at times.
• Weight-  The Worthington bottle was a brick.
• Height-  Utilizing the small bottles buys 3" in height savings.
• Storage-  Ability to share bottles with a Magnum BBQ.

Here is a look at the Worthington cylinder and 10" Sea Choice lid.  With a little more space, this would probably have been the go.  My propane locker was built around this lid, and it's a good option for someone with a little more space.

Having committed to a pry-out lid, and now embracing the small bottles, I felt no regret in getting away from the 10" plastic behemoth from Sea Choice.  In addition to down-sizing the opening, I concocted a plan to ditch the ugly plastic ring altogether.  To do this, I grabbed a 1/4" thick sheet of G10 and roughed out three circles, which were then perforated, stacked and bagged, to create a 3/4" blank.  The next day after work, I set about the task of CNC cutting my own ring, 1mm at a pass with the little, underpowered, 800W spindle.

After tediously milling the top side, in order to perfectly index the top and bottom features when I flipped the part, I milled a fixture in a scrap of MDF, and beat the part in with a mallet and carved out the back side.

With the new ring cut, I tried to plug an 8" Beckson lid into it, but it wouldn't work as the gasket would roll up on itself.  Puzzled, I took a closer look at the Beckson ring in higher detail.  As it turns out, their system is much more clever than I had anticipated.  If you look really closely at the ring, there is a 15 degree ramp, then a flat, and even a counter-ramp to the profile.  The idea is that when you press the lid on, the gasket has an inclined plane which helps it seat, then a reverse to keep it in place.

After chewing on it for a few minutes, I came up with a plan and ran it by Bill Walker, an incredible woodworker near where I live.  He said if I were to do it on a router table, I should pull against my fence, not push.  With that in mind, I sacrificed the wheels off some $5 roller blades I had kicking around from last year's Rotary Auction, and chopped a scrap 2x4 at the appropriate slant.

Finally with the lid fitting, I threw it back on the CNC to cut pry-out rebates.  As I have no Z-control, apart from the bike skewer stopper, this involved breaking the tool path into a series of steps, and lowering the bit manually 0.5mm each time to create the right wedge.