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Old 01-29-2006, 01:00 PM   #1
klutz_100
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HOW TO: Improving/replacing clear parts

I thought I would share with you some thoughts I had over the weekend about clear parts and some ideas I tried out to improve them. A summary of my thoughts can be found here

I was working on a Fujimi Dino 246GT and was really annoyed with the clear parts:
  1. Basically the plastic part is WAY out of scale. Looking through them is like peering through a pair of Mr Magoo’s spectacles. I asked myself what’s the point of trying to detail an interior of you can’t see it clearly after installing the tub into the body?
  1. Apart from being so thick, they are invariably scratched before I even open the bag
  1. The fit of the clear parts leaves a lot to be desired and in fact impacts on assembly of the whole car.
With regards scale, I measured the thickness of the Dino clear parts – at it’s thinnest it was 0,67mm and 1,0mm at it’s thickest (measurements taken AFTER sanding the part!). If we take an average thickness of 0,84mm this scales out to glass 20mm (3/4”). Bullet proof glass isn’t much thicker!

I tried two approaches to remedy this:
1) Thinning and polishing the part
2) Making a replacement part.

1) Thinning and polishing:
For this I used squadron sanding sticks (medium, fine, polishing), various grade sand papers, micromesh system, Tamiya compound (fine, final polish), Maguire’s Carnauba Wax.



First I used the medium and fine polishing sticks to thoroughly sand down the piece on both sides. I went a bit further than just removing scratches and actually thinned out the part somewhat. After this stage the clear part was predictably opaque and look like a disaster. Do not despair!!

Then I began the polishing stage. On one side I used the full Micromesh system (3600-12000) while on the other side, for comparison, I used only a 2-sided squadron stick. After polishing out there was IMHO no noticeable difference between the 2 effects obtained. The only difference was in time and effort required – the squadron polishing stick method was quicker and easier.

After polishing, the clear part was still not crystal clear so I worked further - first with Tamiya compounds followed up with the application of carnauba wax. After this the clear part was sparkling and clear.

I was totally happy with the effect and found that it was worth the effort. However, IMO it is not possible to thin the part very much and it still remains out of scale albeit significantly clearer.



2. Making a replacement part
This approach was more or less forced upon me when I snapped a clear part in half while polishing it and was unwilling to accept a glue line in the middle of the rear window

First I took a piece of clear plastic from some bubble packaging (something I stole form my wife ) and cut out a suitable large piece for my needs. This plastic was 0,16mm thick (3,8mm/0,15” in 1/1 scale) much better!



Before starting work, I cleaned the piece up with Tamiya fine and finishing compounds and then rubbed it with carnauba wax which removed all fine scratches. I felt that it would be much easier to do this while I had a large, flat surface to work with rather than a small, curved part.



Next I made a covered the original part with Tamiya 40mm masking tape and contoured the shape to make a template/mask.



The template was transferred to prepared sheet of plastic and then I cut out the template. I started first with scissors, cutting about 5mm away from the template and then cut carefully along the line with a nr 11 scalpel. The template will inherently give you a new piece slightly larger than the original which is fine. You can adjust to fit later by carefully sanding with fine grit paper or sanding stick.





Once I had the shape cut out, I put the new part up against the original in order to establish where the curves should be. I bent the part in the appropriate places around gradually thinner paint brush handles (without heat).

At this stage the key is test fit, test fit, test fit and test fit again. TBH I was lucky and got it right first time but I don’t suppose I will get that lucky again.
Also, I now know it is important to get any curves just right at this stage. The material is quite springy you cannot expect the glue to hold a part to the body that is pulling too much in the opposite direction. My estimate is at 0,5mm tolerance.





The final part was treated with wax again to clean it up and then fixed in place with GS hypo cement. I think that the final result is excellent. The clear part is now clear and to scale. When looking through through the new window, you can’t see it and that was the point!!



I’m pretty sure that I will be using this technique more in the future. The whole operation took me about 30 minutes which is about what it took me to sand and polish old part before I broke it. Also, the Dino rear window is an exceptionally difficult piece because it has lots of curves and is fitted at an angle so I am sure that regular windscreens and windows shouldn’t present any problems.

I hope that this (rather long ) post will encourage some people to look critically at their clear part sprues and do something about it.

Disclaimer: I accept no responsibility for any broken or damaged clear parts!
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