When I was young and first started to make model kits. I would just bend the parts back and forth and then pull them off from the sprues. I knew about x-acto knives, but my parents weren’t going to let a little kid use one of those unsupervised. I was very very impatient, I just wanted to say that I had made another car or plane, I didn’t want to wait until I had proper adult supervision. Those models were pretty bad, they either had chunks missing or part of the sprue hanging off most of the time.
I am assuming that you are new to modeling if you are reading this article. Welcome to the hobby, it can be very rewarding. I will share what I have learned so that, hopefully, you don’t ruin as many models as I did when I was young.
The steps to getting clean parts from sprues. sometimes also called runners are.
- Use Flush side cutters to separate the parts from the sprues
- Trim excess plastic leftover from the molds
- Use a good file to smooth the area to match the rest of the part
Use a pair of flush side cutters
A good pair of cutters will enable you to cut the parts from the sprues while leaving the least amount of material hanging on. Turn them so that the flat side is closest to the part that you are removing.
If the part is pack in pretty tight and you can’t get around the other parts easily, then cut further away on the sprue so that you can remove it and then trim closer once you have it separated.
This model part, for example, is shaped in a way that makes it difficult to cut near it. But when I intentionally leave a good size part of the sprue, it makes it easier to get the sprue parts cut off. Check out the flush cutters that I use here.
Trim flash with a sharp hobby knife
Models are most commonly created in two-part molds where the plastic, or other material, is poured or injected into the mold. Sometimes there is a small amount of material that will be forced out in between the mold sections. Flash is the term that is commonly used for this extra material.
You can see in this photo that this sprue has quite a lot of flash on it. If this were on model parts you would need to carefully trim it from the part with a sharp hobby knife. This is an extreme example and is not commonly found.
This is the hobby knife that I use.
Remove Mold Lines
Mold lines are the most common type of flash that you will encounter in modeling. This is where you will have a small line that will show up on the side of a model piece. They generally aren’t very pronounced and can easily be missed before you paint.
The problem with missing them is that these types of small imperfections are magnified with many of the techniques used for painting models, particularly if you are doing any type of weathering.
The simplest method that I have found to remove them is to lightly scrape the back of your hobby knife along the line. You will see the plastic curl up as it is removed from the piece. I have to emphasize the importance of patience and a light touch. It is super easy to gouge the soft plastic that models are made from.
A good set of files will help to round things out
After I get things trimmed neatly with a hobby knife I will run my fingernail over the area to see if there are small imperfections left on the model. If there are I will use a small file to help smooth out the blemish.
Be careful not to be aggressive with your filing because it is super easy to remove the soft plastic with your file and end up with a deformed part for your model.