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Monday, October 19, 2020
Monday, October 19, 2020

The start of nearly any model building project starts with the removal of the actual parts from the sprue gates with which they come attached. These parts need to be removed in a way that causes little to no damage to the part itself as this will make the build progress more smoothly providing better results as well as reducing any repair work that may be caused by not removing the parts correctly.

Close examination of the parts will invariably show a whole range of imperfections own various parts that will need attention before the construction process. If not dealt with these imperfections can result in problems with the assembly or possibly result in a less attractive model than we were hoping achieve. No matter how carefully you cut you will almost always end up with parts that will have seam lines, excess flash on the mouldings as well as the remains of the attachment points where you removed the part from the Sprues.

This article will show you that with the correct tools these imperfections can be removed leaving the modeller with a good starting point for which to commence the build.

Tools and Use.

Sprue Cutters.

These are normally the modellers primary tool for the removal of plastic parts from the sprues. Basically there are two types of sprue cutter design with the first being made from a stamped metal sheet attaching the two parts, The second being a forged type . As with most things in life price varies between models but you can generally get a good solid set of sprue cutters for a reasonable price. For personal preference I will alway choose the forged metal sprue cutters over the stamped sheet metal type. But seek others opinions and don’t always assume the most expensive will be the best.

For the removal of parts from the sprue, the flat side of the sprue cutter should be placed close to the part that is being removed leaving a small stub of the sprue connection between the blade and the plastic part. It is possible to to cut right up against the plastic part you are removing but, depending upon the quality of the plastic used it can potentially result in excess removal or damage of the part. Leaving a small part which can be cleaned after the part has been removed may add a little time to the process but can ultimately save you repair work if you damage or remove too much plastic.

Sanding tools.

Sanding products come in a variety of shapes and sizes that are suitable for removing excess plastic from the model during the cleanup process. Depending on the surface that is being cleaned and the size of access will determine the type of sander that you will choose for the task. They come in varying grades of abrasiveness, with the lower numbers for the grit being highly abrasive and the higher numbered grades moving from abrasive to almost a polishing capability. Generally the lowest grade grit I would personally use is 400 to begin with working through various grades to achieve a clean smooth cleanup up with 1000 – 1500 grade. Any higher numbers I would be inclined to avoid for this task, whilst lower numbers run the risk of scratching the plastic and needing repair work.

Basically there are two types of sander I would consider for this task. That being.

  1. Hard sanding sticks. These provide a flat edge which is very convenient when sanding against straight edges and you want to avoid removing excess plastic which would result in gaps when fitting straight edges together during the build.
  2. Sponge sanders. These have a lot softer surface which will conform to shapes and curves that you are sanding. This is very useful in certain parts of the build process but in my opinion not ideal when cleaning flat straight edges as the sponge can conform over the edge and soften the sharp edges you care cleaning up.

Starting with the lowest grade number of sander and keeping is straight with the edge you sanding, gradually removing the excess plastic. As you get closer to the surface of the part, move to finer grades of sander until the finish is smooth and clean with no excess plastic rising from the surface.

Seam Removal.

Seams are normally formed during the moulding process where the two sides of the mould are pressed together and a small raised line of excess plastic is formed. Normally these are fairly small and easy to deal with to remove an unsightly blemish that can be quite visible when the painting has been completed. I would generally use a sharp blade and drag the blade backwards over the seam to gradually shave away the raised area whilst leaving the remaining plastic unaffected. Normally one or two passes of the blade are sufficient for this. Wherever possible I leave the part attached to the sprue for added stability.

Flash Removal.

Flash is also caused during the injection moulding process. Normally either with poorer quality or older worn moulds where excess plastic forms around the edge of parts. Much more visible normally it is usually easy to remove due to it normally being very thin. The process is normally almost identical to seam removal.

And so congratulations. Your parts are now cleaned up and ready for construction. 🙂

 

Last updated bySMWAdmin on 27th July 2020
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