Up until a couple of years ago the extent of converting I did on models was fairly minimal; a weapon swap here and there. Maybe a head swap if it wasn't too difficult. I rarely did anything complex, so there was little in the way of planning involved.
More recently I've been doing a lot more advanced conversions, in some cases involving parts from 5 or 6 different models. With that level of work and commitment to chopping up nice old lead, I've starting implementing a bit of a structured approach to converting my models, illustrated by the image below, which is a walkthrough of the process involved for one of my Gutter Runners for my Skaven Blood Bowl team:
Step 1 - Concept: I'll normally have a fair idea of what I want the finished figure to look like, but I find it helpful to make a visualisation of the concept. Here I've drawn up a collage of images from the GW 1991 catalogue (courtesy of Stuff of Legends). By playing about with different combinations at this stage, I avoid the dreaded scenario of hacking apart a lovely old figure only to find it won't work and leaving you with a pile of useless (and worthless) bits of lead.
Step 2 - Chop: Using the concept as a guide, the source models are carefully dismembered and reassembled in the right pose, with pinning at all the key joins. In the case of the Skaven Gutter Runner above, there's 6 donor models: Skaven Lineman (head); Skaven Thrower (right arm); Skaven Blitzer (torso); Skaven Catcher (left glove); Elf Catcher (legs); Mordheim Skaven Casualty (feet and tail). At this stage the pose needs finalising - you'll notice I changed the head position to alter the feel of the model from the concept, so he now looks like he's fending off a would-be tackler!
Step 3 - Rough Sculpt: Now the pose is sorted, all the damage from the cuts needs repairing, and some elements need sculpting from scratch. I've learnt that sculpting is all about layering and patience - start off with structure and layer up to finished details. At the rough sculpt stage I want to fill in all the gaps and provide areas to sculpt the finished details onto. You can see this best with the left upper arm where I just added bulk to add fur onto.
Step 4 - Detail Sculpt: At this point all the final surface details are worked on; blending joins in armour, sculpting the collar onto the chestpiece and texturing the fur. Hopefully after this, the model will be ready to paint.
Step 5 - Paint: Once the conversion is finished, it can be painted just like any other model, and with any luck people will be blown away by the results!