When I first saw Battlefront's plastic Su-85/Su-100, I was a little surprised. With two hulls, many guns, and piles of additional pieces, the sprues really looked like they made two tanks. Close inspection revealed that this was not so: there was only one set of tracks, one lower hull, and one set of exhausts. I might have forgotten about this, but the same day, a new box of PSC T-34s arrived, and a bright little sticker caught my eye: Includes One Piece Track Option!
Now I always liked PSC's multi-part tracks with their detailed treads. But this seemed like the perfect coincidence: could one use the treads to make a whole new assault gun out of a Su-100's leftovers?
As it turns out, yes!
There are two major steps. First, we need to make the tracks and lower hull. Then the exhaust pipes and covers. I used spare parts for the Su-85, but you might want to do it the other way, see below.
For this conversion, we will absolutely need side cutters, a pin vise, plastic glue, and super glue. We will also use both the angular sprue from the PSC tracks and the round sprue from the Battlefront kit.
PSC's tracks are slightly smaller than battlefront's: in total maybe 2mm shorter. But the difference will hardly be noticeable.
First we use the lower hull to measure a pair of sprue segments. Make them just slightly wider to make sure they contact the tracks. Cut off square with side cutters.
The guide bumps under the Su-85 upper hull make these "lower hull" replacements slat the wrong way. Shave them down to level.
Glue the sprue bits and then the tracks. The tracks contact each sprue bit and the fender. This will make the spare tank ride a little lower: in retrospect, it might be better to make the Su-100 with the extras, as it was heavier and should be lower in its suspension.
One could go on to finish the lower hull, but I left mine open: not a lot of strength to be gained from covering it. Let this cure well!
Now for part two: the exhausts. The sprue gates give us the perfect rounded tube shape for the exhaust covers. Shave them down while still on the sprue.
To get a good cut, remove a section of sprue first, then cut off each exhaust piece.
Now we need room for a pipe. Use some wire and a matching drill bit. Drill a hole into each little cover. If you mess up, there are always more on the sprue.
For the wire, bend it to a sharp angle, then cut down one end and super glue it into the cover. When this dries, cut off the excess with clippers to make the end of the exhaust pipe. I use crappy old clippers for steel and lead to try to keep my betters ones sharp.
This little assembly can be plastic-glued into the slot on the hull. Make sure the pipes point to the rear. There is a little gap, but it will be easy to fill.
From here do the rest of the assembly.
Comparing the two, we see that while there are obvious differences, both tanks will look great on the table!