i have a cobra com lathe, and i had to make sure the com is cutting straight on bit during cutting. adjust the v blocks to where they are no tapering in your com cuts, and onces you get is set perfect becarefull to not let it get banged up in a pit box or else where ,, because of the chance of it getting knocked out of line again. if you just put it together they can be up to .004 off in play in the v blocks,just loosen the screws and adjust the postions of the v block to get a square cut, so i would make sure that is square,, and cutting true. also like people have post make sure the bit is cutting just above the center line in com. also make sure the lathe is truning in the right direction,, if the com seems its trying to jump out of the v block its spenning toward the bit its backwards,, the com should be spinning away from the bit,, or thats how it is on my cobra,, and it want be jumping around on you,, but for just make sure its cutting true with some old coms and calipers,, then you set,, i dont know if this helps any but maybe something will help you from my post.