I didn't have very many Nighthaunt units in my Legions of the Infernal Skull undead army. In fact, the Spirit Hosts are the only unit that I had finished before the release of the Nighthant Battletome. While I'm not about to re-base my Legion from squares, I have decided to re-base the Spirit Hosts to match my round-based Nighthaunt army.
This tutorial will show the process I used to re-base the Spirit Hosts, while preserving all the work I put into their scenic bases. I'll also show you how to deal with those pesky rows of peg tubes under the 40mm square bases.
The simplest solution for re-basing would be to clip away the edges, leaving a flat "plate" that can be glued on top of the round base. This, however, adds a little too much thickness on the top, so the basing won't match the other units that had their sand applied directly onto a round. Furthermore, the peg tubes make it difficult to get a flat plate, which is even more problematic. When re-basing my spirits, I don't want there to be any difference between their bases and the new Spirit Hosts I'll add later.
The diagonal of a 40mm square is also longer than 50mm, so the corners will have to be trimmed away to get everything to fit within the 50mm circle.
Start by clipping away the edge of the base. Don't work too fast, and take care not to crack off any of the important bits of the basing,
Continue until all the edging is gone, leaving the square top with the peg tubes underneath.
Then, carefully clip away bits of the corners, and trim the base as close as you can to the elements like the tombstones and skulls. It's easier if you clip away the peg underneath, and then trim the top, rather than trying to clip through the top and the peg tube in one shot.
Trim the base so it completely fits on the top of the circle, without being too close to the edge. Don't center the base remnant, center the models, so they won't overhang the perimeter of the base too much. When you are satisfied with the position, trace the base with a pencil. Always use pencil when marking things on models (or scenery) because pen or marker will often bleed through the paint.
Carefully trim out the marked section from the top of the base to make a hole that the old base can slot into. Cut inside your line to ensure that you don't remove too much material. Check the fit, and shave a little more off until the base sits comfortably in the recess. Take care not to squish or deform the edge of the circle. Leaving as much plastic as possible on the top will help maintain the integrity of the round base.
Now, the old base will fit inside the round base, pegs and all. We just need to reinforce the round base and provide an attachment point for the old base.
Use a sheet of thin plastic card (about 0.10 or 0.20mm). Superglue the round base onto the card, and then trim away the excess. Ensure that there is superglue all the way around, with no gaps, to avoid the card splitting away from the bottom of the base.
Using a fine sanding stick, sand the edge of the base to smooth out any rough spots of super glue and blend the card and the edge of the base to create a seamless transition that will be invisible once painted.
The thin card ensures that the base doesn't gain any noticeable thickness, and helps reinforce the circle so it won't deform.
Dry-fit the bases again to make sure everything lines up. Now you can see how the project will come together– The pegs will be glued to the plastic bottom, and the top of the old base will line up with the new round base. But don't glue it in place just yet...
The peg tubes were not flush with the bottom edge of the square base, so it will sit a little shorter. You'll notice that the sanded top lines up exactly with the flat top of the round base. If we were to add sand at this stage, the sand around the perimeter would be higher than the existing sand in the middle, creating a depression.
Cut a spacer of 0.50mm-thick plastic card. Glue the spacer into the base (again, do not glue the old base in yet).
Here you can see the old base resting on top of the spacer, and its sand is elevated above the top of the round base. Now, any sand glued around the perimeter will be flush with the existing sand on the old base.
The final step before gluing the old bases is to spray-prime the new round bases. Put a bit of masking tape over the card inside to keep the primer off of it. This will allow the models to glue plastic-to-plastic without having to scrape away the primer first.
Okay, with the primer dry, now you can superglue the models into their new bases.
There will inevitably be gaps between the cut-outs and the old base, so fill them in with modeling putty. This will provide a stronger connection to the round base edge, and will seal the crevice to keep sand out of the hollow cavity. (Otherwise, you'll hear it shaking around in there forever!)
When the putty has cured, super glue sand to match your existing basing scheme. If you used a textured paint for your basing, you could paint more around the perimeter, up to the edge of the old basing.
Paint the new sand and the base rims to match the existing bases.
And finish it off with matching flock or static grass. The grass offers a nice opportunity to hide any obvious seams between the new and old sand.
And that's it! The models are ready to rock and roll on their new round bases!