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Scratchbuild Seminar 6-Sanding/Filing


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#1 GTmike400

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Posted 30 March 2006 - 04:39 PM

Scratchbuild Seminar 6-Sanding/Filing

Introduction:
Believe it or not there is a lot more to sanding than just rubbing gritty paper across a surface; that is just the foundation for several different methods of sanding. Different ideas and methods of sanding just enhance the method of scratch building but still fall on the basic principles of using friction to remove material.

Basics:
Sandpaper:
The basic scratch builder should have an array of sand papers, and should have some of the basic needle files. Sand paper is rated by grit, the higher the grit the smoother the paper. Polishing pads are different; each company rates their pads on a different scale. 3M wet/Dry sandpaper is the best paper to use under most circumstances. Although, the coarsest grit available in wet/dry is 220 you may need a coarser paper for the initial shaping stages, or heavy removal of material. In that case, the regular 3M sand paper is just fine.

Files:
For tight spaces, special shapes, large removal of material, and sharp edges needle files are an essential tool. They are a must for the basic model builder and scratch builders alike. Needle files are often referred to as jeweler files. They come in many shapes and sizes, as well as coarseness. Not as well known are the riffler files, they are double ended and have a curved tip. These help for some unusual tight spaces among other applications. It is always good to have a common size flat file and is fairly rough. These come in handy on lathes, and remove large amounts of material quicker than sandpaper.

Wet Sanding:
The most often mystified term for sanding. It is as simple as the name, sanding while wet; hence the name wet sanding. Wet sanding really helps keep the sandpaper clean. Only use wet/dry sandpaper when wet sanding. The water also acts as a lubricant to the sandpaper, thus material is removed slower and a smoother finish is achieved. Wet sanding most often starts at 400-600grit wet/dry sandpaper and is usually done when preparing for paint.

Process:
Filing:
Files are really good for small flat or circular surfaces. A flat file is good for sanding down an edge on a sheet of styrene. Round files are used to create notches. Triangular files are good with sharp acute angles. Each application has a certain method that suits it best. It is the choice of the modeler to choose which method is most appropriate and works best.

Sanding:
There is a much broader field of applications for sanding than filing. Sanding is very useful for complex curves, scuffing, or smoothing surfaces. Whereas files are generally tools for shaping. Coarse sandpaper would be 80-150grit, medium grit sandpaper is 220-400grit, fine grit is 600-800, and superfine is 1000grit or higher. Coarse sandpaper is useful for large removal of material fast, or shaping putty. Medium is useful for beginning detailing and smoothing. Fine grit would be for finishing. Superfine is used for paint finishing. The highest grit usually attained in scratch building is 600. Slowly work your way up to 600 grit. You may need to go back and retouch areas with a lower grit, and then follow the steps back up 600 in that area. Rarely will you need to use anything higher than 600 for scratch building as the primer will fill those tiny surface scratches.

Tips:
Creating a hard edge:
To really make your scratch building clean and make the paint really pop you need a hard edge. Lines that aren’t crisp or straight can throw off an entire build. To build up a hard edge some applications require files, but there are some that are contoured, such as body panels. Lay a strip of masking tape along one side of the ridge. You can sand up to the edge of the tape on the side of the ridge that is unmasked. This will create a sharp or hard edge.

Sanding Tools:
Certain hard to reach areas may require sanding sticks, or even some ingenuity to create your own sanding tool. Sanding sticks are very useful for flat surfaces, and edges, as well as leveling areas. With sandpaper, the paper contours to your hand whereas sanding sticks have a planar surface. Blocking is a term referring to using a sanding block or sanding stick to level off the high spots of certain areas. It is easy to tell where the high spots are using a guide coat. A block or stick is chosen because it can level a surface better than sandpaper since it has a flat surface.

Sometimes there are areas the sanding stick or block wont work, or fit. For an application like this you could use a piece of sheet styrene to wrap a piece of sand paper around. You could even make a special sanding block out of styrene and wrap the paper around it. Using sheet will give you a flat sanding edge, or you could choose to use tubing to create a radius.

An intermediate between hand sanding and blocks/sticks would be a rubber pad with some sandpaper wrapped around it. A rubber pad is usually about a 1/4" thick and will help create a level sanding area for contoured surfaces. The rubber will conform to the contour but the sandpaper will remain "level" to the surface of the rubber.

Guide Coats:
Often it is hard to tell where high spots are on your work. To be able to tell where the high spots are use a guide coat. Lay down a coat of primer. After that dries lay down another coat of primer that is of a different color. When you begin to block out your work the high spots will show the first color primer you used. The second color will remain in the low spots. After it is completely blocked the second color should have completely disappeared.

#2 Guest_BrianR_*

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Posted 04 April 2006 - 04:25 PM

Mike,
Nice series.
I'm saving them and will be printing it out to take to our club meeting.
Any idea how many you're going to do and/or when?

#3 GTmike400

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Posted 04 April 2006 - 06:03 PM

Mike,
Nice series.
I'm saving them and will be printing it out to take to our club meeting.
Any idea how many you're going to do and/or when?


I plan to do a few more. I come with new ideas everytime I go to the bench. I really need to start jotting them down. Im having trouble coming up with ideas for the next seminar and Im open to suggestions.

I try to pump them out about once every other week.

#4 slotbaker

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Posted 04 April 2006 - 08:25 PM

I agree with Brian, nice series.

Im having trouble coming up with ideas for the next seminar and Im open to suggestions.


Looks like there is a spot open for a guide to airbrush for dummies like me.

I've trawled the internet and various forums trying to find all the info in one spot. There is a stack of info spread all over cyber space, but for this airbrush dummy, it's very confusing. :?
eg All the diferent types with pros/cons for each, best for learner to start with, easiest to clean, easiest to change colours with, etc.
:)

#5 darquewanderer

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Posted 10 February 2007 - 07:15 AM

Excellent series Mike. Looking forward to more of this.