I didn't get a chance to look at your model and split
You can make the interlocking surface between your parting surface and the split sketch
This sketch plane can be above or below the parting surface and should be bigger than the outer edge of the parting surface.
If the outer edge of the parting line is not a regular shape, better make clean before split
Youu can specify the interlocking angle at the split dialogue
Hope this helps
Hi John. I didn't realize there had to be a sketch on the split pane but now that i have I've got another problem with the parting surface. I cannot get the parting surface any bigger than 40 mm without part of it disappearing so therefore cant draw the sketch inside it Have you any idea what could be causing this? it only happens on one side of the model although it is a mirror. I've attached 2 images of the model 1 at 40 mm and the second is 50 mm. Thanks
Ok thanks John ill have a look at that