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Building a wooden mould of a dirt jump

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Building a wooden mould of a dirt jump

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flag minigute
Posted: May 19, 2011 at 6:44 Quote
Do u think its a good idea to make a mould of a dirt jump out of wood so u can have nicer jumps and they wont take as long , what do u think ?
flag cmc4130
Posted: May 19, 2011 at 8:48 Quote
minigute wrote:
Do u think its a good idea to make a mould of a dirt jump out of wood so u can have nicer jumps and they wont take as long , what do u think ?

I don't think it would help. It's not like you can just fill the mold, the dirt will "harden" like cement or ice . . . then take off the mold and your jump is done. You have to shape and pack the dirt as you go.

Get a good strong bow rake and rake the dirt into shape and pack it for every few wheelbarrows dirt you dump on it. The dirt needs to be damp enough to stick together but not too liquid-muddy where you can't pack it.

Unsecure image, only https images allowed: http://www.labsafety.com/images/xl/Structron-Bow-Rake-Long-LSS-_i_LBM113136S.jpg
Something like this .... to me is interesting but kinda weird. Why not just put in the cross braces and make an all-wood landing?

photo
flag minigute
Posted: May 19, 2011 at 12:29 Quote
thanks man this has been helpful but my jumps are taking lots of mud to make and its all going off the sides and isnt getting higher any tips [PI=
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flag Trailboss-Dan
Posted: May 19, 2011 at 14:16 Quote
your dirt is far too dry. you put that in a mold and it will just collapse when you take it away. wait for rain and dig deeper and try find some clay
flag minigute
Posted: May 19, 2011 at 15:18 Quote
the mud was wet i watered it all when building it but it still falls apart i might just try and build the next takeoff out of pure clay cause i found a load of it today but its hard to get cause its so deep in the ground
flag cmc4130
Posted: May 19, 2011 at 15:34 Quote
the main thing is to build and pack the BASE of your jump first. it's going to be a huge rectangular area on the ground. (roughly 6 X 10 feet). you build it higher in layers, like a cake.

as for packing the dirt . . . it does need to be damp enough to stick together. rake it into shape, then walk/stomp on it. hit with flathead shovel . . .hit with heavy 2X4 etc. to pack it. you have to pack as you go, not just make a huge pile of dirt and pack at the end, because the base and middle of the jump needs to be packed too, you can't just have a packed 'crust' on top of loose dirt.


here's a drawing i just did . . . to show how big the base has to be. you're saying that you keep adding dirt but it slides off and it's not getting taller. that's because your base isn't wide enough and you're not packing up each layer at a time....

see, if you're going to have a 4 foot tall jump (at a 55 degree takeoff/arc) or a 5 foot tall jump (at 70 degree arc). even if the sides are slanted relatively steeply . . . you still have to make the base AT LEAST 6 feet wide to get only a 2 foot wide lip at the top. notice also that from the bottom of your transition to the back of the base of the jump along the ground is 10 feet long--most people underestimate the size of the "footprint" of the jump. so at this point, instead of trying to build up... just focus on getting each 1-foot-thick layer packed on to your base rectangle.... does that make sense?

Unsecure image, only https images allowed: http://i255.photobucket.com/albums/hh138/upsetbmx/Pyramid-Method-of-Building-Dirt-Jumps.jpg

Although some people pack the sides up almost vertically (making the launch look like almost a dirt version of wooden launch) . . . . a lot of jumps will be somewhat pyramid shaped, meaning they are a lot wider at the base than at the top, and the sides are packed at a slant.


here's an example of jumped packed with almost vertical sides...
photo

whereas, this line on the right is a good example of jumps that are more pyramid shaped, with slanted sides. the pyramid shape is going to be more durable (stronger, long lasting) even if it doesn't look quite as 'perfect.') Unsecure image, only https images allowed: http://i772.photobucket.com/albums/yy10/stickyfingaz/139.jpg
http://www.ridemonkey.com/forums/showthread.php?t=242376

Another good visual of pyramid style jumps . . . .
photo

Oregon Trails
http://www.ridemonkey.com/forums/showthread.php?t=233036
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