Drawing The All Important Arc:

DO NOT USE STRING!! STRING CAN STRETCH AND DISTORT THE CURVE!! THE PEN AND NAIL MUST BE TIGHT SO THEY DONT MOVE WHEN YOU’R E DRAWING THE CURVE ..STRING WILL  NOT ALLOW THIS. ..THESE PLANS ARE FOR A 9 FOOT HIGH HALFPIPE, BUT YOU CAN USE THE  PLANS FOR ANY SIZE, FROM 5 FEET TO 9 FEET. THERE’S A LITTLE KNOWN FORMULA IN RAMP BUILDING, FOR PROPER TRANSITION, AND IT GOES LIKE THIS:

STARTING AT 5 FEET, USE AN 8 FOOT RADIUS AND ADD 3 INCHES FOR EVERY FOOT OF HEIGHT:

*These size ramps cannot be built using this method, because 9 feet is the max TRANSITION you can get out of one sheet of plywood.....adding 3 feet of vert to make it twelve feet high, however, is no problem!

DRAW ON PAPER, NOT PLYWOOD.........THERE’S A REASON FOR THIS....LATER..

WHERE DO YOU GET PAPER THAT SIZE? YOU MAY ASK......GO TO WALMART, KMART..WHATEVER AND BUY A BUNCH OF SHEETS OF POSTERBOARD, THEY’RE AROUND 2 FEET BY 2 1/2 FEET AND  TAPE THEM TOGETHER, WITH 2 INCH CLEAR TAPE. TAPE EVENLY AND EQUALLY, SO THEY ARE  SQUARE..IMPORTANT! FIND A HARD FLAT SURFACE, AND TAPE THEM TOGETHER IT LIKE THIS, ABOUT 10 FEET LONG AND 10 FEET WIDE ...














LOOKS A LOT MORE COMPLICATED THAN IT IS...HAVE SOMEONE HOLD THE WOOD BLOCK (WHERE THE BOARD IS NAILED) SO IT DOESN’T MOVE...RUN THE PEN OVER THE PAPER WITHOUT TOUCHING THE  PAPER AND POSITION IT AROUND UNTIL THE PEN IS MEETING THE 9 FOOT AND 3 1/2" MARKS SIMULTANEOUSLY ...ON BOTH AXIS..MAKE SURE THIS IS EXACT..ITS A LOT EASIER TO DO IT NOW THAN AFTER YOU HAVE CUT IT OUT OF PLYWOOD:

WHEN IT IS 3 1/2 " INCHES IN AT BOTH POINTS, YOU HAVE A CENTERED ARC. NOW DRAW THE ARC, AND GO OVER IT A FEW TIMES TO RULE OUT ANY MOVEMENT OF THE PEN. MEASURE A 45 DEGREE ANGLE FROM THE LOWER LEFT CORNER TO THE RADIUS EDGE..THIS IS DONE WITH SIMPLE MATH OR A (REAL!)  LARGE PROTRACTOR..FOR THE MATH, MEASURE 12" HIGH, 12" LONG, FROM THE LEFT CORNER , 18"  HIGH, 18 " LONG FROM THE LEFT CORNER AND SO ON TILL U GET CLOSE TO THE RADIUS EDGE; (SEE  DRAWING A ) USE A SQUARE.. DRAW A LINE, CONNECTING ALL THE POINTS..BE EXACT.. IF THEY DON’T  CONNECT, YOU NEED TO DO IT OVER...IF THE ANGLE ISN’T RIGHT, IT WILL WRECK THE CURVE.  NOW CAREFULLY CUT THE TEMPLATE OUT....FIRST CUT THE ARC AND THEN CUT ALONG THE 45 DEGREE  ANGLE LINE... THE 2 HALVES ARE PLACED OPPOSING EACH OTHER ON YOUR 3/4" PLYWOOD (THIS IS  WHY YOU CAN’T DRAW THE ARC ON THE PLYWOOD) SO YOU GET 2 PIECES PER 1 SHEET OF  PLYWOOD...MINIMUM WASTE.

BEFORE YOU GET READY TO CUT THE TEMPLATES OUT OF PLYWOOD, YOU NEED TO MAKE ONE MORE CHECK: PLACE THE TWO PIECES TOGETHER, END TO END, LIKE THIS:
 
 

WHERE THE TWO ENDS MEET, THE BASE OF THE CURVE NEEDS TO BE HORIZONTAL, JUST AT THE POINT WHERE THE 2 PIECES MEET FOR A SMOOTH TRANSITION .SAME WITH THE VERTICAL..THIS RAMP ONLY ATTAINS 90 DEGREES AT THE VERY TOP, AND 0 DEGREES AT THE VERY BOTTOM..IF THE 2 PIECES ARE NOT YET AT HORIZONTAL, OR THEY ARE BEYOND AND START CURVING BACK UP, YOU’LL GET A DIP OR BUMP WHEN YOU RIDE IT..NOT COOL! IF THIS IS THE CASE, REDRAW YOUR RADIUS TRACING STEPS. AFTER MAKING SURE YOUR PIECES MEET PROPERLY, PLACE YOUR TEMPLATES ON THE 3/4" PLYWOOD, AS SHOWN BELOW:

TACK THE TEMPLATES IN PLACE WITH SOME PUSH PINS, MAKE SURE THE TEMPLATES ARE SQUARE WITH THE PLYWOOD’S EDGES, AND AS A SECOND CHECK, THAT THE ENDS ARE 3 1/2" HIGH. TRACE THE TEMPLATES WITH A PEN; PENCIL IS TOUGH TO SEE ON PLYWOOD. REMOVE THE TEMPLATES, CHECK THE PEN LINES, AND CUT THE CURVES FIRST WITH THE SKILLSAW..IF THE BLADE IS BINDING AND DOESN’T WANT TO FOLLOW THE CURVE, BACK THE PRESSURE OFF, AND PROCEED SLOWLY..IF YOU ARE NOT USING A SMALL ( 5 1/4") BLADE, YOU WILL HAVE TOUGHER TIME FOLLOWING THE LINES. WHEN YOU ARE SATISFIED WITH THE CUTS, CUT THE45 DEGREE ANGLES...YOU WILL NOW HAVE 2 PIECES OF PLYWOOD, WHICH, QUITE FRANKLY, DON’T LOOK LIKE MUCH...KINDA SMALL..UNTIL YOU PUT THEM TOGETHER...ALL OF A SUDDEN, 8 FEET BECOMES 9 AND IT STARTS LOOKING A LITTLE MORE IMPRESSIVE..PRETTY COOL, EH?NUMBER THE FIRST 2 PIECES "1" AND "2" AND SUCCESSIVE PIECES "3", "4", ETC..MORE

LATER ON THIS.