Hi. I'm building a custom front wheel from a 48 hole hub with a large flange and a 48 hole 20-inch BMX rim. I'm doing a 2 cross pattern. Have it all laced up now but not tight, about one turn of the nipple onto the spoke. The problem is that the spokes protrude through the rim in 4 different lengths (I'll do my best to explain..) They're grouped in 4's as you go around the rim. The first spoke is just the right length, the next goes through the rim a little bit more , the third maybe an eighth more, and the fourth spoke threads are all the way through the rim hole, way too long. Then the pattern repeats, all the way around. The two longest spokes are the ones that go through the hub from the inside out, the two shortest ones go through the outside in. I went through the spoke calculators several times and came up with a spoke length of 156mm which is what I'm using. Can anyone shed light on what may be wrong?