Difference between revisions of "Monkey Press Construction"
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Revision as of 22:10, 10 July 2011
This is a detailed overview of my pneumatic press, complete with part numbers where applicable. For a more general overview of operation of the press, see The Monkey Press.
The mold is adjustable for different effective edge lengths, and different nose/tail lengths and rises. I tend to stick with a single camber block that has yielded good results for us over a broad range of shapes and lengths. I have an ever growing selection of nose/tail blocks. If a new block shape is needed for a particular build then I’ll design a new one and whip it up on the CNC machine.
The press is designed to handle boards up to 200cm long with ease. It’s built out of steel W12x40 I-beams that are 12” high, 8” wide, 9’ long and weigh 40lbs/ft. There are two beams side-by-side on the top and bottom for a cavity width of 16”. The top beams are supported by two 16” long beams turned on their sides for a cavity height of 12”. That puts the total weight of just the I-beam material in the press at 1,547lbs.
Many question the use of I-beams turned 90 degrees as the separator between the two layers, and yes, in the limit, there is the possibility of minute deflection allowing bowing of the upper and lower beams. In practice, however, I have not found this to be an issue.
Airflow to the bladders is controlled with a hand-operated lever air control valve, 4-way, 3-position, closed center. Part number 3368K26. It’s hooked up so that when the lever is in the center, no air flows. When the lever is to the right, air flows into the bladders, and when the lever is to the left air flows from the bladders out the exhaust.
The exhaust is muffled with a simple sintered bronze exhaust muffler, part number 4450K2. It’s about $2 and completely worth it to save your hearing.
Overall pressure to the system is limited to 90psi with a simple brass pop-safety valve, part number 48435K72.
There is a pressure gauge and pressure regulator on the input side and a gauge on the bladder side to monitor the actual bladder pressure when the valve is closed.
People usually have a lot of trouble constructing leak free bladders. They usually seem to end up with a lot of “goop” involved in an effort to stop leaks at the ends and at the through couplings. The bladders in my press are essentially leak free to 90psi with only Teflon tape.
The ends are held together with standard 1″ angle iron from Home Depot using seven 3/8″ Grade 8 bolts: two on the outside ends, one in between the hoses, and two through each hose. They’re torqued down pretty snug, but we didn’t kill ourselves tightening them. No silicon sealant, plumber’s goop, etc., and no leaks.
The through couplings were more of a challenge. We went through a few tests before settling on what you see below. If you look closely at the full sized image you’ll see a little soapy water around most of it. This picture was taken with the bladders at 90psi. Again, no goop. The secret here is the combination of the three kinds of washers, and the simple fact that the nut for the panel mount coupling is on the outside of the bladder. The washer configuration is repeated on the inside. The 1/8″ thick rubber washers are against the bladder, then the steel, then the Aramid/Buna-N between the steel and the brass nuts. The result is a great seal with the bladder, and a great seal to the nuts. This is not super-tight… just snug, with a little deformation in the rubber washer visible during assembly.
The steel washers are the standard 3/4″ washers from Home Depot. Here are the other parts and the McMaster-Carr part numbers:
- Med-Pressure Extruded Brass Thrd Pipe Fitting 1/4″ Pipe Size, Panel Mount Coupling, 50785K273
- 3/4″ Screw Size, 2″ Od, 1/8″ Thick Large-Od Extra-Thick Reinforced Rubber Washer (10), 90131A106
- Aramid/Buna-N Washer 3/4″ Id, 1-1/2″ Od, .0625″ Thick (5), 93303A317
These parts aren’t super-cheap, but they’re completely worth it.
All aluminum used for mold skins is 0.032” 5052-H32 aluminum that I get from Alaskan Copper & Brass Company here in Seattle. From bottom to top I have the following: the MDF mold, one aluminum skin, the bottom heat blanket, one aluminum skin, the aluminum base mold skin, the snowboard, the aluminum top mold skin, one aluminum skin, the top heat blanket, one aluminum skin, the 1”x16” steel cat track bars, the bladder, the top MDF mold and 2×4 fillers.
Put another way, again from bottom to top, it’s: the mold, the bottom heat assembly, the board assembly, the top heat assembly, the track, the bladder, and the top filler. This allows for easy insertion of the board into the press after wet layup.
Each assembly is held together with a very simple system: 4 holes are drilled near the edges of the aluminum skins, two on each side, and the two sheets of aluminum with either a heat blanket or the laminate are held together with small lengths of 12awg copper wire, or with zip ties. You can see these poking out the sides in some of the pictures.
Cat track suspension8858T21, 100’, red.
- find the part numbers for the small s-hooks
- link for the copper soldering guide.