The Ship Model Forum

This is something which I erroneously thought I was pretty good at doing (at least on white-metal miniatures and parts I am).

But in building my Agano and Fuso, and in starting to apply paint to them I have discovered that I have done a very sub-optimal job, and mold-lines are one of my worst nightmares in painting (being more of a painter than a modeler).

I have googled a few tutorials on the subject, but they mostly cover things I already do (leaving the parts on the sprue to do most of the line removal, ink washes to highlight the lines...).

I thought that would be enough. But it doesn't seem to be.

I still see mold-lines on the smaller parts, like gun barrels, or the fuselages of float-planes, no around the bases of a few parts.

And mold-lines really screw up painting a plastic model. They prevent washes, and dry-brushing from working properly by drawing the eye to the flaws, instead of the features.

So... I would appreciate some tips.

I am currently using a scalpel and a small sanding stick (with about 800grit paper) to try to smooth off the lines, and then I will do an ink wash. After letting the ink wash dry for about 5 minutes (enough for the flat surfaces to dry, but not the nooks and crannies where paint might collect) I then wipe off most of it to reveal where any crevices might still remain. Maybe the tissue paper I use (it is actual tissue paper, and not cosmetic tissues, or tissues for blowing your nose) is soaking up the stuff in the crevices???

Help?

MB

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Working on:


1/700 (All Fall 1942):
HIJMS Nagara
HIJMS Aoba & Kinugasa
USS San Francisco
USS Helena
USS St. Louis
USS Laffey & Farenholt
HIJMS Sub-Chasers No. 4 - 7
HIJMS Sub-Chasers No. 13 - 16

Mold lines....... In the trade they are known as parting lines, or insert lines depending on where they are located. They can also be associated with ejector pins, lifters or ejector sleeves, all of which are there to get the molded part out of the mold (yes, I've been in injection molding for 25 some years and a modeler since childhood)

There is no quick fix to eliminating these unwanted lines. This is why it is critical to look at each piece prior to assembly (during the pre-build stage is always the most useful). I'm currently (and have been for a couple of years) working on the Tamiya 1:350 Enterprise and airwing. One thing that I live by religiously now is wet sanding. I found a 9" diameter white coated cake pan to work in. I put about 3/4" of cold water into the pan and with waterproof sandpaper and I go to work. The water keeps the plastic cool, and helps to keep the sandpaper from loading up allowing it to go further.

I have outfitted my pan with a clear splash shield on 1/2 of the pan about 6" tall from some old packaging. This is because I have outfitted my rotary tool with a flexible extension which keeps the motor well away from water. This extension now gives me the ability to use various grits at slow to medium speeds in the water which has provided great results on difficult parts. I buy waterproof sheet sandpaper (very cost effective vs buying the Dremel or Proxxon stuff), cut multiple copies of the sanding discs using a drafting circle template, cut a center hole, and you have something tailor made to what you need. I found that a plastic backing disk made from some clear packaging to support the sanding disk was also needed. The thickness of the plastic support determines how firm the sandpaper is held. This arrangement help me keep my sanity when dealing with the ninty-some-odd aircraft I had to finish for the Enterprise. This method should work for your contoured parts. This same method works with sanding down fillers too. Just stay patient!

For flat parts that you want to keep flat, I recommend getting a couple of pieces of 6" square glass sheets cut to fit the bottom of your wet sanding pan. With this, you can attach a single wide strip of double sided tape to the glass, then whatever grits you want to the tape. This now goes into the pan and you can wet sand things that need to be kept flat or square. I found this method to be very useful with all of the scratch building needed to outfit the hangar bay. Again, the water keeps the plastic cool, and keeps the sandpaper from loading up.

I hope this helps or gives you some ideas of your own. Lastly, all I can say is that the pre-build time is critical. With the Enterprise, I have taken to keeping a diary/log book of things. I keep measurements, draw sketches, notes, all manner of information on my build. The Enterprise is the largest and most detailed build I have ever tackled. I'm shooting for museum quality, but I will be somewhere less than that. I have found that the time spent in pre-building has been worth it's weight in gold. It makes me more patient, allows me to think and design fixtures to hold parts, think of assembly steps, and so on. Good luck!

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"It's hard to make things idiot proof because idiots are so damned ingenious!"

Thanks for the tips.

In the mean time (between originally posting, and this response) I have discovered quite a few sanding methods.

But the thing I am having the most trouble with is testing to make sure that I have managed to eliminate the parting-lines completely.

I have tried Painting the parts with a coat of primer before hand, to see if a mold-line stands out. But often when I do that I have trouble stripping the part completely to get a smooth finish after cleaning up the area in question that I missed.

This is the base of my existence.

I am thinking about getting a Jeweler's Loupe to inspect the parts.

MB

_________________
OMG LOOK! A signature

Working on:


1/700 (All Fall 1942):
HIJMS Nagara
HIJMS Aoba & Kinugasa
USS San Francisco
USS Helena
USS St. Louis
USS Laffey & Farenholt
HIJMS Sub-Chasers No. 4 - 7
HIJMS Sub-Chasers No. 13 - 16

On intricate moulded parts I always brush a lightly loaded brush of liquid cement like MEK or Tamiya extra thin across the sanded mould line. This removes it without destroying the complex detail.

Of course, care and practise are required so as not to destroy the detail completely.

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Regards

Nigel

Instead of using a primer to check for molding lines, etc., I use Tamiya flat white airbrushed. Tamiya flat white will show up any blemishes just as well as a primer, and removal is easy - just a bath in Windex floats off Tamiya paint in minutes, right down to bare plastic. So you can perform this several times without a build-up of primer.

Here is an old (Aircraft build) method I find useful at times,

With a fine tip brush apply a small line of silver paint (silver shows everything) along the mold line..lightly sand just enough to remove the silver. When it's gone so is the mold line.

A sanding stick or a Flex-I-File can help you here