Here are a pair of homebuilt frames for small cats. The goal was to design a frame that could be fabricated from easily-available parts, with no welding or bending required. Both have been tested in class IV water and with cargo loads. I'll describe the features in each photo, and add a list of materials and sources below. (I also built a breakdown frame for a 15 ft. cat, with similar parts, using double-rail corners and more wood parts.)
NOTE: Double-click attachments to see full-size pix.
Breakdown cargo or 2-passenger frame (shown without the rear seatboard) for Jack's Cutthroat tubes (13' 6' long x 16" diameter). This is all 1.315 OD" galvanized steel top-rail tubing and 1" IPS Hollaender SpeedRail joints. The seatboard is mounted with two U-bolts, kept from slipping sideways by large-headed machine screws. The top-rail tubing should always be plugged at the ends with pieces of 1.25" hardwood dowel, about 2" long. This keeps the set-screws in the SpeedRail joints from indenting the tubing, which causes the joint to loosen up.
Same frame. The floor is PolyMax kennel grid, reinforced with aluminum angle, pop-riveted underneath, and padded with foam pipe insulation (held on with plastic cord ties). A 1" rigging strap helps support the weight. I also use heavy-duty hoseclamps (see pic below) to keep the floor snug on the frame. The NRS oarstands are sized for larger tubing, so I had to: 1) slide a piece of fuel line over the U-bolt; 2) Slit a piece of reinforced hose to fit over the frame tube; and 3) Put extra washers on the bolts, so the nuts don't go beyond the threads. The inboard oarstand bolt is capped with an extra acorn nut, so there's no sharp thread exposed.
This shows the flip-up seatboard, the u-bolts, and (barely) the machine screws that keep them from shifting sideways. You can also see the hoseclamps holding the floor to the frame. I cover the unengaged part of the steel band on the hoseclamp with heat-shrink tubing, so it won't cut the inside of the tube. The hoseclamp screws should be beneath the floor decking (i.e. they need to to be tightened from below).
This is a (rather sketchy) play frame for the Cutthroat tubes. Main differences: 1) the corners are pieces of 1" conduit, drilled and set with 1/4 machine screws and acorn nuts (to cover the sharp threads). 2) The seatboard is a structural element, held with U-bolts (also capped with acorn nuts). 3) The oarstands are welded "rainbow" type, drilled and bolted in place (i.e. not adjustable lengthwise except by drilling more holes). They're also heavier than the NRS model. 3) The rear drop uses 2 heavy-duty plastic conduit ells with top-rail pop-riveted in the middle. Don't use plastic for key parts of the structure.
The only function of this piece is to keep the tubes apart and hold straps from the inside d-rings.
I used some weird double-curve tubing for the inside rails (industrial hog-shelter parts). The floor is a half-panel of PolyMax kennel floor. The front edge is reinforced with aluminum channel, pop-riveted underneath, and supported in the middle with a loop of webbing (twisted so it won't present a foot snare). The seatboard and footbar are covered with a peel-and-stick 3M nonskid that comes in a 4" width. (The gray stuff is just as sticky, but less abrasive than the black sort.)
SpeedRail 1" IPS aluminum joint and 1" conduit ell corner, pinned with 1/4" machine screws and two different types of nut. Brass acorn nuts are pricey, so I mostly use regular plated ones. The other nut is a self-locking type. The important thing is that the sharp threaded ends of the bolts are covered. It's also good practice to smooth the cut ends of tubing (wear gloves) until there's no possibility of slicing flesh or a tube. Both tubing cutters and hacksaws leave vicious edges. Another thing to watch is having the set-screws in the SpeedRail joints facing a tube. In that case, I wrap the joint with the non-sticky Vet Wrap, used for horses' legs and available in feed stores and pet supplies.
NOTES: 1.25" dowel plugs in the ends of the tubing are absolutely required for SpeedRail joints, if you don't want your frame to come apart.
To mate a conduit ell directly to a SpeedRail joint, I had a friend braise a section of toprail over the conduit.
– Chainlink toprail tubing, galvanized steel, 1.315" OD. Any hardware or fencing store, in 21 foot lengths @ 20-30 cents per foot.
– Conduit 90° ells, 1" nominal. Any hardware store. Likewise, machine screws, bolts, U-bolts, acorn nuts, hoseclamps, fuel line, washers, etc.
– 1" IPS SpeedRail joints. Most-used: No. 3 Elbow, No. 5E Tee-E, No. 9 Side Outlet Elbow, and No. 11E, Side Outlet Tee-E.
Minimum order is $100, so plan ahead. See online at <www.hollaender.com> or order at 800-772-8800.
– PolyMax Kennel Flooring, STK# HA2215 or HA2217, 2' x4' panel @ $15.95 from <www.TekSupply.com> or 800-835-7877.
– Oarstands: cast type with U-bolts from Northwest River Supply <nrsweb.com>
"rainbow" type mfg. by Cambridge Welding (also various corners, etc.) from Sid's Sports, 801-261-0300 (for illustrations see the Jack's Plastic Welding website: <www.jpwinc.com>).
That should be enough to keep you out of trouble.