Depending on the sophistication of the injection molding process - and the degree of shrinkage as the injection molded plastic cools - the final parts may have imperfections known as sinkholes in them. These generally occur in thicker areas of the part - and as luck would have it generally obscure some critical detail. On the T-72 visible sinkholes (post construction) appear to be generally confined to the turret stowage boxes.
|Sinkholes in the stowage boxes on the T-72 turret|
There are two sinkholes sometimes found on the rear of the stowage boxes marring the box detail. There is also usually one on the side as well. At this point the modeler has three options:
- Option 1: Do nothing - paint it up and go.
- Option 2: Fill the holes, sand them down, and go. Don't try to recreate the pattern on the boxes
- Option 3: Fill the holes and recreate the original pattern to make the final product look like a part without sinkholes.
Okay - so since this is me we're talking about - which one did I choose? Is that even a question?
|Filled rear sinkholes on T-72 turret - the green areas were formerly recessed|
Step one in restoring the stowage boxes is to fill the holes and sand down the putty. I use Squadron Green Putty for most of my fill work. You should wait until it is completely hardened to sand it. I generally let it sit for 24 hours.
|Filled side sinkhole on T-72 turret - mold line clean-up still needed|
One the putty has dried, I us a combination of sanding sticks and fine files to flatten and smooth out the area. This results in a good flat surface, but it is now devoid of the surface details which were originally supposed to be there (and were obliterated by the sinkholes).
|Ultra-thin styrene sheet and a dental tool are used to emboss new surface detail|
So now comes the hard part - how do you re-create the surface detail? Fortunately the detail on the T-72 turret boxes are relatively simple horizontal lines. Any time I'm making new surface detail, I use ultra-thin styrene sheet (in the U.S. Evergreen is a good source of sheets - I use the 0.005" / 0.13mm for my fine detail work) and emboss it with a dental tool.
|Embossed lines - lines were pre-measured and drawn|
Some surface details are easy enough to do freehand, but in cases like this it is important to at least draw out a rough outline of what needs to be embossed first. In this case I found the entire detail panel to be about 0.15" tall by a little more than 0.4" wide. I split the difference evenly for the horizontal lines.
|Embossed lines - be careful with your pencil! It will emboss as well!|
Once you've generated your surface detail, then comes the tricky part - no really! Extremely thin styrene should be attached with a liquid cement, but you must use the liquid cement sparingly or it will simply begin to dissolve the styrene and obliterate you brand new surface detail. I put on some liquid cement, let it get tacky, then let it dry overnight before trimming the detail to integrate it into the overall part
|Rough detail added - final trimming and sanding remains to be completed|
In the next update I'll post photos of the completed surface detail once it is trimmed back and integrated into the turret. I'll also point out a few other areas of the T-72 that could use just a little attention as well.